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

The cement industry contributes a significant share of global CO 2 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 substitution can lower the Global Warming Potential by approximately 13.6 % per tonne of binder. The results demonstrate that valorizing local volcanic resources enables meaningful CO 2 reductions without compromising structural applicability, thus supporting cleaner production in island and volcanic contexts. • Quarry residues valorized locally, enabling circular economy in the Canaries. • LCA estimates ∼13.6 % GWP reduction per tonne of binder at 20 % replacement. • Microstructure shows glassy matrices and reactive zeolitic phases. • 20 % cement replacement meets ≥25 MPa compressive strength requirement. • Results support low-carbon mortars compliant with UNE-EN performance specs.