Effect of carbonation treatment on fracture behavior of low-carbon mortar with recycled sand and recycled powder

This paper presents a systematic experimental study on the fracture behavior of low-carbon mortars with various contents of carbonated recycled sand and recycled powder (CRS and CRP). Three-point bending tests on pre -notched beams were performed to explore the load-induced fracture processes. Based on the strain and displacement fields measured using the digital image correlation technique, the evolution of the fracture process zone (FPZ) was studied qualitatively and quantitatively. Results indicated that the initial cracking toughness (KIc ini), unstable fracture toughness (KIcun) and fracture energy (Gf) of mortar reduced gradually with the increasing recycled sand (RS) content but kept relatively steady with the rising recycled powder (RP) dosage except for KIc ini. Carbonation treatment could effectively improve the KIcini of mortar with low RP content and Gf with a high proportion of RS but had limited effect on KIcun. A combination of the FPZ evolution characteristics and crack growth resistance curves suggested that the use of RS would increase microcracking in the stable crack growth stage and thus facilitate the connectivity of microcracks in the unstable fracture stage, while the use of RP mainly affected the crack initiation stage of cement paste in the mortar. The improvement of mortar fracture by CO2 treatment of RS or RP also corresponded to these stages. Regarding fracture characteristics and carbon footprint, mortars with CRS and CRP could achieve a synergy of safety and low carbon and thus can be considered as low -carbon cementitious materials compared to normal mortar.