Insights into thermal stability and interface bond performance of sisal fiber in ultra-high performance concrete under different curing conditions

It is well known that plant fibers suffer serious alkali hydrolysis and mineralization in ordinary cement mortar or concrete, resulting in significant degradation of interface bond and mechanical performance. The stability of plant fibers in ultra-high performance concrete (UHPC) is seldom reported until now. In this paper, the degradation of sisal fiber in UHPC under steam curing (90 °C) or standard curing (20 °C, RH ≥ 95.0%) conditions were investigated, and the interfacial bonding between sisal fiber and UHPC was also studied. On the other hand, the mechanical properties of UHPC under two curing conditions were carried out. The experimental results indicated that the bonding between sisal fiber and matrix under steam curing conditions was lower than that under standard curing conditions, which was caused by the thermal contraction of sisal fiber at high temperatures. For sisal fibers in UHPC with two curing conditions, thermogravimetric analysis and X-ray diffractometer results revealed that some amorphous substances underwent alkali hydrolyzation and no significant damage occurred on cellulose. The backscattering scanning electron microscope images also showed that the mineralization of sisal fibers in UHPC was very slight. Therefore, the degradation of sisal fiber in UHPC was limited during the curing period and the long-term performance should be further studied.