This study investigates the effect of a new type of blended pozzolan on the hydration, mechanical and durability performance of cement. A blend of limestone calcined clay pozzolan (LCCP) was produced by grinding calcined clay and limestone in a ratio of 2 : 1 with 2% gypsum. Blends with cement replacement level of 0, 10, 15, 20, 30 and 50% using LCCP were cast. The effect of LCCP on the hydration of cement was investigated using isothermal calorimetry and X-ray diffraction. Mortar and concrete samples were cast to study the influence of LCCP on mechanical and transport properties. The addition of LCCP was found to have a beneficial effect on the early age hydration of cement. The induction period and initial setting time of cement paste were found to reduce on increased cement replacement level. Higher or similar compressive strength was observed for all the LCCP blends as compared to ordinary Portland cement. The pozzolanic reaction of calcined clay and formation of carboaluminates on the reaction of calcium carbonate with alumina helps to develop a refined pore structure that aids in reducing transport properties of concrete such as porosity, rate of water absorption and permeability.

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The influence of the capacity of supplementary cementitious materials (SCMs) to consume portlandite on the carbonation resistance of mortar was investigated. Seven different mineral additives (two types of slag, two types of fly ash, two calcined clays and limestone) were used and their reactivity was measured using isothermal calorimetry, strength index measurements, Chapelle's test and thermogravimetric analysis. Mortar samples were cast by substituting 30% cement by mass with SCMs and their carbonation performance was investigated. The carbonation resistance of cement was found to have no specific correlation with the compressive strength of the mortar cast using it. Different reactivity test methods showed a reasonable correlation between the reactivity of the non-hydraulic SCM and the carbonation resistance of the cement containing that SCM. The performance of different cement binders under carbonation was found to be influenced by the alkaline content and compressive strength collectively.

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