Evaluation of workability, microstructure and mechanical properties of recycled powder geopolymer reinforced by waste hydrophilic basalt fiber

The recycled powder geopolymer (RPG) is an environmental-friendly cementitious material prepared from recycled powder (RP) recovered from construction waste. The preparation of geopolymers has promoted the development of sustainable materials, but the great brittleness limits the application scenarios. In this paper, the waste hydrophilic basalt fiber (WHBF) was used to reinforce RPG and the mechanical properties, toughness and microstructure were evaluated. The results indicated that the addition of WHBF significantly improved the compressive, flexural and tensile strength of the RPG. Adding 0.6% WHBF with 6 mm in length and 13 μm in diameter improved the compressive strength, flexural strength and tensile strength by 59.43%, 85.20% and 121.74% in 28 days, respectively, compared to the control group. The single fiber pull-out test and Digital Image Correlation (DIC) analysis indicated that the interfacial properties of the WHBF with appropriate geometric parameters were high and the direction and rate of crack growth were significantly changed, which greatly improved the toughness of the matrix. The analysis of water absorption and Mercury Intrusion Porosimetry (MIP) showed that although the incorporation of WHBF increased the porosity of RPG, the pore size was small and had no adverse effect on the matrix. The microstructure analysis showed that the addition of WHBF benefited the formation of additional gel, which provided a better bonding and frictional stress transfer path for the composites. Meanwhile, the energy absorption capacity of the composites was significantly improved and the crack propagation was inhibited. Furthermore, the WHBF enhanced the long-term drying shrinkage performance of RPG. This work suggested that the recycled powder geopolymer reinforced by waste hydrophilic basalt fiber shows excellent potential for application.