Study on properties of polypropylene fiber-modified ultrafine cement composite grouting materials

In order to obtain high performance cement-based grouting materials for mining and expand the application of staple fiber in the field of full-length anchorage, Utilizing ultrafine silica cement as the binder material, with the addition of accelerator, expansion agent, and polycarboxylate superplasticizer as additives, a single-factor experiment was conducted to investigate the influence of polypropylene fibers (PPF) content on the mechanical properties, pumpability, bleeding, setting time, volume shrinkage, and microstructure of cement-based grouting materials. For ultrafine cement-based slurries modified with PPF selected as anchor materials, the mechanical load bearing properties and acoustic emission characteristics of the full-length anchoring system were studied under similar pull-out condition. The results revealed that PPF content significantly impacted the slurry characteristics and mechanical property of ultrafine cement grouting materials. It notably enhanced the compressive performance and material toughness while shortening the initial setting time and reducing fluidity. Particularly, there was a positive correlation between flexural strength and PPF content. When the PPF content was 0.1%, the comprehensive performance of composite grouting material S1 was optimal. The compressive strength of the hardened specimens at 3 d and 28 d was 60.1 MPa and 83.7 MPa, respectively, which is 23.4% and 23.2% higher than the reference group S0 without PPF. Microscopic characterizations including XRD, SEM, and FTIR confirmed that the suitable PPF not only facilitated hydration reaction but also improved internal cracks within the hardened body. It acted as a bridge, transferred stress, and delayed crack propagation. Pull-out tests indicated that the mechanical property, residual bearing capacity, and maximum deformation of the full-length anchoring system based on this composite grouting material were significantly enhanced. The maximum pull-out strength was 1.356 times the reference group S0, and the occurrence of acoustic emission events was delayed. It improved the stability of roadway surrounding rocks, providing valuable insights for the similar full-length anchoring applications.