Investigation of particle characteristics and enhancing the pozzolanic activity of diatomite by grinding

Highlights: • Effect of grinding on the pozzolanic activity of diatomite was investigated. • The decline in particle size raised the soluble fraction and pozzolanicity of diatomite. • Grinding was effective in particle size reduction with low energy consumption. • Portlandite content was monitored by XRD-Rietveld refinement in calcium hydroxide-diatomite pastes. • Pozzolanic activity was assessed by physical, chemical and mechanical tests. This study aimed to assess the influence of grinding on improving the pozzolanic activity of a low porosity diatomite. To that end, three diatomites were produced, with 50% passing particle sizes (D₅₀) between 7 and 40 μm, and characterized based on oxide composition, loss on ignition, X-ray diffraction (XRD), particle size distribution, and gas adsorption (specific surface area and porosity). Pozzolanic activity was assessed by electrical conductivity, modified Chapelle test, mechanical testing of lime-based mortar at 7 days, and performance index with Portland cement at 28 days. Additionally, portlandite (CH) consumption by diatomite was monitored up to 91 days of hydration by XRD-Rietveld refinement measurements in CH-diatomite pastes combined with controlled calcination at 900 °C. The grinding procedure ensured effective particle size reduction and produced an ultrafine diatomite (D₅₀ below 10 μm) with low energy consumption. The decline in particle size caused an increase in the specific surface area (SSA) of diatomite without significantly changing pore volume and size. The larger SSA raised the silica solubility and pozzolanic activity of diatomite, altering its classification in terms of pozzolanicity. As evidenced by hydration analysis, the increased reactivity and change in pozzolanicity was due to the rise in CH consumption as the SSA of the diatomite increased.