The combined effect of cement matrix strength and aggregate type on the tensile behaviour of concrete

The study investigates how the type of coarse aggregate and the strength of the cement matrix influence the splitting tensile strength of concrete. Two aggregate types commonly used in structural concrete were considered: gravel and granite. Concrete mixtures with a stronger and a weaker cement matrix were prepared in order to examine the interaction between matrix properties and aggregate behaviour during failure. The obtained results indicated that the governing factor depends on the aggregate used. In concretes containing gravel, the splitting tensile strength increased mainly with increasing matrix strength. In contrast, for concretes made with granite aggregate, the resistance to splitting was influenced to a greater extent by the mechanical properties of the aggregate itself, especially its susceptibility to crushing. To clarify the observed differences, the fracture surfaces and crack trajectories were analysed after testing. Distinct fracture mechanisms were identified for the two aggregate types. In concrete with gravel, cracking developed predominantly along the interfacial transition zone between the grains and the hardened cement mortar. For granite-based concrete, the crack path often penetrated the aggregate particles. These observations demonstrate how matrix and aggregate properties jointly determine tensile behaviour.