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Highlights • Lime sludge utilization in concrete, mortars, fired bricks, ceramics and cement. • 10–30% cement replacement in concrete and mortars by lime sludge is optimum. • 25–30% replacement of fine aggregates by lime sludge is optimum. • Bricks and ceramic production with lime sludge conserves less energy. • Lime sludge eco clinker synthesizes with less carbon footprint and temperature. Abstract This review paper encompasses the inclusive approach of lime sludge valorization in construction materials. Research studies based on cement and aggregate replacement by lime sludge concludes that 10–30% lime sludge is gainfully utilized in sustainable concrete and mortar. Additional prospect for lime sludge application in construction material is the production of cement and ceramics. Significant use of lime sludge in combination with supplementary cementitious materials such as silica fume, nanosilica and fly ash is recommended for the production of cement components and ceramics. The recommendations are also suggested in accordance with the outcome of the study. [ABSTRACT FROM AUTHOR]

Abstract: The use of paper-mill residuals in concrete formulations provides an alternative to landfill disposal. A response surface statistical methodology was carried out to model the influence on the slump and compressive strength of concrete containing paper-mill residuals with and without Class F fly ash replacement. The variables considered in this study included the water/cement ratio (w/c), paper-mill residual content and fly ash content to total cementitious material (FA/CM). The performance of the derived models to achieve good balance between the workability and compressive strength were further discussed by using the contour diagrams. The results showed that the compressive strength of concrete containing paper-mill residuals could be predicted from the referred slump value. [Copyright &y& Elsevier]

Abstract: The use of paper-mill residuals in concrete formulations was investigated as an alternative to landfill disposal. The mechanical and durability properties of concrete containing paper-mill residuals collected from a wastewater treatment-plant were evaluated. Class F fly ash was used as a replacement for Portland cement (PC) when incorporated into concrete mixtures containing paper-mill residuals and the resulting products were compared to normal concrete. Compressive, splitting tensile, flexural strength and drying shrinkage tests were carried out to evaluate the mechanical properties for up to 90days. Rapid chloride-permeability tests and initial surface-absorption tests were carried out at 28days to determine the durability properties. Concrete containing paper-mill residuals showed improvement in the durability test results when PC was replaced with class F fly ash. [ABSTRACT FROM AUTHOR]

Abstract: Making use of industrial by-product or waste clay to partially replace cement in concrete has greatly contributed to sustainable development of environment. This study investigated the optimal activation condition for producing high reactivity metakaolin (MK) by using kaolin by-products (KB) from paper industry. Initially, the material properties of KB were analyzed in this study and the results indicated its great potential to be treated by calcination to be a very effective pozzolan. Afterwards, MK samples produced from different activation treatments of KB, including different calcining temperature, calcining duration, initial temperature rise rime and grinding particle size, were applied in mortar to determine their pozzolanic effect. Results indicated that the optimal activation condition for KB to high reactivity MK conversion is 2-h calcining duration at 750°C and with 7μm grinding particle size. Finally, compressive and flexural strengths of mortar samples produced by replacing cement with 0–25% MK content were tested and the results showed that 15% was the optimal cement replacement level of MK and the mortar so produced exhibited 20% improvement in compressive strength compared to control mortar. [ABSTRACT FROM AUTHOR]

Some errors exist in the above paper. [ABSTRACT FROM AUTHOR]

• The comment concerns a paper published in Construction and Building Materials. • The Mittag-Leffler function is used in the paper. • The Mittag-Leffler function is defined only with dimensionless parameters. • In the paper, in the Mittag-Leffler function dimensional parameters have been used. [ABSTRACT FROM AUTHOR]

Lignosulfonates are water-soluble anionic polyelectrolyte polymers produced during industrial paper manufacturing. This study investigated concrete produced using lignosulfonates with various chemical contents at different concentrations. Therefore, concrete mixtures were produced using Ca-lignosulfonate (LSc), Na-lignosulfonate (LSn), Mg-lignosulfonate (LSm), and K-lignosulfonate (LSk) at concentrations of 0.4% and 0.8% by weight in the cement. Samples containing cements with different C 3 A, C 3 A + C 4 AF, and Na 2 O + K 2 O contents and variable fineness were tested to determine a compatible combination of cement and lignosulfonates. Results revealed that LSc was suitable for use in cements with greater C 3 A content and fineness and 0.8% was an appropriate usage concentration. [ABSTRACT FROM AUTHOR]

Abstract: Two modifications have been proposed for the Nurse-Saul maturity function to get better estimates of compressive strength of concrete cured at different temperatures in this paper. The modifications account for the effect of w/c ratio on the temperature dependence of strength development and the effect of curing temperature on the long-term strength. This discussion focuses on strength development behaviour of concretes cured at different temperatures. Aiming to understand the strength development of cement based materials relevant experimental studies on mortar and concrete specimens in the literature are evaluated. [Copyright &y& Elsevier]

• Mechanical and environmental study performed to identify optimum waste content. • Novel method developed for processing municipal waste cardboard within concrete. • Low inclusion of cardboard can enhance tensile strength of hybrid concrete. • Polypropylene fibers are effective in bridging disruption of cardboard to cement. • LCA impact assessment show favourable comparisons to benchmark concretes. This paper presents an experimental study and findings on the requalification of waste cardboard as a fine-aggregate replacement in the development of waste-based concrete. The design of eco-efficient and green-star concrete has become a significant focus, driven by the impact of industrial and municipal waste on both the environment and the global economy. The study aimed to utilise materials such as waste cardboard, polypropylene, and ground-granulated blast furnace slag as partial replacements for Ordinary Portland Cement and fine natural aggregate. It specifically focused on developing techniques for processing recycled cardboard into an aggregate suitable for this study. Six concrete batches were cast with incremental dosages of finely processed recycled cardboard and a fixed dosage of recycled polypropylene macro-fibres. An experimental program was conducted to determine fresh and mechanical properties at 7 and 28 days. The results were used to identify an optimal dosage level of waste cardboard suitable for commercial use. Additionally, a small-scale life-cycle assessment was performed to evaluate the environmental impact of the hybrid concrete mix. The processed cardboard exhibited desirable rheological and mechanical properties, making it a suitable fine-aggregate replacement. The addition of recycled polypropylene fibres enhanced flexural and tensile strength, establishing the blend as a suitable concrete mixture design for real-world applications. Furthermore, the life-cycle assessment highlighted the effectiveness of the mixture designs when compared to benchmark concrete mixtures. [ABSTRACT FROM AUTHOR]

All-Bamboo Aggregate Concrete (BAC) is a type of cement concrete material where all coarse aggregates are made of bamboo aggregate, a plant material that requires necessary measures to avoid or slow down its degradation in alkaline and natural environments. This paper enhances the durability of BAC materials through the treatment of bamboo aggregate with ACQ-polyacrylate (AP method). Initially, the study explores the impact of polyacrylate dilution concentration on the compressive strength and coating thickness of BAC, and based on a reasonable modification process, conducts freeze-thaw cycles, salt solution immersion, accelerated wet-dry aging, and long-term natural environment tests to assess the durability of BAC materials. The results show that a polyacrylate solution with a dilution ratio of 1:5 can form a coating thickness of 23.8μm, performing better in various durability evaluations. After 25 freeze-thaw cycles, the BAC material's loss rate of compressive strength is lower than that of Ordinary Concrete (OC). Compared with OC, BAC materials are more susceptible to salt damage after salt solution immersion. The compressive strength loss rate under 180 days of natural environment exposure is comparable to that in 10 cycles of accelerated wet-dry aging, 28 days of salt solution immersion, and 10–15 freeze-thaw cycle tests, recommending the use of freeze-thaw cycle tests for evaluating the durability of BAC materials from an experimental efficiency perspective. By exploring the durability of BAC materials, this paper provides an innovative solution in the field of construction materials, promoting the transition of the construction industry towards sustainable development. It emphasizes the feasibility and effectiveness of improving the performance of bamboo-based materials through surface treatment technology, offering a valid reference for developing more environmentally friendly and high-performance new materials in the future. • BAC materials show lower durability than traditional concrete. • Polyacrylate solution can enhance BAC durability. • Polyacrylate solution can enhance BAC durability. • Future research should optimize polyacrylate modification. [ABSTRACT FROM AUTHOR]

Building precise machine learning and deep learning models has traditionally required a combination of mathematical skills and hands-on experience to meticulously adjust hyperparameters that significantly impact the learning process. As datasets continue to expand across various engineering domains, researchers increasingly turn to machine learning methods to uncover hidden insights that may elude classic regression techniques. This surge in adoption raises concerns about the adequacy of resultant meta-models and the interpretation of findings. In response to these challenges, automated machine learning (AutoML) emerges as a promising solution, aiming to construct machine learning models with minimal intervention or guidance from human experts. This paper benchmarks AutoML solutions by providing an overview of their principles and applying them to predict the most important mechanical properties of different concrete datasets, i.e., compressive strength. Nine datasets from various concrete types, sample sizes, and features are utilized, with a detailed discussion on the benchmark dataset from high-performance concrete, applying best practices to the other eight datasets. For each case, the importance of hyperparameter tuning is discussed, alongside the ensemble and stacking models. Tree-based models are employed for each dataset to develop SHAP plots, interpret results, and understand the contribution of each component in the mix design to the overall strength of the concrete. This paper further explores three unique aspects of benchmarking AutoML in material science: (1) "reliability" by contrasting the benchmark dataset's error metric with literature collected over the past 20 years, (2) "uncertainty" by quantifying the variability in the mean and standard deviation of the error metric from different datasets and its correlation with the sample-to-feature ratio, and (3) "dilemma" by discussing the shortcomings of AutoML in specific concrete datasets. • The first comprehensive application of AutoML is presented in the concrete regression model. • Nine different concrete datasets are compared in terms of compressive strength. • AutoML's reliability, and dilemmas are evaluated in predicting concrete strength. • A benchmark problem is discussed to quantify the AutoML uncertainty in material science. • Explainable machine learning is used to identify the key contributing factors in f' c. [ABSTRACT FROM AUTHOR]

This paper not only studies the influence of fiber content on the mechanical properties of steel fiber ultra-high performance concrete (SFRUHPC), but also conducts high-speed impact tests and simulations on high-volume fiber targets with varying thicknesses to evaluate the damage characteristics of the SFRUHPC targets, such as residual velocity and penetration depth of the projectile. The results indicate that compared with ordinary concrete and low fiber content targets, the flexural strength and compressive strength of the target incorporated with 7% steel fiber reach the maximum values of 87.9 MPa and 362.9 MPa, respectively, which are significantly improved. On the other hand, the 7% steel fiber reinforced target demonstrates excellent anti-penetration performance which is evidenced by a 51.9% lower residual velocity compared to ordinary concrete targets in thin target tests, as well as a 37.4% reduction in penetration depth in thick target tests. Additionally, the rebound phenomenon of the projectile is observed during the tests. Furthermore, the three-dimensional mesoscopic numerical model established exhibits a good correlation with the experimental results. Finally, the model adopted in this paper can better predict the residual velocity and depth of penetration of the projectile. • The anti-penetration performance of three types of targets incorporating high content steel fibers were evaluated. • The high content steel fibers attribute to the better penetration resistance. • The phenomenon of projectile rebound is observed in a thick target with a steel fiber content of 7%. • The established three-dimensional mesoscopic numerical model aligns well with the experimental data. [ABSTRACT FROM AUTHOR]

Basalt fiber (BF) is an emerging environmentally-friendly fiber. Adding basalt fiber can improve the deficient recycled concrete's poor mechanical properties and durability. By reviewing nearly 120 related papers, the effects of variables such as BF content and length (0–1.5%, 9–18 mm), recycled aggregate substitution rate (0–100%), and cement mix ratio (w/b, 0.25–0.45) on the mechanical and durability properties of basalt fiber-reinforced recycled concrete (BFRAC) were discussed. Due to the presence of vulnerable interfacial transition zones, the mechanical properties of recycled concrete (RAC) continuously deteriorate over time. However, by adding an appropriate amount of basalt fiber, it is possible to improve these structural defects by forming a network structure that enhances cracking resistance within the matrix and improves interface bonding strength among other benefits. Consequently, this significantly improves the overall mechanical properties of RAC. Additionally, while incorporating recycled aggregate (RA) may reduce compressive strength initially, this deficiency can be mitigated through the proper inclusion of fibers in RAC mixtures. Optimal compressive strength for RAC is achieved with a replacement ratio between 25–50% and a fiber content ranging from 0.2–0.3%. Furthermore, properly incorporating fibers into RAC greatly enhances splitting tensile strength and flexural strength as well; specifically achieving optimal splitting tensile strength with a replacement ratio between 40%− 50%, a fiber content at 0.3%, and utilizing fibers with lengths measuring approximately 12 mm long. The primary cause for poor frost resistance in RAC lies within numerous micro-cracks and pores present in RA aggregates which lead to high water absorption rates ultimately reaching critical water saturation points resulting in freeze-thaw damage occurrences during exposure to freezing conditions. When exposed to sulfate attack, RAC undergoes a chemical reaction with sulfate ions present in the concrete, leading to the formation of numerous expansion products that negatively impact concrete performance. Progressive dehydration of hydration products under high-temperature conditions leads to a porous structure within the concrete matrix. Incorporating fibers can impede microcrack expansion during freeze-thaw, sulfate attack, and high-temperature environments, thus enhancing the erosion resistance of RAC. Compared to conventional concrete, interfacial bonding in RAC is less tight and more vulnerable to damage in complex environments. Current research on RAC suggests that the mechanism behind its damage under complex freeze-thaw load coupling environments remains unclear. It is recommended that future studies combine large-scale component tests with computational simulations to address this issue. • This paper discusses the mechanical properties and durability of BFRAC. • Numerous micro-cracks and pores in RA cause high water absorption. • When exposed to sulfate attack, CH reacts with SO2- 4 to form expansion products. • Hydration products' dehydration at high temperatures results in loose of concrete. • BF inhibits the growth of microcracks and enhances its erosion resistance. [ABSTRACT FROM AUTHOR]

This paper presents a study on the durability testing of a concrete facility located within the North Bay Port region, which has been in service for 200 months. Based on the results of 20 sets of concrete samples, an improved Kolmogorov-Smirnov (K-S) test method and gross error discrimination method are proposed to analyze the random distribution functions of the apparent chloride diffusion coefficient (D app) and the apparent surface chloride concentration (C s), and further explore the time-varying characteristics of chloride ion transmission in concrete. The research shows that the improved K-S method presented in this paper can effectively reduce the probability of type II errors by selecting a rational sample size, which can also improve detection efficiency. When the sample size does not exceed 10, the 2 σ criterion proposed in this paper can effectively identify and eliminate gross errors. In general, D app and C s follow the log-normal distribution, while the time factor (m) follows a normal distribution parameter. The value of C s basically stabilized after exposure to 80 months, whereas D app tended to stabilize after exposure to 100 months. The value of m obtained through fitting short-term experimental data is typically overestimated, and its value decreases as the exposure time prolongs. Therefore, m should also be considered a time-varying parameter that decreases with time. The tested RC structure will begin to experience rebar corrosion after 48.5–60 years of exposure to the marine environment based on the probabilistic assessment. • The 2 σ criterion was introduced to identify and rectify significant errors. • The improved K-S method was developed to minimize the likelihood of type II errors. • Chloride profiles were extracted from 200 months aged harbor concrete structures. • Both D app and C s demonstrated a good fit with the log-normal distribution. [ABSTRACT FROM AUTHOR]

The use of corrosion inhibitors for steel rebar in concrete is one of the best-demonstrated methods to mitigate the corrosion process and extend the service life of reinforced concrete structures exposed to chloride laden environment. However, the research progress on corrosion inhibitors for reinforcing steel is slow and classical, as the traditional experimental methods revealed. Recently, the application of computational methods, such as density functional theory (DFT) and molecular dynamics (MD) simulation, to corrosion research has become an essential area for gaining more insights into the detailed mechanisms of corrosion as well as identifying ways and means of technological innovation. This paper presents a systematic review of the research progress and advances in the molecular simulation of corrosion inhibitors for steel in concrete. The DFT calculations conducted on different inhibitor molecules were reviewed, and the related theoretical chemical reactivity parameters along with the donor-acceptor process were discussed. In addition, the MD simulations of various molecule/surface adsorption systems were studied, considering different steel substrates. The valuable insights gained from the computational models were introduced and consolidated into the experimental inhibition efficiency. Finally, the challenges and future perspectives of the research topic are highlighted. This paper is believed to promote the utilization of theoretical methods in corrosion research of reinforcing steel for a deep understanding of the corrosion process at the atomic level and innovative design of corrosion-resistance materials. [Display omitted] • Atomistic modeling and simulation of corrosion inhibitors for reinforcing steel are reviewed. • Research progress and advances are highlighted. • Theoretical reactivity parameters and adsorption behavior are correlated to experimental inhibition efficiency. • Molecular modeling provides a fundamental understanding of the corrosion mechanism. • Computational methods can derive the innovation process for corrosion-resistance materials. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has emerged as a suitable material for pavement rehabilitation, particularly in the context of bridge engineering. This material' attributes and performance-related characteristics have attracted attention due to the numerous advantages and potential for enhanced long-term durability of deteriorated pavements, either cementitious or asphaltic. Because of its relevance and increased use in recent years for pavement engineering applications, this paper presents a comprehensive review of recent case studies that investigate the application of UHPC in bridge pavement rehabilitation or reconstruction projects. The selected case studies include projects conducted in America, Asia, and Europe, and provide valuable insights into the design, construction, and performance of UHPC overlays. These showcase the effectiveness of UHPC in addressing common issues such as cracking, rutting, and structural deficiencies in bridge pavements. Furthermore, these highlight the superior flexural and compressive strength of UHPC, which contributes to improved load-carrying capacity and resistance to permanent deformation. Moreover, some environmental benefits derived from UHPC such as smaller carbon footprint are highlighted in the paper as well as cost-effectiveness considerations in light of the long-term performance and reduced maintenance obtained with UHPC overlays. Overall, the comprehensive literature review and case studies presented in this paper provide valuable data on material properties, project types, construction techniques, and post-rehabilitation evaluations. These findings can guide future research and assist practitioners in making informed decisions regarding the implementation of UHPC overlays for pavement rehabilitation. Finally, this paper contributes to the existing body of knowledge on UHPC overlays and emphasizes their significance in improving the longevity and sustainability of bridge pavements. • UHPC overlays enhance pavements: cracking, rutting, and structural issues addressed. • UHPC delivers strength and durability: improved load capacity and reduced deformation. • UHPC's environmental benefits: smaller carbon footprint, cost-effectiveness. • Efficient construction with UHPC: reduced time and costs using specialized machinery. [ABSTRACT FROM AUTHOR]

• Parameters of concrete geometry needed for mesostructure generation. • Shape description of aggregate and generation method of ITZ, voids and fibers. • Review and comparison on mesostructural generation strategies. • Critical review of random aggregate model and overlap detection algorithm. • Discussion on 2D or 3D model, parametric or image-based modelling. Numerical modelling at the mesoscale is a time- and cost-efficient tool to optimize concrete mix design and to analyse the phenomenological causes of mechanical failure, e.g. when developing novel concrete with unconventional materials. A successful mesoscale model strongly depends on a compromise between a realistic and an efficient representation of the mesoscale phases of concrete - coarse aggregates, mortar matrix, and interfacial transition zone (ITZ). Different approaches to achieve this goal have been developed. This paper identifies relevant parameters that are needed for general geometric modelling, including geometric properties of aggregates (shape, grading, volumetric fraction), and intrinsic phenomena of the mesostructure of concrete - the ITZ, wall effects and aggregate settlement, as well as model size and boundary. Methods to integrate these parameters into modelling are presented. The main topics of the paper are: (1) methods to model aggregate's geometry, either by parametric equations or by image analysis reconstruction; (2) critical review and evaluation of strategies to construct the mesostructure regarding convenience and realistic modelling; (3) methods related to random aggregate modelling and respective strategies to implement overlapping detection algorithms to be used during the random placement of aggregates; (4) evaluation of methods that deal with the modelling of the ITZ, voids, and fibres. The paper also argues that certain options of mesostructural models are not yet experimentally validated. [ABSTRACT FROM AUTHOR]

• The first large-scale field trial of microcapsule-based self-healing concrete in the UK. • Microcapsules were developed and implemented in concrete on site. • Self-healing process was demonstrated both in field and laboratory assessment. • Crack width and depth and permeability reduction and strength recovery was achieved. Maintaining the health and reliability of our infrastructure is of strategic importance. The current state of the UK infrastructure, and the associated huge costs of inspection, maintenance, repair and eventual replacement, is not sustainable and is no longer environmentally viable. The design of infrastructure, mainly concrete, remains traditional and poor material performance continues to be the main cause of deterioration and failure in our infrastructure systems. Biomimetic materials, that emulate natural biological systems in their ability to self-healing, provide an exciting and plausible solution. Embedding cementitious materials with in-built capabilities to sense and respond to their environmental triggers could potentially eliminate all external interventions and deliver a resilience infrastructure. The work presented in this paper forms part of a national initiative that has been developing biomimetic cementitious infrastructure materials which culminated in the first large-scale field trials of self-healing concrete in the UK testing four different but complementary technologies that were developed. This paper focuses on one self-healing technology, namely microcapsules, which contain a healing agent that is released on their rupture as a result of crack propagation. The paper will present details of the microcapsules used, their implementation in concrete and in the field trials and time-related, field and laboratory, assessment of the self-healing process. It also highlights challenges faced and improvements that are now on-going to produce the next generation of the microcapsule self-healing cementitious system. [ABSTRACT FROM AUTHOR]

This study presented experimental results of mechanical properties of RAC containing mineral admixtures at 500 °C. Four different mineral admixtures (fly ash (FA), waste paper sludge ash (PSA), silica fume (SF), metakaolin (MK)) were used in RAC containing 100% coarse RCA through the addition or replacement method. The results indicated that mineral admixtures significantly enhanced the resistance of RAC to the high temperature. The addition method increased the resistance of RAC to the high temperature better than the replacement method. FA improved the residual compressive strength of heated RAC the most followed by MK, PSA, cement, and SF although SF, MK, and PSA concrete showed the higher improvement of compressive strength than others at 20 °C. The addition of 5% and 10% FA in RAC increased 38.45% and 35.23% the residual compressive strength of heated RAC, respectively. The mineral admixtures had an insignificant effect on the UPV values and density of RAC. The addition of mineral admixtures in RAC substantially improved the slope of ascending branch of stress-strain curves of heated RAC. Moreover, the incorporation of mineral admixtures in RAC contributed to an increase in the elastic modulus, toughness, and critical strain of RAC at the elevated temperature. The study also proposed the equations to predict the residual compressive strength and elastic modulus of heated RAC, which can provide references for practical application of RAC. [ABSTRACT FROM AUTHOR]

• Mechanical properties of SSC concrete were reduced by FA replacement. • Shrinkages of SSC concrete was mitigated by FA replacement. • The replacement of FA decreased the relaxed stress of SSC concrete. • Nonlinear relationship between viscoelastic behaviors was revealed. This paper aimed to study the early-age properties and viscoelastic behaviors of supersulfated cement (SSC) concrete with different replacement ratios (15%, 30%, and 50%) of fly ash (FA). Ordinary Portland cement (OPC) concrete was also designed for reference. Mechanical properties and free shrinkage were tested. Stress relaxation and creep as the significant viscoelastic behaviors were investigated in restrained ring test with different degrees of restraint. The results showed that later mechanical properties of SSC concrete approached or exceeded that of OPC concrete while replacement of FA caused a significant reduction. The workability of SSC concrete was improved with FA replacement. Free shrinkage was mitigated by FA due to the significant reduction on autogenous shrinkage of SSC concrete. At a high degree of restraint, SSC concrete with a FA replacement ratio of 50% exhibited a high cracking resistance. At a relatively low degree of restraint, cracking potential was reduced by FA replacement due to its significant mitigation on shrinkages. Relaxed stress of SSC concrete decreased with an increase on FA replacement ratio. The nonlinear relationship between relaxation and creep coefficients of SSC concrete was established regardless of FA replacement ratios and degrees of restraint, which was different from OPC concrete. The results obtained in this paper might promote the reliable applications of SSC concrete in the future. [ABSTRACT FROM AUTHOR]

• Ultra-high performance concrete (UHPC) is a high-tech concrete composite that swiftly grown in popularity worldwide. • The 2% steel fibers used in UHPC design accounts about 30% and 40% of material cost and carbon emissions. • UHPC requires higher initial materials cost than NSC due to its high OPC content, steel fiber, and lack of design regulations. • This paper systematically reviews the cost of raw materials, carbon emission, and ductility performance of UHPC. • This review can help to improve current design efficiency and standards for the cost-effective, and viable UHPC recipe. • More attentions are required to standardize curing, improve structural ductility, and set cost design guidelines for UHPC. Ultra-high performance concrete (UHPC) is a cutting-edge pozzolan composite material composed of a high proportion of discontinuous internal reinforcing fibers, a water-to-binder material ratio of no more than 0.25, and an optimal gradient of granular particles. Despite various potential concrete applications, UHPC is only utilized on occasion because of a lack of widely accepted design standards, rigid design requirements, high starting costs, and a lack of contractor experience. The creation and widespread adoption of UHPC design code requirements would motivate industry participants to implement large-scale applications. With the recent efforts of institutes (such as ACI) that identified the use of high-strength steel fibers in concrete as a significant research priority, it becomes highly relevant. According to sources, existing UHPC materials comprise 2% or more steel fibers, accounting for around 30% and 40% of material prices and 40% of carbon emissions, respectively. Moreover, it is discovered that UHPC mostly exhibits a lower structural ductility than conventional concrete applications and frequently collapses early after crack localization. Regarding the sustainability aspect, the technological use of cementitious materials in the design of UHPC supports the concept of sustainable development, enabling slender sections, thereby using less concrete (less cement) that leads to lower embodied energy and CO 2 emissions compared to conventional concrete. Therefore, the need to evaluate the major findings of previous researches and exhibit the potential approaches that could lead to lowering fiber volume (to reduce cost) and improve the structural ductility of structural applications of UHPC is urgently required. However, this paper systematically reviews the cost of raw materials, structural behavior, and ductility performance of UHPC. It is also concise and assessed the results of CO 2 capturing strategies and uptake in UHPC that are undertaken with the establishment of a framework for manual guidelines as a sustainable UHPC product. This cutting-edge summary should help engineers, consultants, contractors, and others in the construction industry better understand the unique qualities of UHPC, making this long-lasting and eco-friendly construction material seem less mysterious. Professionals will benefit from this analysis by receiving recommendations on how to enhance present design efficiency and develop possible guidelines and standards for a sustainable, low-cost UHPC formula. Because of this, UHPC can be widely used as a sustainable, long-term solution for civil engineering buildings and networks. [ABSTRACT FROM AUTHOR]

• Need for hydrophobic modification. • Different methods and materials. • Mechanical and durability properties of hydrophobic geopolymer. • Microstructure study of hydrophobic geopolymer. • Pilot study yielding WCA as 106.038˚. The long-term durability of geopolymer concrete is one of the main problems that needs to be overcome before it can be universally acknowledged as a viable alternative to conventional concrete. The main cause of the durability issue is the migration and transport of water in the hydrophilic porous structure of geopolymer materials. To increase the long-term durability of geopolymer concrete, hydrophobic modification of geopolymers has recently garnered the interest of the researchers, and there is a lack of comprehensive summarization of the literature on hydrophobic geopolymer concrete composites, their preparation strategies, characterization methods, and properties, which has been the inspiration behind this literature review. This paper discusses the recent developments in the field of hydrophobic modification of geopolymer concrete, the different modification approaches, surface classification based on wettability, materials used, and the properties affected due to hydrophobic alternation. Properties studied include Water Contact Angle (WCA), surface energy, physical, mechanical, durability, and microstructural properties of the modified composites. Based on the literature reviewed, a pilot study was also carried out using an organosilane-based material to induce hydrophobicity in geopolymer concrete. Integral hydrophobic modification yielded a WCA of 66.083˚ whereas surface modification yielded a WCA as high as 106.038˚, which indicates successful modification of a hydrophilic surface to a hydrophobic one. Although the work on hydrophobic geopolymer concrete is limited, this paper is anticipated to serve as a roadmap for future investigations into the creation, processing, and characterization of hydrophobic geopolymer concrete. [ABSTRACT FROM AUTHOR]

• Paper presents economic and environmental benefits of concrete made with IBWA. • Fine aggregate replaced with 0%, 5%, 10%, 15% and 20% Incinerated Biomedical Waste Ash. • Strength, permeability, water absorption and sorptivity properties investigated. • Use of 5% IBWA improves strength and reduces permeability. • Cement stabilization reduces the leaching of metals from IBWA concrete. Biomedical waste is combination of medical waste from various sources like hospitals, research centers, clinics etc. and that presently or in the future poses a significant risk to human, plant or animal life. As it is produced in abundance and therefore cannot be treated or disposed of without special precautions. Generally biomedical waste is burned in incineration plant and produce Incinerated Biomedical Waste Ash (IBWA). It is considered dangerous or lethal because it may contain toxic substances such as heavy metals (hazardous waste). Typically, IBWA is dumped in a landfill to limit its spreading in the environment. But as none of the landfills is 100% leak-proof. This paper presents the influence of incinerated biomedical waste ash as fine aggregate replacement on the strength and permeation properties of concrete. For this purpose, a control concrete mix was made and four concrete mixes were made with four different percentages (5, 10, 15, and 20%) of IBWA. Results from the experimental study show that the incorporation of 5% IBWA as a partial sand replacement advances the strength and durability performance of the concrete. Compressive and split tensile strength test were performed upto age of 56 days and rapid chloride penetrability test (R.C.P.T.), water absorption, sorptivity and leachate analysis were performed upto age of 28 days. Toxicity characteristic leaching procedure (TCLP) test was performed and results indicates that it is non-hazardous. [ABSTRACT FROM AUTHOR]

• Detailed description of all known MICP mechanisms provided. • Applicability of various MICP mechanisms in microbial concrete discussed. • Potential of certain MICP mechanisms so far not utilized for concrete revealed. • Bacterial selection for concrete under diverse environmental conditions proposed. There are various mechanisms through which bacteria precipitate calcium carbonate, out of which a few have been recognised for application in concrete for crack healing. This paper first presents a review of work carried out on microbial concrete from the viewpoint of microbial induced carbonate precipitation (MICP) mechanisms. The mechanisms so far applied to concrete have limitations, especially with regard to their applicability to structures exposed to different environmental conditions. The paper considers the issue and presents a consolidated study of all the known MICP mechanisms, highlighting their associated advantages and disadvantages, for use in concrete structures. Based on this, guidelines are provided for the selection of the most suitable bacteria for natural crack remediation of a concrete structure exposed to a particular environment. Apart from crack healing, the study also throws light on some significant additional benefits of certain MICP mechanisms for use in concrete. [ABSTRACT FROM AUTHOR]

• The laws of deposition and distribution of shotcrete-rebound are revealed. • The relationship between rheological properties and rebound of fresh concrete is defined. • The relationship between energy dissipation law and rebound is studied. In order to reveal the laws surrounding the rheological properties of fresh concrete on shotcrete-rebound characteristics, this paper aims to study the relationship between the rebound rate of wet-mix shotcrete and the rheological properties of fresh concrete slump, yield stress, plastic viscosity, etc), as well as the relationship between shotcrete-rebound and energy loss by adding additive components of different types and dosages. The additional components involved in this paper include polypropylene fibre, a polycarboxylic water reducing agent, an alkali-free accelerator, and an organic polymer tackifier. The experimental results show that the shotcrete-rebound materials are distributed in a fan shape, and the coarse aggregate in the rebound materials accounts for the largest proportion. If the amount of accelerator (3%–7%) and tackifier (1%–3%) increases, the rebound rate of the wet-mix shotcrete decreases. Also, if the amount of water reducing agent (0.5%–1.5%) increases, the rebound rate of the wet-mix shotcrete increases. Finally, if the fibre content (0.6 kg/m3–1.8 kg/m3) increases, the rebound rate of wet-mix shotcrete first decreases and then increases. Through the analysis of correlation and multiple linear regression, it has been concluded that changes in the slump, yield stress, and bleeding rate significantly affect the concrete rebound rate, and a multiple linear regression equation for predicting the rebound has been obtained. The energy loss of the shotcrete is proportional to the shotcrete rebound rate, and can also be used as an evaluation index of shotcrete performance. [ABSTRACT FROM AUTHOR]

• Thermo-hydraulic damage mechanisms are the cause of explosive spalling of concrete. • X-ray-CT measurements allow tracking of the thermally-induced moisture transport. • CT results provide a temporal record of moisture changes (drying and accumulation). • 1H-NMR measurements show a moisture reconfiguration from gel to interhydrate pores. The thermohydraulic damage mechanism is one of the primary causes for explosive spalling of high-performance concrete. This paper presents the spatially- and temporally-resolved analysis of the thermally-induced moisture transport and reconfiguration processes by means of X-ray-CT and 1H-NMR. Thermal testing results for a high-performance concrete, which is sensitive to explosive spalling and which was prepared with and without added polypropylene fibres, are presented in this paper. These results indicate that the addition of fibres leads to a faster and deeper migration of the drying front and, thus, to a lower likelihood of vapour-pressure induced explosive spalling. [ABSTRACT FROM AUTHOR]

• A comprehensive review on the physical and functional characteristics of foam concrete. • An in-depth review of foamed concrete in terms of its components, fresh state and physical properties. • A brief review of foam concrete prepared using various types of foams. • Various mechanical properties and functional characteristics are also presented. • A brief outline of various applications of foam concrete is also reported. With the increase in global warming, the construction sector is trying to find an alternative to ordinary concrete due to its high dead weight and thermal conductivity. Researches are going in different directions and presently the emerging trend is the use of foamed concrete, which is a lightweight concrete having more strength-to-weight ratio with density varing from 300 to 1800 kg/m3. This reduces the dead load on the structure, cost of production and labour cost involved during the construction and transportation. Also, the large number of pores in the foam concrete reduces the thermal and sound absorption, thus making the structure appropriate for all climatic conditions. The paper reports an in-depth review of foamed concrete in terms of its components, fresh state and physical properties like consistency, stability, workability, drying shrinkage, air-void system and water absorption. It also includes a brief review of foam concrete prepared using various types of foams such as chemically expanded and air cured foams. Various mechanical properties like compressive strength, flexural strength and elastic modulus are also discussed. In addition, to have more understanding about the variable aspects that promote a better habitable atmosphere for all climatic conditions functional characteristics like thermal conductivity, fire resistance, acoustic properties and resistance to aggressive environment are also presented. Apart from this, the paper reports a brief outline of various applications of foam concrete. [ABSTRACT FROM AUTHOR]

• Damaged RC slabs strengthened with UHPC layer were tested in laboratory and applied in field. • Two different load patterns: negative bending moment and positive bending moment. • Two different curing conditions: normal temperature curing and high temperature steam curing. • Calculated flexure capacity by analytical models developed theoretically agreed well with experimental values. Based on strengthening a damaged bridge deck in the field, this paper conducted flexural experiments on a scaled damaged bridge deck strengthened by reinforced ultrahigh performance concrete (UHPC) layer with high temperature steam and normal temperature curing; this paper investigates cracking capacity, ultimate capacity, deformation features and failure mode of RC-UHPC composites under positive bending moment and negative bending moment, respectively. Experimental results indicate that cracking and ultimate capacity of composites increased by about 2.5 and 2 times respectively with UHPC located at tension face comparing with intact RC slab; while for UHPC at compression face, no change in cracking capacity was observed and ultimate capacity was 30% higher than that of intact RC slab. Meanwhile, stiffness also obviously increased with tensile stress in steel reinforcement in RC slabs, decreasing after strengthening for all strengthened slabs; and propagation of cracks in RC slabs was restrained and delayed due to ultrahigh ductility and behavior of strain hardening of UHPC. Based on experimental results and failure mode, analytical equations for cracking and ultimate flexure capacity of UHPC-RC slabs were constructed, and applicability of equations was validated by some experimental results in this paper and other literature with good accuracy by predicted equations. Finally, the research achievements of this paper were effectively applied on the reinforcement design of damaged deck of main girder in a cable-stayed bridge. [ABSTRACT FROM AUTHOR]

• The thicknesses of ITZ around stone and sand were determined by Ca/Si ratio. • The elastic modulus of each phase was determined by nanoindentation technology. • A theoretical model for evaluating elastic modulus of concrete was established. This paper aims to evaluate the elastic modulus of concrete with nanoidentation technique and homogenization method. In this paper, concrete is divided into two parts: coarse pore and matrix. It is assumed that matrix is composed of five phases: stone aggregate, ITZ-1 (interfacial transition zone around stone aggregate), sand, ITZ-2 (interfacial transition zone around sand) and paste. Based on the Ca/Si ratio change in interface region, the thicknesses of interfacial transition zone around stone and sand were determined, respectively. The elastic moduli of stone, ITZ-1, sand, ITZ-2 and paste were determined by nanoidentation technique. The volume fraction of each phase was determined by Lu & Torquato model. The elastic modulus of matrix was calculated by Self-Consistent Method. Then, combining with the porosity of coarse pore determined by hardened concrete pore structure analyzer, the elastic modulus of concrete could be obtained by Mori-Tanaka method. Through comparison, it is found that the error between the theoretical calculation value and the macroscopic test value is within 10%. Therefore, the effectiveness of theoretical prediction model proposed in this paper was verified. [ABSTRACT FROM AUTHOR]

Highlights • Research conducted on external steel-confined concrete are discussed. • Variables of structural performance of steel-confined concrete are summarised. • Closed-form expressions for steel-confined concrete are reviewed. • Finite element analysis models for confined concrete are critically reviewed. Abstract Steel is a cheaper and more environmentally friendly alternative to externally confine concrete compared to the commonly known fiber-reinforced polymer (FRP). Numerous studies have been conducted both experimentally and analytically to understand the compressive behaviour of external steel-confined concrete. This paper presents an overview of four external steel-based confinement techniques for concrete followed up by review on existing closed-form expressions and finite element analysis models for external steel-confined concrete. It is shown that the four techniques can be generalised based on the strengthening mechanisms involved. Through this review, it is shown that effect of pre-load and pre-tension have not been taken into account by most previous research. Additionally, the parameters calibration for existing finite element analysis models were based on FRP-confined concrete experimental data only. The needs for future experimental investigation and analytical work for external steel-confined concrete are presented in the last part of this paper. [ABSTRACT FROM AUTHOR]

Highlights • MgO can compensate and prevent concrete cracking in design and thermal control. • Finding a mathematical model suitable for the deformation process of MgO concrete is crucial. • The new hyperbolic expansive model is a function of MgO content, curing time and temperature. • The calculation results compared with the measured data with good agreements. Abstract To improve concrete crack prevention performance for high concrete dams, several studies have shown that the addition of MgO-type expansive can compensate for shrinkage of concrete and prevent concrete from cracking. In this paper, the Autogenous Volume Deformation (AVD) process of MgO concrete as a function of curing age, temperature and MgO content has been presented. The objective of this paper is to develop a hyperbolic expansive model, in which the parameters are developed and validated for the modeling of AVD process of MgO concrete and compared with Shu-hua Liu's method. In addition, the correction coefficients have been proposed and the relationships between the model parameters and MgO content have been also introduced. The model parameters were obtained based on the experimental data under laboratory conditions for the AVD process. Then the final equation of the hyperbolic expansive model is determined by the MgO content, the curing temperature and time. The calculation results are then compared with the measured data; and the reasonably good correlation between simulated and measured results indicates that the selected values of G pre , c(T) , and the relationships between model coefficients, MgO content, and temperature, are almost perfect. It will enhance the design reliability of the Linxihe RCC arch dam project and others. [ABSTRACT FROM AUTHOR]

Highlights • NSM FRP system has gained considerable popularity worldwide. • This paper reviews current research on concrete members retrofitted by NSM FRP system. • The review focuses on the bond characteristics between NSM FRP, adhesive and concrete. Abstract The use of fibre reinforced polymer (FRP) in civil construction applications with near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. The response of concrete structural members rehabilitated using FRP with externally-bonded (EB) method under monotonic and fatigue loading has been well reported. On the other hand, the monotonic and fatigue response of NSM FRP-rehabilitated concrete structures is less known. This paper reviews current research on concrete members retrofitted by NSM FRP system and exposed to monotonic and fatigue loading. It provides an outline of FRP composites and the fatigue behaviour of concrete, steel and FRP materials. In addition, the review focuses on the bond characteristics between NSM FRP, adhesive and concrete substrate, and on the flexure behaviour of NSM FRP-strengthened and repaired reinforced concrete (RC) beams. Furthermore, the paper reviews the failure modes, factors affecting NSM FRP systems, guidelines and codes for the use of FRP in concrete structures, damage accumulation and residual strength, stress limits in steel reinforcement, and the limitations of using epoxy and polymer-based cementitious adhesives for the strengthening of concrete members. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D Concrete Printing is an emerging technology compared to conventional construction. • This review is about a deep understanding of mix design and testing of printed concrete. • Understanding of various rheological and mechanical properties of printable concrete. • Effect of mix constituents on printed concrete with observations from the literature. • Call for establishing universally accepted standards for 3D Printable Concrete. This review paper aims to provide an inclusive characterization of the use of concrete in additive manufacturing by exploring the various parameters that affect the extrudability, pumpability, buildability, thixotropy, interlayer bonding, and anisotropy of concrete in 3D printing. The effects of using different materials, such as cement, supplementary cementitious materials (SCMS), fiber, superplasticizers, accelerators, aggregate, and nano clay, were examined in the concrete mix design. Results show that using cement, SCMS, and fibers in the concrete mix design can significantly affect the concrete's extrudability, pumpability, and buildability. Evaluating the properties of the concrete mixture, both in its fresh and hardened state, is crucial in determining the optimal mix design for 3D concrete printing. This assessment helps ensure that the resulting structure will have the desired performance. However, the long-term durability and sustainability of 3D-printed concrete structures are still uncertain. The paper concludes with a call for further research and development in the field of concrete in additive manufacturing, with a focus on developing a suitable concrete mix design and investigating the long-term durability and sustainability of 3D-printed concrete structures. Additionally, universally accepted standards for 3D-printed concrete structures should be established and implemented to ensure safety and longevity. [ABSTRACT FROM AUTHOR]

• Carbonated wastewater had uniform particles distribution and stable composition. • Cement mixed with carbonated wastewater showed desired fresh and hardened properties. • Calcite in the carbonated wastewater filled the pores of the hardened cement blocks. • Using carbonated wastewater to produce concrete can reduce CO 2 emissions by half. Recycling the concrete washing wastewater (CWW) of ready-mix concrete plants is significantly important for saving hundreds of millions of tons of water and avoiding water and soil pollution. However, to directly recycle CWW to mix fresh concrete is particularly difficult due to its high alkalinity and high solid content with unstable compositions. To respond these challenges, a feasible approach involving carbonation treatment of CWW and subsequent recycling of the carbonized CWW (CCWW) for concrete mixing is proposed in this paper. To this end, the CWW carbonation test was firstly carried out and the compositional analysis showed that the CCWW became a stable suspension with uniform distribution of fine CaCO 3 particles, stable ions contents and neural pH value. The effects of CWW, CCWW and the tap water on the fresh cement pastes hydration and the mechanical and deformation properties of hardened cement pastes were then comparatively analyzed. The results supported that CCWW contributed to the improvement of workability of fresh paste, the increase of strength, the decrease of dry shrinkage and the pore refinement of harden paste. Approximate 16.6 million tons of CO 2 per year was estimated to be captured by this approach wemix concrete plants. Benefiting from the improved mechanical properties and extraordinary CO 2 sequestration capability, recycling CCWW for concrete mixing resulted in nearly half reduction in CO 2 emission. [ABSTRACT FROM AUTHOR]

• The deterioration of RPC after sulfate freeze–thaw cycles under different replacement rates and mass proportion were studied. • The increase in RP replacement rate led to a decrease in the attack resistance of RPC. • The RPC partition-interface model and RPC damage model was established. Recycled powder (RP) has great environmental potential as a supplementary cementitious material to replace cement. However, the effect of the microstructure of recycled powder on the pore structure of concrete, which is closely related to the macroscopic properties of concrete, has not been understood. In this paper, we focused on the deterioration mechanism of recycled powder concrete (RPC) under the coupled action of sulfate freeze–thaw cycles. Recycled powder was prepared by mixing recycled brick powder (RBP) and recycled concrete powder (RCP) with different mass ratios to replace cement, and the replacement rates were set to 0%, 15% and 30%. Macroscopic physical–mechanical tests and microstructural characterization under the coupled action of sulfate freeze–thaw cycles were conducted to establish the RPC partition-interface model and damage model. The results showed that with the increase in the number of freeze–thaw cycles, the physical–mechanical properties of RPC deteriorated continuously, the critical pore size increased, the connectivity was enhanced, and the attack products ettringite and gypsum were formed. The deterioration of RPC increased with the increase in the replacement rate of recycled powder, but the increase in the mass proportion of recycled concrete powder mitigated the deterioration of RPC. The pore structure defects and distribution characteristics of RPC accelerated the deterioration process. It was concluded from the damage model that the replacement rate of recycled powder was the most important factor affecting the amount of damage. The research results of this paper provide theoretical support for the engineering application of RPC. [ABSTRACT FROM AUTHOR]

[Display omitted] • The silica fume addition enhances the mechanical and permeability properties of concrete. • The refinement of pores due to silica fume was effective in improving the permeability of concrete. • The excess amount of silica fume above the optimum limit shows an adverse effect on concrete. • The thermal performance of concrete using silica fume improves the peak cooling and heating load. • The silica fume has the feasibility to be used with other supplementary cementitious materials. The present paper discussed the silica fume (SF) as the SCM to replace cement partially in concrete. The paper aims to summarize till date literature findings and suggest necessary gaps in utilizing SF as SCM. The study's necessity and framework are highlighted through bibliographic analysis using VOS viewer software and Scopus search engine data and found a lack of research in the field of SCM in the last 5 years. The production process of SF and its physical and chemical properties are studied location-wise. The range of these properties is analysed, and it found that SF mean particle size is 10 times finer than cement which enhances the mechanical and durability of concrete. The mechanical properties studied reported that the optimum percentage of silica fume generally ranges between 7.5 and 12%. However, it is not constant and found to be dependent on w/c. An adverse effect on the characteristics of concrete was observed on excess addition of SF over the optimum limit. The feasibility of SF with other SCM and fibers was found effective in improving the concrete properties. The different properties based on the action of water transport through the concrete are studied, such as permeation, diffusion, migration, convection, void formation, sorption, wick action, absorption, and adsorption. The permeability properties were optimum between 7.5 and 10% SF. Further, the thermal performance of the building with and without SF-added concrete was performed using Revit software (BIM). It was reported that SF concrete is effective by 2.25 % and 4.30 % for cooling and heating load, respectively. Very few papers were found on the utilization of silica fume for the development of different construction products. The review concludes with recommendations for future research, aiming to stimulate more studies in this field. [ABSTRACT FROM AUTHOR]

The incorporation of Graphene Oxide (GO) nanomaterial into concrete has gained significant attention due to its potential to enhance mechanical and durability properties. The addition of GO to concrete creates considerable changes in the morphology of the concrete matrix, creating a densified microstructure. Critical parameters significantly affect these microstructural enhancements and, consequently, the final performance in GO-added concrete. These parameters include GO material properties, superplasticiser (PS) type, and dispersion techniques. Therefore, this study investigates the influence of GO on the mechanical performance of concrete, focusing on these critical factors. Unlike existing studies concentrating on a single parameter's effect, this research comprehensively compares how these parameters impact GO-added concrete. Two commercially available GO types (GO-A and GO-B) and two PS types (PS-A and PS-B) are utilised. At the same time, three commonly used mixing techniques, such as mechanical, high-speed, and ultrasonic mixing techniques, are considered for GO dispersion. GO-A is added to concrete in percentages ranging from 0.02 % to 0.14 % by weight of cement (bwoc), while GO-B ranges from 0.04 % to 0.20 % bwoc. Based on compressive strength test results, the optimum GO dosages are 0.08 % for GO-A and 0.12 % for GO-B. The highest strength results are achieved for GO-B added concrete with PS-A addition and following the ultrasonic dispersion method, highlighting these parameters as optimal for maximising GO-added concrete performance. The optimum concrete mix exhibits 33 %, 24 %, 25 %, and 30 % increments for compressive strength, indirect tensile strength, flexural strength, and elastic modulus properties at 28 days. This paper provides a deep theoretical explanation of the effects of GO material properties, dispersion techniques, and PS type on GO-added concrete performance. The findings provide valuable insights into selecting suitable parameters for optimising the mechanical properties of GO-added concrete, contributing to the advancement and effectiveness of construction materials. • Addition of Graphene Oxide (GO) is effectively improved the mechanical properties of concrete. • Choosing right GO, superplasticiser, & dispersion method is vital for optimal mechanical properties in GO-concrete. • Performance of GO-added concrete is greatly influenced by its dispersion level. • GO-added concrete dispersibility accomplished via ultrasonic dispersion polycarboxylate-ether-based superplasticisers. [ABSTRACT FROM AUTHOR]

Shrinkage cracks pose significant challenges to the long-term durability of concrete structures, and it can be effectively address by incorporating various types of fibres. Synthetic textile fibres show a significant 10–50 % shrinkage reduction, while natural cellulosic fibres achieve a comparable 5–30 % reduction. This improvement is attributed to the bridging and anchorage effects between fibres and the cement matrix, enhancing overall concrete performance. However, the factors such as fibre length, diameter, volume fraction and characteristics have significant effect on shrinkage performance. This paper aims to present a comprehensive analysis of these critical mechanisms and factors that impact the shrinkage behaviour in both synthetic textile and natural cellulosic fibre-reinforced concrete. The inclusion of fibres creates a three-dimensional fibre matrix within the concrete that provide an internal effect to restrain the absorb water and it reduce the shrinkage of the concrete. Moreover, the presence of fibres introduces a secondary reinforcing mechanism to release tension during the drying process, thereby preventing crack propagation. The highly porous nature of the cellulose structure enhances the porosity of the concrete, creating cross-linked pathways for water evaporation. However, pre wetted cellulose fibre mitigates drying shrinkage by providing internal curing of the concrete. Furthermore, various physical, chemical, and combined surface modification methods have been used to improve the properties of natural fibres. • Shrinkage, cracks in synthetic and natural cellulosic fibre concrete were discussed. • Synthetic fibres show 10–50 % shrinkage reduction while cellulose give 5–30 %. • Bridging and anchorage effect between fibres and matrix cause shrinkage reduction. • Fibre volume fraction is a key factor for shrinkage and crack behaviour in concrete. • Fibre dimensions, strength, modulus, water interaction impact shrinkage and cracks. [ABSTRACT FROM AUTHOR]

Under-slab voids are critical to traffic safety, The acoustic vibration method can be used to accurately determine whether the road surface is de-voided or not. This paper utilizes ABAQUS to construct models of concrete pavement panels with various parametric study. The fundamental vibration frequencies of these models are computed, and their characteristics are summarized. Additionally, a model of impacting cement concrete pavement with a falling ball is established to investigate the vibration properties at different points. it can be concluded that the most significant factors affecting the vibration fundamental frequency are the foundation reaction coefficient and the void area. Delamination at the corners of the panels experiences higher maximum vibration accelerations under falling ball impact when support conditions are poorer. Longer delaminated edges correspond to greater vibration accelerations. The frequencies at various points within the delaminated area are identical, while the amplitudes mirror the same acceleration. Indicating that the position of deflation has a small effect on the vibration frequency and a relatively large effect on the vibration acceleration. This study can provide an effective and non-destructive basis for future intelligent traffic pavement inspections. • We found the most important factors affecting vibration fundamental frequency. • We established the ranking parameters based on sensitivity to develop priority. • We established a model of impacting cement concrete pavement with a falling ball. • We established the link between vibrational sound and road de-vacuuming. [ABSTRACT FROM AUTHOR]

Polymer emulsion impregnation is a common method for strengthening recycled fine aggregate (RFA). By mixing Nano carbon black (NCB) into the polymer emulsion, highly conductive modified RFA (MRFA) can be simultaneously obtained. In this paper, highly conductive and self-sensing concrete was prepared by using the MRFA impregnated with the NCB and polydimethylsiloxane (PDMS) solution. The microstructure of MRFA and MRFA concrete physico-mechanical properties were studied. The effects of replacement ratio of MRFA, temperature, water content, and loading rate on the conductivity and self-sensing of prepared MRFA concrete was explored. The results show that the PDMS fills the pores of the RFA surface. The water absorption decreases by 2.53%, the apparent density and fineness modulus increased by 1.5% and 8.3%, respectively. With the increase of MRFA replacement ratio, the resistivity of concrete gradually decreases, and a sharp decline appears from 60% to 70%. The percolation threshold of concrete is calculated to be 3.37 vol% of NCB. Meanwhile, the MRFA concrete has good temperature sensitivity and humidity adaptability. Under the stress cycle loading, the stress sensitivity of the MRFA concrete with 70% replacement ratio MRFA is as high as 4.45%/MPa. Besides, the stress sensitivity of MRFA concrete decreases as the loading rate increases. • Recycled fine aggregate was treated with carbon black and polydimethylsiloxane. • Self-sensing concrete resistivity was measured by four-electrode method. • Self-sensing concrete piezoresistivity was studied. [ABSTRACT FROM AUTHOR]

Environmental characteristics such as low pressure, high-frequency freeze–thaw cycles, and salt erosion in a plateau region have a significant impact on the mechanical properties and durability of concrete. To reveal the damage mechanism of high-performance ecological geopolymer concrete (HPEGPC) incorporating tunnel spoils, slag, and fly ash (FA) in extreme environments, this study used HPEGPC with 12 % alkali-activated binders (AABS) and a binding material to machine-made sand ratio of 0.36 and ordinary Portland cement concrete (OPCC) with 12.4 % cement and a water-cement ratio of 0.5 to simulate the deterioration process of mechanical properties and durability under the action of low-pressure–salt–erosion–freeze–thaw cycles. The mass, compressive strength, relative dynamic elastic modulus loss rate, microstructure, and pore evolution patterns of HPEGPC and OPCC were analysed using experimental and microscopic tests. The results showed that the HPEGPC was significantly more resistant to freezing and salt erosion than the OPCC in both standard and hypobaric environments. The interfaces of HPEGPC before and after the low-pressure–salt-erosion–freeze–thaw cycles underwent a developmental process from a dense structure with microcracks to microcracks expanding into fracture surfaces and the dispersion of hydration products. The cementitious materials of HPEGPC have a high percentage of non-hazardous and less hazardous pores, and their dense structure results in a high resistance to freezing and salt erosion. In addition, by establishing a damage decay model and damage accumulation model for the compressive strength and relative dynamic elastic modulus, this paper provides theoretical guidance for the application of HPEGPC under low pressure, salt erosion, and freeze–thaw cycle environments of the plateau. ● HPEGPC has significantly better resistance to sulfate attack and freezing at both standard and low pressures than OPCC. ● The damage decay models and damage accumulation models were developed to predict the loss rate of compressive strength and dynamic elastic modulus of HPEGPC. ● The microstructure and pore evolution of HPEGPC and OPCC were analysed using SEM and NMR. ● The internal structural degradation mechanism of HPEGPC before and after different pressure–salt–erosion–freeze–thaw cycles was revealed. [ABSTRACT FROM AUTHOR]

In this paper, a new approach of bidirectional electro-migration rehabilitation (BIEM) using pulse currents was proposed. The effect of the duty cycle and frequency of the square wave pulse current on the BIEM was investigated. The results showed that the desalination efficiency was improved by 10 % with the decrease of duty ratio and frequency. Furthermore, With the increase of duty ratio and frequency, the hydrogen permeation of steel bars decreased by 28.5 %. More uniform desalination efficiency was obtained by using pulse current. The half-cell potential of the rebars was also measured and it was higher for the samples using pulse currents than for those using direct currents, indicating a lower risk of corrosion after pulse current treatment. The pH value of the concrete also increased during the BIEM process. • The amount of hydrogen permeation in the rebars of concrete repaired by pulse current is reduced. • Increasing frequency and decreasing duty cycle of pulse current make the desalination efficiency distributed more evenly. • Decreasing frequency and duty cycle of pulse current will increase the efficiency of chloride ions removal. [ABSTRACT FROM AUTHOR]

This paper explored the penetration of chloride into concrete damaged by high-cycle compressive fatigue loading. Two environmental conditions including immersion and wetting-drying cycles were prepared for experimentally investigating the transport performance of chloride in fatigue-damaged concrete. Additionally, a prediction model was developed with the damage index of residual strain. Test results revealed that both apparent diffusion coefficients and contents of chloride at each depth increased in fatigue-damaged concrete, indicating that the fatigue damage significantly degraded the resistance of concrete to chloride penetration. Furthermore, for fatigue damaged concretes with extremely different fatigue cycles and load levels but the same residual strain, the chloride ion content profiles were highly overlapped, which demonstrated the reasonability of selecting residual strains as fatigue damage indexes. The applicability of the transport model was firstly validated with the measured chloride contents and then the chloride transport behavior in gradient fatigue-damaged concrete was investigated numerically using the validated model. The numerical results indicated that the chloride transport was more sensitive to the residual strain at the exposed edge than to the residual curvature and the effect of the later can be neglected. • Fatigue loading definitely accelerate the penetration of chloride ions into concrete. • Transport model of chloride was developed in terms of the residual strain. • The rates of chloride transports were more sensitive to the residual strain at the exposed edge. [ABSTRACT FROM AUTHOR]

Concrete self-healing technology can be applied in tunnel, and it can enhance self-healing and durability performance of tunnel lining. In this paper, response surface methodology was used to investigate the effect of cementitious capillary crystalline waterproofing, fly ash and polypropylene fiber as external admixtures on the mechanical and impermeability self-healing performance of concrete; the optimal content of additional materials is proposed; the self-healing principle of concrete is explained through the results of SEM and XRD tests. A second-order regression model of compressive strength recovery rate and tensile strength recovery rate of concrete was established. Based on these results, the positive synergistic effect of CCCW and PF in concrete self-healing process was revealed by response surface analysis. Moreover, when the FA content was 19.6%, CCCW was 2.4%, and PA was 1.5 kg/m3 (with a volume fraction of 0.16%), the compressive strength and tensile self-healing performance of the concrete were optimized, achieving recovery rates of 88.2% and 88.5%, respectively. The impermeability pressure of the concrete reached 1.5 MPa, representing a 2.14-fold increase compared to the control concrete, and the self-healing rate of impermeability was 93%. Furthermore, SEM and XRD test results of self-repaired concrete revealed that the incorporation of FA and CCCW effectively promoted the hydration reaction of cement, so that a large number of branch-like and needle-like crystals were generated inside the concrete, which can effectively promote the self-healing of concrete cracks, enhance the structural densification, and improve the strength, impermeability and durability of concrete. • The effects of CCCW, FA and PF on mechanical and impermeability self-healing performance of concrete were studied. • The optimal content of CCCW, FA and PF was proposed. • The positive synergistic effect of CCCW and PF in concrete self-healing process was revealed by response surface analysis. • The self-healing mechanism of concrete was elucidated based on the experimental results of SEM and XRD. [ABSTRACT FROM AUTHOR]

The mechanical properties and durability of concrete are significantly affected by early frozen, during the early curing phase, concrete has a relatively low initial strength, and its hydration reaction rate is impeded by the early frost stage, leading to internal water freezing and subsequent expansive stress. The freezing and expansion deformations induce crack formation in the concrete structure. Even if positive-temperature curing is implemented for a specific period, some deformations remain irreparable, significantly compromising the mechanical properties and durability of concrete. Research on early frozen concrete mainly focus on water-cement ratio, freezing temperature, curing age, and additive dosage, which have different effects on the mechanical properties, durability, and microstructure of concrete. This paper systematically summarizes and analyzes the effects of early freezing on the mechanical properties and durability of concrete subjected to early frozen at home and abroad, and predicts and analyzes its future research directions and trends in this field. • Influences of early frost on the mechanical properties, durability, and microstructure of concrete are reviewed. • Effects of different admixtures and dosages on early frozen concrete are discussed. • The directions for further research on the effect of early frost on concrete are proposed. [ABSTRACT FROM AUTHOR]

Vibration can increase the flow ability of fresh concrete and may cause segregation. The rheology behavior of fresh concrete after vibration is different from that in the unvibrated state. In this paper, a CFD-DEM coupling method was developed to investigate the rheological behavior of fresh concrete before and after vibration. The Bingham model and Hershcel-Bulkley were respectively used as the constitutive relationship of fresh concrete in unvibrated and vibrated state. The Hertz-Mindlin with bonding bond is employed to describe the interaction between coarse aggregate. To analyze the effect of vibration on the rheological behavior of fresh concrete, the rheometer test was conducted. The relationship of shear stress and shear strain rate is linear before vibration and is nonlinear after vibration. Vibration reduces the yield stress and plastic viscosity of concrete. The shear zone decreases when fresh concrete is vibrated. • A CFD-DEM method was developed to investigate vibration on rheological behavior. • The velocity is parabolic distribution along the radial direction. • The shear height and width of vibrated fresh concrete decreases. • Vibration reduces the yield stress and plastic viscosity of concrete. [ABSTRACT FROM AUTHOR]

This paper studies the use of municipal solid waste incinerator bottom ash as a supplementary cementitious material in concrete products using an innovative chemical treatment approach. The primary objective is to address emissions associated with waste-to-energy facilities and the heavy reliance on ordinary Portland cement as the primary binder in concrete. The proposed method involves the removal of metallic aluminium from the bottom ash and the subsequent use of the treated bottom ash as a partial cement replacement to produce concrete. Concrete specimens were produced with varying proportions of treated or untreated municipal solid waste incinerator bottom ash, replacing 20%, 35%, and 55% of ordinary Portland cement according to EN 197 European standard for common cement. Moreover, class F fly ash was incorporated in equivalent percentages as a reference supplementary cementitious material, and a control mix was prepared using solely Portland cement. The evaluation encompassed multiple visual and analytical techniques, including scanning electron microscopy, X-ray diffraction, X-ray fluorescence, and setting time analyses on pastes made with Portland cement, fly ash, and bottom ash. All specimens were evaluated in terms of mechanical performance, namely compressive strength. The chemical treatment process facilitated the release of a significant quantity of hydrogen, a by-product of aluminium oxidization. Consequently, this resulted in significantly reduced formation of gas bubbles in concrete in the fresh state and, therefore, diminished expansion during the setting process. As the proportion of cement replacement with bottom ash increased, a decline in strength was observed. However, this decline was less pronounced when using treated bottom ash, particularly with lower levels of incorporation. • Municipal solid waste incinerator bottom ashes as partial cement replacement. • Novel NaOH-based chemical treatment for incinerator bottom ashes. • Mixes with untreated ashes present extensive expansion due to aluminium oxidization. • Treatment led to overall performance enhancement due to lower gas generation. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) members are subject to map cracking owing to the delayed ettringite formation (DEF) by excessive core temperature during the first few days of hydration. Studies on the mechanical properties of concrete with DEF expansion have been conducted to identify the variation in moduli and strength of the material. This paper provides a comprehensive review of the mechanical properties of plain concrete with DEF expansion to examine the degradation characteristics compared to the experimental conditions. The dynamic moduli, static moduli, and compressive strength of the plain concrete decreased up to 60%, 85%, and 65%, respectively, owing to large swelling, where the damage process showed colossal expansion. The reduction amount depends on the aggregate-to-cement ratio, chemical composition of the cement, aggregate type, water-to-cement ratio, and the mix. The static moduli is more sensitive to expansion in the initial expansion stage than other mechanical properties. The structural performance of DEF-affected RC members was also investigated, reviewing the relevant studies to include the structural performance of alkali-silica reaction (ASR) affected structures. The structural performance cannot be appraised using the mechanical properties of plain concrete. It was indicated that the DEF expansion of concrete core can be significantly confined by surrounding reinforcement in RC members. This inhibits the reduction in mechanical properties of concrete and results in maintaining the load-carrying capacity of RC members. Chemical prestress developed in concrete due to the swelling restraint by reinforcement, and anisotropic damage improves the stiffness of the RC members. • Comprehensive review of mechanical properties of DEF-affected plain concrete. • Structural performance of DEF-deteriorated RC members was studied. • Structural performance depends on DEF- induced stress in reinforced concrete. • DEF expansion confinement should be considered to assess structural performance. [ABSTRACT FROM AUTHOR]

At the meso-level, the interface transition zone (ITZ) is an important part of concrete and is closely related to the macroscopic properties of concrete. In this paper, the influences of siliceous iron tailings powder on concrete ITZ have been researched, in order to better reveal the mechanism of the powder as an auxiliary cementitious material in concrete. Based on XRD, SEM, hardness test and numerical simulation, the Ca(OH) 2 (CH) crystal orientation, calcium-silicon ratio (Ca/Si), porosity, microhardness and elastic modulus of ITZ have been explored, and the results are as follows. When water-to-binder ratio (w/b) is 0.38 and 0.48, iron tailings powder increases the complexity of CH crystal orientation in the ITZ, but the effects of w/b and hydration age on the CH crystal orientation index with and without iron tailings powder are similar. The Ca/Si of ITZ blended with iron tailings powder is lower than that of benchmark group with the same w/b. The porosity in ITZ first decreases with the distance from aggregate surface, and stabilizes at about 40 μm, and the ITZ porosity in groups of iron tailings powder is less than that in the reference group at the same w/b and the same age. The microhardness and elastic modulus of ITZ decreases by mixing the iron tailings powder, and microhardness increases with the distance from aggregate surface, and at last stabilized at also about 40 μm, and elastic modulus increased with the decrease of w/b and the extension of hydration age. The findings show that incorporation of iron tailings powder has some degree of improvement on the microscopic structure of ITZ, but does not reduce its size, and the thickness of ITZ both with and without iron tailings powder are all 40μm. In particular, the variation law of pore in IZT needs to be studied more comprehensively and in-depth in the future. • Siliceous iron tailings powder is used as a mineral admixture for concrete. • The iron tailings powder complicates the CH crystal orientation in ITZ. • The iron tailings powder declines the Ca/Si and porosity in ITZ. • The iron tailings powder reduces the microhardness and elastic modulus in ITZ. • The iron tailings powder dose not change the thickness (40μm) of ITZ. [ABSTRACT FROM AUTHOR]

Bio-based concrete, which utilizes recycled agricultural waste as aggregates, has emerged as a sustainable alternative material in the construction industry. Optimizing its combined mechanical and thermal performance can promote its environmental and energy benefits. To achieve this, this paper presents a multi-objective optimization approach to improve the overall performance of bio-based concrete based on multiscale structural features, considering the porosity, shape, orientation, and volume fraction. Optimization strategies are provided for three main industrial applications. Furthermore, this study addresses multiple design requirements, including high-volume bio-aggregates, more demanding performance requirements, low densities, and humid environments. The optimization results demonstrate that the optimal solution varies with industrial applications and requirements. Consequently, we quantitatively provide specific optimal solutions for each case, and offer designers three preferences for mechanical properties, insulation, or balanced performance. Overall, this study optimizes the comprehensive performance of bio-based concrete in terms of multiscale structures, thereby contributing to a more sustainable construction industry. • A customized multi-objective optimization approach for bio-based concrete. • Decision variables of shape, porosity, volume fraction, and orientation. • Differences in high-volume bio-aggregates, lightweight roofing, and humid environment. • Three preferences for mechanical performance, insulation, and balanced performance. • Optimal solutions for various industrial applications, requirements, and preferences. [ABSTRACT FROM AUTHOR]