Abstract

Hybrid alkali-activated cementitious systems incorporating ordinary Portland cement (OPC), slag and alkaline activators enhance sustainability and performance. Several standardized alkali-silica reactivity (ASR) testing protocols, such as ASTM C1260, are available. The applied temperature is one of the main dominating factors that vary from one testing protocol to another. Hence, this study aims to evaluate the ASR for hybrid systems applying various temperatures and durations, while comparing with OPC and alkali-activated slag systems. The Experimental program was designed using the Taguchi method to explore the effect of three main factors on ASR-induced expansion, namely, slag content, activator dosage, and curing temperatures (60 °C, 80 °C, and 130 °C). Nine mixtures were cast and tested for expansion, compressive strength, UPV, TGA, XRD, and SEM to assess hydration, phase development, and microstructural changes. Results indicate that 60 °C reliably detects ASR-related expansion while minimizing confounding thermal effects observed at higher temperatures (e.g., 130 °C). Samples with 100% slag and 10% activator cured at 60 °C exhibited high compressive strength (49 MPa) and minimal expansion (–0.12%), indicating stable hydration products under this condition. In contrast, samples exposed to 130 °C experienced severe expansion and degradation due to accelerated hydration and the formation of expansive ASR gel. The findings suggest that 60 °C is suitable for evaluating ASR susceptibility in alkali-activated and hybrid systems, providing a more accurate method for assessing their durability without introducing thermal artifacts.