Search

Carbon-conditioning or chemical permeation methods can provide excellent microstructural improvements to recycled concrete and brick aggregate; however, the applications have their limitations. Further, recycled brick aggregate cannot be effectively carbon-conditioned with conventional methods as it contains only trace amounts of reactive materials. It is therefore a necessity to use hybrid methods involving dual technologies combining carbon-conditioning and chemical permeation for its improvement. This paper is focused on developing a novel hybrid method for improving the microstructural properties of recycled concrete aggregate and recycled brick aggregate for concrete usage. This study conducts particle density, water absorption and crushing value tests to measure the physical improvements achieved with the novel hybrid method, and utilises a variety of chemicals and a reaction chamber for carbon-conditioning for aggregate treatment. The study evinces that both the recycled concrete aggregate and recycled brick aggregate experienced significant improvements, with 10 mm and 20 mm recycled concrete aggregate and 10 mm recycled brick aggregate exceeding the density of virgin aggregate. Magnesium hydroxide plus carbon dioxide (Mg(OH)2 (s) + CO2 (g)) treatment for recycled concrete aggregate and calcium hydroxide plus magnesium hydroxide plus carbon dioxide (Ca(OH)2 (s) + Mg(OH)2 (s) + 2CO2 (g)) treatment for recycled brick aggregate can be considered as potential candidates for optimal hybrid treatment methods. [ABSTRACT FROM AUTHOR]

To fulfil the needs of the future, the Australian building sector seems to contemplate toward sustainable design. A Green Star Environmental Rating System is one of many green-building rating systems that has been employed throughout the world. For this rating system, the “Material” category occupies 14% of credit points, which could be achieved from eight major categories. To help engineers and designers have simple tools to process sustainable projects, this paper develops a computer-aided model to calculate life-cycle greenhouse gas (GHG) emissions for conventional and high-strength concrete to maximize Credit 19B.1: Life-cycle impacts—Concrete in the Green Star Design and As Built in Australia. The model has been built under Microsoft Excel and Visual Basic platforms; thus, it is flexible and appears to be one of the effective ways to provide concrete mixture design using its life-cycle GHG emissions. Options to maximize Credit 19B.1 have also been discussed for normal and high-strength concrete. The model demonstrates the relationship between the utilization of supplementary cementitious material, coarse and fine aggregates used in concrete, a water-to-cement ratio with concrete strength, as well as sustainable points to be achieved. [ABSTRACT FROM AUTHOR]

Owing to the space shortage for land reclamation in Hong Kong, it is difficult to dispose of tonnes of masonry waste generated daily from construction activities. Adoption of recycled aggregate from concrete waste thus becomes a burning issue. The Hong Kong SAR Government has set up a recycling plant in Tuen Mun Area 38 to transform concrete waste into recycled aggregate with practice notes and specifications issued to control the quality of recycled aggregate. This paper studies the relationships of six parameters describing the characteristics of recycled aggregate: (i) particle size distribution, (ii) particle density, (iii) porosity and absorption, (iv) particle shape, (v) strength and toughness, and (vi) chemical composition. Samples of recycled aggregate from ten demolition sites were obtained with the average service life ranging from 10 to 40 years. In addition, one set of samples was specifically collected from the Tuen Mun Area 38 Recycling Plant. The characteristics of these 11 sets of samples were then compared with normal aggregate samples so that recommendations can be made. A Vandermonde matrix is used to estimate coefficients of 2nd-, 7th-and 10th-order interpolation polynomials. From that, mathematical relationships between pairs of tests can be formed, which can be used to simplify aggregate testing processes. This study reveals that there is strong correlation among the parameters, and by measuring two of them: either “particle density” or “porosity and absorption” or “particle shape” or “strength and toughness”, and “chemical content”, it is sufficient to test recycled aggregate. [Copyright &y& Elsevier]

Recycled Aggregate (RA) has only been used as sub-grade applications, roadwork and unbound materials because it is believed that RA has lower strength and poorer quality than normal aggregate. This paper assesses RA quality by proposing a new testing procedure. The new procedure is developed by using correlation information among the standard twenty three tests commonly employed in the construction industry. Samples of RA from ten demolition sites were obtained with service life ranging from ten to forty years. One additional set of samples was specifically collected from the Tuen Mun Area 38 Recycling Plant, Hong Kong for testing. The characteristics of these eleven sets of samples were then compared with normal aggregate samples. A Vandermonde matrix for interpolation polynomials coefficient estimation is employed to yield detailed mathematical relationships between results of two particular tests, from that redundant tests can be identified. Different orders of interpolation polynomials are used for comparison, hence the best-fit equations with lowest fitting errors from different orders of polynomials can be found. This paper shows that four out of twenty three tests are required in the new testing procedure. [ABSTRACT FROM AUTHOR]

Recycled aggregate (RA) has been used in various construction applications around the world mainly as sub-grade, roadwork and unbound materials, but not in higher-grade applications. The major barrier encountered is the variation of quality within RA, which causes lower strength, and poorer quality. This work studies the relationships among six parameters describing the characteristics of RA: (i) particle size distribution, (ii) particle density, (iii) porosity and absorption, (iv) particle shape, (v) strength and toughness, and (vi) chemical composition. Samples of RA from 10 demolition sites were obtained with service life ranging from 10 to 40 years. One additional set of samples was specifically collected from the Tuen Mun Area 38 Recycling Plant. The characteristics of these eleven sets of samples were then compared with normal aggregate samples. A Vandermonde matrix for interpolation polynomial coefficient estimation is used to give detailed mathematical relationships among pairs of samples, which can be used to work out redundant tests. Different orders of interpolation polynomials are used for comparison, hence the best-fit equations with the lowest fitting errors from different orders of polynomials can be found. Fitting error distributions are then studied by using spectral methods such as power spectra and bispectra. From that, the best equations for result estimations can be obtained. This study reveals that there is strong correlation among test parameters, and by measuring two of them: either “particle density” or “porosity and absorption” or “particle shape” or “strength and toughness”, and “chemical content”, it is sufficient to study RA. [Copyright &y& Elsevier]

• 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]

• This paper overviews the developments of LCA for RAC. • This paper identifies the research trend of LCA shifts with the promotion of RAC technology. • Variations of mix design and inconsistencies from LCA mechanism could be explored further. Recycled aggregate concrete (RAC) is expected to a sustainable solution to alter the virgin aggregate concrete (VAC) in structural use. While it is able to address environmental issues for both virgin aggregate (VA) consumption and waste generation, not so many studies quantify the environmental burdens through life cycle assessment (LCA). RAC is a composite material, which LCA should be analysed by considering its mixtures, and corresponding production technologies. This aggravates the complexity of LCA model since it involves great numbers of unit processes. Through reviewing 90 articles, this paper overviews the developments of LCA for RAC, and identifies the research trend shifts with the promotion of RAC technology. Although many relevant studies have become more comprehensive, there are still numerous inconsistencies and uncertainties existing in LCA processes that avoid LCA results from comparisons. From the review, it clearly points out that results are greatly affected by two aspects that are mix design and LCA mechanism. Cement production has the predominant contribution to the environmental impacts of concrete, and normally followed by transportation process. Accordingly, mix design, together with treatment technology of raw materials, influence the overall environmental performance of concrete. With respect to LCA phases, selections of FU, system boundary, allocation rule, LCI and LCIA methodology are highly subjective, causing more uncertainties that hinder the comparisons across the studies. It is therefore suggested that variations of mix design and inconsistencies from LCA mechanism could be explored further in the field of RAC to establish the holistic and multi-criteria study for comparison and decision making. [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]

There is continuous pressure on sustainable multifunctional concrete production to prevent environmental degradation severity. This material must exhibit improved mechanical performance and durability and comprise functionalities that comply with multiple benefits to fit well for structural applications. Concrete is commonly repurposed — crushed in waste concrete to form recycled aggregate (RCA), which can then be used to produce sustainable fresh concrete for low-grade applications. An innovative phase change materials (PCM) with calcium carbonate (CaCO 3) reinforced-RCA (CaCO 3 -PCM-RCA) is prepared by immersion and injecting carbon dioxide techniques for improving its energy-efficient thermal performance. This paper examines the effect of PCM with CaCO 3 on the multifunctional properties of CaCO 3 -PCM-RCA concrete composite with 100% RCA replacement. The synergistic effect of PCM and CaCO 3 shows an unprecedented range of improved properties of RCA concrete composite compared to standard RCA concrete. These encompass an increase of 38.3% in compressive strength, excellent modulus of toughness, low energy loss coefficient, and durability while simultaneously an exceptional thermal capacity is found compared to standard RCA concrete. A dramatic reduction in water permeability by 61.3% compared to standard RCA concrete allows this unique composite material to be ideal for building applications in areas subject to flooding. By replacing virgin coarse aggregate with CaCO 3 -PCM-RCA composite, concrete could be found as a sustainable multifunctional material in the construction industry. • A novel CaCO 3 -PCM-RCA composite material is developed by immersion followed by carbonation techniques. • Multifunctional RCA concrete is developed for energy-efficient building applications. • The CaCO 3 -PCM-RCA concrete showed an improved compressive strength and thermal storage capacity. • Incorporating PCM and CaCO 3 contributes to the water penetration resistance of RCA concrete. • The CaCO 3 -PCM-RCA concrete offers a new approach to developing future cooling and heating solutions for buildings to support net zero emissions in the future. [ABSTRACT FROM AUTHOR]

• Critical review for methods, and technologies for recycled aggregate. • Various methods are reviewed, including self-healing, bacterial, etc. • Existing studies to improve the properties of the recycled aggregate, are limited. • Density improvement techniques of chemicals and reactions are limited. Recycled concrete aggregate is a demolition concrete waste, which could be an environmental-friendly building material and can be a serious contender for saving natural aggregate and reducing environmental pollution. Nevertheless, the use of the same is limited, as it has inferior qualities compared to virgin aggregate, such as low density, high porosity, high water absorption rate, micro cracks in residual mortar and at the interfacial transition zones. Thereby, the need of improving the properties of recycled aggregate is vital to enable a wider adoption of the same. This paper provides an insight into identifying knowledge gaps and as a critical review for the methods, technologies, its advantages and disadvantages for improving the microstructural and mechanical properties of recycled aggregate, such as self-healing methods of re-hydration, bacterial and micro-encapsulation, sequential mixing approaches, removal of adhered mortar, permeation of solutions, coating with solutions and CO 2 carbonation approaches. The existing studies to improve the properties of the recycled aggregate, are limited and the density improvement techniques by permeation of chemicals and/or reactions have only been superficially studied. [ABSTRACT FROM AUTHOR]

• This paper semi-quantitatively and qualitatively demonstrates ability of CO 2 injection. • Utilise concrete petrography, scanning electron microscopy, x-ray diffraction and thermogravimetric analysis. • Carbonation treatment, or carbon-conditioning, of recycled aggregate greatly increases the amount of calcium carbonate. Mineralisation of CO 2 into cementitious materials improves upon material quality by densifying and reducing water absorption of such materials whilst permanently imprisoning CO 2. This paper aims to semi-quantitatively and qualitatively demonstrate ability of CO 2 injection on microstructure and chemical composition of concrete, cement and recycled aggregate. The injection of CO 2 into recycled aggregate creates CO 2 Aggregate. Furthermore, the mixing of CO 2 aggregate into concrete is referred as CO 2 Concrete. The investigations utilise in the completion of objective include concrete petrography, scanning electron microscopy, x-ray diffraction and thermogravimetric analysis. The petrography as well as scanning electron microscopy reveal that the carbonation treatment, or carbon-conditioning, of recycled aggregate greatly increases the amount of calcium carbonate when compared alongside untreated recycled aggregate or the fresh cement paste CO 2 Concrete itself. The x-ray diffraction semi-quantitatively demonstrates that a lower carbonation pressure of 25 kPa and a longer duration of 120 min produces the greatest amounts of calcium carbonate crystals. This paper provides insight on the mineralisation of CO 2 into cementitious materials, which provides a great opportunity to create sustainable concrete products. [ABSTRACT FROM AUTHOR]

• CO 2 injection into concrete and recycled aggregate concrete made improvement. • Carbonation of recycled aggregate is generally quicker and easier than concrete. • Concrete carbon-curing is effective, but is less practical than recycled aggregate. Employment of recycled aggregate within concrete provides great potential for the reduction of landfilling. Unfortunately, recycled aggregate exhibits a high porosity and water absorption and consequently produces a substandard material when compared to the mainstream virgin aggregate concrete. Recently, the injection of CO 2 into cementitious materials has been studied, for both improving the overall quality of recycled aggregate concrete as well as permanently chemically converting CO 2 into stone. CO 2 treatment can permit recycled aggregate concrete to rival virgin aggregate concrete in phycial and mechanical properties. Currently, there are two primary methodologies for the sequestration of CO 2 into concrete: (1) carbon-conditioning is the injection of CO 2 into recycled aggregate; and (2) carbon-curing involves sequestering CO 2 into new concrete's cement paste. Whilst both technologies permit recycled aggregate concrete for achieving great mechanical property and durability, carbon-conditioning provides a practical implementation. Carbon-conditioning permits a prompt and complete carbonation of recycled aggregate which enhances the final concrete's mechanical property and durability. This paper provides an insight into the available CO 2 technologies for concrete improvement. [ABSTRACT FROM AUTHOR]