Numerical and experimental assessment of thermally exposed textile-reinforced alkali-activated concrete with altered impregnated interphases

Limited thermal resistance and poor chemical compatibility between polymer-bound multi-filament reinforcements and cementitious matrices present significant challenges during upgrading, retrofitting, and constructing structures. For this purpose, the study at hand assesses the use of mineral-impregnated carbon fibers (MCFs) as an innovative reinforcement technology. Direct tensile tests combined with finite element modeling based on the concrete damage plasticity (CDP) constitutive law were employed to unveil the thermomechanical behavior and cracking evolution of textile reinforced alkali-activated concrete composites with altered impregnation matrices and thermal exposure ranging up to 200 °C. To evaluate load bearing capacity against elevated temperatures, results were compared to both a control set (room temperature, 20 °C) and epoxy-impregnated commercial roving. Tensile stress–strain curves exhibited a bi-linear response, characterized by an initial elastic phase, followed by a pseudo-linear stage dominated by matrix cracking and textile load-bearing, consistent with the numerical results. Image analysis using the digital image correlation method and micro-computed tomography ($\mu$CT) demonstrated better crack control and failure behavior at the micro-scale for MCF composites. The application of geopolymer (GP) impregnation indeed achieved enhanced temperature resistance and improved chemical compatibility, promoting the formation of finely distributed crack patterns with reduced crack widths.