Effects of drying and freeze/thaw cycling probed by H-1-NMR

H-1-NMR spin lattice relaxation times, T-1, of water occupying the pore system in white hydrated cement pastes have been measured to probe the effect of drying and freeze/thaw cycling on the pore structure. Surface to volume ratios and specific surface areas are derived from these NMR measurements. Specific surface areas vary from 132 m(2)/g for w/c = 0.30 to 242 m(2)/g for w/c = 0.70. A significant increase in T-1 is observed after drying tests performed at 105 degrees C on pastes with w/c-ratios 0.30, 0.40, 0.60 and 0.70 corresponding to a reduction in specific surface area of 33.0, 25.0, 7.1 and 6.5%, respectively. Line width measurements showed significant reduction only for the w/c = 0.30 sample. The results are in agreement with earlier work and imply that the pore structures related to micro and meso pores are more vulnerable to drying than the coarser pore structures. Freeze/thaw cycling show no significant changes in T-1 after 25 cycles although all samples except one are fragmented by frost action. However, a small increase is observed after 175 cycles for samples with the lower w/c-ratios. (C) 1997 Elsevier Science Ltd.