Compressive strength of cement-based composites: Roles of aggregate diameter and water saturation degree

Concrete structures experience microcracking leading to mechanical damage when submitted to desiccation. This change in mechanical properties can be dependant on the level of drying and also on constituents of the material. This paper focuses on one particular aspect, which is to determine the role of the size of rigid inclusions over cementitious materials under drying. However, concrete is a complex heterogeneous material, where the shape of natural aggregates is variable, and the number of factors to analyze is large. Thus the study was performed on a geometrically simplified material, initially proposed by Bisschop and van Mier (2002) compound of spherical glass inclusions of several diameters in a cementitious matrix to explore the influence of aggregate size. A set of uniaxial and triaxial compressive tests is performed for materials with various water saturation levels. A great dependence is observed between mechanical properties, notably peak strength and damage, linked to aggregate size and water saturation degree. Complementary microtomographic acquisitions are also done, and tend to validate the cracking pattern dependency to the aggregate diameter, and therefore explain changes in mechanical behaviour.