Recycling waste fresh paste through a dormancy—awakening method using CO2 as the awakener

This paper proposed a dormancy—awakening method for the collection and recycling of waste fresh paste (WFP), generated from waste fresh concrete from concrete mixing plant. Sodium citrate was employed to put WFP into the state of dormancy with low rates of cement hydration; whereas gaseous CO 2 was injected, serving as an awakener for the dormant WFP. Experimental results demonstrated that sodium citrate treatment effectively impeded the cement hydration of WFP, allowing a sufficient operational time for further accumulation and centralized processing. CO 2 injection facilitated the in-situ generation of fine-sized CaCO 3 within dormant concrete, providing nucleation sites for accelerated hydration of cement. Application of CO 2 injection for 45 mins or 60 mins resulted in the restoration of 28d compressive strength of WFP to 99 % and 96 % of the blank mixture without dormancy treatment. This approach not only awakens dormant WFP through the in-situ generation of fine-sized CaCO 3 , but also achieves carbon sequestration, offering a sustainable and practical solution for recycling WFP and promoting eco-friendly construction practices. • A dormancy—awakening method was proposed for the collection and recycling of WFP. • CO 2 can be an effective awakener to recover the performance of dormant WFP. • Fine-sized CaCO 3 particles were produced during carbonation, enhancing the hydration of cement.