Use of additives in mortar to enhance the compression and bond strength of masonry exposed to different environmental conditions

Abstract

This paper investigates the effect of using additives in the mortar mix on the mechanical properties of masonry exposed to adverse environmental conditions. Ten mortar mixes were prepared using additives of lime, silica fume (SF) and polypropylene fibers (PPF) with ratios of 2, 5 and 10% of cement weight. Using local clay bricks bonded by the studied mortar types, 90 prisms and 180 cross-couplets were constructed as well as 90 mortar cubes, and were exposed to air or wetting/drying cycles of water and sulphate salts solution for 28 days and six months. Laboratory tests were carried out to determine the brick water absorption, mortar water retention, mortar compressive strength, masonry prism compressive strength and brick-mortar bond strength. Addition of lime, SF or PP as 5% of cement weight improves the mortar water retention by 25–37%. Addition of 5% SF or PPF increased the mortar compressive strength by 35 and 46%, respectively, for water curing; yet it had slight effect on the prism strength. Adding 2–5% SF or PPF improves the bond strength by 70–170% for the various exposure conditions. The results suggest adding lime, SF or PPF to cement-sand mortars as 2% of cement weight to enhance the brick-mortar bond strength.