Hydration of Early-Age Composite Cement Paste Using Low-Field Nuclear Magnetic Resonance

Low-field nuclear magnetic resonance is adopted in this paper for the study of the hydration process of early-age pure and composite cement paste by monitoring the longitudinal relaxation time (T1) of water constrained in the paste. Based on the correlation between the changes of weighted average T1 and the hydration process of paste, the hydration process can be divided into four stages, i.e., initial period, dormant period, accelerated period, and steady period. The effect of water-to-cement ratio (w/c) and admixtures to hydration is discussed in detail. Compared to WC04, the weighted average T1 at the end of the dormant period increased by 4.79, 1.74, and 0.05 ms when 30% fly ash, 30% slag, and 10% silica fume were added, respectively. Based on experimental data and the Avrami-Erofeev equation, a hydration model for both pure and composite cement pastes is proposed, with a correlation that is higher than 0.96, which can describe the hydration process of paste well.