SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 1 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 Task 4 PROPERTIES OF HARDENED CONCRETE Final report Partner: Advanced Concrete Masonry Centre University of Paisley Scotland, United Kingdom Authors: M. SONEBI, P.J.M. BARTOS W. ZHU, J. GIBBS, A. TAMIMI May 2000 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 1 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 Contents 1. INTRODUCTION...................................................................................................3 2. SELECTION AND PROPERTIES OF BASIC RAW MATERIALS 2.1 Aggregates.............................................................................................................3 2.2 Cement and fillers .................................................................................................4 2.3 Admixtures............................................................................................................5 2.4 Fibres.....................................................................................................................5 3. MIX PROPORTIONS USED.................................................................................5 4. FRESH CONCRETE..............................................................................................6 4.1 Mixing procedures: ready mix concrete plant.......................................................6 4.2 Test methods for properties of fresh SCC.............................................................6 4.3 Results of tests on fresh concrete: SCC mixes and reference mixes.....................8 4.4 Settlement and bleeding ........................................................................................9 5. 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 PROPERTIES OF HARDENED CONCRETE DETERMINED USING BS 1881: PART 116 AND OTHER SPECIMENS ..........................................11 Compressive strength..........................................................................................11 Indirect Tensile strength......................................................................................13 Bond strength......................................................................................................14 Modulus of elasticity...........................................................................................17 Drying shrinkage (UoP)......................................................................................18 Shrinkage and creep (LCPC) ..............................................................................18 Water absorption of near surface concrete..........................................................23 Carbonation.........................................................................................................26 Freeze-thaw resistance ........................................................................................26 6. PROPERTIES OF HARDENED CONCRETE IN FULL-SIZE STRUCTURAL ELEMENTS ...........................................................................27 6.1 In-situ testing ......................................................................................................27 6.1.1 Test arrangements ............................................................................................28 6.1.2 Results and discussions of in-situ strength ......................................................29 6.1.3 Results and discussions of the other in-situ tests .............................................33 6.1.4 Statistical analysis of the test results................................................................35 6.1.5 Conclusions .....................................................................................................38 6.1.6 Micro-mechanical study of the interfacial zone ...............................................38 6.2 Structural performance of full-scale elements .................................................44 6.2.1 Design...............................................................................................................44 6.2.2 Concrete placing procedures ............................................................................48 6.2.3 Test set-up for columns ....................................................................................50 6.2.4 Test set-up for beams .......................................................................................50 1 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 2 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 6.2.5 Testing columns ...............................................................................................52 6.2.6 Testing beams...................................................................................................53 6.2.7 Cracking patterns and cracking-spacing...........................................................53 6.2.8 Cracking moment .............................................................................................54 6.2.9 Crack-width......................................................................................................55 6.2.10 Load-deflection response ................................................................................56 7. CONCLUSIONS ..................................................................................................56 APPENDICES A1 A1.1 A1.2 A1.3 A1.4 A1.5 Preliminary investigation...................................................................................60 Materials............................................................................................................60 Observations on effect of materials on concrete properties..............................61 Observations on effect of mixer ........................................................................62 Test methods for fresh properties of SCC.........................................................63 Proportions and fresh concrete properties of preliminary mixes ......................64 A2 Analysis of pull-out test results.........................................................................69 Notation Reference housing Self-compacting concrete housing Reference civil engineering Self-compacting concrete civil engineering Fibre self-compacting concrete housing 2 RH SCCH RC SCCC FSCC SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 3 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 1. INTRODUCTION The fundamental objective of this task was to provide information on the hardened properties of self-compacting concrete produced using easily available local raw materials in Scotland to support the practical work of other partners in assessing the practicability of actually building with SCC, and to facilitate the introduction of SCC technology into general construction practice. To this end, the engineering properties of SCC in sampled specimens and in full size structures were to be compared with those of normal concrete. Two basic categories of concrete were considered: a ‘housing’ category, and a ‘civil engineering’ category, with characteristic cube strengths of 35 MPa and 60 MPa respectively. In addition a steel fibre-reinforced SCC mix was developed. The concrete was produced in a commercial concrete plant, and the following mechanical properties of sampled specimens were tested: compressive and flexural strength, shrinkage, creep, bond strength with reinforcement, and elastic modulus. In addition, in order to assess durability, longer-term comparative tests were made on freeze-thaw resistance, water absorption, and carbonation. Testing of fresh concrete was not part of the task, but necessary for mix design verification and acceptance purposes. To supplement this, special tests were made on settlement and bleeding. The full-size elements were tested in two ways. Firstly a number of in-situ tests were carried out, and secondly, the whole elements themselves were load-tested to failure. Also, for each type of concrete, a full size element has been left at an outdoor exposure site for future assessment of durability performance. Thus the outputs from the task were • Verification of compliance with specifications for hardened SCC provided by external supplies. • Verification of properties of hardened SCC in completed structures using in situ test methods. • Comparison of basic mechanical properties of hardened SCC with those of ordinary concrete. • (Eventually) Comparison of some aspects of the durability of hardened SCC with those of ordinary concrete. 2. SELECTION AND PROPERTIES OF BASIC RAW MATERIALS 2.1 Aggregates A continuously graded crushed microgranite aggregate with a nominal particle size of 20-5mm and a well-graded quartzite sand according to BS 812 grading with a fineness modulus of 2.74 were used (Table 1). The typical relative densities (SSD) of the coarse aggregate and sand were 2.65 and 2.56, and typical absorption values 0.8% and 1%, respectively. 3 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 4 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-5-2 Table 1 - Grading of aggregate Sieve size (mm) 20 – 5 mm 10 – 5 mm Sand 28 20 14 10 6.3 5.0 2.36 1.18 0.6 0.3 100 100 100 95.6 100 100 56.6 28.1 7.8 2.2 0.3 ---100 100 43.6 9.6 0.2 ---100 100 100 99.9 85.6 68.1 50.7 21.0 0.15 0.075 --0.7 --0.1 2.2 Cement and fillers The SCC mixes investigated in this study were prepared with Portland cement, with either limestone powder (LSP) or ground granulated blast slag (GGBS) added as the filler. The reference mixes used PC only. The cement and GGBS used conformed to BS 12:1996 and 6699:1992. The chemical and physical properties of cement, GGBS and limestone powder are presented in Table 2. All the investigated mixes incorporated one of the mineral additives (LSP or GGBS) to enhance workability and segregation resistance. The gradings of the cements and limestone powder are shown in Fig. 1. The limestone powder was produced from carboniferous limestone of a very high purity and was finer than cement. Table 2 - Chemical and physical properties of cement and fillers Limestone GGBS Cement powder SiO 2 -33.5 20.8 Al2 O3 -13.6 5.0 Fe2 O3 -0.62 3.2 CaO -42.7 63.7 MgO 0.2 6.5 2.6 Na2 O eq. --0.39 Free CaO --1.6 LOI -0.67 0.65 CaCO3 99.0 Relative Density 2.65 2.90 -Bulk Density (loose) 0.90 1.00 -Bulk Density -1.24 -(compacted) Specific Surface 460 385 2 area (m /kg) Compressive Strength (MPa) (Mortar Prisms) Age 30% C 100% C + 70% GGBS 7d -28 41.5 28 d -51 57.8 4 Cement Vicat set times(min) Initial Final 119 164 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 5 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-5-2 100 LSP Passing (%) 80 GGBS 60 PC 40 20 0 0.01 0.1 1 10 100 Sieve size (µ m) Fig. 1 - Grading of Portland cement, LSP and GGBS 2.3 Admixtures One of a new generation of copolymer-based superplasticisers, designed for production of SCC was used (Viscocrete 2). This had a solid content and specific gravity of 30% and 1.11, respectively. The Viscocrete was used at dosages varying from 0 to 1%, by mass of fillers. 2.4 Fibres The steel fibres used in the FSCC mix were Dramix from NV Bekaert, Belgium, type RC 65/35BN. Fibre length and diameter were 35 mm and 0.55 mm, respectively. The rate of addition of steel fibres to the mixes was 30 kg/m3 (0.38% by volume). The suffix letters, BN, mean bright surface and normal tensile strength Dramix fibre with hooked ends. 3. MIX PROPORTIONS USED Table 3 summarises the mix proportions of SCCs and reference mixes. The SCC mixes contain high-volume additions of limestone powder or blast furnace slag to enhance fluidity and cohesiveness and limit heat generation. Such materials are also less reactive than cement and can reduce the problems resulting from loss of fluidity of the rich concrete. The incorporation of one or more powder materials having different morphology and grain-size distribution can improve particle packing density and reduce interparticle friction and viscosity, hence improving deformability, selfcompactability, and stability. 5 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 6 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 Table 3 - Mix proportions of concrete, SSD mass, kg/m3 Housing Civil FSCC RH SCCH RC SCCC Free water Portland Cement 42.5 Limestone Powder GGBS Fibre (RC 65/35BN) 200 295 ----- 190 280 245 --- 220 515 ----- 192 330 --200 160 285 270 -30 Total powder content 295 525 515 530 555 Sand (0-5 mm) 20 mm agg. (*10 mm) Viscocrete 2, kg Normal superplasticiser Water/cement ratio 840 970 --- 865 750 4.2 870 750* 5.3 940 715 4.4 0.68 0.68 655 930* --6.4 0.43 0.58 0.56 Water/powder ratio 0.68 0.36 0.43 0.36 0.29 4. FRESH CONCRETE 4.1 Mixing procedure at the ready mixed concrete plant The concrete for the full-size pours (2-3m3 ) was mixed in the plant using a 6m3 capacity tilting drum central mixer. The mixing sequence consisted of ribbon feeding all the materials into the large drum mixer, with the exception of the superplasticiser, which was added at the end. The concrete was then mixed for three minutes. 4.2 Test methods for assessment of properties of fresh SCC The test methods used for assessment of fresh properties of SCC were slump flow, Lbox, Orimet and Orimet/ JRing combined. (See also comments in Appendix) The slump flow test consists of determination of the mean diameter of the concrete sample spread on a base plate after performing a slump test without any compaction. This test judges the capability of concrete to deform under its own weight against the friction on the surface of the base plate with no other external restraint present. Because of the viscous nature of SCC, the slump flow measurement was made only when no further discernible movement of the concrete was observed: approximately 60 seconds after the removal of the slump cone. With the same test, the T50 slump flow time was also measured. The T50 is the time to reach a spread of 500mm. The dimensions of the L-box used are shown in Fig. 2. It is possible to measure different properties such as filling and passing abilities and segregation with the Lbox. The vertical part of the box is filled with 12.7 litres of concrete and left to rest 6 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 7 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 for one minute in order to allow any segregation to occur. After that, the gate is opened and the concrete flows out of the vertical part into the horizontal part through the reinforcement bars. The gap between the reinforcement bars was 35 and 55 mm for 10 and 20 mm coarse aggregate, respectively. The times for the leading edge of the concrete to reach a distance 200 and 400 mm along the horizontal part, and the heights H1 and H2 of concrete were measured and used to determine the L-box result h1 /h2 . (Fig.2) Gaps = 55 mm for SCCH Gaps = 35 mm for SCCC h 2 = 150 – H2 h 1 = 600 – H1 Fig. 2 - L-Box test The Orimet test measures the flow time of concrete through a 120 mm diameter vertical pipe fitted with an orifice. The orifice of the Orimet was 80 mm. The Orimet included two horizontal steel bars of 10 mm diameter to obstruct the passage of concrete through the orifice and thus simulate blocking. Three measurements of the flow time were made, and the final measurement combined with the JRing. The slump flow of SCC through the JRing was measured (Fig. 3). The dimensions of the JRing were 300 mm diameter of its centreline and 100 mm height. The gaps between the bars were 25 and 55 mm for 10 and 20 mm coarse aggregate, respectively. Fig 3 - Orimet and JRing 7 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 8 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-5-2 4.3 Results of tests on fresh concrete: SCC mixes and references mixes The results of tests of the fresh properties of SCCs and reference mixes are given in Table 4. Table 4 – Properties of fresh concrete Housing Slump Flow at 5 min (mm) S. Flow at 60 min (mm) T50 at 5 min (s) T50 at 60 min (s) L-box - T20 and T40 at 10 min (s) - h2 /h1 at 10 min Orimet (orifice 80 mm) - Flow time at 10 min (s) - Flow time at 70 min (s) Orimet + JRing spread - 15 min (mm) - 75 min (mm) Air content (%) Civil RH SCCH RC SCCC FSCC 65 slump 50 slump 650 600 1.02 1.66 70 slump 70 slump 690 640 1.95 1.84 665 640 3.0 3.0 1-2 0.81 0.6 – 1.2 0.99 0.90 2.3 3.0 4.0 3.2 3.3 4.1 670 605 1.5 635 635 1.1 650 615 -- 1.8 Notes: SCCC - 10 mm coarse aggregate, clear spacing bars of JRing = 20 - 25 mm SCCH - 20 mm coarse aggregate, spacing bars of JRing = 50 - 55 mm Orifice of Orimet used for FSCC = 90 mm The SCC tests are not appropriate for the reference mixes, which were therefore assessed by the normal BS1881 slump test. Neither are their fresh properties really comparable with those of the SCCs, whose fundamentally different mix proportions make them significantly more flowable and workable. The volume proportion of coarse aggregate in the reference mixes is significantly higher than that of the SCCs: the SCCs were designed to have more filler, and the volumes of powder in the SCCH and SCCC were 46% and 38% greater than those of the reference mixes. The SCC mixes thus include more paste and less coarse aggregate, and this contributes to the improved workability. The increase in flowability, however, is essentially due to the addition of the superplasticiser, Viscocrete 2. 8 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 9 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 Slump flow: the values for SCCH, SCCC and FSCC at 5 min were 650 to 690 mm. After 60 min, the slump flow of the SCC mixes was still greater than 600 mm, and the slump flow loss was thus 7 to 8%: the loss in fluidity was minimal. The SCC mixes had T50 values at 5 min between 1 to 3 seconds. After 60 min, the T50 values were still less than 3 seconds, again indicating a satisfactory retention of workability. The Orimet time at 10 min of the SCC mixes ranged from 2.3 to 4 sec, indicating excellent deformability without blockage within five seconds. The retention of workability with the Orimet and the combined Orimet/JRing tests was variable. Test results are affected by the different aggregate sizes and gap spacings in the JRing, as well as the different powder types. The L-box results of the SCCs indicated a good deformability and flowability, and the blocking ratio (h1 /h2 ) values were greater than 0.80, often considered a critical lower limit. The blocking ratio was 0.81 and 0.99 for SCCH and SCCC, respectively. The high value for SCCC indicates excellent deformability, without blockage, through closely spaced obstacles, and the excellent capability of this highly flowable concrete to self-compact. The figures for air content indicate normal values for the SCC mixes. 4.4 Settlement and bleeding A test used to evaluate the plastic fresh settlement of concrete and its ability to ensure proper suspension of aggregate and fines is shown in Fig. 4. The stability of fresh concrete was evaluated by casting concrete in a PVC column measuring 200 mm in external diameter and 700 mm in height. The settlement was monitored using a linear dial gauge or LVDT, with a precision of 0.01 mm, fixed on the top of a thin acrylic sheet that was positioned on the top surface of the concrete. The plate was anchored by three 50-mm long screws, cast into the fresh concrete. The bleeding and surface settlement were monitored at set intervals until a steady-state condition was reached. In the case of settlement, this corresponded to the beginning of set. In this test, neither the SCC mixes nor the reference mixes exhibited any bleed water on the surface. The evolution of settlement of SCCs and the reference mixes are shown in Fig. 5. In the case of the housing mixes, the maximum settlement of the RH mix was 0.24% and 0.21% of SCCH - 1.2 and 1 mm, respectively. However, in the case of the civil engineering mixes, the maximum settlement of both mixes also similar. The highest settlement of all mixes was observed with FSCC mix (0.26%). 9 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 10 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-5-2 Gauge 160 mm Base-plate diameter = 150 mm Width = 6 mm 700 mm 4 screws h = 40 mm 490 mm Concrete PVC tube 200 mm Fig. 4 - The settlement test layout, using a 700-mm high column 0.3 Settlement (%) 0.25 0.2 0.15 RH SCCH 0.1 SCCC 0.05 RC FSCC 0 0 5 10 15 20 Time (h) Fig. 5 - Plastic settlement of all mixes (Height of column = 50 cm) 10 25 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 11 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 5. PROPERTIES OF HARDENED CONCRETE DETERMINED USING BS 1881: PART 116 AND OTHER SAMPLED SPECIMENS 5.1 Compressive strength Standard cubes measuring 150 mm were demoulded one day after casting and covered with wet hessian and plastic sheeting. Specimens were then cured either in water or in air at approximately 20 °C, using a curing membrane, until testing was carried out at 1 d, 7 d, 28 d, 90 d and 180 d. The results of standard compressive strength at 28 days are presented in Table 4. The specified characteristic cube strength was 35 MPa for housing mixes and 60 MPa for civil engineering mixes. The results in Table 5 indicate that the actual strengths of the SCC mixes were at the upper end of the normal range for the designed strengths, while the reference mixes were at the lower end. Such differences in actual strength of the SCC mix and the reference mixes make direct comparisons difficult. Table 5 - 28-day compressive strength results of standard specimens Average of compressive Strength at 28 days, MPa Concrete Mixes SCCH 47.0 RH 37.0 SCCC 79.5 RC 61.5 FSCC 63.0 Housing Mixes Civil Engineering Mixes Fibre SCC Mix The strength development up to 6 months is shown in Fig. 6. Rates of strength development relative to 28-day strengths are shown in Fig. 7. As expected, the compressive strength was strongly affected by w/c ratio and filler types. Results in Figures 6 and 7, related to the mix design data in Table 3, indicate that at similar w/c ratio, strengths of the SCC mixes, using the limestone powder as filler, were significantly higher than the corresponding reference mixes. It should be emphasised, however, that both results were within the normal compliance range. The relatively faster strength development for SCCH and FSCC mixes, particularly at early ages, is believed to be mainly due to the inclusion of fine limestone powder, which may have an accelerating effect on C3 S hydration and early strengths [1]. The SCCC mix, which contained GGBS instead of limestone powder, had a lower strength at 1 and 7 days than the corresponding reference mix, RC, but developed significantly higher strength at 28 days and beyond. This is due to the slower, but prolonged 11 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 12 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 reaction (hydraulic and pozzolanic) between cement hydration products and GGBS, which contributes significantly to strength [2]. Results in Figure 7 also indicate that there was no significant difference in the pattern of strength development for all the mixes studied. 100 f'cu (MPa) 80 60 40 20 RH SCCH RC SCCC FSCC 0 0 50 100 150 200 Age (d) Fig. 6 – Compressive strength development Strength relative to 28-day results, % 120 100 80 60 40 SCCH RH 20 SCCC RC FSCC 0 0 50 100 Age (d) 150 200 Fig 7 - Compressive strength at different ages relative to 28-day strength, % 12 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 13 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-5-2 Air cured strength as % of water cured strength The effect of curing conditions on strength development of the SCC and reference mixes were examined, and the air cured strengths relative to water cured strengths are presented in Fig. 8. 100 90 80 70 60 SCCH RC 50 RH FSCC SCCC 40 0 20 40 60 80 100 Age at testing, days Fig. 8 - Effect of curing conditions on compressive strength As expected, the compressive strength of air-cured specimens is lower than that of the corresponding water-cured specimens. However, the extent of strength reduction due to the insufficient curing (i.e. in air) up to an age of 90 days depends on the strength grade and the type of the filler type in the mixes. It appears that the SCC mixes, with limestone filler (i.e. SCCH and FSCC) are less affected by air curing, and that aircured strengths are reduced less than those of reference concretes. For example, as shown in Fig. 8, at 28 and 90 d, the relative strength ratios for SCCH were higher than those for the corresponding reference mix RH (85 vs. 71% at 28 d and 79 vs. 65% at 90 d). This difference could be attributed to the accelerating effect of the limestone powder and also possibly the enhanced water retentivity of the SCC mixes. For the SCCC mix which incorporates GGBS, the strengths up to the age of 90 days are more affected by the air curing, and the strength reduction due to the air curing is greater than in the corresponding RC reference mixes. Such a difference in sensitivity to curing conditions is normal for mixes containing GGBS, as continued presence of water is required for the cement hydrates-GGBS reaction to continue. 5.2 Indirect tensile strength The splitting tensile strength (f ’t) was determined at 28 days and 6 months on cylinders measuring 150 x 300 mm and cured in water until the date of test according the BS 1881: Part 117. 13 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 14 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 Indirect tensile (i.e. splitting) strengths at 28 days and 6 months, tested using φ 150 x 300 mm cylinder specimens, are given in Table 6. For easy comparison, the tensile/compressive strength ratios are also included in the table. It is worth noting that each result in Table 9 is the average of only two specimens, and in some cases the variation of results was as high as 30%. Nevertheless, results in Table 6 indicate that the relationships of the tensile strength to the compressive strength are of similar orders for all the mixes studied. Table 6 - Indirect tensile splitting strength (MPa) Results SCCH RH SCCC RC FSCC Age of 28-d 3.4 2.4 4.7 4.1 4.0 Age of 180-d 3.3 3.1 5.7 3.9 4.5 7.1 6.5 5.9 6.6 6.4 6.0 7.7 6.2 5.5 6.4 28-d Tensile / Compressive Strength Ratio, % 180-d Tensile / Compressive Strength Ratio, % 5.3 Bond strength The bond strength between reinforcing steel and the concrete was determined by pullout tests carried out at different ages. Deformed reinforced steel bars with 12 and 20-mm effective diameters were used to evaluate the bond, in accordance with the recommendation of Rilem set-up TC51ALC, 78-MCA [3]. The test specimen is a prism with a cross-section of 100 x 100 mm and a length of 150 mm. Three specimens were cast per mix. Each specimen had horizontally bonded reinforcing bars of 12 or 20 mm in diameter and 1 m in length. A rigid plastic sheathing was tightly attached to the loaded end of each bar to limit the bond between the bar and concrete to the remaining portion of the bar. The anchorage length was 120 mm for all bars. The bonded length of each bar was properly cleaned to ensure an adequate bond with concrete. Average bond stresses were evaluated by pull-out testing using a 2000-kN hydraulic machine and 200-kN load cell. The pull-out load is applied progressively up to bond failure and the deformation of the bar was measured using two LVDT connected to the unloaded end of the bar (Fig. 9). A data acquisition system was used. The test was terminated when pull-out failure occurred, the reinforced steel began to yield, or the surrounding concrete cover failed in split. The average bond strength was calculated as follows: τ= P π d bls where P, db , and ls correspond to the applied load, bar diameter and bonded length, respectively. 14 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 15 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-5-2 The net slip was calculated as the total measured deformation minus the elastic deformation in the steel and concrete. 150 x 100 x 100 mm ls Rigid plastic sheathing db = 12 and 20 mm P Fig. 9 – Pull-out test arrangement used to determine bond strength It is important to note that with reinforced concrete members, both the concrete and the steel bars are simultaneously placed in tension in positive moment regions. However, in the test arrangement adopted in this study, the pulled-out steel bar was subjected to tension, while the surrounding concrete was in compression. The confining compressive stresses around the steel bar were therefore reduced by positioning the bonded region of the bar away from the loaded end of the specimen. A good reproducibility of bond stress development vs. net slip was obtained for all mixes and bar sizes. Typical variations in bond stress (τmax) vs. net slip for three reinforcing bars of 20-mm diameter of SCCH are shown in Fig. 10. The coefficient of variation (V) of the average bond strength values of the SCC mixes was between 2 to 14%. For all specimens of SCC and the reference mixes with 10 d b and 6 db development lengths, failure resulted from the splitting of the cover. Given the absence of stirrups that provide some confinement and delay crack propagation, the splitting plane propagated through the cover. Therefore in the absence of ultimate average bond strength values corresponding to a bond failure mode, average bond stresses at small net slips were considered in the analysis of all mixes. Fig. 11 shows the variations of the maximum bond strength of all mixes. 15 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 16 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 0.6 SCCH d = 12 mm Net slip (mm) 0.80 0.4 0.3 0.2 V = 1.5% 0.60 0.40 0.20 0.1 V = 6.7% 0 0.00 0.00 2.00 4.00 6.00 8.00 10.00 0 5 10 Average bond stress (MPa) at 75 d Average bond stress (MPa) at 30 d Fig. 10 – Typical changes of bond stress with net slip of RH and SCCH mixes As expected, a reduction in bond strength was observed when the diameter of the bar increased (Fig. 11). The τmax between embedded reinforcement bar and concrete depends on the diameter of the bar, as well as the mechanical property (e.g. strength) of the concrete. At 32 ± 4 d, the τmax of SCCC was about 32-45% higher than that of the reference mix (RC). 40 Z max (MPa) Net slip (mm) 0.5 1.00 RH mix d = 20 mm 30 diam. = 12 mm diam. = 20 mm 36 d 60 d 32 d 20 75 d 30 d 10 0 RH SCCH RC SCCC FSCC Fig. 11 - Variations of max bond strength of all mixes Bond strength is often expressed in terms of tensile strength of the concrete or the square root of f’c. The τmax values are normalised by dividing them by the square root of the mean f’c measured on the cubes. The normalised ratios of τmax values of the SCC housing and civil engineering, and fibre SCC mixes are plotted in Fig. 12. Such ratios for the reference mixes of housing and civil engineering are included for comparison. 16 15 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 17 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 For housing mixes, the normalised ratios (τmax / f' cu ) for both diameters (12 and 20 mm) of SCCH are higher than those of reference. The SCCH normalised ratio was about 10% higher than that of reference mix. For the civil engineering mixes, the normalised ratios of SCCC were also higher than those of RC mix by 18-38%.. The FSCC exhibited the highest values of normalised ratios (3.63 for 12 mm and 2.65 for 20 mm). Thus the SCCH and SCCC mixes exhibited high bond strength, and the normalised ratio values of both were higher than those of the references mixes (RH and RC) for both diameters considered in this project (12 and 20 mm). 4 diam. = 12 mm Zmax / V f' c 3 diam. = 20 mm 2 1 0 RH SCCH RC SCCC Fig. 12 – Variation of ômax / f' cu FSCC ratio of mixes tested 5.4 Modulus of elasticity The modulus of elasticity was determined according to British Standard 1881,Testing concrete: Part 121: Method for determination of static modulus of elasticity in compression. End capped φ150 x 300 cylinder specimens were cured in water and tested at ages of 4 to 13 months for different mixes. Average results obtained from two individual specimens for each concrete mix are given in Table 7. For an easier comparison, the ratios of E modulus to square root of cylinder compressive strength for all the mixes are also included, as a relationship in the form of E / (fc)0.5 has been widely reported [4]. Table 7 - Static modulus of elasticity Test results Age at testing, months Modulus E, GPa E/(fc)0.5 ratio Concrete mix RH SCCH RC SCCC FSCC 13 4 34.1 8 34.4 11 41.9 7 37.7 4.92 4.98 4.43 5.43 17 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 18 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 The results in Table 7 indicate that the SCC mixes had the same relationship between modulus of elasticity and compressive strength as the reference mixes. The E/(fc)0.5 ratio was also close to the value of 4.73 recommended by ACI 318-89 (revised 1992) for structural calculations, applicable to normal weight concrete. 5.5 Drying shrinkage (U of P) The dimensions of prisms used to measure the drying shrinkage were 100 x 100 x 400 mm. Drying shrinkage specimens were demoulded after one day, then cured in water for a further six days. After curing, the specimens were stored in laboratory environment with temperature of 20 ± 5 ºC. A Demec gauge was used to measure the surface drying shrinkage on two parallel sides. The experimental results of drying shrinkage are shown in Fig. 13. The drying shrinkage of SCCs at 7 d was slightly higher than that of the reference mix but at 28 days and later, the reference mixes exhibited greater shrinkage than SCC mixes. The drying shrinkages of the reference mixes were 30% (RH) and 35% (RC) higher than those of the SCCs at 150 days. This is considered to be due to the effect of the volume of paste and W/P. Similarly, the drying shrinkage of FSCC at 120 d was about 47% lower that that of RC (490 µm/m vs. 720 µm/m). 1200 Strain (x10-6) 1000 800 600 SCCH RH 400 SCCC 200 RC FSCC 0 0 50 100 150 Age (d) 200 250 300 Fig. 13 - Drying shrinkage of mixes tested 5.6 Shrinkage and creep (Results from LCPC) Experiments carried out at LCPC aimed at producing two different self-compacting concretes with mean compressive cylinder strengths of 40 MPa and 70 MPa. Two mix designs derived from the proportions proposed in Task 1 were selected and shown in Table 8. 18 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 19 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Table 8 - Composition of the concretes tested at LCPC SCC40 163 319 912 760 192 4.1 169 1.2 0.5287 0.51 Filler (kg/m³) Cement (kg/m³) Val de Reuil 0/4 (kg/m³) Grande Paroisse 4/10 (kg/m³) Water added (kg/m³) Sikament 10 (kg/m³) Free water (kg/m³) Air (%) Free water/cement ratio Filler/cement SCC70 52 444 874 851 176 9.3 156 0.5 0.3512 0.116 Description of the tests The mixing process was the following: − Mixing of dry materials for 1 min. − Introduction of the water and 1/3 of the superplasticizer during 30 sec. − Mixing for 2 min. − Addition of the remaining 2/3 of superplasticizer and mixing for 1 min 30 sec. Two batches of 140 litres were made in a pan mixer. Slump flow was measured and specimens for determination of compressive strength at 28 days were made. The results are summarized in Table 9. Table 9 -Properties of fresh concretes LCPC test SCC40 76 x 76 SCC70 80 x 76 T500 (s) 2.8 4.3 Strength at 28 days (MPa) 46.5 62 Slump flow (cm) Then for SCC40 and SCC70, four Ø 160 x 1000 mm cylinders were cast for shrinkage and creep measurements: • one for autogenous shrinkage (AS, without desiccation) • one for the total shrinkage (TS, with desiccation) • one for basic creep (BC, without desiccation) • one for total creep (TC, with desiccation). In the report the samples are identified by the name of the mix and the type of test (eg: SCC40-AS for autogeneous shrinkage on mix SCC40). The complete methodology 19 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 20 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 used at LCPC for shrinkage and creep tests is described in [5]. Figures 14 and 15 show the creep and the shrinkage frames. The base of the strain measurements is 50 cm long between the two sets of the 3 invar rods. 1 2 3 4 5 b 6 Legend b measurement base = 50 cm 1 LVDT 2 measurement triangle 3 creep frame 4 invar rod 5 concrete specimen 6 nitrogen accumulator 7 steel flat jack 8 3 way valve 9 load cell 10 rod support 7 8 Fig. 14 - Creep frame Fig. 15 – Shrinkage frame [5] 20 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 21 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 For the tests without desiccation, the columns were wrapped with a double layer of self-adhesive aluminium sheet just after demoulding. Table 10 describes procedure used for each concrete cylinder: Table 10- Planning for the preparation of the cylinders Mix Type of test Demolding Aluminum wrapping SCC40 AS at 1 day at 1 day SCC40 TS at 1 day SCC40 BC at 1 day SCC40 TC at 1 day SCC 70 AS at 1 day SCC 70 TS at 1 day SCC 70 BC at 1 day SCC 70 TC at 1 day Start of desiccation Level of stress (MPa) Age of loading 11.51 at 28 days 11.21 at 28 days 19.65 at 28 days 19.69 at 28 days at 1 day at 1 day at 1 day at 1 day at 1 day at 1 day at 1 day The shrinkage test specimens (cylinder) were fitted with a device to measure the internal temperature of the concrete in order to ensure that the strain measurement s were not disturbed by thermal strains. It can be seen on Figure 16 that after 24 hours, the temperature was stabilised in all the cylinders. 31 29 SCC40-AS SCC40-TS 27 Te mp era 25 tur e 23 (° C) 21 SCC70-AS SCC70-TS 19 17 0 1 2 3 4 5 6 Time (in days) Fig. 16 - Temperature of the concrete at early age in the Ø 16 x 100 mm cylinders 21 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 22 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 AS = autogeneous shrinkage (wrapped + sealed) TS = total shrinkage (in air) The following Figures 17 and 18 show the results obtained after one year of test. -700 -600 Strain (µm/m) -500 SCC40-AS -400 SCC40-TS -300 -200 -100 0 0 100 200 300 400 Time (days) -700 -600 Strain (µm/m) -500 SCC70-AS -400 SCC70-TS -300 -200 -100 0 0 100 200 300 400 Time (days) Fig. 17 - Strain due to shrinkage without and with desiccation 22 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 23 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 -1200 Strain (µm/m) -1000 -800 SCC40-BC SCC40-TC -600 -400 -200 0 0 100 200 300 400 Time (days) -1200 Strain (µm/m) -1000 -800 SCC70-BC SCC70-TC -600 -400 -200 0 0 100 200 300 400 Time (days) Fig. 18 - Strain measured in creep tests with and without desiccation Note: strain due to shrinkage is deducted, but elastic strain due to loading is included in the results presented. 5.7 Water absorption of near-surface concrete It is now recognised that the transport properties of near-surface concrete play a major role in the durability of reinforced concrete. This is because most deterioration processes affecting concrete structures involve the transport of aggressive agents (eg. water, pure or carrying aggressive ions, carbon dioxide and oxygen) into the concrete and it is usually the case that the more resistant the concrete is to ingress, the more durable it will be [6]. The transport characteristic of the near-surface concrete is controlled by three mechanisms/processes, namely, capillary absorption, permeability and diffusion. As a starting point the ability of near-surface concrete to absorb and transmit water by capillary action is determined and serves as an indirect measure for concrete durability performance in this study. A recent RILEM recommendation, RILEM TC116-PCD: Permeability of Concrete as a Criterion of its Durability - C: Determination of the capillary absorption of water of hardened concrete, 1999, was adopted and modified for this study [7]. The experimental set-up for the capillary absorption test is shown in Figure 19. The moulded side faces of 150 mm cube specimens were tested, instead of the moulded bottom face used in the RILEM recommendation. The specimens were cured in water 23 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 24 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 for six months and then put into an oven at 50-55o C for four weeks as preconditioning. After cooling, the specimens were prepared and tested according to the test procedures described in the RILEM recommendation. The uptake of water by capillary absorption is measured through the weight of the specimens at time intervals of 10 minutes, 0.5 h, 1 h, 2 h, 4 h, and 24 hours of contact with water. Fig. 19 - Experimental set-up for the capillary absorption test (RILEM TC116-PCD) The test results for the SCC and references mixes, calculated as water absorption per unit area of the test surface i (g/m²), for the respective suction periods, t (minute or hour), are presented in Figure 20 and Table 11. The straight lines in Figure 20 indicate that there exists a relation of the form: i = St0.5. For the absorption of water, 1 g in mass is equivalent to 1000 mm³ in volume, thus S (mm/min.0.5 or mm/hour0.5), usually called sorptivity, can be obtained from the slope of the i vs. t0.5 curve, as described elsewhere [8]. The results for sorptivity, which is an indicator for the rate of capillary water absorption of the test concrete surface, are also given in Table 11. 24 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 25 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 Capillary absorption, g/m² 7000 6000 5000 RC SCCC SCCH FSCC RH 4000 3000 2000 1000 0 0.00 10.00 20.00 30.00 40.00 Time, minutes^1/2 Fig. 20 - Capillary water absorption of concrete surface Table 11 - Results of capillary absorption of water on concrete surface Concrete mixes RC SCCC RH SCCH FSCC Water absorption per unit area of the test surface, g/m² 10 min 30 min 1 hour 4 hours 24 hours 576.5 412.7 752.8 391.1 217.7 867.1 571.4 1192.6 613.3 349.2 1194.5 734.7 1614.4 795.6 471.6 2292.2 1229.0 2956.6 1413.3 1002.2 4584.3 2789.0 6616.2 3173.3 2602.9 Sorptivity, mm/h0.5 0.8895 0.5282 1.298 0.6148 0.5361 The results in Figure 20 and Table 11 clearly indicate that the capillary absorption was considerably higher for the reference concrete mixes than for the SCC mixes of similar compressive strength or w/c ratio. Comparing all the concrete mixes, the rate of water absorption, indicated by the magnitude of sorptivity was in the order of RH > RC > SCCH > FSCC > SCCC. Such results suggest that the near-surface concrete was denser and more resistant to fluid ingress in the SCC mixes than in the corresponding reference mixes. This is likely to be mainly due to the relatively lower water-powder ratio of all the SCC mixes, as well as filling effects of the fine limestone powder in the SCCH and FSCC mixes and the increase of cement hydration products owing to the GGBS in the SCCC mix. Other factors, such as the better dispersion of cement and powder particles and better water retention in the fresh SCC mixes may also contribute to their lower near-surface absorption. 25 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 26 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 5.8 Carbonation As stated earlier, the durability of the hardened concrete was to be assessed through external exposure of one column and one beam for each concrete mix. Although this will provide reliable results, the durability performance (or any deterioration) has to be monitored over a long period. Since the length of the exposure at this time is evaluated from 8 to 15 months only it is still too early to obtain a meaningful evaluation of durability. Assessment of extent of the carbonation carried out at this stage is only intended to serve as a starting point for further monitoring. With respect to durability, the importance of carbonation lies in the fact that it reduces the pH value of the pore solution in hardened Portland cement paste, from above 13 to a value of about 9. The reduction of pH value to a critical value can result in depassivation of the protective oxide film on the steel and thus the initiation of corrosion. In this study, the measurement of carbonation was determined using the common phenolphthalein test. The test procedure is described in RILEM recommendations CPC-18, Measurement of hardened concrete carbonation depth, 1988 [9]. A limited number of readings on the carbonation depth at different exposure periods was obtained and is presented in Table 12. It is impossible to draw a definite conclusion from the very limited results at this early stage. At one year, the C35 grade SCCH and RH mixes both showed a 2 mm carbonation depth, while the C60 grade SCCC and RC showed no sign of carbonation. For the FSCC mix, a carbonation depth of around 0.5 mm was observed at 8 months. Table 12 - Depth of carbonation of concretes exposed to outdoor environment in UK Carbonation depth, mm Exposure period 6-9 months 10-12 months 13-15 months RH 0.5 N/A 2.0 Concrete mixes used SCCH RC SCCC 0.5 0 0 N/A 0 0 2.0 --- FSCC 0.5 --- 5.9 Freeze-thaw resistance Two prisms measuring 75 x 75 x 300 mm were cast for each concrete for evaluating freeze-thaw durability. The specimens were demo ulded after 24 h and cured in limesaturated water at 20 ± 2 ºC for 28 days, then subjected to freeze-thaw cycles. The prisms were monitored for mass loss and change in dynamic modulus of elasticity. The daily freeze-thaw cycle consisted of storing the specimens in a freezer at -30 ºC for 18 hr, then at room temperature for 6 hr to 7 hr. The results of the freeze-thaw durability tests are shown in Fig. 28. It should be emphasised that the concrete was not air entrained. There has been no loss of mass to date in any of the mixes subjected to the freeze-thaw cycles. The civil engineering mixes, both SCCC and the RC show no drop in ultra-sonic pulse velocity (UPV %), 26 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 27 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 and exhibit better resistance than the two housing concrete mixes. After 125 cycles, the UPV of SCCC was reduced by only 5%. Considering the housing mixes, it was observed that the SCC mix exhibited lower resistance to freeze-thaw than the reference mix. The UPV values of the SCC and reference mixes after 125 cycles of freeze-thaw were reduced by 71% and 48% respectively. After 95 cycles of freeze-thaw, the UPV of FSCC mix was reduced by 32% and exhibited lower resistance than the civil mixes. Average UPV (m/s) 6000 SCCH 5000 RH SCCC 4000 FSCC RC 3000 2000 1000 0 0 20 40 60 80 100 120 140 160 Number of freeze-thaw cycles Fig. 21 – Reduction in ultra-sonic pulse velocity (UPV) of all mixes 6. PROPERTIES OF HARDENED CONCRETE IN FULL-SIZE STRUCTURAL ELEMENTS To permit the range of comparisons required, three full-size beams and/or columns were cast for the mixes, as follows: SCCH – columns only, RH – beams and columns, SCCC beams and columns, RC – beams and columns. FSCC – beams only. One of the three was loaded to failure post-28 days, one was used for in-situ testing, and one has been left at an outdoor exposure site for future assessment of durability. 6.1 In-situ testing The quality of the in-situ concrete in the 3-metre high columns and 4-metre long beams was assessed in three ways: • Core test - assesses in-situ compressive strength • Rebound (Schmidt) hammer test - assesses near-surface quality and uniformity • Pull-out (Lok) test - assesses near-surface quality and uniformity The full-scale SCC columns were cast by pouring the concrete directly from the top of the formwork with a free fall of up to 3 metres through the reinforcement (see Fig. 36). The casting of the SCC beams the concrete was poured from one end and allowed to flow to the other over the distance of 3.8 metres. To examine if SCC mixes achieve adequate compaction, and similar uniformity in properties within the 27 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 28 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 element to those obtained with properly compacted reference concrete mixes, tests were carried out at the top, bottom and middle section for the columns, and both ends and the middle section for the beams. 6.1.1 Test arrangements Core tests Tests were carried out according to procedures described in BS1881: Part 120 - Method for determination of the compressive strength of concrete cores. Three 100-mm diameter horizontal cores were taken at each test location within selected columns and beams. The cores were then cut to the required length and their ends capped. The prepared concrete cores were tested at the age of roughly 3 months, and the results were calculated and expressed as estimated in-situ cube strength. Rebound (Schmidt) hammer test Tests were carried out according to the procedures described in Draft European standard prEN12398: Testing concrete – Non-destructive testing - Determination of rebound number. A digitised apparatus, namely “Digi-Schmidt hammer”, which automatically records the rebound number for each testing was used in this study. Testing was carried out at the ages of 7 days and 28 days, and a minimum of 40 readings was taken at each location along the height of columns and along the length of beams. Pull out (LOK) test The Pull out (LOK) test has attracted special attention in recent years because of the excellent correlation obtained between pullout force and standard compressive strength. The system is flexible and produces only a minimal destruction to the structure. The LOK test was selected in this study to provide direct information on the quality of cover concrete and its uniformity in the structural element, i.e. along the height of columns and the length of beams. The test method has been described and standardised in ASTM (ASTM, C-900), British (BS 1881, part 207, 1992), International (ISO/DIS, 8046), Swedish (SS, 137238), Danish (DS, 423.31) and draft European standards (prEN 12399:1996). In this study, 4 cast-in inserts were used at each test location (i.e. top, middle, bottom section of a column, and end A, middle, end B section of a beam). Two of the four inserts at each location were pulled out at 7 days and the other at 28 days, and the pullout forces were recorded (Fig. 22). 28 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 29 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Fig. 22 - Lok test 6.1.2 Results and discussions of in-situ compressive strength The core test results were expressed as estimated in-situ strengths in accordance with British Standard practice to allow for difference in core dimensions and the presence of steel bars. The results of the core test at the age of 3 months for the selected columns and the selected beams are plotted in Figures 23 and 24 respectively. To permit direct comparisons of the strength variation within columns and beams between the different grades of concrete, the results have also been expressed as percentage s of the top section result for columns, and end A result for beams. End A is the casting end of the beams. These variations are shown in Figures 23 and 24 respectively. For the in-situ strength variation in columns , Figures 23 and 25 demonstrate higher strengths at the bottom than the top, as is usual with traditional compacted concrete. The general profile of the results is similar in all the cases, with the exception of the RC mix which shows a lower result in the middle section. The results also show that the strength variation within the column is less significant for C60 strength grade mixes (both SCCC and RC) than for C35 mixes ( both SCCH and RH). Comparisons of the relative results in Figure 25 suggest that the variation of strength in both strength grades is smaller in the SCC mixes than in the corresponding reference mixes. 29 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 30 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 d from bottom of column (mm) 3000 Top RH 2500 RC SCCH SCCC 2000 1500 Middle 1000 500 Bottom 0 20 30 40 50 60 70 80 Estimated in-situ cube strength (MPa) In-situ compressive strength, MPa Fig. 23 - Variation of in-situ compressive strength along height of columns 80.0 End A 70.0 Middle End B SCCC RC FSCC 60.0 50.0 40.0 30.0 RH 20.0 0 1000 2000 3000 4000 D from end A of a beam, mm (End A being casting point for SCC mixes) Fig. 24 - Variation of in-situ compressive strength along length of beams 30 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 31 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 d from bottom (mm) 3000 Top 2500 2000 Middle 1500 RC 1000 SCCC RH 500 SCCH Bottom 0 90 95 100 105 110 115 120 In-situ strength as % of top section of column Fig. 25 - In-situ compressive strength as % of strength at top section of column In-situ strength as % of end A 120 RH RC 115 SCCC FSCC 110 105 100 95 End A Middle End B 90 0 1000 2000 3000 D from end A of a beam, mm 4000 Fig. 26 - In-situ compressive strength as % of end A of beam Compared to the strength variations along height of columns, results in Figures 24 and 26 demonstrate that the strength variation along the length of beams was much smaller. For example, a difference of strength up to 15% was observed in the RH column, while the maximum strength difference in beams was 7%. The general profile and relative variation of the results for beams are also similar for all the mixes studied. 31 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 32 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 In-situ strength as % of 28 day cube strength Comparisons of the in-situ strength re sults with the corresponding 28-day standard cube strengths can also be made by plotting the relative results, as presented in Figures 27 and 28 for columns and beams respectively. Results in Figure 26 indicate that the in-situ strength achieved in the columns (all mixes) varies between 80-100% of the standard cube strength, which is above the average value of 65% reported for such elements [10]. Two other points may be noted: firstly, that the in-situ strength of the SCCH mix is closer to the 28-day cube strength than that of the corresponding reference mix RH in the C35 grade; and secondly, in the C60 grade, that there is no significant difference in the in-situ strength of the two mixes. 105 SCCH SCCC RH RC 95 85 75 top middle bottom Location of cores in column In-situ strength as % of 28-day standard cube strength Fig. 27 - In-situ compressive strength in columns relative to standard 28-day strength 110 RH RC SCCC FSCC 100 90 80 70 End A Middle End B Location of cores in beam Fig. 28 - In-situ compressive strength in beams relative to standard 28-day strength 32 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 33 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Results in Figure 28, however, show a different picture from that in Figure 27. For RH and SCCC mixes, the in-situ strength in beams relative to the 28-day cube strength was significantly lower than in columns cast at the same time. The curing conditions for individual elements explain the difference in performance. The columns were cast inside the laboratory building with a relatively constant temperature of around 20o C all year round, while the beams were cast outdoors with a range of temperatures depending on the month of the year. The reference beams were compacted by poker vibrators and cast outdoors to simulate in-situ concrete construction process (the noise levels were measured in Task 8.5). The casting of RH mix and SCCC mix was carried out in January and March respectively with an average temperature of 5 - 10o C, while the RC and FSCC mixes were cast in June and July with temperature sometimes over 20 degrees in the daytime. Taking the different casting temperatures into account, the results for the beams appear to be reasonable and generally in agreement with the results for the columns as the average relative strength value reported for such elements was 75% [10]. Core testing of larger pours was also carried out by one of the project partners in Sweden. Although the core results were not directly traceable to the standard cube results from the pours, they complied with that element in the Swedish standard which requires a minimum relationship between cores and cubes. 6.1.3 Results and discussions of the other in-situ tests Results of the Lok test pullout load (Table 25 in appendix) and the Schmidt hammer rebound number were analysed in the same manner as for the in-situ strengths, and are presented in Figures 29 and 30 for the test beams and columns respectively. Results in Figures 29 and 30 demonstrate that the results of the Schmidt hammer and Lok test tests generally confirm the pattern of results observed for the cores. The near-surface concrete quality increased towards the bottom of columns, but the difference between top and bottom of the columns was more pronounced in the housing mixes (i.e. C35) than in the civil mixes (i.e. C60). The results also indicate that the concrete properties were less variable along the length of beams than along the height of columns, particularly for the housing mixes. Furthermore, any difference in uniformity of the properties of the SCC and the corresponding reference mixes was not statistically significant, with the uniformity for the SCC mixes being marginally better. 33 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 34 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete Relative results as % of end A of beam Relative results as % of end A of beam 2000-04-26 core strength rebound number 120 115 core strength rebound number pull-out load 120 115 RH 110 105 110 105 100 100 95 95 90 85 120 115 110 105 100 95 90 85 pull-out load RC 90 85 120 115 110 105 100 95 90 85 FSCC End A Middle SCCC End B End A Middle End B Location of test points in beam Location of test points in beam Fig. 29 - Variation of in-situ properties of SCC and reference mixes in beams Relative results as % of Relative results as % of top section of column top section of column core strength rebound number core strength pull-out load 120 115 120 115 SCCH 110 110 105 105 100 100 95 95 90 90 120 120 115 115 110 pull-out load rebound number RH 110 105 105 100 100 95 95 90 SCCC RC 90 Top Middle Bottom Location of test points in column Top Middle Bottom Location of test points in column Fig. 30 - Variation of in-situ properties of SCC and reference mixes in columns 34 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 35 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 6.1.4 Statistical analysis of the test results In sections 6.1.2 and 6.1.3, the test results were analysed and presented in terms of variations along the height of columns and along the length of beams. It is essential to assess the reliability of the results and to determine the statistical significance of any differences of results within the columns or beams, particularly when the variations of results at different sections are high. A significantly larger number of test results on in-situ compressive strength and rebound number was acquired, and has enabled limited statistical analysis of reliability and variation of the strength and rebound number results to be made . The average results of in-situ cube strength obtained from nine cores for each column or beam, and their variations in the columns and beams for all the SCC and reference concrete used are calculated and presented in Table 13. The statistical analysis tool ANOVA (analysis of variance) - was also used to determine the statistical significance of differences of results along the height of column and along the length of beam. It was found that at the 5% significance level (related to 95% confidence), α=5%, the differences of in-situ compressive strength at different sections of the column and beam were not statistically significant. At the 10% significance level,α=10%, however, the difference of in-situ strength along the height of column (ie. top, middle and bottom sections) was statistically significant for the RH, SCCH and RC mixes, while the differences for the SCCC column and all the beams remained statistically insignificant. Table 13 - Statistical analysis of in-situ compressive strength for columns and beams In-situ equivalent cube strength, MPa RH Mean STD * V, % ** Mean STD V, % 31.35 3.02 9.6 29.28 1.94 6.6 SCCH 44.60 2.96 6.6 N/A N/A N/A RC 57.65 3.25 5.6 60.00 3.40 5.7 SCCC 71.82 4.50 6.3 66.04 5.83 8.8 FSCC N/A N/A N/A 56.13 3.24 5.8 Results for columns Results for beams ∑ [x − x] 2 * STD - sample standard deviation (estimate s. d; s = ** V - coefficient of variation i n −1 Similar analysis was applied to the results of rebound hammer testing. Forty readings were taken at each location along the height of columns or along the length of beams. Testing was carried out on two columns and two beams for each concrete mix, and all the data points, including outliers were used in the analysis. The mean values and the 35 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 36 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 variations of rebound number along the height of the columns and along the length of beams for all the SCC and reference concretes used are calculated and presented in Table 14. A typical set of actual rebound number readings for the SCCH and the RH concrete column is presented in Figures 31 and 32 respectively. S-H rebound number Coef. of variation, %: Top=7.3, Middle=8.1, Bottom=10.8 60 SCCH mix 50 40 30 Top Middle Bottom 20 0 10 20 30 40 Test points Fig. 31 - Typical local variation in rebound number readings in SCCH columns The ANOVA was also applied to all the test data and it was found that the differences of rebound number along the height of column were statistically very significant (at α=1% in most cases) for all the SCC and reference mixes. For the variation along the length of beams, however, the differences were found to be not significant even at the 10% significance level, α=10%. S-H rebound number Coef. of variation, %: Top=8.3, Middle=12.9, Bottom=15.7 60 RH mix 50 40 30 Top Middle Bottom 20 Test points 30 20 0 10 40 Fig. 32 - Typical local variation in rebound number readings in RH columns 36 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 37 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Table 14 - Statistical variation of rebound number for columns and beams at 28 days Results for column In-situ rebound number RH SCCH RC SCCC Mean V, % Nb of test points Top, A* 34.8 7.8 160 Middle 37.3 11.0 160 33.7 8.5 80 Bottom, B** 40.8 15.0 160 33.6 8.4 80 Top 35.7 7.1 160 Middle 35.7 7.7 160 N/A N/A N/A Bottom 40.8 11.3 160 Top, A 44.1 6.9 160 41.4 6.0 80 Middle 46.5 6.9 160 42.3 4.4 80 Bottom, B 46.6 5.5 160 42.4 6.7 80 Top, A 45.0 5.2 120 39.8 7.6 80 Middle 46.0 4.7 120 40.5 8.6 80 Bottom, B 46.3 4.6 120 40.2 5.6 80 42.9 7.5 80 43.3 7.5 80 42.3 5.7 80 End A FSCC Middle N/A N/A End B * ** Results for beam Nb of Mean V, % test points 33.3 9.7 80 N/A Top, A - indicating location of test points were eithe r near the Top of the columns, or near the end A (ie. the casting end for SCC mixes) of the beams Bottom, B - indicating location of test points were either near the Bottom of the columns or near the end B of the beams In general, the statistical analysis in this section confirmed the validity/reliability of the results discussed in Sections 6.1.2 and 6.1.3. It is clear from the outcome of the ANOVA that the differences of in-situ strength and surface “hardness” in different sections of beams were not statistically significant for either the SCC or the reference mixes. The differences along the height of columns , however, were statistically significant for all the mixes; this is a normal characteristic of concrete. The results also suggest that variation of results was generally greater in the C35 mixes than in C60 mixes for both SCC and references mixes. 37 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 38 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 In terms of the differences between the SCC and reference elements, the actual level of variation of results within columns and beams was similar, the only observation being that the variations of results within the reference columns was slightly higher than in the SCC columns. 6.1.5 Conclusions The quality of the in-situ concrete properties in the columns and beams was assessed by testing cores for in-situ strength, and pullout of pre-embedded inserts and rebound hammer number, for uniformity in near-surface properties. From the overall test results and analysis, the following general conclusions could be drawn. 1) In-situ strength achieved in the columns for all the SCC and reference mixes was in the range of 80-100% of the 28-day strength for standard cube specimens, the percentage being generally higher for the C60 grade mixes (SCCC and RC) than for the C35 grade mixes (SCCH and RH). This is well above the average value of 65% reported for such elements. In-situ strengths achieved in the beams for the SCC and reference mixes were affected by the different ambient conditions at casting, but all were above the reported average of 75% for such elements 2) The SCCH mix containing limestone powder achieved a significantly higher insitu strength than the corresponding reference RH mix, probably due to the accelerating, and densifying effect of the filler. 3) The in-situ strength and near surface quality of the concrete increased along the height of the columns towards the bottom, the difference being greater in the C35 housing mixes than the C60 civil engineering mixes. These differences were statistically significant. The variation of concrete properties was statistically insignificant along the length of 3.8-metre beams. 4) There were no significant differences in uniformity of in-situ properties between the SCC mixes and the corresponding reference mixes; the properties of the SCC mixes were marginally more uniform. 6.1.6 Micro-mechanical study of the interfacial zone The interfacial transition zone (ITZ) between cement paste and aggregate (or fibre) and around steel reinforcing bars has been an area of particular interest associated with engineering and durability properties of cementitious composites and structural reinforced concrete. As a result of its more porous and heterogeneous/anisotropic nature, the ITZ was recognised to be the 'weak link' in cement and concrete composites and to have a considerable influence on the engineering and durability properties. However, it has been very difficult to assess the micro-mechanical properties of the ITZ in real concrete specimens, as it requires specialised techniques and apparatus. At Paisley, a unique depth-sensing microindentation method was previously used for micro-strength testing and fibre push-in testing to assess interfacial and bond properties in glass fibre reinforced cementitious composites. Significant advances have been made recently in improving the micro/nano-indentation test method and in theoretical analysis of the test data, and this has allowed assessment of micromechanical properties, such as elastic modulus and micro-strength within the ITZ to 38 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 39 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 be made. The depth-sensing microindentation method now offers great advantages over the conventional Vickers microhardness testing. In this preliminary study, the depth-sensing microindentation method was applied to investigate the ITZ in structural reinforced concrete, particularly the mechanical properties of the ITZ above and below a horizontal steel reinforcing bar. The specimens extracted from the SCCC and RC beams were selected for the investigation, thus enabling possible a comparison of the ITZ properties of the SCC and the corresponding reference mixes. Specimens for the microindentation testing were prepared by first drilling φ 100 x 200 mm cores horizontally from the middle section of the beam, the cores intersecting the three φ 16 reinforcing bars of the upper layer in the tensile zone. Small specimens (roughly φ 35 x 20 mm) with only one steel bar at the centre were then extracted from the cores, using a diamond saw. This was then followed by resin embedding, precision sectioning, grinding, polishing and ultrasonic cleaning to obtain the final specimens (φ 40 x 15 mm) for the microindentation test. 6.1.6.1 Measurement of elastic modulus and micro-strength All experiments were performed using a depth-sensing microindentation apparatus, MicroTest 200, available at the University of Paisley. The load and depth (or displacement of the indenter) were continuously monitored during a programmed microindentation load cycling. The operating principle and special features of the apparatus were described in detail elsewhere [11]. A relatively sharp 90o diamond indenter/probe in the shape of a corner of a cube was selected for this study so that smaller but deeper indentations could be made. This would also make the test results less sensitive to the surface effects of imperfect specimen preparation (e.g. roughness and hardening/densification). A typical outcome of the microindentation testing is an indentation load-depth hysteresis curve as shown in Figure 33. As a load is applied to an indenter in contact with a specimen surface, an indent/impression is produced which consists of permanent/plastic deformation and temporary/elastic deformation. Recovery of the elastic deformation occurs when unloading is started. Determination of the elastic recovery by analysing the unloading data according to a model for the elastic contact problem leads to a solution for calculation of elastic modulus E and also microstrength/hardness H of the test area. Details of the theoretical background and methodology for the elastic modulus determination have been reviewed and presented elsewhere [12,13]. 39 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 40 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 LOAD, P Pmax loading unloading hp S hmax DISPLACEMENT (DEPTH), h Fig. 33 - A schematic diagram of an indentation load vs displacement curve Briefly, the specimen elastic modulus is determined using equations (1) and (2): S= dP 2 = Er A dh π ( ) ( 1 − v i2 1 1− v 2 = + Er E Ei (1) ) (2) Where, S = dP/dh is the experimentally measured stiffness of the upper portion of the unloading data; Er is a reduced elastic modulus defined in equation (2); A is the projected area of the elastic contact; E and v are Young's modulus and Poisson's ratio for the specimen; and Ei and vi are the same parameters for the indenter. For the diamond indenter used in this study, Ei = 1141 GPa and v = 0.07. The projected area A can be derived from the plastic depth hp obtained using the unloading data and the indenter shape function, which is dependent on its geometry. For an ideally perfect 900 (corner of a cube) indenter, A = 2.6hp 2 . In the case of imperfect indenter tip geometry, the shape function can be determined by using electron microscopy techniques or through calibration of a hardness (or elastic modulus) - plastic depth curve using a homogeneous material of constant hardness (or elastic modulus). A special defined parameter - microstrength, H = Pmax/A - can also be calculated, where Pmax is the maximum load applied. When the Vickers indenter is used the microstrength is equivalent to the Vicker microhardness. 40 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 41 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 6.1.6.2 Results and Discussions In this study all testing was programmed in such a way that the loading started when the indenter came into contact with the test surface and the load increased at a constant rate of 2.3 mN/s until a depth of penetration of indenter into the specimen reached a specified value of 10 µm. Then the load was held at its maximum for 10 seconds before unloading at the same constant rate. At completion of unloading, the specimen was retracted and moved to another test point. With the maximum depth setting of 10 µm the width of the indent/impression after the load removal was usually about 20 µm or less. The distance between two adjacent test points was thus set to be 60 µm or greater, to avoid possible overlapping of the areas affected. Photographs of a test specimen and a magnified tested interfacial area are shown in Figure 34. To study the interfacial zone around the horizontal reinforcing bar in both SCC and conventional concrete mixes, a large number of indentation tests were carried out in the steel-concrete interfacial areas at the top and the bottom sides (ie. above and below) of the steel bar. Since sand particles also existed in the tested area, the test points which lie closer to the aggregate particles than to the steel bar were considered invalid and discarded. A typical set of results is presented in Figure 35 as plots of modulus of elasticity and microstrength versus distance from the interface. MICRO-INDENTATION TESTING MICROINDENTATION Test point 1 Top CONCRETE STEEL BAR Steel bar Test point 2 Distance between test points = 80 µ m Bottom Test point 3 (a) (b) Fig. 34 - Photographs of the tested specimen: (a) specimen of the indentation test, (b) magnified view of interfacial area after testing 41 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 42 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 1000 under steel bar above steel bar 40.0 (a) Microstrength, MPa E-modulus, GPa 50.0 30.0 20.0 10.0 under steel bar above steel bar 800 (b) 600 400 200 0 0.0 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 Distance from (b) the interface, um Distance from(a) the interface, um Fig. 35 - A typical set of results versus distance from the interface for: (a) Elastic modulus, (b) Microstrength For all the specimens tested in this study, it was found that the micro-mechanical property (i.e. modulus and strength) profiles showed a trough within the ITZ, with the minimum values occurring at 10 - 30 µm from the actual steel interface. The values for their properties then increased when test points moved towards the bulk concrete matrix and became roughly constant at distances greater than 50 - 70 µm. It was also noted that the results showed moderate variations even at the same distance from the interface, and that interference of neighbouring aggregate/sand particles became more frequent at distances greater than 60 µm from the steel interface. The interference of steel bar was also present for test points adjacent to or less than 10 µm from the interface. For comparison of the micro-mechanical properties of different test areas of the ITZ and evaluation of their variations, the test points were classified into two groups according to their distance d, to the actual interface, namely 10 µm < d <30 µm, and 35 µm < d < 60 µm. The results for the 10 - 30 µm distance can be considered to represent the minimum value within the ITZ, whereas the results for the 35 - 60 µm distance may provide an indication of properties of the bulk matrix. Average results and the standard deviations of modulus of elasticity and micro-strength for both the SCC and reference mixes are presented in Table 15. The relative results of interfacial properties below and above the steel bar are compared in Figure 36. 42 70 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 43 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 Table 15 - Modulus of elasticity and micro-strength in the ITZ around steel bar Properties Modulus of elasticity, GPa Reference mix (RC) Test details SCC mix (SCCC) Below steel bar Above steel bar Below steel bar Above steel bar 10<d<30 µ m 9.8 17.6 12.9 15.0 St. deviation 4.0 4.4 4.5 5.5 35<d<60 µ m 17.6 21.5 25.2 24.4 St. deviation 5.1 5.9 4.6 3.8 Micro-strength, MPa 10<d<30 µ m 229 329 197 285 St. deviation 77 84 46 74 35<d<60 µ m 372 462 411 418 St. deviation 82 135 125 61 Interfacial properties below steel bar as % of above the bar E-modulus Micro-strength 120 10 < d < 30 um 35 < d < 60 um 100 80 60 40 20 RC SCCC RC Concrete mixes used SCCC Fig. 36 - Results of ITZ properties below steel bar relative to those above steel bar, % 43 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 44 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 The results in Table 15 and Figure 36 clearly indicate that the elastic modulus and micro-strength of the ITZ were significantly lower on the bottom side of the steel bar than on the top side. The difference was particularly pronounced in the 10 - 30 µm distance from the actual interface, and for the reference mix. For instance, at the distance of 10-30 µm, the interfacial E modulus and micro-strength of the reference mix below the steel bar was only 56% and 70% respectively of those above the bar. The corresponding results for the SCC mix were 86% and 69%, which suggests that the ITZ properties were more uniform in the SCC mix than in the reference mix. This may be due to the lower water content and higher powder volume in the fresh SCC mix. The average results for the distance of 35-60 µm from the interface showed that both properties on the bottom side achieved 80% of those on the top side for the reference mix, whereas for the SCC mix almost identical values were obtained on both sides. This was mainly due to the fact that for the reference mix the weak interfacial zone was found to be wider on the bottom side than on the top side of the bar. Such a phenomenon was not evident in the SCC mix. 6.1.6.3 Conclusions 1) The results obtained for both the SCC and the reference mixes revealed a distribution of micro-mechanical properties within ITZ with a common profile, namely with a trough, or a minimum, occurring at 10-30 µm from the actual steel interface. The width of the ITZ was found to be between 50 and 70 µm, beyond which the micro-mechanical properties became less variable. 2) The results indicated that the elastic modulus and the micro-strength of the ITZ were significantly lower on the bottom side of a horizontal steel reinforcement bar than on the top side. This supported the common perception that the ITZ is weaker underneath a large aggregate particle or steel bar than above it, owing to internal bleeding and settlement of particles during concrete placing. This effect was particularly pronounced at the 10-30 µm distance from the actual interface. 3) The difference of ITZ properties between top and bottom side of the horizontal steel bar seemed to be generally less pronounced for the SCC mix than for the reference mix. 6.2 Structural performance of full-scale elements 6.2.1 Design Columns The full-size columns are shown in Fig. 37 and measured 300 x 300 x 3000 mm. Two arrangements of links, Type A and B were adopted for housing and civil engineering, respectively (Fig. 37). The reinforcement details are shown in Table 16. All columns for housing and civil engineering were made with the same percentage of longitudinal reinforcement (ñg = 1.4 and 1.9% for Type A and Type B) and the same amount of lateral reinforcement, ñh = 0.66% for link configuration Type A and ñh = 1.53% for configuration Type B. Link spacings of 100 mm for housing and 75 mm for civil engineering were used. 44 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 45 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Deformed steel bars were used for longitudinal reinforcement and plain undeformed bars for the lateral reinforcement. Conventional strength steel was used for the longitudinal and confining link steel reinforcement, with nominal yield values of 460 and 250 MPa, respectively. Table 16 – Reinforcement details of columns Column Longitudinal reinforcement ñg (%) fyk (MPa) Lateral reinforcement Dh (mm) S (mm) Housing (Type A), Reference and SCCH 4 No16 + 4 No 12 1.4 460 10 100 Civil (Type B), Reference and 4 No16 + 8 No 12 1.9 460 10 75 SCCC fyk : Yield stress of steel reinforcement in compression (MPa) ñh : Percentage of longitudinal reinforcement (%) ñh : Percentage of lateral reinforcement (%) Dh : Nominal diameter (mm) S : Stirrup spacing (mm) ñh (%) fyk (MPa) 0.66 250 1.53 250 Beams Two configurations of reinforcement bars were used for housing and civil engineering. Beams for housing are reinforced with 2 bars of 16 mm diameter for tension, 2 of 12 mm for compressive and links spaced at 250 mm. Beams for civil engineering are reinforced with 6 bars of 16 mm diameter for tension and links spaced at 180 mm. Details of reinforcement are shown in Fig. 38. The same configuration of reinforcement bars used for housing was used for the steel fibre mix, with links spaced at 300 mm. 45 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 46 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Structural elements : COLUMNS 450 mm 250 mm Section of housing column – Type A 300 mm 40 mm Link Φ = 8 mm, spacing = 100 mm 300 mm 40 mm 4 Φ = 12 mm 4 Φ = 16 mm 3m 300 mm 2500 mm Section of civil engineering column – Type B 300 mm 40 mm Link Φ = 8 mm, spacing = 75 mm 300 mm 40 mm 8 Φ = 12 mm 4 Φ = 16 mm 250 mm 300 mm Fig.3 Fig. 37 - Details of reinforcement and dimensions of the columns 46 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 47 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 BEAM 3800 mm 200 mm Section of civil engineering Steel stirrup Φ = 8 mm, Spacing 180 mm b = 200 mm Steel compression reinforcement, Φ = 16 mm Steel tensile reinforcement, 3 + 3 Φ 16 mm h = 300 mm 50 mm 25 mm 25 mm Section of housing b = 200 mm Steel compression reinforcement, Φ = 12 mm Steel tensile reinforcement, Φ = 16 mm h = 300 mm 40 mm Steel stirrup Φ = 8 mm, Spacing = 250 mm RH and SCCH Spacing = 350 mm for Fibre mix 40 mm Fig. 38 - Details of reinforcement and dimensions of beams 47 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 48 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 6.2.2 Concrete placing procedures Columns . The set up for the placing is shown in figures 39-41. The reference columns were cast in three lifts and compacted using an external vibrator. In the case of the SCC columns, the concrete was cast through a hopper at the top of the formwork without internal or external compaction (Fig. 40). An acrylic plate was provided on one side of the formwork of one of the three columns to permit observation of concrete flow during the placement (Fig. 41). Fig. 39 – Columns with reinforcement detail prior to pour. Note: the gaps in the reinforcement of the left-hand column are to permit subsequent access for coring. Fig. 40 – Casting SCC with skip from the top of formwork 48 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 49 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 Fig 41 - Acrylic plate used for central column to provide observation of flow of concrete during the placement Beams . The reference civil beam was cast and consolidated using a poker vibrator. In the case of the SCC beams, the concrete was poured directly into one end of the formwork from the discharge chute of the truck mixer, and allowed to flow along the length of the beam (Fig. 42). Fig. 42 – Casting SCC beams 49 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 50 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 6.2.3 Test set-up for columns Thin layers of cement were used as capping over the top and bottom ends of each column to ensure parallelism of specimen end surfaces and uniform distribution of the load during testing. To ensure that the failure would occur in the central instrumented region on the column, the tapered ends were further confined with bolted boxes made from thick steel plates. Two hydraulic jacks, each with maximum compressive load capacity of 4000 kN were used. The axial displacement of specimens was recorded using three LVDTs located at three corners of the column and attached to upper and lower clamped steel collars with vertical bars fixed to the gauge length of 100 mm. The columns were subjected to monotonic concentric axial loading until failure, to determine the overall load carrying capacity, and hence the overall in-situ compressive strength (Fig. 43). Fig. 43 – Load testing of column 6.2.4 Test set-up for beam The beams were instrumented with a LVDT at mid-span to monitor deflection. The beam, spanning 3800 mm, was then subjected to four-point flexural testing as illustrated in Fig. 44. An automatic data acquisition system was used to monitor loading and mid-span deflection. The load was applied step-by-step to the beam at a rate of 5 KN per step by means of two 220 kN-hydraulic jacks and measured with a load cell (Fig. 45). At the end of each step, cracks were sketched and crack-width measured using a microscope (Fig. 46). 50 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 51 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 1.1 m P P 3.3 m 3.8 m Fig. 44 - Four point-flexural test on beams. Fig. 45 – Set-up for full-scale test of beam Fig 46 – Measurement of crack-width 51 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 52 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 6.2.5 Testing of columns The experimental results obtained from the testing of four reinforced columns are shown in Table 17, and Figure 47 shows the axial load versus strain curves of the four confined columns. Table 17 – Compressive test results of columns Columns Axial load AC Housing Reference 88743 SCCH 88743 Civil Eng. Reference 88291 SCCC 88291 Po = 0.67 f’cu Ac + fy Asc where: Age Pmax (kN) Pmax /Po 90 d 90 d 3420 3020 2.07 1.18 6 months 5203 5414 1.40 1.35 6 months Ac = b2 - Asc Po = calculated ultimate capacity of the column f’cu = in-situ compressive strength of the concrete (note: air cured strength used for columns) fy = yield stress of steel reinforcement in compression Ac = area of concrete (net) Asc = area of embedded steel 6000 Housing section 300 mm 40 mm 5000 Column axial load, P (KN) D = 8 mm (S=100 mm) SCCC RC 4 D = 16 mm 300 mm 4000 40 mm 4 D = 12 mm RH 3000 SCCH Civil section 300 mm 2000 40 mm D = 8 mm, (S=75 mm) 300 mm 1000 40 mm 8 D = 12 mm 4 D = 16 mm 0 0 0.0005 0.001 0.0015 0.002 0.0025 Concrete axial strain Fig. 47 – Comparison of concrete axial load vs. axial strain for columns 52 0.003 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 53 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 In this figure, Pmax is the maximum load sustained by the reinforced columns; Po is the calculated ultimate capacity of the column (Po = 0.67 f’cu Ac + f y Asc, the compressive axial strength of the column calculated in accordance the BS 8110 standard). A number of observations may be made: • • • • The maximum load, Pmax, varied from 3020 to 5415 kN. In all cases this exceeded the design load. The ratio Pmax/Po was lower in the SCC mixes, though only slightly so in the case of the civil engineering category. Examining the behaviour of the C60 (civil engineering) columns, the high observed toughness of both SCC and reference is due to the close spacing of the lateral confining reinforcement, which delays the buckling of the longitudinal bars and permits the full development of the steel strength of the links. The maximum load of the SCCC column was slightly higher than the RC column (reference) (5415 kN vs. 5203 kN), a consequence of the higher compressive strength of concrete at the time of testing (66 MPa vs. 61 MPa). The SCCC column did not behave in the same manner as the RC column in terms of initial stiffness and axial strain at the maximum load. The RC exhibited considerably greater toughness than the SCCC column. Examining, now, the behaviour of the C35 (housing) mixes, the maximum load of the SCCH was slightly lower than the RH column (3020 kN vs. 3420 kN) but both columns exhibited similar behaviour in terms of initial stiffness, axial strain at the maximum load, and toughness. 6.2.6 Testing beams The flexural behaviour of reinforced SCC and conventionally-compacted beams was investigated in terms of cracking behaviour, load carrying capacities and mode of failure, and load deflection response. 6.2.7 Cracking patterns and cracking-spacing Typical cracking patterns of beams at ultimate load are shown in Figure 48. At the service load level, cracking in the flexural span is composed predominantly of vertical cracks perpendicular to the direction of maximum principal stress induced by pure moment. Cracking outside the pure bending zone starts similarly to flexural cracking but, as the load is increased, other cracks are formed and as shear stresses become important, more inclined cracks appear. Table 18 presents the average crack-spacing at 90% ultimate load. The average crack-spacing of SCC civil and RC is around 80 and 160 mm. The crack-spacing of FSCC was higher because the link spacing of this beam was 350 mm compared to 250 mm which was used for other beams. 53 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 54 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 Table 18 – Average crack-spacing, mm Beam Average crack spacing at 90% Multimate RH RC SCCC FSCC 138 160 82 270 Fig. 48 – Typical failure mode of SCC beam 6.2.8 Cracking moment Experimental and theoretical results for moments at the first cracking are given in Table 19. The theoretical cracking-moment, Mcr, is computed in two different ways, (a) and (b) below: [a] Mcr = (fr I) / yt Where:fr is the modulus of rupture of concrete (see [b]) I is the moment of inertia of beam section yt is the distance from the centroid to extreme tension layer of the section. Values in Table 19 entitled Mcr-th1 are calculated by taking into account the moment of inertia of all reinforcement (tension and compressive reinforcement) and using the equation [2] according to principles in EC2 as well as CEB-FIP model Code 1990: 54 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 55 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 fr = 0.40 (f’cu)2/3 [b] Where f’cu is the compressive strength of concrete on cubes). Those in Table 19 entitled Mcr-th2 represent the cracking-moment calculated as recommended by BS code; that is neglecting the moments of inertia of all reinforcement and assuming the section of the beam made only of concrete. Comparison between Mcr-th1 and Mcr-th2 shows that the effect of the reinforcement is not neglected and the computation of the moment of inertia is very simplified when the reinforcement is neglected. The average value of Mcr-th2 is seen to be close to Mcr-exp. Note that the experimental cracking moment includes the self-weight of the beam. Table 19 – Experimental and theoretical moments at first cracking (kN.m) Beam RH RC SCCC FSCC M cr-exp 6.6 23.1 22.0 15.4 M cr-th1 10.6 26.2 31.4 22.1 M cr-th2 9.6 20.3 24.4 19.9 6.2.9 Crack-width Figure 49 shows the maximum observed crack-widths plotted against the applied load. Comparing the beams in the civil engineering category, it can be seen that the cracks in the reference beam are wider than those in the SCCC beam. Crack-width, ( µm) 1400 FSCC 1200 1000 RC 800 600 400 200 SCCC 0 0 50 100 150 200 250 Maximum applied moment, (KN.m) Fig. 49 – Variation of crack-width vs. applied load 55 300 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 56 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-04-26 Table 20 presents the average-crack width at different load levels. At the same moment (< 110 kN.m), the cracks in the fibre FSCC beam are less wide than those in SCCC and RC beams. This difference in crack-widths can be attributed to the use of the fibre in concrete, which affects the mechanism of development of cracks. Table 20 - Average crack-width, ìm at different load levels Beam RC SCCC FSCC Moment 88 kN.m 110 kN.m 100 160 100 120 28 40 66 kN.m 100 55 20 132 kN.m 180 120 1200 6.2.10 Load-deflection response Figure 50 traces typical experimental load-deflection of RC, SCCC, FSCC and RH. Initially, the beams are uncracked and stiff. With further loading, cracking occurs at mid-span when the applied moment exceeds the cracking moment Mcr, causing a reduction in stiffness. 350 SCCC (6 months) RC (4.5 months) 300 Applied moment (KN.m) 250 200 FSCC (3 months) 150 RH (6 months) 100 50 0 0 20 40 60 80 100 120 Midspan-deflection (mm) Fig. 50 – Load-deflection of RH, FSCC, RC and SCCC beams 7. CONCLUSIONS The workability requirements for successful placement of SCC necessitate that the concrete exhibits excellent deformability and proper stability to flow under its own weight through closely spaced reinforcement without segregation and blockage. Insuring high stability is important to limit bleeding, segregation, and surface settlement of concrete after placement and secure uniform properties of the hardened 56 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 57 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 concrete, including bond to embedded reinforcement. In general, the SCC exhibits low yield value and adequate cohesiveness (moderate viscosity). In addition to slump flow test used to evaluate deformability, the L-box and the Orimet with JRing test should be used to evaluate the ability to achieve smooth flow through restricted spacing without blockage. The ultimate load of the SCC civil column was slightly higher than the reference civil column (RC) given the higher compressive strength at the time of testing (66 MPa vs. 61 MPa). The SCC civil column did not seem to behave in the same manner as the RC column in terms of initial stiffness and axial strain at the maximum load. The difference could be due to the difference of elastic modulus and the presence of greater density of microcracking in concrete that affects mostly tensile properties and stiffness. The SCC housing column seemed to have the same behaviour in terms of initial stiffness and axial strain at the maximum load. Typical cracking patterns of SCC and reference beams at ultimate load are very similar. With four point-flexural test of beam, at the service load level, cracking in the flexural span is composed predominantly of vertical cracks perpendicular to the direction of maximum principal stress induced by pure moment. Cracking outside the pure bending zone starts similarly to flexural cracking but, as the load is increased, other cracks are formed and as shear stresses become important, more inclined cracks appear. With the comparison of SCC and reference civil beams, it can be seen that the number of cracks in the reference beam were higher than those in the SCC civil beam. The cracks in fibre FSCC beam were smaller than those in SCC and reference civil beams. This difference in crack-widths can be attributed to the use of the fibre in concrete which affect the mechanism of development of cracks. The beam with SCC civil developed similar load deflection response to that of the reference beam mix. (Further conclusions will be added) 57 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 58 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 REFERENCES [1] Pera, J., Husson, S., and Guilhot, B. ‘Influence of finely ground limestone on cement hydration’, Cement & Concrete Composites, 1999 (21), 99-105. [2] Hogan, F.J. and Meusel, J.W., 'Evaluation for durability and strength development of a ground granulated blast furnace slag’, Cement, Concrete and Aggregate, 3, No.1, (1981), pp.40-52. [3] Rilem recommendation, reinforcement’, 1992. [4] Neville, A. M., ‘Properties of concrete’, Edition Longman, 1995. [5] R. Le ROY, J-M CUSSAC, and O. MARTIN: ‘Structures sensitive to creep: from laboratory experimentation to structural design. The case of the Avignon high-speed rail viaduct’, Special Issue of Revue Francaise du Génie Civil: Creep and Shrinkage of Concrete, vol 3 n°3-4, ed. by Ulm, Prat, Calgaro and Carol, pp 133-157, 1999. [6] Buenfeld, N.R., ‘Measuring and modelling transport phenomena in concrete for life prediction of structures’, Chapter 5 of Prediction of Concrete Durability, Edited by J. Glanville and A.M. Neville, E& FN Spon, London, 1997. [7] RILEM TC116-PCD: 'Permeability of concrete as a criterion of its durability, C: determination of the capillary absorption of water of hardened concrete', Materials and Structures. 32, April 1999, pp178-179. [8] McCarter, W.J. and Ezirim, H., 'Influence of constituents on the surface absorption characteristics of concrete', Proceedings of 9th International Congress on the Chemistry of Cement, pp39-45. [9] RILEM recommendations CPC-18, ‘Measurement of hardened concrete carbonation depth’, Materials and Structures, 1988. [10] Bungey, J.H. and Millard, S.G., ‘Testing of concrete in structures’, 3rd Edition, Blackie Academic & Professional, London, 1996. [11] Zhu, W and Bartos, PJM, 'Assessment of interfacial microstructure and bond properties in aged GRC using a novel microindentation method', Cement and Concrete Research, 27 (1997), pp.1701-1711. TC51-ALC, 58 78-MCA, ‘Pull-out test for SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 59 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-04-26 [12] Oliver, WC and Pharr, GM, 'An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments', Journal of Materials Research, 7 (1992), pp.1564-1579. [13] Doerner, MF and Nix, WD, 'A method for interpreting the data from depth sensing indentation instruments', Journal of Materials Research, 1 (1986), pp.601-609. 59 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 60 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 APPENDIX A1 Preliminary investigation A preliminary investigation was necessary in order to determine suitable materials and mix designs for the full-scale work. These had to comply with the specified requirements of the overall program. A1.1 Materials The characteristics of local aggregates are given in Table 21. Figures 51 and 52 present the grading of cement and additive powders and aggregates used in preliminary mixes. Mix proportions are given in Table 22 and test method details of fresh concrete in paragraph 5. Three types of filler, namely PFA (Scottish Power, Longannet ), GGBS (Castle GX5), and LSP (limestone powder, Longcliffe), were used. The PFA was classified as BS3892: Part 1, GGBS and LSP were finely ground. The coarse aggregate (both sizes) was microgranite (Cloburn quarry), sand 1 a quartzite building sand, and sand 2 a coarser quartzite concrete sand (both Douglasmuir quarry). Two superplasticisers, Sikament 10 and Viscocrete 2 were used. Table 21 – Properties of coarse aggregate and sand Properties Relative density (Oven Dry), kg/m³ Relative density (SSD), kg/m³ Concrete shrinkage Water absorption, % Water absorption (from room dry), % B.D. Uncompacted, kg/m³ B.D. Compacted, kg/m³ Loose Packing Density (SSD) (without tamping) Coarse aggregate 2.60 2.62 0.029 0.80 0.20 1446 N/A 0.552 Sand 1 Sand 2 2.47 2.53 N/A 2.40 1.70 1550 N/A 0.614 2.51 2.56 N/A 1.00 0.10 1610 1730 0.629 Note: The loose packing density is the volume occupied/unit volume 60 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 61 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 100 Passing, % 80 60 PC 40 LSP GGBS 20 PFA 0 1 10 100 Particle Size, µ m Fig. 51 – Particle size distribution of cement, GGBS, PFA and LSP Grading curve for aggregates Grading curve for sands 100 80 10 mm Passing, % Passing, % 100 60 20 mm 40 20 0 Sand 1 80 60 Sand 2 40 20 0 1 10 100 10 100 1000 10000 Size, µ m Size, mm Fig. 52 – Grading of coarse aggregates and sands A1.2 Effect of local materials and superplasticisers on concrete properties A considerable amount of preliminary work was necessary to assess the materials’ performance in and suitability for fresh SCC. The main conclusions were: 61 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 62 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 • Generally, at equal water content and slump flow value, PFA mixes were more cohesive than GGBS mixes. In other words, GGBS mixes have lower viscosity than corresponding PFA mixes; thus the GGBS mixes flow faster, but tend to segregate at a lower slump flow value. Compared to GGBS and PFA mixes, LSP mixes require lower water content and SP dosage for achieving the same slump flow. • Content of fines in sand had a very significant effect on SCC mix proportions. Fine sand requires more water and SP, but less filler than coarse sand. The SP dosage, water content and cement/filler content could be adjusted by treating the fines (<150 µm) in sand as part of the filler. • The mixes using Sikament 10 lost flowability faster than mixes using Viscocrete 2. Compared to Sikament 10, the Viscocrete 2 produced more cohesive mixes, but at dosages higher than 1.2% (by weight of powder) large quantities of air bubbles and low early strength were observed (see Table 18). This was particularly true with the combination of PFA and Viscocrete 2. • Segregation tendency is significantly higher for mixes with large size (20mm) aggregate than small aggregate, and the self-compacting properties of such mixes tend to be more sensitive to small changes in mix proportions. It seems that greater slump flow and cohesiveness are required for mixes using 20mm aggregate. • Satisfactory compressive strength results could be obtained for both SCC housing and civil engineering mixes, by adjusting the W/C ratio and the dosage of superplasticizer. 28-day cube strengths were ~55 MPa and ~70 MPa respectively for housing and civil engineering SCC mixes. At this preliminary stage, it was found difficult to reduce the 28-day strength of the housing SCC mixes to the target, c45Mpa. This is mainly due to the requirements of large amount of fillers (450-550 kg/m³) and water content (<195 kg/m³) for achieving satisfactory performance in fresh SCC mixes. A.13 Effect of mixer All mixes in the laboratory were prepared in 25 litre batches and mixed in an open pan mixer. The mixing sequence consisted of mixing the sand and the coarse aggregate with ¼ of water content, waiting 5 minutes for absorption, addition of cementitious materials, addition of the rest of the water with most of the superplasticizer. The concrete was mixed for five minutes then after measuring slump flow the dosage of superplasticizer was adjusted to achieve slump flow greater that 600 mm. In the case of fibre SCC, the fibre was added after all other materials Three mixer types were used: a small free-fall drum mixer and two different sizes of pan mixer. The type of mixer had a strong effect on the water and SP requirement in SCC mixes. The pan mixer, due to its strong shear action, appeared to produce SCC mixes of 62 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 63 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 equal slump flow value at water content 10 kg/m³ lower, or SP dosage a third less, than the small lab drum mixer. The Viscocrete 2 seemed to be more sensitive to the mixer types than Sikament 10. There were even noticeable, though minor differences between the two pan mixers. The stronger action pan mixer seemed to promote aggregate segregation and faster loss of workability with time. A1.4 Test methods for fresh SCC Test methods used on the fresh concrete were: slump flow, L-box, Orimet, Japanese ring (JRing), and sieving test for assessing coarse aggregate segregation. Modifications were made on L-box, Orimet, and JRing tests. a) Slump flow – easy to carry out, can provide an indication of flowability; requirement on flow and T50 values should be different for different maximum sizes/shapes of aggregates, and admixtures; difficult to assess the segregation/settlement tendency. b) L-box – not easy to carry out; simulates better the real flow/blocking condition; if bar spacing is selected appropriately it can provide information on self-levelling and on likelihood of blocking – but the blocking ratio depends on slump flow and surface condition/wall effect, as well as on the geometry and bar spacing of the Lbox; difficult to identify segregation/settlement. c) Orimet – easy and quick to carry out, can provide an indication of flowability and cohesiveness/viscosity; possible to assess segregation and blocking tendency by appropriately selecting/adjusting the size of orifice and by adding steel bars to limit the passage of materials. d) JRing – easy to carry out, represents an improvement on slump flow, simulates better the real flow condition; possible to assess blocking if the clear gap is selected/adjusted properly. e) Visual assessment of segregation – difficult to assess, often time consuming; large dependence on sampling and efficiency of the mixer used. f) Combination of Orimet and JRing – seems to be able to provide all the information about flowability, cohesiveness/viscosity, likelihood of blocking; with further modification on Orimet, may be able to assess segregation/settlement. 63 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 64 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 A1.5 - Table 21 - Mix proportions and fresh concrete properties in preliminary investigation Test Series No.1 % of Filler in Powder Type of Mixer Used No.2 No.3 No.3x No.4 No.5 No.6 30% 30% 30% 30% 30% 25% 25% GGBS GGBS LSP LSP LSP PFA PFA blue pan blue pan blue pan blue pan blue pan blue pan blue pan Mix Proportions, kg/m³ Filler GGBS 160 144 - - - - - PFA - - - - - 110 115 LSP - - 140 145 135 - - Portland Cement, 42.5 368 332 325 338 315 330 340 Coarse Aggregate, 6-20 mm 785 782 790 745 790 760 760 Sand1, 0-5 mm, (6.6%<150 um) 800 876 885 920 910 910 875 Sand2, 0-5 mm, (0.7%<150 um) - - - - - - - Effective Water 200 188 182 188 176 185 190 Total Powder 528 476 465 483 450 440 455 Total Powder +fines in sand 581 534 523 544 511 501 513 Sikament 10 8.04 7.14 7.00 7.88 7.20 8.80 7.96 Viscocrete 2 - - - - - - - Orimet Test (80 mm orifice) Average flow time, ~ 10 min. - - - - - - - seconds ~ 90 min. - - - - - - - Max and Min flow ~ 10 min. time, seconds ~ 90 min. - - - - - - - - - - - - - - ~ 15 min. 595 572 713 722 613 545 688 ~ 90 min. - - - - - - - ~ 15 min. - - - - 9.2 16.96 7.73 ~ 90 min. - - - - - - - ~ 15 min. - 47 30 30 45 45 35 ~ 90 min. - - - - - - - ~ 15 min. - 12 18 12 13 10 15 ~ 90 min. - - - - - - - JRing Test (~40 mm gaps) slump flow, mm T50, seconds Hin, mm H50, mm 64 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 65 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 Table 21 - Mix proportions etc in preliminary investigation (continued) Test Series No.7 No.8 No.9 No.10 No.11 No.12 25% PFA Yellow pan 35% GGBS Yellow pan 35% LSP yellow pan 25% PFA yellow pan 30% PFA yellow pan 35% GGBS yellow pan - 174 - - - 185 PFA 115 - - 115 140 - LSP - - 182 - - - Portland Cement, 42.5 335 330 318 335 320 330 Coarse Aggregate, 6-20 mm 750 750 757 750 750 750 Sand1, 0-5 mm, (6.6%<150 um) 900 895 919 - - - Sand2, 0-5 mm, (0.7%<150 um) - - - 900 900 900 Effective Water 185 185 168 185 180 180 Total Powder 450 504 500 450 460 515 Total Powder +fines in sand 509 563 561 456 466 521 Sikament 10 7.65 8.46 7.56 6.75 - - Viscocrete 2 - - - - 5.75 5.15 % of Filler in Powder Type of Mixer Used Mix Proportions, kg/m³ Filler GGBS Orimet Test (80 mm orifice) Without internal bars With two 16 mm internal bars Average flow time, ~ 10 min. 4.39 3.35 5.08 4.85 6.29 6.34 seconds ~ 90 min. 5.07 3.36 4.02 - - - Max and Min flow ~ 10 min. time, seconds ~ 90 min. 4.88,4.0 6 5.16,4.9 8 JRing Test slump flow, mm T50, seconds Hin, mm H50, mm 3.63,3.21 5.70,4.70 5.74,4.17 6.85,5.82 3.41,3.30 4.03,4.01 ~40 mm gaps - - 6.67,5.92 - ~50mm gaps, combined with Orimet 738 673 575 ~ 15 min. 660 580 535 ~ 90 min. - 570 635 - - - ~ 15 min. 9.74 7.48 8.91 - - - ~ 90 min. - 11.45 10.71 - - - ~ 15 min. 40 52 55 30 - 47 ~ 90 min. - - 45 - - - ~ 15 min. 16 11 10 14 - 15 ~ 90 min. - - 15 - - - 65 SCC Self Compacting Concrete Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 66 (73) final report t4 Task 4 – Properties of Hardened Concrete 2000-03-3 Table 21 - Mix proportions etc preliminary investigation (continued) Test Series No.13 No.13x No.14 No.14x No.15 No.15x % of Filler in Powder 30% PFA yellow pan 30% PFA yellow pan 30% PFA yellow pan 30% PFA yellow pan 40% GGBS yellow pan 40% GGBS yellow pan - - - - 220 219 PFA 139 139 150 150 - - LSP - - - - - - Portland Cement, 42.5 318 318 350 350 330 328 Coarse Aggregate, 6-20 mm 746 746 750 750 750 746 Type of Mixer Used Mix Proportions, kg/m³ Filler GGBS Sand1, 0-5 mm, (6.6%<150 um) - - - - - - Sand2, 0-5 mm, (0.7%<150 um) 896 896 865 865 860 856 Effective Water 184 184 190 190 185 189 Total Powder 457 457 500 500 550 547 Total Powder +fines in sand 463 463 506 506 556 553 Sikament 10 - - - - - - Viscocrete 2 3.66 4.57 5.00 6.25 5.5 5.5 4.66 - 4.80 Orimet Test (80 mm orifice) With two 16 mm internal bars Average flow time, ~ 10 min. - seconds 3.26 - ~ 90 min. - - - - - - Max and Min flow ~ 10 min. time, seconds ~ 90 min. - 3.41,3.09 - 4.88,4.15 - 5.24,4.41 - - - - - - JRing Test ~50mm gaps, combined with Orimet slump flow, mm T50, seconds Hin, mm H50, mm ~ 15 min. - 658 - 658 - 595 ~ 90 min. - - - - - - ~ 15 min. - - - - - - ~ 90 min. - - - - - - ~ 15 min. - 33 - - - - ~ 90 min. - - - - - - ~ 15 min. - 17 - - - - ~ 90 min. - - - - - - 66 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 67 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 Table 21- Mix proportions etc preliminary investigation (continued) Test Series No.16 No.17 No.17x No.18 No.19 No.20 % of Filler in Powder 25% PFA small drum 30% PFA small drum 30% PFA small drum 33% PFA small drum 38% GGBS small drum 37% GGBS small drum - - - - 199 190 PFA 114 140 140 159 - - LSP - - - - - - Portland Cement, 42.5 333 320 320 318 318 325 Coarse Aggregate, 6-20 mm 746 750 750 746 746 745 Sand1, 0-5 mm, (6.6%<150 um) 896 900 900 871 886 885 Sand2, 0-5 mm, (0.7%<150 um) - - - - - - Effective Water 189 180 180 185 185 185 (+5) Total Powder 447 460 460 477 517 515 Total Powder +fines in sand 506 519 519 534 575 573 Sikament 10 7.65 - - - - - Viscocrete 2 - 5.75 6.50 7.50 8.00 8 (+0.75) Type of Mixer Used Mix Proportions, kg/m³ Filler GGBS Orimet Test (80 mm orifice) With two 16 mm internal bars Average flow time, ~ 10 min. - - - seconds ~ 90 min. - - - Max and Min flow ~ 10 min. time, seconds ~ 90 min. - - - - - - JRing Test slump flow, mm T50, seconds Hin, mm H50, mm With two 16 mm internal bars 13.00 10.97 - - - 8.05 14.81,11.2 8 - 13.48,9.38 - - 9.34,7.24 ~50 mm gaps, not combining with Orimet ~50mm gaps with orimet 685 - ~ 15 min. 670 - 610 525 ~ 90 min. - - - - - 700 ~ 15 min. 8.79 - 8.56 11.71 - - ~ 90 min. - - - - - - ~ 15 min. 35 - 45 60 40 - ~ 90 min. - - - - - 35 ~ 15 min. 22 - 12 12 18 - ~ 90 min. - - - - - 12 67 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 68 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 Table 21- Mix proportions etc in preliminary investigation (continued) Test Series No.21 No.21x No.22 No.22x No.23 No.24 % of Filler in Powder 28% PFA small drum 28% PFA small drum 27% PFA small drum 27% PFA small drum Ref. C30 Ref. C60 small drum small drum - - - - - - PFA 130 129 120 119 - - LSP - - - - - - Portland Cement, 42.5 330 327 330 328 350 445 Coarse Aggregate, 6-20 mm 750 743 750 746 1225 1195 Sand1, 0-5 mm, (6.6%<150 um) 890 881 900 896 575 510 Sand2, 0-5 mm, (0.7%<150 um) - - - - - - Effective Water 185 194 185 189 196 196 Total Powder 460 456 450 447 350 445 Total Powder +fines in sand 519 514 509 506 388 479 Sikament 10 - - - - - - Viscocrete 2 6.5 8 (+0.75) 8.16 8.16 - - Type of Mixer Used Mix Proportions, kg/m³ Filler GGBS Orimet Test (80 mm orifice) With two 16 mm internal bars Average flow time, ~ 10 min. - - - 6.84 seconds ~ 90 min. - 7.53 - - Max and Min flow ~ 10 min. time, seconds ~ 90 min. - - - 7.11,6.42 - 8.46,6.92 - - JRing Test slump flow, mm T50, seconds Hin, mm H50, mm ~50 mm gaps, combined with last orimet test ~ 15 min. - - - ~ 90 min. - 680 - - ~ 15 min. - - - 9.87 ~ 90 min. - - - - ~ 15 min. - - - 40 (45) ~ 90 min. - 35 - - ~ 15 min. - - - 20 (14) ~ 90 min. - 13 - - 68 653 (565) SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 69 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 A2 - Table 23 - Statistical analysis of the pull out test results carried out by Lok test (British standard 1881 part 207, 1992 and ISO/DIS 8046) 1. HOUSING REFERENCE MIX A. 7 DAYS TEST No. COLUMN (kN) BEAM (kN) CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 15 18 18 17 1.732 10.1 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW ((kN) C.O.V (%) 18 18 23 24 22 20 20.83 2.56 24 18 12.2 16 15 14 17 18 18 16.33 1.63 18 14 9.9 B 28 DAYS TEST No. COLUMN (kN) BEAM (kN) CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 22 22 23 22.33 0.577 2.5 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) 30 30 29 -- 36 28 30.6 3.13 36 28 10.2 24 26 20 24 27 30 25.166 3.37 30 20 13.3 2. HOUSING SCC MIX A. 7 DAYS CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 20 21 22 21.00 1.00 4.8 69 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 70 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 TEST No. COLUMN (kN) BEAM (kN) 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) 28 30 31 34 35 32 31.66 2.58 35 28 8.2 33 30 30 30 27 30 30.00 1.89 33 27 6.3 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) 40 34 37 34 38 32 35.83 2.99 40 32 8.3 35 35 36 32 37 34 34.83 1.72 37 32 4.9 B 28 DAYS TEST No. COLUMN (kN) BEAM (kN) 3. CIVIL REFERENCE MIX A. 7 DAYS TEST No. COLUMN (kN) BEAM (kN) CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 23 27 25 25.00 2.00 8 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) 40 38 35 42 38 40 38.83 2.40 42 35 6.2 25 26 30 26 28 25 26.26 1.96 30 25 7.5 B 28 DAYS CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 30 28 30 29.33 1.15 3.9 TEST No. 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) COLUMN (kN) 40 38 35 35 49 44 40.16 5.49 49 35 13.6 70 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 71 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 4. CIVIL SCC MIX A. 7 DAYS CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 34 34 34 34.00 0.00 0 TEST No. 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) COLUMN (kN) 36 40 40 48 48 44 42.66 4.84 48 36 11.3 B 28 DAYS TEST No. COLUMN (kN) BEAM (kN) CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 44 40 -- -- -- -- 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) 56 48 58 54 52 48 52.66 4.13 58 48 7.8 38 42 40 42 38 36 39.33 2.42 42 36 6.2 5. SFRSCC MIX A. 7 DAYS CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 30 32 30 30.66 1.15 3.8 TEST No. 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) BEAM (kN) 30 38 38 36 33 36 35.16 3.12 38 30 8.8 71 SCC Brite EuRam Proposal No. BE96-3801 Brite EuRam Contract No. BRPR-CT96-0366 Page 72 (73) final report t4 Self Compacting Concrete Task 4 – Properties of Hardened Concrete 2000-03-3 B 28 DAYS CUBES 1 2 3 MEAN (kN) S.D. (kN) C.O.V (%) (kN) 35 34 32 33.67 1.52 4.5 TEST No. 1 2 3 4 5 6 MEAN (kN) S.D. (kN) HIGH (kN) LOW (kN) C.O.V (%) BEAM (kN) 40 38 38 38 40 37 38.50 1.22 40 37 3.2 72