回收钢纤维对超高性能混凝土和易性和力学性能的影响

为了探究回收钢纤维(RSF)在超高性能混凝土(UHPC)中替代工业钢纤维(SF)的可行性,以SF作为对比,采取流动度试验、流变试验及钢纤维分散度试验,分析了RSF对新拌超高性能混凝土和易性的影响,并通过抗折抗压试验,研究了RSF对硬化超高性能混凝土力学性能的影响。结果表明:新拌回收钢纤维超高性能混凝土(RSFUHPC)与工业钢纤维超高性能混凝土(SFUHPC)流动性经过统计学分析无明显差异,由于RSF长径比不均,RSFUHPC屈服应力及塑性黏度均大于SFUHPC,但RSFUHPC剪切增稠程度明显降低,同时RSF在新拌及硬化UHPC中的分散度均明显大于SF;当钢纤维掺量一定时,统计学假设检验P值(P-value)＞0.05,表明相比于SF,掺入RSF对UHPC荷载-位移曲线、抗折强度以及抗压强度没有显著影响。因此,掺入RSF可以在保证UHPC力学性能的同时,显著增强其在UHPC中的分散性,降低实际工程中人工振捣的施工难度,提高施工质量。

Effect of Recycled Steel Fiber on Workability and Mechanical Properties of Ultra-high Performance Concrete

The aim of this study is to explore the feasibility of replacing industrial steel fiber (SF) with recycled steel fiber (RSF) in ultra-high performance concrete (UHPC). With SF as a comparison ,the effect of RSF on workability of freshly mixed ultra-high performance concrete was analyzed by means of fluidity test, rheological test and steel fiber dispersion test. The effect of RSF on mechanical properties of hardened ultra-high performance concrete was also studied by means of flexural and compressive test. Statistical analysis results indicated no significant difference of fluidity between freshly mixed RSFUHPC and SFUHPC. The yield stress and plastic viscosity of RSFUHPC were greater than those of SFUHPC, which can be attributed to the uneven aspect ratio of RSF. However, the shear thickening degree of RSFUHPC was significantly lower than that of SFUHPC, and the dispersion of RSF in freshly mixed and hardened UHPC was significantly greater than that of SF. Using the same mixed amount of RSF as that of SF, a P-value larger than 0.05 was obtained, indicating that, compared with SF, RSF had no significant effect on the load-displacement curve, flexural strength, or compressive strength of UHPC. Therefore, the addtion of RSF would ensure good dispersion in UHPC and excellent mechanical properties of UHPC, and would also reduce the construction difficulty associated with artificial vibrations in actual engineering structures and improve the construction quality.