The potential impact of size effects on compressive strength for the estimation of the Young’s modulus of concrete

Abstract

Concrete, a highly heterogeneous material, exhibits a clear size-dependence of its compressive strength. As the Young’s modulus is generally assumed to be proportional to the compressive strength, this would, in principle, implies a dependence on sample size for this modulus. However, the elastic modulus is directly related to linear elastic deformation, while the compressive strength results from strongly non-linear processes due to the progressive development of damage and microcracking. In other words, the elastic modulus, a material-dependent parameter, should not depend on the sample size, unlike the compressive strength. Here we show, from an extensive experimental program including non-destructive and destructive tests carried out on 527 cylindrical concrete specimens with three different concrete mixtures and four different sizes, the size-independence of elastic properties of concrete regardless of the concrete mixes. This is in full contrast with the size-dependence of the compressive strength, and implies that (i) there is no direct proportionality between the elastic modulus (linear property) and the compressive strength (non-linear property) of concrete, and (ii) the use of empirical expressions given in building codes (e.g. ACI 318-05; EN 1992) for estimating the elastic modulus from the compressive strength can lead to incorrect designs.