HYDRATION AND PORE STRUCTURE EVOLUTION OF WHITE CEMENT PASTE AT EARLY AGE BASED ON ¹H LOW-FIELD NUCLEAR MAGNETIC RESONANCE

In order to investigate the hydration and pore structure evolution of wet white cement paste at early age, the transverse relaxation time (T₂) spectrum signals of wet white cement paste were tested by¹H low-field nuclear magnetic resonance (NMR). The effects of water to cement (W/C) ratio on the T₂ spectrum, T₂ geometric average values, hydration degree and pore structure of the cement paste samples hydrated within 168 h were studied. The results show that the T₂ can characterize the hydration process and pore structure of wet white cement paste. With the increase of hydration time, the T₂ peak area and T₂ geometric average values decrease gradually. The hydration degree of cement increases rapidly within the first 24 h, and then slows down gradually after 24 h. For the cement pastes hydrated from 0 h to 7 h, most of the evaporable water is filled in the capillary pores in the range of 10 nm ~1000 nm. With the continuous hydration of cement, the water in these pores is consumed and the peak pore radius decreases constantly. The increase of W/C ratio can improve the hydration degree, but results an increase in the porosity and the proportions of larger pores.