Characterisation of reciprocating sliding friction for a cracked brick-mortar interface

Abstract

The mechanical behaviour of masonry is strongly influenced by the brick-mortar interface. To isolate and benchmark the pure frictional response of this interface in mortared masonry, this study uses a reciprocating sliding tribometer test on cracked brick-mortar specimens. Tests were conducted under varying pre-compression levels and two reciprocating sliding frequencies, using unreinforced clay brick masonry with lime-cement mortar. Frictional behaviour was analysed through hysteresis curves relating the measured friction force to the sliding displacement. From these, the mean sliding friction coefficient and tangential stiffness were extracted for each cycle. Both parameters showed considerable variability across tests. The mean kinetic friction coefficients, typically ranging between 0.4 and 0.6, aligned with values from indirect tests methods (e.g., triplet or couplet shear tests), and their variability appeared independent of the applied normal load. In contrast, tangential stiffness showed a qualitative correlation with the normal load, despite a high scatter. To interpret the observed variability, statistical analyses including ANOVA and Principal Component Analysis were performed. Although further testing is required, these initial results offer valuable insights into the frictional mechanics of cracked masonry interfaces and suggest new testing avenues for more accurately characterising brick-mortar interaction in structural assessments.