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 thecurrent 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 wasassessed using an AHP model. Laboratory tests, including polarizing optical microscopy, hydric tests, ultrasound, uniaxial compressivestrength, salt crystallization cycles, freeze–thaw cycles and slake durability index tests, were performed. Accelerated ageing testscaused some changes in the dry weight, P-wave velocity, slake durability index and uniaxial compressive strength, especially duringsalt crystallization cycles. The results from our laboratory investigations show that sandstones from the same stratigraphic layer canshow 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 ofthis 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, strengthreduction factor (R), Initial porosity, weight loss (%) in salt crystallization test, Id15 under salt crystallization test, main grain contacttype and main mineralogical composition, and 23 secondary level criteria were selected as input parameters. Results showed that theAHP model can considerably predict the suitability of building stones. Of the analysed sandstones, samples B and C are very suitablefor construction purposes because of their good strength properties (high compressive and tensile strength, low softening degree) aswell as their low porosity. Furthermore, samples Tr, S and S1 are very unsuitable sandstones for use in construction due to their highnumber of lithoclasts, high porosity and low compressive and tensile strength.