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Fly ash, river sand, and ordinary gravel, which are used in concrete as the admixture, fine aggregate, and coarse aggregate, respectively, were replaced by iron tailing powder, sand, and gravel. The influence of the iron tailings on the bond properties between concrete and steel bar was studied by conducting pull‐out tests on 16 groups and 48 specimens. At a curing age of 90 days, the splitting tensile strength of the iron tailing powder concrete (ITPC) for strength grades C25 and C30 was the lowest and was only 71.8% and 66.6% of the splitting tensile strength for the corresponding strength grade of conventional concrete (CC). The lower splitting tensile strength of ITPC caused the bond strength between the concrete and steel bar to be lower than that between the CC and steel bar, with a maximum difference of 14.67%. The bond strength between the iron tailing powder–sand concrete (ITPSC) and steel bar was slightly worse than that between the CC and steel bar, with a maximum difference of 6.88%, and better than that between the ITPC and steel bar. The bond strength between the full iron tailing concrete and steel bar was better than those between the CC and steel bar and between the ITPSC and steel bar. In addition, the bond slip characteristics were investigated. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) is one of the most widely used building materials. However, RC, especially in coastal seaside or humid environments, can suffer reinforcement corrosion with the result that the reinforcement fails to perform its function over time. The effect of a retarder additive used to eliminate loss of consistency in hot, windy and humid weather on the corrosion of RC elements was investigated in this work. Four different concrete types were assessed, with 0%, 1%, 1.5% and 2% additions of the chemical additive. Along with accelerated corrosion and pressure tests, physical properties such as electrical resistivity, water absorption, porosity, unit weight and capillary water absorption were also determined. The results of this work indicate that the use of up to 2% of the setting retarder did not pose a problem in terms of the physical and mechanical properties of the concrete. However, in terms of the frequently encountered corrosion problem, the use of 1.5% is more appropriate. Many chemical additives are used for different purposes in concrete and it is suggested that, alongside physical and mechanical properties, durability characteristics should also be examined when determining the suitable ratios of these additives. [ABSTRACT FROM AUTHOR]

The application of recycled coarse aggregate (RA) in structural concrete can save non-renewable resources and reduce land occupation. Developing comprehensive knowledge of chloride penetration and service life modeling of recycled coarse aggregate concrete (RAC) is a prerequisite for practice. However, compared with the natural aggregate concrete (NAC), the inferior durability performance, especially chloride penetration resistance, of RAC hinders its application in structural concrete. Therefore, many RAC performance enhancement methods have been proposed. This paper presents a holistic review focused on the chloride penetration of RAC with/without enhancement methods and service life prediction. The current RAC performance enhancement methods are introduced. The improvement effect of the corresponding enhancement methods on the chloride penetration resistance of RAC are discussed and analyzed in turn. Based on the reviewed data on the chloride diffusion coefficient, the modification efficiencies of assorted enhancement methods are summarized. With the hope of promoting RAC application in structural concrete, the current literature on chloride-ingress-based service life prediction for RAC is also overviewed. In addition, the typical influencing factors on chloride transport properties are also discussed, i.e., RA quality. It can be concluded that enhancement techniques can effectively improve the chloride penetration resistance of RAC. The old mortar enhancement or removal methods can improve the chloride penetration resistance by 15–30%, depending on the specific treatment measures. The modification efficiency of the modifier material depends on the specific type and content of the incorporated substance, which ranges from approximately 5% to 95%. The estimated service life of RAC structures decreases with the increasing RA replacement ratio. Finally, concluding remarks are provided concerning future research on the chloride transport behavior of RAC. [ABSTRACT FROM AUTHOR]

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility. [ABSTRACT FROM AUTHOR]

The current study reports on the long-term structural performance of novel reinforced marine geopolymer concrete beams under accelerated weathering conditions. The study covers the flexural performance of 40 geopolymer concrete beams reinforced with basalt fibre-reinforced polymer (BFRP) bars, including 12 beams under sustained loading when exposed to 3, 6 and 12 months of accelerated marine environment consisting of tidal cycles of seawater at a temperature of 50°C. The experimental results revealed that the novel marine geopolymer concrete reinforced with BFRP bars reported minimal micro- and macro-mechanical degradation compared to geopolymer concrete or ordinary concrete beams under the same exposure environment, with and without sustained loading. The BFRP-reinforced self-compacting geopolymer concrete (SCGC) beams reported 87% residual ultimate load after 12 months of exposure to marine environments, while the sustained loaded BFRP-SCGC beams reported a residual strength of 79%. In addition, microstructural assessment using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis revealed that after 12 months of exposure there was a trace of chloride salts, indicating the chemical ingress over time; however, the impact on structural properties is not distinct. [ABSTRACT FROM AUTHOR]

Ferrocement, a versatile building material, is becoming increasingly popular in structural and architectural applications. It is suitable for high degrees of prefabrication due to its durability, weather resistance, and relatively low cost. Additionally, there is the possibility to achieve considerable improvements in various properties of these thin structures by using some alternates. A study has been made on the behavior of ferrocement trough shaped panels (FCTSP) under static load using clay silica for partial replacement of cement and manufacturing sand for partial replacement of river sand. First, the strength characteristics of mortar cubes were determined by varying the percentage of cement with silica sand (0%, 5%, 10%, 15%, 20% and 25%). Incorporating the optimum percentage of clay silica replacement, a study on the flexural behavior of trough shaped panels reinforced with skeletal steel and wire mesh layers by replacing fine aggregates with manufacturing sand and varying the percentage of replacement was found. According to the findings, panels made with a combination of 10% clay silica sand (CSS) replaced for cement mix and 50% manufacturing sand (MS) replaced for the fine aggregate used in FCTSP showed better results in mechanical properties and microstructural bond behavior. [ABSTRACT FROM AUTHOR]

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility. [ABSTRACT FROM AUTHOR]

The incorporation of waste glass and glass fiber, as replacements for fine aggregate and cement respectively, offers a sustainable strategy to mitigate landfilling and virgin aggregate extraction. The present study delves into the influence of these waste derivatives on the mechanical and thermal attributes of concrete. Fine aggregate was substituted by crushed glass shards in a weight-to-weight ratio ranging from 5% to 30%, and cement was replaced by glass fiber in a weight-to-weight ratio of 1%. Mechanical attributes such as compressive, flexural, and splitting strength were evaluated, along with thermal characteristics of the concrete. A concrete mix ratio of 1:2:4 and a water/cement ratio of 0.45 were employed. The results revealed that concrete designated as Mcf20% demonstrated superior mechanical properties compared to the reference concrete. After 28 days, compressive strength of 51.2 MPa, flexural strength of 6.5 MPa, and splitting tensile strength of 3.78 MPa were recorded for Mcf20% concrete, signifying the beneficial effects of the combined use of glass fiber and crushed glass. Furthermore, an inverse relationship was observed between the percentage of waste additives and thermal conductivity. This investigation underscores the potential of recycling glass and glass fiber as eco-friendly additives in concrete, improving both mechanical properties and thermal performance, thus endorsing their use in structural and architectural concrete applications. [ABSTRACT FROM AUTHOR]

This article demonstrates the possibility of producing hybrid cementitious materials (pastes, mortars, concretes, and precast elements) based on fly ash (FA) and construction and demolition wastes (CDW) using alkaline activation technology. Sodium sulfate was used as an activator and fine and coarse aggregates were obtained from CDW residues. An addition of Portland cement (OPC) (10 to 30%) allowed for improvement in the mechanical behavior of the hybrid cements and them to be cured at room temperature (25 °C). The FA and CDW cementitious materials obtained compressive strengths of 37 MPa and 32 MPa, respectively. The compressive strength of FA and CDW alkali-activated concretes at 28 days of curing was 22 MPa and 18 MPa, respectively, which identifies them as structural concretes according to NSR-10 title C in Colombia. The potential use of these concretes was validated by obtaining and classifying precast materials. [ABSTRACT FROM AUTHOR]

The studied Schiff-base compounds in this work are multitasked investigated as corrosion inhibitors and also, to improve the physical and mechanical properties of reinforced concrete. The efficiency inhibition of the two novel Schiff-base compounds named (DHSiMF) and (DHSiB) for corrosion of carbon-steel in aqueous media of 1 M HCl was assessed via electrochemical methods and loss in weight. FT-IR, 1H-NMR spectra and elemental analysis were used to confirm the structure of such compounds. It was found to have successful inhibition even at low concentrations in tested media, as an increase in inhibitor concentration led to an improvement in the inhibition efficiency. The weight loss results clearly demonstrate that DHSiMF of C-steel in 1 M HCl has a higher inhibition efficiency than DHSiB, with a maximum inhibition efficiency (85%) attained at 1 × 10–2 M from DHSiMF. Electrochemical experiments likewise revealed the same order, but with a maximal inhibitory efficiency of 98.1%. The addition of inhibitors to the corrosive media dramatically changed the anodic Tafel constants (βa) and cathodic Tafel constants (βc), indicating a mixed type nature. Electrochemical polarization curves illustrated the functions of mixed-type inhibition and the action of adsorption matching with the Langmuir adsorption isotherm. The ∆Gads values for DHSiMF and DHSiB at temperatures (ranging from 303 to 333 K) are − 34.42 kilojoule/mole to − 37.51 kilojoule/mole. These values indicate that the compounds' adsorption types are chemo-physical adsorption. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) experiments were used to check the existence of the protection layer on the surface of carbon steel by analyzing the morphologies of the corrosion effects and the formed chemical compositions of the corrosion outcomes. For the concrete, the findings suggest that the chemical reaction that takes place between the DHSiMF and DHSiB and the concrete mix will result in an increase in the flexural strength, the compressive strength, and the indirect tensile strength of the concrete that is made of the gravel and dolomite aggregate. [ABSTRACT FROM AUTHOR]

This study assesses the durability of coated and uncoated concrete surfaces protected with four different coating materials: water-soluble (BW), solvent-based (BR), mineral (MI), and epoxy (EP). The durability assessment includes evaluating the absorption rate of water, pull-off adhesion strength, and coating material thickness. Concrete samples were subjected to immersion in regular water and a 7% urea solution, followed by cyclic freezing and thawing. Furthermore, the diffusion of chloride ions in concrete was evaluated using the impressed voltage method, with the samples exposed to the aging process immersed in a 3.5% NaCl solution. The results indicate that EP and BW coatings were significantly affected by the presence of urea and freeze–thaw cycles, resulting in a 43% and 47% reduction in pull-off adhesion strength, respectively. Notably, the MI-coated concrete samples exposed to urea solution and the freeze–thaw cycles exhibited a significant reduction in the absorption rate due to the accumulation of crystals on the coating surface, resulting in reduced porosity of the material. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures can experience various harsh environments during their service life, among which chloride ion exposure, especially in marine environments, can cause the durability reduction and deterioration of concrete structures. Artificial intelligence (AI)‐based modeling of the non‐steady‐state apparent chloride diffusion coefficient (DC) of concrete for a long exposure time using the experimental field results can assist in identifying the influential factors and better estimating the service life of a concrete structure. In this study, two novel extensions of ensemble AI algorithms, including genetic programming forest (GPF) and linear genetic programming forest (LGPF) algorithms, were proposed to model the DC of concrete. The experimental field data were gathered from the literature. Different structures of the proposed ensemble methods were developed and examined, and the best‐developed model was selected for further analysis, including sensitivity analysis and parametric study. In addition, the random forest (RF) method was used as the control ensemble technique to have a comparison. The results show that the best LGPF model possesses superior performance than the best‐developed GPF and RF models. In addition, the results show that silica fume‐to‐binder ratio, exposure time, and exposure conditions have the most significant impacts on the DC of concrete. This study contributes to the civil engineering practice by developing a new tool to model the DC of concrete that facilitates the durability assessment of concrete structures. [ABSTRACT FROM AUTHOR]

Global warming triggered efforts on sustainable materials in any area of production. Thus, the construction materials were also at the edge of a sharp change to achieve less harm to the environment by reducing the carbon print. Consequently, researchers have been trying to replace the cement from the mixtures of reinforced concrete as cement production causes large amounts of carbon dioxide emissions. Alkali‐activated binders are proved to be versatile alternatives to cementitious binders; however, accurate mathematical models to predict the capacities of these structural elements are limited in number. Therefore, in this study, a new stress–strain model has been developed to estimate the flexural capacity of geopolymer structural elements originated from construction and demolition waste. The study was initiated by formulating a novel stress–strain model applicable for defining the compressive behavior of geopolymer concrete. The formulation was based on recent experimental findings on flexural behavior of geopolymer beam specimens. Then, the performance of the proposed stress–strain model in estimating the ultimate moment capacities was investigated by using 36 bending tests from the literature. The results showed that the proposed model had very little deviations and enhanced accuracy compared with the literature available estimation method recommended by the ACI318. In addition, a soft database composed of 50 different beam specimens with varying mechanical properties and reinforcement patterns was formed. Numerical models corresponding to all possible combinations of each parameter were generated, and their load capacities were determined. After that, the estimation performances of the proposed method and the stress–strain models from the literature, and also the ACI318 procedure were examined. The conclusion of this check also yielded promising results with an absolute mean percentage error of 5.13% regardless of the mode of failures. [ABSTRACT FROM AUTHOR]

This paper introduced a new concrete composites made by quaternary binder by partially replacing ordinary Portland cement (OPC) with different percentages of supplementary cementitious materials (SCMs). The motivation is to reduce our dependency on OPC to reduce CO2 emission and carbon foot print. As the main substitute for the OPC, siliceous fly ash was used (FA). Moreover, silica fume (SF) and nanosilica (nS) were also used. This study utilized the following contents of SCMs used: 5% of nS; 10% of SF; 0, 15, and 25% of FA. During examinations the main mechanical properties of concrete composites, i.e. compressive strength (fcm) and splitting tensile strength (fctm) were assed. The brittleness of these materials was also analysed. Based on the conducted studies, it was found that concrete composite based on quaternary blended cements, of series Mix3, has shown the best results in terms of good strength parameters, whereas the worst mechanical parameters were characterized by concrete of series Mix4. On the other hand, concrete including only SF and nS (Mix2 series) were characterized by the greatest brittleness. It was observed that fcm of concrete composites for series Mix2, Mix3, and Mix4 increase of 41%, 48%, and 31% respectively compared with the concrete without additives, i.e. series Mix1. In addition, fctm also increase of 39%, 47%, and 30%, respectively, for the three series mentioned above, compared with the control concrete. Concrete of series Mix3, with high mechanical properties and demonstrating the features of quasi-plastic material, i.e. having lower brittleness, can be used in concrete and reinforced concrete structures subjected mainly to dynamic and cyclic loads. Therefore, it can be used, in the construction of foundation structures for machines and other types of structures in which the above-mentioned loads are dominant. [ABSTRACT FROM AUTHOR]

Using multi-walled carbon nanotubes (MWCNTs) as an additive in a concrete mixture with an amount of 0.05 to 0.2% wt. of cement weight with a constant W/C ratio using local materials was investigated in this research. Specimens were cured in water and the Caspian Seawater curing conditions, and compressive strength tests were performed on samples up to 365 days of age. Also, flexural strength, water absorption after immersion, water permeability and porosity tests and, SEM studying were performed on specimens. Results showed that increasing the amount of MWCNTs up to 0.2% of cement weight improved the workability, compressive, and flexural strength of concrete mixtures. The addition of MWCNTs caused a mild improvement in concrete specimens' strength which were cured in Caspian Seawater compared with control concrete. In the water absorption and water permeability tests, it was seen that a lower percentage of MWCNTs decreased the results, but more amount of MWCNTs may affect vice versa. In porosity studying, it was seen that more amount of MWCNTs may cause smaller pore sizes, however may increase the porosity and CNTs' agglomeration in concrete. [ABSTRACT FROM AUTHOR]

Corrosion resistance of concrete and reinforced concrete products is one of the main properties that affect the strength of structures built from these materials. Improving the corrosion protection of such products is an urgent task of modern materials science. The article is devoted to the study of the effect of a new complex additive on the physical and mechanical properties, such as water absorption and strength, of a heavy concrete mix. The object of the study was B22.5 grade concrete. The complex additive was obtained by homogenizing an aqueous emulsion of petroleum resin and C-3 superplasticizer. The water absorption and strength of the samples were determined according to State Standard 12730.3-2020 and State Standard 28570-2019, respectively. The results of the study gave evidence showing that the complex additive imparts plasticizing and water-repellent properties to a heavy concrete mix. The effect of the concentration of the complex additive on the water absorption and compressive strength was assessed, which made it possible to determine the optimal concentration range of the additive in the concrete mixture for use in the manufacture of concrete and reinforced concrete products. [ABSTRACT FROM AUTHOR]

Steel corrosion is major reason of the deterioration of reinforced concrete structures. Decreasing the transportation of erosion ions in concrete is one of effective methods to protect the steel from corrosion. In the present work, a novel nano-hydrophobic admixture is introduced to improve the ion-diffusion properties and the corrosion resistance of reinforced steel. Compared with unmodified concrete, the nano-hydrophobic admixture effectively decreases the water adsorption, water evaporation, and chloride ions transport in a concrete structure, and then improved the concrete's durability. The concrete's water adsorption decreased more than 78%, and the initial corrosion time of reinforced steel is prolonged more than one time by treatment with the nano-hydrophobic admixture. The inhibition penetration of the medium in concrete modified by hydrophobic nanoparticles is the key to provide the protective properties of steel reinforcement from chloride erosion. [ABSTRACT FROM AUTHOR]

Based on an exposure test of concrete with admixtures under a simulated tidal environment, the free chloride ion concentrations at different exposure times were measured, the apparent chloride diffusion coefficients of test concrete were fitted with Fick's second law, and the pore structural parameters of concrete at the same time were measured by mercury intrusion porosimetry (MIP). Based on the measured results, the time-varying characteristics of porosity and pore size distribution of test concrete have been analyzed, and the time-varying relationship between the proportion of different pore diameters as well as porosity and apparent chloride diffusion coefficients of concrete have been investigated. Results indicate that, under the simulated tidal environment, the total porosity and apparent chloride diffusion coefficient of test concrete have obvious time-variation, an obvious correlation between porosity and apparent chloride diffusion coefficient can be observed, i.e. both of them decrease with time. It has been found that the time-varying proportion of various pore diameters in concrete is different. Moreover, the correlation coefficients between contribution porosities of different pore diameters and apparent chloride diffusion coefficients show an increasing trend with exposure time. [ABSTRACT FROM AUTHOR]

The structural foundations in southern Iran face a formidable challenge due to extensive corrosion. To enhance concrete strength and durability, the construction industry in this region typically incorporates micro silica at a rate of 8% by weight of cement. Nonetheless, given that a significant amount, around 70%, of the concrete expenses in these projects can be attributed to micro silica, and the cost of natural pozzolan in proximity to project sites amounts to only 10% of the price of micro silica, the primary goal of this study is to investigate the durability of concrete incorporating both micro silica and natural pozzolan. The aim is to potentially replace a portion of the micro silica with natural pozzolan while maintaining the required durability and strength of the concrete as specified in the project requirements. To achieve this, eight different concrete mix designs were proposed and subjected them to assessments of compressive strength and various durability standard tests, including water absorption, resistance to rapid freezing and thawing, water permeability, chloride migration coefficient, electrical resistivity, and electron microscopy (Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS)/MAPPING). The obtained results indicated that the concrete sample containing 4% micro silica and 12.5% natural pozzolan exhibited similar characteristics to the project's mix design with 8% micro silica in terms of the durability and distribution of permeable spaces within the material. In addition, concerning the pozzolanic reaction, one kilogram of micro silica is nearly comparable to three kilograms of natural pozzolan. Moreover, despite the non-uniform nature of the concrete environment, the EDS and MAPPING results, obtained through random sampling of study points, closely mirrored trends observed in other controlled experiments. • Raising the proportion of natural pozzolan in the concrete up to 25% enhances the durability of reinforced concrete. • The mixture with 30% natural pozzolan displays the most significant reduction in compressive strength. • 4% micro silica + 12.5% pozzolan blend excels in durability and compressive strength compared other mixtures. [ABSTRACT FROM AUTHOR]

In this work, novel calibration curves and calibration surfaces of Electromagnetic (EM) characteristics are modeled as a function of the water and chloride contents of concrete. An experimental campaign was carried out on cores extracted from two types of concretes: C1 (Ordinary Portland Concrete) and C3 (62% slag + 38% clinker). The cores were initially saturated at three sodium chloride (NaCl) concentrations and then oven-dried to attain different degrees of saturation. They were tested with the electromagnetic and electrical cell to determine the dielectric permittivity and electrical resistivity, respectively, at the targeted hydric and chloride ion contents. The calibration curves and calibration surfaces, which represent the resistivity and permittivity as a function of chloride content and/or degree of saturation, were adjusted and presented for both concretes. The calibration surfaces developed herein serve as an essential tool to study complex phenomena, such as the coupled water-chloride ingress. • Developing novel calibration curves and calibration surfaces that correlate the permittivity and resistivity of concrete to its chloride and water content. • Investigating the impact of slag on the permittivity and resistivity of concrete. • Proposing a non-destructive methodology to monitor chloride and water content for reinforced concrete structures exposed to a tidal zone. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO 2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO 2 corrosion utilizing an SO 2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO 2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (E corr) and corrosion current density (i corr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO 2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe 2 O 3), rozenite (FeSO 4 ·4 H 2 O). The formation of FeSO 4 ·4 H 2 O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO 2. ● Simulate typical industrial SO 2 corrosion environments. ● Surface analysis reveals the corrosion mechanism of steel rebars in concrete. ● Corrosion products contain ferrous sulphate hydrates. [ABSTRACT FROM AUTHOR]

Concrete structural properties are compromised largely due to corrosion susceptibility of steel reinforcements. This results in weakening and eventual failure of structures. Several strategies have been employed in past to control corrosion and increase mechanical strength of concretes, in particular for structural applications. In this study, fly ash and polypropylene fibers were utilized as the admixtures for preparation of concrete blocks with variable water-cement (w/c) ratios i.e. 0.45, 0.5 and 0.65. Three different grades of cements were selected in this study namely OPC 43, OPC 53 and sulphate resistant one. Also, two different steel alloys were used i.e. ASTM-615 and ASTM-706, since both of them are very common reinforcement materials (rebars). The curing time of 56 consecutive days was employed before testing and characterization. The results suggest remarkable improvement in the mechanical properties of blocks upon the incorporation of admixtures. However, rebars exhibited highest corrosion rate in the presence of OPC 43 cement at w/c ratio of 0.65. [ABSTRACT FROM AUTHOR]

Consolidating previous research on the development of novel microcapsules for self-healing in cementitious systems, this work forms a base for developing an implementation strategy and guidance for microcapsule-based self-healing technology. The study presents details of the first commercial deployment of this technology, as a ready-mix self-healing additive for commercial application. This involved the on-site construction of two slabs in a new development at the University of Cambridge. This paper describes the optimization of the mix, the structural concept and design, and processing and casting procedures. Prior to application, the compliance and compatibility of the healing additive with the concrete according to specifications and requirements of the design were investigated, validating the use of the developed system. These were complemented by large-scale laboratory testing of the healing efficiency under damage scenarios identified as critical for the on-site application. The performance of the site installation was monitored over 12 months through a combination of nondestructive testing methods. Results are presented with durability indicators confirming the in situ enhanced performance of the proposed self-healing system. [ABSTRACT FROM AUTHOR]

Underground reinforced concrete utility vaults play a vital role for the functioning of urban centers, providing space for all kinds of utility equipment. Underground structures are subjected to harsh environmental conditions that can impact their life and eventually trigger structural damage—potentially becoming hazardous to equipment and personnel carrying out routine inspections. A study was conducted to determine the main causes for deterioration in underground reinforced concrete structures observed during routine inspections in the southwest United States. Petrographic examinations of concrete samples cored from seven unique structures with significant damage showed that concrete carbonation has reached the reinforcing steel in some structures and there was evidence of minor sulfate attacks. Chloride ions were found at high concentrations, which had indications of being introduced through the concrete admixture. This is consistent with the practice of the precast industry around the 1960s–1980s to use calcium chloride admixtures to increase fabrication throughput. The presence of chlorides in the concrete matrix, coupled with gradual concrete carbonation, moisture, and oxygen, are the main causes of deterioration and damage observed in these structures. [ABSTRACT FROM AUTHOR]

The purpose of this article is to present the results of the study of the operational suitability of the existing induced airfield coating by experimental and theoretical methods. Based on the analysis of the results of the research, it was determined that the material that provides performance characteristics, namely: crack resistance, tensile strength, impact strength, abrasion resistance - is a modified concrete, i.e. concrete with additives that have a positive effect on the structure and operational properties. This paper presents the results of studies of the reinforcement layer made of concrete with the introduction of the most common modifiers of polymeric substance (polymer-cement RCC - Polymer Cement Concrete) and basalt chopped fiber - fiber (basalt fiber concrete FRC - Fiber Reinforced Basalt concrete). [ABSTRACT FROM AUTHOR]

The strength behavior of Corn Husk Ash polymer concrete reinforced with coconut fibre was investigated in this study. The study assessed the suitability of using coconut fibre in concrete to improve its strength properties. The concrete was prepared and cured based on British Standard. Different proportions of the coconut fibre as well as the Corn Husk Ash (CHA) polymer were used in the concrete mixes, with a total of nineteen different mix proportions. The specimens were cured for 28, 90 and 180 days. Compressive strength, tensile splitting strength, torsion and toughness were determined using specimens from the various mixes. Tests were conducted on the 28th, 90th and 180th days of curing, following (Compression) and (Tensile Splitting). Analysis of Variance (ANOVA) test was conducted to determine the differences in the behavior of the different mixes as well as the correlation between the different constructs. The addition of coconut fibre to the concrete improved the toughness, torsion and to some extent the tensile strength of the concrete at the standard curing age of 28 days. CHA as an additive to the concrete resulted in a positive relationship with the Torsion and Toughness properties of concrete at later curing age at 1% level of significance (r = 0.480 and r = 0.730, p < 0.01 respectively). Compressive strength of concrete correlated positively with tensile strength, torsion and toughness of concrete (r = 0.830, r = 0.721 and r = 0.452 respectively with p < 0.01). [ABSTRACT FROM AUTHOR]

This study was conducted to ascertain the effect of nanoplastics on corrosion permeability resistance of concrete. Various percentages of nanoplastics ranging from 5% to 25% were used to replace cement in this study. The corrosion permeability resistance test and bond strength test were conducted in conformity with BS EN 12,504–3:2005 and ASTC 1202, respectively. The results of this study depicted that specimen with 15% nanoplastics lost 40% of their bond strength from the zero corrosion stage to severe corrosion stage, while the specimens with no nanoplastics lost 90% of their bond strength. The addition of nanoplastics as an admixture to concrete provided an average range of 40% to 65% better corrosion protection than the plain concrete. The lower current reading of concrete specimens with nanoplastics compared to that of plain concrete signified the beneficial effect in using nanoplastics as an admixture in concrete to protect the reinforcing bars from corrosion. The study concludes that the initial lower current passing, lower current reading with prolonged time to reach the severe corrosion stage, smaller percentage loss of bond strength, mass and rib profile of concrete specimens with nanoplastics indicated higher resistivity of the concrete with nanoplastics. The study therefore recommends that nanoplastics should be used as an admixture to concrete up to 15% replacement level. [ABSTRACT FROM AUTHOR]

• Development of structural concrete at low molarities 4 M and 6 M of NaOH. • The effect of different curing conditions on compressive strength is assessed. • Effect of composition on mechanical and durability properties is assessed. • The study results indicate the possibility of multi-parameter optimization. The present study explores the application of low molarity geopolymer concrete for structural applications. In this context, 35 compositions with 4 M and 6 M NaOH concentrations have been developed to yield compressive strength ranging from 10 to 40 MPa. The flow values at low water to binder (w/b) ratio are shown to be influenced by molarity of NaOH while it remains range bound at higher w/b ratio. The effect of curing conditions reveals low reactivity rate under ambient conditions with significant enhancements at elevated curing conditions. Three compositions with compressive strength of 30 ± 2 MPa have been further investigated for tensile strength, elastic modulus, plastic strain, sorptivity and chloride migration. The results reveal that despite similar compressive strength, the mix compositions have significant impact on the fresh and hardened properties indicating possibility of multiparameter optimization. The development of low molarity geopolymer concrete with possibility to optimize other structural/durability parameters in addition to compressive strength would enhance sustainability, economy and structural performance of geopolymer concrete. [ABSTRACT FROM AUTHOR]

• The adequacy of rapid chloride migration test (RCMT) of concrete was assessed. • Natural marine environment results were compared with RCMT results. • A chloride penetration resistance classification was proposed according to the RCMT. • A service life range was suggested for the RCMT classification. This paper analyses the use of the rapid chloride migration test (RCMT) in assessing the long-term chloride penetration resistance of concrete in real marine environment. Based on extensive experimental data, RCMT results were related to the diffusion and penetration properties of a wide range of normal weight and lightweight aggregate concretes, 5-year exposed under real submerged (XS2) and wetting and drying (XS3) conditions. Most usual structural concrete with different water/binder, types of aggregates and binders were covered. Concretes were ranked in terms of their chloride durability performance in real environment and a new classification was proposed to evaluate the durability of concrete to chloride attack. Classes were established based on service life prediction analysis. Overall, it is shown that the RCMT classification can distinguish the resistance to the chloride penetration of different concretes under distinct exposure environments, allowing for an expeditious method to evaluate the concrete quality. [ABSTRACT FROM AUTHOR]

Strategies for the reinforcement for 3D‐concrete‐printing The ingenious bridge, hall and shell structures of the last century were designed from the understanding of the congenial interaction of the two materials concrete and steel. Nowadays, reinforced concrete is the most widley used material in construction. The use of system formwork and easy‐to‐install reinforcement support structures that are optimized in terms of labor costs, but often have an inefficient use of material. In this context, Stefan Polónyi has repeatedly criticised the engineerś lost understanding of the interaction of concrete and reinforcement. With Additive Manufacturing, an innovative digital manufacturing technology is now available that allows new freedom in concrete design while at the same time making resource‐efficient use of materials. With regard to practical application, the integration of reinforcement represents a central challenge in 3D‐concrete‐printing. The authors see here the future chance of a force‐flow controlled reinforcement layout. The paper shows new strategies for the combined additive manufacturing of concrete and reinforcement and presents first 3D‐printed reinforced concrete elements. [ABSTRACT FROM AUTHOR]

The interfacial transition zone (ITZ) has a major detrimental impact on the structural performance of concrete. This negative impact can be modulated by introducing mineral admixtures to a concrete mix, which fill the excessive voids within ITZ and react with portlandite to form more compact products. The approach described here, consisting of characterization of phases and micromechanical modeling, enabled assessment of the effect of silica fume, fly ash, and metakaolin on ITZ thickness and strength. The proposed model was based on the Mori-Tanaka scheme coupled with an estimation of deviatoric stress within ITZ. This study suggests that silica fume is efficient in reducing ITZ thickness, while the addition of fly ash more significantly contributes to ITZ strength. Moderate replacements of Portland cement for silica fume or fly ash, up to 20%, can positively influence concrete performance; in case of metakaolin, replacement up to 10% is recommended. [ABSTRACT FROM AUTHOR]

Fly ash has been used more and more often to take the place of cement as the admixture of concrete in the construction of concrete buildings. However, with the increase of the carbon dioxide (CO2) concentration in the atmosphere, carbonization damage has become an essential factor affecting the durability of fly ash concrete. Here a long-term bending load device was developed to explore how the pouring surface and the bending load affect the carbonization resistance of reinforced concrete under rapid carbonization. In addition, the relationship between the bendingtension and bending-compression loads with respect to the carbonization damage of test blocks was also investigated. Due to the differences in the concrete compactness, the carbonization depth of the pouring surface was found to be greater than that of the bottom at the same position. To a certain extent, with the increasing bending-load stress, different carbonization resistances were observed in the bending-tension zone and the bendingcompression zone of the concrete test blocks. Meanwhile, to study the relationship between the carbonization damages in the bending-tension zone and the bending-compression zone of concrete test blocks, a carbonization influence coefficient of bending tension-compression load was proposed, which provides a convenient and scientific guidance for the detection and evaluation of concrete carbonization damages in practical engineering. [ABSTRACT FROM AUTHOR]

A study has been made of the influence of adding a nanostructured-carbon-based plasticizing admixture to a self-compacting concrete mix on the properties of heavy-weight structural concrete produced from it. It has been shown that this admixture in the concrete mix changes its structure and makes it possible to produce concrete with exceptional physicomechanical properties. Furthermore, the plasticizing admixture added to a concrete mix ensures the high degree of preservation of its placeability to provide a possibility of transporting this mix for a long period and of using it in monolithic construction. The indicated admixture in the concrete mix reduces its water–cement ratio to 0.2 and ensures good placeability of the mix, which guarantees the high rate of its hardening and considerable improvement in the strength of concrete based on this mix. [ABSTRACT FROM AUTHOR]

In this paper, the bond behaviour of reinforced concrete exposed to high temperature at early age has been investigated. The influence of temperature, curing age before exposing to high temperature and repair agent on the ultimate bond stress and bond displacement of reinforced concrete are analysed. The ultimate bond stress of specimens decreases with the increase in temperature, while the ultimate bond displacement increases with the increase in temperature. After being subjected to the same temperatures, the ultimate bond stress of the specimen heated at a curing age of 28 d is found to be lower than that of specimens that were heated at curing ages of 3, 7 and 14 d. However, the ultimate bond displacement of the specimen heated at the age of 28 d is larger than that of specimens heated at the ages of 3, 7 and 14 d. The ultimate bond stress of the specimen using a repair agent is greater than the ultimate bond stress of the specimen without using the repair agent. On the contrary, the ultimate bond displacement of the specimen using a repair agent is found to be less than that of the specimen without using a repair agent. [ABSTRACT FROM AUTHOR]

An innovative hybrid fibre system of steel fibres, polyvinyl alcohol (PVA) fibres and inexpensive (approximately US$230/t) calcium carbonate whiskers (CW) was assessed as a way of improving the mechanical behaviour of fibre-reinforced concrete under static and impact loads and reducing production costs. Static mechanical properties and repeated drop-weight impact tests of the designed hybrid-fibre-reinforced cementitious composites (HyFRCCs) are presented in this paper. The reinforcing effect of the new hybrid fibre system was found to be very close to that of conventional HyFRCCs (incorporating only steel and PVA fibres) under both static and impact loads. It is thus suggested that steel and PVA fibres can be partly replaced with CW to reduce production costs in large-scale construction applications. Ultrasonic pulse velocity, dynamic elastic modulus and crack width assessments were carried out to quantify the degree of damage in samples during mechanical testing. The impact energy absorbed by the specimens could be predicted using linear modelling. There is therefore potential for using such tools to evaluate the in situ structural damage under dynamic loads. [ABSTRACT FROM AUTHOR]

An experimental investigation is conducted on the influence of the degradation of fibre-reinforced-polymer (FRP) bars on their bond performance with concrete. A basalt fibre-reinforced vinyl ester (BV) bar, basalt fibre-reinforced epoxy (BE) bar, carbon fibre-reinforced epoxy (CE) bar and E-glass-fibre-reinforced vinyl ester (GV) bar are adopted. The bars are pre-exposed to 40°C alkaline solution for 0, 15, 30 and 45 d and then tested under a direct pull-out condition. The test parameters include the resin type, fibre type and conditioned age. The test results indicate that, for the unconditioned bars, the bond strength of CE bars is the largest, next are the GV bars and BE bars, whose strengths are very close to each other, and the BV bars have the least bond strength. For the conditioned FRP bars, the bond strength retention of BE bars with an epoxy matrix are generally greater than those of BV bars with a vinyl ester matrix. The bond strengths of the conditioned CE bars and BE bars with the epoxy matrix both increase, whereas the BV bars and GV bars show a decreasing trend. It is concluded that the order of bond durability is CE > BE > GV > BV for the bars used in this paper combining the test results with a mechanism analysis. [ABSTRACT FROM AUTHOR]

Concrete resistivity in reinforced concrete structures is used as an indicator of durability related to the corrosion risk. This study aims to develop a quantitative analysis method of geometric effects of nearby reinforcement in the electrical resistivity measurement. The A-REM proposed in this study is a mathematical model to enable analysis of not only concrete (or mortar) and reinforcement resistivity, but also of geometric effects such as rebar diameter, cover depth, electrode interval, and the spatial relationship between the rebar and electrodes. The effect of nearby reinforcement on the electrical resistivity measurement was presented to be obtained from the apparent resistivity rate (AR rate) calculated by the A-REM. The A-REM for the estimation of the nearby reinforcement effects was verified by comparing the apparent resistivity values obtained from mortar specimens having different reinforcement diameters and cover depths. The result shows that the calculated values of the A-REM are correlated with the experimental values of apparent resistivity. [ABSTRACT FROM AUTHOR]

• A novel strengthening technique incorporating section curvilinearization (SC) using UHP-ECC and FRP confinement is proposed. • Large-scaled FRP-confined square RC columns with SC using UHP-ECC were prepared and tested. • Parameters of FRP thickness, the rise-to-span ratio and the strength of the additive concrete were investigated. • The current design models for FRP-confined curvilinearized RC columns were assessed by the experimental results. In this paper, a novel column strengthening technique incorporating section curvilinearization (SC) using ultra-high performance engineered cementitious composites (UHP-ECC) and fiber-reinforced polymer (FRP) confinement is proposed and validated. Eleven large-scaled FRP-confined square reinforced concrete (RC) columns with SC using UHP-ECC as the additive material were prepared and tested. The main parameters investigated in this paper included the FRP thickness, the rise-to-span ratio, and the strength of the additive concrete. Test results show that the SC technique with FRP jacketing and UHP-ECC as the additive material enhances the load-bearing capacity of the RC columns by 52% with a 17% section increment. By assessing the existing design-oriented stress–strain models of confined concrete in curvilinearized square columns (CSCs) using the test results obtained in this study, it reveals that the current models could underestimate the ultimate strength of the confined concrete in CSCs with a two-layer FRP wrap, and therefore further research on the improvement on the stress–strain model of confined concrete in CSCs becomes necessary. [ABSTRACT FROM AUTHOR]

In this contribution, an additive strain model is used to describe the deformation behavior of concrete. The model assumes that elastic, viscous, thermal, and damage‐induced strains occur in concrete. The strain components develop independently of each other as a function of the number of load cycles, test duration, and characteristic parameters of the stress cycles. The focus of this paper is on the determination of a creep‐relevant stress level to estimate the magnitude of the viscous deformation component as a function of the fatigue stress. Experimentally measured strains of fatigue‐loaded concrete specimens are divided into the strain components assumed by the additive strain model and analyzed. The investigations yield new insights into the strain and material behavior of fatigue‐loaded concrete. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • Nano-additives accelerated the self-healing of the textile reinforced concrete (TRC). • Decorating the textile surface with micro silica particles accelerated the self-healing process and enhanced TRC tensile strength and toughness. • Salt-cured TRC samples showed more fine cracks than tap-water-cured which promotes the self-healing process. Textile reinforced concrete (TRC) is an attractive alternative to the classic steel rebar reinforcement since the textile is stronger, more flexible, and non-corrosive compared to steel. Moreover, the TRC approach promotes the formation of multiple thin cracks pattern upon loading instead of a few wide cracks in rebar reinforcement. We found that the self-healing of these multiple thin cracks was accelerated by modifying the concrete matrix (addition of crystalline additive and alumina nanofibers) and by decorating the carbon-based textile with micro silica particles. Exposing the TRC samples to a saturated NaCl environment (as in coastal constructions) improved the bonding strength between the textile and the matrix, hence increasing the self-healing capability (compared to samples cured in tap water). [ABSTRACT FROM AUTHOR]

Textile-reinforced mortar (or textile-reinforced concrete, TRC) may be used to repair and/or strengthen structural elements of existing construction works (buildings, bridges, etc.) or may be used as constituent elements of new structures. When structures are subjected to fire, they are simultaneously submitted to high temperatures (potentially up to 1200 °C) and mechanical loadings. The elevated temperature thermomechanical behaviour of TRC remains both poorly understood and poorly studied. This study describes the experimental identification, at the macroscale level, of the thermomechanical behaviour of two TRC composites. It shows that the thermomechanical behaviour of two TRC composites is nonlinear and progressively evolves with the increase of the temperature level. The evolution of certain characteristics (the ultimate stress, the stress corresponding to the loss of linearity of the first zone of the stress/strain curve, the stress corresponding to the start of the post cracking stage, the maximum thermomechanical strain, the initial stiffness, the stiffness of the post cracked composite) of the studied materials as a function of the temperature levels will be identified. When temperature levels vary from 100 °C to 300 °C, the main parameters (the ultimate stress, the stress corresponding to the loss of linearity of the first zone of the stress/strain curve, the stress corresponding to the start of the post cracking stage, the initial stiffness, the stiffness of the post cracked composite) of the studied materials are in general gradually decreased with the increase of the temperature level. The influence of a grid and chopped strand textile reinforcement on the cement based composite under thermomechanical loading is analysed and discussed. The experiments show a clear difference between the thermomechanical responses of two TRC composites. Additionally, the cracked specimens are examined. [ABSTRACT FROM AUTHOR]

• Concrete expansion due to expansive additives in reinforced concrete has been studied. • Expansions decrease in restrained directions but remain unchanged in the free direction. • Volumetric expansion decreases with an increase in the reinforcement ratio. • Expansion characteristics of expansive concrete have been compared with that of ASR and DEF. Expansive additives in higher dosages induce chemical prestress in concrete by imparting higher early-age expansion. However, induced stress and concrete expansion can vary significantly, depending on different restraint conditions. In addition, concrete expansion can be highly anisotropic depending on the nature of external restraints and boundary conditions. Experimentations have been performed to study the effect of uniaxial (anisotropic) restraint on the concrete expansion (in both restraint and stress-free directions) and induced prestress. A higher degree of restraint resulted in a substantial decrement in the longitudinal expansion. In contrast, expansion in the stress-free (lateral) direction was not much affected by the restraint in other direction. As a result, an overall decrement in the volumetric expansion was observed with an increase in the reinforcement ratios. Stress induced in concrete due to the restraint expansion in the longitudinal direction was found to be higher for a higher reinforcement ratio. Data provided from the current work can be used for the comprehensive modelling of expansive concrete under external restraints. [ABSTRACT FROM AUTHOR]