Petrophysical and durability tests on sandstones for the evaluation of their quality as building stones using Analytical Hierarchy Process (AHP)

Due to their widespread availability, sandstones are commonly used as a natural stone for buildings, monuments and sculptures. In the current study, nine sandstone samples from the Upper Red Formation (specified by the letters A, B, C, CG, S, S1, Sh, Tr and Min) were studied from a petrophysical point of view and their durability was evaluated. Then, their suitability as building stones was assessed using an AHP model. Laboratory tests, including polarizing optical microscopy, hydric tests, ultrasound, uniaxial compressive strength, salt crystallization cycles, freeze–thaw cycles and slake durability index tests, were performed. Accelerated ageing tests caused some changes in the dry weight, P-wave velocity, slake durability index and uniaxial compressive strength, especially during salt crystallization cycles. The results from our laboratory investigations show that sandstones from the same stratigraphic layer can show major differences in their petrophysical and weathering properties. These differences result from their different diagenesis (causing varying pore space, water balance and strength properties) and also from the mineralogical composition. In the next stage of this study, an AHP model was developed to classify the qualities of sandstones according to their physical and mechanical properties, and also their resistance against weathering processes. Seven primary-level criteria, including uniaxial compressive strength, strength reduction factor (R), Initial porosity, weight loss (%) in salt crystallization test, Id15 under salt crystallization test, main grain contact type and main mineralogical composition, and 23 secondary level criteria were selected as input parameters. Results showed that the AHP model can considerably predict the suitability of building stones. Of the analysed sandstones, samples B and C are very suitable for construction purposes because of their good strength properties (high compressive and tensile strength, low softening degree) as well as their low porosity. Furthermore, samples Tr, S and S1 are very unsuitable sandstones for use in construction due to their high number of lithoclasts, high porosity and low compressive and tensile strength.