Predicting the compressive strength of concrete: the effect of bleeding

Abstract

Models for predicting concrete compressive strength, such as those of Bolomey and Abrams, base their validation on producing concrete mixtures of optimised packing density. More advanced models such as the Laboratoire Central des Ponts et Chaussées (LCPC) model predict an increase in concrete strength as a result of a high coarse aggregate content, which results in a simultaneous reduction in the volume of entrapped air and a decrease in the space between coarse aggregate particles. It is therefore important to find out if mixtures rich in coarse aggregate really perform better than mixtures containing the same volume of binding paste but with an optimised size distribution. Observations show that this is not the case and that the strength drops significantly, apparently due to bleeding which affects most mixtures and alters the bond between aggregates and the binding matrix. The bond parameter of the model is therefore correlated to a qualitative bleeding index so as to reflect the experimental strength. This index is also linked with the internal fine phase, which governs the phenomenon and therefore enhances the prediction of the compressive strength of mixtures based upon bleeding. This work may lead the LCPC model to incorporate the effect of bleeding in the mix design of concrete in general and of high-performance concrete in particular.