Sustainable prepacked alkali-activated concrete: influence of natural zeolite, recycled aggregate, and curing conditions on mechanical, durability, and thermal performance

With the increasing emphasis on sustainable materials in the construction industry, this research explores the combined influence of natural zeolite (NZ) and recycled asphalt pavement (RAP) aggregates (5-8 mm) on the mechanical properties, physical performance, and durability characteristics of prepacked geopolymer concrete (PGC).Ground blast furnace slag (GBFS) was used as the primary binder, partially replaced by NZ at levels of 0%, 10%, 20%, 30%, and 40%. Waste marble powder (WMP) was incorporated as a fine aggregate to enhance matrix densification and sustainability. The impact of curing temperature (ambient, 50 degrees C, and 80 degrees C) on compressive strength, flexural strength, dry density, sorptivity, water absorption, sulfate resistance, freeze-thaw resistance and high-temperature performance was evaluated. The results showed that increasing curing temperature significantly enhanced early-age strength. Among the NZ-containing mixtures, the 10% NZ mixture achieved the highest compressive strength, increasing by 6.1%, 11.7%, and 6.2% at ambient, 50 degrees C, and 80 degrees C, respectively, compared to the reference. The 20% NZ mixture also improved strength, with gains of 10.1%, 2.7%, and 2.2% under the same conditions. The 20% NZ mixture cured at 80 degrees C showed the least strength loss at 400 degrees C and 600 degrees C, demonstrating the positive impact of NZ incorporation and high-curing temperature on the thermal resistance of PGC. Compressive strength loss decreased with higher NZ content and curing temperature, with the 10% NZ mixture cured at 80 degrees C showing the least strength loss after sulfate exposure. NZ incorporation (10-20%), combined with elevated curing, significantly enhanced the long-term durability of geopolymer concrete against sulfate attack. The 20% NZ mixture cured at 80 degrees C had the lowest compressive strength loss (7.2%) after 25 freeze-thaw cycles, highlighting its improved durability.