Influence of leaching on the local mechanical properties of an aggregate-cement paste composite

• Characterization of the mechanical behaviour at cement-aggregate interface of concrete.
• Calcium leaching mechanism at the interfacial transition zone (ITZ) of composite.
• Alteration of the mechanical properties due to leaching at ITZ.

This paper presents an experimental study to characterize the mechanical behaviour, at the local scale, of sound and degraded concrete after leaching. An experimental protocol was developed to study the effects of the calcium leaching mechanism at the interfacial transition zone (ITZ) on the mechanical properties of the cement-aggregate interface and bulk paste of model material. The process of lixiviation with deionised water occurs very slowly. The experimental study in the laboratory was accelerated by replacing the water with an ammonium nitrate solution. To quantify the development and kinetics of degradation at the cemented bond, the concrete leaching fronts were characterized at different levels of degradation using phenolphthalein and local mechanical tests (compression and tensile) and performed on samples consisting of two aggregates bound by cement paste. Tests were performed on sound samples at different hydration times and on chemically degraded samples. The results show the effect of leaching on the mechanical properties of the samples and making it possible to correlate the progress of leaching to the evolution of these locally considered properties. The experimental results show that there is an ITZ effect on the alteration of the mechanical properties due to leaching.