Sustainable utilization of hybrid recycled powder and recycled polyethylene terephthalate fiber in mortar: Strength, durability and microstructure

The effects of hybrid recycled powder (HRP) from composite concrete and brick waste as well as recycled polyethylene terephthalate fiber (RPETF) on the performance of mortar were investigated in this study. Recycled brick powder (RBP) was used as comparison to evaluate the influence of HRP. The mechanical properties, including compressive strength, flexural strength and elastic modulus as well as durability, including capillary water absorption, chloride penetration resistance, carbonation resistance and frost resistance were tested. The hydration products and micro pore structure of mortar were studied to reveal the influence mechanism of HRP and RPETF. The results show that the 28 d compressive and flexural strength of mortar with 30% HRP reached 78.60% and 80.36% of that of cement mortar, respectively, which was similar to that of RBP. The addition of HRP reduced the capillary water absorption, chloride ion permeability coefficient of mortar. This is related to the refined pore structure of mortar. The proportion of pores with the diameter lower than 100 nm increased due to the filling effect, nucleation effect and secondary hydration of HRP and RBP. When the volume fraction of RPETF was in 2%, the mechanical properties of mortar increased with the increase of RPETF content. The 28 d compressive strength and flexural strength of mortar with 2% RPETF were 14.25% and 22.50% higher than that without RPETF, respectively. The utilization of RPETF improved the durability of mortar with HRP. A greater reduction of mass loss and increase of dynamic elastic modulus of mortar with RPETF compared to that without RPETF after freeze-thaw cycles were obtained.