Page 6 - Open Access - Feb 2020

TECHNICAL PAPER

Phase 2. It is evident from Figure 5(a) that the rates of strength component such as clinker and pozzolan. For both fly ash and
development of LC concrete are similar to OPC concrete and calcined clay, compressive strengths at 7 days and 28 days
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significantly higher than FA30 concrete, which needs extended were marginally higher for ternary mixes than binary mixes with
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curing to achieve similar ultimate strengths. LC was able to 42% SCMs. Even in CCL20 with limestone substitution of 20%,
produce comparable strength development despite lower there is a steady development of strength up to 180 days. In
clinker content than FA30. On the other hand, the Phase 2 results CC42 with 42% binary substitution of calcined clay, there was
in Figure 5 (d) indicate that it is possible to produce concrete a stagnation in the strength development beyond 28 days at
strengths with calcined clay-limestone combinations on par with higher substitution levels of calcined clay due to a probable
OPC strengths when the calcined clay is at 30-35% replacement portlandite-deficient state. The compressive strength results
level, and limestone is used up to 15% replacement level. from ongoing Phase-2 studies indicate the compositional
robustness of calcined clay-limestone combination to produce
The compressive strength development (up to 180 days) in comparable early and later age mechanical strengths to plain
concretes reaffirmed the influence of limestone on the early portland cement and accommodate varying levels of limestone-
age mechanical properties (See Figure 5(c) and (d)). This can calcined clay ratio. In fly ash-limestone combination, early age
be identified from the comparable strength development of strength of ternary mixes was found to be comparable to binary
ternary mixes with limestone to binary mixes. The early increase fly ash binders. However, a consistent difference in strengths
in hydration and strength were possible despite the fact was visible at later ages with increasing dosage of limestone as
that limestone is replaced at the expense of a more reactive shown in Figure 5c.

(a) (b)

(c) (d)
Figure 5: Results for compressive strength evolution a) comparison of strength evolution from phase-1 concrete made with OPC, FA30 and LC 3
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(reproduced from [38] ) and Influence of fly ash/calcined clay-limestone ratio on strength development of LC concrete from Phase-2 studies
(c) fly ash and (d) calcined clay [44] .

36 The IndIan ConCreTe Journal | FeBruarY 2020