Abstract
The fabrication of conventional concrete, as well as remains from demolition, has a high environmental impact. This paper assessed the eco-efficiency of concrete made with uncarbonated recycled concrete aggregates (RCA) and fly ash (FA). Two concrete series were produced with an effective water/cement ratio of 0.50 (Series 1) and 0.40 (Series 2). In both series, concretes were produced using 0% and 50% of RCA with 0%, 25% and 50% FA. After analysing the compressive strength, and carbonation and chloride resistance of those concretes, their eco-efficiency based on the binder intensity and CO2-eq intensity was assessed. We found that the use of 50% uncarbonated RCA improved the properties of concretes produced with FA with respect to using natural aggregates. The concrete made of 25% FA plus RCA was considered the most eco-efficient based on the tests of compressive, carbonation and chloride properties with the values of 4.1 kg CO2 m−3 MPa−1, 76.3 kg CO2 m−3 mm−1 year0.5 and 0.079 kg CO2 m−3 C−1, respectively. The uncarbonated RCA improved carbonation resistance, and FA improved chloride resistance. It can be concluded that the use of 50% un-carbonated RCA combined with FA considerably enhanced the properties of hardened concrete and their eco-efficiency with respect to concretes produced with natural aggregates.
Highlights
Concrete production has a high environmental impact due to the abundant energy consumption and CO2 emissions of cement production, releasing approximately 5–7% of total global anthropogenic CO2 emissions and 3% of total greenhouse gases emissions in the atmosphere [1,2,3]
In concretes produced with a water/cement ratio of 0.50, the use of 50% uncarbonated recycled concrete aggregates (RCA) together with Portland cement did not influence the reduction of compressive strength
When the concrete was produced with fly ash (FA), the use of RCA improved the compressive strength of 41.8 MPa compared to concrete employing natural aggregates
Summary
Concrete production has a high environmental impact due to the abundant energy consumption and CO2 emissions of cement production, releasing approximately 5–7% of total global anthropogenic CO2 emissions and 3% of total greenhouse gases emissions in the atmosphere [1,2,3]. According to Corinaldesi and Moriconi [36], the addition of FA proved to be effective in reducing the chloride ion penetration depth in concrete, even when RCA was used They concluded that the addition of FA to RAC increased the carbonation rate. The compressive strength and durability properties of carbonation and chloride resistance were determined and compared with conventional concrete. The eco-efficiency of the produced concretes was assessed by measuring Bi and Ci values with respect to those obtained for compressive strength, carbonation coefficient and chloride resistance. CRAFA achieved a higher level of eco-efficiency than the concretes made with Portland cement and natural aggregates
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