Development of Sustainable Asphalt Mixtures Incorporating Recycled Carbonated Aggregates

The aim of this proposal is to develop high-performing sustainable asphalt mixtures using locally recycled concrete aggregate (RCA). The proposal includes several innovative aspects such as improving RCA properties through carbonation techniques, using asphalt mixtures as CO2 sink within the road systems, and the design of long-lasting, low-energy asphalt mixtures. Currently, the State of Qatar imports all aggregates used in pavement construction from countries in the region. The partial replacement of virgin, imported aggregate with RCA would bring significant economic and environmental benefits. Upcycling concrete waste into a value-added material would reduce the consumption of natural resources and energy, and at the same time will effectively transform roads into carbon sinks. The major technical challenge in using RCA comes from the cementitious mortar adhered to the aggregates, which has a higher porosity and is weaker compared to natural aggregates (NA). Therefore, the RCA material will be subjected to different quality improvement methods (including carbonation, microwave heating, and grinding) to decrease its porosity and increase its density. The main innovative aspect of this proposal is the investigation of the influence of the carbonation technique on the structural strength of the adhered mortar and aggregate. The most promising RCA materials obtained from the different improving methods will be further used in asphalt mix design in different proportions. The asphalt mixtures will be designed in such a way that they meet all the volumetric and performance requirements of Qatar Construction Specifications (QCS). The main focus of this project will be to study the interface between the adhered mortar of RCA and asphalt using various advanced testing tools: scanning electron microscope (SEM) to observe the microstructure, energy dispersive spectroscopy (SEM-EDS) to analyze the chemical composition, nanoindentation to measure the viscoelastic properties. During the carbonation process, the cement mortar in RCA will effectively become CaCO3 (limestone) and it will form C-S-H and silica gel. The interaction of asphalt binder with RCA may not be as same as with NA because the silica gel present in RCA may affect the binder's viscoelastic properties. Therefore, the extracted binders will be characterized using Atomic Force Microscope (AFM) to investigate the influence of RCA carbonation on changes in microstructural and micromechanical properties. Considering the material properties, traffic conditions, and climatic conditions of Qatar, the pavement performance and life cycle cost analysis will be conducted to quantify the performance, economic and environmental benefits. Finally, the research team of this project will coordinate with the Qatar Public Works Authority (PWA) and the road construction industry to develop a plan for the construction of field trials using the proposed technology.

Hamad Bin Khalifa University (HBKU)