Experimental study on mechanical properties and durability of grafted nano-SiO2 modified rice straw fiber reinforced concrete

As a green building material, plant fiber has been applied to replace traditional fiber in concrete in the past years. In this paper, the rice straw fiber was pretreated by NaOH and grafted with Nano-SiO2. The modified rice straw fiber reinforced concrete (RSFRC) was prepared. The mechanical properties of grafted Nano-SiO2 modified RSFRC were tested, and GA-BP neural network model was established to predict the compressive strength of RSFRC. The dry and wet cycles were carried out to investigate the durability of RSFRC. The SEM and TG-DTA tests were adopted to analyze the interfacial transition zone. The results showed that grafted Nano-SiO2 can improve the mechanical properties of RSFRC. With 3% Nano-SiO2 concentration used on concrete with 2% rice straw fiber, the 28-day compressive strength increased by 28.6%, and flexural strength increased by 27.9% compared with ordinary RSFRC. On the other side, compared to the ordinary RSFRC, the compressive strengths of grafted Nano-SiO2 modified RSFRC were increased by 8.3%, 20.7%, 40.1% with 1%, 2%, and 3% of fiber added after 90 dry-to-wet cycles. From the microstructure of RSFRC, it was found that the content of Ca(OH)2 was reduced, and CSH gel was tightly wrapped in the interfacial transition zone due to the grafted Nano-SiO2 modification. This research could promote the application of plant rice straw fiber in civil engineering.