Thermal degradation and crack analysis of self-compacting geopolymer concrete

This study explores the performance of self-compacting geopolymer concrete incorporating varying proportions of recycled concrete aggregate (RCA) when exposed to elevated temperatures. Three mixes were designed – M-0 (0% RCA), M-25 (25% RCA), and M-50 (50% RCA) – in accordance with IS 17452 and EFNARC guidelines. Specimens were subjected to heat exposure for 1, 1.5, and 2 h following the ISO 834 fire curve. The residual compressive strength, crack width, and surface crack area were evaluated to assess thermal degradation. Results indicated that compressive strength decreased by 67%–70% after 1 h and by 78%–86% after 2 h of heating. Crack width progressively increased with both RCA content and exposure duration, ranging from 0.1 to 1.2 mm. Crack area quantification using image analysis techniques showed a consistent increase in damage for higher RCA mixes, with the M-50 mix exhibiting the most severe degradation. The study demonstrates the effectiveness of image-based evaluation in damage quantification and highlights the influence of RCA on fire resistance. These findings support informed RCA usage in geopolymer concrete for fire-exposed structural elements.