Factors influencing the time dependence of porosity relaxation in cement during sorption: Experimental results from spatially resolved NMR

We use ${}^1$H nuclear magnetic resonance (NMR) methods to show that the relaxation time governing the redistribution of the gel-pore porosity in cement pastes during sorption depends, not surprisingly, on the dry state saturation and also, more surprisingly, on the sample size. The relaxation time is typically in the range 20 to 40 h for cylindrical samples 60 mm long dried to saturations between about 40 and 55%. It increases up to 200 h for samples dried to between 20 and 30% saturation. The times are all very much longer than for 1 mm samples. There is additional evidence to support the idea that the relaxation of hydrate inter-layer sized spaces occurs on at least two timescales, one of which is very much longer (months) than any of those listed above.