In situ characterization of early-age hydration process of recycled powder blended cement paste using low-field NMR.

The relaxation signal intensity and transverse relaxation time of Portland cement pastes with different dosages of recycled powder at different ages were measured by low-field nuclear magnetic resonance (NMR) technology. Combined with scanning electron microscopy (SEM), the effect of recycled powder on early-age hydration and microstructure of Portland cement was studied. The results show that the hydration process of composite slurry can be divided into four stages, namely, induction period, acceleration period, attenuation period and stable period. As the hydration progressed, the T2 distribution of evaporable water in the composite slurry shifted to short relaxation time, indicating the pores were filled by hydration productions and pore diameter was getting smaller. Recycled powder has high water-adsorption capacity and water slowly-release function, which will lead to the formation of interfacial transition zone (ITZ) and compromise the mechanical property. The transverse relaxation time T2 of samples with higher recycled powder content always maintains obvious bimodal distribution during hydration. [ABSTRACT FROM AUTHOR]