Experimental studies of self-healing cementitious materials incorporating mineral admixtures

In order to limit the release of CO2 produced in cement manufacturing, clinker (the major cement component) is often partially replaced by mineral admixtures like blastfurnace slag. The use of mineral admixtures presents different advantages such as the recy cling of industrial waste and the improvement of different material properties (workability, sulfate resistance, compressive strength at long term…). Nevertheless, several civil engineering constructions made with blast-furnace slag cement presented cracking at early age due to restrained shrinkage (autogeneous, thermal and drying shrinkage) that affects significantly the material transfer properties and their durability in aggressive environments (chloride, CO2). Under certain conditions however, it is known that cementitious materials present a self-healing capacity. The purpose of this research work is to study the beneficial influence of the natural selfhealing capacity of mortars with blast-furnace slag cement on the lifetime of civil engine ering constructions. A new experimental device has been designed in order to understand the selfhealing capacity of mortars at early age. The novel apparatus allows developing micro- cracks in a mortar ring specimen by restrained shrinkage and monitoring the evolution of self-healing by gas permeability and effective diffusivity measurements. The effects of different slag contents (0%, 50%) and curing conditions (air conditio ned room at 25±1°C and 45±5% R.H., in tap water) on the self-healing kinetics are studied. Optical measurements in 2D (optical microscope, SEM) and 3D (tomography), chemical analyses of the self-healing products and quantification of the properties of cement with blast-furnace slag (compression and tensile strength, autogenous and drying shrinkage, heat release) complete the study.