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TECHNICAL PAPER

(a) (b)

(c) (d)

Figure 4: Hydration heat of fly ash (a) and calcined clay (b) mixes and Setting characteristics of fly ash (c) and calcined clay (d) mixes as presented in [42] .

was significantly higher for increasing dosage of fly ash than to the presence of limestone addition, to compensate for the
calcined clay, as noticed in Figure 4(a) and Figure 4(b). The early delay in setting characteristics of fly ash binders and bring it
interaction of calcined clay and the consequent acceleration in close to plain portland cement. Similar results were previously
the hydration process contribute to the heat release in calcined reported for high volume fly ash concretes with a minor dosage
clay binder combinations as opposed to fly ash binders. A of limestone in literature [43] .
combination of limestone-fly ash showed higher heat release
than FAF42, which is characteristic of the positive influence of In contrast to the fly ash mixes, an increase in calcined clay
limestone on early hydration characteristics. Figure 4(b) shows dosage from CC30 to CC42 resulted in early hardening, and
that the change in heat release was not significant between the Vicat resistance was further accelerated in the presence
CC30 and CC42, and only a marginal variation was observed of limestone-calcined clay combination. The combined early
in the cumulative heat release due to limestone addition in contribution of both calcined clay and limestone can also be
calcined clay binders. High reactivity potential of the calcined noticed in the energy pattern in Figure 4(b), which collectively
clay starts dominating hydration from the early stages itself. The accelerates the setting characteristics of calcined clay-
onset of energy rise for calcined clay binder is similar to OPC in limestone binders. The penetration resistance was found to rise
3
Figure 4(b). between 3-4 hours, which indicates that LC formulations have
regular setting characteristics and could adequately meet the
Setting characteristics of all binder compositions with fly ash and requirements of blended and masonry cement applications. In
calcined clay is presented in Figure 4 (c) and (d), respectively. fly ash mixes, limestone addition was found to be beneficial in
The penetration resistance reduces with increasing dosage of improving the kinetics of heat release rate, and correspondingly
fly ash (See FAF30 and FAF42 in Figure 4 (c)). Increase of dosage reduced the delay in setting characteristics that are typical in
of fly ash from 30% to 42% shifts the time taken to develop higher dosage of fly ash additions as a cement substitute.
resistance from nearly 6 hours to 7 hours. Addition of limestone
manages to delay and shift the time taken between 5-6 hours Figure 5 presents the evolution of compressive strength for
in all ternary binders with limestone-fly ash combination. This the concrete mixes. Figure 5(a) and 5(b) shows the results from
shift signifies the acceleration in hydration characteristics due Phase 1 [38] , while Figure 5(c) and (d) shows the results from

The IndIan ConCreTe Journal | FeBruarY 2020 35