Study on improving the performance of engineered cement-based composites by modifying binder system and polyethylene fiber/matrix interface

In this study, cement, rice husk ash (RHA), silica fume, mineral powder and fly ash were used as multi-component cementing materials, and the polyethylene (PE) fiber was modified by cellulose nanocrystal (CNC) to develop an Engineered Cementitious Composites (ECC) with high ductility and strength. The hydration heat and X-ray diffractometer (XRD) results indicate that RHA delays the early hydration of cement, its pozzolanic effect refines the internal porosity of hydration matrix and improves the compactness of ECC samples. Moreover, RHA increases the interfacial properties between fiber and cement matrix, reduces the first cracking strength and significantly improves the tensile strain rate of ECC. With the increasing content of RHA, its reinforcement effect becomes more obviously. The strain rate of ECC samples that uses RHA to replace 40 % of cement can reach 6.81 %. However, once the content of RHA is too high, the quality of cement involved in hydration will be significantly weakened, which reduces the amount of hydration products and has a negative impact on the compressive strength. By CNC coating, the active groups can be coated to the fiber surface to improve the fiber’s wettability. Which has promoted the growth of hydration products on the fiber surface, enhancing the fiber/matrix interface properties, and improved the ductility of ECC. CNC coating can also make up for the loss of compressive strength caused by RHA. The molecular dynamics simulation results show that unmodified PE fiber hardly to form a stable bond with C-S-H. However, CNC can adsorb with C-S-H through hydrogen and Ca-O bonding, and can also interaction with PE fiber by hydrogen bonding. Herein, CNC acts as an intermediate to connect PE and C-S-H, increase the interface stability of fiber/cement matrix, improve the interface bonding, and thus enhance the ductility of ECC. Developing multi-binder system and reinforced fiber/interface can significantly reduce the amount of cement used in ECC, and understanding the enhancement mechanism is beneficial to guide the optimal design of ECC.