Durability assessment of Arucas Ignimbrite as a natural building stone under freeze–thaw and thermal shock ageing

Arucas ignimbrite, commercially known as Lomo Tomás de León , is a volcanic building stone widely used in the Canary Islands and exported internationally. This study evaluates its durability after 60 freeze–thaw and 60 thermal shock cycles using apparent density, open porosity, water absorption, ultrasound propagation velocity, mercury intrusion porosimetry, fluorescein-impregnated thin sections, uniaxial compressive strength and colour variation. Both ageing procedures produced descriptive changes, but with different intensity and evolution. Although pairwise changes in physical properties did not reach statistical significance after Bonferroni correction, freeze–thaw ageing showed larger changes in mean open porosity (+20.5%) and water absorption (+5.8%), together with ultrasound propagation velocity reductions of up to 12.6% and compressive-strength losses of approximately 21–22%. Thermal shock produced more moderate and partly non-monotonic changes in pore-related properties, with strength losses of 8.9–18.4% and ultrasound propagation velocity reductions of up to 13.5%. Apparent density remained virtually unchanged under both treatments. Microstructural observations suggested that deterioration may have been influenced by the anisotropic flow fabric, large feldspar crystals, porous glassy matrix and pore-size distribution. The porous matrix may have partially accommodated thermally induced strains, whereas freeze–thaw ageing was associated with a more developed fracture network, consistent with opening and propagation of pre-existing discontinuities and possible formation of new microcracks. Colour changes remained moderate and were mainly related to surface lightness. Overall, the results show greater susceptibility to freeze–thaw ageing and support durability assessment of volcanic-stone building elements.