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This paper addresses two important worldwide environmental concerns: disposal of waste tyres and attenuation of trains induced vibration. To this end, use of the waste materials in construction of railway concrete slabs for reduction of train induced vibration is investigated in this research. For this purpose, rubber tyre particles with different dosages were used in the concrete mixtures of test specimens. Extensive laboratory tests were conducted on the rubberized concrete specimens to measure their compressive strength, density and damping of the specimens. The effect of rubberized slab track on attenuation of vibration propagated from slab track was investigated by numerical modeling using results of laboratory tests as the input data. The laboratory results obtained indicate that adding rubber particles to the railway slab causes up to 96% increase in damping ratio (for concrete with 10% rubber). Results of numerical analysis elucidates that the rubberized slab track causes up to 21% reduction of the train induced vibration. By compromising between compressive strength and damping of vibration, it is shown that the optimum amount of crumb rubber in the concrete of railway slabs is 2.5% by which the best performance of the railway slabs is obtained. • This paper addresses two important environmental challenges in the world. • A method for recycling waste tyres and reducing railway vibration is developed. • Optimum amount of crumb rubber integrated into railway concrete slab is derived. • Environment-friendly solution for mitigation of train induced vibration is derived. [ABSTRACT FROM AUTHOR]

In this paper, an orientation method with pre-tensioning at both ends is proposed to successfully prepare continuously directional steel fibre reactive powder concrete (DSFRPC). The tensile and fracture properties are determined by splitting tensile, axial tensile and three-point notch fracture tests. The paper sets three different groups named C0, Group S and Group D, which presents non-fibre, randomly distributed fibre and directional fibre, respectively. The test results showed that: the splitting strength of Group D specimens increased quite significantly with the increase of fibre dosage. Compared to the Group S, the splitting strength of Group D was improved by 46.5%, 69.8%, and 66.1%, respectively. The specimens of C0 and Group S in the axial tensile test suffered typical single-seam brittle failure, which showed obvious strain softening characteristics. With the increase of fibre dosage, the damage mode of specimens in Group D changed from single-seam brittle damage to multi-seam ductile damage, showing better energy dissipation capacity. Under the same converted fibre dosage, the fracture energy enhancement ratios of Group D specimens were 14.7, 18.9 and 19.55, respectively. At a lower water-cement ratio, the toughening effect of continuous directional steel fibre specimens is more obvious. The toughening effect of the reactive powder concrete (RPC) of with continuous directional steel fibre is mainly reflected in the directional distribution of steel fibre produced by the interfacial adhesion and friction caused by the increase in energy dissipation, as well as the maintenance of a stronger grip between the "dispersed rebar" and the matrix. Based on current study, the future research should be focused on a wider range of materials, structural design, and environmental conditions to verify the effectiveness and reliability of DSFRPC in various applications. • A novel directional method to prepare a new type of directional steel fibre concrete material. • The method can reduce the cost and improv the reinforcing and toughening effect of steel fibre. • The properties were experimental studied by splitting tensile, axial tensile and three-point notch fracture tests. • The research reveals the reinforcement mechanism of continuous directional steel fibres on RPC. [ABSTRACT FROM AUTHOR]

This work focuses on how different aspects of design, testing, and field implementation of fiber-reinforced polymer (FRP) in concrete have gained attention from the scientific research community. FRP composites have gained significant recognition after being implemented in civil engineering applications over the past three decades. This paper conducts a comprehensive survey of the existing literature on FRP in concrete from different engineering aspects. Since its advent, FRP research has resulted in numerous peer-reviewed papers available in various scientific databases such as Elsevier, ASCE, Springer Nature, ACI, and MDPI. Researchers investigated the use of FRP in concrete from different aspects, including material systems, element types, and applications, accounting for 35.8%, 50.3%, and 13.9% of the research publications, respectively. This paper aims to present an overview and summarize the use of FRP based on highly cited literature and to support FRP's continued growth and development in concrete applications. Consequently, this paper is expected to offer advantages to stakeholders involved with FRP use, such as owners, engineers, and professionals, by emphasizing the number of available research publications, which can increase confidence in adopting FRP. It offers scholars and researchers the opportunity to become acquainted with the use of FRP in the application of concrete. • Interest in fiber-reinforced (FRP) in concrete is growing within the scientific research community. • Research on FRP in concrete focuses on material systems (35.8%), element types (50.3%), and applications (13.9%). • The paper provides an overview of FRP use in concrete, citing influential works and promoting its ongoing growth. • The study identifies research gaps, helping academicians and scientists understand the challenges in incorporating FRP into concrete. [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]

To comprehensively utilize the abundant solid wastes of superfine river sand and fly ash, a mixed sand of superfine river sand with coarse manufactured sand and high-flowability concrete made of mixed sand and high-content fly ash were developed. To address the critical question about the long-term strength of this new concrete, this paper presents an experimental study on the long-term development of cubic compressive and tensile strengths of the concrete over a curing age from 7 days to 360 days. In the study, the mixed sand was a hybrid of 40 % superfine river sand and 60 % coarse manufactured sand, and the fly ash content varied from 30 % to 75 % of the total binders by weight. The law of strength development of concrete with fly ash content was analyzed, combined with explanations of the mechanism and observations of hydration exotherms and microstructures of the concrete. Equations were proposed for predicting the long-term development of cubic compressive and tensile strengths, incorporating coefficients to reflect the effects of fly ash on the binder's compressive strength and the development tendency of concrete strength. The validity of the proposed prediction equations was verified against the test results and compared with the extended application of the equation specified in CEB-FIP MC 2010. • Mixed sand of superfine river sand with coarse manufactured sand was developed. • High-flowability concrete made of mixed sand and high-content fly ash was produced. • Long-term strength of the concrete was measured within the curing age of 360 days. • Formulas for predicting strength development were proposed. • Coefficients reflecting the effect of fly ash on strength development were suggested. [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]

Although recycled aggregate concrete (RAC) has been used in structural engineering, the application of brick-concrete recycled aggregate concrete (BCRC) in structural engineering remains limited. Bond-slip behavior is critical for the co-work between concrete and reinforcement bars. This study investigated the bond-slip behavior between BCRC and reinforcement bars through 45 pull-out tests. The variables studied include concrete type (natural aggregate concrete (NAC) and BCRC), recycled brick aggregate (RBA) replacement ratio (0 %, 25 %, and 50 %), concrete cylinder compressive strength (30 MPa and 40 MPa), concrete cover thickness (30 mm, 50 mm, and 68 mm), reinforcement diameter (8 mm, 14 mm, and 20 mm), bond length (5 d , 10 d , 15 d , and 20 d), stirrup ratio (0.5 %, 0.7 %, and 1.0 %), and reinforcement shape (deformed and plain). The results show that compared with NAC, the normalized ultimate bond strength of BCRC with RBA replacement ratios of 0 %, 25 %, and 50 % increased by 7.5 %, 3.6 %, and 19.2 %, respectively. As the cylinder compressive strength of BCRC increased from 30 MPa to 40 MPa, the ultimate bond strength increased by 24.5 %, and the ultimate slip decreased by 20.0 %. Based on the test data, a bond stress-slip model for BCRC was proposed, demonstrating high accuracy. The models proposed in this paper can provide a reference for the engineering structural design of BCRC. • Bond strength between reinforcement and BCRC is higher than that of NAC. • Effect of variables on bond stress-slip between BCRC and reinforcement was investigated. • Models for calculating the bond strength and slip were proposed. • Bond stress-slip model between BCRC and deformed reinforcement was established. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical investigation on the compressive performance of concrete cylinders internally reinforced with steel-fiber-reinforced composite bars (SFCBs) and externally confined with fiber-reinforced polymer (FRP) sheets, termed herein as S-F-RC cylinders. Eleven concrete cylinders, with different confinement conditions and with (or without) longitudinal SFCBs, were tested under monotonic compression. Two distinguishable failure mechanisms, global buckling and local buckling, were discovered for SFCBs in S-F-RC cylinders, under weak and strong confinement conditions, respectively. The S-F-RC cylinders exhibited a marked increase in failure strain of the confinement, directly translating to an enhanced compressive failure strain for the longitudinal SFCBs under strong confinement conditions. Existing models for FRP-reinforced concrete cylinders were found to underestimate the load-carrying capacity of S-F-RC cylinders. An existing compressive stress-strain model for SFCB was extended to the case of S-F-RC cylinders. The proposed method offers accurate predictions, effectively mitigating the discrepancies caused by varying confinement and material properties across different SFCBs. • Compressive performance of FRP-confined SFCB-reinforced concrete is presented. • Different buckling failure mode observed for SFCB under weak or strong confinement. • Model is developed for axial compressive strength of SFCB in FRP-confined concrete. [ABSTRACT FROM AUTHOR]

In the exploration of the moon and outer space, our preliminary mission lies in the construction of lunar base. To make lunar concrete with local materials on the moon becomes the key technology to promote the construction of lunar bases. In order to further study the feasibility of using lunar in-situ resources to prepare concrete and build a lunar base, the environment and resources on the lunar surface are analyzed, and the severe challenges brought by extreme environment to concrete preparation and the prerequisites of in-situ resources are clarified. In this paper, the research progress of lunar concrete is summarized from the aspects of raw material acquisition, concrete preparation methods and performance, and the comparative analysis of cement concrete, sulfur concrete, geopolymer concrete and polymer concrete is carried out. Existing studies have shown that in the acquisition of raw materials, sulfur concrete has more advantages, cement concrete and geopolymer concrete are also feasible, but polymer, as a scarce resource on the moon, is difficult to obtain. In terms of preparation methods, cement concrete and geopolymer concrete are more suitable for the production of prefabricated components in artificial environment due to the limitation of external environment and the demand of water circulation, while the in-situ preparation methods represented by sulfur concrete and polymer concrete can be used for the connection and node reinforcement of prefabricated components on the moon. In terms of performance, the mechanical properties of the four kinds of concrete all meet the basic requirements, but the service performance in the harsh environment of the moon needs to be further studied. Meanwhile, the key location characteristics for lunar base construction in different regions are analyzed in terms of topography, environment and in-situ resources. Finally, the future exploration direction of the construction of the lunar bases is proposed. • Comparative study on lunar concretes: cement, sulfur, geopolymer, and polymer. • Sulfur concrete's raw material acquisition advantage; polymer's scarcity on moon. • Prefabrication versus in-situ production methods for lunar habitat construction. [ABSTRACT FROM AUTHOR]

When concrete is subjected to freeze-thaw (FT) cycles, its mechanical properties under multiaxial stress states will deteriorate. In order to establish corresponding failure criteria, it is common practice to conduct FT and multiaxial tests. However, due to the multiple FT factors, extensive multiaxial tests are required, resulting in low applicability of the existing failure criteria for FT damaged concrete. In this paper, according to the collected multiaxial test data, a rule has been revealed that the normalized failure surface of FT damaged concrete is related to the relative uniaxial compressive strength (f cD / f c), regardless of the types of FT factors. This correlation is related to the degree of confined state. On this basis, a uniaxial strength-dependent method has been proposed to predict the multiaxial ultimate stress state of FT damaged concrete. Through the proposed method, to facilitate various applications, three models including two types of failure criteria for concrete and a peak axial stress model for confined concrete after FT cycles have been established with broad applicability and good accuracy. The proposed method and models might be extended to other damaged concrete with the same mechanism of developing internal cracking. • f cD / f c has proved to characterize the multiaxial ultimate stress degradation after multifactor freeze-thaw cycles. • The piecewise pattern of normalized failure surface after freeze-thaw cycles was revealed. • The multiaxial failure mechanism of concrete after freeze-thaw cycles was clarified. • An innovative prediction method for failure surface of damaged concrete was proposed. • Two unified triaxial failure criteria for freeze-thaw damaged concrete were proposed. [ABSTRACT FROM AUTHOR]

Heavy-weight concrete (HWC) is currently the most widely used radiation shielding material in the nuclear industry. However, the pre- and post-fire mechanical behavior of HWC containing Iron sand (IS) and/or fly ash (FA) is not thoroughly studied. This paper fills in the research gap by testing 12 HWC mixes, which replaced river sand (RS) with 50% or 100% IS and/or ordinary Portland cement (OPC) with 15%, 25% or 35% FA by volume. The temperature-time curve, mass loss, surface change, onset of spalling, failure modes, residual compressive strength, elastic modulus of concrete and stress-strain curve after having exposed to 400, 600, 800 and 1000°C were investigated. Additionally, the pre- and post-fire chemical compositions were analyzed by X-ray diffraction. Results demonstrated that the flowability of HWC increased with the IS / FA replacement ratio due to the more spherical shape and the improved packing structure. Replacing 50% of RS with IS and 15% of OPC with FA could effectively enhance the thermal insulation capacity, compressive strength (increased by 9.5% at 25°C and 400°C, 12.9% at 600°C, 46.0% at 800°C and 63.6% at 1000°C compared with normal concrete) and elastic modulus (increased by 26.3% at 25°C, 17.5% at 400°C, 20.5% at 600°C, 120% at 800°C and 100% at 1000°C compared with normal concrete) of HWC. Lastly, all obtained results suggested that the pre- and post-fire characteristic of HWC containing IS is explicable/predictable by the theory of wet packing density. • The effect of elevated temperatures on iron sand HWC is investigated. • Adding iron sand can effectively increase the unit weight and flowability of concrete. • Iron sand and fly ash can improve the thermal insulation capacity of HWC. • An exponential equation is established to estimate the residual strength index of HWC. [ABSTRACT FROM AUTHOR]

Concrete structure is often in an aqueous environment, and it will be subjected to impact load when the vehicle passes. Infrared radiation can reflect the concrete crack development and energy dissipation. To reveal the effect of water and impact load on infrared radiation of concrete, this paper studied the time-varying law of infrared response of concrete with diverse soaking time under dynamic load damage, and quantitatively analyzed the infrared thermography properties of concrete impact failure process by infrared thermal image frequency distribution histogram. The results show that the infrared radiation temperature increment of water-containing concrete was inversely proportional to the soaking time. Its Δ T max and Δ T ave are 1.6 – 7.5 times and 1.4 – 5.4 times that of dry concrete, respectively. The peak proportion of high temperature precursors (S H max) and the peak proportion of low temperature precursors (S L max) of dry concrete are almost equal, while the S H max of water-containing concrete is 4.9 – 44.6 times of S L max. When the S H curve begins to rise rapidly or the S L curve begins to fluctuate violently, it can be considered as a precursor to the destruction of concrete. Water affects concrete's infrared radiation response in two ways. As the soaking time increased, the water-containing concrete's absorption energy increased, the S H and S L areas decreased, and the cumulative infrared radiation energy increment and infrared radiation energy conversion ratio decreased. The absorption energy of water-containing concrete was inversely proportional to the cumulative infrared radiation energy increment. The research results provide a feasible method for dynamic failure early warning and structural stability evaluation of water-containing concrete structures. • The effect of immersion time on the impact damage of concrete was studied. • Water had dual effects on the infrared radiation response of concrete. • Absorption energy was inversely proportional to accumulated IR energy increment. • The effect of water on the energy dissipation of concrete impact damage was revealed. [ABSTRACT FROM AUTHOR]

This paper presents the results of an extensive experimental campaign related to the use of Coal Mining Waste Geomaterials (CMWGs) as recycled constituents (fine and coarse aggregates) in Ordinary Portland Cement mortars and concretes. To this purpose, a reference mix and other mixes with different percentages of replacement of natural aggregates by CMWGs, up to 40% by volume, were investigated. CMWGs came from different providers: Central Mining Institute (GIG), POLTEGOR, both in Poland, and SUBTERRA in Spain and tests were performed at two different laboratories working on similar, but not identical, compositions. This represents a novelty in the literature, generally focusing on one single-source waste and single-lab results. The physical and mechanical properties of all the mixes were evaluated and correlated with respect to the percentage of replacement of natural aggregates by CMWGs. While the presence of CMWGs, likely because of their grain size distribution, reduced the porosity of mortars (decrease of 9.5 and 20.4% for 10 and 20% of replacement respectively) and concretes (70% reduction for concretes with 10% of fines and 30% of coarse aggregates replaced by CMWGs), the mechanical properties decreased when natural aggregates were replaced with CMWGs, likely because of the reduced strength of the CMWGs aggregates. This decrease was found to be roughly proportional to the percentage of replacement of aggregates (for instance, a 12–23% reduction of flexural strength in mortars with 25% replacement of sand and, a decrease of 25% in concretes for a 25% replacement of fine and coarse aggregates); nonetheless the concrete performance remained in the range of applicability for several civil engineering applications without affecting their functionality. In conclusion, the replacement of natural aggregates by CMWGs has resulted an interesting option for real applications providing an added value to the implementation of circular economy concepts in the management and up-cycling of coal mine tailings and CMWGs. • Recycling Coal Mine Waste Geomaterials as partial replacement of fine and coarse aggregates in concrete is feasible.. • Complementarity and coherence of results from two different labs with aggregates from three sources validate the methodology. • Thin section analysis provides insight into microstructural reasons of macroscopic properties highlighting the interaction of CMWGs with cement paste. • Reduction in compressive strength induced by weaker CMWG aggregates does not jeopardize the possibility of producing concrete still retaining values of compressive strength fit for several structural applications. [ABSTRACT FROM AUTHOR]

This paper presents experimental and analytical investigations on the tensile and bond behaviour at elevated temperature of a polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) system for strengthening concrete elements. Direct tensile (DT) and single lap direct shear tests (DS) were performed under steady-state conditions at the following temperatures: 20 °C, 85 °C, 150 °C, 230 °C and 300 °C. The results obtained were evaluated in terms of strength, stiffness, ultimate strain, load vs. slip response at the interface PBO FRCM/concrete and failure modes. Overall, the tensile and bond properties were significantly affected by the temperature increase. These results are mainly associated with the reductions of mechanical properties of the FRCM constituent materials as well as the degradation of the interaction between the fibres and the inorganic matrix at elevated temperatures. The experimental results were then used (i) to evaluate the suitability of the Aveston–Cooper–Kelly (ACK) model in describing the tensile response of FRCM at elevated temperatures and (ii) to calibrate temperature-dependent local shear bond stress vs. slip laws for the FRCM-concrete interaction. • PBO fibres, mortar, PBO FRCM coupons and PBO FRCM-to-concrete joints exposed to temperatures ranging from 20°C to 300°C; • Steady-state mechanical properties determined at : 20°C, 85°C; 150°C; 230°C and 300°C; • Results obtained evaluated in terms of strength, stiffness, ultimate strain, shear stress and slip; • Assessment of the Aveston-Cooper-Kelly model in describing the tensile response of the PBO FRCM at elevated temperatures. • Parameters of the local shear bond stress vs slip laws calibrated using 1 1 It is important to note that due to the proprietary nature of the patented product used herein, detailed information regarding its composition is not available. the experimental results. [ABSTRACT FROM AUTHOR]

The development of self-moderating and self-sensing concrete composites with high and stable thermal/electrical conductivity is essential to mitigate and monitor the temperature deformation behaviours (TDB) of engineering infrastructures such as highways, bridge pavements, airstrips and ports. Owing to the micron-scale diameter and high aspect ratio, stainless steel wires (SSWs) can establish a comprehensive and extensive thermal/electrical, as well as reinforcing, three-dimensional network within the concrete matrix, even at a low content. This paper thus investigated the TDB self-moderating and self-sensing performances of SSWs enhanced ultra-high performance concrete (UHPC). The main experiments were carried out on SSWs enhanced UHPC slabs, measuring 250 mm×225 mm×16 mm. The volume contents of SSWs studied were 0 %, 0.5 vol%, 1.0 vol% and 1.5 vol%. The TDB self-moderating and self-sensing experiments were carried out under different conditions, including indoor and outdoor environments. Such composites showed effective and highly stable capabilities in reducing the temperature difference and diminishing the strain of pavement slabs under different environmental conditions. Compared with the UHPC without SSWs, UHPC with 1.5 vol% of SSWs can reduce the temperature difference by 7.4 °C (39.4 %) when being heated from 21.6 °C to 50 °C, thus, reducing the maximum tensile/compressive strains by 83.1 %/82.2 %, and the tensile/compressive stresses by 70.8 %/82.0 %. At a heating rate of 67.1 °C/min, incorporating 1.5 vol% of SSWs results in significant reductions in both vertical displacement and stress, amounting to 98.6 % and 89.6 %, respectively. The 1.5 vol% SSWs reinforced UHPC slab also suppressed 25.0 % of temperature difference, 76.6 % of strain and 70.7 % of stress in scorching outdoor environments. The TDB of SSWs reinforced UHPC can be real-timely reflected by monitoring the quick and small-scale resistance fluctuations, and the fractional changes in resistivity can reach 5.24 % with a response time of 0.23 s. The self-moderating and self-sensing performances of such composites remained stable after repeated heating experiments, thus suggesting its potential for promising applications in engineering infrastructures which are susceptible to deformation under high-temperature conditions. • Thermally and electrically conductive concrete was used to mitigate and monitor the temperature deformation behaviours. • Stainless steel wires were used to develop high-performance self-moderating and self-sensing concrete. • Self-moderating and self-sensing performances of the developed composite were evaluated. • The developed composites were featured with strong, stable and precise self-moderating and self-sensing capabilities. [ABSTRACT FROM AUTHOR]

The low water-cement ratio has a significant effect on increasing the compacted density of the concrete, thereby enhancing its mechanical properties and microstructures. This paper introduces an innovative approach of utilizing the cold isostatic pressing method to prepare reactive powder concrete (RPC) specimens with an ultra-low water-cement ratio which not exceeds 0.16. And it is compared with the specimens prepared by the traditional vibrational method which conversely requires the minimum water-cement ratio of 0.21. The results show that the RPC specimens under cold isostatic pressing exhibit enhanced compressive strength and microhardness, as well as improved matrix compactness. Conversely, the RPC matrix produced under the vibrational method not only contains a small number of air-entrained bubbles that can influence the strength of matrix but also exhibits a significantly larger cumulative volume of harmful pores that affect the performance of RPC compared to cold isostatic pressing. Therefore, cold isostatic pressing technology based on all-directional hydroforming is a powerful tool for the preparation of high-strength RPC, which significantly reduces the internal defects of the specimen, and the prepared RPC has superior mechanical properties and matrix structure. • Significant increase in the compressive strength of RPC has been achieved by cold isostatic pressing. • The molding method has a significant influence on the Vickers hardness of RPC. • The hydration reaction of cold isostatic pressing specimens after autoclave curing is still incomplete. • Specimens prepared by cold isostatic pressing exhibit dense matrix without air-entrained bubble observed. [ABSTRACT FROM AUTHOR]

The steel corrosion in Ultra-High Performance Concrete (UHPC) would cause degradation of structural performance or even structural failure. It is an urgent need to monitor and predict the steel corrosion in UHPC, however it is still a tough task. In this paper, Fiber Bragg Grating (FBG) sensors are applied for monitoring the steel corrosion process in UHPC, by combining with steel bar, which is equidistant winding with the sensors, and connected with power supply for accelerating corrosion. The UHPC specimens embedded with steel bars are surrounded by sodium chloride (NaCl) solution, and the steels are artificially corroded with different current densities for investigation. The steel corrosion in Original C60 and Marine Concrete 60 (Marine C60) are applied for comparison. The volume expansion coefficient for monitoring the steel corrosion process, is carried out by FBG sensors, and further comprehensively monitored by three grating sensors. The results suggest that the steel corrosion process in UHPC is slowly with current density lower than 100 μA/cm2, and largely increases with current density higher than 500 μA/cm2, the volume expansion coefficient of corroded steel in UHPC is in range of 2.02–2.62 in this test, which is much different from Original C60 and Marine C60. • FBG sensor has merits in monitoring the steel corrosion process in UHPC. • By observing the wavelength shift of FBG, the steel corrosion process in UHPC is monitored. • The volume expansion coefficients of corrode steel , are carried out for quantitatively predicting the corrosion condition in UHPC. • By applying there grating sensors, the steel corrosion manner in UHPC is comprehensively investigated. [ABSTRACT FROM AUTHOR]

By considering the current global challenges such as greenhouse gas emission and waste disposal management, the exploration of geopolymer concrete is highly focused now-a-days. On the other hand, the use of costlier commercial activators acted as the major drawback for the practical existence. Although the recent geopolymer researchers suggested the use of alternative activators from various resources such as palm oil ash, olive ash etc, the application of which are not appreciably promoted due to the complex derivation process. To overcome these effects, in this paper, first time, an attempt is initiated to develop a cost-effective geopolymer concrete by using textile mercerizing water as an alternate activator system. The viability of using mercerizing water instead of commercial sodium hydroxide activator was studied initially. By conducting the pH electrode test and Infrared Analysis, the alkalinity and the presence of sodium metal cations responsible for the reaction kinematics were confirmed. Also, the molar concentration of sodium cations in the mercerizing water was quantified using chemical titration analysis. The feasibility of using mercerizing water in the preparation of geopolymer was assessed using workability, mechanical strength and sustainability. From the results, it was inferred that the developed geopolymer concrete with 100 % textile mercerizing water exhibited the maximum strength of 46.9 MPa, 5.16 MPa and 5.81 MPa respectively under compression, tension and flexure which are almost equivalent and slightly better than the control geopolymer concrete. Also, the developed geopolymer concrete using 100 % textile mercerizing water and the combined flyash-GGBS binder system showcases the highest post-fire residual strength and 48 % reduced water absorption. The cost of construction of geopolymer concrete was significantly reduced by 58.43 % and showed 10.28 % reduced carbon footprint due to the complete replacement of sodium hydroxide solution using textile mercerizing water. The findings of this research work will lead to the development of equivalent molar sustainable activator from the textile mercerizing water and the exploration of eco-friendly and durable geopolymer concrete in an affordable price. [Display omitted] • TMW waste as a 100 % alternative to commercial hydroxide activator. • Alkalinity and reactive metal ions of TMW induced the maximum strength of 46.9 MPa. • GF-TM100 % offered 48 % reduced rate of water absorption and better fire resistance. • Consumption of TMW showed 10.28 % lower carbon footprint than commercial activator. • 58.43 % reduced construction cost in GF-TM100 % geopolymer. [ABSTRACT FROM AUTHOR]

The construction industry seeks innovative solutions like smart concrete. Traditional concrete faces durability issues, environmental impact, and high rehabilitation costs. To address this, smart concrete combines eco-friendly materials with advanced nano-technology, featuring self-sensing and self-healing properties to detect damage early and autonomously repair cracks. Researchers explore methods to reduce concrete's carbon impact through clinker replacement and alternative binders. The industry moves toward sustainable and technologically advanced practices, where "smart concrete" marks a transformative shift in construction, promising eco-conscious, technology-driven building methods. This review explores smart technology in concrete construction, focusing on structural health monitoring and autonomous crack repair advancements. It consolidates diverse self-sensing and self-healing mechanisms, emphasizing their role in viable construction goals. The paper delves into the impact of nanomaterial on the mechanical and durability of self-sensing, self-healing, and self-adjusting concrete, showcasing smart concrete's potential for transformative construction practices. Biomimetic Structural Health Monitoring (SHM) systems using self-sensing concrete and nanomaterials detect strain changes independently, which is vital for effective monitoring. Real-time Structural Health Monitoring using embedded sensors aids in timely decision-making for asset management and ensures continued structural safety. Self-activated bacteria in concrete provide an eco-friendly solution for crack healing by producing calcium carbonate and reinforcing structural integrity. Bacteria-based agents show promise in enhancing concrete's crack repair potential, aligning with better construction practices. In conclusion, smart concrete presents a significant opportunity to transform the construction sector, emphasizing eco-friendliness, resource optimization, and robust infrastructure. • Smart concrete features self-sensing and self-healing properties to detect damage early. • Researchers are exploring methods to improve the properties of smart concrete through alternative binders. • Structural Health Monitoring (SHM) systems using self-sensing concrete aid in effective monitoring. • Self-activated bacteria in concrete provide a solution for crack healing, enhancing construction practices. [ABSTRACT FROM AUTHOR]

Concrete carbonation has an important influence on chloride penetration. The chloride distribution profiles found in carbonated concrete are often different from those found in uncarbonated concrete even when they have the same exposure conditions. In this paper we present an experimental study on chloride penetration in carbonated concrete specimens when they are subjected to stationary, splash, submerged, and pressured exposure conditions. Free chloride concentration profiles were measured in the specimens to examine the effect of carbonation and exposure condition on chloride diffusion. In addition, material characterisations were carried out using x-ray radiography imaging tests and thermogravimetric analysis to understand the influence mechanism of concrete carbonation on chloride penetration in concrete. The experimental results showed that the chloride distribution curve in carbonated concrete exhibits a second peak under marine exposure conditions. The exposure condition can significantly affect the position and value of the second peak point in the profile. It is also shown that concrete carbonation can drastically change the distribution of pores in concrete, leading to a sudden change in porosity, which is the reason for the carbonated concrete to have the zone-dependent chloride variation profiles. • The chloride distribution curve in carbonated concrete exhibits a second peak under marine exposure conditions. • The exposure condition can significantly affect the position and value of the second peak point in the profile. • The different carbonation zones can be identified based on the distribution curve of the calcium carbonate. • Change in porosity caused by carbonation leads to a zone-dependent chloride variation profiles. [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]

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]

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]

Electrochemical kinetics of corroded steel bars is of importance in evaluating corrosion process and subsequent structural deterioration under different aggressive environments. This paper presents an experimental programme to investigate corrosion kinetics of steel bars in pseudo-transparent concrete subjected to different levels of chloride contamination and alkalinity in pore solution. The results show that corrosion current density increased with the rise of chloride content in simulated pore solution until C l − / [ O H − ] ratio reached around 10. However, further chloride contamination with C l − / O H − = 12.5 , 15 or 20 tended to reduce current density. The phenomenon of decreasing corrosion rate and increasing corrosion potential when concrete was severely contaminated by chloride ions has not been widely reported in previous publications. An electrochemical mechanism was proposed based on the concepts of thermodynamics, anodic and cathodic polarisation kinetics to explain this extraordinary phenomenon, in which the decrease of corrosion current density when C l − / [ O H − ] ratio increased from 10 to 20 was due to the rises of both anodic and cathodic Tafel slopes. On the other hand, a more neutralised pore solution in pseudo-transparent concrete induced a greater corrosion current density. When pH value was larger than 13, corrosion current density was negligible, while it substantially increased once pH value decreased to lower than 12.5. • Corrosion rate increases with a rise of chloride content until C l − / [ O H − ] ratio reaches 10 • Further chloride contamination with C l − / O H − = 12.5 , 15 or 20 decreases corrosion rate • Corrosion rate is negligible when pH is larger than 13 with no chloride attack • A more neutralised pore solution with a smaller pH induces a greater corrosion rate • Electrochemical mechanisms account for variations of corrosion rate under different corrosive environments [ABSTRACT FROM AUTHOR]

New-to-old concrete interfaces are commonly found in reinforced concrete (RC) structures due to precast splices, repairs, and construction joints. The interfaces provide access for chloride ions, oxygen, and water, which intrude on the concrete, reducing its durability with new-to-old concrete interfaces. Although the mechanical bonding properties of new-to-old concrete interfaces have been extensively studied, there is a notable gap in the durability of old-new concrete, particularly concerning chloride ion penetration resistance. This paper examined the interface bonding properties and the chloride ion penetration resistance of old-new concrete through ultrasonic nondestructive testing and rapid chloride migration (RCM) tests. Influences of water-cement ratio, casting interval, and interface treatment were considered. The test results indicated that the interface treatment has minimal effect on ultrasonic velocity while the w/c ratio is the primary factor influencing ultrasonic velocity. The bonding quality of the interface between new and old concrete is more accurately reflected by ultrasonic velocity than by the amplitude of the first wave. The chloride penetration in the old and new concrete specimens is primarily influenced by the water-cement ratio and curing age. As the casting interval increases, the difference in the chloride penetration between the new concrete area and the old concrete area becomes more pronounced. When the strength of new concrete exceeds that of old concrete, the chloride penetration at the interface is primarily influenced by the characteristics of the old concrete. The difference in chloride migration coefficients between the interface and new concrete ranges from 40% to 54%, while the difference between the interface and old concrete is only 4.5–22.2%. However, when the new and old concrete has the same strength, the chloride penetration at the interface tends to be closer to that of new concrete. The impact of interface treatment on the depth of chloride penetration is minimal. An influence coefficient was proposed to assess the effect of the interface on the chloride penetration resistance. With a shorter casting interval, the chloride ion penetration resistance is more affected by different interface treatments. As the casting interval increases, this influence gradually diminishes. • The water-cement ratio is the primary factor influencing ultrasonic velocity. • Chloride penetration in new and old concrete depends on the w/c ratio and curing age. • Whether Interface chloride migration is closer to old or new concrete was discussed. • Proposed an coefficient to evaluate the effect of interface on chloride penetration. [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]

Fire is one of the most severe conditions encountered during the lifetime of a structure. Consequently, the provision of proper fire safety measures for structural members is a major safety requirement in building design. In this paper an experimental study is reported on the axial deformation of GGBS-FA-SF blended geopolymer mortar and geopolymer concrete with and without steel fibre when they are subjected to both mechanical and thermal loadings. The transient tests were conducted in Instron machine with additional heating facility. During the test the specimen was first subjected to a pre-defined mechanical load and followed by thermal heating. The transient axial deformations of the tested specimens were recorded using digital image correlation camera. By using the experimentally obtained temperature-dependent thermal strains of the specimen with different preloads the transient strains of the geopolymer mortar and geopolymer concrete with and without steel fibre are analysed and evaluated. Finally, empirical formulas are also proposed to reproduce the influence of the preload, heating temperature and constituents of the mix on the transient strain of geopolymer mortar and geopolymer concrete. • Experimental results are reported for thermal strains of free expansion of geopolymer concrete. • Experimental results are reported for thermal strains of prestressed geopolymer concrete. • Experimental results of transient strains of geopolymer concrete are reported. • Temperature- and prestress-dependent transient strain formulas are proposed. • The effect of coarse aggregate and steel fibre on transient strains is examined. [ABSTRACT FROM AUTHOR]

The substantial increase in infrastructure construction has led to a scarcity of river sand and freshwater resources in most countries. To address this issue, the replacement of freshwater river-sand with abundant seawater sea-sand in concrete is considered a sustainable construction method. To this end, this paper investigates the effect of replacing freshwater river-sand with seawater sea-sand on the dynamic compressive mechanical properties of concrete. First, compressive tests were conducted on both types of concrete at different strain rates using static compression testing machine and large-diameter splitting Hopkinson pressure bar. Then, the effects of strain rate on the stress-strain curve, peak stress and strain, dynamic increase factor (DIF) of compressive strength, ductility coefficient, and energy absorption density for both types of concrete were analyzed. The static and dynamic failure modes of specimens were obtained. The experimental results showed that the replacement of freshwater river-sand with seawater sea-sand had no substantial effect on the static and dynamic failure modes of concrete. Furthermore, this replacement did not change the basic shape of the stress-strain curve of concrete. At high strain rate, the DIF for the compressive strength of seawater sea-sand concrete (SSMC30) exceeded that of freshwater river-sand concrete (NC30). The ductility coefficient and peak strain of SSMC30 were both smaller than those of NC30 at the same strain rate. The energy absorption density of SSMC30 was lower than that of NC30 under the same strain rate. Following experimental investigation, a unified stress-strain constitutive relation model of SSMC30 under static and dynamic compression was established using numerical regression. The model is useful for evaluating the dynamic response of SSMC30 structures. • The dynamic mechanical properties of SSMC30 and NC30 were investigated. • The failure process and pattern of SSMC30 and NC30 are similar. • A unified stress-strain constitutive model of SSMC30 was established and validated. • This study can provide technical support for structural dynamic analysis of SSMC30. [ABSTRACT FROM AUTHOR]

Cementitious concrete is considered potentially the largest avenue to utilize the captured carbon dioxide (CO 2). Its capacity is significantly influenced by various parameters, including the CO 2 introduction method for sequestration. This paper attempted to study the variation in carbon sequestration potential of ordinary Portland cement (OPC) based concrete and paste when the CO 2 is introduced to the samples during mixing, curing and both. The carbonated samples obtained using the abovementioned methods have been compared in terms of CO 2 uptake capacity, microstructural densification, porosity reduction, and strength variations. A maximum CO 2 Uptake Capacity of about 25% was achieved under Standard Ambient Temperature and Pressure (SATP) conditions, with a maximum CO 2 Conversion of 70.35% and 93.80% obtained at the surface for CO 2 Mixing and CO 2 Curing, respectively. Further, carbon-sequestered concrete (CSC) resulted in enhanced compressive strength, and reduced the size of pores in addition to making them uniform in size. • A CO 2 Uptake Capacity of 13.9% was obtained using the CO 2 Mixing regime. • A CO2 Uptake Capacity of 19.75% was achieved using the CO 2 Curing regime. • A CO 2 uptake of 25.17% was observed using the CO 2 mixing + CO 2 curing regime. • A maximum CO 2 Conversion rate of 70.35% was achieved in the CO 2 Mixing case. • A maximum CO 2 Conversion rate of 93.80% was achieved for the CO 2 Curing case. [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]

The geometric tortuosity of pores is a critical parameter for assessing the transport characteristics of eroding agents in concrete. Based on the porous, multiphase, and multiscale features of concrete composite materials, this paper establishes a model for geometric tortuosity of pores in concrete composite materials, correlating it with water-cement ratio, volume fraction and shape factor of aggregates, and quantitative analysis is conducted on the influencing factors of tortuosity. The results demonstrate a close alignment between the developed geometric model and experimental results obtained through Mercury Intrusion Porosimetry (MIP). The quantitative analysis reveals that the geometric tortuosity of pores in concrete composite materials increases with an increase in aggregate shape factor and aggregate volume fraction, while it decreases with an increase in water-cement ratio. For instance, as the aggregate shape factor increases from 1.0 to 3.0, the tortuosity of mortar increases from 8.42 to 25.28, and the tortuosity of concrete rises from 10.41 to 93.69. Similarly, as the water-cement ratio rises from 0.2 to 0.6, the tortuosity of hardened cement paste, mortar, and concrete decreases from 13.68, 18.22, and 29.33 to 7.23, 9.42, and 14.76, respectively. Furthermore, an increase in aggregate volume fraction from 0.1 to 0.5 leads to an increase in the tortuosity of mortar from 12.29 to 13.79 and the tortuosity of concrete from 18.08 to 22.76. • A model proposed for the geometric tortuosity of concrete. • A model reflected the time-varying characteristics of concrete microstructure. • A close alignment between the developed geometric model and MIP test results. [ABSTRACT FROM AUTHOR]

Post-filling coarse aggregate concrete (PFCC) is a new type of concrete that achieves energy conservation and emission reduction by optimizing the material proportion. The post-filled coarse aggregate can save the amount of cement material, improve the strength, and prolong the service life. This paper conducted multiaxial compression tests on the PFCC cubes, analyzed the strength rules under different post-filling ratios and different stress ratios, and proposed a failure criterion applicable to PFCC. The results indicated that the peak strength of the maximum principal stress under multiaxial compression was always greater than the uniaxial compressive strength under the same post-filling ratio, and the strength change was affected by both the stress ratio and the post-filling ratio. Under the same post-filling ratio, with the stress ratio (triaxial compression as the intermediate principal force) increasing, the strength first increases and then decreases. Both the uniaxial and multiaxial compressive strength reached the highest at the post-filling ratio of 20%. The failure criteria for PFCC under biaxial and triaxial compression have been established, and the calculated values agree with the test values. This study provides reference and research data for studying PFCC under complex stress environments. • The mechanical properties of post-filling coarse aggregate concrete under multiaxial compression were studied. • The optimal post-filling ratio of coarse aggregate is 20% based on test results. • Both uniaxial and multiaxial compressive strength vary with the increase of PFR, first increasing and then decreasing. [ABSTRACT FROM AUTHOR]

In practical engineering, chloride ions often attack concrete structures through non-uniform small regions, whose microstructure and stress forms are very complex and are usually influenced by the water-to-binder (W/B) ratio. In this paper, the chloride diffusion in concrete with three different W/B ratios under biaxial compression was tested, and the microstructure characterization and property analysis were carried out using digital image correlation (DIC), mercury intrusion method (MIP), and nanoindentation test. It was found that the chloride diffusion coefficient showed a trend of first decreasing and then increasing with the increase of biaxial compressive load, regardless of W/B ratios. A larger W/B ratio resulted in a larger porosity of concrete, poorer micromechanical properties of the interface transition zone, and a greater sensitivity to microcracks under load, thereby accelerating the chloride diffusion. Finally, a theoretical model considering the biaxial compressive stress level and W/B ratios was developed and effectively validated by the experimental results. [Display omitted] • Chloride ion diffusion in concrete is affected by compressive load and water-cement ratio. • An increase in thickness of nanoindentation ITZ accelerates the chloride ion diffusion. • A theoretical model for chloride ion diffusion is proposed considering the influence of multiple factors. [ABSTRACT FROM AUTHOR]