Effect of different treatment methods on the interfacial transition zone microstructure to coarse recycled concrete aggregate

Sustainability and awareness of the environment are increasingly becoming important for transportation agencies worldwide. In Canada, many agencies are interested in maximizing the use of recycled materials into roads. The main objective of this investigation study is to examine the effect of different treatment methods on Coarse Recycled Concrete Aggregate (CRCA) for usage in roads. One of the key material properties related to using CRCA is the interfacial transition zone (ITZ). ITZ characteristics particularly microcracks and intermix phases on both sides of ITZ are calculated. Mortar properties including pore size and matrix (macro) cracks properties: Width, length and crack density are also examined. Heat treatment includes various temperatures (250°C, 350°C and 500°C). Pre-soaking method involves the use of strong acid HCl and weak acid C2H4O2. In order to achieve surface characterization of the ITZ region and CRCA surface of both of the treated and untreated CRCA, different advanced techniques are used such as Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Microanalyzer (EDAX). The obtained results revealed that the use of heat treatment is highly successful in improving properties of microcracks ITZ including width and length of microcracks. Heat treatment at 250°C exhibits the best performance by considerably decreasing the Ca/Si ratio resulting in big transformations for aggregate side, whereas the optimum behavior for mortar side improvement is recorded at 350°C. A successful acid treatment is recorded for both types; strong and weak acid for decreasing pore size and lowering width and length of the ITZ microcracks. However, the weak acid appears to be more successful in terms of improving the mortar in the ITZ, whereas the strong acid is more effective on the aggregate. The outcomes also indicated that there is a positive influence with the heat treatment at a temperature range between (0-350°C) on lowering pore size, whereas various negative impacts are observed at higher temperatures including width and length of matrix cracks and pore size. The crack density on the mortar side is highly related to properties of matrix cracks including width and length though behavior of properties is completely different.