Coarse aggregate effectiveness in concrete: Quantitative models study on paste thickness, mortar thickness and compressive strength

The paste thickness is an essential parameter related to mix proportion and properties of concrete. The quantitative models of paste thickness could be classified as volume-based paste thickness (VPT) and surface area-based paste thickness (SPT), while the widely-used SPT doesn’t consider the dilatation effect of aggregate. The aim of this paper is to modify the SPT model by comparing the derivation of different quantitative models, then the mortar thickness is calculated and its relationship with compressive strength of concrete is investigated. Taking the dilatation effect (λ) into account, a modified SPT model is derived, which also could be more accurate than VPT as a parameter in mix design of concrete. Regarded the concrete as two-phase composites of mortar and coarse aggregate, the compressive strengths of mortar and concrete conform to the hyperbolic model proposed by de Larrard, and the interlocking-effect of coarse aggregate is quantitatively characterized. Besides, the compressive strength of concrete is linear to −0.13 power of mortar thickness, which provides a foundation for the prediction of compressive strength and the mixture design of concrete.