Reactivity of olivine-derived amorphous silica and its potential for use as a supplementary cementitious material

Traditional supplementary cementitious materials (SCM) are declining in availability because of ongoing transitions in the energy and steel sectors. Olivine is a globally abundant mineral that can be processed to produce low-carbon amorphous silica (APS) with the potential for use as an SCM. This study aims to investigate the reactivity of olivine-derived silica during cement hydration, to optimise its use in concrete. Portland cement pastes at a 0.5 water-to-binder (w/b) ratio with up to 20 wt.% APS and up to 4 wt.% gypsum, for sulfate adjustment, were assessed. Samples were tested for pozzolanic reactivity, hydration kinetics and phase assemblage using the R 3 test, isothermal calorimetry, quantitative XRD and TGA. Mortar samples at a 0.63 w/b ratio containing up to 40 wt.% APS were produced for assessing workability and compressive strength development. The results show that APS is highly reactive. High specific surface area and a porous structure promote early sulfate depletion, workability loss and delayed hydration. The dilution effect dominates the early age hydration, resulting in low strengths compared to the control sample. However, additional gypsum can mitigate these undesirable effects by improving the degree of hydration and early age strengths. APS promotes pozzolanic reactions and strength gain over time, achieving compressive strengths ∼50 MPa at 90 days for 20 wt.% APS, which exceeds the control. • APS is a viable SCM for producing low-carbon blended cement. • The inherent characteristics of APS promote ettringite formation and its stabilization although sulfate depletion is accelerated. • Dilution effect dominated early age hydration while pozzolanic reaction prevails at later age (7days). • 20 wt.% APS content is the highest replacement rate allowing significant 28 days strength improvement.