Executive Summary : | The continuous increase in the demand of concrete necessitated the International Energy Agency (IEA) to project a road map for the concrete industry to reduce its carbon footprint. In this context, the carbon dioxide (CO₂) capture in concrete preparation through the accelerated carbonation technique can contribute to reduce the carbon footprint of construction industry by up to 56%. An innovative accelerated carbonation process is proposed to induce the CO₂ sequestration in ready-mix concrete, which will help to enhance the efficiency of CO₂ sequestration in fresh concrete and overcome the the limitations in upscaling the accelerated carbonation process of precast concrete. Dry ice as a source of CO₂ will be added to the saturated aqueous solution of limestone powder to form calcium bicarbonate. Its reaction with calcium hydroxide, calcium silicate hydrate, tricalcium silicate and dicalcium silicate will produce CaCO₃ precipitants. The deep-rooted poor performance of recycled aggregate concrete (RAC) due to flawed recycled concrete coarse aggregate (RCCA) can be reduced by forming a dense microstructure through accelerated carbonation. Moreover, for a better packing of aggregates mixture the Particle Packing Method (PPM) mix design approach will be employed. A three-stage concrete mixing method with specified mixing time will be designed to form an uniform mix. An accelerated carbonation protocol using the mixture of dry ice and saturated aqueous solution of limestone powder will be determined in this research to prepare ready-mix RAC. The influence of dry ice content in carbonated aqueous solution of limestone powder on induction period and setting time of cement will be studied by analyzing the isothermal calorimetry results. The compressive strength, tensile strength and modulus of elasticity will be evaluated, and the influence of curing period will be studied. The modifications in the microstructural characteristics due to the accelerated carbonation will be analyzed by using X-ray diffraction, scanning electron microscope images and thermogravimetric analysis techniques. The sustainability of RAC, prepared by employing the proposed method will be quantified by conducting a Life Cycle Assessment study. The findings of this research are expected to contribute the current state-of-the-art and eventually encourage the construction industry toward preparing the ready-mix RAC using the proposed accelerated carbonation process. |