Property study of sustainable mortar containing modified rubber, metakaolin and limestone

This study investigated the effects of modified rubber (MR) particles as partial sand replacement (up to 20%) on the mechanical properties, durability performance, and microstructure of cement mortars. In addition, metakaolin (MK) and limestone (LP) were used as supplementary cementitious materials to replace 30% of the cement. Rubber was chemically treated to obtain MR. The results indicated that the air content of fresh MR-mortar was lower than that of mortar containing unmodified rubber (UR), due to the hydrophilicity of MR grains. The combination of MK, LP, and MR maintained the compressive strength and did not significantly degrade the flexural strength compared to pure cement mortar. The electric flux and migration coefficient of both MR and UR contained mortars are measurably lower than that of control mixtures, which shows an increased resistance to chloride ion permeability. MR addition can effectively degrade the drying shrinkage of cement mortar compared to UR-mortar, which may be ascribed to the improved interface transmission zone (ITZ) between MR grain and paste. Compared with UR-mortar, the quantity of large pores and thickness of ITZ in mortar containing MK, LP, and an appropriate dosage of MR would be measurably reduced thus enhancing the strength and durability.