Characterization of concrete containing reclaimed asphalt pavement by superpave indirect tensile test and X-ray computed tomography

Portland Cement Concrete (PCC) and concrete containing Reclaimed Asphalt Pavement (RAP) as aggregate were evaluated by the Superpave Indirect Tensile (IDT) strength test using a constant force-control and a displacement-control rate. The tensile strength computed from the maximum load at 28 days curing time from the Superpave IDT strength test as well as the elastic modulus and Poisson’s ratio of the concrete obtained at 40% of its ultimate stress were found correlated well with the convention tests. When the toughness was calculated by determining the area under the stress-strain plot up to the maximum stress, it can be used to differentiate between concretes containing different percentage of RAP. The tensile strength of concrete without RAP at early age was seen to increase as the temperature decreased. However, this effect of temperature was not seen among the concrete at later ages. In addition, the tensile strength of concrete containing RAP was seen to decrease as the percentage of RAP and temperature increased. The addition of RAP in concrete noticeably reduced the elastic modulus of the concrete but increased the toughness. It is recommended to adopt the Superpave IDT strength test using a constant displacement-control rate of 0.00075 in/sec to test concrete mixtures in tension. Furthermore, the test procedures of X-ray Computed Tomography (CT) in conjunction with the Superpave IDT were developed. An image-processing technique was established to assess the distribution of air voids and the maximum variation of air voids measured from the central area of the specimen was within ± 0.3%. The volume of air voids in the concrete was observed to increase significantly when a concrete specimen was loaded to fracture. As a concrete specimen was loaded and unloaded, air voids which were formed tended to develop in the cement paste. The path of crack propagation in concrete containing 100% RAP was found to be longer than that in concrete without RAP, as examined on virtual slices from X-ray CT scan. This explained the higher toughness in the concrete containing RAP.