A Research Of Fiber-Interface Processing Approach And Tensile Properties Of High Performance Fiber Reinforced Cementitious Composites

In consideration of the decisive influence of the interfacial performance on High Performance Fiber Reinforced Cementitious Composites, based on the improvement of the interfacial performance, this paper measured the improved mechanical performance by the fiber treatment with four different oils. The main mechanical performance included compressive strength, flexural strength and fracture energy, etc.. Besides, the influences of water-binder ratio (W/B), fiber volume fraction and type of oil on the mechanical performance were investigated, and direct tensile strength test method which can reflect the toughness property directly was explored as well. At last, with different water-binder ratios and ages, the direct tensile strength of High Performance Fiber Reinforced Cementitious Composites was measured.The experiment results showed that:At the same water-cement ratio(W/B), the compressive strength of High Performance Fiber Reinforced Cementitious Composites first decreased and then increased with the growth of the PVA fiber content, while its flexural strength and fracture energy increased, but the growth rate decreased;At the same PVA fiber volume fraction, with the water-cement ratio increasing from0.27to0.45, the flexural and compressive strength of High Performance Fiber Reinforced Cementitious Composites continued to lower, while the fracture increased, however the fracture energy of blank mortar group continued to increase.After coated with different oil agents, the PVA fiber showed different effects. The oil agent A didn’t play a significant role in improving the interface, the rupture-strength and compression strength of High Performance Fiber Reinforced Cementitious Composites had been reduced. The oil agent B had some effects on improving the fiber-matrix interface, therefore improved the rupture strength and compression strength of matrix at low W/B. The oil agent C had obviously improved the fiber-matrix interface, improved the rupture strength, compression strength and fracture energy of matrix at low W/B. The oil agent D had greatly reduced the compressive strength and fracture energy of PVA-ECC, but had improved the flexural strength. In conclusion, the oil agent C had the optimal treatment effect. After treated, the mechanical performance of High Performance Fiber Reinforced Cementitious Composites at low W/B was better.The lubrication of oil not only could reduce the bond strength between the fiber-interface but also could reduce the matrix cohesion. The effect of oil on low W/B matrix mechanical properties was significantly higher than that of high W/B. High water-cement ratio (0.45) fiber-matrix interface improved with oil could not achieve the desired results; The author speculated that the high water-cement ratio (0.45) fiber-matrix interface did not require oil to improve, and between0.45-0.36there is a critical interfacial bond strength, and was not required to reduce the maximum value of the interfacial bond strength.The volume of PVA fiber influence on tensile strength was more obvious than the phenomenon of strain hardening, and with its increase, phenomenon of strain hardening is even more distinct.The effect of PVA fiber fraction volume on the tensile strength, when water-cement ratio was0.45, there was not significant effect, but the impact of the strain hardening phenomenon was more obvious. With the volume increasing, the strain hardening phenomenon was more and more obvious; when water-cement ratio was0.36, PVA fiber volume had obvious effects on tensile strength and strain hardening phenomenon, which was, raising the PVA fiber content was the key to improve its tensile properties.The effects of ages on the tensile properties had two aspects. On the one hand, with age increasing, the specimen tensile strength fluctuated fell with the age increasing, On the other hand, the stability of load-deformation curve at hardening stage decreases, but it needs to be further studied.With the age increasing, the degree of hydration of cement was to be deepening further, and the bond strength of the substrate also increases. But the formation and variation of the PVA fiber surface chemical bond strength is uncertainty. So that the High Performance Fiber Reinforced Cementitious Composites tensile strength was showed fluctuations downward trend, which needing further microscopic structure of the ascertainment and research.