Study on fracture parameters and fracture process zone of manufactured-sand recycled aggregate concrete

This paper studied the fracture parameters and fracture process zone (FPZ) of manufactured-sand recycled aggregate concrete (MSRAC) with different replacement rates of recycled coarse aggregate (RCA) by three-point bending test on single-edge notched beams. A threshold crack identification method (TCIM) was proposed to locate the crack tip and identify FPZ. Combined with TCIM and digital image correlation (DIC) technology, the fracture mechanism of MSRAC was investigated and the FPZ evolutions of MSRAC and manufactured-sand normal aggregate concrete (MSNAC) were comparatively analyzed. The results indicated that the crack tip and FPZ could be well identified by TCIM and it had good stability. The initial fracture toughness of MSRAC was not obviously different from that of MSNAC, while the unstable fracture toughness and fracture energy of MSRAC were significantly reduced. The brittleness of MSRAC increased with the RCA replacement rates. According to the difference of fracture behaviors between MSRAC and MSNAC, the FPZ evolutions of MSRAC were divided into three stages, including FPZ stable development, FPZ unstable development, and FPZ retraction development. The FPZ length increased with the RCA replacement rates while the FPZ width and FPZ area were opposite. The RCA reduced the aggregation interlocking effect of MSRAC, resulting in a faster crack growth rate and fewer secondary cracks and damage behaviors of MSRAC than MSNAC.