Chemical mineralogical and mechanical characterization of ombe basalt from the cameroon volcanic line as a potential supplementary cementitious material

Abstract Cement production contributes approximately 7–8% of global anthropogenic CO₂ emissions, motivating the search for supplementary cementitious materials (SCMs) capable of reducing clinker consumption. This study evaluates Ombe basalt, a volcanic rock from the Cameroon Volcanic Line, as a potential SCM for blended cement production. The raw basalt was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) coupled with external-standard amorphous-content quantification, and optical petrography. The material contained 78.83 wt% of SiO₂ + Al₂O₃ + Fe₂O₃ and an estimated amorphous phase content of approximately 40 wt%, while plagioclase (anorthite) and pyroxene (augite) constituted the dominant crystalline phases. These characteristics satisfy the chemical requirements for Class N natural pozzolans specified in ASTM C618. However, no direct pozzolanic activity tests (Strength Activity Index, Frattini, or Chapelle) were conducted; therefore, pozzolanic reactivity cannot be confirmed solely from chemical and mineralogical characteristics. Four cement formulations were investigated: an industrial reference cement containing 20 wt% pozzolana (CEM0; 75.5 wt% clinker) and three experimental blends incorporating Ombe basalt at 20 wt% (CEM1; 75.5 wt% clinker), 25 wt% (CEM2; 70.5 wt% clinker), and 30 wt% (CEM3; 65.5 wt% clinker). Standard consistency, setting time, and compressive strength were determined according to EN 196 procedures. Twenty-eight-day compressive strengths were 53.2 ± 1.1 MPa (CEM0), 50.6 ± 0.9 MPa (CEM1), 47.7 ± 1.2 MPa (CEM2), and 41.6 ± 1.3 MPa (CEM3). CEM1 and CEM2 satisfied the EN 197-1:2011 CEM II/B (42.5R) strength requirement, whereas CEM3 did not. Since CEM1 maintained the same clinker content as the reference cement, effective clinker reduction was achieved only in CEM2 and CEM3. A transparent clinker-substitution assessment indicated a gross reduction of approximately 45 kg CO₂/t cement for CEM2 relative to the industrial reference cement. This estimate excludes emissions associated with basalt processing and transport. No inferential statistical analysis was performed because of the limited number of replicates ( n = 3), and comparisons are therefore based on mean values and standard deviations. The results demonstrate that Ombe basalt can function as a partial clinker substitute at replacement levels up to 25 wt% while maintaining compliance with EN 197-1 strength requirements. Nevertheless, direct pozzolanic activity testing, long-term durability assessment, extended-age strength evaluation, life-cycle analysis, and techno-economic assessment are required before industrial implementation can be recommended.