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To improve the defects of low electroosmosis efficiency in the later stage and high energy consumption of conventional vacuum preloading combined with electroosmosis, the vacuum preloading-stepped electroosmosis method (VP-SEO) with prefabricated horizontal drain (PHD) was proposed for dredged sludge in this paper. In the test, waste concrete fine aggregate was used as the horizontal drainage cushion to alleviate the clogging of the PHD. The results showed that compared to vacuum preloading combined with electroosmosis (VP-EO), more drainage channels throughout the soil were produced after VP-SEO treatment, and VP-SEO could maintain a higher drainage efficiency in the later stage of treatment with improved final drainage and consolidation. The sludge treated by VP-SEO showed a significant increase in vane shear strength and a reduction in water content. Furthermore, the water loss and shrinkage of the soil surface after VP-SEO treatment were more uniform than that of VP-EO treatment, and the electroosmotic energy consumption and anode erosion were also lower. This study provides an effective improvement scheme for solidifying sludge with a high water content by conventional vacuum preloading combined with electroosmosis method. • The effectiveness and advantages of VP-HSEOA for sludge are explored by the model tests. • The sludge treated by VP-HSEOA can form a large number of drainage channels throughout the soil. • After VP-HSEOA treatment, water loss and shrinkage of the surface soil are more uniform. • VP-HSEOA has the advantages of deep reinforcement, low energy consumption, and less anode corrosion. [ABSTRACT FROM AUTHOR]

After the CO 2 mineralization reaction of cement-based materials, on the one hand, the microstructure of the materials is improved, and the hardening performance is improved. On the other hand, CO 2 is effectively stored and good environmental benefits are generated. This paper reviews the thermodynamic and kinetic models of mineralization of cement-based materials. Secondly, the variation of pore structure and the durability of cement-based materials after CO 2 mineralization were reviewed. Then, the factors influencing mineralization degree in ordinary Portland cement system, non-hydrated silicate system, active magnesia system and recycled concrete waste were reviewed. On this basis, the fundamental problem of limiting the degree of mineralization of cement-based materials was identified, i.e., the CO 2 mineralized product layer limits the dissolution of Ca2+ and the diffusion of CO 2. • The present paper reviewed the existing methods for evaluating the mineralization degree of cement-based materials and applicability. • The factors affecting the mineralization degree of each cement system are reviewed. • Two possible solutions to improve the mineralization degree of cement system are proposed. [ABSTRACT FROM AUTHOR]

Compared to cast-in-situ construction, prefabricated construction reduces the generation of construction waste; however, construction waste cannot be entirely eliminated through prefabrication and can be generated at each stage of its life cycle. This paper generates a system dynamics model, comprising two causal-loop diagrams and one stock-flow diagram, to simulate the effectiveness of policies on decarbonizing prefabricated concrete building waste. The model can predict the annual and total construction waste, along with the associated carbon emissions, under different policy scenarios in China by 2030. This paper focuses on prefabricated concrete buildings in China, with specific attention to the wastage of concrete, bricks, mortar, and metal. In single-factor scenario simulations, increasing landfilling fee is the most effective policy for waste decarbonization, potentially reducing carbon emissions by 31%. Increasing prefabrication rate and enhancing regulation degree at the design phase of prefabrication can directly reduce prefabricated building waste generation, subsequently resulting in an 18% and 7% carbon emissions reduction. Multi-factor scenario simulations demonstrate that the simultaneous application of all four policies is most effective, achieving a 44% reduction in carbon emissions. This research establishes a theoretical framework for prefabricated concrete building waste management and provides the Chinese government with practical insights on optimizing policies for waste decarbonization in the dynamic landscape of prefabrication. • This paper develops the prefabricated building waste generation and disposal systems. • The model predicts the construction waste and associated carbon emissions by 2030. • Raising landfill fee is an effective policy for decarbonizing construction waste by 31.06%. • Prefabrication rate reaching 100% can reduce 18.04% of carbon emissions from waste. • Applying all policies is most effective, achieving a 44.34% carbon emissions reduction. [ABSTRACT FROM AUTHOR]

This paper deals with the possibility of partial replacement of aluminate cement in refractory concretes with waste material from calcined shale production. The waste "metashale" was combined with super-reactive alumina and boehmite powder in order to design a low-cement binder for high-temperature-resistant composites. Designed binders were studied at ambient temperature as well as after exposures to temperatures of 400 °C, 1000 °C and 1400 °C. Firstly, blended binder-based pastes were observed in an electron microscope to determine structural changes in the material, while XRD and DSC characterization was performed as well for determining phase compositions and their changes. Metashale application lead to the creation of different C-A-S-H phases, which were found to be contributing to the higher temperature resistance of designed binders. The further monitored parameters were basic physical and mechanical properties and thermal strain. Despite that the application of metashale caused an increase of porosity at an ambient temperature, the designed low cement binder showed more stable properties during the temperature exposures. Considering the reached properties and the environmental aspects, the most promising mixture was found to be the one, with metashale and cement in a 60:40 ratio. This binder was used to prepare refractory. Because it reached substantially better performance compared to the pure calcium aluminate-based composite, the designed binder proved its applicability. [ABSTRACT FROM AUTHOR]

Concrete waste recycling has been considered an efficient way to reduce environmental impacts in the end-of-life treatment of construction waste materials compared to traditional landfilling. Developing advanced and sustainable technologies in recycling processes grows with significance for enhancing the performance of recycled products. However, there is still a lack of systematic analysis and comparison of the studies adopting life cycle assessment (LCA) to examine environmental potentials of varied concrete waste recycling processes. This paper identifies up-to-date enhancement techniques for recycling concrete waste and provides a comprehensive analysis of selected cases that evaluated environmental impacts of recycling processes with LCA approaches. A total of 22 representative case studies were compared systematically using the key parameters involved in four major steps of LCA framework. Critical issues were identified from previous research studies. It is of great importance to standardize the rules for determining system boundaries and functional units, validate foreground and background inventory databases, and improve the utilization of combined uncertainty and sensitivity analysis. A specialized LCA computational tool for concrete waste recycling is in high demand for industrial decision-makers and practitioners. The proposed system boundaries of advanced recycling technologies and conceptual framework of platform development highlight potential directions for future research. [Display omitted] • A systematic comparison from perspectives of the LCA framework has been adopted on the 22 case studies that involve detailed processes of concrete waste recycling. • Standardized rules for defining system boundaries and functional units are expected to be developed for enhancing the comparability and quality of LCA outcomes. • The availability, integrity, and authenticity of the LCI databases with primary datasets are of great importance in obtaining accurate results of the assessment. • A conceptual framework for constructing a semi-developed LCA computational tool specialized for concrete waste recycling is proposed and its feasibility should be investigated in further studies. [ABSTRACT FROM AUTHOR]

• The feasibility of waste concrete powder-based geopolymer reclaimed concrete was verified. • Carbonation depth, uniaxial compressive strength and dynamic elastic modulus of under different carbonation time were studied. • The changes of mineralogical phases and micromorphology characteristics of reclaimed concrete were analyzed. • The deterioration mechanism of carbonization and freeze–thaw-carbonization of reclaimed concrete was revealed. • It makes it possible to achieve the complete recycling of waste concrete. In order to realize the complete recycling of waste concrete, this paper used waste concrete powder (WCP), fly ash (FA) and granulated ground blast furnace slag (GGBS) as raw materials to prepared geopolymer, mixed with recycled waste concrete aggregates to prepare waste concrete powder-based geopolymer reclaimed concrete (WCPGRC). The WCPGRCs cured for 28 days were carried out carbonization test (group C-28d) and freeze–thaw cycle carbonization test (group DC-28d), and the WCPGRCs cured for 84 days were carried out carbonization test (group C-84d) to study their durability. The carbonation depth, uniaxial compressive strength (UCS) and dynamic elastic modulus (DEM) of three groups of WCPGRC under different carbonation times and different freeze-thawed-carbonation times were tested respectively. The mineralogical phases and micromorphology characteristics of WCPGRC before and after carbonization and freeze-thawed-carbonization were characterized through XRD and SEM. The results show that: (1) The carbonation depth of WCPGRC in groups C-28d, DC-28d and C-84d all increased with the carbonation time and freeze-thawed-carbonation time, and the maximum carbonation depth was 4.4 mm, 4.9 mm and 4.1 mm, respectively. (2) The UCS of C-28d increased by 9.7% from 39.11 MP to 42.56 MPa with carbonization time; The C-84d increased by 4.6% from 40.51 MPa to 43.31 MPa; The DC-28d first increased and then decreased with the increase of freeze–thaw-carbonization time, and the maximum UCS was 40.51 MPa on the 28th day. (3) The DEM of C-28d increased by 16.5% from 17.22GPa to 20.06GPa with carbonization time; The C-84d increased by 7.6% from 20.05GPa to 21.57GPa; The DC-28d first increased and then slightly decreased with the increase of freeze–thaw-carbonization time, the maximum DEM was 18.41 GPa on the 14th day. (4) Prolonging curing time increased the UCS and DEM, while freeze–thaw decreased the UCS and DEM of WCPGRC. (5) After the carbonization of WCPGRC, new carbonate crystals and geopolymer gels were generated, continued to fill the voids and cracks, making the overall structure denser. However, after the freeze–thaw-carbonization, the freeze–thaw cycle inhibited the geopolymerization, and the freeze–thaw damage intensified the carbonization, which reduced the structural integrity of WCPGRC. [ABSTRACT FROM AUTHOR]

The recycling utilization of waste foundry sand (WFS) in concrete is a promising approach to solve the problems of solid waste treatment and the scarcity of natural resources in construction sector. To further evaluate the durability of WFS-incorporated concrete, this paper conducts an experimental investigation and numerical analysis of the water absorption behavior of lightweight aggregate concrete (LWAC) incorporating with various WFS content after exposure to high temperature. The effects of different temperature levels (20°C, 100°C, 200°C, 300°C, 400°C) and WFS substitution rates (0 %, 25 %, 50 %, 75 %, 100 %) on the water absorption properties of LWAC-WFS are experimentally investigated to indirectly characterize the degree of high-temperature damage of concrete. The results showed that the water absorption properties can be used as the evaluation index of LWAC-WFS durability after high temperature. The addition of WFS into LWAC significantly increased the amount of water absorption. After exposure to high temperature, the amount of water absorption of LWAC-WFS was increased with the temperature level. The water absorption properties of LWAC-WFS were increased due to an increase in internal crack connectivity caused by thermal strain and thermal incompatibility of multiphase composites after exposure to high temperature. Interestingly, the specimens with 50 % WFS substitution showed better resistance to water absorption after exposure to high temperatures than that of the control group. Based on the unsaturated flow theory and heat conduction theory, a prediction model of water content distribution in the high-temperature damaged LWAC-WFS was established, and the water absorption behavior was further analyzed using COMSOL finite element software. In addition, the water penetration depth of LWAC-WFS with varying WFS replacement ratios at various time points (t =10, 20, 40, 80, and 100 min) after exposure to 20, 200 and 400°C were predicted. The cumulative mass curve of water absorption calculated by the proposed prediction model was in good agreement with the obtained testing results. The visual numerical results can accurately and visually show the spatial distribution of relative water content in LWAC-WFS after exposure various high temperature. The proposed approach of this study could provide a fundamental basis for further investigation on the unsaturated transport of corrosive medium in damaged LWAC. • Water absorption tests of LWAC-WFS after exposure to high temperature were conducted. • Effect of temperature levels and WFS substitution rates on water transport was analyzed. • Prediction model of water content distribution in damaged LWAC-WFS was developed. • Mesoscale numerical analysis on water absorption of damaged LWAC-WFS was explored. • LWAC-WFS50 showed the better resistance to water penetration for all temperature levels. [ABSTRACT FROM AUTHOR]

Based on the thermal activation method, utilizing fine particles of waste concrete to prepare low-carbon recycled cement (RC) is currently one of the research hotspots. Based on existing literature research results, this paper identifies four calcination temperature conditions (120, 450, 750, 1000 ℃) and uses replacement rates of 10 %, 30 %, 50 %, 70 %, and 100 % of RC to replace ordinary Portland cement (OPC).The main physical properties, hydration characteristics, mechanical properties, and microstructure of RC are studied. The study elucidated the influence of RC thermal activation temperature, replacement rate, fineness, and age on its hydration characteristics, mechanical properties, and microstructure, establishing a macro-micro correlation for RC and revealing the mechanism of improvement in mechanical properties of thermal-activated RC. The research indicates that in the initial stage of hydration, RC exhibits a relatively fast hydration rate, with higher initial total heat release than OPC. Hydration products include internal hydration products (formation of C-(A)-S-H gel) and external hydration products (formation of plate-shaped AFm). Furthermore, RC exhibits a faster hydration rate at a hot activation temperature of 750°C, with CH and C-S-H gel transforming into the highly hydrated α´L-C 2 S, forming a denser microstructure at an early stage. Moreover, at a replacement rate of 30 %, the compressive strength of cement mortar reaches its optimum at 28 days, achieving 13.81 MPa, equivalent to 60.7 % of OPC cement mortar, with a 66.67 % reduction in carbon emissions. Microstructure analysis reveals that when the temperature reaches 1000°C, excessive combustion of RC leads to the formation of low-reactivity C 2 AS and β-C 2 S, resulting in a decrease in macroscopic mechanical properties. Additionally, increasing the fineness of RC significantly enhances its rehydration capability, especially as the age increases. This study is of great significance for the preparation of green cement-based composite cementitious materials. • Studied the impact of thermal activation, substitution rate, and fineness on RC's mechanical properties. • The hydration characteristics of RC under different thermal activation temperatures were discussed. • The microstructure and mechanism analysis of thermally activated RC were explored. • The carbon emissions of RC at different thermal activation temperatures were compared to identify the optimal temperature. [ABSTRACT FROM AUTHOR]

Combining the two advantages of mitigation of dependence on cement and natural sand resources and recycling waste concrete material, the utilization of recycled concrete powder (RCP) and recycled fine sand (RFS) to produce geopolymer concrete is of great value. However, the insufficient compressive strength and inherent brittleness of the existing RCP or RFS geopolymer concrete hampered its application. This paper aims to develop a high-performance engineered geopolymer composite (EGC) by maximizing the recycle amount of RCP and RFS. The effects of RCP and RFS on the physical, mechanical, and microscopic properties of EGC were investigated. The results indicated that, the less reactivity of RCP decreased the amount of gel products and compromised the strength development, while favored the multi-cracking behavior and the robust ductility. RFS showed a stronger interfacial bond with paste than quartz sand, compensating the degradation of strength driven by RCP and marginally affecting the tensile strain capacity. The developed EGC incorporating 50% RCP and 100% RFS possessed an 84 MPa compressive strength, 7.4 MPa tensile strength, and 8.1% tensile strain, which are at the highest level among the existing RCP or RFS geopolymer concretes. The main products included the coexistence of calcium aluminosilicate hydrate and alkali aluminosilicate (C(N)-A-S-H) gel and layered double hydroxide (LDH). The energy- and carbon-reduction were 16% and 57%, respectively, compared to the M45-ECC.The current findings prove the feasibility of utilizing high amounts of recycled materials to produce high value-added concrete. [ABSTRACT FROM AUTHOR]

The use of cement in construction causes large amounts of CO 2 emissions into the atmosphere. Moreover, the use of large amounts of natural coarse aggregate causes environmental damage, and the availability of such natural aggregate is also depleting. The present experimental study explores and optimizes the impact of various parameters on the fresh, mechanical, and durability properties of recycled waste concrete coarse aggregate (RWCA)-based geopolymer concrete (GPC) in combination with ground-granulated blast furnace slag (GGBFS) and fly ash (FA) using the Taguchi-Grey Relational Analysis Method (TGRAM). The coarse aggregates in GPC were fully replaced with RWCA produced by crushing waste concrete. The effects of FA inclusion (%), Na 2 SiO 3 /NaOH ratio (SS/SH), molarity of NaOH (SH), dosages of superplasticizer (%), and alkaline solution to binder (Al/Bi) ratio are investigated under ambient curing conditions. The obtained maximum compressive strength and split tensile strength along with minimum water absorption of GPC at 28 days were 67.90 MPa, 3.85 MPa and 2.92 % respectively. The microstructural studies of GPC having low, high, and optimal strength are carried out using XRD, FE-SEM, and EDAX analysis. These studies confirmed the presence of calcium-based hydration products such as CSH and N(C)ASH, which makes the matrix of optimized GPC more compact. • This paper explores and optimizes the mix composition of GGBFS-FA based GPC using TGRAM. • FA inclusion had a dominant effect on flow value, mechanical strength, and water absorption of GPC. • Microstructure analysis shows the presence of N-(C)-S-H and C-S-H-based hydration products in GPC. • Confirmation test on optimized GPC confirmed competence of TGRAM. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the compressive behavior of eco-friendly concrete containing glass waste (GW) and recycled concrete aggregate (RCA). In all mixtures, cement and water are stayed constant while fine and coarse aggregates were varied. The studied parameters are: utilizing fine recycled glass (FRG) instead of fine natural aggregate (FNA) at substitution levels of 0, 10, 25, 50 and 100 %, performing coarse recycled glass (CRG) instead of coarse natural aggregate (CNA) at replacement ratios of 0, 10, 20 and 40 %, conducting both CRG at constant ratio (20 %) as well as RCA at varied levels (0, 16, 40 and 80 %) and replacing CNA by RCA at varied levels (0, 16, 40 and 80 %). The experimental results showed that replacing 10, 25, 50 and 100 % of FNA by FRG declined the compressive strength of concrete by 12.8, 18.5, 24.5 and 49.8 %, respectively. Also, the compressive strength of concrete decreased by 18.5, 23.3, and 32.83 % when 10, 20, and 40 % of CNA were substituted by CRG, respectively. Additionally, the current study investigates the efficacy of machine learning (ML) techniques in evaluating the compressive strength of eco-friendly concrete containing GW and RCA separately. Four tree-based ensemble methods—decision trees, random forest, gradient boosted regression trees, and extreme gradient boosting—were trained and tested using 241 and 319 datasets to predict the compressive strength of eco-friendly concrete containing GW and RCA, respectively. The data employed in constructing the ML model were gathered from both the current experimental study and previous studies. The findings indicate that the XGBoost model demonstrates exceptional accuracy. The impact of each parameter on the predicted outcomes was discussed. • Eco-friendly concrete with GW and RCA investigated using cube compression tests • Replacing FNA with FRG reduced f cu by 13–50 % at varying replacement levels • Replacing CNA with CRG reduced f cu by 18.5–33 % at varying replacement levels • Increasing FRG/CRG replacement lowers concrete density; enhances fluidity greatly • XGBoost ML predicts eco-friendly concrete's compressive strength accurately [ABSTRACT FROM AUTHOR]

Traditional methods for designing concrete materials typically rely on labor-intensive laboratory experiments, resulting in time and cost inefficiencies. Recently, designing concrete using artificial intelligence (AI) methods has shown high efficiency, but existing AI methods often rely solely on data, which can lead to violation with scientific principles and result in models lacking reasoning abilities. To overcome these challenges, this paper presents an interpretable knowledge graph-guided data-driven design approach. By integrating advanced computing techniques with domain knowledge via knowledge graphs, this approach enables the interpretation of data-driven models and uncovers the underlying mechanisms behind predictions. This approach is applied to ultra-high-performance concrete (UHPC) involving complex physicochemical reactions. The domain knowledge about UHPC is imparted using a knowledge graph, and UHPC properties are predicted using a machine learning model considering mixing proportions, processing methods, and physiochemical properties of materials via natural language processing. The results show that the knowledge graph displays crucial design variables and their effects on UHPC properties, aiding in selecting variables for machine learning models and interpreting their results. The prediction accuracy of the machine learning model reached 0.95. The research paves the way for more transparent and scientific AI models for material design and AI-enabled discovery of scientific knowledge. [Display omitted] ● An artificial intelligence (AI) approach is presented to design concrete with solid wastes. ● The AI approach achieves interpretability by combining machine learning and knowledge graph. ● Knowledge about the physicochemical reactions and properties of concrete is learned and used. ● The AI approach is applied to low-carbon cost-effective ultra-high-performance concrete. ● The AI approach can interpret the underlying mechanisms and generate new knowledge. [ABSTRACT FROM AUTHOR]

Due to the fast proliferation of electrical and electronic equipment (PCs, TVs, and cell phones, among others), the disposal of plastic waste, such as acrylonitrile butadiene styrene derived from discarded electrical and electronic equipment (e-Waste), is becoming a big issue. This paper addresses this subject by utilising granulated ABS as an aggregate replacement material in concrete. The compressive strength and abrasion resistance of granulated ABS derived from electronic waste in concrete were evaluated in different replacement intervals (0 %, 5 %, 10 %, 25 %, 50 %, 75 %, and 100 %). The current investigation included microstructural and morphological characterisation utilising scanning electron microscopy and X-ray diffraction pattern analysis. It was found that increasing the replacements of granulated ABS for the natural aggregate reduced concrete's workability, strength, and abrasion resistance. To compensate for the loss in strength and abrasion wear resistance, mixes were subjected to a precarbonation curing regime to densify the microstructure of the cementitious paste. [ABSTRACT FROM AUTHOR]

Due to the depletion of river sand, the construction industry is eager to develop upcycling techniques for transforming secondary by-products derived from construction and demolition (C&D) waste into quality fine aggregates. This paper presents a study of replacing river sand with enhanced recycled fine aggregate through a wet carbonation process developed by the authors previously. The fine recycled concrete aggregate (FRCA) ranging from 0.15 to 5 mm was prepared by demolishing a concrete with a known mixture design. After wet carbonation, the particle size, water absorption, and density of the FRCA were tested and compared with the original samples. The chemical characteristics of the original and carbonated FRCA (C-FRCA) were analyzed by a series of experiments. The results showed that (1) an increase of carbonation products and a significant reduction of hydration products; (2) microscopic observation of the C-FRCA showed a surface layer densified by calcite after wet carbonation; and (3) no significant strength loss were observed when replacing up to 50% river sand by C-FRCA in mortar specimens. The potential environmental and economic impacts were also analyzed. [Display omitted] • Wet carbonation significantly improved the quality of FRCA. • The carbonation efficiency of wet carbonation excelled conventional carbonation methods. • Up to 50% river sand replacement ratio was achieved by carbonated FRCA. [ABSTRACT FROM AUTHOR]

The large-scale recycling of concrete waste and its high-value utilization are key research topic in the field of sustainable building materials. This paper investigated the properties of fully recycled mortar made with thermoactivated recycled cement and recycled fine aggregate (RFA) up to 100%. The 600 °C thermoactivated recycled cement contained active compounds such as C 2 S and CaO. Substituting recycled cement for ordinary Portland cement reduced the hydration reaction and enlarged the pore structure of paste, but mixing active admixture could improve the micro-structure of recycled cement paste. Incorporating recycled cement and RFA decreased the mechanical strength of mortar, as well as elevated the drying shrinkage and transport properties. The detrimental impact of incorporating recycled cement on the performance degradation was more prominent than that of RFA incorporation. Nevertheless, the properties of fully recycled mortar with both 100% recycled cement and RFA still achieved a relatively satisfactory level. Besides, recycled mortar made with recycled cement derived from cement paste waste exhibited superior performance to that made with recycled cement from concrete waste. Substituting active admixture for 10% recycled cement could obviously improve the strength and permeability resistance of fully recycled mortar. Therefore, optimizing the replacement rate of recycled cement, RFA and active admixture is expected to prepare the fully recycled mortar with good performance. The maximal utilization of concrete waste could be achieved through preparing fully recycled mortar with the use of recycled cement and RFA completely instead of natural sand and ordinary Portland cement. This approach resulted in lower CO 2 emissions and provided superior environmental benefits. [ABSTRACT FROM AUTHOR]

• The activity index of solid waste based composites is higher than 95%. • Solid waste based composites can replace 40% cement in concrete. • The total amount of solid wastes in concrete is up to 83%. Waste rock is stripped from open pit iron mines, which is often used to prepare aggregate in concrete because of its stable performance. However, with the continuous improvement of aggregate performance, a vast amount of stone powder produced in the process of aggregate preparation causes secondary solid waste pollution. In this paper, the feasibility of preparing supplementary cementitious materials (SCMs) by using solid waste based composites was investigated. The results show that the 28-d activity index of iron ore waste powder (IOWP) based admixture is higher than 95%, and when it is used to replace cement in concrete, the admixture can reach 40% and the performance of concrete is stable. When iron ore waste completely replaces aggregates and IOWP based admixture replaces part of cement for concrete, the solid waste content of solid waste aggregate concrete (SWAC) is up to 83% compared to natural aggregate concrete (NAC). This study provides a new idea for high value, high efficiency and scale development of solid wastes. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of internal flaws in recycled aggregate concrete (RAC) on its mechanical properties. RAC is an effective material for repurposing waste concrete; however, its flaw evolution process under different loading conditions remains unclear. Monotonic and cyclic loading tests were performed on RAC specimens with different recycled coarse aggregate (RCA) replacement rates. These tests revealed that the flaws in RAC can be divided into two types: porous defects (gradually compacting and strengthening the RAC as the stress increases) and induced cracks (continuously propagating and damaging the RAC). Based on the competition evolution of these two types, the stress–strain curve of RAC under monotonic loading is divided into four stages: porous defect-dominated, induced crack-dominated, rapid induced crack extension, and continuous damage stage. In addition, two more stages occur under cyclic loading: the unloading stage and the reloading stage. Based on the competition effect and evolution of two flaw types, a constitutive model, which describes flaw evolution with stress, is proposed. This model can reveal the flaw evolution laws of RAC with different RCA contents for each stage, which can describe the stress-flaw strain relationship of RAC with varying RCA content. The proposed models overcome the inherent limitations of empirical models, which lack physical parameter significance and rely on ambiguous mechanical theories for cyclic loading. • The flaw evolution law with stress in RAC is studied, and the thresholds for flaw closure and expansion are determined. • The proposed flaw competition coefficients reflect flaw evolution and quantitatively reveal damage degree of RAC. • The parameters in the proposed constitutive models under monotone and cyclic loading have clear physical significance. [ABSTRACT FROM AUTHOR]

Concrete, renowned for its strength and durability, stands as the primary material in infrastructure construction. Despite its extensive use over millennia, its response to fire remains inadequately understood, posing threats to structural resilience and human safety. The consideration of fire resistance becomes paramount in selecting building materials. Throughout their operational lifespan, structures may encounter fire-related risks. Although there is a prevailing belief in the inherent fire resistance of concrete, its performance at high temperatures is subjected to alterations in both physical and chemical properties, impacting its strength and durability. Cracking and spalling may occur, resulting in economic losses and, in severe cases, loss of lives. Moreover, the production of concrete contributes to the depletion of natural resources, causing adverse environmental effects. In the world of building materials, the pursuit of innovative solutions for strength and resilience has been incessant. Consequently, researchers globally recognize the need for an environmentally friendly alternative to concrete. As concerns about fire safety grow, attention has shifted to geopolymer concrete, presenting itself as a promising eco-friendly substitute with significant potential to enhance fire resistance. Geopolymer concrete entirely replaces traditional cement concrete with waste materials rich in Alumina and Silica. Apart from mitigating environmental impacts, it exhibits superior resistance to high temperatures compared to ordinary Portland cement concrete, with the ability to endure temperatures ranging from 1000°C to 1200°C.Enhancements in the high-temperature behavior of geopolymer concrete can be achieved by incorporating materials such as fibers, marble powder, waste glass, rubber crumbs, nanoparticles, etc. This review explores the realm of geopolymer concrete, specifically delving into its fire-resistant properties. It provides a brief overview of the mechanical performance of geopolymer concrete subjected to elevated temperatures and elucidates the role of various materials in enhancing its behavior. It has been seen that in high temperature study of GPC, residual compressive strength is crucial and it mostly rises up to 150°−350°C but declines beyond 400°C due to micro-crack formation. Also, superior tensile strength is shown up to 300°C, with notable decline beyond 800°C. Incorporating fibers in GPC improves these residual properties. Different fibers, such as carbon, glass, basalt, polypropylene, and steel, have specific advantages and considerations. Recycled tire fibers prove cost-effective alternatives improving fire resistance in GPC, with an optimum content of 1.2–2 kg/m3.Usage of rubber particles in GPC prevent spalling at elevated temperatures by allowing water vapor escape, but increased amounts decrease compressive strength, while as using waste glass in GPC enhances microstructure, compressive strength and thermal stability but care is needed to address alkali-aggregate reactions. By comprehending the intrinsic characteristics and performance of geopolymer concrete with suitable additives at high temperatures, this paper aims to highlight its potential to revolutionize fire safety measures within the construction industry. This article not only initiates possibilities for future research on the fire-resistant qualities of geopolymer materials, but it also lays the groundwork for assessing elevated temperatures behavior of Geopolymer Concrete. • Investigation into how elevated temperatures impact the mechanical characteristics of GPC. • Role of aggregates on the performance of GPC at elevated temperature. • Role of various materials and fibers in improving the behavior at elevated temperature. [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]

This paper covers the result of physico-mechanical, microstructural, optimization, and environmental impacts of alkali-activated paste (AAP) produced from recycled waste concrete (RWC) powder and metakaolin (MK). The experimental findings revealed that RWC powder up to 40 % effectively reduced setting time. The specimens with M s ratios of 1.25 and 2.00 had similar setting periods, while the mixes activated with 0.50 had greater setting time variance. The compressive strength significantly increased with an increase in RWC powder, and the mix formulated with 40 % RWC powder and M s ratio of 2.00 showed maximum strength of 79.1 MPa at 28 days. However, further inclusion of RWC powder beyond 40 % constantly decreased the strength. A statistically significant model to predict compressive strength was obtained by response surface methodology study, and the obtained optimum mix design (RWC=36.33 % and M s :1.89) was experimentally validated with an absolute error of 0.17 %. The microstructural analysis indicated that N-A-S-H type gels were the major reaction products, and the inclusion of RWC powder led to the generation of C-(A)-S-H type gels along with N-A-S-H type gels. Furthermore, an increase in the RWC powder ratio increased the crystallinity index values of AAP samples, as shown by X-ray diffraction results. Life cycle assessment (LCA) analysis was performed for all AAP mixes, including the optimum mix. LCA results indicated that the addition of RWC powder consistently reduced the CO 2 emission, cumulative energy demand, and cost of the resulting AAP mixes; however, these parameters slightly increased with an increase in M s ratio of alkaline solution. [Display omitted] • Investigation on AAP containing recycled waste concrete (RWC) and metakaolin (MK). • Compressive strength of paste mixes enhanced up to 40 % RWC powder substitution. • A statistically significant RSM model was obtained to predict compressive strength. • CO 2 emission and energy demand decreased with an increase in RWC powder ratio. • RWC powder can be used to produce economical and green building materials. [ABSTRACT FROM AUTHOR]

Agriculture waste generation is increasing daily, and agricultural waste management has become one of the most challenging issues for many countries. To contribute towards a sustainable waste management system, this experimental study evaluates the impact of using agricultural waste materials in concrete. Concrete that does not harm the environment and has improved engineering properties can be produced using agricultural waste ash such as green gram pod ash. Green concrete has been examined for its mechanical, durability and microstructure properties when partially replaced with Portland cement by green gram pod ash (GGPA). Conducting various tests using concrete containing different weight proportions of green gram pod ash in a mix at 2%, 4%, 6%, 8%, and 10%, respectively. This paper examines the mechanical, durability and morphological characteristics of green gram pod ash blended with cement concrete. It has been shown that concrete containing 8% green gram pod ash enhances the properties of GGPA concrete. It was observed that the addition of 8% green gram pod ash enhances the compressive strength. Split tensile strength, flexure strength, modulus of elasticity and impact strength of concrete by 4.26%, 4.07%, 35.19%, 16% and 10.3% at 28 days of curing. It was concluded that green gram pod ash was shown to satisfy engineering application design requirements and significantly reduce concrete production costs and environmental pollution. The cement replacement with 8% of GGPA is optimum for achieving better concrete properties. • Evaluations of the impacts of using Green Gram Pod Ash (GGPA) in cement and cementitious material production were conducted. • Incorporation of Green Gram Pod Ash (GGPA) in concrete improves the strength and ductility performance of concrete. • Substitution level of GGPA in concrete should be limited to 8% (by weight) • GGPA concrete samples containing 8% green gram pod ash displayed maximum static modulus of elasticity and higher impact energy. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of environmentally friendly, easy to use and cost-effective construction and demolition waste (CDW)-based geopolymer mortars activated solely with low-alkalinity NaOH and along with large share of recycled concrete aggregates (RCAs). The low-activity CDW-based precursors used in this study included brick waste and concrete waste. Additionally, slag and silica fume were utilized as industrial waste-based precursors to provide additional sources of Ca and Si, promoting enhanced geopolymerization. NaOH was utilized at molarity levels of 4, 5, 6, 7, and 8 M. The study employed a comprehensive test methodology, enabling a thorough investigation of the different properties and performance of the geopolymer mixtures, ultimately achieving the goals set for this research. The results indicated that the 4 M NaOH concentration was insufficient for early strength development of CDW-based geopolymer systems, although it eventually provided adequate alkalinity for strength development at later ages (e.g., compressive strength of 7.2 Mpa at the end of 28-day). While higher NaOH concentrations generally improved performance, the optimal choice was found to be 5 M NaOH. Nevertheless, 100% CDW-based geopolymer mixtures activated solely with low molarity NaOH solutions showed lower performance (compressive strength of 10.5 Mpa and flexural strength of 2.3 Mpa at the end of 28-day) and were found to be susceptible to water ingression and unable to withstand freeze-thaw cycling. Incorporation of slag significantly enhanced the mechanical and durability properties of CDW-based geopolymer regardless of alkaline content. The inclusion of coarser RCAs (0–4.75 mm) and a higher amount of finer RCAs (0–2 mm) resulted reduction in the performance of the mixtures. Nevertheless, the observed negative impacts were mitigated through 5% silica fume substitution. The findings of the study indicate that low-alkaline activated CDW-based geopolymer mortars can achieve an impressive compressive strength of 24.9 MPa and flexural strength of 4.7 Mpa along with superior durability performance. • Rheology of geopolymer can be customized by adjusting NaOH, precursor & aggregate content. • Slag can enhance the mechanical, transport and durability properties of geopolymer. • NaOH molarity of 5 M was optimal for activating the CDW-based geopolymer. [ABSTRACT FROM AUTHOR]

This paper analyzes manufacture of a new eco-cement (reduced CO 2 footprint and LC3 clinker content) by replacing natural limestone with fine limestone concrete demolition waste (CDW H). The ternary cement's content was partially replaced by a binary pozzolanic admixture (10%, 20%, and 30% proportions; 1:1 by weight) composed of CDW H and commercial metakaolin (MK). Results show the ternary eco-cement meets current standards' chemical and physical requirements. The pozzolanic synergy of the additives —CDW H and MK— is comparable to silica fume, as reflected in the new mortars' intrinsic properties (capillary water absorption and electrical resistivity), microporosity, and physical and mechanical characteristics, achieving maximum performance at 20% replacement. Kinetically, in ternary eco-cements, the formation of monocarboaluminate and hemicarboaluminate phases, the non-conversion of ettringite to monosulfoaluminate, and the reduction of the Ca/Si ratio in CSH gels all benefit kinetically as the replacement content increases. Use of limestone concrete demolition waste in manufacture of LC3 eco-cements is a viable option. • Recycling of the fine fraction of limestone CDW for the manufacture of LC3 cements. • Analysis of the scientific and technical feasibility of ternary eco-cements. • Good synergy of the binary mixture CDW-MK. • New ways to recycle RCD. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of using cross-linked polyethylene (XLPE) waste as a partial replacement of conventional stone aggregates to produce concrete. Specifically, the effects of XLPE waste content (0, 5, 10, and 15 vol% of coarse and fine aggregates) and water-to-cement (W/C) ratio (0.45, 0.50, and 0.55) on the fresh properties (slump, unit weight, and air content) and hardened properties (bulk unit weight, ultrasonic pulse velocity, uniaxial compressive strength (UCS), split tensile strength (T), and flexural strength (F)) of concrete were investigated. Moreover, scanning electron microscopy (SEM) analysis was performed to study the interfacial transition zones (ITZs) at the different conditions. The results show that the addition of more XLPE improves the workability or slump (by 8% to 51%), decreases the unit weight (by 0.16% to 2.20%), but does not noticeably affect the air content of the fresh concrete (all ∼1.5%). Increasing the XLPE content results in a decrease of the UCS (by 23% to 60%) but improves the ductility and increases the T/UCS (by 19% to 144%) and F/UCS (by 22% to 174%) ratios of the concrete. The decrease of the UCS with a higher XLPE content is mainly due to the weaker ITZ between the XLPE and the binder. The study clearly indicates that the XLPE waste can partially replace the conventional stone aggregates to produce concrete for different applications specified by industry. • Studied utilization of XLPE waste to partially replace conventional stone aggregates to produce concrete. • Increasing XLPE content improves workability, decrease unit weight, but barely affects air content. • Using more XLPE reduces UCS but improves ductility and increases T/UCS and F/UCS ratios. • XLPE waste can partially replace stone aggregates to produce concrete satisfying industry requirements. [ABSTRACT FROM AUTHOR]

• Demolished concrete waste can be potentially utilised as recycled aggregates (RA). • Multi-stage processing and mechano-chemical treatment enhances the quality of concrete RA. • RAC incorporating treated RA shows better mechanical and durability properties. • Additional C S H formation is observed for RAC incorporating 35% treated RA. On account of the shortage of naturally occurring coarse aggregate, recycled aggregate (RA) made from crushed concrete debris is now used in the construction industry. With this rise in the utilisation of recycled aggregate in the construction sector, there has been extensive research into ways to improve its quality. The significant fraction of mortar remains that are left on the RA surface is the primary factor that affects its quality. Concrete made from RA loses strength and mechanical performance due to the attached mortar's increased porosity and water absorption values and the frailer transition region between the new mortar and aggregates. In order to minimise the old cement fractions and increase the quality, this paper studies the effect of concrete incorporating multi-stage processed RA from demolished concrete waste, followed by treatment with mechanical abrasion and sodium silicate immersion. The recycled aggregates were produced through multi-stage jaw crushing, followed by utilising natural aggregate, recycled aggregate, and recycled aggregate obtained after mechanical abrasion, followed by sodium silicate treatment for concrete mix design at various substitution percentages as coarse aggregates. The experimental investigation further progresses with the evaluation of mechanical and durability properties of concrete mixes, which is additionally followed by microstructural studies such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetry-differential thermal analysis (TG-DTA). The outcomes demonstrate that two-stage treatment, such as mechanical abrasion followed by sodium silicate immersion, yields superior-quality RA. Recycled aggregate concrete (RAC) made with these treated aggregates illustrated an increase in workability and density with respect to an untreated RAC mix. Furthermore, comparable strengths in compression, flexure, and tension are found in treated RAC mixes, particularly at 35% replacement levels, with respect to concrete mixes comprised of natural aggregates. A similar trend is detected in the chloride penetration tests and water sorptivity tests. In addition, the microstructural investigation confirmed the formation of additional calcium silicate hydrate for treated RAC mixes, particularly for the 35% substituted RA mix. On the basis of the results, it is suggested that multi-stage jaw crushing followed by treatment through mechanical abrasion and sodium silicate can potentially enhance the mechanical, microstructural, and durability performance of RAC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recycled waste geopolymer bricks were developed as alternative bricks for sustainable development. • Technical, Economic, Environmental and Social feasibility were studied and reported. • Multi-criteria decision-making methodology was adopted to select the suitable alternative brick. The pursuit of sustainable development has become increasingly important in addressing the challenges of environmental degradation and resource depletion. The construction industry accounts for significant global resource consumption and pollution. The study aims to investigate the selection of alternative bricks for sustainable development. Social, Economic, Environmental and Technical feasibility was studied to identify the best alternative brick. Five different bricks, i.e., Fired clay brick (FCB), Fly ash cement brick (FACB), Fly ash geopolymer brick (FAGB), Recycled concrete waste geopolymer brick (RCWB) and recycled brick waste geopolymer brick (RBWB), were developed and their technical and environmental impacts were studied. A life cycle analysis (LCA) of one brick was carried out, and seven impacts were studied and reported in this paper. Multi-criteria decision-making methodology (MCDM) was used to select the best brick. In addition, the microstructural properties of recycled geopolymer brick were investigated to study the morphology and mineralogy of the brick's mixes. Sustainability Index (SI) indicates that fired bricks contribute a higher environmental impact per compressive strength in comparison with alternative bricks. According to the Analytical Hierarchy process (AHP), RBWB is the preferred choice with an overall weight of 0.22, followed by fly ash cement brick (0.217). The mineral resource scarcity (MRS) of 82–87 % can be reduced if alternative recycling waste materials were used in production of brick. [ABSTRACT FROM AUTHOR]

[Display omitted] • Comprehensive review of recent advances in incorporating wastes into foamed concrete. • Utilization of various wastes as binder, aggregate, and modifier replacements. • Effect of physicochemical properties of wastes on foamed concrete were analyzed. • The challenge and development direction of waste-based foam concrete were discussed. Globally, various solid wastes are produced and stockpiled in large quantities, causing serious environmental, social, and economic problems. Foamed concrete has attracted worldwide attention because of its excellent functional properties. Incorporating recycled waste and byproducts into foamed concrete is considered a win–win strategy for sustainable waste management and green transformation of foamed concrete. However, the reviews of alternative forms of different wastes/byproducts and their effects on foamed concrete are limited, which has hindered the promotion of this concept. Therefore, this paper compiles and reviews the reuse potential of various types of waste and byproducts as cementitious materials, aggregates, and modifier replacements. Together with the chemical and physical properties of the waste byproducts, the effects of different waste/by-product substitution pathways on the properties, pore structure, hydration products, and carbon emission reduction of foamed concrete were comprehensively evaluated. Our findings are important for guiding the rational introduction of wastes/byproducts and optimizing the combination of the inherent characteristics of waste byproducts and the requirements of foamed concrete. Furthermore, this review also discusses the challenges and development directions of waste-based foam concrete. This study provides an important basis and guidance for sustainable waste management, and low-carbon foamed concrete manufacturing. [ABSTRACT FROM AUTHOR]

This paper involved both experimental and numerical investigations on the behaviour of twelve types of recycled-concrete filled double-skin steel tubular (RCFDST) structures subjected to the cyclic loading with reinforced ribs at the column–steel beam joints, of which the damage pattern and seismic performance were analysed by varying the ratio of beam–column flexural linear stiffness, axial compression ratio, hollow ratio, type and strength of the concrete, and the length of ribs. The results indicate that the specimens primarily exhibited the damage pattern of the plastic hinge at both ends of the beams, and that the horizontal load–displacement hysteresis curves with full loop at the top of the column were observed. Moreover, the structures composed of recycled concrete from 40 MPa to 60 MPa presented no reduction in ultimate load as well as the joint ductility to those of the ones with normal concrete. Regarding the performance of RCFDST, the optimal ratio of beam–column flexural line stiffness (k i) is found in the range of 1.0 to 1.5. This study demonstrated that the recycled concrete made from the industrialized aggregate formed by crushing waste concrete from road bases has potential application prospects in Concrete-filled double skin steel tubular (CFDST) structures due to its low cost and good seismic performance, including high ultimate load capacity and low energy consumption. • Reinforced ribs are added to the inner tube in the RCFDST column area to transfer internal forces. • The coarse aggregate is made from crushing waste concrete from the road base. • 12 joints were tested under cyclic loading and a suitable FEM was established. • The seismic performance of various parameters was analysed. [ABSTRACT FROM AUTHOR]

The construction industry has been focused on sustainability, particularly with regards to reducing CO 2 emissions and recycling construction and demolition (C&D) waste. This study focuses on the alternative technology adaptation of carbonized pavement compact production by using waste concrete powder (WCP) which can be a substitute material to concrete and also able to absorb CO 2. While material scientists embraced and developed this technological application, the financial perspective for adopting this technology has yet to be properly addressed. This paper conducts a feasibility assessment, which includes technical, environmental, social, and financial factors, from different stakeholders' perspectives (government, construction contractors, and material manufacturers) to launch the production of carbonized pavement compact by utilizing WCP. The benefit-cost analysis underlies the Evolutionary Game Model functions' formulation, which emphasizes not only the obvious financial benefits from WCP or its carbonized compacts sale but the benefits from the absorption of CO 2 during the compacts production and avoiding WCP disposal at a landfill. The results based on a Hong Kong case (typical multistorey apartment building) identify promising scenarios where a minimum of 2300t of WCP is required for stakeholder interest in recycling, and a WCP wholesale price of 150HKD/t is suitable for the C&D contractor to participate in the recycling market. The study also estimates a cost-effective selling price of finished carbonized WCP compacts, which is competitive with similar products on the market. Important insights are drawn to initiate the WCP market and consequently increase the sustainability of the C&D recycling market. [Display omitted] • Providing a solution for reducing CO 2 emissions during pavements production. • Assessing the feasibility of launching carbonized WCP pavement compact market. • Considering technical, environmental, social, and financial factors for assessment. • Obtaining feasible conditions for carbonized pavement compact production from WCP. [ABSTRACT FROM AUTHOR]

• The paper reviews the effects of the RA moisture states on the performance of RAC. • Workability, the mechanical performance, the long-term properties, and durability of RAC were discussed. • A model describing the water absorption/desorption behavior of RA in RAC was proposed. • This review can provide suggestions on setting the appropriate RA moisture states in practical use. Recycled aggregate (RA) presents times higher water absorption compared to the natural aggregate (NA). The moisture states of the RA can be quite variable when exposed to certain environments, which can largely influence the performance of the prepared recycled aggregate concrete (RAC). This paper reviews the published papers dealing with the effects of the RA moisture states on the workability, the mechanical performance, the long-term properties and durability of RAC, and discusses the controversy between different studies. This paper suggests that the effects of the RA moisture states on the RAC performance at the fresh state or after hardening should be considered in combination with the water supply scheme or the water-to-cement ratio as taken in certain scenarios. Basically, pre-wetting RA is reported to be beneficial for the performance of RAC at the hardened state in most cases: higher compressive/tensile/flexural strength and lower drying shrinkage/autogenous shrinkage could be achieved by using the partially saturated RA as reported in many references. However, the use of the surface-saturated dry (SSD) RA should be avoided as it can lead to great loss in the compressive/tensile strength as well as the resistance of RAC to carbonation and chloride ingress. As for the workability, the pre-saturated RA is regarded to be favorable for the RAC slump when the mixing water supply is fixed, while in the case with a consistent total water supply, using the dry RA can lead to a larger slump. This paper proposes a model describing the water absorption/desorption behavior of RA at varying moisture states, and relates it to the microstructural changes in the ITZ and mortar phases so as to provide possible explanations for the RAC performance influenced by the RA moisture states. Recommendation is also given in terms of the shortcoming and challenges on this research topic encountered thus far. [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]

• Carbonation is a promising technology to sequester CO 2 emissions. • The locational aspects and transportation can influence the carbonation value chains significantly. • Regionalizing the analysis is of importance in order to obtain accurate results. • The economic feasibility will play a major role in determining the extent of utilizing the potential capacities. • Tracking the changes in the construction industry should be considered as they can significantly influence the supply chain. Carbon capture and utilization (CCU) is an essential method to sequester unavoidable CO 2 emissions in regions with insufficient geological storage capacities. Nonetheless, there are several uncertainties and knowledge gaps in terms of the future value chains of some CCU technologies (e.g. carbonation). This paper analyzes the potentials of coupling CCU with the supply chains of the construction industry by means of carbonating the concrete products and waste concrete in the German federal state of North Rhine–Westphalia. Based on extensive data and statistical analyses, the locations and outputs of the concrete and recycling plants have been determined in order to quantify their CO 2 sequestration capacities. Location-allocation models have been applied to allocate the carbon sources to the potential carbon sinks and calculate the minimum transportation costs. The analysis shows that the total annual sequestration capacity is up to 1 Mt CO 2 with an average transportation distance of 37.4 km (8.3 EUR/ton). Nonetheless, some emission sources have a clear comparative advantage in terms of their proximity to the carbon sinks as the distance ranges between 0.7 km and 99.7 km. Also, some carbon sinks have a comparative advantage in terms of capacities and technology readiness levels. Therefore, the paper also presents models for the different products in order to display the potentials of each category separately and offer more flexibility to the stakeholders. [ABSTRACT FROM AUTHOR]

The rapid urbanisation and infrastructure development projects have increased infinite property regeneration and construction projects in the developed countries. This study aims to examine the current construction waste management literature, including key authors, university networks, and relevant information systems, considering four selected countries, including Australia, Canada, the United Kingdom, and the United States. This paper uses a set of novel metrics, query-based search, and social network analysis techniques for evaluating a dataset of 2337 papers published in a decade by authors from different countries investigating the topic of recycling and reuse of construction and demolition waste in order to identify prominent researchers, influential universities, collaboration practices, and research trends. The dataset of publications is collected from Scopus and analysed using a set of network analysis techniques and statistical analysis. An additional dataset of keywords was collected from the Twitter pages of engineering firms and other relevant industry organisations to assess any possible connection between industry interests and research trends. In order to present a solid analysis of the current investigations in the field, a scientometric analysis along with a rigor statistical method was adopted to carefully identify trends, detailed sub-topics, and the materials investigated in the literature. A probit regression model for testing differences between countries in recycling practices was utilised in the STATA environment. The findings show a set of network analysis and clusters that can help scholars to set their future studies based on the current advances and limitations identified in the literature. Within the dataset, 42% of publications referred to concrete waste, whilst only 2.2% included glass, 2.5% included brick, 4.3% included steel and none included wood, which shows the most common building materials have not been fully covered in the literature. Only 48 publications, or 7.4% of the dataset, originated from the three selected concrete-focused journals. It was also found that information systems appeared in the database lately; however, there is less discussion in the literature on how the integration of Geographic Information System (GIS), Buidling Information Model (BIM), 3D Printing and geo-spatial data analysis can help waste management in the field of construction. The bibliographic analysis of the selected cases shows that universities in Canada and the US exhibit more evidence of domestic collaboration and industry partnerships than universities in Australia and the UK. Additionally, there is evidence to suggest that publications with at least one industry co-author are more likely to address the issue of regulation. The outcome of this paper enables academics, engineers, and regulators to predict research trends, improve industry collaborations and utilise information systems and assign more research resources to address the identified gaps in the literature. • Developed a network of 1408 authors within the dataset and apply Total Publications metrics. • Examined the collaboration of 529 institutions within Australia, Canada, the UK, and the US. • Utilised a probit regression model for testing differences between countries in recycling practices. • Visualised an online GIS-based dashboard of landfills and recycling facilities using geo-spatial data. • Identified gaps in two different directions of material technology and management systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural coarse aggregates were partially replaced by electronic plastic waste coarse aggregates (EPWCA). • Electronic waste concrete modified with nano iron oxide particles (NIOP) and sisal fiber (SsF) was investigated. • Mechanical and durability properties improved with the NIOP addition. • The addition of SsF greatly enhanced the concrete's resistance against tensile stresses. • Synergistic behavior of NIOP and SsF proved to be effective in improving the overall performance of EPWCA concrete. The utilization of electronic plastic waste (EPW) as a substitute for traditional aggregates in concrete has gained attention for its potential to reduce environmental waste. However, the incorporation of EPW aggregate leads to reduced mechanical properties, limiting its structural applications. This paper aims to address this issue by enhancing the mechanical and durability properties of EPW aggregate concrete by incorporating nano iron oxide particles (NIOP) and sisal fiber (SsF) reinforcement. Natural coarse aggregates were partially replaced with 30% EPW coarse aggregate (EPWCA). The performance of the resulting concrete was thoroughly investigated by incorporating 1% SsF and varying NIOP content from 1.0% to 4% of the cement's weight. The workability of concrete is compromised by the intrusion of both NIOP and SsF. However, the addition of SsF and NIOP decreases and increases the hardened density of the resulting concrete, respectively. The combined effect of NIOP and SsF reinforcement led to enhanced performance of EPW concrete, with the superior performance observed in the EPW concrete modified with 4% NIOP and 1% SF. This modification led to increases of approximately 15.81% in compressive strength, 22.80% in splitting-tensile strength, 21.75% in flexural strength, and 28.79% in bi-surface shear strength. In terms of durability, ultrasonic pulse velocity (UPV) values demonstrated a net increase of approximately 6.50%, while sorption and water absorption capacity showed reductions of approximately 8.04% and 4.52%, respectively. Moreover, the modified EPW concrete exhibited a net decrease of 28.79% in linear shrinkage compared to the control virgin concrete. Forensic investigations confirmed microstructural densification resulting from the addition of NIOP. Thus, the modified EPW concrete with NIOP and SsF reinforcement shows promise in enhancing overall performance and promoting eco-friendly construction practices. [ABSTRACT FROM AUTHOR]

• FRP-confined SSC cores show effectiveness in enhancing RAC-filled steel tube columns. • RAC-filled steel tube columns with FRP-confined SSC cores show promising performance. • Effects of FRP-confined SSC core configurations and concrete strength were analyzed. • A reasonable load capacity model for the proposed columns was presented. • Seamless steel tubes could exploit compressive performance of the proposed columns. Recycled aggregate concrete (RAC) prepared from waste concrete can achieve the green recycling of resources; however, its inferior material properties hinder its applications. Sea-sand concrete (SSC) can help alleviate the resource shortage of fresh water and river sands but is prone to steel corrosion. To address these challenges, this study developed a new RAC-filled steel tube column with a small-diameter circular fibre-reinforced polymer (FRP)-confined SSC core. This paper presents and discusses the results of the axial compression tests conducted on RAC-filled steel tube columns, with and without small-diameter circular FRP-confined SSC cores. The study investigated the effects of the configuration of the FRP-confined SSC core, diameter-to-thickness ratio of the FRP tubes, compressive strength of RAC and SSC, and cross-sectional shape of the column. The results revealed that using small-diameter circular FRP-confined SSC cores to partially replace RAC was effective in improving the compressive performance of RAC-filled steel tube columns. The increase in the number of FRP tubes, in-filled concrete strength, and confinement stiffness of the steel and FRP tubes contributed to improvements in the structural strength and ductility, resulting in progressive ladder-shaped declines in the post-peak curve. Finally, a reasonable load–capacity model is presented for the proposed columns. [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]

The large-scale application of high-strength mortar in engineering will inevitably generate a significant amount of high-strength mortar waste in future, but there has been relatively limited research to date on the reuse of high-strength mortar waste as recycled building materials. Therefore, this paper studied the microstructure and chloride transport in cement-based materials using recycled fine aggregate (HCRA) and recycled powder (HCRP) derived from high-strength mortar waste or from high-strength mortar waste separated from high-strength concrete waste recycling. HCRA had much better physical and mechanical properties than ordinary recycled aggregate. HCRP contained some active components, and mixing appropriate HCRP refined paste pore structure; besides, reducing HCRP particle size could further refine the pore diameter of HCRP doped mortar. The strength of mortar first raised and then declined with the increment of HCRA replacement, but the strength decreased as HCRP was incorporated. Incorporating HCRA slightly reduced the chloride migration in mortar, and the mortar with HCRA had better chloride resistance than the mortar with recycled fine aggregate crushed from ordinary mortar waste. Mixing appropriate HCRP could reduce the chloride diffusion coefficient and chloride concentration. Reducing HCRP particle size further declined the chloride transport in HCRP blended mortar, and the mortar with HCRP had superior chloride resistance to the mortar with ordinary recycled powder. Mixing HCRA and HCRP both raise the chloride binding capacity. Particularly, fully recycled mortar with 100% HCRA and 30% HCRP exhibited even better chloride resistance than reference mortar. Incorporating appropriate HCRA and HCRP could prepare durable cement-based materials with good chloride resistance. [ABSTRACT FROM AUTHOR]

Replacing natural aggregates in concrete with waste rubber particles is an effective method to solve environmental problems, but the use of rubber due to its unknown characteristics can change the fracture performance and cracking behavior of self-compacting concrete. Hence, through experimental analysis and discrete element method (DEM) simulation, this paper aims to investigate the influence of different rubber contents (0%, 10%, 20% and 30%) on fracture characteristics of self-compacting concrete. Compared with natural river sand, rubber particles have more flexible structure and stronger deformation ability, and these unique properties enhance the bridging effect between matrices and weaken the stress concentration at the crack tip, which shows that the fracture parameters of self-compacting rubberized concrete (SCRC) increase linearly with the increase of rubber content, and this linear growth rate will increase with the increase of beam size. Moreover, the addition of rubber particles absorbs most of the energy generated in the fracture process, which significantly enhances the anti-cracking ability of SCRC, and this ability to prevent crack propagation will be enhanced with the increase of rubber content, which is manifested by the significant decrease of acoustic emission (AE) activity. Based on the shapes of real aggregates and rubber particles, a universal DEM fracture prediction model for SCRC is established, which can better describe the fracture response of SCRC with different rubber contents and sizes under flexural loads. The evaluation of economic and environmental benefits indicates that adding rubber particles into self-compacting concrete can not only save costs, but also produce considerable environmental benefits. • Fracture tests were carried out on self-compacting rubberized concrete (SCRC). • A DEM fracture model considering the shapes of aggregate and rubber was established. • Economic and environmental benefits for SCRC were evaluated. [ABSTRACT FROM AUTHOR]

• Modification study of dispersive soil by recycled concrete is performed. • Recycled concrete powder is capable of decreasing the dispersivity of soil. • Water stability of dispersive soil is enhanced by recycled concrete powder. • Recycled concrete powder improves the mechanical property of dispersive soil. Recycled concrete was used in dispersive soil as admixture in this paper to improve the mechanical properties and dispersivity of dispersive soil. Recycled concrete blocks were collected, ground to powder and mixed into dispersive soil with the weight ratios of 1%, 2%, 3%, 4%, and 5%. Soil samples were prepared and cured in a curing chamber for 0, 1, 3, 7, 14, and 28 days with temperature and humidity at 20 °C and 98%, respectively. Dispersivity, pH, and electronic conductivity of soil samples were determined at different curing time. Flow speed of seepage water and eroded soil weight were measured during pinhole test. Unconfined compression test and splitting test were performed to determine compressive strength and tensile strength of soil samples. Microstructures and mineral changes were obtained by SEM, XRD and TG/DTG tests. Validation test was performed on a natural dispersive soil to prove the effectiveness of recycled concrete powder on the dispersivity. Experiments show that dispersive soil turns into nondispersive soil with increase content of recycled concrete powder. Results of remoulded sphere sample crumb test are more conservative due to the remoulding process of soil during the test. Compressive and tensile strength of soil samples present a significant increase tendency with both the mixing ratio of recycled concrete powder and curing time. Results indicate that recycled concrete powder can be used to improve both the dispersivity and mechanical properties of dispersive clay, simultaneously help to solve the disposal of abandoned construction concrete waste. Enhancing of water stability of dispersivity soil would also ensure the safety and normal operation of both agricultural irrigation facility and hydraulic engineering. [ABSTRACT FROM AUTHOR]

• The mechanical properties of specified-density concrete under static and dynamic compression were studied. • Specified-density concrete had superior dynamic mechanical properties. • The differences in the failure modes and mechanisms of specified-density and ordinary concrete were analyzed. • The dynamic increase factor (DIF) and an energy absorption model of specified-density concrete were established. • A dynamic constitutive model of specified-density concrete was established. As a green alternative building material for aggregates and admixtures in concrete, domestic waste incineration tailings recently have gained increasing attention from the scientific community, and can improve the sustainability of building materials. This paper studies the performance and mechanism of the specified density concrete reinforced by waste incineration tailings under dynamic impact, focusing on the influence of the dosage (25, 50 and 75 wt%) and the intermediate strain rate (20–80 s-1) of the incineration tailings, and the feasibility of using them as the lightweight aggregate in the specified density concrete. The results show that the failure morphology of the static and dynamic mechanical properties of the specified density concrete (SDC) is similar, and the failure crack passes through the weak interface between the tailing lightweight aggregate and the ordinary aggregate mortar. The addition of incineration tailings is conducive to improving the anti-impact properties of specified density concrete under intermediate strain rate. Due to the internal and external interlocking structure effect of aggregate, the dynamic increase factor (DIF) and energy absorption (ω s) of three types of specified density concrete (SDC-25, SDC-50 and SDC-75) are 79.6%∼99.1% and 1.09 ∼ 1.79 times higher than that of ordinary concrete respectively, and the degree of fragmentation, peak stress and peak strain are significantly improved. The dynamic constitutive equation of specified density concrete with good applicability is proposed and successfully applied to numerical calculation. Considering the engineering performance and potential economic benefits of specified density concrete, incineration tailings can be used as a sustainable and cost-effective substitute for some cement-based materials. [ABSTRACT FROM AUTHOR]

• The mechanical properties and damage evolution of a new type of green concrete with porcelain waste were investigated. • Compared to crumb rubber concrete, concrete with 25% porcelain waste shows high cubic compressive and flexural strength. • Analysis of the fracture process of concrete with 25% porcelain waste is based on acoustic emission parametric study. • Concrete with 25% porcelain waste is a sustainable alternative to normal concrete for use in bending members. The utility of crumb rubber concrete (CRC), a green concrete containing waste tire rubber particles as partial replacement for natural fine aggregate, is limited by its lack of strength. It is found that the addition of steel fibers is a solution to the limitation. This study proposes using porcelain waste coarse aggregates and steel fibers to improve the cubic compressive strength and flexural strength of CRC and avoid the pollution caused by porcelain waste. Porcelain waste was incorporated at replacement percentages of 25%, 50% and 100% by volume. Steel fibers were incorporated at volume fractions of 1% and 1.25%. The cubic compressive strength and flexural strength of CRC, steel-fiber-reinforced CRC (SFRRC) and SFRRC with porcelain waste were then tested. The results obtained show that the strengths of CRC are greatly improved by the incorporation of steel fibers and 25% porcelain waste. With the increase in porcelain waste content, the strengths of SFRRC containing porcelain waste decrease. Scanning electron microscopy was then conducted and the findings show that the strengths decrease at high porcelain waste content due to the weak bond between the glaze of porcelain waste and the cement matrix. The fracture processes of three types of concrete under four-point bending were monitored by using acoustic emission (AE) technique. Based on the AE data, the parametric analyses, including cumulative hits analysis, b-value analysis and RA-AF analysis, were performed for three types of concrete and presented characteristics of damage evolution of them. This paper provides information about the mechanical properties and fracture process of a new type of green concrete that can be used in bending members of concrete structures. [ABSTRACT FROM AUTHOR]

• Performance of concrete with glass powder (GP) and crushed glass (CG) after high temperature were investigated. • Compressive strength dropped after 150 °C, whereas the split-tensile strength continued to decline as rising temperature. • Mixtures showed increasing in water absorption and damage degree while decreasing in UPV, as raised temperature. • Concrete with 10% GP substitution and 10%-20% CG substitution exhibited better performance. • The combined substitution of CG and GP for natural aggregates can improve the performance of concrete after elevated temperature. Recycling waste glass (WG) to produce concrete is a crucial step towards building sustainability. In this paper, a new approach of substituting coarse aggregate (CA) and fine aggregate (FA) with crushed glass (CG) and glass powder (GP) respectively was proposed to investigate the effect of different CG and GP replacement rates on the performance of concrete after high temperature. A total of 10 groups of mix proportions were designed, and the substitution rates of GP and CG varied from 0 to 30 % by volume. The specimens were heated from 20 °C to 600 °C at a rate of 5 °C/min. After reaching target temperature, they were kept for 2 h and naturally cooled to ambient temperature. Subsequently, mixtures were tested to evaluate the apparent changes, weight loss, volume change, ultrasonic pulse velocity (UPV), damage degree, dynamic elasticity modulus, compressive strength and split-tensile strength before and after high temperature. Results show the compressive strength increased by 3 %-6% from 20 °C to 150 °C, then gradually decreased and a strength loss of 30–40 % was observed after 600 °C. Whereas the splitting tensile strength continued to decline as rising temperature, with a 60 %-70 % change in strength loss after 600 °C. Concrete with 10 % GP substitution and 10 %-20 % CG substitution exhibited better performance in this experiment at room temperature and high temperature in terms of mechanical, physical and durability properties compared to others. Besides, as raised temperature, an increase in water absorption and mass loss was observed for all mixtures, while the UPV reduced until it became doubtful. In conclusion, the combined substitution of CG and GP for natural aggregates can improve the performance of concrete after elevated temperature. [ABSTRACT FROM AUTHOR]

• AC and AAC as low-cost alternative adsorbents for phosphate removal. • Activation with white cement enhances adsorption (46.3%) and desorption (51.3%). • Pore filling, ligand exchange, attraction and precipitation in adsorption. • Repulsion from competition PO 4 −3 and P-displaced hydroxides by OH- in desorption. Adsorbing phosphate (PO 4 −3) from aqueous solutions onto concrete-based construction waste represents a low-cost, nontoxic, and sustainable technique. The novelty of this paper focuses on the adsorption and desorption of PO 4 −3 from aqueous solutions using autoclaved concrete (AC) chemically activated with white cement (AAC), representing an innovative adsorbent. Pseudo-second-order model better represent adsorption for AC (0.29 mg g−1; pH 6.35) and AAC (0.54 mg g−1; pH 6.53). The experimental data adjusted better with Freundlich and Langmuir models for AC (8.87 mg g−1) and AAC (3.90 mg g−1), suggesting physisorption and chemisorption, respectively. The presence of calcite could promote ligand exchange onto adsorbent surfaces. For desorption, pseudo-first-order model better explained for AC (0.19 mg g−1) and pseudo-second-order model for AAC (0.39 mg g−1). Sips model better fitted the equilibrium data (0.45 mg g−1 AC; 1.97 mg g−1 AAC), related to ionic exchange and electrostatic repulsion. Phosphate adsorption tends to be more reversible in AC. The chemical activation with white cement enhanced the phosphate removal and recovery by the alternative low-cost autoclaved aerated concrete. Finally, AC and AAC presented potential of reducing phosphate with 64.7% and 92.6% for raw wastewater and 83.1% and 84.8% for primary-treated effluent of a corn flour processing, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

The need to increase the sustainability of the construction industry is leading to the search for alternative sources of raw materials. Liquid crystal display (LCD) screens have been used for many years and are also rapidly ageing as a result of fast development. Therefore, the use of waste from LCD screens is an interesting avenue for the construction industry. This paper presents a very practical study of the use of old LCD screen of ground material to replace various fine aggregates. Fifteen concrete mixes of different strength levels and with different amounts of LCD powder were prepared. These are C20, C25, and C35 grade concretes, all of which contain LCD powder in quantities ranging from 15% to 60%. Results of density, compressive strength, and tensile strength at 7 and 28 days after concreting. The results are correlated with the number of replacement components and are also correlated with each other. The data presented to improve our understanding of the practical application of LCD waste aggregate in concrete. The results show that the amount of LCD powder has a direct linear effect on the compressive strength and also a direct lognormal effect on the tensile strength of concrete. [ABSTRACT FROM AUTHOR]

A significant body of research has been carried out to find suitable waste materials or industrial by-products that could replace portland cement and reduce the environmental footprint of the concrete industry. Many studies focus on technical aspects, lacking an assessment of environmental impacts associated with using these alternative materials, and the contribution to the sustainability of the sector remains unclear. In this paper, we present the development of lightweight blocks containing the finest fractions of waste concrete along with a holistic study of the developed product's structural and environmental performance. The results demonstrate the feasibility of such a recycling strategy and its environmental benefits. However, despite replacing 60 wt.% of portland cement in the developed lightweight blocks, their carbon footprint is not negligible, and to reduce CO 2 emissions in the construction sector significantly will require holistic measures that promote the reuse of whole building elements instead of their disintegration and subsequent recycling. [ABSTRACT FROM AUTHOR]

• Recycling and recovery of local waste. • Saving of natural resources. • Reduction in material costs. • Reduction of greenhouse gas emissions. • Improvement of the quality of construction concrete. Disposing glass into open spaces and landfills is among the most serious environmental threats, as well as a source of potential health risks around the world. Therefore, in the construction sector, recovering discarded glass as a building material is gaining popularity since it reduces greenhouse gas-footprint and associated environmental problems. Our paper investigates experimental and numerical modeling of the uni-axial compression behavior at 28 days of concrete cylinders containing colored waste glass (WG) and confined by a polypropylene textile. In doing so, an experimental protocol was performed by partial substitution in concrete to reduce the cement and sand levels of 0%, 5%, 10% and 15%. The best-performing variant is confined with textile sourced from the salvage sector too though. In this section, we studied the experimental and numerical behavior taking into account the type of confinement such as total confinement (TCC), partial confinement concrete circular (PCCC), and partial confinement concrete helical (PCCH). The obtained results in terms of stress evolution are presented and discussed, indeed, they represent a promising revelation regarding the improvement in terms of rigidity. The confrontation of the experimental and numerical results shows a satisfactory agreement. [ABSTRACT FROM AUTHOR]

• The particle size of CWS after wet-grinding decreased (D50 = 0.7 μm) and the pH value increased. • The C S H gel of CWS increased after wet-grinding. • The addition of CSW has significantly improved the early hydration rate of cement-based materials. Adding nano particles were supposed to displace steaming curing in manufacturing prefabricated components of concrete for avoiding thermal damage. Nevertheless, there were not yet appropriate nano particles adapted for practical production, and the main reason was those existing nano particles involved complicated technological processes and high costs. Last incompatibility with cement-based materials confined to its application. In this study, a new early strength agent was prepared by wet-grinding concrete waste slurry (CWS). The physicochemical properties of CWS after wet-grinding were analyzed by means of XRD, the particle size distribution (PSD), ICP, SEM, pH, resistivity, and TG. Finally, the effects of CWS on the early hydration processes and mechanical properties of cement-based materials were explored by means of setting time, hydration heat, chemical shrinkage, resistivity, mechanical properties, and MIP. The results showed that the particle size of CWS after wet-grinding decreased (D50 = 0.7 μm). Meanwhile, the surface area and the dissolution of alkaline ions in the solution increased, which provided nucleation sites and the alkaline environment for the early hydration of cement-based materials. Moreover, the early hydration rate of cement and mechanical properties were greatly improved. For instance, the cumulative heat release at 12 h increased by 111.7%, the induction period was shortened, the gel hole increased by 8% in 12 h, the large hole decreased by 37%, and the initial and final coagulation time was shortened by >30%, the compressive strength at 12 h increased by 406.3%, and the compressive strength was basically equivalent in the later period. The research in this paper showed that it was feasible to prepare the new early strength agent from CWS through the wet-grinding treatment, which provided a new reference for the green development of the prefabricated component industry. [ABSTRACT FROM AUTHOR]

• 48 concrete-filled GFRP tube stub columns were tested under eccentric load. • RCA decreased of bearing capacity and deformation capacity of bias specimen. • Steel fiber finitely made up for the negative effect causing by recycled concrete. • Finite element model in good agreement with test results was established. • Simplified calculation model for bias bearing capacity was proposed. Recycled concrete-filled GFRP tube (CFGT) columns can not only meet the recycling of waste concrete but also use FRP tubes to improve the mechanical properties of recycled concrete. This paper proposes a new structural form of steel fiber reinforced recycled concrete-filled GFRP tube column, and carries out research on the performance of CFGT column under eccentric compression. The variables considered in the experiment include GFRP tube thickness, the replacement rate of recycled coarse aggregate (RCA), steel fiber volume content, and initial eccentric distance. The bias bearing capacity, load-lateral mid-span deflection relationship, and nominal stress–strain relationship of the columns was analyzed. The tested results indicated that the addition of steel fiber kept the core concrete relatively intact after the specimen was destroyed and finitely compensated for the negative effect of recycled concrete on the whole specimen. In addition, a finite element model which was in good agreement with the experimental results was established, and the relatively complete N u - M u curves and N u / N 0 - M u / M 0 curves were obtained by parameter analysis. Finally, formulas for calculating the bias bearing capacity and the corresponding mid-span bending moment of CFGT columns were proposed. [ABSTRACT FROM AUTHOR]

CO 2 is released during the manufacture of ordinary Portland cement (OPC). The utilization of wastes and byproducts in concrete can lead to new sustainable constructions. To replace OPC in high-strength Portland cement concrete (HSPC), ground granulated blast furnace slag (GGBS) is utilized. GGBS is a by-product of the blast furnace used for iron manufacturing. It has a high silicate gel content and is used to produce good concrete. This paper investigates the load-deformation behavior of high-strength reinforced geopolymer concrete (HSGC) beams that were tested in flexure after being repaired. Six beams were placed using HSGC and HSPC. The original beams were tested, and deflections were measured. Specimens were tested under static stresses, then repaired with epoxy resin injection and re-tested for flexural strength. For both the original and repaired beams, load versus deflection graphs were recorded. Maximum deflection, ultimate load, cracking load, and crack pattern were all determined. The findings suggest that the restored HSGC beams' strength is equivalent to that of the original beams. The strength of the beam has been recovered. The cracks do not re-open after retesting, instead, new nearby cracks developed. The repaired beams showed superior flexural behavior and greater ductility than the original beams. [ABSTRACT FROM AUTHOR]

Great autogenous shrinkage has become a common problem in cement-based materials with a low water-to-binder ratio (w/b). To limit the autogenous shrinkage in ultra-high performance concrete (UHPC) during the process of hydration and curing, sustainable use of recycled micropowder (RMP) made from autoclaved aerated concrete waste (AACW) to cure UHPC internally is proposed in this paper. The influence of RMP (at the levels 5%, 10%, and 15% by mass) with three particle size classes ranging from 0 to 600 μm on the autogenous shrinkage, hydration reaction, internal relative humidity, and compressive strength of UHPC were investigated. The results show that mixtures with different dosages and particle sizes improve the fluidity of UHPC, and its internal curing effect can effectively inhibit the early-age autogenous shrinkage of UHPC and maintain a higher internal humidity compared with the control group. The incorporation of RMP can advance the appearance of a hydration peak and increase the cumulative heat of hydration. Microscale analyses show that the curing water released from RMP promotes the hydration of the unhydrated cement around RMP. The generated hydration product filled the surface pores of RMP and weakened the negative effect of the pores introduced by RMP on the compressive strength of UHPC. Thus, RMP can be utilized as internal curing materials for UHPC to reduce autogenous shrinkage. • The potential for internal curing of RMP in UHPC is investigated. • Autogenous shrinkage of UHPC with RMP is reduced by 65%. • The underlying mechanism behind internal curing of RMP has been explored. • Compressive strength of UHPC with RMP can still exceed 160 MPa at 28 days. [ABSTRACT FROM AUTHOR]