Local volcanic pozzolans from the Canary Islands as low-carbon cement substitutes: Linking microstructure, performance and CO2 reduction

Abstract

The cement industry contributes a significant share of global CO2 emissions, positioning clinker substitution as a priority pathway for decarbonization. This study evaluates local volcanic pozzolans from the Canary islands—both natural pyroclastic deposits and quarry residues—as supplementary cementitious materials. A comprehensive morphological and compositional characterization of the mortars was conducted using optical and scanning electron microscopies, energy-dispersive X-ray spectrometry, and X-ray diffraction and fluorescence analysis, as well as their mechanical testing. The pozzolans display trachytic–phonolitic–rhyolitic compositions with abundant zeolitic phases and amorphous content, meeting ASTM C618 Class N criteria. Mortars with up to 20 % cement replacement achieve compressive strengths above 25 MPa in line with UNE-EN 998-2, while flexural strength remains satisfactory. A cradle-to-gate assessment indicates that a 20 % clinker