Influences of different modification methods on surface activation of waste tire rubber powder applied in cement-based materials

Abstract

This study aimed to investigate the effects of different modification methods on the surface activation of waste tire rubber powder. The improvement of surface activation and hydrophilicity is necessary when considering the use of waste tire rubber powder in cement-based materials. Physical cleaning and chemical reaction methods were applied to activate the 20-mesh waste tire rubber powder. Specifically, deionized water, 5 wt% NaOH solution, and CCl4 solution were used in the physical cleaning method, whereas silane coupling agents (KH-550, KH-560, and KH-570) and NaClO solution were used in the chemical reaction method. The activation index and contact angle were selected to characterize the activation effects on waste tire rubber powder. The microscopic morphology and modification mechanism of waste tire rubber powder were explored using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and testing of particle size distribution. Moreover, the mechanical performance of cement mortar containing modified rubber powder was tested, which confirmed the practical application value of the proposed modification method in this study. Test results showed that both physical cleaning and chemical reaction methods improved the surface activation and hydrophilicity of rubber powder. The physical cleaning method results revealed that 5 wt% NaOH solution removed hydrophobic impurities and increased the number of pores on the surface of rubber powder. Consequently, 5 wt% NaOH solution was considered more appropriate to improve the hydrophilicity and activity of rubber powder compared with deionized water and CCl4 solution. After the chemical reaction method, results showed that KH-550 had the highest activation effect on rubber powder since activated substances were generated and agglomerated on the surface of rubber powder. Moreover, the modification increased the mechanical strength and toughness of cement mortar containing rubber powder, and the modification effect was more prominent while using KH-550.