Service Life Of Concrete Structures Research Articles

A numerical study on chloride diffusion in freeze-thaw affected concrete

Existing concrete in cold or coastal regions is attacked by chloride penetration under freeze-thaw cycles (FTCs). The combined deterioration process accelerate the damage evolution of concrete and reduces the service life of concrete structures. This paper presents a mesoscopic numerical model, which is 2-D and 3-phases, to investigate the mechanism of chloride diffusion under FTCs in a quantitative manner. Unlike most of existing models, the present model considers the FTCs-induced damage affected chloride diffusion by adopting a time-dependent variable of porosity, which can not only reflect how freeze-thaw action affects the concrete pore structure, but also couple the freeze-thaw process together with the chloride diffusion process at time scale. The reliability of the proposed model is validated against a third-party experiment. Based on the obtained concentration distribution profiles, a series of significant influencing factors, i.e., w/c ratio, ITZ effects, external chloride concentration, aggregate volume fraction and inner temperature are clarified. A grey relational analysis is further conducted to rank the correlative degrees of influencing factors on diffusivity of chloride under FTCs. The findings of this study can bring insights to the preparation technique of concrete in cold or coastal regions as well as the durability prediction on existing concrete structures suffering chloride attack and freeze-thaw action.

Evaluation of Chloride Diffusion and Corrosion Resistance in Reinforced Concrete Using Internal Curing and Shrinkage Reducing Admixtures

The properties of high-performance concretes obtained by the internal curing technique were studied in the fresh and hardened states. In some of the concrete mixtures, fine normal weight aggregates were replaced with lightweight aggregates (LWA) at 20 % vol. and ordinary portland cement was replaced by pulverized class F fly ash at 20 % by mass. Additionally, some mixtures were prepared including a shrinkage-reducing admixture, either as part of the mixing water or pre-soaked into the lightweight fine aggregates. The prepared concretes were subjected to degradation tests, such as accelerated carbonation and chloride ion deterioration. In addition, the reinforced concretes were analyzed through electrochemical corrosion tests with the linear polarization resistance technique. It was found that the internally cured concretes presented a mechanical resistance similar to those reported for the reference concretes (conventional concretes), but provided a higher resistance to carbonation, rapid penetration of chloride ions, and a lower chloride ion diffusion coefficient. The reinforcing steel structure in the internally cured concretes showed lower corrosion currents (Icorr) and corrosion potentials (Ecorr) in comparison to the reference concretes. Therefore, the use of the internal curing technique in concretes with pre-soaking in either water or a solution of shrinkage-reducing admixture can be considered as a viable alternative to extend the service life of concrete structures in contact with harmful environments.

The Influence of Supplementary Cementitious Materials on Climate Impact of Concrete Structures Exposed to Chlorides

Abstract Addition of fly ash or GGBS in concrete has shown to increase the durability and thus the service life of concrete structures exposed to chlorides. Currently, the durability relies on regulations, which beside a minimum cover thickness also put constraint on amount and type of SCM in different environments. Swedish regulations do not, however, consider the actual durability of different binders. As a consequence, a LCA might be misleading. This paper investigates the climate impact of concrete with SCM in chloride environment. Current prescriptive design approach is compared with a performance based service life approach and applied to bridge parts.

Prediction of Concrete Structure Service Life Based on the Principle of Neural Connections in Brain Circuits

Concrete is the most widely used structural material in the world; however, its structural safety is affected by concrete carbonization and reinforcement corrosion. According to the principles and characteristics of concrete carbonization and reinforcement corrosion, this paper establishes artificial neural network prediction and evaluation models for the depth of carbonization and the degree of reinforcement corrosion based on the principle of neural connections in brain circuits. The results show that the artificial neural network prediction models are of high accuracy, and that the RBF neural network prediction model is more accurate and requires far less training time than the BP neural network model.

Study on water and chloride transport in cracked mortar using X-ray CT, gravimetric method and natural immersion method

Concrete structures are frequently suffered to physical and chemical damage in the service period and then cracking is unavoidable. Cracks provide rapid access to aggressive agents and have a significant effect on the durability and service life of concrete structures. In this work, water and chloride transport in cracked mortars were investigated systematically. Firstly, the dynamic process of water transport in cracked mortars was visually monitored by X-ray CT and water absorption of cracked mortar was also quantitatively investigated by the gravimetric method. Later, chloride transport in saturated and unsaturated cracked mortars was studied by natural immersion method. What’s more, the effect of gravity on chloride transport in cracked mortar was considered in this study. The results show that the threshold crack width for water absorption of cracked mortar is 0.1 mm. The effect of crack width on chloride transport in saturated and unsaturated mortars is different. The gravity effect improves the rate of chloride transport in cracked mortars.

Influence of diffusion properties on the service life of concrete structure under chloride exposed environment

Recently, a variety of studies has been carried out to predict or design service life of concrete. To obtain a controlled durability and long-term performance of concrete structures under chloride attacking environments, durability analysis on chloride diffusion needs to be conducted with major design variables such as the diffusion coefficient, chloride corrosion threshold value, and chloride ion content at surface as random variables. Therefore, this study has explored the influence of diffusion properties on the service life of concrete structures.Keywords: Durability, Service life, Chloride, Concrete

Evaluation of carbonation service life of slag blended concrete considering climate changes

Climate changes, such as increasing of CO2 concentration and global warming, will impact on the carbonation service life of concrete structures. Moreover, slag blended concrete has a lower carbonation resistance than control concrete. This study presents a probabilistic numerical procedure for evaluating the impact of climate change on carbonation service life of slag blended concrete. This numerical procedure considers both corrosion initiation period and corrosion propagation period. First, in corrosion initiation period, by using an integrated hydration-carbonation model, the amount of carbonatable substances, porosity, and carbonation depth are calculated. The probability of corrosion initiation is determined through Monte Carlo method. Second, in corrosion propagation period, a probabilistic model is proposed to calculate the critical corrosion degree at surface cracking, the probability of surface cracking, and service life. Third, based on the service life in corrosion initiation period and corrosion propagation period, the whole service life is calculated. The analysis shows that for concrete structures with 50 years service life, after considering climate changes, the service life reduces about 7%.

Análise da vida útil de estruturas de concreto armado sob corrosão uniforme por meio de um modelo com RNA acoplado ao MEF

O presente trabalho apresenta uma análise numérica da vida útil de estruturas de concreto armado sujeitas à corrosão uniforme. O processo de modelagem foi dividido em dois estágios, iniciação e propagação. A modelagem da fase de iniciação foi feita via Redes Neurais Artificiais (RNA) enquanto que a fase de propagação foi modelada através do Método dos Elementos Finitos (MEF). Os resultados demonstram que o modelo gerado pelo acoplamento das RNA ao MEF, possibilita de forma eficiente, a simulação da degradação de estruturas de concreto armado devido à ação da corrosão uniforme e, a aplicabilidade da ferramenta numérica quanto a previsão da vida útil destas estruturas.

A conceptual framework for service life prediction of reinforced concrete structures

This paper presents a conceptual framework methodology concerning service life prediction of concrete structures by using deterministic or probabilistic processes, which are included from collecting data until the decision-making. This methodology provides guidelines to generate new degradation models and accomplish new service life studies of either existing structures or new ones in literature. In the first case, it is possible to estimate how many years are necessary for the structure to reach the desired limit state (durability, service or of security). It can also provide support in project design by selecting durability requirements such as covering thickness, concrete strength, type of cement, water–cement ratio, among other factors that influence the service life of concrete structures.

Tensile creep and cracking potential of high performance concrete internally cured with super absorbent polymers at early age

High performance concrete (HPC) has been extensively applied in practice. However, the water-to-cement (w/c) ratio of this concrete is low, high temperature rise and high self-desiccation will occur, and both of which can increase the cracking potential of HPC at early age and then decrease the service life of concrete structures. Therefore, super absorbent polymers (SAPs) are applied in HPC as an internal curing (IC) agent. Although the autogenous shrinkage, relative humidity, and stress relaxation of concrete internally cured with SAPs have been studied, investigations on the influence of SAPs on the tensile creep and cracking potential of HPC are still lacking. In present study, the influence of SAPs as an IC agent on the temperature, autogenous shrinkage, restrained stress, basic tensile creep, and cracking potential of HPC were simultaneously studied by Temperature Stress Test Machine. Test results and corresponding analysis showed that: (1) the adiabatic temperature rise of HPC was 27.6, 29.3, 31.0, and 34.9 °C and increased with the increase of amount of SAPs; (2) the rate of restrained tensile stress of HPC was 1.7, 1.5, 1.4, and 1.2 MPa/day and decreased with the increase of amount of SAPs; (3) the specific basic tensile creep of HPC at the age when the restrained specimen of mixture SAP-0 cracked was 45, 23, 13, and 7 με/MPa and decreased with the increase of amount of SAPs; (4) a model for predicting the basic tensile creep compliance function of HPC considering the influence of amount of SAPs was proposed; (5) the cracking potential of HPC which was based on the integrated criterion decreased with the increase of amount of SAPs.

Sensitivity of Service Life Extension and CO2 Emission due to Repairs by Silane Treatment Applied on Concrete Structures under Time‐Dependent Chloride Attack

This paper presents sensitivity of service life extension and CO2 emission due to silane (alkyltriethoxysilane) treatment on concrete structures under time‐dependent chloride attack. The service life is predicted by the Crank–Nicolson‐based finite difference approach for avoiding the complexity in solving Fick’s second law. The complexity occurs due to time‐dependent chloride attack and nonconstant diffusion coefficient of concrete with silane treatment. At the application time of silane treatment, the cumulative CO2 emission is assessed. The effectiveness of silane treatment is defined as the ratio of the service life extension to the cumulative CO2 emission assessed within the corrosion‐free service life. The service life extension is defined as the difference between corrosion‐free service life of concrete structures without and with time‐based application of silane treatment. From the study, the diffusion of chlorides in concrete with silane treatment is found to be retarded. In comparison, the strategy without deterioration of silanes during effective duration is more suitable for service life extension but less effective than that with deterioration. In the sensitivity analysis, there are up to eight parameters to be determined. The service life of concrete structures without silane treatment is most sensitive to the water‐to‐cement ratio and the threshold depth of concrete structures. Considering only five parameters in silane treatment strategies, the service life is most sensitive to the first application time of silane treatment. The cumulative CO2 emission is most sensitive to either the first application time of silane treatment or the amount of CO2 emission per application.

Perpendicular-to-crack chloride ingress in cracked and autonomously healed concrete

Cracks in reinforced concrete structures exposed to a marine environment or de-icing salts can cause major durability issues due do accelerated ingress of chloride ions. In this study, the influence of autonomous crack healing by means of encapsulated polyurethane on the chloride ingress perpendicular to cracks was evaluated. This was done quantitatively by determining perpendicular-to-crack chloride profiles by means of profile grinding followed by potentiometric titration and qualitatively through visualization of the chloride penetration front by means of the AgNO3 spray method. The resulting chloride profiles showed that the healing mechanism was able to reduce the chloride concentrations in the direct vicinity of the crack to a large extent and to reduce the perpendicular-to-crack chloride penetration, especially further away from the exposed surface. Visualization of the chloride penetration front showed some variation in crack healing. For some healed samples almost no additional chloride ingress was found compared to uncracked samples, others showed a slightly enhanced ingress at the crack location but less perpendicular-to-crack chloride penetration compared to untreated cracked samples. Generally, the reduced amount of chlorides present in the concrete matrix due to crack healing will enhance the durability and service life of concrete structures.

Influence of Pore Structure on Chloride Distribution in Surface Layer of Cement Paste under Cyclic Wet-Dry Condition

This research focuses on influence of pore structure on chloride distribution in surface layer of cement paste under cyclic wet-dry condition. The results of chloride distribution reveal that drying and wetting cycles can lead to a peak value of chloride content (Cmax) occurring in surface layer of cement paste. Cmax increases with the increase of W/C. While the depth (Δx) at which Cmax appears does not show a regular change. Moreover, Cmax should be used to predict service life of concrete structures when Cmax appears in the chloride profiles. For the influence of pore structure, there exists an obvious hyperbolic relationship between chloride diffusion coefficient (D), Cmax and pore structure parameters. D and Cmax increase with total porosity and the most probable pore diameter, decrease with tortuosity, and stabilize gradually. And the most probable pore diameter has the most significant impact on D and Cmax. In addition, XRD and SEM-EDS results indicate that the deposition of Friedel’s salt results in the formation of more inkbottle shaped pores, which may cause the appearance of Cmax under cyclic drying-wetting conditions due to hysteretic moisture effect.

A Probabilistic Study on Hydraulic Conductivity of Concrete at Mesoscale

Hydraulic conductivity of concrete can be used as a key indicator in assessment of service life of concrete structures. In this paper, a probabilistic investigation on hydraulic conductivity of concrete is conducted, allowing for variation in hydraulic properties of concrete constituents. Concrete is modeled as a three-phase composite at mesoscale, consisting of mortar, aggregates, and the interfacial transition zone (ITZ). A finite element (FE) method is developed to calculate the hydraulic conductivity of concrete, which is then verified using available experimental results. Based on a large pool of samples generated from Monte Carlo simulation, a conceptual model relating hydraulic conductivity of concrete to aggregate volume fraction ratio and hydraulic conductivity of mortar and the ITZ is proposed. It is shown from the probabilistic-based sensitivity analysis that hydraulic conductivity and thickness of the ITZ are among the most influential factors affecting the bulk hydraulic conductivity of concrete. It is also shown that for high aggregate volume fraction ratios, due to increasing volume of the ITZ, the coefficient of variation of hydraulic conductivity can be as high as 0.36.

Modelling of chloride ingress in concrete based on benchmarking field results

Modelling the ingress of chloride ions into the cover of a concrete structure is a phenomenon that is gaining an increasing attention of the research community, but even more, from the engineering practice. As the mechanism that drives the ingress of chlorides is implicitly responsible for the service-life of concrete structures, its input parameters are a major issue whenever predicting the service-life of new concrete structures. In this paper most relevant parameters involved in the evaluation of chloride ingress models are discussed and related to the benchmark activities that currently run in RILEM TC 270-CIM on benchmarking Chloride Ingress Models. The results provide an overview of the models used in the structural design stage, mostly analytical models, and in the rehabilitation stage, mostly numerical models.

Viscoelastic properties of self-consolidating concrete: Influence of the sustainable approach

The service life of concrete structures is primarily affected by cracking. Concrete with a lower cracking potential is consequently more sustainable. In order to estimate the risk of shrinkage-induced cracking, at least four properties should be studied: shrinkage, Young's modulus, creep/relaxation and tensile strength. A mixed experimental and numerical approach, taking into account these properties is presented and used in this paper to improve our understanding of this complex phenomenon. The study is focused on restrained shrinkage of thin structures exposed to drying. Based on the viscoelastic and solidifying theories and on the experimental results from an adapted ring test some explanations of the observed cracking tendencies can be given. The efficiency of this method is shown when it is applied on two experimental studies linked with the sustainability issues. The first one concerns the greener mix-design which was found to have a positive effect on the cracking resistance, with two ways of reducing cement content. The reduction of the paste volume as well as the substitution of Portland cement by supplementary cementitious materials (SCMs) delayed cracking with different mechanisms. The second study aims to analyze the effect of the sealed curing duration on cracking, where the extracted aging-viscoelastic Young's modulus decreases with the curing duration and explains the observed results.

A review of the application Acoustic Emission (AE) incorporating mechanical approach to monitor Reinforced concrete (RC) strengthened with Fiber Reinforced Polymer (FRP) properties under fracture

Concrete durability may be affected by so many factors such as chemical attack and weathering action that reduce the performance and the service life of concrete structures. Low durability Reinforced concrete (RC) can be greatly improved by using Fiber Reinforce Polymer (FRP). FRP is a commonly used composite material for repairing and strengthening RC structures. A review on application of Acoustic Emission (AE) techniques of real time monitoring for various mechanical tests for RC strengthened with FRP involving four-point bending, three-point bending and cyclic loading was carried out and discussed in this paper. Correlations between each AE analyses namely b-value, sentry and intensity analysis on damage characterization also been critically reviewed. From the review, AE monitoring involving RC strengthened with FRP using b-value, sentry and intensity analysis are proven to be successful and efficient method in determining damage characterization. However, application of AE analysis using sentry analysis is still limited compared to b-value and intensity analysis in characterizing damages especially for RC strengthened with FRP specimen.

The influence of carbonation process on concrete bridges and durability in Estonian practice

Concrete as one of the most widely used construction material in building industry, has considerable implementing in bridge engineering due to its extensive number of effective technical characteristics. However, according to exploitation environment, there are substantial factors such as aggressive liquids (e.g. deiced salts, sulfates, etc), rapid temperature alterations and the increasing rate of CO2 to take into account predicting actual retained service life of concrete structure and the need of repairmen to increase the lifespan of the bridge. According to several measuring, concentration of atmospheric CO2 is reported linearly increasing and is modeled to appear as exponential increase in the next decade. This environmental influence leads to accelerated carbonation process of concrete and brings up the importance of its potential untimely degradation mechanism. Hence, the main aim of this research is to give an analyzed overview of the carbonation depths of selection of 11 concrete bridges in Estonia built in the period of 1976-2007 and their relation with compressive strength of concrete. In addition to in situ tests, laboratory research was performed to understand natural carbonation rate and compressive strength relations of concrete.

Predicting Service Life of Concrete Structure Exposed to Sulfuric Acid Environment by Grey System Theory

This paper investigated the sulfuric acid resistance of concretes with fly ash (FA) replacement ratios of 0, 20, 30 and 40% and coated with two types of concrete surface coatings. As an index for degree of acid corrosion, the acidification depth with corrosion time was evaluated by an accelerated laboratory test. The test program involved continuous acid immersion of specimens and alternate wet–dry cycles of acid exposure of other specimens. The relations between the acidification rate coefficient, its FA replacement as well as the pH value of the acidic exposure solution was investigated while assuming Fick’s 1st law of diffusion. The grey model (GM) for concrete acidification prediction was established by adopting the grey system theory, which comprehensively considered the effects of the FA replacement and pH value of acid. The GM model was then applied to predict the impact of pH value, thickness of concrete cover and surface coatings on the service life of concrete structure in different sulfuric acid environments. It was found that the concrete deterioration due to alternate wet–dry cycles of exposure to acid is more severe than continuous acid immersion, and the water-based protective coatings for as-cast finish concrete (PCC) and the deep penetrating sealer (DPS) were highly effective in reducing the acid attack. Compared with the increase of the thickness of concrete cover, the application of the PCC and DPS coatings significantly extended the service life of concrete.

Prediction of internal relative humidity in concrete modified with super absorbent polymers at early age

Shrinkage of high-performance concrete (HPC) mixtures may ultimately lead to early-age cracking and a reduction of service life of concrete structures. Autogenous and drying shrinkage are direct consequences of the decrease of internal relative humidity (IRH) due to self-desiccation and external drying. Therefore prediction of shrinkage of HPC requires the knowledge of IRH variations. Internal curing (IC) with super absorbent polymers (SAPs) is utilized to mitigate the shrinkage of HPC. Although investigations on IRH in concrete have been conducted, the prediction model for IRH in early-age concrete internally cured with SAPs in consideration of both water-to-cement (w/c) ratio and critical time is still lacking. Therefore investigations on predicting the IRH in early-age concrete internally cured with SAPs were conducted in present study and results showed that: (1) a prediction model for the working w/c ratio in early-age concrete internally cured with SAPs was proposed in consideration of age, effective and IC w/c ratios of concrete; (2) a prediction model for the critical time of IRH was proposed in consideration of both effective and IC w/c ratios; (3) a prediction model for the IRH in early-age concrete internally cured with SAPs was proposed in consideration of working w/c ratio, critical time, and age. These models showed the good accuracy of the test results.