Construction and Building Materials 254 (2020) 119326
Contents lists available at ScienceDirect
Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat
A study on fresh properties of limestone calcined clay blended
cementitious systems
Nithya Nair, K. Mohammed Haneefa, Manu Santhanam ⇑, Ravindra Gettu
Department of Civil Engineering, IIT Madras, India
h i g h l i g h t s
Fresh properties of limestone – calcined clay (LC3) cementitious systems are studied.
LC3 systems show a different rheological behaviour as compared to other systems.
Slump retention performance of concrete with LC3 is poorer than the other systems.
PCE based admixtures are more compatible than SNF in LC3 systems.
a r t i c l e
i n f o
Article history:
Received 14 January 2020
Received in revised form 20 April 2020
Accepted 22 April 2020
Keywords:
Limestone calcined clay cement
Workability retention
Rheology
Concrete equivalent mortar
Retarder
a b s t r a c t
This paper reports the assessment of rheological characteristics of cementitious pastes prepared with
Limestone - Calcined Clay Cement, in comparison with ordinary Portland cement and Portland - Fly
Ash cement. The impact on workability retention in concrete is also assessed. Further, a comparison of
the performance of different commercially available superplasticizers is done using mortar flow retention
tests (done on concrete – equivalent mortars) and slump retention tests on concrete. The results bring out
the impact of calcined clays on increased superplasticizer demand, and also show the difficulties in
retaining the workability for extended durations.
Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction
The use of supplementary cementitious materials (SCMs) and
alternative fuels are the common strategies adopted to reduce
environmental impacts arising from cement production and its
use in concrete. SCMs can reduce the CO2 emissions from 0.81 to
0.64 kg/kg of cement [1,2]. However, the reduction of clinker is
not possible beyond a certain level of replacement with these
SCMs. For fly ash, even though it is available in large quantities,
the substitution level is limited to 30–40%. Slag can substitute up
to 70% of clinker; however, its availability is inadequate compared
to clinker production [3,4]. Comparing the overall production of
clinker with the total volume of conventional SCMs produced, it
is insufficient to meet the global demand. In this context, it is necessary to identify new sources of SCMs in view of sustainability
and environmental protection, the only potential source for SCM
that is available in large quantities is clay [4].
⇑ Corresponding author.
E-mail address: manusanthanam@gmail.com (M. Santhanam).
https://doi.org/10.1016/j.conbuildmat.2020.119326
0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.
The presence of kaolinite in the clay is a key factor to use it as an
SCM. Kaolinite calcined at temperatures of 600–800 °C exhibits
high potential for interaction with Ca(OH)2 when mixed with
cement [5,6]. Though the replacement of clinker with metakaolin
has several advantages and better performance compared to Portland cement, production of high grade metakaolin is energy intensive and demands clay with high degree of purity, which makes it
expensive [7]. In this context, it is useful to look at reject clays in
mines that have higher proportions of impurities, resulting in an
effective kaolinite content of 40–60%.
The use of a ternary blend of limestone, calcined clay, and clinker called as Limestone Calcined Clay Cement (LC3) with 50% clinker replacement was demonstrated as part of collaborative
research between the Laboratory of Construction Materials (LMC)
at EPFL, Switzerland, and CIDEM in Cuba [3]. The use of a combination of limestone and calcined clay is a good choice because the
availability exceeds the other SCMs [8]. The kaolinite used for
the production of LC3 can be obtained from low grade clays, with
kaolinite content under 60%. In India, there is abundant amount
of low-grade clays available in existing quarries, which are mostly
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N. Nair et al. / Construction and Building Materials 254 (2020) 119326
regarded as waste [9]. The use of low grade clays directly reduces
the environmental burden, and also avoids the need for new quarries. High levels of substitution without compromising the
strength and durability are possible for cement by calcined clay
due to its highly pozzolanic nature, and the synergy exhibited with
limestone [10,11]. Such a blend also provides ecological benefits
because of lower embodied energy of the blends compared to ordinary cement [12,13].
One of the problematic issues with the use of calcined clays is
the increase in the water demand due to high fineness (caused
by the sheet like structure) and narrow particle size distribution
[14]. Hence, to maintain the required workability, the superplasticizer dosage has to be increased [15–17]. Clays have the ability to
readily exchange cations in order to balance the inherent electrical
charges on the surface. When chemical admixtures are added, the
cations in the clay are readily exchanged with the organic materials present in the admixture. This causes less dispersion and
adsorption of chemical admixtures on the surface of the clay.
Therefore, a large part of the admixture added is consumed by
the clay particles and higher dosages are required to attain the
required workability. The high admixture dosage increases the cost
and also causes longer setting time, delay in strength gain and
removal of formwork [18].
Comparing poly-condensates and polycarboxylic ether based
super plasticizers with respect to dispersing ability, it was
observed that polycarboxylic ethers (PCEs) are more sensitive to
clays [18]. The dispersing ability is impeded because of the incorporation of PCEs into the layered structure of clay through their
side chains. It was observed that different types of PCEs showed
noticeable sensitivity to clay and the dispersing force decreased
significantly in its presence [19,20]. Liu et al. [21] investigated
the reduction in swelling potential of montmorillonite by using
KCl in the presence of PEG (Polyethylene glycol) and PAG (copolymers of ethylene oxide and propylene oxide). PAG forms a complex
structure with K+ ions that considerably reduces the swelling
potential of the clay. Therefore, copolymer PAGs are more commonly used on the side chain for PCE based superplasticizer to
be used in cementitious systems containing calcined clay. The
decrease in dispersion also depends on the type of clay. Montmorillonite clays have expanding lattices which allow the intercalation, swelling and exchange of cations [22]. This is the main
reason why kaolinite clays are preferred to montmorillonite, due
to their less harmful effect on concrete fluidity [23]. Ng and Plank
[24] found that PCEs undergo physisorption and chemisorption
onto clays by a factor of 100 times compared to cement.
Chemisorption takes place when polyethylene oxide side chains
intercalate into the interlayer region of aluminosilicate layers
and physisorption occurs on the clay surfaces which are positively
charged by the adsorption of Ca2+ ions present in cement pore
solution. Both physisorption and chemisorption are dependent on
the dosage. At higher dosages, the side chain intercalation dominates and at lower dosages, electrostatic attraction through the
anionic backbone of clay surfaces prevails.
Lei and Plank [20] developed a new type of PCE to mitigate the
clay effects and for robustness. The new PCE is modified from
methacrylic acid and hydroxyl-alkyl methacrylate esters. The
adsorption of PCE was limited only to the clay surfaces and not into
the layered structure of clay. The research showed that the modified new PCE was less affected by clay and was able to disperse
cement more effectively. Ng and Plank [24] found that PCEs with
high grafting density are more susceptible to influence of clay on
their dispersion abilities. They found that poly-glycols can be used
as sacrificial agents when PCEs with high grafting chains at high
dosages are used in clays. However, it was also suggested that
more understanding and experience has to be gained to establish
this in practice.
In the case of blends of limestone with calcined clay, the addition of limestone has a positive influence on rheology as it
decreases the flow resistance of concrete [25,26]. Vance et al.
[27] studied the rheology of binders containing Portland cement,
limestone and metakaolin or fly ash. Combinations of OPC, limestone (10 and 20% replacement with different particle sizes of
0.7, 0.3 and 15 mm) and metakaolin (5 and 10% substitution by
mass) with volumetric water-to-solid ratio (w/s) of 0.40 and 0.45
were used in the study. The rheological studies of binary blend
combination of coarser limestone of size 15 mm (5% replacement)
and OPC showed that there was reduction in yield stress and plastic viscosity with respect to the control mix. For limestone particles
coarser than cement, there was a decrease in particle packing and
specific surface area. This reduced the ability of the paste to resist
shear, thus explaining the reduced yield stress. When fine limestone powder (0.7 and 0.3 mm) was used as replacement and
OPC, there was increase in yield stress and plastic viscosity. Therefore, replacement with limestone particles coarser than OPC
decreased the yield stress and plastic viscosity, whereas, particles
finer than OPC increased the yield stress and plastic viscosity. In
the case of metakaolin replaced Portland cement paste, yield stress
and plastic viscosity were significantly increased because of the
high surface area and the tendency of particles to agglomerate.
The rheology of the ternary blend combination of limestone and
metakaolin is quite complex. For ternary blends with fine limestone addition and metakaolin, with increase in limestone content,
the plastic viscosity also increased, similar to that of binary blend
with fine limestone particles and OPC. However, for ternary blend
with coarser limestone addition, the plastic viscosity remained
unchanged, as the viscosity is predominately affected by the fine
metakaolin particles. The plastic viscosity increased with an
increase in metakaolin content and was invariant with the limestone content. On the other hand, in the case of ternary blends with
the increase in finer limestone additions at fixed metakaolin content, there was decrease in yield stress. Even though the addition
of fine limestone reduces the particle spacing and increases the
yield stress, the electrostatic attraction between the negatively
charged metakaolin and positively charged limestone particles
increased the interparticle spacing and thereby reduced the yield
stress. The influence of superplasticizer into this ternary combination system was not covered in the study.
Zaribaf et al. [28] studied the compatibility of superplasticizers
with limestone-metakaolin blended cementitious systems. ASTM
C595 Type IL cement (15% limestone) with 10 and 30% metakaolin
substitution by mass was used for the study [29]. The superplasticizers used were commercially available polycarboxylic ether
(PCE), sodium lignosulfonate, naphthalene formaldehyde condensates (SNF) and polymelamine formaldehyde (SMF). The pastes
were prepared at water-to-binder (w/b) of 0.40. The saturation
dosages of superplasticizers were selected from the mini-slump
tests for a corresponding spread of 12 cm. Also, flow tests were
done at different substitution levels of metakaolin ranging from
10 to 40% metakaolin substitution by mass and compared with
control cement paste (no metakaolin) to understand the relation
between metakaolin substitution and superplasticizer dosage
requirement. The results showed that out of the four types of
superplasticizers, SMF and lignosulphonate required dosages of
superplasticizer greater than the maximum recommended dosage
to attain the flow values similar to control pastes. PCE and SNF
based superplasticizers were found more compatible with
limestone-metakaolin blended cement. The increase in metakaolin
substitutions shortened the setting time and decreased the workability. This was compensated by the addition of adequate dosages
of compatible superplasticizers. Finally, the mortar specimens prepared with the combination of Type1L cement and 30% metakaolin
substitution by mass with PCE based admixture showed an
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N. Nair et al. / Construction and Building Materials 254 (2020) 119326
increase in compressive strength compared to control blend (no
metakaolin).
Santos et al. [30] studied the rheology of cement paste with
metakaolin and/or limestone filler blended system. The pastes
were prepared with different metakaolin and/or limestone filler
(maximum replacement level up to 20%) with constant watercementitious materials ratio of 0.3 and 0.5 wt% polycarboxylic
ether type superplasticizer. The fresh properties such as slump
and spread, Marsh cone time, yield stress and plastic viscosity, viscoelastic properties and thixotropy were evaluated. The results
showed that spread was low and Marsh cone time was high when
the metakaolin content increased to more than 10%. The rheology
studies were done using stress controlled oscillatory rheometer.
Metakaolin increased the plasticity and thixotropy of cement paste
up to 5–8%. However, beyond 10% of metakaolin the workability
was adversely affected. It was found that the increase in metakaolin content increased the yield stress and G0 (storage modulus) of
the pastes, whereas limestone filler up to 10% did not change the
yield stress compared to the Portland cement pastes. The workability was improved by the addition of PCE based superplasticizer.
The study concluded that the blend with 90% Portland cement,
5% metakaolin and 5% limestone filler gives good thixotropy.
It is seen from the available literature that the ternary system
involving limestone, calcined clay and cement is complex, and
leads to interactions at different levels in the presence of a superplasticizer. The current study aims to understand the interaction
between superplasticizers and LC3 system, in comparison to the
OPC and fly ash replaced systems. The specific objectives of the
experiments performed in the study are as follows:
To determine the saturation dosage and compatibility of PCE
and SNF superplasticizers with pastes prepared using the
cementitious blends for different w/b ratios.
To study the rheological characteristics of LC3 blended systems
with PCE and SNF superplasticizers.
To evaluate the performance of concrete mixes with LC3 at different binder content and water-to-binder ratio to attain high
workability.
To assess the slump retention performance of concrete prepared
with LC3 using different types of commercially available
superplasticizers.
2. Materials and methods
2.1. Materials
For mixes in the first phase, the cementitious blends used were:
(i) Ordinary Portland cement (OPC) – 53 grade conforming to IS
12269 – 2009 [31],
(ii) FA30 (lab scale production of OPC blended with 30% fly ash).
Class F fly ash conforming to IS 3812 (Part 1):2003 was used
as a supplementary cementitious material for partial
replacement of cement [32]. The Class F fly ash was obtained
from North Chennai thermal power station
(iii) Limestone calcined clay cement (LC3), a ternary blended system – with 50% clinker, 30% calcined clay (the clay had 60%
kaolinite content), 15% limestone and 5% gypsum (produced
in an industry trial by inter-grinding the components in a
ball mill).
The chemical composition and physical properties of the
cementitious materials are presented in Table 1. River sand (0–
4.75 mm) conforming to Zone II of IS 383 (2016) was used as fine
aggregate [33]. Crushed granite coarse aggregates of size range
4.75–10 mm and 10–20 mm were used in 50:50 proportion. Polycarboxylic ether (PCE) and sulphonated naphthalene formaldehyde
(SNF) superplasticizers conforming to IS 9103–2004 were used for
the Phase 1 study [34]. In Phase 2, five different commercially
available PCE superplasticizers (PCE1 – also used in Phase 1,
PCE2, PCE3, PCE4, and PCE5) were used along with a lignosulphonate - based retarding admixture. The PCE admixtures used
in this study are commercial chemical combinations available in
India, with slight variations in their physical properties as presented in Table 1. According to the data sheet provided by the
manufacturers, these PCEs are formulated for extended slump
retention and improved rheological performance. All PCE admixtures in the study had solids content in the range of 32–38%, while
the SNF had solids content of 40%.
In the first phase of the study, LC3 from an industrial trial was
available for use. However, the second stage was executed after a
considerable time gap, and the industrially produced LC3 was not
Table 1
Properties of the cementitious materials.
Properties
OPC
FA30
LC3
Specific gravity
Water demand for standard consistency (%)
Initial setting time (min)
Final setting time (min)
Blaine’s fineness (m2/kg)
Soundness (mm)
Mortar compressive strength at 28 days (MPa) as per IS 4031–6 [35]
3.16
30
124
245
340
0.2
61.0
2.77
31
120
280
330
0.2
46.0
3.01
33
101
165
520
0.1
43.7
Chemical composition
Quantity (% by mass)
OPC
Fly ash
Calcined Clay
Limestone
LC2
LC3
64.59
19.01
4.17
3.89
0.88
0.59
1.40
1.28
59.32
29.95
4.32
0.61
1.07
–
PCE2
0.53
49.50
41.52
1.88
0.38
0.23
2.42
48.54
10.07
1.74
1.62
0.47
0.10
37.09
28.29
34.28
19.45
3.43
1.38
0.48
9.21
33.92
30.02
19.46
3.59
2.16
0.45
7.47
CaO
SiO2
Al2O3
Fe2O3
MgO
Na2Oeq.
LOI (%)
PCE Admixtures used
PCE1
Appearance
Relative density
pH
Chloride ion content
Solid content (%)
Reddish brown liquid
1.08±0.02 at 25℃
6
<0.20%
32.86
Brown hazy liquid
1.08±0.02 at 25℃
6
Nil
38.05
PCE3
PCE4
PCE5
Light yellow liquid
1.09±0.02 at 25℃
6
Nil
35.23
Light yellow liquid
1.085 ±0.02 at 25℃
6
Nil
37.62
Yellowish Liquid
1.07±0.03 at 25℃
6
<0.10%
33.85
4
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
paste was mixed for two minutes at the same speed. The mixer
was then stopped and sides of the bowl and blades were scraped
(15–20 s), and then the paste was again mixed for two minutes.
For the mixes without superplasticizer, the same procedure was
followed except that all the water was added at once. The binary
blend combination of OPC with fly ash (FA30) was dry mixed for
one minute for homogenization prior to the procedure described
earlier. For all the mixes, the total mixing time was five minutes
excluding the time taken for dry mixing [40,41]. In this study,
1000 ml of paste was poured into the Marsh cone by closing the
bottom orifice of 8 mm diameter. Then the orifice was opened
and the stopwatch was started. The time taken for 500 ml of the
paste to fill the cylinder kept under the cone was noted. The Marsh
cone test results – expressed as a flow time v/s superplasticizer
dosage curve, indicates the flow time of cement-admixture combination with increasing dosage of superplasticizer. The saturation
dosage is the point beyond which the fluidity does not significantly
increase with further addition of superplasticizer [36,37]. The saturation dosage was fixed based on the method proposed by Gettu
et al. [42].
Rheology studies were carried out in this study using Brookfield
HA DV II + Pro viscometer with a vane test set up. The type of vane
spindle used was V71 of the following dimensions: (i) vane length
6.878 cm and (ii) vane diameter – 3.439 cm. Tests were conducted on cement paste with water-to-binder ratio 0.35 and
0.40. The rotation speed was increased from 4 rpm to 10 rpm in
steps and then ramped down, maintaining 20 s for each step, as
shown in Fig. 1. Three trials were done for all the combinations
of binder and admixture at different w/b ratios and repeatability
was observed. The data from the downward ramp was used for
the assessment. The output from the software is the torque (expressed in percentage with respect to the maximum torque capacity of the instrument) and viscosity. From the test setup, only the
viscosity data can be reliably obtained and used for assessing the
paste behaviour at saturation dosage. There is no valid conversion
factor in this setup for the conversion of % torque to shear stress.
Therefore, the results are shown with respect to viscosity v/s speed
in rpm. The viscosity is calculated by the instrument based on the
assumption of a Couette flow when the applied angular velocity is
below 10 rpm.
Fig. 1. Shearing profile in the vane test.
available at this stage. In this scenario, LC2 – or the blend of limestone (LS) and calcined clay (CC) (from the same sources as for the
industrial LC3 production with a 1:2 ratio [LS:CC]) was used in the
second phase of the study. Both the blends (i.e. LC3 and
Cement + LC2-45) had the same percentage (30%) of calcined clay.
2.2. Experimental methods
2.2.1. Phase 1
Determination of saturation dosage of superplasticizer was carried out by the Marsh cone test [36–39] while the mini slump test
was used to study the spread of the paste mixes. The cementitious
blends used were OPC (100% cement), FA30 (OPC blended with 30%
fly ash) and LC3. Tests were conducted on cement paste with
water-to-binder ratios of 0.35, 0.40 and 0.45. All the test materials
were kept in the environmental chamber at a temperature of 25℃
and 65% relative humidity for 24 h prior to testing. The paste was
prepared using a 5-litre Hobart-type blender and a B-flat beater
with a shaft speed of 139 rpm and planetary speed of 61 rpm. Initially, cement and 70% of the water required were mixed together
in the mixer for one minute. The superplasticizer and remaining
water were then added to the cement paste. The water content
in the superplasticizer was deducted from the water added. The
Table 2
Grades of concrete and their relevance.
Grades
M30
M45
M60
Relevance/use
Slump requirement
Challenge
Ready Mix Concretes (RMC) for residential construction.
80 mm at placement.
Travel time 30 min to 2 h.
Slump retention of 2 h required.
For infrastructure projects such as bridges
120 mm at placement.
Travel time 30 min to 2 h.
Slump retention of 2 h required.
For high rise buildings
120 mm at placement
Travel time + vertical pumping
Slump retention of 3 h required
Table 3
Summary of saturation dosage determined from Marsh cone tests and mini slump spread.
Type of Binder
w/b ratio
OPC
FA30
LC3
OPC
FA30
LC3
OPC
FA30
LC3
0.35
0.35
0.35
0.40
0.40
0.40
0.45
0.45
0.45
Saturation dosage of superplasticizer (SP) by
weight of cement (%)
Flow time
corresponding to
saturation dosage (s)
Mini-slump spread
at saturation dosage
(mm)
PCE
SNF
PCE
SNF
PCE
SNF
0.15%
0.20%
0.40%
0.10%
0.15%
0.30%
SP not required
0.05%
0.20%
0.40%
0.50%
0.70%
0.20%
0.30%
0.40%
SP not required
0.10%
0.30%
26
47
50
11
16
14
–
11
10
21
43
49
8
19
16
–
10
8
165
180
180
180
200
180
–
150
150
200
200
175
150
150
175
–
160
170
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
Further, concrete trials were conducted incorporating LC3 to
assess the fresh properties and sensitiveness with water content
and superplasticizers. In this phase, a comparison was also done
between the saturation dosage obtained from the LC3 paste study
with the dosage required for LC3 concrete in order to achieve a target slump of 180–200 mm. The corresponding hardened properties
of the concrete were also determined. LC3 concrete studies were
done for a fixed binder content and w/b ratio to attain high workability, i.e. slump of 180–200 mm. The aggregate proportion and
superplasticizer dosages were fixed based on the target slump.
The details of the mix designs and the trials are presented in the
section describing the results of the study.
5
55% cement). Trials were conducted on each grade of concrete with
OPC, LC2 30% and LC2 45%, in order to produce the requisite grades
of concrete. The flow properties and workability retention of mortar fractions of the concrete mixes were studied as per ASTM
C1437 [29] for each type of PCE and the blend of one of the PCE
admixtures with retarder (in a 75:25 ratio). The study was conducted using the Concrete Equivalent Mortar (CEM) approach,
which accounts for the reduction of the effective water content
encountered from the coarse aggregate. It replaces the coarse
aggregate mass by an equivalent mass of fine aggregates corresponding to its surface area in the designed mix [44]. Additionally,
slump retention studies were performed on concrete mixtures
incorporating the different blends of admixtures.
2.2.2. Phase 2
In this phase, slump retention properties of different grades of
concrete were studied including M30, M45 and M60 (as per IS
456:2000) [43]. In this grade classification as per IS 456:2000, ‘M’
stands for mix and the numerals indicate the 28 day compressive
strength of 150 mm cubes (cured in moist conditions) in MPa.
The relevance of these grades of concrete is described in Table 2.
Five commercially available PCE based admixtures and a retarder were used in this study. Concretes with ordinary Portland
cement (OPC) were used as reference mixes. To prepare lab grade
LC3, the OPC was replaced by combinations of limestone and calcined clay – called LC2 – at 30% (20% calcined clay, 10% limestone
and 70% cement) and 45% (30% calcined clay, 15% limestone and
The saturation dosages identified for the various combinations
of cementitious material and admixture at different w/b ratios
from Marsh cone tests are presented in Table 3. The w/b ratio
has significant influence on the flow time. The flow time decreases
with increase in w/b ratio as expected. At low w/b ratios, there is
less amount of water, which decreases the relative fluidity and
increases the flow time. It can be seen that OPC showed much
Fig. 2. Viscosity at saturation dosage of PCE for binders at w/b ratio 0.35.
Fig. 4. Viscosity at saturation dosage of SNF for binders at w/b ratio 0.35.
Fig. 3. Viscosity at saturation dosage of PCE for binders at w/c ratio 0.40.
Fig. 5. Viscosity at saturation dosage of SNF for binders at w/b ratio 0.40.
3. Results and discussions
3.1. Phase 1: Saturation dosage, mini slump flow and initial concrete
trials
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N. Nair et al. / Construction and Building Materials 254 (2020) 119326
lower flow times at saturation dosage for all w/b ratios. At w/b
ratios of 0.35, 0.40, and 0.45, FA30 and LC3 showed comparable
flow times at saturation dosage.
As expected, dispersing ability of the superplasticizer affects the
fluidity [45]. For all w/b ratios, the dosage required to reach saturation was higher for SNF as compared to PCE. For PCE admixtures,
the dispersion is caused by both steric and electrostatic repulsion
mechanisms, whereas for SNF based admixtures, the dispersion is
only due to electrostatic repulsive forces. Due to this reason, higher
dosage of SNF is required for better dispersion [46,47].
The saturation dosage required for LC3 is greater compared to
OPC and FA30 at all w/b ratios. This may be due to the intercalation
of superplasticizer molecules between layers of clay [48]. The
higher SP requirement may also be due to higher fineness of LC3
as compared to the other blends. The specific surface area of the
binder is an important parameter that affects the adsorption of
superplasticizers. The saturation point increases with the fineness
of the cementitious material [38].
The mini-slump spread values were found to increase up to saturation dosage. Beyond the saturation dosage, there was no significant change in the spread value. Bleeding was observed at very
high dosages of superplasticizer. For brevity, only the mini slump
spread at saturation dosage is presented in Table 3. It can be understood from the results that LC3 can achieve similar spread as OPC at
the saturation dosage at higher water-to-binder ratios.
3.2. Phase 1: Rheological characterization
Figs. 2–5 show the variation of viscosity at saturation dosage of
PCE and SNF for w/b ratios of 0.35 and 0.40. The viscosity is
observed to reduce with increase in w/b ratio. For the w/b ratio
of 0.35, OPC and FA30 exhibited shear-thinning behaviour,
whereas LC3paste showed a different pattern with almost constant
viscosity at increasing shear rates – this trend is reflected in both
PCE and SNF pastes, and could be attributed to the highly cohesive
nature of LC3, arising from its high fineness. The viscosity of FA30 is
low compared to OPC and LC3 for w/b ratio of 0.35 at saturation
dosage. As the w/b ratio increased from 0.35 to 0.40, the flow behaviour of LC3 was shear-thinning, similar to OPC and FA30. It should
be noted that for LC3 systems, there was a significant change in the
flow behaviour when the w/b ratio was increased from 0.35 to
0.40. While the viscosity was significantly higher than OPC at the
lower w/b, there was a considerable reduction below OPC for the
higher w/b for LC3 systems with PCE. However, the viscosity of
LC3 blends with SNF still remained much higher than the OPC
and FA30 systems.
3.3. Phase 1: Trials on LC3concrete
The combinations of cement content and w/b ratio used to
design the concrete mixes were 300 kg/m3 (w/b 0.60), 350 kg/m3
(w/b 0.50), 400 kg/m3 (w/b 0.40) and 450 kg/m3 (w/b 0.30). The
first trial was done for the binder content 300 kg/m3, aggregate
proportion 60:40 (coarse aggregate: fine aggregate) and w/b ratio
0.60. In the paste studies, the w/b ratio was limited to 0.35, 0.40
and 0.45. Therefore, in order to compare the superplasticizer (SP)
requirement for concrete with that of paste studies, the saturation
dosages for w/b ratios 0.30, 0.50 and 0.60 were also found on paste
mixes, using Marsh cone test. This was done only for the LC3
cement. For w/b ratio of 0.6, the saturation dosage obtained for
LC3 cement pastes was 0.05% using PCE based admixture (PCE1).
However, in concrete, even when the superplasticizer dosage was
increased by 50% of the saturation dosage for the paste, the mix
was very stiff and zero slump was obtained. This indicates that
the LC3 concrete mixes had a large demand of superplasticizer to
achieve high workability. Trials were repeated with increasing
dosages of superplasticizer but the maximum slump that could
be attained was only 70 mm. Further addition of PCE caused bleeding issues. After multiple number of trials, the aggregate ratio was
fixed as 50:50 (coarse aggregate: fine aggregate), and the resultant
Table 4
Summary of tests done to attain the target slump using PCE and SNF admixtures for concrete mixes incorporating LC3.
Binder content (kg/m3)
w/b ratio
Aggregate ratio
sp/c %
Slump (mm)
PCE
300
0.60
350
0.50
50:50
50:50
50:50
50:50
400
0.40
50:50
450
0.30
50:50
0.60
0.65
0.70
0.50
0.60
0.65
0.70
0.60
0.65
0.70
0.60
0.70
0.90
1.20
1.30
115
190
Bleeding
No slump
50
185
Bleeding
60
150
190
No slump
No slump
50
200
Bleeding
SNF
300
0.60
50:50
350
0.50
50:50
400
0.40
50:50
450
0.30
50:50
0.80
1.00
1.10
0.90
1.00
1.10
1.00
1.10
1.30
1.40
1.30
1.60
Above 1.60
60
200
Bleeding
110
195
Bleeding
0
180
195
Bleeding
0
80
Incompatible
7
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
Fig. 6. Correlating saturation dosage of PCE superplasticizer (PCE1) from paste
studies with the finalized dosages from concrete.
mix had a slump of 190 mm for superplasticizer dosage of 0.65% by
weight of cement.
The details of the trials performed to attain the target slump
using PCE and SNF are summarized in Table 4. The results showed
that for all the mixes, the superplasticizer requirement was significantly higher than the saturation dosage obtained from paste
studies for a corresponding w/b ratio. Similar to paste studies,
the superplasticizer requirement reduced with increase in w/b
ratio. For a reduction of the w/b ratio from 0.60 to 0.40, there
was not much variation in the superplasticizer requirement. When
the w/b ratio was reduced below 0.40, a sudden increase in
demand for superplasticizer was noted. This can be related to the
viscometric studies described in the previous section, where the
behaviour of LC3 paste changed significantly when the w/b ratio
was reduced from 0.40 to 0.35.
The requirement of SNF to achieve the target slump was significantly higher compared to PCE. At w/b ratio of 0.30 and 450 kg/m3
binder content, the superplasticizer dosage was even greater than
1.6% by weight of cement and the target slump was not achieved.
Therefore, the LC3 – SNF combination for w/b ratio below 0.40 was
deemed not compatible. From the slump tests, it can be concluded
that PCE based admixture is better suited for LC3 systems as compared to SNF. This result is also in agreement with the viscometer
data presented in the previous section.
Since the SP required to get the target slump was less using PCE
admixture compared to SNF with LC3, further workability studies
were done using PCE based admixture (PCE1). In both paste and
concrete studies, it was observed that for LC3, when the w/b ratio
was reduced below 0.40, there was a sudden increase in the
requirement of superplasticizer. The correlation between saturation superplasticizer dosage of paste and dosage required to
achieve the target slump in concrete for the mixes is shown in
Fig. 6. Two additional mixes (370 kg/m3, w/b ratio 0.45 and
Fig. 7. Water content and PCE superplasticizer (PCE1) dosage requirement for each
mix.
Table 5
Summary of concrete mix proportions for evaluating the influence of mix water
content on LC3 concrete.
Mix ID
Binder content (kg/m3)
Water content (kg/m3)
w/b ratio
MIX1
MIX2
MIX3
MIX4
MIX5
MIX6
300
350
370
400
420
450
180
175
167
160
147
135
0.60
0.50
0.45
0.40
0.35
0.30
Fig. 8. Compressive strengths of concretes in Phase 2.
Table 6
Concrete compositions and initial slump obtained for Phase 2 mixes.
Composition
w/b ratio
Cement (kg/m3)
% sp/c (solid)
CA:FA
Initial slump obtained
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
0.50
0.45
0.40
0.50
0.35
0.30
0.50
0.35
0.30
310
360
420
450
350
420
350
420
420
0.40
0.34
0.27
0.49
0.80
1.20
0.60
0.85
1.25
50:50
50:50
50:50
50:50
50:50
50:50
50:50
50:50
50:50
195
200
210
200
200
215
200
210
210
8
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
420 kg/m3, w/b ratio 0.35) were also tested to increase the size of
the data set. Three replicates were included for each mix in order
to get a range of superplasticizer dosages for achieving the target
slump. As seen from Fig. 6, while the saturation dosage of PCE
superplasticizer in the paste increases steadily with a decrease in
the w/c, the corresponding dosage to produce a high slump of
180–200 mm in concrete does not significantly change until a w/
c of less than 0.40. Below this w/c, there is a major increase in
the PCE dosage required for achieving the target slump.
In order to understand the influence of water content reduction
with respect to the superplasticizer dosage, the variation in water
content and PCE superplasticizer (PCE1) requirement for each mix
was plotted as shown in Fig. 7 for the mixes listed in Table 5. It can
be seen that for a reduction in water content from 180 kg/m3 (MIX
1) up to 167 kg/m3 (MIX 3), there was no significant change in the
SP dosage required to produce the target workability. However,
below 167 kg/m3 (i.e. for MIX 4, MIX 5 and MIX 6), the SP dosage
required increased significantly with the reduction in water
content.
3.4. Summary of phase 1 studies
The paste and concrete studies performed in Phase 1 gave valuable insights into the behavior of LC3 systems in the fresh state.
One of the clear outcomes was the identification of a critical w/c
of 0.40, which defines the point below which significant differences arise between LC3 and other cementitious systems with
respect to the flow behavior. This impact was also seen in the concrete studies, in terms of a significant enhancement in the dosage
of PCE superplasticizer required for a suitable slump to be achieved
in concrete for w/c below 0.40. Further, there was a clear understanding that water contents below 160 kg/m3 may not result in
suitable concrete performance in the fresh state for mixes with
LC3. In the second phase, the attention was focused towards eval-
Table 7
Summary of workability (flow) retention of concrete equivalent mortars.
Flow (mm)
Composition
Initial
Flow (mm)
1hr.
2hrs.
3 hrs.
PCE1
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
230
215
210
220
215
210
210
205
205
220
210
185
190
185
155
170
165
160
205
185
185
180
160
140
100*
100
100
190
180
160
145
130
100
100
100
100
235
220
230
200
190
200
200
200
195
210
220
220
180
180
170
175
170
160
210
200
195
180
160
155
175
160
150
200
200
220
200
200
210
180
180
190
190
200
200
170
160
180
170
165
150
170
180
175
165
155
140
150
130
120
PCE3
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
240
240
230
230
220
220
210
215
210
220
210
230
230
225
210
220
220
210
1 hr.
2 hrs.
3 hrs.
240
235
230
230
230
220
210
200
205
240
220
220
220
210
200
200
190
200
220
210
200
210
190
170
175
180
180
200
210
190
190
180
155
170
165
145
230
210
220
200
200
200
200
185
190
220
205
200
190
200
180
200
175
190
195
180
175
180
185
170
180
170
175
220
210
180
210
220
200
205
200
180
220
190
180
200
210
180
190
185
170
PCE4
PCE5
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
Initial
PCE2
230
220
230
200
210
220
210
200
215
75% PCE1 + 25% Retarder
230
220
240
220
230
220
210
220
220
230
220
210
220
210
220
210
215
210
*100 mm flow means no flow.
Table 8
Dosage (solid) of superplasticizers in Phase 2 study to achieve initial slump in the range 170–200 mm.
Mix
PCE1
PCE2
PCE3
PCE4
PCE5
PCE1 + Retarder
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
0.40
0.34
0.27
0.49
0.80
1.20
0.60
0.85
1.25
0.35
0.40
0.34
0.45
0.75
1.15
0.70
0.95
1.25
0.37
0.35
0.30
0.55
0.90
1.25
0.65
0.80
1.25
0.37
0.35
0.30
0.52
0.75
1.25
0.72
0.87
1.27
0.42
0.45
0.35
0.52
0.95
1.25
0.85
0.87
1.30
0.40
0.34
0.27
0.49
0.80
1.20
0.60
0.85
1.25
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
Fig. 9. Slump retention performance of concretes with PCE1.
9
Fig. 12. Slump retention performance of concretes with PCE4.
Fig. 13. Slump retention performance of concrete with PCE5.
Fig. 10. Slump retention performance of concrete with PCE2.
Fig. 11. Slump retention performance of concrete with PCE3.
Fig. 14. Slump retention performance of concrete with PCE1 and retarder
combination.
10
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
uating the slump retention performance of concretes prepared
with OPC and LC3.
3.5. Phase 2: Slump retention studies on LC3 concretes
The mixture designs of concretes with the three binder types,
namely OPC, LC2-30% and LC2-45%, to achieve the specific strength
grades (M30, M45 and M60) are presented in Table 6. In all the
mixes, the superplasticizer (PCE1) was dosed to produce a slump
of 190–220 mm, and coarse to fine aggregate ratio was maintained
constant (50:50). The binder content and w/b were varied to attain
the desired strength levels, which are presented in Fig. 8. The compressive strength results in Fig. 8 clearly show that all the concretes were able to achieve the target strengths, irrespective of
the binder type.
In order to assess the slump retention performance, the flow
table test (as per ASTM C1437) was first conducted on concrete
equivalent mortars [29,44]. The results of these tests are presented in Table 7, in terms of the flow values (mm) until 3 h
after preparation of the mortar, along with the temperature at
the time of testing. It must be noted that the diameter of the
base of the flow cone is 100 mm; hence, a flow value of
100 mm in the table indicates that the mortar did not have
any flow. These tests were conducted in controlled environment
in such a way that the temperatures of mortars tested were in
the range of 27 ± 0.50 ℃.
The results in Table 7 indicate the following:
(i) The initial flow values with all the admixture types were in
the range 200–240 mm.
(ii) There was a decline in the workability retention characteristics with increased replacement of OPC with LC2.
(iii) The workability retention reduced with increasing
grade of concrete, which is indicative of the w/b of
the mix.
(iv) Among the five commercial PCEs, the best performance was
obtained with PCE4. As per the data sheet of this product, it
is intended to function as a superplasticizer and retarder,
unlike the other four PCEs.
(v) The worst performance among all products was for PCE1 but
when this admixture was replaced with a lignosulphonatebased retarder (at a 25% replacement level), the performance
was seen to be as good as the best performing PCE, namely
PCE4.
The assessment of the concrete equivalent mortars was followed by an investigation of the slump retention characteristics
of concrete prepared with the five brands of PCE, and the blend
of PCE1 with retarder. The dosages of each admixture required to
produce the initial slump in the range of 170–220 mm are presented in Table 8. It can be clearly seen that for a given mix, the
dosage across a range of admixtures is much similar. The workability retention performance of the different blends is presented in
Figs. 9–14. The concrete slump performance clearly shows that
increased substitution of OPC with LC2 increases the loss of slump,
for all grades of concrete. It is, however, important to view the
result in the perspective of the information presented in Table 2,
to give a clear picture about the suitability of the combination of
cementitious blend and admixture. This assessment is provided
in Table 9.
Table 9
Workability retention performance of blends in comparison with original requirements (stated in Table 2).
Grade of concrete
Initial slump satisfied
M30
M45
M60
Final slump (80 mm @ 2 h for M30, 120 mm @ 2 h for M45, and120 mm @ 3 h for M60,
as in Table 2) satisfied
OPC
LC2-30
LC2-45
OPC
LC2-30
LC2-45
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes, except for PCE3 and PCE5
Yes, except for PCE2 and PCE3
Yes
Only for PCE1 + Retarder Combo
Only for PCE1 + Retarder Combo
No
No
No
Table 10
Compressive strengths of concrete with the different combinations of mixes and PCE superplasticizers.
Composition
PCE1
PCE2
PCE3
1d
7d
28d
1d
7d
28d
1d
7d
28d
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
6.32
9.35
10.86
5.70
9.31
9.36
6.66
9.35
9.60
30.61
40.03
51.71
31.92
45.42
52.31
34.27
46.02
51.04
39.64
54.98
62.16
39.34
55.57
62.43
39.23
55.01
64.01
5.78
8.79
11.01
6.78
7.74
9.57
5.16
8.75
10.41
28.10
45.07
55.78
29.78
43.41
55.47
30.14
45.24
56.84
35.00
53.17
64.25
36.67
51.22
63.17
36.11
54.37
63.59
4.98
7.48
9.87
5.97
7.54
9.42
5.81
6.94
10.47
25.87
45.78
53.48
30.01
42.15
52.47
28.17
48.74
57.87
33.89
52.48
65.78
40.01
52.66
65.57
37.25
53.27
66.27
Composition
PCE4
OPC-M30
OPC-M45
OPC-M60
LC230- M30
LC230- M45
LC230- M60
LC245- M30
LC245- M45
LC245- M60
PCE5
75% PCE1 +25% Retarder
1d
7d
28d
1d
7d
28d
1d
7d
28d
6.01
9.10
10.78
5.58
7.23
10.17
6.87
8.67
11.37
29.14
40.15
52.18
29.78
43.40
49.92
32.45
48.97
50.10
38.31
52.10
60.20
37.88
53.21
64.01
40.10
57.55
63.17
6.10
8.96
11.00
6.75
8.31
11.01
7.12
7.87
11.04
32.45
40.87
56.85
34.78
43.75
55.81
37.47
46.49
59.47
38.01
49.78
64.17
42.58
52.40
66.78
41.27
56.87
67.14
5.44
8.10
8.92
6.00
9.34
9.77
6.20
9.01
9.23
28.25
42.78
49.70
28.55
40.10
46.45
29.77
40.41
50.78
36.54
52.37
61.57
37.48
52.10
63.04
38.74
53.87
65.11
N. Nair et al. / Construction and Building Materials 254 (2020) 119326
The results in Table 9 seem to indicate that the concretes with
OPC have a satisfactory slump retention performance except for a
few cases as shown in the table. However, when LC2 is used as
replacement for OPC, the slump retention is only good at the
replacement level of 30% for the M30 mix – for the M45 and
M60 mixes, only the PCE1 and retarder combination works for
the 30% replacement mixes. On the other hand, when the replacement level is 45%, none of the concretes are able to match the
expected slump retention performance. This is an important result
as it clearly shows that when calcined clay based binders are used,
long travel times must be avoided. The results also seem to indicate that the use of concrete equivalent mortar may be able to pick
the best performing superplasticizers but is unable to accurately
predict the concrete performance.
Contrary to the results of workability retention, there is no significant difference in the compressive strengths of the different
concretes produced with the various binder types, as indicated
from the data in Table 10. Thus, when dealing with calcined clay
based concretes, the primary emphasis has to be for the workability related characteristics.
4. Conclusions
The influence of combinations of limestone and calcined clay on
the workability characteristics of paste and concrete, in comparison with fly ash based cement and ordinary Portland cement
was presented in this paper. The systematic investigations performed in this study indicated that:
i) Significantly higher dosages of superplasticizer are required
for limestone – calcined clay cement blends in comparison
to fly ash based or ordinary Portland cement systems. However, the flow / workability characteristics at saturation
dosages of superplasticizer are similar across different binder systems.
ii) The viscosity of paste with LC3 was found to be lower with
PCE admixture than SNF admixture for all w/b ratios (at saturation dosage of superplasticizer). The superplasticizer
requirement for concrete prepared with LC3 was significantly higher than the saturation dosage obtained from
paste studies for all the w/b ratios used in the study. For
w/b ratios from 0.60 to 0.40, the SP requirement was 0.65%
for PCE based admixture to maintain the target workability
and there was not much variation in the superplasticizer
requirement. When the w/b ratio was reduced below 0.40,
a sudden increase in demand for superplasticizer to 1.2%
was noted.
iii) The superplasticizer requirement for LC3 concrete using SNF
based admixture to achieve the target slump was significantly higher than PCE. At w/b ratio of 0.30 and 450 kg/m3
binder content, the superplasticizer dosage was even greater
than 1.6% by weight of cement and the target slump was not
achieved. Therefore, the LC3 – SNF combination for w/b ratio
below 0.40 was deemed not compatible.
iv) Rheological assessment using vane arrangement indicated a
change in the flow behavior of LC3 pastes when the w/b was
reduced to below 0.40. This tendency was also indicated in
the concrete studies.
v) Slump retention performance of concrete with LC2 as a mineral additive was not adequate in comparison with ordinary
Portland cement systems, unless the level of substitution
was controlled to less than 30%. When the replacement level
is 45% (i.e. similar to LC3 used in the first phase), none of the
concretes are able to match the expected slump retention
performance. Thus, when limestone - calcined clay based
binders are used, long travel times must be avoided.
11
CRediT authorship contribution statement
Nithya Nair: Investigation, Methodology, Data curation, Writing - original draft. K. Mohammed Haneefa: Investigation,
Methodology, Data curation. Manu Santhanam: Conceptualization, Writing - review & editing, Supervision. Ravindra Gettu:
Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared
to influence the work reported in this paper.
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