Mechanical properties of hydraulic lime mortars and fired clay bricks subjected to dry-wet cycles

Abstract

This paper examines the influence of moisture and chlorides on the mechanical properties of natural hydraulic lime mortars, fired clay brick materials and masonry components. Besides assessing three types of mortars incorporating limes with different hydraulicity levels, a cement-only mortar was also investigated for comparison purposes. The test results indicate that all the hydraulic lime mortars had mass accumulation in the range of 11–14% after being subjected to wet-dry cycles in a sodium chloride solution, whilst the mass uptake was in the range of 3–8% for those made of cement. Salt accumulation produced a denser material leading to compressive cube and flexural strength enhancements by factors ranging between 1.6 and 4.7 in comparison to those in ambient-dry conditions, with even higher factors obtained for compressive cylinder strengths and elastic moduli. In contrast, lime mortar subjected to water-only wet-dry cycles showed constant mass or mass loss, due to cracking. Uniaxial compressive strengths of cylindrical brick cores were about 8.5% higher due to wet-dry cycles in chloride solution, and by about 14.9% lower due to wet-dry cycles in water, compared to the ambient-dry case. Complementary compressive tests on masonry cylinders in ambient-dry conditions were also used to assess the adequacy of existing compressive strength assessment expressions. After modifying the expressions by a set of proposed calibration factors, these are employed to undertake a sensitivity study using the mechanical properties of mortars and bricks subjected to wet-dry cycling. The results of the sensitivity study, combined with strength ranges available in the literature, lead to an identification of a suitable range of materials that can be considered for rehabilitation of some forms of historic masonry.