Mechanical properties of concrete pavements produced with modified recycled asphalt aggregate

In today's construction industry, the use of sustainable materials and recycling practices is becoming increasingly important. In particular, recycling asphalt pavement waste and using it again as a construction material offers environmental and economic advantages. In this context, using recycled asphalt pavement (RAP) aggregates in concrete production is a notable solution for reducing the consumption of natural aggregates and contributing to waste management. However, the bitumen layer on the surface of RAP aggregates prevents sufficient adhesion with the cement paste. This leads to the formation of weak interfacial transition zone (ITZ) at the aggregate-cement interface, which negatively affects the concrete's mechanical performance. This significantly limits the use of RAP aggregates in concrete production. This thesis study aimed to overcome this problem by coating the surface of RAP aggregates with cement paste in multiple layers using the cold bonding technique. Three different concrete mixes were designed for the experimental study, with a water/cement ratio of 0.45 and cement dosages of 350, 425 and 500 kg/m³. Both uncoated RAP aggregates and RAP aggregates with three different coating thicknesses were used at a ratio of 100% in the concrete mixes. The target slump range for the concrete mixtures was 20–40 mm, and superplasticiser admixtures were added to the mixtures in varying proportions to achieve this consistency. The mechanical properties of concrete specimens containing raw and coated RAP aggregates were determined by performing compressive, flexural and splitting tensile strength tests. Additionally, XRD (X-ray diffraction) and SEM (scanning electron microscopy) analyses were conducted to evaluate the microstructural properties of the concrete specimens. The results showed that using coated RAP aggregates increased the compressive, flexural and splitting tensile strengths of the concrete by around 42%, 29% and 25% respectively. Furthermore, XRD and SEM analyses revealed that coated RAP aggregates improved the microstructural properties of concrete by increasing the crystalline phase ratio, forming a dense and cohesive ITZ, and reducing crack formation.