The effects of various operational- and materials-oriented parameters on the carbonation performance of low-quality recycled concrete aggregate

Abstract

This study focuses on the examination of the parameters affecting the carbonation performance of low-quality recycled concrete aggregates (RCA) obtained from end-of-life buildings and having low mechanical and chemical properties. The accelerated carbonation process was implemented by using a lab-scale carbonation reactor, providing a dynamic carbonation process. In the scope of this study, as the main operational parameters, relative humidity (RH) (50-70-90%), medium pressure (1-2-3 bar), and temperature (50–90 °C) were determined. Carbonation processes were implemented on the low-quality RCAs with 5 different particle size ranges, including <0.85, 0.85–2.00, 2.00–4.75, 4.75–9.50, and 9.50–14.00 mm. Effects of carbonation durations (2-4-6-12-24-48-72-96-120 h) on the carbonation performance of RCAs were also investigated. Thermogravimetry was the test method used to quantify the CO2 uptake rate of low-quality RCAs. In addition, the water absorption capacity of RCAs was determined to gain insight into precipitated calcium carbonate. To evaluate the microstructure of carbonation products, scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods were used. Mortar specimens were prepared using uncarbonated and carbonated RCAs to assess the effects of the carbonation on the workability and mechanical properties of the RCAs-incorporated cementitious system. Results showed that all parameters tested were effective on the carbonation performance of the RCAs. Implementing carbonation with an optimal condition (70% RH, 1 bar, 90 °C, 48 h) resulted in an increase in the quality of low-quality RCAs in favor of increasing the compressive strength of the cement-based systems. Therefore, valuable upcycling of low-quality RCAs for the construction industry is possible in high-tech applications with accelerated carbonation under optimum conditions.