Tensile fracture behavior and notch-insensitive mechanism of Strain-Hardening Cementitious Composites (SHCC) with recycled fine aggregates

Enhancing the material sustainability and understanding the tensile fracture behavior of Ultra-High-Toughness Cementitious Composites (UHTCC) are of great significance for large-scale structural applications. In this study, we designed and developed green UHTCC incorporating recycled fine aggregates (RA) with the maximum particle sizes of 1.18, 2.36, and 4.75 mm. A comprehensive investigation of compressive strength, microstructures, and notched/unnotched tensile performance was conducted. Compared to silica sand UHTCC (SS-UHTCC), the compressive strength of RA-UHTCC decreased by 10.2 % and 12.2 % using 1.18- and 2.36-mm RA, respectively, due to weaker interfacial transition zones (ITZ), while UHTCC with 4.75-mm RA exhibited a slight increase in strength due to fewer ITZ. Unnotched tensile performance of RA-UHTCC showed slight reductions in tensile strength and ductility with increasing RA size, but all the RA-UHTCC maintained multiple cracking behavior. For notched tensile performance, the nominal tensile strength of RA-UHTCC was close to or slightly higher than their unnotched counterparts, with notch strength ratios (NSR) between 1.01 and 1.11. All the notched RA-UHTCC demonstrated multiple cracking, particularly in the notched regions, and the tensile ductility decreased with increasing notch length. Overall, UHTCC using 1.18- and 2.36-mm RA exhibited mechanical properties comparable to SS-UHTCC. All the RA-UHTCC displayed notch insensitivity and the NSR was higher than those of ordinary cementitious materials, alumina ceramic, and Poly (ethyl methacrylate) (PMMA) glass, and the mechanism behind it was also revealed.