Experimental investigations on fracture parameters of random and aligned steel fiber reinforced cementitious composites

Abstract

Experimental research was carried out to evaluate the comparative fracture performance of random steel fiber-reinforced composite (SFRC) and aligned steel fiber-reinforced composite (ASFRC). The desired direction of steel fiber in the fresh cementitious mortar was achieved by the electromagnetic field. Three-point bending tests were conducted on geometrically similar notched beam specimens. Various dimensions and steel fiber contents by volume Vf were considered to study fracture performance and investigate the size effect. The fracture parameters were analyzed by nonlinear fracture models, namely the size effect model (SEM), work of fracture method (WFM), and double-K fracture criterion (DKFC). Initial fracture energy, critical fracture toughness KIC, length of fracture process zone, and critical tip opening displacement from SEM, total fracture energy, and characteristic length from WFM was studied for SFRC and ASFRC. The initial cracking load was detected with strain gages to evaluate initial fracture toughness KICini. Unstable fracture toughness KICun from DKFC with special emphasis on size effect was obtained. The results show that the rise of specimen depth has no considerable effect on the KICun while the size effect of KICini is not significant. As the increment of Vf, both the KICini and KICun show a linear ascending trend and both of them are greater for ASFRC than those of SFRC specimens. It is found that there exists a strong correlation between the fracture toughness measured by DKFC and SEM (KIC from SEM≅KICun from DKFC). Generally, the fracture performance of ASFRC relative to that of random SFRC is improved by more than 80%.