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The critical climate change has raised concern about the decarbonization of the cement and concrete industry, which is responsible for 8% of global CO2 emissions. Portland limestone cement (PLC), which is made by partially replacing the clinker with up to 15% interground limestone fines (LFs), has been recognized as a viable solution for its feasibility to match the engineering properties of ordinary portland cement (OPC). However, with the necessity of further increasing the LFs contents to meet the desired eco-efficiency, the dilution effect brought by less ultimate hydration products may be detrimental to the long-term performance of reinforced concrete structures, such as chloride-induced corrosion. Thus, this research explores the potential of combining PLC and alumina-rich supplementary cementitious materials (SCMs) to improve the resistivity of the concrete. Concrete specimens were fabricated with PLCs from two sources of three LFs replacement ratios (15, 20, and 25%). MK (8%) is used as the source of alumina. The bulk and surface resistivity results showed that combining PLC with MK can notably improve concrete resistivity even in mixtures with lower amounts of cement. Additionally, compressive strength demonstrated poor correlation with electrical resistivity, which highlights the significance of performance-based design. [ABSTRACT FROM AUTHOR]

Corrosion of steel in reinforced and prestressed concrete members exposed to a marine tidal zone is a serious durability problem. This study presents a methodology for rationally estimating the safe cover thickness for steel in concrete structures exposed to the tidal zone. The proposed methodology was implemented for the case of six Indian coastal stations using 100-year-long simulations of chloride transport in concrete. Real-time meteorological and tidal height data were used for simulating the model boundary conditions. Using simulated results of chloride threshold depths (CTDs), safe cover thickness to steel was assessed. Estimated safe cover thicknesses to steel across coastal stations differed significantly (25–30 mm), indicating a need for corrosion vulnerability zonation of coastlines. Conventionally used tide models were improved by superimposing with an annual component of astronomical tides, which expanded the range of wet-dry regimes simulated by the tide models. The study also compared the chloride ingress predictions from the modified tide models with those from real tides. The superimposed tide model was found to be a better approximation of real tides than the diurnal tide model. The modified tide models very well simulated chloride ingress around the critical sections in the tidal zone. [ABSTRACT FROM AUTHOR]

In a variety of applications, such as in tidal zones, abutments of bridges and concrete tunnel linings, reinforced concrete is exposed to both carbonation and chloride ingress. The exposure can be either simultaneous or sequential. However, durability design rarely considers synergistic effects due to carbonation and chloride ingress, even though this may have detrimental consequences for performance. Comparative implications of exposure sequence across different concrete compositions are also unknown. In this study, an experimental investigation on the effects of the sequence of carbonation and chloride ingress was conducted, using two concretes which differ by 50% cement replacement with ground granulated blast furnace slag (GGBS). Specimens were exposed to a combination of 10% CO2 accelerated carbonation and immersion in 3% sodium chloride solution, in either sequence, and compared with companion samples subjected to only one of these aggressive environments. The extent of carbonation was measured using phenolphthalein indicator solution, while silver nitrate and Rapid Chloride Testing provided indicators of the chloride ingress. For both concrete mixes, specimens with prior chloride ingress exhibited a decreased rate of carbonation when compared to specimens with no prior exposure. Conversely, specimens with prior carbonation displayed an increased rate of chloride ingress compared to non-carbonated counterparts and a step in the acid soluble chloride content in the region of the carbonation front. The concrete composition appeared to play a role since a greater increase in chloride diffusion coefficient due to prior carbonation was observed in the mix with 50% GGBS replacement than the mix without. These findings suggest that in concrete structures exposed to air and saline environments, the effects of sequential exposure should be characterised. [ABSTRACT FROM AUTHOR]

In this work, a series of durability requirements are proposed for the construction of long-service-life reinforced concrete (RC) structures in a coastal environment with extreme atmospheric corrosivity. RC specimens were exposed in a coastal outdoor site in Cuba for three years. Carbon steel corrosion evaluation revealed an annual average atmospheric corrosion rate over the maximum limit established (ISO 9223:2012) for extreme (CX) atmospheric corrosivity. The service life of the RC structures, considered as the sum of the time-to-corrosion-initiation and time-to-corrosion-induced concrete cracking, was determined as a function of durability requirements. The most important durability requirements to achieve a long service life (>70 years) in RC structures subjected to a CX corrosivity category were defined as follows: water/cement ratio, compressive strength, percentage of effective capillary porosity, and concrete cover thickness. Under these hostile environments, the expansion of the corrosion products formed on the reinforcement steel and the induced cracking of the concrete could be attributed partially to the formation of the akaganeite phase in reinforcement steel, which revealed a different morphology compared to the akaganeite typically formed in bare carbon steels. [ABSTRACT FROM AUTHOR]

Ingress of chlorides (Cl−) in concretes is influenced by external applied loads, and it is difficult to conduct a quantitative conclusion via experiments due to the geometry of concrete components and their different mechanical and chemical properties. To assist in-depth understanding on Cl− ingress in loaded concretes, a numerical model considering different mechanical and transport properties of three concrete components (paste, aggregate, and interfacial transition zone), heterogeneously distributed stress generated by axial loads and the consequent change in Cl− diffusion property at micro level, is established with COMSOL. Its accuracy and functionality have been verified with lab-based results from compressed and tensile samples at a macro level. The obtained results suggested that the model can effectively reveal stress distribution, generation, and propagation of cracks and Cl− diffusion in loaded concretes. Based on this model, it can be deduced that without considering the heterogeneous mechanical and transport properties of concrete components, the extent of Cl− ingress in concretes could be quite close when the induced stress is lower than 40% of the ultimate damaging stress; in comparison, it would be underestimated once the compressive or tensile loads exceed 60% of the ultimate damaging stress. Under 60% compressive loads, the Cl− ingress depth is decreased by 66%, while that is increased by roughly 40% for a 60% tensile loads. [ABSTRACT FROM AUTHOR]

The recent emphasis on sustainable development in the construction industry has made it essential to develop construction and building materials that are not only affordable, but have minimal negative impact on the environment. This study investigates the valorisation of steel slag, which is mostly considered to be a waste material in several parts of the world, by blending with calcined impure kaolinitic clay to partially replace ordinary Portland cement (OPC) in the preparation of self-compacting concrete (SCC). OPC was substituted with steel slag at a constant level of 10%, whereas calcined clay replaced OPC at varying levels, ranging from 10 to 30% in a ternary blended mix. The hardened properties evaluated include compressive and flexural strengths. Samples containing only calcined clay showed a lower fluidity, which was significantly improved when steel slag was added to the mix. SCC containing 10% steel slag and 20% calcined clay obtained 28 days compressive strength, which was 3.6% higher than the reference cement concrete. An XRD analysis revealed a significant decrease in the peak heights of portlandite in mixtures containing steel slag and calcined clay, regardless of their replacement percentage. Generally, all the blended cement samples performed appreciably in resisting sulphate attack. The results of this study demonstrate that using steel slag and calcined clay together can significantly improve the fresh and hardened properties of SCC without compromising its mechanical properties. [ABSTRACT FROM AUTHOR]

In this work, a series of durability requirements are proposed for the construction of long-service-life reinforced concrete (RC) structures in a coastal environment with extreme atmospheric corrosivity. RC specimens were exposed in a coastal outdoor site in Cuba for three years. Carbon steel corrosion evaluation revealed an annual average atmospheric corrosion rate over the maximum limit established (ISO 9223:2012) for extreme (CX) atmospheric corrosivity. The service life of the RC structures, considered as the sum of the time-to-corrosion-initiation and time-to-corrosion-induced concrete cracking, was determined as a function of durability requirements. The most important durability requirements to achieve a long service life (>70 years) in RC structures subjected to a CX corrosivity category were defined as follows: water/cement ratio, compressive strength, percentage of effective capillary porosity, and concrete cover thickness. Under these hostile environments, the expansion of the corrosion products formed on the reinforcement steel and the induced cracking of the concrete could be attributed partially to the formation of the akaganeite phase in reinforcement steel, which revealed a different morphology compared to the akaganeite typically formed in bare carbon steels.

This paper concerns the protective performance of maintenance strategies, i.e. silane impregnation (SI) and electrochemical chloride extraction (ECE), against chloride-induced corrosion for concrete elements in marine environment. The effectiveness of SI treatment is researched through long-term exposure tests, and the efficiency of ECE treatment is considered using a quantitative expression. The failure probability evolution is calculated through reliability theory and Monte-Carlo simulations. The maintenance planning is established, and relevant maintenance costs are determined. The obtained results show that (1) the effective protection life of initially applied silane is longer than 12 years, but the protective performance of reapplied silane is not as pronounced as the silane initially applied; (2) the chloride ions at steel surface are efficiently removed after ECE which is more conducive to sustain the steel rebars free from corrosion; (3) ECE treatment attains the optimal cost and is recommended for long life-span concrete elements in marine environment.

There is still a significant problem associated with corrosion of steel bars embedded in concrete structures as a result of simultaneous chloride ingress and carbonation. This results in a decrease in the durability and service life of reinforced concrete structures. An experimental study was conducted to investigate the effect of carbonation on the diffusion of chloride ions in concrete mixtures containing 8% silica fume and 10% natural zeolite. To accomplish this, concrete specimens with water-to-cementitious materials (w/cm) ratios of 0.40 and 0.50 were placed in a system that simulated pure carbonation, tide cycles of the marine environment, and spraying conditions separately. Carbonation results in the release of bound chlorides from concrete pores, which further facilitates chloride ingress into rebar. Additionally, the simultaneous chloride ingress and carbonation can lead to a lower carbonation progress and an increase in the chloride diffusion coefficient. Consequently, rebar corrosion increased and concrete structures were less likely to last for a long period of time. When supplementary cementitious materials (SCMs) are used in concrete mixtures, this problem may become solely important. Based on the results of the present study, it is concluded that adding 8% silica fume or 10% natural zeolite to concrete reduces its carbonation resistance while increasing its carbonation-induced corrosion resistance. Additionally, when carbonation and chloride ingress occur simultaneously, the addition of 10% natural zeolite to concrete improved its diffusion coefficient more than 8% silica fume. [ABSTRACT FROM AUTHOR]

Chloride ingress induced depassivation of reinforcing steel leading to corrosion is a major durability concern for concrete structures. The influence of the presence of cracks commonly occurring in concrete structures on chloride ingress should be accounted to improve the accuracy of service life predictions. This study investigates the depassivation probability of the reinforcement in both cracked and uncracked concrete using both analytical and 1D numerical models. The probabilistic service life prediction is realized using the Monte Carlo simulation to incorporate the uncertainty and variability in the input variables. For uncracked concrete the result of the numerical model agreed well with the fib chloride model. For cracked concrete, the numerical simulation suggests that the optimal engineering approach to account for cracks in a service life analysis is the adaptation of crack depth. Although, the approach could lead to an overestimation of chloride concentration because the 1D numerical simulation did not consider lateral diffusion in cracked concrete. [ABSTRACT FROM AUTHOR]

The phase transformations and microstructural properties of a drilled cylinder specimen from a C40 concrete dam used for mining wastewater disposal were evaluated in this study, covering a span of up to 20 years. Various analysis methods, including PT, ICP-MS, XRD, FTIR, TGA, MIP, and SEM-EDS, were employed to assess the performance of powder samples obtained through layer-by-layer grinding. The results obtained from XRD, FTIR, and TGA analyses indicated that the presence of calcite in all ground powder samples, suggesting that carbonation can occur in all layers, even including the inner layers. Moreover, the MIP and SEM-EDS results illustrated that the microstructural properties of the concrete could be influenced by phase transformations induced by various ions present in the mining wastewater, resulting in increased porosity and looser interfacial transition zones (ITZs) in the sample closer to the outer layer. The PT results confirmed the penetration of chloride into the concrete, although the relative chloride content decreased with the increasing depth of the layers. It was observed through TGA analysis that a portion of the chloride ions could attribute to the formation of Friedel’s salts, derived from ettringite or calcium aluminate monosulfate. Additionally, SEM-EDS examination revealed that some chloride ions could bind to the C-S-H gels. The presence of different ions, particularly magnesium ions in the mining wastewater could lead to decalcification of the hydrated gels. These research findings provide significant support for the safety assessment of the concrete structure exposed to mining environments.

The corrosion‐related damages on concrete infrastructure account globally for several billion US dollars annually. Up to 38 % of these costs could be saved by the application of optimized materials and/or more efficient monitoring technologies. In this contribution a novel sensor technology is presented, based on luminescent pH sensitive dyes, to quantitatively determine the pH distribution in cement‐based construction materials. Different sensor platforms were explored resulting in high‐resolution imaging techniques, as well as in miniaturized sensor probes for field application and in situ monitoring. To this point, pH sensors were successfully applied for cementitious materials to (i) quantitatively characterize the carbonation state in the lab, (ii) gain further understanding on phase assemblages and internal pH evolution related to carbonation, (iii) reveal that the actual pH at the inflection point of phenolphthalein may strongly vary depending on physicochemical material properties, (iv) monitor the pH evolution during the early hydration of different cementitious materials, and (v) measure carbonation depths using miniaturized sensor probes adopted for field applications. [ABSTRACT FROM AUTHOR]

Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.

Chloride ingress and carbonation pose a significant risk of steel rebar corrosion in concrete structures. Various models exist to simulate the initiation phase of rebar corrosion, addressing both carbonation and chloride ingress mechanisms separately. These models also consider the environmental loads and material resistances, typically determined through laboratory testing based on specific standards. However, recent findings show significant differences between material resistances obtained from standardized laboratory specimens and those extracted from real structures, with the latter exhibiting inferior performance on average. To address this issue, a comparative study was conducted between laboratory specimens and on-site test walls or slabs, all cast using the same concrete batch. This study encompassed five construction sites featuring different concrete compositions. While laboratory specimens adhered to European curing standards, the walls were subjected to formwork curing for a predetermined period (typically 7 days) to simulate practical conditions. In some instances, a portion of the test walls/slabs received only one day of surface curing to emulate inadequate curing conditions. Subsequent testing of compressive strength and resistance to chloride ingress revealed that field specimens exhibited lower material resistance compared to their laboratory counterparts. This trend was also observed in the modulus of elasticity and carbonation rate. Notably, shorter curing periods further compromised performance, particularly resistance to chloride ingress and carbonation. These findings highlight the importance of establishing acceptance criteria not only for concrete delivered to construction sites but also for ensuring the quality of the actual structure. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The recent emphasis on sustainable development in the construction industry has made it essential to develop construction and building materials that are not only affordable, but have minimal negative impact on the environment. This study investigates the valorisation of steel slag, which is mostly considered to be a waste material in several parts of the world, by blending with calcined impure kaolinitic clay to partially replace ordinary Portland cement (OPC) in the preparation of self-compacting concrete (SCC). OPC was substituted with steel slag at a constant level of 10%, whereas calcined clay replaced OPC at varying levels, ranging from 10 to 30% in a ternary blended mix. The hardened properties evaluated include compressive and flexural strengths. Samples containing only calcined clay showed a lower fluidity, which was significantly improved when steel slag was added to the mix. SCC containing 10% steel slag and 20% calcined clay obtained 28 days compressive strength, which was 3.6% higher than the reference cement concrete. An XRD analysis revealed a significant decrease in the peak heights of portlandite in mixtures containing steel slag and calcined clay, regardless of their replacement percentage. Generally, all the blended cement samples performed appreciably in resisting sulphate attack. The results of this study demonstrate that using steel slag and calcined clay together can significantly improve the fresh and hardened properties of SCC without compromising its mechanical properties.

Probabilistic service life analyses for assessing the risk of chloride‐induced corrosion in uncracked concrete are often realized using the well‐known chloride ingress model of the fib Model Code for Service Life Design. In practice, however, concrete includes cracks, which alter the resistance of the concrete against the chloride ingress. In the past, different approaches to account for preexisting cracks, were developed. In this study, these modeling approaches are summarized and compared in context of the probabilistic service life prognosis. Furthermore, a new approach to account for cracks by theoretically adapting the convection zone is presented. This study demonstrates that the choice of model extension to account for cracks vastly influences the prediction results and shows the limits of application of the current extensions. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corrosion damage in the tidal zone, despite very high (above-threshold) chloride contents. To develop a full understanding of the severity of marine exposure conditions with regard to the actual deterioration, it is imperative that other factors that directly affect corrosion, such as oxygen availability at the steel surface (which is influenced by concrete quality, cover thickness and moisture condition), are carefully considered. The laboratory experimental work in the study presented in this paper comprised of different cover depths (10, 20 and 30 mm) and w/b ratios (0.5 and 0.8) and simulated marine tidal, splash and submerged environments. The results show that for any give exposure environment, the relative influence of each of the various factors considered should be considered in conjunction with the other factors; this finding can be generalized to include all relevant factors that can affect corrosion in a given exposure environment including ambient temperature. For example, a cover depth of 30 mm in the tidal zone with a simulated intertidal duration of 6 h effectively resulted in similar corrosion behavior to that in the submerged zone. The paper concludes that engineers should consider these factors when applying standard exposure classes in the design for durability of marine structures.

• A three-stage framework for assessing life-cycle seismic resilience is proposed. • Stochastic environmental and durability model is built and experimentally verified. • Life-cycle seismic demand variations of piers in various environmental zones are revealed. • Efficient surrogate models are developed to predict the life-cycle seismic resilience. • Time-dependent probabilistic characteristics of seismic resilience are identified. The life-cycle seismic resilience assessment of sea-crossing highway bridges plays a crucial role in guiding decisions for their long-term operation, maintenance, and rehabilitation. Due to the inherently stochastic nature of marine environments, evaluating the resilience of bridges while considering all possible environmental scenarios throughout their service life necessitates substantial computational efforts and presents practical challenges. Thus, this study develops a three-stage framework for predicting the life-cycle seismic resilience of sea-crossing highway bridges. Stochastic models for marine environmental conditions and bridge durability are developed and validated using experimental measurement data. A modified Good Lattice Point-Partially Stratified Sampling (GLP-PSS) method is employed to generate a uniform and limited number of samples. A typical prestressed concrete sea-crossing highway bridge is selected as the benchmark bridge, and parameterized numerical models are established using 460 representative environmental parameter samples on the OpenSees platform. Leveraging the environmental model and material properties, the durability of the bridge is predicted over its service life. Nonlinear time history analyses are carried out for each bridge model using 120 real ground motion records, which allow the identification of variations in seismic demands, capacities, and system fragilities at different time intervals. Subsequently, the life-cycle seismic resilience of the bridge is predicted utilizing surrogate models based on the response surface method (RSM) and artificial neural networks (ANN), respectively. Finally, the time-dependent probabilistic characteristics of seismic resilience are thoroughly discussed. Results indicate that ANN demonstrates a higher degree of generalization capability in predicting the life-cycle seismic resilience. Focusing solely on changes in mean resilience over the service time may lead to an underestimation of bridge resilience, as it may ignore the tails of its distribution, potentially resulting in an overestimation of bridge resilience. Furthermore, global warming may expedite the decline in resilience. [ABSTRACT FROM AUTHOR]

Recycled aggregate produced from crushed waste concrete is suitable for use in structural concrete. It reduces the demand for non-renewable resources and also for energy in general. However, RA is more porous than most natural aggregates. The porosity of the concrete cover defines the corrosion resistance of reinforced concrete, and it is therefore disputed how the use of recycled aggregate may affect the durability of reinforced concrete. This paper describes the corrosion-related performance of reinforced concrete with recycled aggregates in the initiation stage (determined by the carbonation and chloride ingress) and propagation stage (determined by the electrical resistivity and cracking) of corrosion. The aspects of interest are not only the porosity of RA but also its effects on the chloride binding, carbonation, electrochemical properties and corrosion cracking development.

Corrosion of steel reinforcement due to chloride attack remains a major reinforced concrete durability concern. The problem is prevalent for concrete structures located within marine environments or frost-prone locations where chlorides containing de-icing salts are used. This paper is a state-of-the-art review into chloride binding in Portland cement concrete, with consideration of the differences induced by the presence of sulphates, such as found in seawater. The review also considers the use of supplementary cementitious materials (SCMs), the use of which has increased because of their potential to enhance durability and reduce the carbon footprint of concrete production. Such materials impact on phase assemblage and microstructure, affecting chloride binding and transport properties. Therefore, field and laboratory studies are critically reviewed to understand how these could help in the design of more durable concretes. The contributions of chloride binding, hydrate compositions and microstructures of the binding materials affecting chloride transport in concretes are also evaluated to suggest a more robust approach for controlling the problem of chloride attack. [ABSTRACT FROM AUTHOR]

Concrete structures are considered as durable construction material, but corrosion of the embedded steel reinforcement occurs under chloride exposure as concrete has porous properties. Herein, a cyclic drying–wetting test was performed for two years using saltwater to accelerate steel corrosion in a reinforced concrete (RC) member. The open-circuit potential (OCP) was measured using a newly developed and replaceable agar sensor. The corrosion potential was measured considering the chloride concentration, water-to-cement (w/c) ratio, and cover depth at three levels. Furthermore, its relationships with influential parameters were evaluated using averaged OCP results. The measured OCP showed a linear relationship with the cover depth, and this tendency was more distinct with increasing retention period and higher chloride concentration. For the highest w/c ratio (0.6), values below −100 mV were monitored after only six months regardless of the cover depth, and values below the critical potential level (−450 mV) were evaluated at lower cover depths (30 and 45 mm). The results of regression analysis considering the exposure environment showed a clear relationship in the case of high chloride concentration (7.0%). A linear relationship between cover depth and OCP was derived with a reasonable determination coefficient ranging from 0.614 to 0.771. [ABSTRACT FROM AUTHOR]

In this paper, the recent research progress on the corrosion of reinforced alkali-activated materials (AAMs) concrete structures is reviewed. The corrosion mechanisms induced by carbonation and chloride ingress in AAMs concrete are discussed, from the perspectives of composition, microstructure and pore solution chemistry, in comparison to ordinary Portland cement (OPC) concrete. The steel–alkali-activated concrete interface is a key to investigating corrosion initiation and propagation, which has different physical and chemical characteristics of the steel–concrete interface in OPC concrete. Moreover, the electrochemical process testing methods including half-cell potential and linear polarization resistance are critically discussed with a focus on what could be inherited from the OPC concrete and what criteria are no longer suitable for AAMs concrete due to underestimation in most cases. New data and theories are urgently needed for using AAMs in concrete structures to replace OPC. At the end of this paper, the research gaps and future research needs are summarised for the sake of widespread application of AAMs in concrete structures for sustainable and low-carbon construction.

The use of calcined clays as supplementary cementitious materials is one of the strategies to reduce the CO2 emissions from cement and concrete industry as they provide good mechanical and durable properties after proper calcination and grinding. In Argentina, calcined common brick clays have a significant relevance due to their proximity to the largest Portland cement plants. The aim of this study is to analyze the resistance to chloride ingress and natural carbonation up to 36 months of concretes using calcined common brick clay and calcined low-grade kaolinitic clay. The latter exhibits a much lower chloride migration coefficient than the Portland cement concrete from 28 days on, while the calcined common brick clay requires a 90 days curing to obtain lower chloride ingress. Although the blended concretes exhibit greater carbonation depths than the reference after 36 months, it is lower than the given threshold of 10 mm. Hence, durable concretes with calcined clay can be obtained if they are properly cured.

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corrosion damage in the tidal zone, despite very high (above-threshold) chloride contents. To develop a full understanding of the severity of marine exposure conditions with regard to the actual deterioration, it is imperative that other factors that directly affect corrosion, such as oxygen availability at the steel surface (which is influenced by concrete quality, cover thickness and moisture condition), are carefully considered. The laboratory experimental work in the study presented in this paper comprised of different cover depths (10, 20 and 30 mm) and w/b ratios (0.5 and 0.8) and simulated marine tidal, splash and submerged environments. The results show that for any give exposure environment, the relative influence of each of the various factors considered should be considered in conjunction with the other factors; this finding can be generalized to include all relevant factors that can affect corrosion in a given exposure environment including ambient temperature. For example, a cover depth of 30 mm in the tidal zone with a simulated intertidal duration of 6 h effectively resulted in similar corrosion behavior to that in the submerged zone. The paper concludes that engineers should consider these factors when applying standard exposure classes in the design for durability of marine structures. [ABSTRACT FROM AUTHOR]

Corrosion-induced deterioration poses a significant threat to the serviceability of reinforced concrete (RC) structures. This study develops a comprehensive mesoscale model utilizing dual-phase field methods to capture the entire time-dependent chloride-induced corrosion and cracking mechanisms, incorporating interactive multi-physics. The model accurately delineates the evolution of corrosion morphology and cracking patterns, focusing on their interdependent interactions within localized areas through detailed electro-chemo-mechanical processes, from steel dissolution to precipitation. The robustness of the proposed numerical method is confirmed through alignment with previously reported experimental results. Extensive parametric studies investigate the impacts of various geometric and material characteristics on corrosion processes. Furthermore, the model's applicability to RC configurations with multiple reinforcements is also demonstrated. These findings offer pivotal insights into the substantial correlations between rebar corrosion and concrete cracking across multi-physics fields, with their coupling driven by the variable corrosion current density. • A multi-physics method with electro-chemo-mechanical interaction simulates corrosion. • A dual-phase field approach captures the coupled processes of corrosion and cracking. • Pitting corrosion is modeled with smeared rust, distinct from the elliptical form. • Extensive parametric study emphasizes the impact of interactive multi-reinforcement. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures in seismic coastal areas often suffer from the coupled effects of corrosion and earthquakes due to prolonged exposure to harsh environmental conditions. Previous research on the seismic performance of buildings primarily focused on uniform corrosion(UC), disregarding the impact of varying concentrations of chloride-ions on corrosion rate. This discrepancy will overestimate the seismic performance of building structures. The framework proposed in this study aims to evaluate the resilience of RC structures to non-uniform story corrosion(NUSC). The framework encompasses an innovative functional recovery function and considers the influence of chloride-ions concentration on the corrosion rate, time-varying initial functional function, and degradation model for corroded reinforced concrete. NUSC model is established within the proposed framework via OpenSees software. The proposed framework integrates the seismic hazard, fragility, resilience, and recovery models. A nonlinear time history analysis method is employed to simulate the structural response to the seismic action. The findings demonstrate that NUSC leads to a reduction in seismic resilience by 7.3% and 10% compared to UC when considering service times of 35 and 55 years, respectively. This indicates an escalation in seismic risk as well as a decline in structural seismic capacity. • Propose a non-uniform story corrosion resilience assessment framework for RC structure. • Propose a novel functional recovery function with greater recovery potential. • Non-uniform story corrosion makes structures more fragile than uniform corrosion. • Non-uniform story corrosion reduces seismic resilience compared to uniform corrosion. [ABSTRACT FROM AUTHOR]

We developed a simplified coupled model to simulate the chloride ingress of cement paste and mortar fabricated with CEM II/C-M (S-LL) and CEM VI (S-V) cements. Diffusion of chloride, calcium, sodium, potassium, sulphate and hydroxyl ions is considered, resulting in a set of coupled mass balance equations. Source and sink terms are introduced to represent the dissolution/precipitation processes due to leaching, and interactions between free chloride and hydrated phases are considered through binding isotherm curves. Electrodiffusion phenomenon is introduced through a modified Poisson equation to enforce local electroneutrality. The model is applied to simulate bulk diffusion tests with exposure solutions containing NaCl, and NaCl + KOH to reduce leaching. The main features observed experimentally are correctly reproduced: a higher chloride content is predicted for the materials made with CEM II binder, and a much clearer peaking behavior near the exposed surface is predicted in the case of NaCl exposure. [ABSTRACT FROM AUTHOR]

The safety and reliability of bridges gradually decrease over time under the influence of disadvantageous environmental factors, primarily due to reinforcement corrosion caused by chloride ingress. The traditional lateral load distribution (LLD) theory does not consider the influence of corrosion, which degrades the accuracy of bridge performance and reliability calculation. A time-dependent reliability assessment method for simply supported T-beam bridges is proposed in this paper, which considers the influence of reinforcement corrosion on LLD. Firstly, the steel corrosion process and degree are predicted based on the chloride ingress model, into which the water/cement ratio and concrete strength are innovatively introduced in order to improve the prediction accuracy. Secondly, the effective stiffness calculation method for corroded reinforcement bridges is established with the moment of inertia and section crack condition employed. Thirdly, the modified eccentric compression method is improved by the effective stiffness and iterative algorithm, which is suitable for the LLD calculation of corroded reinforcement bridges. The time-dependent vehicle load effect can be computed combined with the probability distribution of live load. Finally, the time-dependent reliability of the flexural bearing capacity is obtained by the Monte Carlo method and Bayesian theory without prior information. A simply supported bridge with five T-beams is taken as an example for analysis. It is indicated that the results calculated by the traditional reliability method are conservative, which cannot make a true and accurate evaluation. The method proposed in this paper can effectively reduce the assessment error caused by model uncertainty while considering the interaction between reinforcement corrosion and vehicle live load effect. [ABSTRACT FROM AUTHOR]

Due to the attack of harmful environmental substances, the reinforcements in concrete can be corroded. The corrosion of reinforcements induces the concrete crack and the reduction in structural capacity. The complex durability deterioration at the material scale is commonly oversimplified in the structural analysis, and the influence of reinforcement corrosion distribution can hardly be evaluated in traditional methods. Benefitted from the accurate material model and efficient solution technologies, a structural life-cycle probabilistic evaluation method is proposed based on the material uncertainty influence. The computational framework consists of three steps. First, the simulation of chloride ingress in structural cross-section considering mesoscopic variation; second, the finite element analysis of structural response with modifying reinforcement corrosion states; third, the structural life-cycle performances are evaluated probabilistically with the trained Artificial Neural Network model. Focussed on the life-cycle hysteretic performance of the reinforced concrete column, the whole procedure is operated for illustration, and the time-dependent decreasing structural performance are investigated. Compared with widely used macroscopic methods, the model precision can be refined over 90%. By discussion effects of different measures to improve structural performance are studied, including increasing concrete strength and concrete cover. The results show that the thicker concrete cover can postpone the initial deterioration and significantly increase structural life-cycle performance probabilistically, and with the same designed action effect, the structural service life can be extended over 85% to reach same reliability. [ABSTRACT FROM AUTHOR]

Steel corrosion in reinforced concrete (RC) structures in the marine environment is a major concern for engineers and asset managers. This paper presents an assessment of the application of a deemed-to-satisfy durability design and specification approach on the newly constructed RC bridges on the Swakopmund–Walvis Bay Freeway upgrade in Namibia, with a desired service life of at least 100 years. The deemed-to-satisfy design and specification approach comprised a combination of South African recommendations for binder type, minimum binder content and w/b ratio, EN 206-1 recommendations for cover depth, and South African National Roads Agency Limited (SANRAL) durability index targets along with on-site concrete quality control guidelines on placement, compaction and curing. As-built concrete durability properties (i.e. water sorptivity, oxygen permeability and chloride conductivity) and cover depth were measured and used to check (using a Fickian-based service life model) if the deemed-to-satisfy specifications were adequate. The results showed that the as-built concrete durability properties surpassed the deemed-to-satisfy durability performance targets, while the on-site cover depth values showed significant inadequacies in some bridge elements. The service life estimations showed that the deemed-to-satisfy durability performance specifications were adequate. Considering the relatively high concrete quality achieved on site, it is clear that the 100-year service life could have been achieved more sustainably using a good balance of concrete quality and cover depth [e.g. a lower concrete quality (using less cement) or lesser coved depth] if a more rigorous performance-based durability design and specification approach had been used. Ultimately, the service life analyses using the as-built concrete model input parameters highlight not only the critical importance of both concrete quality and cover depth in achieving durable RC structures prone to steel corrosion, but also the inherent limitations of the deemed-to-satisfy durability design and specification approach. [ABSTRACT FROM AUTHOR]

Recycled aggregate produced from crushed waste concrete is suitable for use in structural concrete. It reduces the demand for non-renewable resources and also for energy in general. However, RA is more porous than most natural aggregates. The porosity of the concrete cover defines the corrosion resistance of reinforced concrete, and it is therefore disputed how the use of recycled aggregate may affect the durability of reinforced concrete. This paper describes the corrosion-related performance of reinforced concrete with recycled aggregates in the initiation stage (determined by the carbonation and chloride ingress) and propagation stage (determined by the electrical resistivity and cracking) of corrosion. The aspects of interest are not only the porosity of RA but also its effects on the chloride binding, carbonation, electrochemical properties and corrosion cracking development. [ABSTRACT FROM AUTHOR]