Compressive Strength and Microstructural Evaluation of Geopolymers Produced from Red-Fired Ceramic Waste (RFCW)

This study investigates the compressive strength development of geopolymers produced from red-fired ceramic waste, a material that poses growing challenges in terms of waste management and environmental sustainability. The red-fired ceramic waste (RFCW) was dried, crushed, and sieved to achieve a particle size below 500 µm. Chemical and mineralogical characterizations were conducted using X-ray fluorescence (XRF) and X-ray diffraction (XRD), respectively. Based on varying proportions of NaOH and Na₂SiO₃ as alkaline activators, several geopolymer formulations were prepared and subjected to curing under both ambient conditions and at 80 °C. The results indicated that increasing the degree of geopolymerization led to a decrease in crystalline quartz and albite phases, accompanied by the formation of sodium-containing zeolite structures, particularly in oven-cured samples. These mineralogical findings were further supported by scanning electron microscopy (SEM) observations. The JE9 sample, cured at 80°C, achieved the highest compressive strength (25.29 MPa), attributed to its dense microstructure and effective particle packing. In contrast, ambient-temperature-cured specimens exhibited higher porosity and correspondingly lower strength. Most geopolymer samples surpassed the 10 MPa compressive strength threshold, aligning with the C8/10 concrete class and demonstrating potential for use in low-strength structural applications. Overall, the study underscores the feasibility of valorizing RFCW as a sustainable raw material in geopolymer technology.