Feasibility of utilising porous aggregates for carbon sequestration in concrete

Carbon sequestration in concrete has attracted increasing research attention. CO₂ may be permanently stored in the cement paste of concrete by chemical reaction with the hydration products of cement, but this method leads to a significant reduction of the pH value of the concrete pore solution and may thus put the steel reinforcement at risk of corrosion. This paper proposes a new method for carbon sequestration in concrete using the space in porous coarse aggregates; the method involves presoaking the porous aggregates in an alkaline slurry and then using them for CO₂ sequestration. The potential of utilising the space in the porous aggregates and the cations in the alkaline slurry is first discussed. An experimental study aiming to demonstrate the feasibility of the proposed method is then presented. The results show that CO₂ can be successfully sequestrated and fixed as CaCO₃ in the open pores of coarse coral aggregate presoaked in a Ca(OH)₂ slurry. The amount of CO₂ sequestration by concrete produced using the presoaked coral aggregate was around 20 kg/m³. Importantly, the proposed CO₂ sequestration method did not affect the strength development of the concrete or the pH value of the concrete pore solution.