Evaluation of sustainable high-volume fly ash concretes

This article presents experimental research work oriented toward developing practical design tools for industrial application, and illustrates the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) and a high-range polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with mass substitutions of cement by FA between 15% and 75%, and a target slump of 200 mm ± 20 mm. The total water content was minimized through the use of an optimum SP dosage that resulted in water reductions of 18%, 15% and 11% respectively for the reference mixtures of w/b = 0.5, w/b = 0.55, and w/b = 0.6, which leads to the same percentage reductions of cement. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b ratios. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful tools for the practical applications of the results. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.