Low-carbon footprint approach to produce recycled compacted concrete

Achieving a closed-loop recycling process with low CO2 emissions remains a challenge for the concrete industry. To improve the recycling of concrete debris, a powder compaction process for concrete waste was designed to obtain recycled compacted concrete (hereinafter referred to as compact) and thermal treatment was proposed to be utilized to improve its strength. However, non-specific investigations of treatment parameters, like-treatment temperature, and duration, do still exist, and the required high production pressure (100 MPa) is impracticable. Therefore, this study aims to evaluate the effectiveness of two novel treatments on compact in improving its strength and reducing its carbon footprint. First, the heat treatment process used in a previous study [1] was expanded by varying immersion durations and treatment temperatures. Second, autoclaving was employed to obtain a stronger compact with different treatment settings. Additionally, in both treatment processes, the ef-ficacy of low production pressure (<100 MPa) was evaluated. For this, eighteen different concrete wastes, having different industrial wastes, like-fly ash, slag, were collected, crushed, and powdered to produce compacts. The treated compacts were characterized based on both compressive strength and carbon footprint to compare the environmental performance of a compact prepared via thermal treatments in the production phase. The test results revealed that increasing water immersion duration (to 48 h) during the heat treatment process improved the compact strength to up to 48 MPa, and autoclaving at higher temperatures (at 220 <degrees>C) resulted in a compact strength of up to 98 MPa. Additionally, a strength of 30 MPa was attained even at a low production pressure (10 MPa) after autoclaving. The estimated CO2 emissions of the compact production process developed in this study were as low as 70.6 kg/m3 of compact. At the present stage of the study, it can be deduced that the compact manufactured possesses potential for implementation in various non-structural applications, including the pro-duction of pavement blocks and bricks, with lower CO2 emissions.