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Abstract This paper examines the mechanical properties and durability of recycled aggregate concrete (RAC) containing 100% coarse recycled concrete aggregate (RCA) and industrial by-products. The by-products, including waste paper sludge ash (PSA), fly ash (FA), silica fume (SF), and metakaolin (MK) of different proportions (5%, 10%, 15%) in RAC, were used in two methods: replacement and addition methods. The use of by-products (mineral admixtures) to mitigate the low quality of RAC was demonstrated through experimental outcomes in this study. The addition of industrial by-products was presented as a promising alternative for the addition of more Portland cement in RAC to enhance RAC's quality. The results showed that the strength and durability of RAC containing mineral admixtures in the addition method were higher than the addition of more cement or the replacement method. Notably, PSA considerably improved the mechanical properties of RAC at an early age, and it substantially improved the resistance of RAC to acid and sulfate attacks. At 90 days, FA and MK improved mechanical properties of RAC greater than SF and PSA did. Among combinations, the proportions of by-products in RAC of 5% PSA, 10% SF, 15% MK and 15% FA can produce the highest performance of RAC with 100% coarse recycled concrete aggregate (RCA). Highlights • The paper investigated properties of RAC with 100% coarse RCA and by-products. • The addition of MAs improved the performance of RAC better than the addition of more cement. • PSA significantly enhanced the strength at early age and sulfate attack resistance of RAC. • FA and MK concrete exhibited higher strength than SF and PSA concrete at 90 days. • 5% PSA, 10% SF, 15% FA and 15% MK produced the higher quality of RAC than other proportions of MAs. [ABSTRACT FROM AUTHOR]

Ferronickel slag (FNS) is a solid waste produced in the smelting of ferronickel alloys. FNS is classified as blast furnace ferronickel slag (BFS) and electric furnace ferronickel slag (EFS). They are useful in many fields, such as metal recovery and glass manufacturing. In fact, replacing cement or concrete aggregate is the best way to achieve large-scale resource recycling of FNS, while generating environmental and economic benefits, which is consistent with the concept of sustainable development. This paper summarizes the research papers of FNS as supplementary cementitious materials (SCMs), aggregates and precursors and comprehensively analyses of the sustainable utilization of FNS. The results suggest that BFS is suitable for use as SCMs with small replacement and relatively high activity, but it needs to be ground to 400–500 m2/kg. EFS is suitable for use as aggregate due to its high discharge and strong interlocking ability of particles. The influence of FNS on the performance of geopolymer concrete is mainly related to the types of precursor and activator. Combined with the results of this paper, the research direction of further improving the recycling efficiency and cleaner production of FNS is given. [ABSTRACT FROM AUTHOR]

This paper investigated the Electrochemical Chloride Extraction (ECE) process in concrete with carbonated surface layers. First, the ECE model for surface carbonated concrete was proposed based on pore size distribution function. Subsequently, to validate the model, concrete cube specimens exposed to natural coastal environments were modified and designed for ECE tests. Based on the validated ECE model, parametric studies were conducted. Parametric studies show that increasing the thickness of the surface carbonation layer up to 20 mm leads to a 57% increase in extraction duration, whereas the thickness of the partially carbonated zone has a relatively minor impact on the ECE process. The parametric study shows that the surface carbonated zone will pose hindrances to the extraction of chloride ions. Due to the simultaneous presence of concrete carbonation and chloride ion ingress in the actual marine atmospheric environment, considering the actual carbonation depth is of significant importance for predicting chloride ion migration during Electrochemical Chloride Extraction. [ABSTRACT FROM AUTHOR]

Disposal of industrial waste is a worldwide problem. Additionally, the non-biodegradable nature of these wastes further increases severity of the problem. The shortage of land to accommodate the waste landfills, increased transportation cost and other associated problems have forced industries to search for other viable alternatives. Moreover, over-exploitation of natural resources by the construction industry has led to their depletion. Thus, the construction industry is compelled to look for other economic and sustainable substitutes for conventional raw materials (river sand, natural aggregates) and cement. Past studies suggest that waste of discarded rubber tyres, silica fume, glass, slag, pond ash, bottom ash, metakaolin, stone etc. can effectively replace a part or the whole of conventional materials used for concreting. Recycling of these wastes as construction material can be a sustainable practice. However, the green concrete so produced needs to satisfy certain parameters for its applicability. In recent years, studies have claimed that waste from dimensional stone industry can be effectively recycled into concrete, a practice certainly benefiting the stone as well as construction industries. This paper reviews the applicability of dimensional stone waste in concrete. The effect of stone waste substitution on workability, strength and durability parameters such as permeability, chloride migration, porosity, water absorption, carbonation, acid and sulphate resistance have been reviewed in the paper. It is suggested to investigate in-detail the durability of concrete containing dimensional stone waste to establish the same as popular construction material. [ABSTRACT FROM AUTHOR]

The concrete industry has been responsible for significant depletion of natural resources and at end-of-life significantly contributes to global waste production. To date experimental studies have typically explored the use of single generation recycled aggregates (RA) in concrete production, however, to move towards a circular economy the concrete industry needs to embrace the use of multi-generation recycled aggregate concrete (MGRAC). In this paper the physical and mechanical performance of 45 concrete mix designs over 4 generations of concrete production is explored. At each generation a series of mixes are conducted at various water to cement ratios (w/c) and with a range of blends of virgin and recycled aggregates from differing generations to capture the impact on material properties. The physical and mechanical properties are quantified for both the aggregates and the concretes at each generation. The results show that the physical properties and some mechanical properties of the concrete and RA decrease with respect to virgin aggregate concrete and virgin aggregate but, implementing a 50% replacement of VA can slow down intergenerational degradation. Furthermore, the blending RA from a range of generations can also slow intergenerational degradation but to a lesser extent. Effective aggregate properties are determined, and direct relationships confirmed indicating potential for informed mix design based on an understanding of a few simple aggregate properties. [ABSTRACT FROM AUTHOR]

Aggregate interlocking concrete (AIC) is a kind of high-performance concrete with high aggregate content. Compared with normal concrete, AIC has the advantages of fast construction speed, low engineering cost, and a high material utilization rate. AIC is a novel construction technology. The principle of AIC is to form a dense skeleton in the concrete by presetting or post-filling the aggregate and then forming an interlocking structure between the aggregates inside the concrete, thus the compactness of the concrete is improved. The main performance index of AIC including mechanical properties and durability can be changed by the aggregate volume, particle size, and shape. AIC has been applied to numerous pavement and water conservation projects thus far, which offers excellent possibilities for use in engineering projects. This paper provides a state-of-the-art review of the technical and production properties of AIC, including the construction process, mechanical properties, durability, aggregate model, and engineering application. The deficiencies of AIC in research are further pointed out with the objective of providing a reference for realizing its high-value utilization in the project. [ABSTRACT FROM AUTHOR]

Many steel industries are adopting electric arc furnace (EAF) technology due to the growing demand for steel recycling and reducing greenhouse gas emissions. Nevertheless, the major issue with EAF is the co-production of slag and dust (EAFD). Slag is a hard, dense, and rock-like material, while EAFD is fine dust. EAFD contains oxides of several heavy metals mostly present in input scrap steel or additives used for alloy making. Many environmental agencies have categorised EAFD as hazardous waste as EAFD disposed off in land leach heavy metals, contaminating the groundwater. Due to its hazardous nature, EAFD disposal imposes a substantial landfill cost on steel industries. Several studies have reported that EAFD can be utilised in the construction sector as a supplementary raw material for cement concrete, asphalt, bricks and ceramics, and other applications, instead of being disposed off in landfills that trigger environmental complications. Yet a review of EAFD reuse in sustainable building material production is lacking. This work reports EAFD production during steel manufacturing and its serious impact on environment, analyses the mechanisms involved in after the addition of EAFD as a secondary filler material in various construction components, namely concrete, asphalt, bricks, ceramics, and glaze. Insights into EAFD morphology and chemical composition and the effect of EAFD addition on the performance of the above components are also presented. This paper also provides an in-depth synthesis of the performance of building materials after EAFD incorporation in terms of workability, hydration, hardening process, mechanical performance, and durability. Literature reports that the fine nature of EAFD improves the workability of concrete and the plasticity of clay used in ceramic tiles and bricks. EAFD fills up the voids and improves water absorption, mechanical strength, and durability of the final product. Eventually, the performance of construction materials blended with EAFD is governed by the bond, quantity, and characteristics of EAFD, including morphology, particle size distribution, and composition. Laboratory trials are required to obtain the optimum mix of EAFD and the binder. Adding EAFD to construction materials is an economical and efficient approach to recycle waste and can be used to build infrastructure while reducing the environmental impact. The paper also discusses a few challenges in the current research and development and future perspectives on using EAFD as a supplementary material. The review anticipates providing a valuable guide to recycle EAFD in construction materials. Incorporating EAFD in building materials production could be a promising approach to a circular economy and cleaner production. [Display omitted] • Generation, chemical composition and impact of Electric Arc Furnace Dust. • Overview of reuse of Electric Arc Furnace Dust in Construction industry. • Reuse in cement concrete, asphaltic concrete, ceramics, glass-ceramics and glaze. • Electric Arc Furnace Dust in other construction components. • Discussion and future prospects of reusing Electric Arc Furnace Dust. [ABSTRACT FROM AUTHOR]

Industrial by products such as granite cutting waste (GCW) are suspected to have a detrimental effect on environment. This paper emphasizes on a sustainable way of getting rid of GCW by using it as a partial replacement of natural fine aggregate (river sand) in conventional concrete. In this paper, strength and durability behaviour of concrete containing GCW is examined so as to determine its viability in concrete production. Concrete was prepared with GCW in 4 different proportions i.e. 10%, 20%, 30%, and 50% and various tests such as compressive strength, flexural strength, abrasion resistance and permeability test were performed and the experimental values were compared with the control mix. Microstructural studies of control mix (CM) and mixes with different percentages of GCW were also performed using SEM and XRD techniques to identify effect of incorporating GCW on performance of concrete with respect to C–S–H gel, silica and other hydration products, which has not been investigated in the past. Microstructural investigation helps in understanding the variation in strength of concrete with different percentages of GCW. Test results, SEM and XRD analysis of concrete mixes indicates that optimum replacement percentage of fine aggregate with GCW is about 30% as the performance of concrete is significantly improved at this replacement level. Hence, GCW can be used as a partial substitute of river sand and thereby reducing cost of concrete production. Optimal replacement of sand by GCW can open up new avenues in sustainable construction techniques and reduce the detrimental effect on environment due to waste disposal. [ABSTRACT FROM AUTHOR]

The growing demand of construction around the world has led to the increased usage of concrete. However, conventional concrete-making materials are not entirely environmental-friendly and this has enthused research on seeking greener alternative for concrete production. In the past, extensive research works had been carried out to utilize farming waste materials such as those from palm oil, coconut, sugarcane as well as the paddy industry and these findings indicate potential of utilizing such materials in concrete. The re-use of the farming waste materials in concrete could reduce the dependency on conventional concrete-making material as well as minimizing the negative impact on the environment besides ensuring waste conservation and reduction in waste disposal from these sectors. In this paper, a review on the utilization of emerging alternative farming waste materials in concrete such as from the farming of bamboo, corn, wheat, olive, sisal, seashells and more is carried out with the aim of examining the benefits and shortcomings of using these materials. This review shows the possible usage of farming waste materials in different form in concrete, such as partial cement and aggregate replacement, as well as fibre reinforcement. The main finding from the paper is that although usage of farming waste materials resulted in lowering of some concrete properties, appropriate treatment methods and selection of the waste materials would enable the production of concrete with improved performance. The summary and discussion provided in this paper should provide new information and knowledge on a greater variety of farming waste materials which are suitable to be used for the production of a greener and sustainable concrete. [ABSTRACT FROM AUTHOR]

An extensive growth in pavement life cycle assessment studies is noticed in recent years. Current literature in pavement life cycle assessment demonstrates a wide range of implications on environmental burdens associated with the pavements. However, immature parts still remain, needing further research, in the next years, in different stages of pavement life cycle assessment. Most of these papers focused on the implementation of new technologies on pavements construction, the use of recycled materials, and the investigation of various phases of the pavement life cycle rather than improving the applicability and the adequacy of life cycle assessment methodology to the pavement problems. These stages are based on ISO 14040 and 14044 frameworks: the goal and scope definition, the inventory analysis, the life cycle impact assessment and interpretation. In this paper, a comprehensive review (i.e. a critical review and research gaps investigation) of life cycle assessment studies on pavements was conducted. The presentation comprises (not an extensive list) inventory analysis such as surface roughness, noise, lighting, albedo, carbonation, and earthwork in addition to locally applicable data collection, consequential and temporal consideration of pavement life cycle, and sensitivity analysis. Addressing these inadequacies will permit enhanced pavement life cycle assessment studies. This will then be useful for policy makers, project managers, construction engineers, and other stakeholders in identifying prospective in sustainable development of the pavement sector. [ABSTRACT FROM AUTHOR]

The consumption of various forms of plastics is a challenging environment protection issue. All forms of consumed plastic become waste and require large areas of land for storage because several tons of waste plastics cannot be fully recycled at once. The low biodegradability of plastic and the presence in large quantities of waste plastic negatively impact the environment. Previously, various studies were performed to identify safe and environmentally friendly methods for disposing of plastics. Recently, various forms of plastics have been incorporated in concrete to prevent the direct contact of plastics with the environment because concrete has a longer service life. However, this method is not a dominant method for disposing of waste plastic. This paper presents an overview of some published research regarding the use of waste plastic in concrete. The effects of waste plastic addition on the fresh, mechanical and thermal properties of concrete are also presented in this paper. [ABSTRACT FROM AUTHOR]

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editors. Following receipt of whistle-blower complaints, an investigation of this and related papers was conducted. The Editor-in-Chief no longer has confidence in the scientific integrity of this paper as similar images have been used in various articles in multiple journals claiming varying conditions, which violates our publishing policies. The XRD pattern in Figure 5 in this article was reported differently in previous articles (e.g., Construction and Building Materials, 2021, 267, pp.121806, https://doi.org/10.1016/j.conbuildmat.2020.121806). These results are carefully checked and reviewed by a duly constituted expert committee, and are concluded to be unreliable findings. Communication with the corresponding author raised further concerns with the integrity of this work and proposed revisions deepened, rather than clarified, the uncertainty as to what materials were used in this study. One of the conditions of submission of a paper for publication is that authors of reports of original research should present an accurate account of the work performed as well as an objective discussion of its significance. Underlying data should be represented accurately in the paper. A paper should contain sufficient detail and references to permit others to replicate the work. Fraudulent or knowingly inaccurate statements constitute unethical behaviour and are unacceptable. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process. [ABSTRACT FROM AUTHOR]

The use of supplementary cementitious materials (SCMs) in concrete blends is often promoted as a way to reduce the environmental impacts of concrete. SCMs can include fly ash, silica fume or steel slag. Another SCM, and the focus of this paper, is ground-granulated blast furnace slag (GGBFS), which can be co-produced with pig iron. Previous studies that cite environmental benefits of GGBFS in concrete do not account for supply conditions of GGBFS. In this paper, this supply assumption is challenged through a market analysis. The environmental consequences of GGBFS supply conditions are assessed using a system expansion approach to life cycle assessment. When the supply of GGBFS is not constrained, greenhouse reductions of a given GGBFS-concrete blend are in the order of 47.5%. However, market analysis indicates that the supply of GGBFS can be constrained. Under a supply constraint, the 47.5% additional greenhouse reductions from the use of GGBFS are no longer applicable. Environmental certification schemes could ensure ongoing benefits of GGBFS by promoting the use of steel sourced from a supply chain which co-produces granulated blast furnace slag at the blast furnace. [ABSTRACT FROM AUTHOR]

Developing green materials for infrastructure construction is of vital importance for sustainable development. Limestone calcined clay cement (LC3) is an appropriate alternative for the reduction of CO 2 emissions and resource consumption in the cement industry. Recycled concrete aggregate (RCA), seawater and sea sand are potentially advantageous from a sustainability perspective, especially in coastal regions. Fiber-reinforced polymer (FRP) bars with excellent corrosion resistance are ideal alternative materials for steel bars in a corrosive environment. In this paper, a new type of green concrete structure incorporating LC3, seawater, sea sand, RCA, and FRP bars was investigated, and the performance was assessed to verify the considerable sustainable advantages while considering life cycle cost and environmental impacts. The results showed that the proposed LC3 concrete exhibited lower environmental impacts: compared with traditional concrete, and the CO 2 and energy consumption of LC3 concrete were reduced by 32%–41.7% and 23.3%–28%, respectively. Although the initial cost was higher for LC3 and CFRP bars, this disadvantage could be offset by their longer service life and lower maintenance costs during their life cycle. Compared with traditional RC structures, the total cost, CO 2 and energy consumption in the life cycle were reduced by 39%, 30.5%–65.4%, and 18.5%–58.9% for the LC3 concrete structure, respectively. In contrast to the life cycle cost, the LC3 replacement ratio had a negative effect on the environmental indices for the LC3 concrete and structure. Considering the promising advantages in economy and environmental impact, the proposed LC3 concrete and structure provides an effective approach for the sustainable development of the construction industry. • A type of green concrete structure incorporating LC3, seawater, sea sand, RCA, and FRP bars. • LC3 concrete exhibits lower environmental impacts, decreased as the LC3 replacement ratio increases. • LC3 concrete structure shows excellent environmental and economic advantages. [ABSTRACT FROM AUTHOR]

The use of industrial solid wastes (e.g., slag, fly ash) and recycled concrete aggregate (RA) to manufacture geopolymeric recycled aggregate concrete (GRAC) has been proved as a sustainable and environment-friendly approach for the concrete industry, and has received an extensive prospect. Understanding the specimen size effect of GRAC is fundamental and essential in the entire design and analysis of concrete components and structures. This paper presents an experimental study on the specimen size effect on compressive and splitting tensile strengths of GRAC, with the influence of RA replacement ratio and water-to-binder (w/b) ratio emphasized. A total of 168 GRAC cubes with four different specimen sizes (70.7, 100, 150 and 200 mm) are tested. The results show that the compressive and splitting tensile strengths of GRAC decrease with increasing RA contents due to the increased amount of defects, with the decreasing amplitudes of about 4%–30.4% for compressive strength and 2.96%–34.91% for splitting tensile strength, respectively, except that their size effect becomes more apparent. While the strengths and specimen size effect degrees of GRAC all decrease with the increase of w/b ratio. Based on Weibull's, Bazant's and Capinteri's size effect laws (SELs), analytical models for SELs of compressive and splitting tensile strengths of GRAC are respectively established. The comparison results indicate that the Bazant's SEL is more suitable for the cubic compressive strength of GRAC, while the splitting tensile strength using Weibull's statistical SEL achieves the most accurate prediction results. Moreover, conversion factors are suggested for the transformation of the compressive and splitting tensile strength measurements of GRAC. Finally, a life cycle assessment method is conducted to evaluate the carbon emission potential of GRAC, which is proven to be a green and low-carbon construction material with an over 60% carbon reduction compared to cement-based plain concrete. [ABSTRACT FROM AUTHOR]

An emerging strategy to remove CO 2 from the atmosphere and compensate for the greenhouse-gas emissions of cement and concrete is based on incorporating biochar into concrete. With this approach, concrete can be turned into a functional carbon sink (C-sink). Until now, biochar has been mainly used without modification to replace part of the cement or of the aggregates in concrete. However, this technology comes with a number of practical problems, which include the high water absorption of the biochar (due to its high specific surface) and hazards (dust, risk of combustion). In this paper we present an alternative approach, in which biochar is first processed into lightweight aggregates in a cold-bonding process. To this end, biochar is pelletized together with water and a small amount of hydraulic binder forming round pellets that further harden with hydration. In this way, carbon-rich lightweight aggregates (C-LWA) are obtained that are easier to handle than the original biochar. The C-LWA pellets have similar porosity and strength as conventional LWA and can be used for similar applications. Yet, the CO 2 emissions from sintering traditional LWA are avoided and the C-LWA are instead an effective C-sink. We demonstrate that it is possible to incorporate in the pellets and eventually in the concrete a sufficient amount of carbon to compensate for the original emissions of concrete. The net-zero emissions concrete obtained with this approach possesses mechanical performance sufficient for typical structural applications in buildings. • Biochar is processed into lightweight aggregates in cold-bonding process. • The biochar-rich lightweight aggregates added to concrete act as a safe carbon sink. • Structural concrete with net-zero greenhouse gas emissions becomes possible. [ABSTRACT FROM AUTHOR]

To realize the sustainable development of concrete, it is vital to mitigate its consumption and environmental footprint (especially CO 2 footprint) from prolonging the service life through upgrading mechanical and durable performances of concrete. Incorporating nanofillers can effectively tailor the microstructures and performances of bulk cement paste and cement paste at interfacial transition zone in concrete. The hydrated calcium silicate (C–S–H) gels account for half of the volume of hardened Portland cement pastes, and they are the fundamental source of overall properties of concrete. However, the underlying mechanisms of nanofillers on C–S–H gels remains unclear. Herein, this paper underpinned the role of 5 types of representative nanofillers in tailoring the nanostructure of C–S–H gels in cement composites. The research results demonstrated that through the nano-core effect, nanofillers induce the formation of two new C–S–H gels in outer hydration products, namely nano-core-shell element doped low-density C–S–H (NEDLD C–S–H) and nano-core-shell element doped high-density C–S–H (NEDHD C–S–H). The indentation modulus/hardness of NEDLD and NEDHD C–S–H reaches 25.4/0.80 GPa and 46.7/2.72 GPa, respectively. Such superior performances of NEDLD and NEDHD C–S–H derive from the existence of nano-core-shell elements in C–S–H gels rather than the increase in C–S–H packing density. In a short-range, nanofillers form nano-core-shell elements by adsorbing silica tetrahedrons during the hydration process, improving the mechanical properties of C–S–H basic building blocks. In the long-range, the nano-core-shell elements modify the nano-scale performances of C–S–H gels in outer hydration products due to the increase of C–S–H gels' integrality. [Display omitted] [ABSTRACT FROM AUTHOR]

The depletion of natural resources is accelerating due to increased construction activities across the world. The search for alternative materials used in concrete is becoming a prominent measure to reduce greenhouse gas (GHG) emissions in the construction industry. Cement in concrete produces 4–8% of all GHG emissions annually worldwide. Alternative materials such as waste cardboard provide an opportunity to be utilised further in such applications. This study focuses on using nondominated sorting genetic algorithm (NSGA-II) to optimise the economic cost and GHG emissions of concrete incorporating recycled waste cardboard as a partial cement substitute. The multi-objective optimisation solutions produced three key regions that corresponded with trade-offs between the lowest costs, carbon emissions or a combination of both. Region 1 was the most economical but created the most carbon emissions. Region 2 was a compromise between both economical, and environmental factors and region 3 demonstrated the lowest carbon emissions but also produced the highest costs. These regions produced three mix designs which were experimentally analysed for their compressive strength. The results indicated a cost increase of 17, 27 and 36% for three key optimised regions. This is primarily due to increased material costs and further manufacturing requirements when converting waste cardboard into kraft fibres (KFs). Increasing the amount of KFs then reduced the compressive strength from 36 to 56%. However, there was a 7, 18 and 28% GHG emission saving when KFs partially replaced cement. • Optimisation and mechanical testing methods are applied to kraft fibres in concrete. • Waste cardboard kraft fibres can be used as a partial cement substitute. • Supplementing cement with waste kraft fibres can reduce GHG emissions. • Multi-objective optimisation is utilised to optimise cost and GHG emissions. • Increasing the amount of kraft fibres in concrete can reduce the mechanical strength. [ABSTRACT FROM AUTHOR]

Recycled chloride-attacked aggregate concrete (RCAAC) requires special treatment to reduce the corrosion risk of the steel bars embedded in it. This paper proposes bidirectional electromigration (BIEM) rehabilitation as a recommended step to construct concrete components from RCAAC. The electrochemical parameters were investigated to obtain the highest chloride ion removal efficiency (CRE). An assembled laminated slab was then prepared as a case study of the possible application of the RCAAC. Results proved that the durability of assembled laminated slab was improved, the flexural capacity remained in an ideal state and the crack distribution characteristics did not change. This paper can provide a feasible method to solve the issue of concrete waste pollution during urbanization construction for islands or coastal cities. [Display omitted] • The chloride ion content can be effectively reduced to a practicable level after electrochemical treatment. • The electrochemical treatment applied curing period shows high efficiency of durability improvement. • The parameter optimization method considering electrochemical treatment efficiency and concrete performance is discussed. • The performance of assembled laminated slab remained in an ideal state after electrochemical treatment. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review of the utilization of industrial wastes in 3D concrete printing processes. Concrete 3D printing processes are introduced, highlighting the need for unique material requirements. The literature on the different wastes that have been used for producing 3D printable mixtures is reviewed, including waste generation, material properties, and the roles of these materials in improving the fresh properties needed for concrete printing. Factors affecting successful utilization of these waste materials in 3D printable concrete are discussed in addition to their environmental impacts. This paper underlines the positive impacts of using industrial wastes for improving the sustainability of 3D printable concrete. It is expected that printable concrete formulations containing high volumes of industrial waste (and chemical admixtures) can be developed to improve the sustainability index of this emerging construction technique. [Display omitted] o Critical review of 3D printed concrete made with industry waste is presented. o Factors affecting successful utilization and effects of these waste materials are discussed. o Sustainability assessment of 3D printable mixes is presented. o The challenge is to produce high performance 3D printable concrete using high volume of industry waste. [ABSTRACT FROM AUTHOR]

Geopolymer is an environmental-friendly cementitious material, but few systematic designed methods for the mix proportion of geopolymer concrete have been developed due to the multitudinous factors. In this paper, a method for the mix proportion of the geopolymer concrete was proposed based on the paste thickness of coated aggregate and the close packing theory. In this method, the water-to-metakaolin ratio was selected based on the minimum water requirement method. Aggregate gradation was designed according to the close packing theory and the amount of metakaolin was determined by the paste thickness of coated aggregate. In addition, geopolymer concretes with the paste thickness of 10 μm, 20 μm and 30 μm were prepared by the alkali activated-metakaolin at ambient temperature, while the effect of the paste thickness on the compressive strength, sulphate attack and electrical resistivity of geopolymer were examined. Results showed that geopolymer concrete had a well fluidity and the strength degree of C30∼C50 can be achieved. Moreover, the relation among alkali content, modulus and compressive strength of geopolymer mortar was proposed. • A systematic designed methods for the mix proportion of geopolymer concrete were proposed. • The relation among alkali content, modulus and compressive strength of geopolymer mortar was proposed. • The effect of the paste thickness of coated aggregate on the property of geopolymer concrete was discussed. [ABSTRACT FROM AUTHOR]

Utilizing bentonite in composites such as concrete mixture is one of the practical approaches for adsorption of heavy metals. The mixture of bentonite and normal concrete is known as bentonite plastic concrete (BPC). This type of concrete is commonly utilized as the material of cutoff walls under earth dams with the aim of minimizing or preventing water seepage. Plastic concrete should possess high workability and consistency since it is poured into trenches by tremie pipe; this fact highlights the importance of predicting the slump of BPC. Different strength parameters of BPC such as compressive strength and elastic modulus can be predicted by utilizing prediction models. This information is exceedingly useful for modifying mixing design of BPC which results in reducing the cost and time of constructing a project. Consequently, it is vital to propose models that can predict the parameters of BPC with high precision. In this research, 158, 169, and 119 data records respectively for slump, compressive strength of cubic samples (f' c,cube), and elastic modulus (E c) of BPC were collected from literature in order to propose prediction models. Three soft computing methods of artificial neural network (ANN), Multivariate adaptive regression splines (MARS), and M5 model tree (M5Tree) were utilized and compared in this paper. Then, parametric studies were conducted to study the effect of different variables such as silty clay addition, bentonite dosage, water content, and curing time on the outputs (i.e., slump, f' c,cube , and E c). Results indicate that ANN models are more accurate than the other models for prediction of all three parameters. The water variable produces the greatest effect on the slump of BPC while the sand variable has the least influence. In addition, both for f' c,cube and E c models, variables of cement and curing time have the maximum and minimum impact on the outputs, respectively. • Three datasets of Slump, f' c,cube , and E c of BPC were gathered from the literature. • Three methods of ANN, MARS, and M5Tree were compared. • ANN models were more precise than the other models. • The parametric studies were performed to investigate the behavior of ANN models. • The sensitivitsy analysis showed the influence of input parameters on models output. [ABSTRACT FROM AUTHOR]

The unique fresh and hardened properties of high-performance self-consolidating concrete (HPSCC) led to an extensive application of this mixture in high-rise buildings. In this paper, the elevated temperature resistivity of 19 HPSCC mixtures incorporating binary and ternary blends of fly ash, silica fume, natural zeolite, and metakaolin was investigated. Changes in mass, compressive strength and ultrasonic pulse velocity (UPV) of the mixtures were measured at different temperatures (20, 300, 500, and 700 °C). A life cycle assessment (LCA) was also employed to explore the environmental performance of the mixtures. The test results revealed that in ambient temperature, ternary mixtures incorporating natural zeolite and fly ash or natural zeolite and metakaolin have lower compressive strength than that of the control mixture. The residual compressive strengths of fly ash-silica fume-incorporated mixture was similar to those in binary mixtures. The UPV test results revealed a larger than 50% reduction in transition velocity when the temperature was above 500 °C, and there is a strong association between the UPV and compressive strength test results of the mixtures at different temperatures, but the correlation decreased inversely proportional to the exposure temperature. Among the ternary mixtures, those mixtures that incorporate natural zeolite indicate the most significant mass loss after exposing to elevated temperature. The environmental results indicate that the substitution of pozzolanic materials with Portland cement may not always be beneficial. The ecosystem quality results of binary fly ash mixtures were larger than the control mixture due to the extensive transportation distance of import. In addition, metakaolin binary mixture exposes larger damage to the resources. Silica fume-incorporated mixtures had significant damage to human health. The ternary blended mixtures can be a remedy to obtain the optimized fire-resistant results and to compensate the environmental burdens of the inferior pozzolan in all the damage categories. [ABSTRACT FROM AUTHOR]

Geopolymer concrete (GPC) has been researched during the past few decades as an alternative to sustainable construction materials, which can minimize CO 2 emission for its use of industry by-products. Past researches on GPC show that it can be suitable for the structural applications, with a workable slump, and comparable grade of strength to ordinary Portland cement concrete. In this review paper, the mix design, mechanical properties, durability and microstructure of GPC have been discussed to figure out and report the last data and information regarding geopolymer concrete. In addition to that, the microstructure of GPC and OPC concrete have been investigated to understand the internal structure of GPC and evaluate its engineering properties such as strength and durability etc. Review of literature revealed that the production of geopolymer concrete requires great care and correct material composition. During the activation process in making the geopolymer, high alkalinity also requires safety risk and enhanced energy consumption and generation of greenhouse gases. Furthermore, the production of GPC is also affected by the curing time and curing temperature. Therefore, there is an urgent need to develop user-friendly design geopolymer concrete procedure/code that can be used in a variety of construction areas. In summary, this literature review offers guidance for civil engineers and industrial community in future researches regarding geopolymer concrete. Production of geopolymer concrete using waste materials. A descriptive model. Image 107908 • Superiority of geopolymer concrete over the conventional concrete from environmental sustainability view point. • Mechanical properties, fire resistance and durability of geopolymer concrete. • Factors affecting the mechanical properties of geopolymer concrete. • Microstructure of geopolymer concrete. [ABSTRACT FROM AUTHOR]

Abstract The reuse of mining waste-rocks as construction material constitutes an innovative management approach consistent with the principles of sustainable development. Nevertheless, the implementation of this approach is still limited by most guidelines due principally to insufficient knowledge of these materials performances and to unjustified presumptions related to their chemical instability (presence of sulfide). This paper approaches these issues by assessing the reuse potential of low-sulfide mining waste-rocks as aggregates for concrete regarding to the Quebec (Canada) recycling guidelines of non-hazardous inorganic wastes as construction materials. Toxicity characteristic leaching procedure (TCLP), comprehensive physical, chemical (XRF and ICP-AES) and mineralogical investigations (XRD and SEM) as well as modern automated mineral liberation analyses have been carried out. In addition, UCS results of various concrete mixtures using different binders were then presented to illustrate the reuse potential of the waste-rocks. The TCLP test showed the nonhazardous character of the waste rocks. They contained low sulfide content (0.5 wt%), which classify them as non-acid generating and able to meet the classification in recycling category including concrete production. Moreover, liberation analyses showed that most sulfides are concentrated in the fine fraction as pyrite occurrence with a liberated fraction of only 2%. These results influenced significantly the properties of the resulting concretes, which presented good mechanical performances especially when coarse waste rock above 20 mm and fine one below 80 μm was removed. Highlights • TCLP test showed that waste rocks is a non-hazardous material. • Grain size distribution of coarse waste rocks fraction was similar to reference gravels used for concretes production. • Total sulfur content of waste rocks was not exceeding 0.5 wt%, classifying the material as non-acid generating. • Iron sulfides (mainly of pyrite) are almost encapsuled within gangue mineral. Only 2% of pyrite is free. • Natural sand instead of the waste rocks fine fraction improve the concrete strength. [ABSTRACT FROM AUTHOR]

Abstract This paper addresses an effective way to apply recycled construction and demolition waste (C&D waste) in developing ultra-high performance concrete (UHPC). To be specific, the modified Andreasen & Andersen (A&A) particle packing model is employed firstly to achieve a dense packed structure of UHPC. Secondly, C&D waste is used to replace cement and aggregate synchronously in order to minimize negative effect on the dense packing structure aforementioned. After that, the impact of replacing cement and aggregate by C&D waste on the properties of UHPC is assessed. Experimental results reveal that benefits including reduction of early heat accumulation and auto-shrinkage, low energy consumption are generated when replacing up to 50% of cement and 19% of fine aggregate by C&D waste. In this case, a comparable compressive strength can be obtained. Additionally, the scanning electron microscope (SEM) analysis results also highlight improved microstructure owing to the addition of this solid waste. Conclusively, recycling of C&D waste as filling material in developing UHPC provides a promising view to develop a sustainable cement based material with advanced properties. Highlights • C&D waste with maximum size of 0.6 mm can be well used in UHPC. • C&D waste has no negative effect on the dense packing structure of UHPC. • The addition of C&D waste contributes a lower total heat release. • The capillary pores less than 20 nm deteriorate with the addition of C&D waste. • The UHPC with C&D waste is demonstrated as a cleaner construction product. [ABSTRACT FROM AUTHOR]

Abstract Concrete is one of the most widely used construction materials in the world. However, its sustainability is currently being challenged by the depletion of natural resources necessary to produce it (mainly due to the mining of aggregates) and the use of landfill space for its final disposition after service use. At the same time, the need for faster construction has encouraged the utilization of precast concrete structures, including pre-stressed elements. Recycled concrete aggregates could make the fabrication of concrete more sustainable; several studies demonstrate the technical feasibility of recycled concrete aggregates in Portland cement concrete for structural use. However, the sustainability of recycled concrete aggregates needs more reliable methodologies to assess it. This paper presents a stochastic simulation model of the precast fabrication process that considers obtaining materials, materials transportation, and precast elements production to evaluate the use of water, generation of CO 2 emissions, and costs incurred when using natural coarse aggregates versus recycled concrete coarse aggregates from several sources. The model is based on data from companies in the United States, Canada, and Chile. The results show that replacing natural coarse aggregates with recycled concrete coarse aggregates reduces CO 2 emissions and costs for the production of precast concrete elements, compared with the conventional system. However, water consumption is increased when recycled concrete coarse aggregates is used. Therefore, this research shows that the use of recycled concrete coarse aggregates for precast plants can be beneficial in terms of CO 2 emissions and cost in contexts where water is not a scarce resource. Graphical abstract Image 1 Highlights • Recycled Concrete Aggregates in precast elements reduce CO 2 emissions. • The cost of precast elements is reduced using Recycled Concrete Aggregates. • Recycled Concrete Aggregates in precast elements increase fresh water consumption. [ABSTRACT FROM AUTHOR]

Abstract Kaolin tailing sand (KTS) generated as a by-product from kaolin mining sorting, is usually disposed of by delivering to landfills. Effective utilization of KTS in concrete could be an attractive solution for the waste disposal with the value-added advantage of conservation of natural resources and as an eco-friendly alternative for natural river sand (NRS). This paper explored the potential feasibility of recycling KTS, as a substitute for NRS as a fine aggregate in producing cement mortar and concrete. Material characterization tests revealed that KTS possessed a high content of quartz and comparable physical properties to NRS. The fresh and hardened properties of mortars and concretes with varying KTS replacement combinations were determined. The experimental results revealed that the introduction of KTS reduced workability of the resulting mortar, attributed to the high water absorption of KTS particles. However, the introduction of KTS led to a reduction of expansion induced by alkaline silicic acid reaction (ASR) as well as an improvement in flexural strength and compressive strength of the resulting mortar, closely relating to the rough texture and angular nature of KTS. In the case of concrete test, KTS was superior to NRS in enhancing the compressive strength and splitting tensile strength, while decreasing the chloride ion penetration of concrete regardless of whether fly ash or slag was incorporated as a mineral admixture. It is noteworthy that for both mortars and concretes, specimens with 60% of KTS replacement by mass exerted the best mechanical performance. Beyond this ratio led to a slight reduction in mechanical strength, but still acceptable, mainly due to the relatively low inherent strength and depressed packing induced by the flaky shape of KTS particles. Highlights • KTS presented similar chemical and mechanical properties with NRS. • Use of KTS as a substitute for NRS improved compressive and splitting strength of concrete. • Introduction of KTS enhanced the cohesiveness and the durability of the concrete system. • Recycling of KTS as a construction material lessens the burden of land occupation for mining waste disposal. • Use of KTS as a substitute for NRS provides a sustainable alternative in minimizing the depletion of natural resources. [ABSTRACT FROM AUTHOR]

This paper presents a novel process to recycle the fine fraction of ground concrete waste as a construction binder. The fine fraction of ground concrete is rich of partly hydrated cementitious products, whose binding capacity is further enhanced by treatment at relatively moderate temperatures. The viability of the recycled binder has been demonstrated through the stabilisation of two earth building materials with kaolinitic and illitic clay fractions, respectively. At the microstructural level, X-ray diffractometry tests, mid-infrared spectroscopy tests and thermogravimetric tests have been performed to investigate the mineralogical composition and chemical bonds of the stabilising phase. At the macrostructural level, unconfined compression tests have been performed to evaluate the influence of stabilisation on the elastic modulus, peak strength and energy at failure. Results show that the addition of untreated recycled concrete to both earth types induces an average increase of 4% in apparent elastic modulus, 52% in compressive strength and 108% in failure energy relative to the unstabilised material. The addition of thermally treated recycled concrete induces an even larger increase of 30% in apparent elastic modulus, 93% in compressive strength and 187% in failure energy relative to the unstabilised earth. This is due to the higher hydration capacity of the thermally treated recycled concrete and the consequent formation of stronger inter-particle bonds. These preliminary results indicate a promising way to recycle concrete waste into earth stabilisers, which would ease difficulties associated to the disposal of demolition waste while, at the same time, improving the sustainability of current building practices. • A recycling protocol is proposed to valorise residual binding capacity of concrete waste. • Two earth materials were stabilised with untreated and thermally treated recycled concrete. • Mineralogical (micro-scale) and mechanical (macro-scale) tests were performed. • Recycled concrete induced formation of carbonate bonds within the earth materials. • Stabilisation with thermally treated recycled concrete produced best mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for developing sustainable building materials through Sequential Learning. Data sets with a total of 1367 formulations of different types of alkali-activated building materials, including fly ash and blast furnace slag-based concrete and their respective compressive strength and CO 2 -footprint, were compiled from the literature to develop and evaluate this approach. Utilizing this data, a comprehensive computational study was undertaken to evaluate the efficacy of the proposed material design methodologies, simulating laboratory conditions reflective of real-world scenarios. The results indicate a significant reduction in development time and lower research costs enabled through predictions with machine learning. This work challenges common practices in data-driven materials development for building materials. Our results show, training data required for data-driven design may be much less than commonly suggested. Further, it is more important to establish a practical design framework than to choose more accurate models. This approach can be immediately implemented into practical applications and can be translated into significant advances in sustainable building materials development. • Innovative approach to designing sustainable building materials using sequential learning. • Provides clear guidance for design process, can advance sustainable material development immediately. • Challenges data-driven materials dev. practices by prioritizing practical design frameworks over accurate models. • Significant reduction in dev. time, lower research costs, and straightforward predictions through sequential learning. • Large data sets of different types of alkali-activated building materials used for evaluation. [ABSTRACT FROM AUTHOR]

The punitive environmental legislation set by the global community has shifted the direction of research involve in construction industry towards the utilization of secondary raw materials in designing and constructing new structures. Rice husk (RH) is a by-product obtained from the rice mill process whose generation accounts up to 200 kg per ton of rice. The existing literature showed the vast potential of using rice husk ash (RHA) as a replacement for cement or as admixtures. This paper aims to critically review previous studies on RHA as a waste material. The utilization of this waste in concrete contributes to nurturing more sustainable and greener development, thereby lessen carbon footprints and minimize solid waste disposal issues. A state-of-the-art-review of literature on the use of RHA is presented in this paper. The impact of RHA on the properties of concrete such as workability, density, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, durability properties as well as its impact on sustainability are compiled. In addition, the technical results are complimented with the microstructural analysis evaluated through scanning electron microscopy (SEM). From the data garnered, it is postulated that RHA beneficially enhance the mechanical strengths coupled with improvement of resistant to sulfate and acid attack. This paper advances novel recommendations and directions for future research towards the application of green RHA-based construction products. [ABSTRACT FROM AUTHOR]

This paper comprehensively reviews the factors influencing the autogenous shrinkage and drying shrinkage of recycled aggregate concrete (RAC). Compared with natural aggregate concrete (NAC), RAC has a lower autogenous shrinkage because of the internal curing effect of recycled concrete aggregate (RCA). However, the internal curing efficiency of RCA is less than that of the lightweight aggregate because of its lower porosity and different pore structure. The drying shrinkage of RAC is larger than that of NAC, which is mainly caused by the mortar attached to the original virgin aggregate (OVA). Therefore, the methods of strengthening adhered or removing adhered mortar can reduce the drying shrinkage of RCA effectively. Some methods of strengthening adhered mortar are more environmentally friendly than removing adhered mortar. Finally, the existing autogenous shrinkage and drying shrinkage prediction models of RAC are discussed. The models obtained by seeing RCA as the two-phase composite has a higher degree of accuracy. This paper can support a better and more comprehensive understanding of the autogenous and drying shrinkages of RAC and how to reduce the cracking risk of RAC, which provides a theoretical base for future research and applications of RAC in the construction industry. [ABSTRACT FROM AUTHOR]

This paper addresses a development for a novel sustainable Ultra-High Performance Concrete (UHPC) incorporating lead-zinc tailings. The modified Andreasen & Andersen particle packing model is utilized to achieve a densely compacted cementitious matrix and the lead-zinc tailings are utilized to replace cement by 10%, 20%, 30% and 40% (wt.), while the packing densities of all the designed UHPC mixtures are almost keep the same. Then, the impact of added lead-zinc tailings on the fresh and hardened behaviors of the developed UHPC is investigated. The obtained experimental results reveal that the workability, compressive strength and chlorine anion penetration resistance of the UHPC decrease with the addition of lead-zinc tailings. However, it is possible to develop self-compacting UHPC with up to 30% replacement of cement by lead-zinc. Moreover, it is noteworthy that the addition of lead-zinc tailings could significantly decrease the early autogenous shrinkage of UHPC, which is beneficial for its microstructure development and application. Additionally, the leaching toxicity of heavy metals for this developed sustainable UHPC is far lower than that of the National Standard of China. The ecological evaluation demonstrates that replacing cement by lead-zinc tailings in the production of UHPC can significantly reduce its environmental impact, which provides a promising view for developing and applying a novel cleaner construction product with advanced properties. [ABSTRACT FROM AUTHOR]

Fly ash-based geopolymer binders have been identified as one of the alternatives to the Ordinary Portland Cement (OPC), which qualify the criteria of green construction material. In the process of enhancement of the properties of geopolymer; engineered geopolymer composite (EGC) is a recent development that is classified as the high-performance fiber reinforced geopolymer matrix. The philosophy of the development of EGC is to achieve high compressive strength and ductility. In this paper, statistical models are developed to predict the mechanical and post-cracking properties of EGC using Response Surface Methodology (RSM). In this regard, effects of three principal variables; molarity of sodium hydroxide, sodium silicate to sodium hydroxide ratio, and curing temperature on the properties of fresh and hardened EGC (setting time, compressive strength, elastic modulus, flexural strength, flexural toughness, ductility index, tensile strength, tensile first crack strength and tensile strain capacity) were investigated. All models are found significant because, and the difference between predicted R 2 and adjustable R 2 was found less than 0.2. The optimized mixture proportion was assessed using multi-objective optimization technique as discussed in the RSM literature. Finally, an experimental program was performed to validate the optimized mixture proportion. The predicted and experimental results were found in a close agreement because the variation between the predicted and the experimental results was obtained less than 5%. The proposed method can be performed for any objective value of the EGC property with desirability almost equal to one, improving the yield, the reliability of the product and the processes. [ABSTRACT FROM AUTHOR]

Coal fly ash (FA) is abundant in countries that use steam coal for power production. The resultant FA is Class F FA (<20% CaO, Al 2 O 3 + SiO 2  > 70%, <6% Loss on Ignition) and can be used as an excellent scrubber and fixation reagent for acidic wastes containing toxic trace elements. In Spain, less than 50% of the abundant FA is currently being used. This paper reports on the potential use of Class F FA as a neutralization and fixation reagent for the hazardous sludge waste of the phosphate industry. Several analytical techniques (ICP-MS, ICP-AES, SEM-EDX, and XRD), and leaching experiments (EN12457-2) were used for this study. The results identify the best FA/waste ratios for full neutralization and fixation. Furthermore, adding a high calcium carbonate material prevents the excessive leaching of As, Mo, and Se, and facilitates full neutralization and fixation. Furthermore, the use of a safe aggregate (produced by mixing coal phosphate waste with fly ash and/or bivalve shells) as a partial substitute for sand improves the quality of concrete for civil engineering projects and is environmentally safe. [ABSTRACT FROM AUTHOR]

As construction increases through a rise in development in Vietnam, the environmental performance of recycling construction and demolition waste is not well documented. This paper addresses this lack of knowledge, by mapping the current recycling system and estimating recycling performance of a key component in construction and demolition waste in Vietnam, concrete. Primary data were collected directly from six Vietnamese construction enterprises involved in the life cycle of construction and demolition waste management. The results indicated that potential net environmental benefits exist for all impact categories examined if a mechanised plant were considered. Moreover, construction demolition waste may then be used for more permanent applications such as building foundations and in new building materials. The results confirm benefits to technological advancements in concrete recycling in the construction demolition waste sector. Fostering investment and interest in such strategies could be achieved by imposing clear and consistent construction demolition waste classifications, establishing clear lines of responsibility, and coordinating activities amongst key stakeholders to promote the benefits of concrete recycling. These findings consolidate the need of further research in Vietnam and other developing nations, where more detailed life cycle inventory development and stakeholder engagement could help. Then better environmental outcomes through the concrete recycling management may be delivered. [ABSTRACT FROM AUTHOR]

Waste from Electric and Electronic Equipment is one of the most rapidly developing waste streams worldwide. The aim of this paper is to investigate and evaluate the reuse methods of glass derived from electric lamp recycling. A detailed record of the various reuse methods of recycled glass is given, focusing on the use of glass in concrete industry, ceramic building materials and asphalt. Also, the necessary prerequisites, in order to produce final products within specifications, are highlighted for each case. The glass-cullet used in the research was produced in Oikokiklios S.A. lamp recycling company, where lamps are collected for recycling from all over Greece. Moreover, in order to investigate each case study, production data of three different companies (asphalt, cement, bricks) within close distance from Oikokiklios S.A. were used. As a result, three scenarios were studied in order to describe the glass-cullet reuse options and examine the benefits of introducing glass in each production process. More precisely, each scenario was evaluated concerning energy, environment and economic impact. The main conclusion of the research was that introducing glass is beneficial for all the above production processes leading to an important reduction of the released carbon dioxide emissions and energy consumption. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of incorporating slag waste (Ground Granulated Blast Furnace Slag; GGBS) as cement replacement in high early strength concrete. GGBS was used in various replacement ratios and resulting properties of the developed concretes were evaluated. Compressive strength, heat of hydration and shrinkage were determined for evaluating hydration attributes while chloride penetrability and carbonation resistance were investigated for studying the durability-related characteristics of the resulting concretes. The optimum ratio of GGBS as SCM has been determined, in this study, as 30% at which there is merely an average strength decline of 11% while reducing the total carbon dioxide emissions by 30%. Similarly, at this replacement level, the decreased chloride ion penetrability (15%) and higher carbonation resistance (3%) further encourage its use in precast concrete incorporating (HESC). Finally, the beneficial effects of using slag waste in concrete were quantified by determining associated CO 2 emissions. It is concluded that slag incorporation in concrete significantly reduces the CO 2 emissions, (up to 68%) depending on the cement replacement level, thus promoting green construction and sustainable development. [ABSTRACT FROM AUTHOR]

Natural aggregates are non-renewable resources used in excess of 40,000 Mt annually to produce concrete. Artificial aggregates from industrial by-products can be produced as environmentally friendly alternatives. The cold bonding method to produce aggregates uses much less energy compared to the sintering method. This paper reports the results of an experimental investigation on phase characterizations, physical properties and strength of environment-friendly cold-bonded fly ash lightweight aggregates. High calcium fly ash was used as the lightweight material, whereas Portland cement or calcium hydroxide was added as the binder with a small amount in the range of 5–15% by weight to produce lightweight aggregates. Increased density and enhanced crushing strength with low water absorption were found in the fly ash aggregates with the addition of Portland cement or calcium hydroxide. This is due to the occurrence of both hydration and pozzolanic reaction when compared with the fly ash mix. Furthermore, the thermogravimetry results indicate that calcium silicate hydrate, calcium hydroxide, and calcium carbonate phases were observed in all the mixes, while ettringite was also present in fly ash lightweight aggregates incorporated with Portland cement mixes. In this research study, the optimum content of Portland cement and calcium hydroxide were observed to be 10% and 5% by weight respectively. The highest crushing strength was obtained from fly ash lightweight aggregates incorporated with Portland cement at 10% by weight. [ABSTRACT FROM AUTHOR]

The paper aims to study the effects of LSSW fillers on different properties of foamed concretes (also known as cellular lightweight concretes (CLCs)) with a wide range of concrete densities 650–1200 kg/m 3 . The LSSW fillers was collected from the western end of the Vindhyan range of India. A unique mix-design methodology with eight design steps was empirically-cum-numerically derived for CLCs, based on specifying targeted green or plastic density as primary criterion, which is an unexplored area till date. Cement to NRS ratio was kept as 1:1.35 for the development of CLCs. NRS was replaced by LSSW fillers, ranging from 25% to 100% with the increment of 25% in NRS fractions. The natural protein based foaming agent used in this study, was in the ratio of 1:20 parts of water. In total, fifteen trials were cast for five phases of each series using cement as main binder. Each phase was based on the variation of water/cement (w/c) ratio, foaming agent/water (fa/w) ratio and NRS/LSSW ratio. Moist curing was adopted for 3, 7 and 28 days. Experimental studies include compressive strength (CS) with performance factor (ratio of CS (in Pa) to oven dry (OD) density (in N/m 3 )), consistency, achieved density ratio, thermal properties, X-ray diffraction, scanning electron microscopy and image analysis. The results indicated that incorporation of LSSW fillers up to 50% replacement of NRS into CLCs; enhanced CS and corresponding performance factor. It was found that maximum PF c.28d was 382 and 319 at w/c ratio 0.86 for block of density 1002 kg/m 3 and 819 kg/m 3 , respectively. For these two mixes, filler effect as well as nucleation effect was dominant than other mixes. LSSW fillers did not show any pozzolanic, hydraulic or latent hydraulic properties. Thus, use of LSSW is not only beneficial to the concrete industry, but also is friendly to the environment promoting sustainable development. [ABSTRACT FROM AUTHOR]

Coal Bottom Ash (CBA) is one of the widely-produced residues of coal incineration in thermal power plants. The annual extraction of such a huge amount of waste needs a massive transfer field, which constitutes a threat to the environment. However, the utilization of such residue as a fine aggregate in concrete can be an environmentally-friendly opportunity. Hence, the main purpose of this paper is to evaluate the microstructure and mechanical properties of the usage of BA as a fine aggregate replacement in mortar mixtures. It is observed that BA has a reactive fraction with pozzolanic characteristics. This provides stronger mortar when a medium volume of the material (up to 40%) is substituted. In addition, the CBA based mixture can be classified as lightweight concrete. The compressive strength value of the specimen using 40% CBA at 56 days was 55 MPa, which reached the same strength limit of control mortar mixture. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of investigations of hybrid concrete containing scale and granulated lead–zinc slag wastes as substitutes for sand. Specifically, scale and granulated lead–zinc slag wastes are completely substituted for natural sand in concrete. The aim of this study was to investigate the effects of these waste materials on gamma radiation shielding and on the compressive strength properties of concrete. The linear attenuation coefficient (μ, cm −1 ) and compressive strength of the samples were measured experimentally and calculated, and the experimental values were subsequently compared with those of conventional concrete. The results clearly showed that hybrid scale waste/granulated lead–zinc slag waste concrete (Sc/Glzs-C) has better radiation shielding and compressive strength properties than conventional concrete. An additional objective of this study was to calculate the thickness of the hybrid concrete shield to be used instead of conventional concrete. The results showed that the produced concrete demonstrates better radiation attenuation properties with thinner thickness compared to conventional concrete. As a result, the new concrete containing scale waste and granulated lead–zinc slag waste is suitable for gamma radiation attenuation. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the mix design and properties evaluation of an eco-friendly Ultra-High Performance Concrete with recycled coral based materials. The modified Andreasen & Andersen particle packing model is utilized to achieve a densely compacted cementitious matrix. Micro-coral sand and coral sand are used to replace cement and sand, respectively. By adopting the Response Surface Method, the effect of blending micro-coral sand and coral sand on the mechanical properties of the designed UHPC is analyzed, aiming at a maximum use of recycled coral based materials. After that, the individual and interactive effects on the durability, autogenous shrinkage and ecological properties of the designed Ultra-High Performance Concrete are evaluated. The results show that the addition of individual recycled coral based materials can improve the workability and reduce the autogenous shrinkage of Ultra-High Performance Concrete without decreasing the durability of Ultra-High Performance Concrete. Compared to the mixture with micro-coral sand, the one with coral sand has less autogenous shrinkage and better durability. Moreover, the designed Ultra-High Performance Concrete with 15% micro-coral sand and 30% coral sand together show the best properties in this study. Additionally, the ecological evaluation demonstrates that the designed Ultra-High Performance Concrete with recycled coral based materials has relatively low environmental impact, which is promising to generate a cleaner product in the near future. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregates from rubble and demolition waste in combination with cementitious additions in concrete has several practical, ecological and economic advantages by reducing carbon dioxide emissions, reducing the excessive consumption of natural resources and contributes to a cleaner production of concrete. In this paper, rheological, mechanical and durability properties of self-compacting concrete (SCC) using recycled concrete aggregates and natural pozzolan (PZ) are evaluated. Four concrete mixes were manufactured, by varying the level of substitution by weight of both coarse and fine natural aggregates by fine and coarse recycled aggregates. The substitution levels were fixed at 0%, 50%, 75% and 100%. The cement was also partially replaced by weight from 5% to 25% by natural pozzolan. The performance at the fresh state of SCC was discussed using the following tests (slump test, J-Ring, flow time test V-funnel, L-Box and sieve stability tests). Compressive strength was measured at the ages of 7, 28, 56, 90 and 120 days. Considering the importance of studying the durability of SCC in aggressive environments, the behavior of chloride ions diffusion was analyzed using the Fick’s second law and the loss in mass after immersion in sulfuric acid (H 2 SO 4 was also investigated). The results indicate the possibility of using 50% recycled coarse and fine aggregates for performing self-compacting concrete. The NSCC and RSCC mixtures containing PZ develop a comparable compressive strength to mixtures without PZ at 120 days. The incorporation of 15% and 20% PZ in NSCC and RSCC decreased the penetration depth of chloride ions to 50% and also decreased the mass loss under sulfuric acid attack. [ABSTRACT FROM AUTHOR]

Fly ash (FA) and recycled coarse aggregate (RCA) have been extensively studied, aiming to improve the sustainability of concrete. The biomineralisation method has also been researched to enhance the performance of concrete. However, introducing FA and RCA may decrease the strength of concrete, and the biomineralisation method may create extra environmental impact (EI) due to the production of bacteria and corresponding chemical agents. It is hard to directly judge the influence of these methods on the sustainability of concrete. This paper proposes to explore the sustainability of concrete with FA, RCA, and biomineralisation methods by life cycle assessment. Six scenarios were established, and Six EI categories of the six scenarios were quantified. The quantified EI values considering their corresponding strength were obtained and compared. The results showed that: using FA decreased EI, using RCA showed a limited effect on decreasing EI, the biomineralisation method significantly decreased EI, and using the treated RCA increased EI due to its high consumption of chemical agents in the treating procedure. In summary, biomineralisation enhanced FA concrete performance is recommended to substitute traditional concrete widely after comprehensively comparing sustainability, workability, strength, and durability. Finding more sustainable calcium sources and nutrition can further improve its sustainability. [ABSTRACT FROM AUTHOR]

Waste phosphogypsum (PG) has been proved recyclable in producing qualified aggregate and binder for concrete, with a substitution rate of above 70% in aggregate and 40% in binder. Therefore, it is feasible to use phosphogypsum with high content as recyclable aggregate and binder. This paper provides a detailed description of high-content phosphogypsum-based concrete (HPGC) preparation process, together with evaluation of mechanical properties, impurity stability, and radioactivity of the concrete. The prepared HPGC is heavier than typical lightweight concrete, with reduced mechanical properties and qualified leaching performance. The compressive strength of the concrete prepared in this experiment at 28d was generally in the range of 18 MPa–40 MPa. Upon significant drop in compressive strength, critical PG content in coarse aggregate is around 80%, while the content in binder is about 60%. The concrete makes a good solidification of waste PG, with release of hazardous matters acceptable according to local building codes. Featuring a substitution rate of above 800 kg/m3, the PG concrete technology would find large-scale applications in recycling massive phosphogypsum waste. [Display omitted] • The fresh bulk density of HPGC was between 2140 and 2200 kg/m3. • The 28-d compressive strength of HPGC was generally in the range of 18Mpa–40Mpa. • The modulus of elasticity of HPGC lower than that of typical concrete. • HPGC shows good solidification capability for hazardous matters. • Consumption of phosphogypsum exceeds 800 kg per 1 m3 of HPGC produced. [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]

The consumptions of artificial light especially in urban area leads to carbon footprints and global warming. The introduction of light-transmitting concrete (LTC) enables light to be transmitted through opaque concrete and reduces building energy consumptions. The aesthetic value and the light transmittance properties of LTC attracted the attention among researchers on the investigations and development of this type of concrete. However, the application of LTC in construction industry is still immature due to several reasons including intensive labour cost and complexity of the manufacturing process, insufficient reliable data on the mechanical properties and durability, as well as the lack of design modelling. This paper reviewed the types of LTC as well as the research findings regarding the mechanical properties, durability, microstructure analysis as well as the light transmittance properties. This paper also critically discussed the assessment, design modelling, theoretical studies and cost analysis of LTC based on various parameters. LTC was proven to reduce the total energy consumptions of a building significantly. More investigations are required to examine the light transmitting properties and durability of LTC especially when exposed to the various environmental conditions. • Detailed review on the types of LTC, its properties, applications and development. • Critical discussion on mechanical strength and light transmittance of LTC. • Simulation modelling and theoretical studies of LTC are reviewed. • Manufacturing cost and total energy expenditure of LTC are discussed. • Suitability and durability of LTC should be more focused in future research. [ABSTRACT FROM AUTHOR]

In recent years, with the aim of lowering the environmental impact of concrete, the partial replacement of cement in concrete with fly ash (FA) and ground granulated blast furnace slag (GGBS) has received significant attention. This paper presents the first experimental study on the properties of concrete containing ternary binders with high volume Class-F FA and GGBS partially replacing cement up to 90%. A total of 15 batches of concrete were manufactured with binary and ternary binders based on FA, GGBS, and cement. Experimental tests were performed to establish the density, workability, compressive strength, elastic modulus, flexural strength, splitting tensile strength, and water absorption of different mixes. The results indicate that the compressive strength of concrete containing FA decreases significantly with an increase in the FA content from 50% to 90%. The concretes containing GGBS at up to 90% cement replacement exhibit a similar compressive strength to that of conventional concrete after 28 days. It is found that ternary mixes with a 70% replacement ratio and relative FA to GGBS ratio ( Ψ ) of 1:2, and those with a 50% replacement ratio and Ψ of 1:1 develop a similar 28- and 90-day compressive strength to that of conventional concrete. A further increase in the replacement ratio and Ψ results in a decrease in the compressive strength. The results also show that GGBS mixes develop a slightly higher 28-day elastic modulus than that of conventional concrete mix. Although the elastic modulus of FA and the majority of the ternary mixes is lower than that of conventional concrete, ternary mixes with 70% ( Ψ of 1:2) and 50% ( Ψ of 1:1) replacement ratios develop a similar elastic modulus to that of conventional concrete. It is observed that an increase in the FA and GGBS content, respectively, results in a significant increase and moderate decrease in the water absorption of concrete. All ternary mixes with up to 90% cement replacement exhibit lower water absorption than conventional concrete mix. These highly promising findings suggest that the technology used in this study can provide an attractive avenue for high volume use of FA and GGBS in concrete with the possibility of significantly reducing its environmental impact. [ABSTRACT FROM AUTHOR]

This paper critically compares methods for allocating the environmental impact of fly ash production in a Life Cycle Assessment (LCA) study of concrete, based on an evaluation of the variability in LCA outcomes. LCA models of concrete containing 10, 25 and 50% fly ash as cement replacement are created based on four allocation scenarios: i) Baseline- No Allocation, ii) Mass Allocation, iii) Economic Allocation, and iv) Disposal Avoidance. LCA results are generated and compared to the Baseline scenario. A sensitivity analysis was also conducted. The results show that concrete containing increasing percentages of fly ash have lower environmental impacts. The environmental impacts associated with for the Economic Allocation and Mass Allocation scenarios are higher than those determined from the Baseline and Disposal Avoidance approaches and for all mix designs. This is due to the allocation of environmental impacts from coal mining, preparation and combustion processes by both the Mass Allocation and Economic Allocation scenarios which reduces the normalized green indicator compared to the baseline scenario. Therefore, the results from the analysis indicate that increasing the fly ash content in concrete can yield a concrete with lower environmental impacts but the extent of the reductions strongly depends on the allocation scenario that is applied. [ABSTRACT FROM AUTHOR]