Thermal Effects on the Engineering Properties of Ashaka Limestone: A Pilot Investigation for Mining and Geotechnical Applications

Limestone exposed to elevated temperatures undergoes progressive thermo-mechanical degradation that compromises its engineering performance in mining, construction, and industrial applications. This pilot study examines the thermal response of Ashaka limestone, a commercially significant carbonate formation in northeastern Nigeria, across temperatures ranging from 25°C to 800°C. Fifteen cylindrical core samples (n = 3 per temperature condition) were subjected to controlled thermal treatment followed by comprehensive laboratory characterization. Measured parameters included uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), point load index (Is(50)), ultrasonic pulse velocity (UPV), porosity, and mineralogical composition via X-ray diffraction (XRD). Results demonstrate temperature-dependent degradation with critical thresholds at approximately 400°C and 600°C. UCS decreased from 82.3 MPa at ambient conditions to 26.4 MPa at 800°C (68% reduction), while BTS declined from 8.7 MPa to 2.4 MPa (72% reduction). UPV decreased from 5.82 km/s to 2.90 km/s, correlating with porosity increases from 3.2% to 18.7%. XRD analysis confirmed calcite decarbonation initiating near 600°C with progressive conversion to lime (CaO). These findings provide essential data for fire safety protocols in limestone mines, optimization of thermal processing parameters, and stability assessments for thermally exposed rock structures.