Effect of carbonation curing time during early age on mechanical and microstructural properties of cement-based materials incorporating superabsorbent polymers

This study investigated the effects of varying early-age carbonation curing time and curing regimes on the compressive strength and carbonation depth of mortars incorporating different superabsorbent polymers (SAP) dosages. The comprehensive characterization was conducted using thermogravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray computed tomography (X-CT) to evaluate the pore structure and its distribution, as well as the content and morphology of hydration products. The results indicate that the combined curing regime of early-age carbonation curing followed by standard curing is particularly effective for mortars incorporating SAPs, with the compressive strength reaching more than 92 % of that of the reference group.The incorporation of SAPs increased the carbonation depth of mortar, and the longer the early-age carbonation duration, the greater the carbonation depth. With the increase in SAPs dosage, the calcium carbonate content gradually increased; however, when the early carbonation duration was extended from 3 d to 14 d, the calcium carbonate content first increased and then decreased. At different curing regimes, the addition of SAPs did not alter the types of hydration products, which were mainly calcium carbonate, calcium hydroxide, and tricalcium silicate. The addition of SAP increased the porosity of the mortar. After carbonation curing, the mortar matrix becomes denser and the contrast between the three phases decreases. The content of large pores decreases, the number of small pores increases, and the pore shape index decreases.