Modeling high-temperature strength evolution in nanosilica-modified geopolymers using a nondimensional framework

Abstract For geopolymers to be used reliably in high-temperature, fire-resistant applications, it is crucial to understand how strength changes with increasing temperature. A nonmonotonic thermal response, characterized by an initial gain in compressive strength at moderate temperatures followed by progressive degradation at higher temperatures, is commonly reported in experimental research. Nevertheless, a cohesive and physically comprehensible mathematical framework seldom addresses this two-stage phenomenon. At the same time, mechanical strength values acquired in controlled laboratory settings are frequently used to assess the engineering performance of cementitious binder systems. Although these conditions offer repeatable standards, they are idealized settings that stifle the environmental interactions that determine long-term durability. As a result, performance obtained in laboratory settings may not accurately reflect behavior in actual service conditions, leading to a conceptual inconsistency known as the field-relevance gap. This study proposes a nondimensional framework based on differential equations to explain the evolution of high-temperature strength in nanosilica-modified geopolymers and to offer a durability-focused interpretation of laboratory results. According to experimental compressive strength data collected at ambient temperature and at 300 °C, 600 °C, and 900 °C, the thermal response is characterized as a two-stage process: thermal preconditioning followed by degradation. The initial strength augmentation is integrated via a temperature-dependent starting strength, whereas high-temperature degradation is characterized by a first-order kinetic degradation model. Nondimensionalization condenses the interrelated effects of temperature and nanosilica content into a concise set of governing parameters, facilitating uniform comparison across various geopolymer systems. Model parameters are adjusted by nonlinear regression, and prediction efficacy is assessed using statistical metrics. A nondimensional sensitivity analysis is conducted to assess the relative impact of temperature and nanosilica content on strength development. The results indicate that the suggested framework effectively captures both the initial strength improvement and the following deterioration behavior. The study not only offers predictive capabilities but also establishes a conceptual link between laboratory-defined strength evolution and performance under service conditions by situating model results inside durability-related mechanisms. The suggested method provides a physically interpretable and generalizable instrument for assessing geopolymer performance at high temperatures, facilitating durability-informed material design and engineering evaluation.