Use of reclaimed asphalt pavement as aggregate substitute in alkali activated concrete

• Use of Reclaimed Asphalt Pavement with alkali activated concrete was investigated • RAP material inclusion increased the workability of the concrete • Compressive strength of the concrete samples was negatively affected by RAP inclusion. • 50% RAP substitution of coarse aggregate resulted in 28-day strength exceeding 35 MPa. • No correlation between the age of the RAP material and the compressive strength was observed. Reclaimed Asphalt Pavement (RAP) is a form of waste aggregate material obtained from highway resurfacing operations that has limited uses and is often left in storage sites for many years. This research investigated the use of RAP material as a recycled aggregate in alkali activated concrete to reduce reliance on primary aggregate sources, and suggests a possible recycling route. RAP aggregate of different ages, i.e., fresh, 5-year-old and 10-year-old, was used to substitute natural coarse aggregate at rates of 0%, 50% and 100% for the manufacture of alkali activated concrete cubes with nominal compressive strength > 40 MPa. Results showed that RAP material increased the workability of concrete according to the substitution percentage. Slumps up to 10 times higher than the benchmark were recorded when 100% of coarse material was substituted with RAP. However, the compressive strength of concrete was in general negatively affected by RAP inclusion. A reduction of compressive strength in the range 29% to 67% at 28 days compared against reference sample was observed, and the strength decrease seemed correlated with the RAP substitution rate. Nonetheless, 50% RAP substitution of coarse aggregate resulted in 28-day strength exceeding 35 MPa, i.e. structural grade concrete. No correlation between the age of the RAP material and the compressive strength of the specimens was observed. This study describes for the first time the effects of combining alkali activated binders with RAP aggregate of different ages, providing an important reference for local authorities and contractors dealing with legacy RAP stockpiles.