Sustainable Concrete Production Using Granodiorite, Alkali Feldspar Granite, and Mafic Metavolcanic Rock Powders as Supplementary Cementitious Materials

This study aims to explore the effect of using three distinct silicate- and aluminate-rich rock powders—granodiorite (GDP), alkali-feldspar granite (AFGP), and mafic metavolcanic (MMVP)—sourced from Egypt’s largely unexploited Eastern Desert geological resources, as supplementary cementitious materials (SCMs) in concrete production. Rock samples were processed into ultrafine powders (1.4–1.5 μm average particle size) and utilized as partial cement replacements at 3%, 6%, 9%, and 12% by weight. These rock powders were confirmed to meet ASTM C618 requirements for natural pozzolans, qualifying them as viable SCMs. Pozzolanic activity was confirmed through Strength Activity Index (SAI) testing, with values of 79%, 82%, and 76% for GDP, AFGP, and MMVP, respectively, all exceeding the 75% minimum threshold required by ASTM C618. Fresh concrete workability decreased progressively with increasing rock powder content. Mechanical testing demonstrated optimal replacement levels of 9% for GDP and AFGP, and 6% for MMVP, achieving 28-day compressive strength improvements of 14.1%, 16.0%, and 14.9%, respectively, compared to plain Portland cement concrete without any rock powder replacement (control mix). Splitting tensile strength increased by 14.7%, 12.7%, and 16.3% at optimal dosages. Microstructural analysis via SEM revealed enhanced matrix densification and reduced porosity through physical filler effects and pozzolanic reactions. Energy-dispersive X-ray spectroscopy (EDX) confirmed reduced Ca/Si ratios, indicating enhanced calcium silicate hydrate (C-S-H) gel formation with superior binding characteristics. Results demonstrate that these previously unexploited rock powders effectively function as sustainable SCMs, reducing cement consumption by up to 12%, offering significant environmental benefits through reduced CO2 emissions and efficient utilization of natural geological resources in sustainable construction practices.