A broad-line nuclear magnetic resonance study of water absorption and transport in fibrous cement roofing tiles

Abstract

The 1H nuclear magnetic resonance spin–spin relaxation time of water in a fibrous cement roofing tile has been measured as a function of hydration using the Carr–Purcell–Meiboom–Gill pulse sequence with a pulse gap sufficiently short to negate most of the attenuation effects of water diffusion in the pore space magnetic susceptibility gradients of the tile. The data reveal pores with three characteristic sizes, consistent with earlier mercury intrusion porosimetry results and details of the manufacturing process. The relaxation times are constant as a function of hydration, suggesting that, at intermediate hydrations, some pores fill completely while others remain empty. There is also evidence that the smallest pores fill first. Complementary imaging studies reveal a three-layered heterogeneous structure which is consistent with the manufacturing process. The images show the establishment of a dynamic equilibrium water concentration gradient across the slate when one side is exposed to water. The mutual diffusion coefficient of water in the tile is estimated as 4×10-7 cm2 s-1. Finally the effects of a water-resistant coating on water transport are shown. © 1998 Chapman & Hall