Towards a sustainable concrete: "Sandless" concrete

Abstract

As a step towards ensuring the sustainability of concrete as a construction material, an investigation was carried out on the mechanical and durability properties of concrete made without natural sand, termed "sandless" concrete, and with cement partially replaced by fly ash. Four groups of concrete mixes, with water-cement (w/c) ratios of 0.40, 0.45, 0.50 and 0.55, respectively, were studied. For each w/c ratio, there were six mixes with 0, 10%, 20%, 30%, 40% and 50% of cement content replaced by fly ash by mass, and one normal concrete mix containing natural sand. The difference in mechanical properties between normal and "sandless" concrete was not significant. "Sandless" concrete mixes with cement replaced by fly ash by <30% showed comparable compressive, splitting tensile and flexural strengths as those without fly ash. However, the elastic modulus was reduced with the incorporation of fly ash. In addition, use of fly ash led to reduced drying shrinkage of "sandless" concrete, and significantly improved the resistance to chloride ion penetration. The resistance to sulfate attack, on the other hand, seemed to decrease with higher fly ash content. From the study, it appears that "sandless" concrete with cement replaced by fly ash up to 30% could be considered for structural applications. © 2011 by Walter de Gruyter Berlin Boston 2011.