Rubber aggregate-cement matrix bond enhancement: Microstructural analysis, effect on transfer properties and on mechanical behaviours of the composite

Limited strain capacity and low tensile strength of cement-based materials make them brittle and sensitive to cracking, behavior that limits durability of cement-based applications. Rubber aggregates (RA) incorporation appeared to be a suitable solution to improve the strain capacity and to limit the propensity of such materials for cracking. However, bond defect between RA and cementitious matrix is well-known and detrimental to mechanical and transfer properties of rubberized cement-based composites. This paper is dedicated to the enhancement of rubber-cement matrix interface and then investigates effect of this bond on transfer properties and mechanical behaviors of rubberized mortars. To achieve this goal, RA were coated with styrene-butadiene copolymer and after densification of this copolymer resin on their surface, they were mixed with the premixed-cementitious mixture. Another approach implemented was the use of an air-detraining admixture to produce rubberized mixture with the similar air content as the control mortar. Microstructural studies firstly clarified that cement paste bonded firmly on copolymer-coated RA. Air-permeability of the rubberized mortar incorporating copolymer-coated RA was lower than that of the control mortar. Moreover, rubber coating approach was beneficial to reduce water capillary absorption and to limit reduction in direct tensile strength. It also results in a better residual post-peak behavior and higher fracture energy, contributing to improve the resistance of the composite to shrinkage cracking even under high restrained condition.