Abstract
Abstract Early-stage hydration heat development in blended Portland cement-based binders containing natural zeolite in an amount of up to 40% by mass is investigated using an isothermal heat flow calorimeter. Experimental results show that the presence of natural zeolite in the blended binders accelerates the onset of C 3 S hydration and boosts the first phase of C 3 A hydration. The second phase of C 3 A hydration gains on importance in the hydration process with the increasing zeolite dosage. For the zeolite contents higher than 30%, the maximum specific hydration heat power in this phase is even higher than the maximum corresponding to the C 3 S hydration. The effectiveness of the natural zeolite as a binder, as expressed by the difference specific hydration heat per 1 g of zeolite, is found to decrease with its increasing dosage in the blends. The replacement of Portland cement in an amount of 10% by mass by natural zeolite can be considered as a limit for its effective use. Above this limit, a substantial part of zeolite does not directly participate in the hydration process and plays a role of a fine filler instead. The limited zeolite participation in the blended-cement hydration can explain the lower compressive strength of zeolite concretes containing higher amounts of natural zeolite, which was reported before.
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