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• This paper investigates and compares the performance of CO 2 Concrete against that of the ordinary virgin aggregate concrete on durability performance. • It is found that optimal carbonation variables is with a 120-minute duration and a 25 kPa pressure CO 2 Concrete. • The CO 2 Concrete always surpassed the performance of the untreated recycled aggregate concrete. • CO 2 Concrete with 100% replacement could provide a similar performance with optimised carbonation variables. • The employment of various cements can also be utilised within CO 2 Concrete whilst still appreciating an enhancement. • The concrete shrinkage reversibility of the concrete largely did not correspond to aggregate quality and therefore the injection of CO 2 is negligible for the parameter. The uptake of CO 2 gas into recycled aggregate to create CO 2 Concrete both improves the properties of recycled aggregate and traps the greenhouse gas. This paper aims to investigate and compare the performance of CO 2 Concrete against that of the ordinary virgin aggregate concrete in terms of shrinkage, concrete shrinkage reversibility and permeability. To complete the objective CO 2 Concrete is compared to virgin aggregate concrete in examinations such as drying shrinkage, its shrinkage reversibility and water permeability. Whilst utilising optimal carbonation variables with a 120-minute duration and a 25 kPa pressure CO 2 Concrete is able to consistently achieve similar to greater performance than the virgin aggregate concrete for both the drying shrinkage and permeability. The CO 2 Concrete always surpassed the performance of the untreated recycled aggregate concrete. CO 2 Concrete with 30 % and 50 % recycled aggregate content surpassed the virgin aggregate concrete in many cases whilst the 100 % replacement could provide a similar performance with optimised carbonation variables. The employment of various cements can also be utilised within CO 2 Concrete whilst still appreciating an enhancement. The concrete shrinkage reversibility of the concrete largely did not correspond to aggregate quality and therefore the injection of CO 2 is negligible for the parameter. [ABSTRACT FROM AUTHOR]

• The developed artificial neural network allow accurate prediction of the compressive strength for CO 2 Concrete. • The artificial neural network exhibited a strong relationship with the experimental specimens. • The artificial neural network was also validated by 22 laboratory validation concrete mixes. • The successful prediction of compressive strength of CO 2 Concrete can help a greater mainstream use of the green material. Concrete is a very effective material for the construction of buildings and infrastructure around the world. Unfortunately, typical concrete is a large contributor to CO 2 emissions and consumption of natural reserves. CO 2 Concrete allows the mitigation of these downfalls by carbonating recycled aggregate, reducing CO 2 emissions, reusing crushed masonry materials and conserving virgin aggregate. CO 2 Concrete can also be considered reliable as its compressive strength can be accurately predicted by both regression analysis and artificial neural networks. The artificial neural network created for this paper allow accurate prediction of the compressive strength for CO 2 Concrete. The artificial neural network exhibited a strong relationship with the experimental specimens, revealing a multiple R of 0.98 and an R square of 0.95. The artificial neural network was also validated by 22 laboratory validation concrete mixes. The artificial neural network displayed an average error of 1.24 MPa or 3.43% in the validation mixes with 59% of concrete samples within 3% error and 77% being within 5% error. The successful prediction of compressive strength of CO 2 Concrete can help a greater mainstream use of the green material. [ABSTRACT FROM AUTHOR]

The injection of CO 2 into concrete, recycled aggregate and other cementitious materials provides potential for both sequestration of undesirable gas and strengthening of said materials. This paper endeavours to extend upon CO 2 injection research by comparing carbon-conditioned recycled aggregate concrete (named as CO 2 Concrete) to virgin aggregate concrete in terms of mechanical performance. To complete this objective, a primary investigation is to experiment different carbonation variables such as carbonation duration and pressure. A secondary investigation provides a starting point for further research by mixing carbonation technology with other supplementary concrete strengthening procedures. The primary investigation found that a practical 2-h carbonation duration couple with a low pressure of 25 kPA provided the best strengthening of mechanical properties. CO 2 Concrete with 30% and 50% recycled aggregate replacement is very comparable in performance when rivalled against virgin aggregate concrete. Furthermore, CO 2 Concrete with 100% replacement of virgin aggregate generally exceeded the control recycled aggregate concrete by 20% and achieved a mechanical property very close to that of the virgin aggregate concrete. However, whilst CO 2 Concrete experienced an excellent enhancement, the modulus of elasticity of the environmental concrete must be improved as virgin aggregate concrete still surpasses CO 2 Concrete by a fair margin. The secondary investigation shows that the mixing of techniques such as the two-stage mixing approach and carbonation of recycled aggregate can be used in conjunction with each other. This paper provides insight with evidence for the potential practical applications of CO 2 Concrete. [ABSTRACT FROM AUTHOR]