Quick-setting mortars are essential for time-sensitive construction applications such as masonry repair and emergency infrastructure work, particularly in tropical climates where rapid curing is advantageous. This study addresses the dual challenges of developing environmentally sustainable construction materials while utilizing industrial byproducts and recycled aggregates. The research investigates the effect of recycled asphalt pavement (RAP) aggregate on the performance of high-calcium fly ash (HCFA)-based alkali-activated material (AAM) for quick-setting mortar applications in tropical environments. Using a full factorial design, the research examined the influence of three key factors: alkali solution ratio (AS), RAP content (RP), and curing time (CT) on the mechanical properties and environmental impact of AAM mortar with controlled flow workability. ANOVA analysis revealed that curing time exhibited the strongest influence on compressive strength (F-value = 330.26), followed by alkali solution ratio (F-value = 272.31) and RAP content (F-value = 97.09), with significant AS × RP interaction (F-value = 33.13). For bulk density, alkali solution ratio showed the dominant effect (F-value = 40.94). Increasing AS enhanced compressive strength, with optimal performance at AS values between 1.0-1.5, while RAP content showed an inverse relationship with strength development. An environmental assessment revealed RAP aggregate effectively reduced the overall carbon dioxide equivalent (CO 2 -E) in AAM production, with the lowest total CO 2 -E occurring at 75% RAP replacement. The study achieved a maximum compressive strength of 18.46 MPa at 28 days using AS of 1.5 and RP of 50%, while an environmentally optimized mix with AS of 1.0 and RP of 75% achieved 16.52 MPa strength with CO 2 -E of 516.68 kg/m³. Microstructural analysis confirmed successful geopolymerization with the formation of both N-A-S-H and C-A-S-H gel products. Based on these findings, the study recommends mix proportions of 1.0–1.5 AS and 50–75% RAP for practical applications requiring both adequate strength and environmental sustainability, with 80% RAP established as the upper limit for achieving satisfactory compressive strength. This research demonstrates that HCFA-based AAM incorporating RAP aggregate provides a viable pathway for developing quick-setting, environmentally friendly construction materials suitable for tropical climates.
Yangsukkasem et al. (Mon,) studied this question.