Efforts to reduce global carbon emissions have intensified, leading to the exploration of alternatives to ordinary Portland cement (OPC). Limestone Calcined Clay Cement (LC3) has emerged as a promising candidate. This study was centered on the development of LC3 through the activation of low-grade kaolinite clay by acid. The low kaolinite clay was initially calcined at 800 ℃ for 2 h. Afterward, LC3 was prepared by reducing OPC by 25% (LC3-25). Then LC3 mortar was prepared and oxalic acid was introduced in powder and liquid forms, as an admixture, with varying molar concentrations (1M and 2M). In contrast, calcined clay was chemically activated with an oxalic acid solution, after which LC3 mortar was developed. For comparison, control specimens of OPC mortar were also prepared. All types of specimens were tested under compression on 7 and 28 days. The findings revealed that LC3 holds significant potential as a viable alternative to OPC. Furthermore, the thermo-chemical activation of clay, facilitated by the oxalic acid treatment showed 9% more strength than OPC at 7 days and almost similar strength at 28 days with a difference of only 3%.