Characteristics of Concrete Utilizing CBA and RAPA as Total Replacement of Conventional Aggregate

Efforts to mitigate global carbon emissions require addressing the environmental impact associated with natural aggregate production. Despite the availability of Coal Bottom Ash (CBA) and Reclaimed Asphalt Pavement Aggregate (RAPA), with properties similar to natural aggregates, they mostly end up in landfills. This study contributes to sustainable construction, waste management, and resource preservation by evaluating the characteristics of concrete incorporating CBA and RAPA as complete replacements for fine and coarse aggregate in pavement construction. The results showed that CBA and RAPA concrete exceeded the predicted flexural strength at all ages, reaching 110% strength in 28 days. However, the compressive and splitting tensile strengths exhibited lower values, reaching only 53% and 66% of the predicted strength, respectively, at 28 days. This reduction was attributed to the large size, large pores and fewer hydration products at the interfacial transition zone due to the old asphalt surrounding the RAPAs, as well as weak agglomerated aggregates in the mix. Additionally, the drying shrinkage and air void parameters remained within acceptable ranges, suggesting favorable durability. While this concrete meets the recommended design criteria based on 28-day flexural strength, its low compressive strength may pose challenges in scenarios with compressive stress failures, such as concrete blow-ups.