Page 4 - Open Access - Feb 2020

TECHNICAL PAPER

Table 2: Binder systems investigated in the study

tyPe miX id: oPc (**clinker) % scm % limestone* % gyPsum %
Phase-1 OPC OPC 100 - - -
FA30 FA30 70 30 - -
LC 3 LC 3 50 ** 31 15 4
Phase-2 OPC OPC 100 - - -
FAF30 66 30 3.5 0.5
FAF42 54.5 42 3 0.5
Class F FAFL10 54.5 34 11 0.5
FAFL15 54.5 30 15 0.5
FAFL20 54.5 25 20 0.5
CC30 65.0 30 3.5 1.5
CC42 53.5 42 3 1.5
Calcined Clay CCL10 53.5 34 11 1.5
CCL15 53.5 30 15 1.5
CCL20 53.5 25 20 1.5
Note: *inclusive of limestone contributed from 5% calcite present in OPC

Gypsum amount was adjusted for the calcined clay - admixed A major part of this paper reports the results of three types of
binder to ensure that the aluminate peak is pushed beyond the concrete produced with the three binder systems: (i) Concrete
main silicate hydration peak based on isothermal calorimetry of grade M30 (i.e. characteristic compressive strength of 30
profiles. This ensures proper early hydration of tricalcium MPa), (ii) Concrete of grade M50 (i.e. characteristic compressive
silicates as recommended in the literature [11,41] . Figure 3 shows strength of 50 MPa), and (iii) Concrete with binder content of
the impact of proper gypsum dosage on the silicate hydration 360 kg/m and w/b of 0.45 (designated as C mix). A second
3
peaks with (w-G) and without (w/o-G) gypsum correction. The investigation reports the results of binary and ternary blended
additional aluminates from calcined clay and acceleration in mixtures with fly ash/ calcined clay and limestone, as indicated in
clinker reaction due to fine substitutes increase the demand for Table 2. In all the mixes in Phase-2, the binder content and w/b
gypsum marginally for LC binder composition. The additional were maintained at 360 kg/m and 0.45 respectively.
3
3
gypsum (1.5% in this case) delays the appearance of the
aluminate peak outside the silicate peak and ensures proper For all concrete mixes, the coarse aggregate was crushed
silicate reaction. A detailed investigation on the influence of granite with a maximum size of 20 mm, and the fine aggregate
gypsum dosage on the hydrate phase assemblage of LC binder was well-graded river sand. The coarse to fine aggregate ratio
3
can be found in Krishnan et al. (2019) [33] . was maintained at 60:40 by weight and a polycarboxylic ether
(PCE) based superplasticizer was used to obtain a slump of 80
– 120 mm. The actual composition of cement paste used in the
study is mentioned in the different sections.

4. RESULTS
4.1 Hydration, Hardening and Compressive
strength

Figure 4 presents hydration heat and setting characteristics
of the cement paste (w/b: 0.4) for all binder compositions
investigated in Phase-2. The cumulative heat release in these
binder systems reflects the kinetics of hydration reaction in
binary and ternary combinations. It is clear that an increase in
Figure 3: Effect of gypsum addition on the hydration profiles of the amount of SCM, i.e., fly ash or calcined clay from 30% to
LC3 binder. 45%, reduces the total heat release by 7 days. The reduction

34 The IndIan ConCreTe Journal | FeBruarY 2020