Flexural Toughness Evolution of Modified Secondary Recycled Concrete

Abstract

In this paper, secondary recycled concrete was modified using basalt fiber (BF) and nanosilica (NS) to form modified secondary recycled concrete (MSRC), to promote the recycling of concrete. The flexural toughness and influence of pore size distribution of the MSRC were analyzed through the four-point flexural mechanics test and nuclear magnetic resonance test, respectively. The results showed that with an increase in the content of BF and NS, the fracture of the coarse aggregate increased and the flexural strength of MSRC increases. According to different evaluation standards, the flexural toughness of the MSRC exhibited a similar trend in different evaluation standards. As the NS content increased, the equivalent flexural strength increased, and as the BF content increased from 2 to 4 kg·m−3, the equivalent flexural strength decreased. Additionally, scanning electron microscope and nuclear magnetic resonance spectroscopy showed that NS and BF had significant influence on the pore structure of the MSRC. When the BF content was 2 kg·m−3, the content of micropores was minimal; and with further increase in BF content, the content of micropores increased, the internal defects increased, and the flexural toughness decreased. Moreover, with the increase in NS content, the content of internal pores decreased and the flexural toughness increased. Therefore, the results showed that BF and NS had a significant toughening effect on the MSRC.