Lithof acies and petrophysical properties of Portland Base Bed and Portland Whit Bed limestone as related to durability

摘要

This study focuses on the differences in lithofacies and petrophysical properties of Base Bed and Whit Bed Portland limestone and the presumed relationships between these characteristics and the durability of this building stone. As Portland limestone probably will be used as a stone for several restoration projects in the Netherlands in the near future, it is of great importance to know the weathering behaviour, especially its resistance against freeze/thaw decay. Samples of Portland limestone were analyzed by means of thin section microscopy, X-Ray fluorescence spectroscopy, and measurements of petrophysical properties such as watersaturation, porosity, permeability and specific surface area. Distribution of pore throat diameters were analyzed by mercury porosimetry. Results of a freeze/thaw test performed on Whit Bed limestone were also taken in account. The Whit Bed consists of a medium grained, fine to coarse bioclastic oolitic limestone (oobiosparite; oolitic grainstone). Generally the fabric is grain supported showing a large amount of open inter-particle pores. High effective porosity combined with high permeability (1000 - 1400 milliDarcy), predominantly reflect the open interparticle porosity. The Base Bed is also a coarse bioclastic oolitic grainstone, but the oolitic fabric shows a tighter, matrix-rich compacted texture. Samples from the Base Bed show differences in primary matrix contents compared to the Whit Bed and differences in diagenesis, resulting in different physical properties. For example, a lower effective porosity (15.11 - 15.99 vol.%) and a lower permeability (35.0 - 80.1 milliDarcy). It is concluded that a thorough study of lithofacies (especially microfacies) and analysis of microporosity reveal basic data for selecting the most durable type of limestone. In this particular case, using only samples from one quarry, the Whit Bed samples are thought to be the most durable ones.