The impact resistance of masonry units bound with fibre reinforced mortars

► In masonry, flexural bond strength is more rate sensitive than MOR of mortar. ► Stress-rate sensitivity of bond strength drops with fibre content. ► Plain mortar leads to failure at the stone-mortar interface. ► Fibre reinforcement transfers the fracture plane into the stone block. The seismic rehabilitation of stone masonry buildings requires a quantitative understanding of the constituent materials under variable rates of loading. The stress-rate sensitivity of cementitious composites and rock has been intensively investigated. However, the literature on the impact resistance of masonry joints is scarce, particularly with regard to the bond behaviour using fibre reinforced mortars. This paper describes the stress-rate sensitivity of masonry units bound with fibre reinforced Type S mortars. A drop-weight impact machine was used to generate stress rates in the range of 1kPa/s–108kPa/s. The dynamic impact factor and stress-rate sensitivity were evaluated for the flexural strength of the mortar and the bond strength and further, the pattern of failure was noted for each mix and loading rate. Polypropylene micro-fibres were incorporated as discrete reinforcement at 0%, 0.25% and 0.5% volume fraction into the mortar. Results show that the impact resistance of the masonry units increased in the presence of fibres. However, the stress-rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, where as the mode of failure in those masonry units bound with plain mortars was through fracture at the mortar-block interface, the addition of fibres transferred the failure plane to within the masonry block.