Exploring the potential of Eocene carbonates through petrographic, geochemical, and geotechnical analyses for their utilization as aggregates for engineering structures

A detailed geochemical, petrographic, and geotechnical investigation was conducted to explore the potential of Eocene carbonates from Pakistan’s Kohat Basin as aggregate sources. The Kohat Basin comprises extensive exposures of Eocene limestone from the Shekhan (SF) and Kohat formations (KF). The geochemical study of the investigated limestone revealed that CaO was the main component, with trace levels of SiO 2 , MgO, Fe 2 O 3 , Na 2 O, K 2 O, TiO 2 , Al 2 O 3 , MnO, and P 2 O 5 . The petrographic study revealed that calcite and bioclasts were the primary constituents of SF and KF, which were categorized as wackestone and mudstones, respectively. Geochemical and petrographic studies of SF and KF aggregates showed that neither was susceptible to alkali-aggregate reactions (AAR) and was innocuous. The coefficient of determination revealed that strength properties such as unconfined compressive and tensile strength (UCS and UTS) were directly related to calcite contents and inversely related to bioclast concentration. According to the ASTM and BS standards, the results of geochemical, petrographic, and geotechnical studies of the studied aggregates were within the acceptable range. After obtaining satisfactory results, the absolute volume method was used to develop concrete mix designs for classes A, B, C, and D. The target UCS considered were 27.6, 20.7, 13.8, and 10.3 MPa for A, B, C, and D types, respectively. After 28 days, the results showed mean UCS values of 30.4, 23.8, 18.3, and 12.3 MPa for SF and 30, 24, 17.8, and 11.6 MPa for KF, for A, B, C, and D-type concrete, respectively. As compared to the KF, SF demonstrated superior quality. In conclusion, the carbonate rocks of the Kohat basin, SF and KF, have a significant potential for usage as aggregate sources for concrete, road, railway ballast, and other infrastructure projects.