Effects of silica fume and Fly ash on properties of mortar reinforced with recycled-polypropylene

Adding polypropylene (PP) plastic into concrete or mortar partially instead of sand is an effective way to recycle plastic waste, but its low strength is still a problem to be solved. This work investigated the possibility of improving the mechanical properties and inhibiting the shrinkage of cement mortar with recycled PP plastic by incorporating silica fume (SF) and fly ash (FA) into the mortar. An experimental study was conducted to evaluate the effects of SF, FA, and the composite admixture of SF and FA on the fluidity, physical properties, mechanical properties, compressive strength, flexural strength, and microstructure of PP-filled cement mortar. The results showed that the addition of SF or FA reduced the porosity and water absorption of the PP-filled mortar. The combination of SF and FA reduced the porosity and water absorption, improved the compressive and flexural strength, and promoted the strength development of the PP-filled mortar in later stage. Compared with control group, the 28-d compressive strength and flexural strength of PP-filled mortar with 7% SF and 15% FA increased by 10.04% and 8.48%, and its 56-d autogenous shrinkage just increased by 1.62% and drying shrinkage decreased by 3.23%. Considering the strength and shrinkage characteristics, the optimal combination contents of SF and FA were 7% and 15%, respectively. Adding SF and FA into PP-filled mortar provides a new solution to solve the problems of low strength and large shrinkage of plastic mortar, which can not only promote the application of plastic waste in mortar, but also consume the industrial wastes, and protect the ecological environment.