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In marine environments, traditional ordinary Portland cement (OPC) and reinforced concrete structures are prone to corrosion, reducing their durability and service life dramatically. Geopolymers, with exceptional corrosion resistance, have great value and application potential in marine engineering. This paper presents a comprehensive overview of the research advances on geopolymer cements and concretes in marine environments in terms of mechanical properties, durability, and structural properties. The research so far has demonstrated that geopolymers exhibit superior mechanical properties and durability due to their denser interface and lower porosity compared to OPC. However, geopolymers have significant brittleness defects, and their performance in marine environments, especially in splash and tidal zones with alternating wet and dry conditions, is severely affected. This is due to the influence of chloride ions, divalent cations, pH, and sulfate in seawater, which promote or inhibit the formation and transformation of reaction products and microstructures, thereby affecting their mechanical properties and stability. Nevertheless, the use of composite technologies such as modified precursors, fibers, and nanomaterials has a positive effect on enhancing their structural properties and durability. This provides guidance and solutions for the application of high-durability, low-carbon emission, and more sustainable building materials in maritime engineering. [ABSTRACT FROM AUTHOR]

This study investigated the chloride-induced durability deterioration mechanism at the interface of carbon fiber reinforced polymer (CFRP) and steel joints exposure to wet-dry cycling environment, using 27 specimens with varying corrosion levels of steel and aging periods of bonded joints. Characterization including macro and microscale observation, quantification of topographical structure, analysis of surface wettability and adherent residues, were employed to understand the steel surface conditions and their relationship with durability performance under prolonged wet-dry cycles. The results indicated that various steel surface characteristics influenced the interface in both the short and long terms; however, the priority shifted from topography for new steel to cleanliness for corroded steel. As the corrosion level of the steel increased with the aging period, notable declines were observed in the joint's ultimate capacity (∼33.4 %) and its displacement (∼9.94 %) in general responses, along with decreases in maximum slip (∼31.0 %) and shorter plateaus in local responses. This corresponded to an undesirable shift in the triggering failure mode at the ends. Additionally, deterioration mechanism encompassed "foreign attacks" as external factors, marked by corrosion at the bonding edges and inward capillary diffusion of chloride ions, and "domestic unrest" as internal factors, exemplified by the development of those adherent chloride/rust residues, weakening steel-adhesive bonds, and risk of separation. Finally, a time-dependent environmental reduction factor for the capacity model was proposed and verified using collected test data. • Optimizing surface preparation for corroded steels to enhance the bonding behavior of CFRP-steel joints. • Revealing chloride-induced deterioration mechanism, encompassing "foreign attacks" and "domestic unrest". • Developing a time-dependent reduction factor based on the energy release rate. [ABSTRACT FROM AUTHOR]

The incorporation of fly ash (FA) and MgO expansive additive (MEA) is a frequent practice to satisfy the functional prerequisites of temperature control and crack prevention for dam concrete. Nonetheless, the internal environment of concrete dams is comparatively intricate and the expansion of MEA is susceptible to a variety of factors. Consequently, this study systematically delves into the evolution law and influencing mechanism of the durability of FA-blended cement paste modified by MEA, utilizing the rapid chloride ion penetration test, accelerated carbonation test, rapid freeze-thaw cycle test, mercury intrusion porosimetry (MIP), electrochemical impedance spectroscopy (EIS) and thermogravimetry (TG). The findings suggest that by increasing the curing temperature, the joint use of FA and MEA can prevent the decline of durability caused by 10% MEA efficiently and convert the impact of FA on durability into a positive effect. The inward transport path of external chloride ions, CO 2 and water is obviously obstructed by the refinement of pore size and the increase of tortuosity, leading to a reduction of the migration rate. The electrochemical equivalent circuit R s (Q 1 (R ct1 W 1))(Q 2 (R ct2 W 2)) is suitable for analyzing the EIS of FA-blended cement paste modified by MEA, and there was a strong correlation between R s and the resistance to chloride ion penetration. The substantial generation of hydroxides boosts significantly the stockpile of carbonizable substances. Furthermore, compared to Portland cement, it is a cleaner cementitious material, reducing economic costs, carbon emissions, and energy consumption by 8.2%, 29.1%, and 43.9%, respectively. This study can provide effective guidance for the green high-performance design of dam concrete mix proportions. • The increase in curing temperature and the addition of MgO jointly promote the positive effect of FA on durability. • The refinement of pore size and the increase in tortuosity hinder the transport of chloride ions, CO 2 and water. • FA-blended cement paste modified by MEA has higher economic and environmental benefits, fully reflecting sustainability. [ABSTRACT FROM AUTHOR]

Shortly after casting, offshore reinforced concrete structures are exposed to sulfate and chloride ions without undergoing any proper curing procedures, which are crucial for enhancing their strength and durability. Furthermore, there persists a lack of comprehensive understanding concerning the coupled impact of the attack of sulfate and chloride ions on cementitious materials with current existing research still yielding conflicting outcomes. This paper investigates the influence of curing on the chemical interactions between low-carbon cementitious materials (substituting 45 % of cement with industrial by-products like slag, fly ash, and metakaolin to reduce CO 2 emissions) and coupled sulfate and chloride ions. To achieve this, powder samples were obtained from prismatic-shaped specimens of ordinary Portland cement (CEM I) paste, binary, ternary, and quaternary blends. Some solid specimens were ground into powder after 24 hours post-casting while others were powdered after a 90-day curing period. Subsequently, the acquired powders underwent exposure to chloride, sulfate, and sulfate-chloride solutions over a duration of 25 days. Results indicate that curing time does not alter the interplay between sulfate and chloride ions in the cementitious matrix. Sulfate presence accelerates chloride ion ingress, while chloride presence mitigates sulfate attack in both uncured and pre-cured samples. However, the curing process accelerates sulfate attack, proven through excessive ettringite and gypsum formation, high consumption of portlandite and AFm, diminution of sulfate ions concentration in the attacking solution after 5 days of exposure, increase of pH of more than 0.5 units, aspect changes observed through visual inspections, and porosity distribution changes showed by an increase of 10 % of the total porosity in the reference mix. Additionally, curing promotes the formation of Friedel's salt, thereby attenuating chloride ions ingress. [Display omitted] • Chemical interactions of sulfate-chloride attack are highlighted. • The presence of sulfate accelerates the chloride ingress in the materials. • Chloride diffusion mitigates the sulfate attack in the materials. • Curing duration does not affect the sulfate-chloride coupling chemical process. • Raman spectroscopy serves as a quick chemical characterization technique on solutions. [ABSTRACT FROM AUTHOR]

The durability of ultra-high performance concrete (UHPC) with initial micro-cracking subjected to coupled freeze-thaw and chloride salt (FT-CS) attacks was investigated. The initial micro-cracking was introduced under controlled condition in the laboratory by pre-tensioning the dog-bone specimens and unloading them at a target strain of 1500 με. The micro-cracked UHPC specimens were then submerged in a sodium chloride solution with the concentration of 4 wt % and subjected to freeze-thaw (F-T) cycles. The micro-cracked UHPCs exhibited excellent chloride penetration resistance as evidenced by the consistently low chloride ion concentration (generally less than 0.5%) and the limited penetration depth (not exceeding 6 mm) even after undergoing 300 cycles of the coupled FT-CS attacks. The tensile strength and compressive strength of the micro-cracked UHPC were improved by 28.0% and 18.3% at 200 F-T cycles, respectively. The improvement in the mechanical properties can be attributed to the self-healing effect which densified the fiber-matrix interface and the matrix. Secondary hydration and carbonation were confirmed quantitatively by thermogravimetric test and qualitatively by scanning electron microscopy test. However, the detrimental effects stemming from the coupled FT-CS attacks outweighed the beneficial effect of self-healing at 300 F-T cycles, resulting in a decline in mechanical performance. [ABSTRACT FROM AUTHOR]

In this study, three major properties of concrete were compared, viz: water absorption, compressive strength and chloride ion penetration. The percentage amounts of Induction furnace slag (IFS) varied in concrete to replace cement were 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% and 60%. These specimens were made to undergo curing for 7, 14, 28, 56 and 90 days following which the aforementioned tests took place. The results of the three tests (i.e. compressive strength test, water absorption test and chloride ion penetration test) showed an optimal performance of concrete at 25% IFS replacement. Some of the specimens containing varying amounts of slag (i.e. 0%, 25% and 45%) were subjected to microstructural and phase identification tests in other to establish their distinguishing properties. These tests include Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Meanwhile the IFS was also examined for its composition through X-ray Fluorescence (XRF). Predictive models were generated from all the results obtained. The models developed can predict the compressive strength of concrete (Y) if information on the percentage of IFS replaced (X 1), the depth of chloride ion penetration into concrete (X 2) and the amount of void left in concrete after water is absorbed (X 3) are all known. There existed a high correlation; strong relationship between compressive strength and the depth of chloride ion penetration; and between compressive strength and the percentage volume of void. • Induction furnace slag is a good pozzolan for cement replacement • At 25% replacement, induction furnace slag has the best durability properties. • The compressive strength of concrete yields the optimum at 25% replacement with slag • XRF, SEM, XRD tests validate the experimental behaviors of induction furnace slag. [ABSTRACT FROM AUTHOR]

• The proposed mix design method produced SCCs with low binder contents. • The use of ground fly ash led to good durability indicators. • The CO 2 /MPa·m3 emission is among the lowest reported in the literature for HPSCCs. • HPSCCs with the lowest reported binder content (365 kg/m3) were produced. The use of high-performance concrete (HPC) is widespread as an eco-efficient building solution because it provides greater durability and, hence, a longer lifetime than conventional concrete, reducing the need for repairs and demolitions. In addition, HPCs require lower binder contents per unit of compressive strength. However, self-compacting HPCs (HPSCCs) generally require high binder contents to ensure the fresh state stability of the concretes, which could hinder the ecological advantage. Thus, this work aimed to produce HPSCCs with low binder contents. A mix design method was proposed to optimise the material proportions. A fine fly ash was used to replace Portland cement from 0 to 30%. The rheological properties of the SCCs were evaluated by the workability tests slump flow, T500, V-funnel, L-box and VSI. Compressive strength, resistance to chloride ion penetration, volume of permeable voids and capillary water absorption were determined at 28 and 91 days. Finally, the CO 2 intensity (kg CO 2 /m3·MPa) of the mixtures produced was estimated and compared to those of HPSCCs reported in the literature. The mix design method allowed for the production of SCCs with 365 kg of binder/m3 of concrete, with slump flow of 700 ± 25 mm and stable in the fresh state (VSI of 0 or 1). The fly ash-containing concretes showed compressive strengths up to 59 MPa at 28 days (10% fly ash) and 71 MPa at 91 days (20 and 30% fly ash), with good indicators of durability: down to 403 Coulombs for RCPT and up to 41.8 kΩ·cm for surface electrical resistivity. The CO 2 intensity of the concretes produced are among the lowest reported in the literature for HPSCCs (down to 4.7), together with the lowest binder content reported for this type of concrete (365 kg/m3 of concrete). [ABSTRACT FROM AUTHOR]

• This paper first reports the influence of nano-silica on high strength mortar. • Pore system was refined and more disconnected. • Compressive strength and transport properties were improved. • Drying shrinkage was reduced due to the refined microstructure. • The enhancing efficiency was compared in high strength and normal strength mortar. Recent studies have demonstrated the advantages of using nano-silica in building materials such as concrete due to its nano-filler effect as well as the pozzolanic reaction. However, most of the previous findings are based on normal strength cement composites. In this study, a wide range of properties of high performance cement composites are investigated with addition of colloidal nano-silica (CNS) at dosage of 0.5%, 1.0%, 1.5% and 2.0%. Attributed to the pozzolanic reaction of CNS, the microstructures are denser and more homogenous. SEM observation, accelerated hydration rate and reduced Portlandite content verify this beneficial reaction. Hence, the CNS can help produce cement composites with higher mechanical strength and better durability regards to the impermeability to water and chloride ions. Also, it is found that the influence of CNS is more pronounced for composites with lower water-cement ratio at 0.30, in comparison with those at 0.50. [ABSTRACT FROM AUTHOR]

• A novel lightweight and high-strength engineered cementitious composite was developed. • The deterioration degree of salt solutions on tensile properties of LECC was LECC-S > LECC-CS > LECC-C. • The external sulfate–chloride environment under low temperature offered highly suitable conditions for the formation of expansive thaumasite. • The combined physical and chemical attacks of sulfate promoted chloride diffusion, but chloride ion delayed sulfate's diffusion and expansion reaction. A novel lightweight high-strength engineered cementitious composite (LECC) was developed, and its mechanical property changes and the resultant durability evolution under the triple coupling factors of chloride attack, sulfate attack, and freeze–thaw cycles were studied. The results indicate that the salt solutions can accelerate the failure of LECC under freeze–thaw cycles. Salt solutions accelerated the tensile properties degradation of LECCs, and the deterioration degree was LECC-S (sulfate) > LECC-CS (chloride-sulfate) > LECC-C (chloride). The influence degree of salt solutions on mass loss was LECC-CS > LECC-C > LECC-S, while their influence on relative dynamic elastic modulus was LECC-S > LECC-CS > LECC-C. The surface spalling and internal structure destruction of LECC after salt freezing provided a favorable channel for CO 2 penetration in the environment and the external sulfate–chloride environment under low temperature offered highly suitable conditions for the formation of expansive thaumasite. The combined physical and chemical attacks of sulfate promoted chloride diffusion, but chloride ion delayed sulfate's diffusion and expansion reaction. This study more comprehensively revealed the durability development of LECC in some abominable environments and provided data support for the engineering application of LECC. [ABSTRACT FROM AUTHOR]

• The mix of 3DPC was designed based on the MA&A model. • The anisotropy mechanism of 3DPC was explained by CT scanning. • The distribution, connectivity, and porosity of pores in 3DPC were investigated. • Effect of pore structure on durability and mechanical properties of 3DPC was studied. • Effect of freeze-thaw cycle on mechanical properties of 3DPC was studied. The application of 3D printed concrete (3DPC) technology in the construction industry has become widespread in recent years. This paper provided a method for the 3DPC mix design and investigated the mechanical performance and durability of 3DPC. In this study, two optimized mixes were obtained based on the particle dense packing theory and the least squares method for calculating the proportions of binder for 3DPC. The microstructure of 3DPC was investigated by X-CT scanning to characterize its porosity for discussion of the anisotropic mechanical performance in the 3DPC. In addition, the frost resistance and chloride ion penetration resistance of 3DPC had been investigated. The results showed that the pore connectivity of 3DPC was better than that of casting concrete and the pores accumulated near the interface. In addition, the porosity calculation results showed that the porosity of the interface between layers was lower than that of the interface between filaments in 3DPC. All specimens of 3DPC showed excellent frost resistance with a maximum mass loss of only 0.18% and the average flexural strength and compressive strength of 3DPC were only reduced by 31.2% and 21.0% respectively after 300 freeze–thaw cycles. The maximum chloride migration coefficients for the 3D printed concrete specimen was 79 × 10-14 m2/s and the glass fiber enhanced the chloride ion penetration resistance of the specimens. [ABSTRACT FROM AUTHOR]

• The uses of recycled sand and carbonated recycled sand are favorable in our research. • The total replacement of natural sand by carbonated recycled sand in mortar decreases only by 5% of strength. • Some tests of durability show that carbonated recycled sand is more favorable than recycled sand. This study presents the durability of mortars made with leftover recycled sand. In order to take the outside storage of this young concrete into consideration, with its ensuing carbonation, two series of recycled sands are studied, one non-carbonated and the other carbonated. First, all the basic characteristics, such as water absorption, density, cement content, and thermogravimetric characteristics of the sands and their fractions are studied. Since the idea of recycling leftover sand is still new and not much studied, an indepth study of its fractions is necessary. The results show that recycled sand presents two layers: an old cement paste layer and a natural sand layer. It is the old cement paste layer that varies with the size and fractions, influencing the characteristics of the sands and the durability of their mortars. Second, many indicators of durability are studied (strength, air permeability, chloride ion migration, capillarity, carbonation and porosity accessible to water) according to the mortar composition, and are compared with those of reference mortars made with natural sand. The results demonstrate that, for both kinds of mixtures, the durability range is very close to the reference. However, a marked increase of durability was observed through the chloride ion migration index of the mortar with carbonated recycled sand. It can also be underlined that the mixture with carbonated recycled sand showed equal or even better performances than non-carbonated sand (better compressive strength index, migration index and carbonation index). Overall, this study demonstrates that the recycling of these kinds of leftover sand is possible. [ABSTRACT FROM AUTHOR]

• Influence of PCMs in concrete deck under combined freeze-thaw and chloride-ingress. • Microstructure-guided numerical simulation establishing macro-micro relation. • Significant increase in frost and chloride-durability in concretes with PCM. • Reliability-based probabilistic analysis shows significant gain in life of bridge. • Helps to tune dosage and transition temperature of PCMs to maximize life of bridge. Use of phase change materials (PCMs) to tailor the thermal performance of concretes by efficient energy storage and transmission has gained traction in recent years. This study incorporates microencapsulated PCMs as sand-replacement in concrete bridge decks and performs numerical simulation involving multiple interactive length scales to elucidate the influence of PCM-incorporation in concretes subjected to combined freeze-thaw and chloride ingress-induced deterioration. The simulations show significant increase in durability against combined freeze-thaw and chloride ingress-induced deterioration in concretes when microencapsulated PCMs are incorporated. In addition, a reliability-based probabilistic analysis shows significant increase in life expectancy of bridge decks with PCM-incorporation. The numerical approach presented here provides efficient means to develop design strategies to tune dosage and transition temperature of PCMs to maximize durability of concrete structures in regions that experience significant winter weather conditions. [ABSTRACT FROM AUTHOR]

Highlights • Focus on characteristics changes of geopolymer concrete after indoor/outdoor curing. • Compressive strength reach over 53 MPa after 180 days of indoor/outdoor curing. • Geopolymer concrete has excellent chloride resistance over prolonged curing time. Abstract The purpose of this study is to focus on the durability of geopolymer concrete after nine months of an indoor and outdoor curing period. The geopolymer paste was prepared with fly ash and ground granulated blast furnace slag as raw materials and sodium silicate/sodium aluminate as an alkali activator. The geopolymer concrete was prepared with a 1:2.5:2.4 geopolymer:sand:gravel ratio. The influence of sodium aluminate, wollastonite additions and NaOH concentration on the microstructure, physical and mechanical properties were evaluated. The compressive strength of the geopolymer concrete can reach 67 MPa and 53 MPa after 180 days of indoor and outdoor curing, respectively. Rapid Chloride Ion Permeability Test (RCPT) shows the geopolymer concrete has excellent chloride resistance over prolonged curing time. After 180 days of accelerated wetting-drying cycles, the continued growth of compressive strength indicates the good weathering resistance of geopolymer concrete. According to the test results obtained during this study, the geopolymer has a high potential to be a key material for civil construction. [ABSTRACT FROM AUTHOR]

Highlights • Carbonation curing behaves an effective strength enhancement for PC-CG blends. • Drying shrinkage and transport property were improved by carbonation curing. • Carbonation cured paste containing 10–20% of CG has better strength than the PC paste. • Sequestrated content of CO 2 reaches around 10% of PC-CG blends by weight. Abstract To promote the recycling of self-ignited coal gangue (CG) as a partial substitute for Portland cement (PC) and reduce carbon footprint of fossil fuel, carbonation curing was applied to PC-CG blend pastes as a novel strength enhancement method. Compressive strength, drying shrinkage and chloride ion permeability of PC-CG mixtures with or without carbonation curing were investigated and related mechanisms were demonstrated by X-ray diffraction (XRD), 29Si solid-state nuclear magnetic resonance spectroscopy (NMR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and back scattered electron imaging (BSE) measurements. Results showed that carbonation curing behaves a better improvement effect on compressive strength of PC-CG pastes with the higher incorporation of CG. The accelerated carbonation curing can improve drying shrinkage and chloride ion penetration resistance of cement paste specimen due to the refinement of pore structure. The captured CO 2 content reached around 10% of PC-CG blend by weight with this carbonation curing. On the other hand, up to 20% CG can be recycled to replace PC without sacrifice of strength. Therefore, this technology presents a great potential in both sequestration of carbon dioxide and recycling of coal gangue. [ABSTRACT FROM AUTHOR]

Highlights • BS increases mechanical strengths but ES decreases mechanical strengths. • BS has a more positive impact on durability than ES. • Na 2 SO 4 ·10H 2 O, CaSO 4 ·2H 2 O and AFt result in the deterioration of the concrete. Abstract This study investigated the influence of ferronickel slag replacing sand as fine aggregate on the properties of concrete under the same superplasticizer content. The results indicate that the addition of two types of ferronickel slag decrease the workability of fresh concrete. The addition of blast furnace slag (BS) obviously decreases the apparent density of concrete while the addition of electric furnace slag (ES) slightly increases the apparent density. Mechanical strengths increase with BS content increasing, but decrease with ES content increasing. High BS content can improve the resistance of concrete to chloride ion penetration while using ES as fine aggregate has little effect on the resistance to chloride ion penetration. Water absorption of concrete decreases with BS content increasing but increases with ES content increasing. BS has a positive impact on sulfate attack resistance and fire resistance. Using 25% ES also has an active effect on resisting sulfate attack. However, the addition of ES has little effect on improving the fire resistance of concrete. As a result, using 75% BS or 25% ES is the best choices in engineering application. [ABSTRACT FROM AUTHOR]

Highlights • Durability and rheological characteristics of high-volume GGBFS mixtures were experimentally assessed. • High-volume GGBFS replacements with a CaCO 3 /anhydrate-based alkali activator improved overall durability. • The rheology was noticeably affected by GGBFS replacement, use of alkali activator, and elapsed time after mixing. • 70−80% GGBFS replacements appear to be an effective strategy for enhancing both durability and sustainability. Abstract In this paper, durability and rheological characteristics of binary blended mixtures incorporating high-volume ground-granulated blast-furnace slag (GGBFS) were assessed based on a series of laboratory tests. Various durability characteristics such as restrained shrinkage cracking, freeze-thaw resistance, carbonation resistance, and chloride ion diffusion resistance were comprehensively investigated. The experimental results verified that the high-volume GGBFS replacements with a CaCO 3 /anhydrate-based alkali activator effectively improved the overall durability performance, especially when a replacement level of 70% was used. The promoted durability was mainly attributed to the formation of dense microstructure and low capillary porosity resulting from the enhanced degree of latent hydraulic and pozzolanic reactivity of GGBFS in the presence of alkali activator, which transformed a number of weak phases in cement hydrates (Ca(OH) 2) into dense calcium silicate hydrate (C S H) phases. It was also found that the flow behavior was largely affected by the GGBFS replacement level, use of alkali activator, and elapsed time after mixing. Based on the findings of the present study, the high-volume GGBFS replacement, up to 70–80 wt%, appears to be a substantial strategy for enhancing the durability and sustainability of concrete. [ABSTRACT FROM AUTHOR]

Highlights • Post-fire durability properties of concrete has been reviewed. • Supplementary cementitious materials and their impact on post-fire durability of concrete has been reviewed. • All concretes, regardless of the ingredients, lose durability at elevated temperatures. • Durability recovery of fire-damaged concrete has been discussed. • Much work is needed in this area to completely understand the performance of concrete under fire conditions. Abstract Fire poses serious threat to the life of structure and occupants, as it induces detrimental effects at structural level both short term and long term. Keeping in view the importance of fire performance of concrete, various researchers have evaluated the behavioral characteristics of concrete under such conditions. The safety and serviceable life of concrete structures after exposure to fire depend on two important factors i.e. residual strength and durability. In this paper, a comprehensive and updated review on the durability of concrete containing various mineral admixtures after being exposed to elevated temperatures is presented. Durability of concrete after fire exposure is measured through indirect tests such as chloride ion permeability, water permeability, absorption and sorptivity. Thus the test methods and available literature on the aforementioned techniques has been elaborately reviewed and summarized. The recent trends followed to improve the durability performance of concrete in the post-fire conditions have also been discussed and future research needs have been identified. However, to properly understand the durability performance of fire exposed concrete structures constructed with sustainable concretes, a great deal of work is required in this particular domain. [ABSTRACT FROM AUTHOR]

Highlights • A novel HPGC was developed by the partial replacement of cement with FA, nanoparticles and inhibitor in conventional concrete. • Evaluation of mechanical and durability properties were carried out on 28 day cured specimens and compared with individual modifications. • The synergistic action of fly ash, nanoparticles and inhibitor facilitated the improvement in early age strength and permeability characteristics. • The pore size reduction and pore structure refinement resulted in enhanced permeation resistance. Abstract This work reports a novel high performance green concrete fabricated by incorporating fly ash, nanoparticles and corrosion inhibiting admixture into conventional M45 grade concrete. The optimal composition of the new mix was found to be 40 wt% fly ash, 2 wt% nano-TiO 2 and nano-CaCO 3 in 1:1 ratio, 2 wt% sodium nitrite based corrosion inhibitor and 56% Ordinary Portland Cement, referred hereafter as CFNI. The properties of CFNI were compared with that of conventional concrete to assess the synergistic role of various additives. Field Emission Scanning Electron Microscope images of CFNI showed a homogeneous distribution of hydration products over the surface. The Confocal Laser Scanning Microscopy images of concrete surfaces and pore size estimation from Mercury Ion Porosimetry confirmed that only gel pores at the nanoscale are present in the CFNI specimens. The compressive strength, flexural strength and split tensile strength of CFNI, measured as per ASTM/Indian standards, showed noticeable enhancement. The chloride ion penetration resistance, carbonation, water permeability and water sorptivity of CFNI was found to be superior as compared to conventional concrete. This study establishes that synergistic action of fly ash, nanoparticles and inhibitor facilitated the improvement in strength and durability of the new green concrete CFNI, which is very promising not only for cost reduction and improved properties of concrete structures, but also reduces energy consumption and green house gas emissions. [ABSTRACT FROM AUTHOR]

Highlights • Crumb rubber concrete (CRC) has high resistance to chloride-ion erosion. • High resistance when the temperature is lower than 20 °C. • Concrete ductility factor of CRC is higher than that of ordinary concrete. • CRC has a better energy-absorption property. • CRC has a different durability with the test environment temperature. Abstract The corrosion of steel bars in concrete is one of the most important factors that affect the durability of concrete structures, which can be caused by several factors, including marine environments, deicing salt environments, saline and alkaline land, and saline pollution in industrial environments. Research has shown that the addition of crumb rubber can increase the capillary saturation of concrete and reduce the corrosion degree of steel bars in concrete, and with the increase of crumb rubber content, the weight-loss rate of steel bars decreases. The effects of temperature on its resistance to chloride-ion erosion and the durability of crumb rubber concrete are analyzed based on concrete-accelerated corrosion tests by controlling the ambient temperature. The results showed that crumb rubber concrete has high resistance to chloride-ion erosion, especially when the temperature is lower than 20 °C. The concrete ductility factor of crumb rubber concrete with chloride-ion corrosion at different temperatures is generally higher than that of ordinary concrete, indicating that crumb rubber concrete has a better energy-absorption property. It is shown that the crumb rubber concrete has a different durability with the test environment temperature, and can provide a reference for the application of crumb rubber concrete in anti-chloride ion penetration. [ABSTRACT FROM AUTHOR]

Highlights • The ornamental stone processing waste (OSPW) was heat treated at 1200 °C. • Heat-treated ornamental stone processing waste (HTOSPW) presents pozzolanicity. • Durability properties of concretes using HTOSPW were evaluated for the first time. • 10% addition increased the mechanical strength and reduced chloride ion penetration. Abstract In the present study, the ornamental stone processing waste was heat treated at 1200 °C, with the goal of converting it into a pozzolan. At first, the treated waste characterisation was performed in order to assess its physical and chemical characteristics along with its pozzolanic activity. Then, concretes with 5% and 10% waste content were produced, and their compressive strength and chloride penetration resistance were evaluated. The heat-treated waste presented pozzolanic activity, and its addition into concrete mixtures provided an increase in compressive strength and reduction in chloride ion penetration; mainly in the mixtures with 10% addition. [ABSTRACT FROM AUTHOR]

• Kenaf fibre (KF) is used to produce an environmentally friendly composite. • The effect of the content and length of kenaf fibre on the durability properties of geopolymer concrete is reported. • KFRGC with longer length and higher volume fraction of KF exhibited lower durability performances. The use of fibres in concrete has attracted the interest of many researchers to improve the tensile properties of geopolymer concrete. While adding natural fibres has gained popularity as an eco-friendly alternative to synthetic fibres. This combination of natural fibre-reinforced geopolymer concrete is an interesting composite that has not been reported by many, particularly when kenaf fibre is applied. Hence, this article aims to understand the performance of kenaf fibre-reinforced geopolymer concrete (KFRGC) in terms of water absorption, porosity, sorptivity, water penetration, and resistance against chloride ions penetration and chemical attacks. The results showed that the addition of KF increased the porosity of the geopolymer, thus increasing the water absorption-related properties. It's observed that the porosity tends to increase with increasing length and volume content of fibres. Compared to control specimens, the highest increment (12.5%) in the porosity was recorded with specimens prepared with a 1.5% volume of fibre and a length of 40 mm. Likewise, the water permeability reading increased with increasing volume and fibre length in the geopolymer matrix. In specimens containing 1.5% fibre, increasing the length of fibre from 20 to 30 mm caused an increment in water permeability from 7.42 cm to 8.9 cm, respectively. However, the chloride, sulphate and acid resistance could be improved due to the ability of the fibres to bridge across the cracks. Furthermore, increasing the length of the fibre to 40 mm, reduced the acid resistance of the proposed concrete and increased the loss of strength to 16.3% and 19.2% at the age of 180 and 365 days, respectively. The outcomes of this research show that using kenaf fibres as a fibrous material in the production of environmentally friendly and durable concrete has a promising future. [ABSTRACT FROM AUTHOR]

This study compares the resistance against chloride-induced steel corrosion of two alkali-activated materials (AAMs) and a CEM III concrete. The AAMs studied are: a metakaolin activated with sodium silicate (AAMK), and a GGBS activated by sodium carbonate (AAS). In order to study the corrosion of the reinforcement due to chloride, electrochemical measurements were performed on reinforced samples kept in a humid room (passive conditions) and samples dried (40 °C) before their immersion in a 35 g/l chloride solution (active conditions). AAMK showed the highest transfer properties whereas AAS and CEM III showed similar performance. The highly interconnected porous network of AAMK concrete presented low resistance to the penetration of chloride ions and very low resistivity compared to CEM III and AAS concrete. AAS had a finer porosity and a high chloride fixation capacity, which led to better resistance to chloride penetration and high resistivity. However, in AAS, sulfide ions from the slag dissolution led to low corrosion potential compared to values measured in traditional concrete. The drying of these samples at 40 °C caused a drop in the resistivity and a sharp increase in the chloride migration coefficient, which was explained by damage of the material. No corrosion products were observed after 2 years on rebars embedded in AAMs (AAMK and AAS). However, in CEM III reference concretes, pits of corrosion were identified when the reinforced samples were split. AAMs seemed to provide good protection of the reinforcement regarding chloride corrosion in immersed samples. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review of the progresses in high-performance coral aggregate concrete from raw materials, design principle, mechanical properties, volume stability, durability and microstructure. In comparison to natural concrete (NC) of the same strength grade, coral aggregate concrete (CAC) exhibits higher early strength and better fatigue and impact resistance. It is possible to design an ultra-high strength CAC with a compressive strength of 135–150 MPa at 28 days. However, the volume stability of CAC is inferior to that of NC. There is a critical relationship between the internal curing and porous structure of coral aggregate on durability of CAC. Adding supplementary cementitious materials (SCMs) can reduce the chloride ion permeability of CAC by about 60%. The cube compressive strength of CAC and the microhardness of interface transition zone (ITZ) in CAC can be increased by about 20% through aggregate modification. Finally, the current problems of CAC research are pointed out, and the prospect of future research are also discussed. [ABSTRACT FROM AUTHOR]

The objective of this research is to enhance concrete produced with high content of fly ash (FA) and recycled concrete aggregates (RCA), individually and jointly, with low (with superplasticizer) and high (without superplasticizer) water to binder ratio (w/b), according to their chloride ion penetration resistance (CIPR)-related service life and embodied energy (EE). For that purpose, the EE was determined for the production of 1 m 3 (declared unit) of concrete considering the primary energy, non-renewable (PE-NRe) of the “Cumulative Energy Demand” environmental impact assessment method, and the CIPR of concrete are considered the conditioning factors. The environmental assessment of the mixes was evaluated by considering the Life Cycle Assessment (LCA) standardized methodology. In addition, the assessment was mostly made either according to the local Life cycle inventory (LCI) data or environmental product declaration (EPD) report and selected according to NativeLCA methodology on typical conditions in Portugal. Generally, the CIPR of concrete decreases when the RCA content increases, and the opposite occurs by replacing cement with FA. After 28 days, the rate of CIPR development of the concrete made with incorporating both FA and RCA is higher than that of concrete containing either FA or RCA. Therefore, it is positive to use simultaneously RCA and FA in concrete. This rate increased even more when SP was used. Furthermore, the EE significantly reduced with increasing replacement level of cement and coarse natural aggregates (NA) with FA and coarse RCA, respectively. Nonetheless, the changes in EE caused by the incorporation of SP and fine RCA are small. In term of the influence of combining FA and RCA in low and high w/b concrete, the EE linearly changed with each individual effect. Nevertheless, the optimal solution of mixes by means of both EE and CIPR (measured by the yearly EE of the mixes relative to the reference concrete) does not necessarily consider the one that requires less EE or that has higher CIPR. According to this parameter, the best-case scenario is always the low w/b mixes with high volumes of RCA and FA, followed by the corresponding high w/b mixes. [ABSTRACT FROM AUTHOR]

Chloride ion has the highest proportion of chemical compounds present in seawater. This research utilized the chloride curing conditions in order to study the effect of chloride ion on properties of concrete containing zeolite as a mineral admixture and micro-nano-bubble water. The objective was to improve the durability and the mechanical properties of concrete. It was observed that the addition of zeolite-pozzolan and micro-nano-bubble water to the concrete under chloride curing conditions improved the mechanical properties and durability of concrete of 28 days old by forming Friedel’s salt. With increasing age of concrete and decomposition of Friedel’s salt in concrete samples, the process of improvement was reduced. The greatest effect on improving the mechanical properties and durability of 28 days old concrete was related to the mixture containing 15% zeolite and 100% micro-nano-bubble water under chloride curing conditions. Results also showed that in the mixture containing 15% zeolite and 100% micro-nano-bubble water, under chloride treatment condition, there was 45% increase in the compressive strength. Also, tensile strength and electrical resistance were improved 78 and 254%, respectively, and the chloride penetration and water absorption were reduced by 83 and 49%, respectively, compared to the control mixture. [ABSTRACT FROM AUTHOR]

Transport of chloride ion into concrete can induce depassivation of reinforcement, which seriously threatens the durability of concrete subjected to marine environment. In this paper, the chloride ion transport and binding capacity of different concrete samples located in marine atmosphere zone, splash zone, tidal zone and submerged zone for 9 and 13 months were tested. And the chloride ion profiles of one whole concrete sample exposed to all the corrosion zones for 13 months was also detected. The effect of fly ash and ground granulated blast furnace slag (GGBS) on the chloride ion transport and binding capacity of all the concrete samples were studied and the optimized replacement ratios of mineral admixtures in marine environment was proposed. The contents of Ca(OH) 2 and Friedel’s salt in paste exposed to different corrosion zones were also tested by XRD and DSC-TG. Results showed chloride ion content in separate concrete samples exposed to splash zone and atmosphere zone were lower than that of the other zones, but the opposite results were observed for one whole concrete sample throughout all the corrosion zones. For separate samples, the chloride binding capacity of concrete in atmosphere zone was the lowest, and would decrease with corrosion time in marine environment. The washing effect by tidal action would lead to the loss of Ca(OH) 2 , abrasion of surface, and decrease of compressive strength of concrete. [ABSTRACT FROM AUTHOR]

In this work, the different techniques for non-destructive in situ measurement of chloride ion concentration are presented. Non-destructive (ND) in situ measurement is crucial for reliable and continuous determination of chloride ion concentration in concrete. Over the last 20 years, several studies have been performed on ND measurements. These were mainly focused on the application of electrochemical and electromagnetic techniques. Each technique has its advantages and disadvantages. Depending on the requirement of assets managers and constructors and considering the limitations, these techniques can be well applied. The main concepts and comparative analysis, in view of possibilities and limitations, of these non-destructive techniques are presented in this paper. [ABSTRACT FROM AUTHOR]

Long-term durability and sustainability of crucial infrastructure systems such as bridges and pavements are of utmost importance for the economic health of any society. Understanding factors that affect long-term deterioration of reinforced concrete structures can help enhance durability and sustainability of these systems. This paper investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability. Twelve coarse aggregate types of different geologic formations (sedimentary, igneous, and metamorphic) were used to prepare fresh concrete in which silica fume and class C fly ash were used. All mix parameters including gradation and volumes of different aggregates were held constant in different mixes with the only variable being the aggregate type. The Rapid Chloride Penetration Tests were conducted on concrete specimens made with various aggregate types at ages of 28, 56, 91 and 365 days. Analysis of test results showed that the aggregate type as well as aggregate absorption rates have significant influence on the electrical charges passed through concrete, especially in early ages of concrete containing aggregates with sedimentary rock origin and relatively high absorption. These specimens exhibited the highest RCPT results indicating higher capacity to allow chloride ion penetration when compared to specimens with igneous and metamorphic rock aggregate of lower absorption values. This influence (discrepancy) diminishes with time for both aggregate type and absorption rates in terms of the magnitude of measured total charge passed. [ABSTRACT FROM AUTHOR]

This investigation intends to analyse the effects of the variation of different types of recycled concrete aggregates (RCA) on structural concrete. For this purpose, two source concrete (SC) mixes, one produced in the laboratory and another in a precasting plant, were considered. The experimental campaign included mechanical, durability and long-term tests: compressive strength in cubes; splitting tensile strength; modulus of elasticity; abrasion resistance; water absorption by immersion and by capillarity; resistance to carbonation; resistance to chloride ion penetration; shrinkage and creep. The recycled aggregate concrete (RAC) mixes were compared with a reference concrete (RC) produced solely with natural aggregates (NA). Concerning the replacement percentages for fine and coarse recycled concrete aggregates (FRCA/CRCA%), the following were considered: 25/25; 50/50; 100/0; 0/100 and 100/100%. The results show that it is possible to achieve similar performances using RCA from different SC but with similar compressive strengths. In fact, RAC mixes achieved results comparable to RC in several properties. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental-analytical research program aimed at assessing the durability of a hybrid fiber-reinforced polymer (FRP) composite shell, incorporated as a protective barrier during construction to impede the ingress of deleterious elements into the lower flange of a prestressed concrete girder. A series of tests were performed on the FRP composite shell and FRP-concrete specimens to examine the effectiveness of the FRP shell as a barrier against ingress of aggressive elements, such as moisture and chlorides in controlled environments. In addition, scanning electron microscopy (SEM) was used to determine the effects of aging, temperature variation and chloride diffusion in the FRP-concrete specimens. These experimental results were used to model the ingress of chlorides and moisture into the FRP-concrete system to predict the service life of prestressed concrete bridge girders reinforced with FRP composite shells. The results showed that the FRP composite shell can provide significant resistance against chloride ingress by impeding the rate of its ingress and the total amount of chloride ions, thus considerably help in retarding the resulting deterioration reactions and significantly enhancing their service life. [ABSTRACT FROM AUTHOR]

This paper presents the FE formulation for the numerical modelling of chloride ions diffusion accounting for the chloride binding capacity in meso-scale concrete. The finite element formulation is built through a discrete (lattice) finite element model and the meso-structure is based on a two-phase 3D representation of heterogeneous materials, such as concrete, where stiff aggregates are embedded into a mortar matrix. In order to take into account these heterogeneities in the mesh, we turn to the Embedded Finite Element Method (E-FEM). The E-FEM allows to use meshes not necessarily matching the physical interface (aggregates/mortar matrix) while retaining the accuracy of the classical finite element approach. This is achieved by introducing a weak discontinuity in the chloride concentration field for finite elements where the physical interface is present. A numerical solving strategy is presented to efficiently resolve the FE problem both in terms of chloride concentration field variables and weak discontinuity parameters. We investigate through 1D simulations the influence of the microstructure properties and the chloride binding capacity on the chloride concentration profiles. We show that taking explicitly into account the diffusion coefficients of the microstructure and the chloride binding capacity are important to consider for a better prediction of the time span until corrosion initiation. This is important for accurately estimating the service life of a structure. Numerical homogenization experiments are also performed on 3D meso-structures to compute macroscopic diffusivity tensors accounting for two-phase material. Comparison with Maxwell's equation are performed to show the accuracy of the proposed numerical approach. [ABSTRACT FROM AUTHOR]

• The strong electric field showed required remarkably less chlorine removal time, and the distribution of residual chloride ions in the specimen was more uniform than the conventional electric field. • After 28 d of standard curing, the width of the interfacial transition zone and the microhardness were not affected by electrochemical chlorine extraction intervention. • The electric field attracted a large amount of Ca2+ in the electrolyte, so the number of regular hexagonal Ca(OH) 2 crystals increased. Electrochemical chloride extraction (ECE) technology can effectively reduce the harmful chloride ions in concrete and decline the durability failure risk of concrete structures. In this study, early-age sea-sand concrete was treated by ECE with strong electric field and conventional electric field, respectively. The chloride ion content analysis and microscopic observation were adopted to evaluate the durability improvement effect with ECE treatment. The results showed that at the early ages of 3, 5, and 7 d, the chloride ions were drastically reduced upon the application of a strong electric field for 40, 80, and 120 min or the conventional electric field for 15 d. Treating time of ECE with strong electric field is 0.19 %–0.56 % of that of ECE with conventional electric field. Under a strong electric field, the distribution of residual chloride ions in specimens was more uniform. Application of an electric field during the curing period caused the directional migration of ions and subsequently changed the pore structure and microhardness of the specimen. However, these changes were recovered with the continuous hydration of concrete during the curing period. Finally, based on engineering cases, the field implementation schemes of the strong electric field and conventional electric fields were analyzed. The energy consumption of ECE with strong electric field is 17.8 %–53.3 % of that of ECE with conventional electric field. The results of this study provide the technical means for the timely treatment of excessive chloride ion concentration in sea-sand concrete structures. [ABSTRACT FROM AUTHOR]

Chemical aggressions from the environment, such as salt ions, can damage reinforced concrete structures before they reach their service life. These deterioration mechanisms are coupled. The current research on cementitious material's durability has thus gradually shifted to the field of durability damage caused by the combined action of multiple factors. The research in this study concerns the case of combined chloride-sulfate attacks to provide a better understanding of the coupling phenomena by studying the mutual effect of the chloride and sulfate ions on the materials. The effect of the type of cement and curing duration on the chloride-sulfate attack is also investigated. Experimental results based on different investigation techniques (ICP, XRD, NMR, etc.) clearly show the competition between chloride and sulfate ions, and how the physico-chemical involved mechanisms completely change with respect to the cases of an exposure to a single type of ion. • The presence of sulfate ions reduces the chemical fixation of chloride ions. • This increases the possible risks of steel corrosion by increasing the propagation front. • The decalcification of C-S-H in the combined sulfate-chloride attack is drastically reduced. • The presence of sulfate ions decomposes the Friedel salt and turns it into ettringite. [ABSTRACT FROM AUTHOR]

• Enhancing the efficiency of steel fibers in high-performance concrete. • Promoting the utilization of rice husk ash (RHA) to valorize agro-wastes. • Comparison between the mechanical performance of SFRC with RHA and MS. • The efficiency of fiber was better at low levels of RHA and MS. • The modification effect of MS was superior compared to RHA. To improve the fiber-matrix bond and enhance the macro-mechanical performance of SFRC, this study is focused on the modification of the cement matrix by using two eco-friendly supplementary cementitious materials (SCMs), rice husk ash (RHA) and micro-silica (MS). The modification effects of SCMs on the steel fibers were observed and characterized by conducting several macro-mechanical tests i.e., compressive strength, splitting tensile strength, and load-deflection behavior. Besides that, ultrasonic pulse velocity, water absorption, and chloride migration tests were performed to characterize the durability of modified SFRC mixes. The results showed that the incorporation of RHA and MS at low levels notably enhanced the efficiency of steel fibers under splitting tensile and flexural strength testing. SFRC made with 7.5% MS and 7.5% RHA showed 79% and 96% more flexural strength than plain concrete (PC), respectively. Whereas SFRC experienced 14% and 26% further improvement in flexural toughness with the addition of 7.5% RHA and 7.5% MS, respectively. The addition of 7.5% and 12.5% RHA showed a beneficial effect on the resistance of SFRC against the penetration of chloride ions and water. The results of this study confirmed the synergistic interaction of steel fiber and SCMs. [ABSTRACT FROM AUTHOR]

To estimate the actual durability of CFRP-concrete bond, an investigation into bond behavior of the interface between CFRP and concrete under field conditioning (FC) in a subtropical area is presented. Single lap-shear tests were conducted on CFRP-concrete specimens subjected to FC for up to 360 days. Bond slip law and fracture characteristics were evaluated using a generalized approach based on the experimental load-displacement curves. The results show that the local bond strength decreased by 30% in the initial 90 days and a 10% recovery appeared after additional 270 days, while the interfacial fracture energy showed a 30% increase after 360 days. Analytical modeling incorporating the evaluated bond slip law was performed and the effect of FC on the stress transfer was revealed. The effective bond length increased by 50% throughout FC. Besides, it can be found that an electromechanical impedance method (EMI) via the use of PZTs was able to monitor the CFRP-concrete interface during single lap-shear tests, and the monitoring results can indicate the bond deterioration. • Field conditioning affects the bond slip law and fracture energy. • Analytical modeling captures the deterioration of the CFRP-concrete bond. • Effective bond length increases by about 50% throughout 360-day filed exposure. [ABSTRACT FROM AUTHOR]

In this present study, copper slag (CS) is proposed as an alternative to river sand as fine aggregate in alkali-activated slag concrete (AASC) mixes. The relative performance of alkali activated slag concrete mixes with CS as fine aggregate is compared to conventional Ordinary Portland Cement concrete (OPCC) mix in terms of their workability, strength and durability parameters. The results indicate that, AASC mixes with CS, as a replacement to sand upto 100% (by volume), show no marked loss in strength characteristics. AASC mixes with either sand or CS possess similar modulus of elasticity, lower total porosity, lesser water absorption and reduced chloride ion penetration as compared to OPCC. Strength-retention characteristics of AASC mixes with sand/CS on exposure to sulphate and acid-rich environment are also studied. Use of AASC mixes for structural application reduces carbon footprint, decreases water consumption and cost. Use of CS as fine aggregate reduces river sand consumption as an added benefit. [ABSTRACT FROM AUTHOR]

Information on the effects of incorporating fine recycled ceramic aggregates on concrete's durability is very scarce. This paper presents an experimental study using aggregates sourced from crushed red clay ceramic bricks (CBAs) and sanitary ware (SWA). Different concrete mixes were produced where the fine natural aggregate fraction was partially or fully replaced (20%, 50% and 100%, by volume) by each of these materials. Shrinkage, water absorption by immersion, water absorption by capillary action, carbonation and chloride ion penetration tests were carried out. Results show that using fine CBA provides better performance in terms of water absorption by capillarity and chloride ion penetration, contrarily to shrinkage, water absorption by immersion and carbonation penetration. Using fine SWA leads to a similar performance in terms of shrinkage, but all other properties are significantly and detrimentally affected. Notwithstanding the increased water requirement due to the high absorption capacity of CBA and the formation of agglomerated particles with SWA, this paper shows that a judicious use of these materials may allow the production of adequate structural concrete; in mixes with SWA the use of superplasticizers is a very effective approach in preventing the formation of clusters, even providing a better performance than the control concrete. [ABSTRACT FROM AUTHOR]

• UHPC mixes outperformed conventional concrete in all durability tests. • Chloride ion penetration tests should be performed on UHPC without steel fibers. • UHPC mixes achieved negligible chloride ion penetration after 90 days. • NPUHPC outperformed PUHPC in corrosion testing with a lower compressive strength. The purpose of this study was to evaluate a proprietary (PUHPC) and non-proprietary (NPUHPC) UHPC mix for chloride ion penetration, freeze–thaw resistance, and scaling resistance to assess durability. Also, large-scale specimens were subjected to an impressed current to accelerate corrosion of embedded reinforcing steel to evaluate the severity of the potential for halo effect when using each concrete as a repair material for aged concrete. Each of the UHPC mixes outperformed conventional concrete in every test. Also, the PUHPC and NPUHPC had similar durability performance, and the NPUHPC outperformed the PUHPC in corrosion resistance, despite having a lower compressive strength. [ABSTRACT FROM AUTHOR]

• The ECE with strong electric field saves the electrifying time significantly. • The material properties can recover after 28d curing period. • It is suitable for prefabricating components with sea-sand concrete. Electrochemical chloride extraction (ECE) technology can effectively reduce the harmful chloride ion content of concrete structures and thus decrease their durability failure risk. This paper applied the ECE technology to sea-sand concrete with an excessive chloride ion content through a strong electric field. Further, testing the chloride ion content, meso- and micro-mechanical properties, and mechanical performance of the concrete columns verified their durability performance after the action of the strong electric field. The results show that, for the early-age concrete with a curing period of 3, 5, and 7 days, the strong electric field with an electrifying time of 40, 80, and 120 min can significantly enhance the ECE efficiency, and the chloride ion content of the concrete can fulfill the specification requirements. During the curing period, compared with the unelectrified concrete components, the strain and displacement of the electrified columns increase under the same load when the components are loaded immediately after the action of the strong electric field. However, after applying the electric field, if the member is standardly cured for 28 days, its ultimate bearing capacity increases, and its mechanical properties improve. The bearing capacity of ECEC-3, ECEC-5 and ECEC-7 after curing 28 days are 315.2kN, 320.1kN and 340.9kN which are closed to 326.2kN of ECEC-28. Regarding the adverse effect of the electric field on the performance of the columns, a technical scheme was designed to avoid their hydrogen embrittlement and plastic reduction. [ABSTRACT FROM AUTHOR]

• Micro-cracks, induced by mechanical loading, were characterized in width and depth. • Sound and micro-cracked specimens were subject to pure diffusion of chloride ions. • Chloride diffusion coefficient was evaluated via colorimetric and titration methods. • In uncracked conditions good correlation subsisted between the two methods. • The effect of micro-cracks resulted more pronounced in more impervious concretes. Concrete resistance to chloride penetration is one of the main design parameters for the assessment of reinforced concrete structures durability in chloride-contaminated environments, and it is usually determined through one of the accredited accelerated tests in uncracked configuration. In this study, the resistance to chloride penetration was evaluated on six different concrete types, in uncracked and load-induced micro-cracked configurations, subject to pure diffusion and considering two different analysis techniques, colorimetric and potentiometric titration. Results showed that in uncracked conditions, good correlation subsisted between the diffusion coefficients evaluated through the two techniques. In cracked configuration (micro-cracks 10–75 μm wide and 5–45 mm deep) with both techniques a significant increase in chloride diffusion coefficient was detected for concretes with lower w/c ratio, suggesting that the effect of cracks may be more pronounced for more impervious concretes. [ABSTRACT FROM AUTHOR]

• Innovative methodology to utilize WAS waste was proposed. • WAS and GGBFS were used to manufacture sintered lightweight aggregate. • Optimum sintering temperature and duration were 1150 °C and 15 min, respectively. • Sintered aggregate can efficiently replace natural aggregate up to 30% in concrete. • Concrete chloride permeability slightly altered with sintered aggregate inclusion. The aggregate occupies the highest volume of concrete and alternative methods to replace it using waste materials or by-products are required which can consequently preserve the natural resources. This paper investigates the utilization of washing aggregate sludge (WAS) waste generated from a local aggregate quarry and ground granulated blast furnace slag (GGBFS) to manufacture sintered aggregate. The properties of sintered aggregate were characterized by physical and mechanical tests and microstructural analysis. The aggregate was incorporated in concrete as a substitute for the coarse aggregate to determine its effects on the physical, mechanical, and durability properties. Test results showed that the inclusion of sintered aggregate slightly reduced the oven-dry density and considerably increased the water absorption and permeable voids of concrete. The compressive strength and modulus of elasticity of concrete decreased by up to 16 and 15%, respectively, with increased sintered aggregate ratio. The chloride ion penetrability and chloride migration coefficient of the concrete insignificantly changed with the incorporation of sintered aggregate. The research outcomes indicated the possibility of manufacturing sintered aggregate using WAS and GGBFS and its efficient utilization in concrete production and the optimum replacement ratio of sintered aggregate was found as 30% which yielded 28-day compressive strength of more than 50 MPa and comparable durability properties with reference concrete. [ABSTRACT FROM AUTHOR]

This research work focuses on the performance of mortars containing ichu ash as a potential environmentally-sound alternative to traditional pozzolans (at 6% and 10% replacement levels) under CO 2 and chloride ion rich environments, in order to evaluate the capacity of this material to produce more sustainable and durable blended cements. The results indicate that ichu ash increases the susceptibility to carbonation, although mortars with 6% ichu ash content behave similarly to OPC ones. However, both density and mechanical strength improve after 250 days of carbonation for both ichu-blended mortars. In terms of resistance to chloride penetration, the addition of ichu ash contributes to retaining the ions in the superficial layers of the mortars, inhibiting their advance. It was found that formulations with both 6% and 10% ichu ash content produced a reduction in the chloride diffusion coefficient of approximately 60%. This phenomenon was mainly attributed to the refinement and increased complexity of the microstructure of the mortars due to the pozzolanic effect. Therefore, it was found that in certain types of environments, ichu ash can be an interesting tool to improve the durability of cements while reducing their environmental footprint and exploiting local resources. [ABSTRACT FROM AUTHOR]

As the demand for display devices increases, the disposal of liquid crystal display (LCD) glass waste becomes an emerging issue. It is thus necessary to make efforts to recycle bulk LCD glass waste. The construction industry can propose a solution to this by using LCD glass waste as an alternative resource for construction materials. This paper presents a state-of-the-art review on the utilization of LCD glass waste as replacements for cement and fine aggregate. Its applications in special types of concrete, e.g. , ultra-high-performance concrete (UHPC), self- compacting concrete, and geopolymers, are also investigated. Thanks to the high pozzolanicity with abundant alumina, the LCD glass powder can partially replace the cement in a classical concrete and filler of UHPC. The matrix modified with the LCD glass powder is effective in improving the medium- to long-term mechanical strength (generally at a replacement level of up to 10% or 20%) and the overall durability, with respect to alkali-silica reaction expansions, sulfate attacks, and chloride ion penetration, and freeze–thaw, as well as the pull-out resistance. However, the alternative use of LCD glass powder in metakaolin negatively affects the mechanical strength of the geopolymer, owing to the increased heterogeneity, pore size, and volume. The use of LCD glass waste as sand decreases the mechanical strength in general but leads to better workability, durability, and volume stability. Thus, LCD glass waste can be used as a new alternative ingredient for concrete , as a replacement for cementitious materials or sand. [ABSTRACT FROM AUTHOR]

There has been an increasing focus on the development of test methods to evaluate the durability performance of concrete. This paper contributes to this focus by presenting a study that evaluates the effect of water accessible porosity and oven-dry unit weight on the resistance of both normal and light-weight concrete to chloride-ion penetration. Based on the experimental results and regression analyses, empirical models are established to correlate the total charge passed and the chloride migration coefficient with the basic properties of concrete such as water accessible porosity, oven dry unit weight, and compressive strength. These equations can be broadly applied to both normal and lightweight aggregate concretes. The model was also validated by an independent set of experimental results from two different concrete mixtures. The model provides a very good estimate on the concrete’s durability performance in respect to the resistance to chloride ion penetration. [ABSTRACT FROM AUTHOR]

In this study, the influence of nanosilica hydrosols and rice husk ash (RHA) on the compressive strength, chloride permeability, electrical resistivity and capillary absorption of single and binary blended mortars was investigated. Results showed that the incorporation of nanosilica improved mortar performance, while RHA did not have a significant influence and mainly attributed to lower strength and durability at early ages. It was found that the addition of RHA in mixes containing nanosilica, dramatically decreased compressive strength at ages of 3 and 7 days. However, binary mixtures displayed the best results for strength development and durability at ages of 28 and 90 days. [ABSTRACT FROM AUTHOR]

• The influence of coarse aggregate on the workability, compressive, tensile, flexural properties, elastic modulus, durability, high-temperature performance, and shrinkage of UHPC, are reviewed. • The recommendations on the study of compression constitutive properties of UHPC containing coarse aggregate are given. • The elastic modulus prediction equations of UHPC with coarse aggregate are summarized. • Various applications of UHPC with coarse aggregate are introduced. • UHPC with coarse aggregate performance is evaluated by radar chart, and a performance-based method for designing UHPC with coarse aggregate mixtures is proposed. Ultra-high-performance concrete (UHPC) is a distinguishing material used in new construction and in conjunction with conventional concrete. However, some issues limit its broader applicability, such as high autogenous shrinkage, high cost, and insufficient elastic modulus increase compared with the normal strength concrete. Therefore, this paper reviews the key properties of UHPC containing coarse aggregate – added as a novel ingredient to the UHPC matrix to solve the issues mentioned above. This review covers the following aspects: (1) the influence on workability and mechanical properties (including compressive, tensile, flexural properties, and elastic modulus); (2) the recommendations on the study of compression constitutive properties of UHPC containing coarse aggregate (UHPC-CA); (3) the elastic modulus prediction; (4) the durability, high-temperature performance, and shrinkage of UHPC-CA; (5) the successful structural applications; and (6) UHPC-CA performance radar chart, and a design method based on performance. The results show that the introduction of coarse aggregate has significant effects on the mechanical performance of UHPC. For compressive properties, there is an optimal coarse aggregate content for each mix proportion; For tensile and flexural properties, coarse aggregate has negative effects mainly due to the decline of efficiency coefficient of fibers; On the contrary, for elastic modulus, coarse aggregate has positive effect attribute to its high rigidity. Besides, the durability, including the resistance to chloride ion penetration, salt crystallization and frost heaving, and high temperature performance and shrinkage, of UHPC-CA is superior. This review is expected to give an overview of the research field and provide guidance for future research. [ABSTRACT FROM AUTHOR]

• The durability life prediction model is proposed for localized corrosion in chloride environments. • The localized corrosion process is divided into three stages, and an analytical approach is presented to predict the durability life. • The effects of main influencing factors on the three stages of localized corrosion are investigated. In this study, an analytical model for evaluating the durability life of reinforced concrete (RC) piles subjected to localized corrosion under chloride attack is proposed. The localized corrosion process is divided into three stages, and a predictive method is presented to predict the durability life of the pile by calculating the time of each stage. The time of each stage is determined based on the chloride diffusion model, the pitting corrosion model and the crack propagation model. The effects of the water-cement ratio, concrete cover thickness, pile concrete quality, relative humidity, chloride threshold level, pitting factor, corrosion current density and initial surface chloride ion concentration on the various stages of localized corrosion and the durability life of the pile are investigated. The analysis results show that the effects of the water-cement ratio and concrete cover thickness on the durability life of the pile are the most significant in the corrosion initiation stage. The durability life is increased by a reasonable choice of both concrete water-cement ratio and concrete cover thickness with constant concrete quality. The durability life of the pile increases with increasing concrete cover thickness, concrete quality, chloride threshold value and limit crack width, while it decreases with increasing water-cement ratio, relative humidity, corrosion current density and initial surface chloride concentration. The influence of the pitting factor is minimal and is mainly in the pit nucleation stage. [ABSTRACT FROM AUTHOR]

Nanosilica (NS) is a nanomaterial with excellent performance. The microstructure and durability of cement-based materials are significantly affected by the addition of NS. Based on existing studies on NS, this paper summarizes the influence and mechanism behind the influence of NS on the hydration characteristics, pore structure, internal interface, chloride ion corrosion resistance, sulfate corrosion resistance, carbonation resistance, and freeze–thaw resistance of cement-based materials. NS was found to promote cement hydration and the formation of a hydrated calcium silicate (C–S–H) gel through nucleation and chemical reactions. In addition, the pore structure and internal interface of cement-based materials could be optimized and their durability improved by NS. Currently, relevant research conclusions on the influence of NS on the microstructure and durability of cement-based materials have not been reached (e.g., optimal amount of NS and optimal particle size). Therefore, further research is essential. [Display omitted] [ABSTRACT FROM AUTHOR]

• Ceramic waste slag-based lightweight aggregate services well after 14 years' curing. • Chloride ion permeability level of 14-year-old LWAC is very low. • Enhanced interfacial transition zone is observed in LWAC with CLWA. • Consuming ceramic waste slag in LWAC is feasible and effective. Lightweight aggregate concrete (LWAC) characterized with low dead weight and high performance, has been applied widely in concrete structures in the past two decades. Mostly, LWAC components play a crucial role in reducing structural weight and keeping structures in good service condition. However, long-term properties of LWAC, especially those prepared with industrial waste-based aggregate, directly affect the durability of structure but have not been explored yet. In the present study, 14-year LWAC incorporating with ceramic waste-based lightweight aggregate (CLWA) were experimentally studied. Traditional LWAC with furnace slag lightweight aggregate (FLWA) was designed as a contrast. Properties of 14-year LWAC such as compressive strength, chloride ion permeability, X-ray diffraction and open porosity were evaluated. In addition, high magnification electron microscope, scanning electron microscope and energy dispersive spectroscopy (SEM-EDS) were adopted to characterize the interfacial transition zone (ITZ) and microstructure of LWAC. Results indicates that after 14 years' curing, no strength reduction is detected and the chloride ion permeability maintains in very low level for LWAC. Long-term performance of LWAC with CLWA is superior to that with FLWA, thanks to the disconnected uniform pores/rough particle surface distributed in CLWA and the compact ITZ between aggregates and mortar. [ABSTRACT FROM AUTHOR]