A Geostatistical Investigation into Changing Permeability of Sandstones During Weathering Simulations

The ability to predict the behavior of masonry materials is crucial to conserve building stone. Natural stone, such as sandstone, is not immune from the processes of weathering in the built environment and suffers from decay by granular disintegration, contour scaling, and multiple flaking. Spatial variation of rock properties is a major contributing factor to inconsistent responses to weathering. This has implications for moisture movement and salt input and output and storage, and results in unpredictability in the decay dynamics of masonry materials. This article explores the use of variography and kriging to investigate the spatial interactions between the trigger factors of stone decay, in particular, permeability and its effect on salt penetration. Sandstone blocks were used to represent fresh building stones from a weathering perspective and gave baseline characteristics for the interpretation of subsequent deterioration and decay pathways. Simulated weathering trials involved preloading a sandstone block with salt and subjecting a separate block to 20 cycles of a weathering trial designed to simulate a temperate weathering regime. Geostatistical analysis indicated differences in the spatial variation of permeability of the fresh rock and that subjected to the weathering regimes. Spatial prediction and visualization showed differences in the spatial continuity of permeability in a horizontal and vertical direction through the preloaded block after salt weathering. Continual wetting with salt and alternate heating increased permeability in a vertical direction, enabling the ingress and movement of salt and moisture more effectively through the stone.