Hybrid effects of basalt and polyvinyl alcohol fibers on the mechanical properties and macro-microscopic analysis of low-heat portland cement concrete

In this study, the pattern of the effect of hybrid basalt fibers (BF) and polyvinyl alcohol fibers (PVAF) on low-heat Portland cement (LHPC) concrete was investigated through mechanical properties and microstructural tests. The compressive stress-strain relationship law for hybrid fiber-reinforced LHPC-C is also summarized by the test data. The test results showed that BF reduced the slump of LHPC-C more significantly than PVAF, and hybrid fibers were better than individual fibers for the strength enhancement of concrete. When the total fiber content was less than 0.4%, the two fibers showed a positive hybrid effect. The optimum hybrid fiber contents for 28 d compressive, splitting tensile, and flexural strength of concrete were 0.15% BF and 0.1% PVAF, 0.2% BF and 0.1% PVAF, and 0.15% BF and 0.3% PVAF, respectively. Compared with the control group, the three mechanical strengths were increased by 30.05%, 56.79%, and 43.51%, respectively. Meanwhile, the toughness of LHPC-C became more apparent as the fiber contents grew. Concrete with BF contents of 0.2% and PVAF of 0.3% had the highest toughness index. At the microscopic level, the components in LHPC-C were mainly SiO2, Ca(OH)2 and C–S–H gels. The surfaces of BF and PVAF were well-bonded to the hydrated cement matrix, and appropriate amounts of hybrid fibers can effectively reduce the porosity of LHPC-C.