Combined Effect of Multistage Processing and Treatment Methods on the Physical, Chemical, and Microstructure Properties of Recycled Concrete Aggregates

This research aims to examine the effects of multi-stage processing on reducing the old cement fractions and enhancing the quality of CRA (concrete recycled aggregate). The investigation involves the use of demolished concrete debris and subsequent treatments in both single and multi-stage processes. The recycled aggregates (RA) were obtained using a multi-stage jaw crushing process followed by utilising natural aggregate, untreated RA, RA treated with hydrochloric acid and sodium silicate immersion (single stage treatment) and RA treated with mechanical scrubbing and sodium silicate immersion in two separate stages (multi-stage treatment). The subsequent phase of the experimental inquiry involves assessing the physical attributes of both treated and untreated RA. This is followed by conducting microstructural examinations utilising techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetry-differential thermal analysis (TG-DTA). The findings indicate that employing a two-step process, involving mechanical abrasion followed by immersion in sodium silicate, yields high-quality CRA. This conclusion is reinforced by the favourable physical performance observed. The water absorption values of CRA were lowered by 78% through single-stage treatments such as immersion in hydrochloric acid. The similar treatment is found to show densest concrete with Ca/Si ratio reduced to around 81% to that of untreated CRA. Additionally, for single stage treated CRA samples, microstructural study using FTIR verified the creation of additional hydration products, whereas for two stages treated CRA specimens, TGA analysis demonstrated the formation of stable CSH. According to the findings, it is advised to use a multi-stage process of jaw crushing, then treating it with mechanical abrasion and sodium silicate. This has the ability to improve the physical, chemical, and microstructural properties of CRA.

This is an accepted manuscript of an article published in Journal of Testing and Evaluation, DOI: 10.1520/JTE20230511, www.astm.org.