Fracture Mechanics of Concrete and Concrete Structures High Performance, Fiber Reinforced Concrete, Special Loadings and Structural Applications- B. H. Oh, et al. (eds) ⓒ 2010 Korea Concrete Institute, ISBN 978-89-5708-182-2 Experimental research on high-fluidity and super high-early strength concrete for cement pavement repairing * D.P. Chen & C.L. Liu Anhui University of Technology, Ma’anshan, China C. X. Qian Southeast University, Nanjing, China ABSTRACT: The concrete for pavement repair must have very high-early strength for opening to traffic as soon, good anti-shrinkage and anti-cracking performance, interfacial bond between old and new concrete surface besides the basic pavement performance. High fluidity is also needed for simplifying repairing operation and for guaranteeing the repair quality. In a sense, high fluidity is conflict with super high-early strength. In this paper, focusing on the early flexural strength, interfacial bond, shrinkage and cracking performance, the preparing and testing of high-fluidity and super high-early strength concrete (HFESC) for pavement repair was investigated. The repair concrete material, which prepared with Sulphoaluminate cement, Amino-superplasticizer and RF admixture, has 3.5MPa 5h-flexural strength, 20MPa 5h-compressive strength and 200mm slump value. The laboratory test and field pavement repairing results revealed that the concrete has high fluidity and good mechanics performance and durability, which can be used in rapid repair of concrete pavement. 1 INSTRUCTIONS Cement concrete pavement (CCP in short) is possessed of traffic safety, stability and durability comparing with asphalt pavement. Besides which, the comprehensive cost especially maintenance expanse of CCP is lower than that of asphalt pavement. While the rehabilitation of pavement surface distress, once it occurs, must be conducted in time for avoiding the serious pavement damage. Along with the increasing of pavement service life, driving speed, especially the road traffic volume and axle load, more and more CCP was destroyed in different degree in China (Li et al. 1998, Xie 2000). The local damage is the main type of pavement failure results form nature disaster and the deficiencies involving pavement design, materials, construction technology, management and quality control. The further deterioration of local damage in pavement will affect the ride comfort even destroy vehicles which may result in traffic accidents. It is very important to investigate feasible rapid repair materials and methods for the use and development of CCP. The rapid repair concrete for pavement must have many performances including very highearly strength for opening to traffic with 3.5MPa flexural strength and 20MPa compressive strength (Wang & Li 2006), good anti-shrinkage and anticracking performance (Yang et al. 2000, Morgan. 1996), interfacial bond between old and new concrete surface for long term repair effect besides the basic properties (Morgan 1996). High fluidity is also needed for simplifying repairing operation and for guaranteeing the repair quality (Palacios et al. 2009, Yang et al. 2000). Considering the stress characteristics of CCP and the actual specifications of cement concrete pavement design, flexural strength was used as control index and compressive strength as reference one in experiment test. In a sense, high fluidity is conflict with super high-early strength (Chen et al. 2006). In this paper, focusing on the early flexural strength, interfacial bond, shrinkage and cracking performance, the preparing and testing of concrete with high-fluidity and super high-early strength for pavement repair was investigated. Based on the all kinds of experiments relevant with compatibility of cement and addictives, strength, interfacial bond and freezethaw durability, HFESC was prepared and applied for pavement damage repair. Many kinds of materials, such as Sulphoaluminate cement, magnesia-phosphate cement, early strength agent, fiber and polymers etc (Chung 2004, Yang et al. 2000, Huang et al. 2004), can be used for concrete pavement repairing. In this paper, the concrete repairing material was prepared with Sulphoaluminate cement, Amino-superplasticizer (ASS in short) and RF admixture. The repair J = − D ( h, Tpossessed ) ∇h materials of 3.5Mpa 5h-flexural strength, (1) 20MPa 5h-compressive strength and 200mm slump value could meet demand for D(h,T) traffic recovery. Theand proportionality coefficient is called The laboratory test and field pavement moisture permeability and it is a nonlinearrepairing function results revealedhumidity that theh concrete has highT (Bažant fluidity of the relative and temperature and good mechanics performance and durability, & Najjar 1972). The moisture mass balance requires which be used in of rapid repair mass of concrete that thecan variation in time the water per unit pavement. volume of concrete (water content w) be equal to the divergence of the moisture flux J 2 ∂EXPERIMETN PROGRAM (2) − = ∇•J ∂ 2.1 Basic materials TheCement water content w can be expressed as the sum 2.1.1 water, water of the evaporable we (capillary Industrial blended water Portland cement, produced by vapor, andPortland adsorbed water)andandmixing the non-evaporable grinding clinker with up to 3 1966, (chemically water wn (Mills mass% gypsumbound) and about 6 mass%~15 mass% of Pantazopoulo & Mills(type 1995).PO42.5 It is reasonable the mixing materials according to assume that the evaporable a function of GB175-1999) in the Tianjin water cementisWorks (PO in relativewas humidity, degree of hydration, αc, and short) used inh, this study. Rapid hardening degree of silica fume reaction, Sulphoaluminate cement (SA inαshort) s, i.e. wwas e=walso e(h,αused c,αs) = experiment. age-dependent sorption/desorption isotherm in The basic performance indexes of (Norling Mjonell 1997). Under this assumption and cements were listed in Table 1. by substituting Equation 1 into Equation 2 one Table 1. Basic performance indexes of cements. obtains w t ______________________________________________ Performance SA PO ∂w ∂w ∂w ∂h ______________________________________________ e e e α& + α&s + w1&n + ∇ • ( D ∇h ) = − (3) Fineness sieve h residue), ∂α % c 1.5 ∂α ∂h ∂(80µm t c s Volume stability qualify qualify Initial setting, min 40 220 Final setting, min 100 380 where ∂we/∂h is the slope of the sorption/desorption Cement strength, MPa isotherm (also called moisture capacity). The 12h flexural strength 6.4 - completed governing equation (Equation 3) must be 12h compressive strength 39.7 byflexural appropriate 1d strengthboundary and initial 7.2 conditions. The relation between the amount of- evaporable 1d compressive strength 49.8 3d flexural water andstrength relative humidity 8.6 is called 5.1‘‘adsorption 3d compressiveif strength 36.6 relativity isotherm” measured with-62.4 increasing 28d flexural strength 9.4 humidity and ‘‘desorption isotherm” in54.8 the opposite 28d compressive strength case. Neglecting their difference (Xi et al. 1994), in _____________________________________________ the following, ‘‘sorption isotherm” will be used with reference to both sorption and desorption conditions. By theAggregates way, if the hysteresis of the moisture 2.1.2 isotherm would be taken into account, Crushed limestone aggregate is usedtwoasdifferent coarse relation, evaporable water vs relative humidity, must aggregate in concrete. Limestone is a natural stone be used according to the sign of the variation of the material composing of more than 97 mass% calcium relativity humidity. The shape of the sorption carbonate. The used coarse aggregate is continuous isothermwith for HPC influenced by many grading the issize of 5~15mm. Theparameters, apparent 3 especially those that influence extent and rate density of the coarse aggregate is 2470kg/m . of the chemical and, with in turn, determine pore The riverreactions sand (quartz) the fineness modulus 3 structure and pore size distribution (water-to-cement of 2.5 and apparent density of 2610kg/m is used as ratio,aggregate cement inchemical fine the study.composition, SF content, curing time and method, temperature, mix additives, etc.). In the literature various formulations can be 2.1.3 Water found to the sorption Tap waterdescribe from municipal pipe isotherm network of wasnormal used concrete (Xi etofal. 1994). However, in the present for production concrete. paper the semi-empirical expression proposed by Norling Mjornell (1997) is adopted because it Proceedings of FraMCoS-7, May 23-28, 2010 explicitly accounts for the evolution of hydration 2.2 Admixtures reaction and SF content. This sorption isotherm 2.2.1 Water reducing agent reads For insure the high fluidity of concrete, the commercial water reducer agent of Amino⎡ superplasticizer was used after being ⎤⎥selected ⎢ through on the efficiency ) − we (h α c comparative α s ) = G (α c αexperiment + ⎢ ⎥ s ∞ (water g α c −reducers. α )h ⎥ The and compatibility of different ⎢ c ⎦ water e ⎣ (4) experiment result of compatibility between ∞ −section reducer and binder will be⎡ given in ⎤ (g α α )h 3.1. 1 , , , 1 1 10 1 c K (α c α s )⎢e ⎢ 2.2.2 Early strength admixture ⎣ 10 , c − 1 1 ⎥ ⎥ ⎦ 1 Early strength admixture is the key to preparing HFESC pavement repair Considering the where the first term (gelmaterial. isotherm) represents the requirement that HFESC must posses both high physically bound (adsorbed) water and the second fluidity and super-high early strength,the numerous term of (capillary isotherm) represents capillary kinds early strength admixtures were investigated water. This expression is valid only for low content by comparative test on the early strength. The result of of SF. The coefficient G1 represents the amount showed that the super high-early strength of water per unit volume held in the gel pores at 100% concrete was impossible be be prepared only(Norling relying relative humidity, and it tocan expressed on some one early strength agent without weakening Mjornell 1997) as using Amino-superplasticizer as the fluidity when water reducer.c Fortunately we have developed a s ( ) G α α = k α c + k α s (5) ternary strength admixture (named c compound s vg c early vg s RF admixture) composing of active powdered admixture salts such as sulfate and c and inorganic ksvg are material parameters. the where kwhich vg andobviously nitrite, improved the earlyFrom strength maximum water per unit that can of concreteamount and alsoof guaranteed the volume high fluidity of fill all pores (both capillary pores and gel pores), one fresh concrete. one obtains canThe calculate K1 aseffect improving of RF on cement mortar and concrete will be showed in section 3.2. ⎤ ⎡ , 1 w ⎢ ⎢1 − 1 ⎢ ⎣ α s + 0.22α s − G − 0.188 c Concrete mixture s ⎛ 10⎜ e ⎝ g α c∞ − α c ⎞⎟h ⎥ 1 ⎠ ⎥ ⎥ 2.3 ⎦ (6) K (α c α s ) = ⎛ ⎞ ∞ Experiment investigation⎜ g αon −28 groups of concrete ⎟h c α cmix ⎝ ⎠ − proportion was specimen with basic e different carried out for further research on sthe reasonable g1 can Theofmaterial parametersfluidity kcvg and usage RF admixture, of kfresh vg andconcrete, be calibrated by fitting experimental data relevant to compressive strength and flexural strength based on freeoptimizing (evaporable) water content in concrete the experiments and analysis of the rawat various ages Luzio &preparation. Cusatis 2009b). materials for(Di concrete Based on the selected basic mix proportion form 28 groups, four kinds of concrete mixtures were further investigated. 2.2 Temperature Table 2 shows the evolution mix proportions of concrete. Note that, at early age, since the chemical reactions Table 2. Composition of concrete mixturesand(kg/m associated with cement hydration SF 3).reaction ______________________________________________ are exothermic, the temperature field is not uniform Mixture PO SA systems RF Water ASS for non-adiabatic evenSand if theGravel environmental ______________________________________________ temperature can be PO 380 is- constant. - 190 Heat656conduction 1090 42 described in concrete, at least for temperature PO+RF 335 45 190 656 1090 37 not SA - 100°C 380 -(Bažant 190 &656Kaplan 1090 1996), 42 by exceeding SA+RF 335 45 190 656 1090 37 Fourier’s law, which reads 0 , 1 10 1 1 _____________________________________________ q = − λ ∇T (7) where q is the heat flux, T is the absolute temperature, and λ is the heat conductivity; in this 3 RESULTS AND DISCUSSION 3.1 Early strength of cement mortar using RF The effect of RF admixture on early strength of cement mortar was investigated by early flexural and compressive strength based on the methodology proposed in the GB/T 17671-1999: Method of testing cements-Determination of strength. The experiment results were showed in Figures 1-2. 8 7 6 5 4 3 2 1 0 a P M / h t g n e r t S l a r u x e l PO PO+RF SA SA+RF F 10 24 Age /h 72 Figure 1. Early flexural strength of cement mortar using RF. 50 45 aP40 M / 35 thg30 ne trS25 ev20 is se15 rp10 m o5 C 0 PO PO+RF SA SA+RF 10 24 Age /h 72 Figure 2. Early compressive strength of cement mortar using RF. From the figures 1-2, we can see that the early strength of cement mortar is obvious increased when use RF admixture. The flexural strength using RF is nearly 2-3 times of that without RF admixture, and the compressive strength is nearly 3-5 times. 3.2 Compatibility between admixture and cement The compatibility between binder (including cement and RF admixture) and ASS was analyzed through the time-dependent slump extension (Qin 2000). Fluidity of cement paste was measured According to GB 8077-2000: methods for testing uniformity of concrete admixture. J = − D ( h, T )∇h slump extension of The results of time-dependent cement paste without RF admixture were showed in Figure 3, the results cement paste coefficient using RF D(h,T) Theofproportionality admixture were shown in Figure 4. moisture permeability and it is a nonlinea of the relative humidity h and temperature & Najjar 1972). The moisture mass balanc 230 that the variation in time of the water mas volume of concrete (water content w) be eq 220 divergence of the moisture flux J m /m210 no is ne200 tx e p190 m ul S180 − ∂ = ∇•J ∂ w t The water content w can be expressed a of the evaporable we (capillary wa 0.60% 0.80% water1.00% vapor, 1.20% and adsorbed 1.40% water) and the non-e (chemically bound) water wn (Mil 170 Pantazopoulo & Mills 1995). It is reas 0 10 assume 20 that 30 the 40 evaporable 50 60 water 70 is a fu T /min relative humidity, h, degree of hydration , i.e. we=w degree of silica fume reaction, Figure 3. Slump extension of cement mortar usingαsRF = age-dependent sorption/desorption admixture. (Norling Mjonell 1997). Under this assum by substituting Equation 1 into Equati 240 obtains 230 m220 m / no is210 ne tx e200 p m ul 190 S 180 − ∂w ∂h e + ∇ • ( D ∇h) = ∂we h ∂α ∂h ∂t ∂w α&c + e α&s + w ∂α c s where ∂we/∂h is the slope of the sorption/ isotherm (also called moisture capac governing equation (Equation 3) must be by0.60% appropriate0.80% boundary and initial conditi 1.00% 1.20% 1.40% The relation between the amount of e 170 water and relative humidity is called ‘‘ 0 10 isotherm” 20 30 if 40 50 60 measured with 70increasing /min‘‘desorption isotherm” in th humidity Tand case. Neglecting (Xi et al. Figure 4. Slump extension of cement their mortardifference without RF the following, ‘‘sorption isotherm” will be admixture. reference to both sorption and desorption c By thegood way,compatibility if the hysteresis Figures 3-4 shows betweenof the isotherm be taken account, two ASS, RF admixture andwould cement. The into obvious relation,byevaporable water relative humi increasing of fluidity using ASS alsovs occurs used according the sign of the varia whether using RFbeadmixture or not.to The optimum relativity humidity. The shape of the dosage of ASS is 1.0 mass% of cement. isotherm for HPC is influenced by many p especially those that influence extent and 3.3 Early strength of concrete chemical reactions and, in turn, determ structure and size distribution Early strengths of four kinds pore of concrete mixture (waterratio, cement chemical SF (see Table 2) were investigated according composition, to GB-T curingfortime method, temperature, mix 50081-2002: Standard testand method of mechanical etc.). concrete. In the literature various formulatio properties on ordinary The fluidity of fresh found to describe the sorption isotherm concrete was also measured according to GB-T concrete (Xi etforal. ordinary 1994). However, 50080-2002: Test method fresh in th the semi-empirical expression concrete. And allpaper the slumps of them were over pro Norling Mjornell (1997) is adopted b 200mm. Proceedings of FraMCoS-7, May 23-28, 2010 J =The − D (hresults , T )∇h of early strength of concrete were (1) showed in Figures 5-6. The 7.0 proportionality coefficient D(h,T) is called moisture permeability and it is a nonlinear function of the6.0relative humidity h and temperature T (Bažant & Najjar 5.0 1972). The moisture mass balance requires that the variation in time of the water mass per unit 4.0 of concrete (water content w) be equal to the volume divergence of the moisture flux J 3.0 a P M / h t g n e r t s l a r u x w e l F PO PO+RF SA SA+RF (2) − ∂ 2.0 = ∇•J ∂ 1.0 The 0.0 water content w can be expressed as the sum of the evaporable 0 20water we40(capillary60water, water 80 vapor, and adsorbed water)Ageand/h the non-evaporable (chemically bound) water wn (Mills 1966, Figure 5. Early flexural strength of concrete. t Pantazopoulo & Mills 1995). It is reasonable to assume that the evaporable water is a function of 45 humidity, h, degree of hydration, αc, and relative degree a 40 of silica fume reaction, αs, i.e. we=we(h,αc,αs) = PMage-dependent sorption/desorption isotherm / 35 Mjonell 1997). Under this assumption and (Norling ht 30 by gnesubstituting Equation 1 into Equation 2 one rt 25 obtains s ev 20 is PO se ∂ ∂ ∂w w w rp 15 ∂h e α& + e α&PO+RF & + ∇ • ( D ∇h ) = − me c s + wn h ∂α ∂α ∂oh10 ∂t SA c s C (3) 5 SA+RF 0 where ∂we/∂h is the slope of the sorption/desorption isotherm0 (also 20called moisture capacity). The 40 60 80 Age /h3) must be completed governing equation (Equation by appropriate boundarystrength and initial conditions. Figure 6. Early compressive of concrete. The relation between the amount of evaporable waterIt and relativetohumidity is calledhigh ‘‘adsorption is difficult get super-early strength isotherm” measured with increasing (with in 10 ifhours) using Ordinary Portlandrelativity Cement humidity and ‘‘desorption isotherm” in the opposite even the RF admixture is added, the flexural case. Neglecting difference et al.as1994), in strength of it is nottheir enough to open(Xi traffic early as the hours. following, ‘‘sorption isotherm” will cement be used such with 10 While using rapid hardened reference desorption conditions. as ASS, ittoisboth easysorption to open and traffic in 10 hours. As to By the way, if the hysteresis of the moisture HFESC prepared with ASS and RF admixture, its 5isotherm wouldstrength be takenis into different hour flexural as account, high as two 3.7MPa and relation,toevaporable water vs relative humidity, must enough open traffic. be used according to the sign of the variation of the relativity humidity. The shape of the sorption 3.4 isotherm for HPC is influenced by many parameters, those thatofinfluence extentwasand used rate of for the Sespecially plitting strength concrete chemical reactions and, inbond turn,strength determine representing the interfacial basedpore on structure and pore size distribution (water-to-cement the methodology proposed in reference (Zhao et al. ratio, cement composition, SF test content, 1999). Half ofchemical the specimen after split was curing time and method, mixHFESC additives, placed in specimen mouldtemperature, and then cast in etc.). Inasthetheliterature various formulations can for be mould other half of specimen using found to test. describe sorption isotherm normal splitting Thethespecimen, with theofsize of concrete (Xi et al. was 1994).placed However, present 150×150×150mm, with inthetheold-new paper theinterface semi-empirical by concrete vertical expression after 28d’sproposed curing for NorlingFigure Mjornell (1997) is adoptedresult. because it testing. 7 gives the experimental Interfacial bond strength Proceedings of FraMCoS-7, May 23-28, 2010 explicitly accounts for the evolution of hydration 1.8 and SF content. This sorption isotherm reaction PO reads1.6 PO+RF 1.4 SA 1.2 ⎡ ⎤ ⎢ ⎥ SA+RF we (h1.0 α c α s ) = G (α c α s )⎢ − + ⎥ ∞ 0.8 (g α ⎢ c − α c )h ⎥⎦ (4) e ⎣ 0.6 ∞ − α )h ⎤ ⎡ 0.4 (g α c c − ⎥ ⎢ K (α c α s ) e 0.2 ⎢ ⎥ ⎣ ⎦ 0.0 10h 1d 3d 28d 90d where the first term (gel isotherm) represents the Age physically bound (adsorbed) water and the second Figure Interfacial bond strengthrepresents of concrete. the capillary term 7.(capillary isotherm) water. This expression is valid only for low content shows that Gthe using of RF admixture of Figure SF. The7 coefficient 1 represents the amount of increases bond strength between old water per the unitinterfacial volume held in the gel pores at 100% concrete and new repair HFESC especially in early relative humidity, and it can be expressed (Norling age. The enhancement of RF admixture on concrete Mjornell 1997) as early strength may result form the active effect of early strengthccompound s αins RF. G (α c α s ) = k vg α c c + k vg (5) s 3.5 ksvg are of material parameters. From for the wherefrost kcvg and The resistance concrete is essential maximumdurability, amount ofespecially water per in unitthevolume that can concrete area existing fill all pores (both capillary pores and gel pores), one freeze-thaw circle. The freeze-thaw durability was as one obtains can calculate K 1 evaluated according to GB/T 50082 200×: Standard for test method of long-term performance⎤ and ⎛ ⎞ ∞ durability of ordinary concrete⎡⎢ (opinion ⎜ g α −α c soliciting c ⎟⎠h ⎥⎥ − + −G ⎢ −e ⎝ w α s α s draft). c s ⎥ ⎢ Figure 8 gives the freeze-thaw circle experiment ⎦ (6) ⎣ K (α c α s ) = ⎛ ⎞ ∞ results. ⎜ g α − α ⎟h a P M / 1 h t g, n e r t s , , 1 1 g n i t t i l p S 10 10 , 1 1 1 1 , 1 Freeze-thaw durability 10 0 0.188 0.22 1 1 1 , 1 10 3.0 e ⎝ 1 c c⎠ −1 PO The material parameters kcvg and ksvg and g1 can 2.5 SA be calibrated by fitting experimental data relevant to free 2.0 (evaporable)SA+AF water content in concrete at % / s s o l various ages (Di Luzio & Cusatis 2009b). 1.5 h t g n e r t S 1.0 2.2 Temperature evolution Note0.5 that, at early age, since the chemical reactions associated with cement hydration and SF reaction 0.0 are exothermic, the temperature field is not uniform for non-adiabatic systems even environmental 0 50 100 if the150 200 temperature is constant. Heat can be Freeze-thaw circleconduction times described in concrete, at least for temperature not Figure 8. Freeze-thaw exceeding 100°C durability (Bažantof concrete. & Kaplan 1996), by Fourier’s law, which reads The experiment results reveal that Group SA posses the q = − λ∇ T best frost resistance performance and the strength loss of Group PO is the highest. All (7) the strength loss of concrete after 200 times freeze-thaw where is qlower is the is the substitute absolute circle than heat 30%. flux, The 12T mass% temperature, and λ is the heat conductivity; in this of cement with RF admixture lower the freeze-thaw durability of concrete, which may result form the resoluble salt in RF admixture. 4 CONCLUSIONS Based on the experimental research on RF admixture, water reducing agent, mechanical performance and freeze-thaw durability of HFESC, we can draw some conclusions as follows: (1) Good compatibility between sulphate aluminium cement, Amino-superplasticizer and RF admixture makes the preparing of HFESC possible. (2) The 5h flexural strength of HFESC is over 3.5MPa and 5h compressive strength over 2MPa. HFESC, possessing both high fluidity and super high-early strength, is qualified as an efficient rapid pavement repair material. The application of HFESC in actual pavement repair also verifies the high performance of HFESC. (3) The facts such as easy gain of materials for and open to preparing HFESC, traffic as early as 5 hours make HFESC a suitable pavement repair material. HFESC is worth popularizing. convenient construction REFERENCES Chen D, Liu C, Zhao F (2006). A Study on Preparing HighFluidity and Super High-Early Strength Repairing Concrete. Highway. (11):129-144. Chung D. D. L (2004). Use of polymers for cement-based structural materials. Journal of Materials Science 39(9): 2973-2978. GB175-1999: Portland Cement and Ordinary Portland Cement. GB/T17671-1999: Method of Testing Cements-Determination of Strength. GB 8077-2000: Methods for Testing Uniformity of Concrete Admixture. GB/T 50080-2002: Test Method for Ordinary Fresh Concrete. GB/T50081-2002: Standard for Test Method of Mechanical Properties on Ordinary Concrete. GB/T 50082 200×: Standard for Test Method of Long-term Performance and Durability of Ordinary Concrete (opinion soliciting draft). Huang S, Chang J, Liu F, Lu L, Ye Z, Xin C (2004). Poling process and piezoelectric properties of lead zirconate titanate/sulphoaluminate cement composites. Journal of Materials Science 39(23):6975-6979. Li H, Miao C, Jin Z (1998). Repair technology for cement concrete pavement. Beijing: China Communications Press. Morgan D.R (1996). Compatibility of concrete repair materials and systems. Construction and Building Materials 10(1):57-67. Palacios M, Puertas F, Bowen P, Houst Y. F (2009). Effect of PCs superplasticizers on the rheological properties and hydration process of slag-blended cement pastes. Journal of Materials Science 44(10): 2714-2723. Qin W (2000). Construction engineering materials. Beijing: Tsinghua University Press. = − D (hHigh-early-strength , T ) ∇h Wang S, Li V.C J(2006). engineered cementitious composites. ACI Materials Journal. 103 (2): 97-105. The technology proportionality Xie, Y (2000). Rapid repair of thin coefficient layer cement D(h,T) moisture concrete pavement. Highway.permeability (7): 62-65. and it is a nonlinea Yang Q, Zhu B of (2000). Properties and applications of the relative humidity h and temperature magnesia-phosphate cement mortar for rapid repair of balanc & and Najjar 1972).Research The moisture mass concrete. Cementthat Concrete 30(11):1807the variation in time of the water mas 1813. volume concrete (wateroncontent Zhao Z, Zhao G, Huang C of(1999). Research adhesivew) be eq divergence of the moisture flux J splitting tensile behavior of young on old concrete. Industrial Construction. 29 (11): 56-59, 50. − ∂ = ∇•J ∂ w t The water content w can be expressed a of the evaporable water we (capillary wa vapor, and adsorbed water) and the non-e (chemically bound) water wn (Mil Pantazopoulo & Mills 1995). It is reas assume that the evaporable water is a fu relative humidity, h, degree of hydration degree of silica fume reaction, αs, i.e. we=w = age-dependent sorption/desorption (Norling Mjonell 1997). Under this assum by substituting Equation 1 into Equati obtains − ∂w ∂h e + ∇ • ( D ∇h) = ∂we h ∂α ∂h ∂t ∂w α&c + e α&s + w ∂α c s where ∂we/∂h is the slope of the sorption/ isotherm (also called moisture capac governing equation (Equation 3) must be by appropriate boundary and initial conditi The relation between the amount of e water and relative humidity is called ‘‘ isotherm” if measured with increasing humidity and ‘‘desorption isotherm” in th case. Neglecting their difference (Xi et al. the following, ‘‘sorption isotherm” will be reference to both sorption and desorption c By the way, if the hysteresis of the isotherm would be taken into account, two relation, evaporable water vs relative humi be used according to the sign of the varia relativity humidity. The shape of the isotherm for HPC is influenced by many p especially those that influence extent and chemical reactions and, in turn, determ structure and pore size distribution (waterratio, cement chemical composition, SF curing time and method, temperature, mix etc.). In the literature various formulatio found to describe the sorption isotherm concrete (Xi et al. 1994). However, in th paper the semi-empirical expression pro Norling Mjornell (1997) is adopted b Proceedings of FraMCoS-7, May 23-28, 2010