Study on the Influence of Curing Regime on the Microstructural and Mechanical Properties of Alkali-Activated Concrete with Coarse Recycled Aggregates

This study investigates the influence of curing regimes on the microstructure and mechanical properties of alkali-activated concrete (AAC) containing coarse recycled aggregates (CRA) for structural applications. Building on prior research at BITS, Pilani Hyderabad Campus, AAC specimens were prepared by replacing natural aggregates (NA) with processed and unprocessed CRAs. Class F fly ash and ground granulated blast furnace slag (GGBFS) served as precursors, activated by sodium hydroxide and sodium silicate solutions. A consistent mix design employed a 4% sodium concentration and 60:40 fly ash-to-slag ratio. The target compressive strength was 40 MPa for structural use. Curing conditions are known to affect various AAC properties, including early and long-term strength, hydration kinetics, durability, and dimensional stability. While prior research explored these aspects under different curing regimes, the influence on microstructure development in AACs with high CRA content remains under-reported, especially considering curing regime variations. This research addresses this gap by employing three distinct curing regimes: ambient temperature (30°C) for 28 days, ambient temperature with plastic wrap for 28 days, and oven curing at 75°C for 72 hours followed by 25 days at 30°C. Microstructural investigations using XRD, FESEM, and stereo microscopy were complemented by ultrasonic pulse velocity and compressive strength tests. Notably, specimens subjected to oven curing at 75°C exhibited superior performance compared to those cured at ambient temperature with or without plastic wrapping