The fast industrialization, infrastructural development, and urbanization that have made building materials like coarse and fine aggregate the preferred material for humans and contributed to the depletion of natural resources are to be regretted. A sustainable ecosystem, on the other hand, aims to limit the use of natural resources (fine and coarse aggregate in materials) and replace them with readily accessible extensive waste. One option is to use alternative by-products or raw materials in place of pumice stone (PS) as a coarse aggregate in concrete. To analyze the strength parameters such as flexural strength (FS), split tensile strength (STS), and compressive strength (CS), this study seeks to replace the natural material (coarse aggregate) as a waste (PS) replacement. In addition, the experimental design, model optimization, and validation processes are carried out using the Response Surface Methodology (RSM) tool in the Design Expert program. At 0%, 10%, 20%, 30%, 40%, 50%, 75%, and 100%, the PS varied, and the curing times were 7 days, 28 days, and 56 days. According to the experimental findings, increasing the PS percentage causes a drop in the strength characteristics while maintaining the curing days. Up to 30% of PS may be substituted in lightweight aggregate (LA) for all curing days, resulting in the desired and expected limits of CS, STS, and FS. The CS was determined to be 20 MPa with an STS of 1.88 MPa, or 9.38% of the CS, after 56 days of curing and 30% replacement. Additionally, this study supports the idea that PS replacement in LA concrete may be utilized for structural purposes up to a 30% replacement, but that it can also be used for non-structural purposes beyond that. ANOVA and model fitness were developed using the proposed quadratic model, and the coefficient of determination (R2) for all three outcomes was above 0.99 (99%), indicating the model's high significance.