A BROAD-LINE NUCLEAR-MAGNETIC-RESONANCE STUDY OF WATER-ABSORPTION ANDTRANSPORT IN FIBROUS CEMENT ROOFING TILES

The H-1 nuclear magnetic resonance spin-spin relaxation time of water in a fibrous cement roofing tile has been measured as a function of hy dration using the Carr-Purcell-Meiboom-Gill pulse sequence with a puls e 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, cons istent with earlier mercury intrusion porosimetry results and details of the manufacturing process. The relaxation times are constant as a f unction of hydration, suggesting that, at intermediate hydrations, som e pores fill completely while others remain empty. There is also evide nce that the smallest pores fill first. Complementary imaging studies reveal a three-layered heterogeneous structure which is consistent wit h the manufacturing process. The images show the establishment of a dy namic equilibrium water concentration gradient across the slate when o ne side is exposed to water. The mutual diffusion coefficient of water in the tile is estimated as 4 x 10(-7) cm(2) s(-1). Finally the effec ts of a water-resistant coating on water transport are shown. (C) 1998 Chapman & Hall.