Carbonation induced changes in the mechanical performance, water and chloride permeability of Portland cement-slag-limestone ternary cement concretes

Abstract

Carbonation and chloride-induced deterioration of reinforced concrete can cause infrastructure damage and potential collapse. This study evaluated the impact of carbonation on compressive strength, dimensional stability, water and chloride permeability of concretes made with ternary slag cement containing 10 or 20 wt.% limestone, compared to ground granulated blast furnace slag (GGBFS) blended cement or CEM I. The carbonation rates of binary and ternary concretes were higher than those of CEM I concrete. The existing equation correlating natural and accelerated carbonation coefficients holds for the concretes evaluated and the selected carbonation exposure condition studied. The carbonation depths estimated adopting this correlation are within the limits of the cover depths recommended by the BS 8500–1:2023 for concretes for a 50 years’ service life, when exposed to exposure classes XC3/XC4. Despite the higher carbonation rates, water and chloride permeability of the carbonated ternary and binary slag cement concretes were significantly lower than those of a CEM I equivalent. No clear correlation was identified between compressive strength, porosity, bulk conductivity, water sorption coefficient and carbonation rate. Each of these properties alone did not give a good indication of the overall durability performance of binary or ternary concretes. The results demonstrate that 10 % limestone addition has no adverse effect on carbonation resistance of composite cement concrete. Therefore, it is demonstrated that partial replacement of GGBFS by limestone is a practical and technically sound solution for producing concrete with a reduced clinker content and comparable durability to CEM I or binary GGBFS concretes.