Design and optimization of physical, mechanical and elevated temperature properties of one-part alkali-activated slag mortars with recycled geopolymer aggregate and micro-silica via response surface methodology

YILMAZ Y., Hatipoglu S., NAS M., BAKİ V. A., NAYIR S., ERDOĞDU Ş.

CONSTRUCTION AND BUILDING MATERIALS, cilt.541, 2026 (SCI-Expanded, Scopus)

Özet

This study investigated the effects of using recycled geopolymer aggregate (RGA) and micro-silica (MS) in onepart alkali-activated slag (OP-AAS) mortars, and the results were statistically evaluated. MS was replaced with 0-15% slag by mass, while RGA was replaced with 0-100% natural aggregate by volume. Fresh, physical and mechanical properties of the mortars were determined, as well as residual compressive strengths after exposure to 400 degrees C and 800 degrees C were also determined. In addition, the phase assemblage and microstructural properties of the binder system were investigated regarding changes caused by MS replacement and exposure to elevated temperatures. The results showed that mixtures containing 5% MS exhibited improvements in compressive and flexural strength, porosity, and capillary at all RGA ratios due to matrix densification. The mixture of 5% MS and 25% RGA yielded the highest flexural and compressive strengths, which were 1.18 and 1.52 times that of the reference mortar. Conversely, RGA ratios higher than 25% negatively affected physical and mechanical properties due to increased porosity and a weak interfacial transition zone resulting from the old binder phase. Exposure to elevated temperatures was observed to limit strength losses, particularly at 400 degrees C, due to the addition of MS and increased pore size and gel stability. However, significant strength losses were observed in all mixtures at 800 degrees C due to gel degradation and microcracking. Response Surface Methodology results showed that the developed models successfully represented water absorption, porosity, capillary, flexural and compressive strength with R2 values of 0.9832, 0.9807, 0.9833, 0.9591, and 0.9714, respectively.