Influence of the composition of high-strength concrete and mortar on the compressive fatigue behaviour

The results of compressive fatigue investigations on four high-strength concretes and their corresponding mortars are presented. The influences of coarse aggregates generally, the substitution of basalt coarse aggregate by granite, the addition of silica fume and the variation of the water to cement (w/c) ratio are investigated systematically. The numbers of cycles to failure, the developments of strain, stiffness, dissipated energy and acoustic emission hits are focused on in the analyses. The results clearly show that coarse aggregates can influence the fatigue behaviour of concretes in a negative way at higher stress levels and in a positive way at lower stress levels compared to mortars. The granite coarse aggregate decreases the adverse effect at higher stress levels due to its lower modulus of elasticity compared to that of the basalt aggregate. Silica fume improves the fatigue behaviour of concrete and mortar strongly. The increase of the w/c ratio and, thus, the increase in porosity reduces the fatigue resistance of concrete and mortar significantly, due to the weakening of the mortar matrix and of the interfacial transition zone. The results demonstrate the interaction of the coarse aggregates and the mortar matrix with their specific properties, which leads to a certain fatigue behaviour. The acoustic emission gives additional valuable strain-independent information of the damage processes occurring, possibly also on micro- and nanoscales.