Quantifying the effects of hydration enhancement and dilution in cement pastes containing coarse glass powder

Various non-standard filler materials are used in concretes to improve fresh and hardened concrete properties. This paper reports results from investigations on the effects of a coarse glass powder on the hydration and strength development of cement pastes. It is shown that the incorporation of glass powder results in enhancements in the degrees of hydration of the cement grains in the system. Using a mixing model for non-evaporable water content, a methodology to quantify the enhancement in the degree of hydration of cement as a result of the presence of glass powder is proposed. In order to quantify the relative effects of dilution (reduction in cement content, and thus of the hydration products) and increase in degree of cement hydration on the mechanical properties, a strength index, which accounts for the mass fraction of the reacting material, is proposed in this paper. Using the strength index, it is shown that the use of coarse glass powder filler is beneficial in pastes with lower water-to-cement ratio (w/c), where a portion of cement remains unhydrated. Increasing glass powder contents are observed to result in increased heat of hydration per unit mass of cement. However, beyond a certain glass powder content, the heat of hydration decreases due to the dominance of the dilution effect. The ultimate heat of hydration obtained from a three parameter model, the cement content, and the ultimate degrees of hydration are used to specify a new parameter termed the total ultimate heat of hydration. It is suggested that the total ultimate heat of hydration per unit volume of paste can be used to compare between mixtures made with different w/c and glass powder contents since this term, as defined in this paper, accounts for both the hydration enhancement and dilution effect from filler addition.