Effect of Nano-TiO2 on Capillary Water Absorption of Recycled Aggregate Concrete

Abstract

To improve the durability performance of recycled aggregate concrete in actual use, this paper uses nano-TiO2-modified recycled coarse aggregate to study, through experiments, the effects of nano-TiO2 on the pore distribution of recycled coarse aggregate concrete after freeze–thaw. The capillary-water-absorption law was used as the evaluation index. The recycled coarse aggregate concrete was prepared with different contents of nano-TiO2, and changes in the 24 h capillary water absorption and porosity of the recycled aggregate concrete after freeze–thaw cycles were analysed. With the help of high-resolution image recognition and binary-image-processing technology, the pore distribution of the recycled aggregate concrete before and after freeze–thaw cycles was obtained. Through the analysis of the water-absorption data at different times, the initial capillary-water-absorption rate, S1, is obtained. The capillary water absorption of recycled aggregate concrete is reacted with S1, and the initial capillary-water-absorption prediction model of nano-TiO2 recycled aggregate concrete under freeze–thaw cycles is established. The results show that under the action of freeze–thaw cycles, the capillary water absorption of recycled coarse aggregate concrete increases with the increase in the RCA substitution rate and decreases with the increase in nano-TiO2 content. After 150 freeze–thaw cycles, the cumulative water absorption and porosity of RC25-NT1.2 decreased by 25.52% and 14.57%, respectively, compared with the test block without nanomaterials. It was found that nano-TiO2 has a prominent role in modifying recycled aggregate concrete. Nano-TiO2 can reduce the cumulative water absorption and porosity of recycled aggregate concrete and alleviate the negative impact of the recycled coarse aggregate on capillary water absorption of concrete after freeze–thaw cycles. It was observed by scanning electron microscopy that a large amount of C–S–H gel was produced inside the concrete mixed with nano-TiO2, which bonded the internal pores and cracks to form a dense structure.