Chloride Ingress Research Articles

Chloride Penetration of Recycled Fine Aggregate Concrete under Drying-Wetting Cycles.

Recycled fine aggregate (RFA) produced from concrete waste is commonly used in the construction industry; however, its use for structural concrete members has not been extensively studied. Moreover, its durability in a drying-wetting cycle environment still needs to be examined. In this study, the intrusion process of chloride in concrete under the drying-wetting cycles is experimentally characterized. Chloride penetration tests are carried out on concrete with the incorporation of different RFA replacement rates and mineral admixtures (i.e., fly ash and silica fume). The results show that the chloride penetration of recycled fine aggregate concrete (RFAC) is dependent upon the performance of the concrete itself, while the deterioration of chloride ion erosion resistance is due to the combined action of the replacement rate of RFA and the drying-wetting cycles. The incorporation of RFA degrades the properties of RFAC owing to its drawbacks in the degradation of interfacial properties of RFAC. Exposure to the drying-wetting cycle environment causes the content of free chloride ions in RFAC to increase initially before decreasing with the erosion depth, thereby showing an obvious convection zone and diffusion zone. The incorporation of the mineral admixture can effectively improve the compactness of the concrete microstructure and make concrete less susceptible to chloride ions ingress. RFAC mixed with 15% fly ash and 10% silica fume has a comparable resistance to chloride penetration as a natural aggregate concrete, which is a feasible method for the application of RFA.

Assessment of long term durability properties of blended fly ash-Rice husk ash alkali activated concrete

This study evaluates the long term (up to 365 days) durability properties (i.e., absorption and permeability properties) of a blended fly ash-rice husk ash (RHA) AAC and compares the results with 100 % fly ash AAC. The results showed that the addition of RHA adversely affected the durability characteristics. Degradation of the alkali-activated binder through long-term crack propagation (initiated during heat curing) due to the formation of efflorescence products is identified as one of the major factors contributing to the deterioration observed. The combined effect of the degree of crack propagation and the homogeneity within the microstructure are the main factors that influence the long-term durability properties of blended fly ash-RHA AAC. However, the blended fly ash-RHA AAC had a lower chloride diffusion coefficient at both 28 and 365 days and a higher maturity factor than 100 % fly ash AAC, indicating improved resistance to chloride ingress over time. Overall, the crack propagation becomes the dominant mechanism over the longer term (365 days) despite initial ongoing alkali activation.

Estimation of safe cover thickness to steel reinforcement in coastal structures addressing several tidal stations

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.

Multifunctional silane-based superhydrophobic/impregnation treatments for concrete producing C-S-H gel: Validation on mockup specimens from European heritage structures

Many of the concrete structures that conform our modern cultural heritage are in need of repair and protective interventions. Silane-based impregnation treatments can be used to repair onset cracks and reinforce the surface due to their ability to produce silica and C-S-H gels, and can be modified by incorporating hydrophobic precursors to create multifunctional treatments that also protect from water ingress.Since the effectiveness of impregnation treatments is dependent on substrate properties and chemical-physical changes it may have experienced over time, validation using standard materials may not always be representative of on-site application. In this work, the effectiveness of three innovative silane-based impregnation treatments developed by our group (two of them combining superhydrophobic properties) was evaluated on mockup specimens, which simulate the properties of the cementitious materials from six different heritage structures across Europe, artificially aged to simulate weathering by three methods: carbonation, chloride ingress and physical damages (freeze–thaw and thermal cycles).The characterization of the treatments showed they are compatible in terms of chemical interaction, applicability and minimal aesthetical alterations. Surface resistance and ultrasound pulse measurements have been used to assess the improvement in mechanical properties. The incorporation of hydrophobic components and fumed silica has a relatively low impact over the mechanical properties while it significantly reduces water absorption and grants water repellent properties to the surface, giving rise to a superhydrophobic performance.

Durability evaluation of reinforced concrete with surface treatment of soy methyl ester-polystyrene under freeze-thaw cycles and calcium chloride

This study provides an advanced understanding of the durability performance of reinforced concrete (RC) with the surface treatment of soy methyl ester-polystyrene blend (SME-PS) when simultaneously subjected to freeze-thaw (F/T) cycles and CaCl2 solution. A three-in-one nondestructive test, which included salt scaling test, electrochemical measurement, and acoustic emission (AE), was developed to enable the advanced investigation on the performance of SME-PS. Compared with control specimens, RC specimens treated with SME-PS exhibit superior salt scaling resistance with only minor damage after 60 F/T cycles. SME-PS can also reduce the corrosion risk of embedded steel by mitigating carbonation and chloride ingress in concrete. The physical protection of SME-PS lies in the modification of the concrete surface by changing its hydrophobicity and occupying/blocking a portion of capillary pores. Petrographic examinations and AE results revealed that a portion of penetrated SME-PS in concrete surface (i.e., top ∼ 1 mm) could be leached by external fluids, which indicated the long-term effectiveness of SME-PS should be further studied.

Comparison of different types of self-healing concrete under extreme conditions

Extreme environments are aggressive for concrete structures, hence a performance-based design is crucial to guarantee the durability during the service life. Nonetheless, there is a knowledge gap regarding the influence of cracks on standard and self-healing concrete. This research focuses on monitoring cracked self-healing concrete with two commercial healing agents: a bacteria-based healing agent (BAS) and a crystalline admixture (CA). After crack formation and a healing process of three months in wet/dry conditions (4 days/3 days), several extreme conditions were considered: (1) submerged in artificial seawater, (2) submerged in a solution with 33 g/L sodium chloride and (3) freeze-thaw (FT) cycling with de-icing salts. Microscopic images were used to quantify the healing efficiency of the two different healing agents, while chloride ingress and scaling were measured to determine durability. The results of the microscopic measurements indicated significant healing efficiency for both healing agents after the healing regime reaching 72% for CA, and 67% for BAS. After exposure to a marine environment, this efficiency increased to 95% and 92%, respectively. The uncracked BAS samples achieved a scaling reduction of 93% under FT exposure relative to the uncracked REF samples, while this was 49% for the CA samples. In cracked samples, scaling was reduced by 50% for BAS and 24% for CA, relative to the cracked REF samples. In all tested conditions, the BAS samples partially prevented the chloride ingress through the crack, while CA samples showed a great reduction. Overall, both healing agents reduced the degradation and could decrease the chloride ingress.

Efeito da duração e pressão da cura por carbonatação do concreto em perfis de cloreto

Abstract Carbonation curing alters the characteristics of the concrete's microstructure and can interfere with the penetration of aggressive ions. The objective of this article was to evaluate the influence of CO2 pressure and carbonation cure time on chloride profiles. Concrete specimens were cured by carbonation with CO2 pressures ranging from 5 to 25 Psi, for a time within the carbonation chamber of 8, 24, and 36 hours. These concretes were subjected to 30 wetting and drying cycles in NaCl solution to stimulate the chloride ingress. The carbonation depth and the microstructure of the concrete were monitored over time. Chloride profiles were obtained and modeled by 4 mathematical equations. The results showed that the combination of less time and CO2 pressure during carbonation curing potentiated the reduction of chloride penetration in concrete. Also, the carbonation curing conditions of 5 and 10 Psi for 8 hours reduced the chloride diffusion coefficient.

Electrical Resistivity of Crumb Rubber Concrete (CRC) exposed to coastal zone- An Experimental Investigation

Electrical resistivity is a material property that can be used for analysis of concrete durability and also can be used to determine early age characteristic of fresh concrete. Electrical resistivity has developed as a new form of non-destructive testing technique. In this study, an experimental study is carried out to determine the electrical resistivity of crumb rubber concrete exposed to normal and coastal environment. Crumb rubber concrete (CRC) is a concrete in which sand is replaced with fine rubber crumb obtained by shredding of waste vehicle tires. In this study, sand was replaced up-to 15% in multiples of 2.5% and then a set of samples were kept for curing and exposure in normal environment and other set of samples were exposed to coastal environment along the coast of Visakhapatnam, Andhra Pradesh. The result obtained indicated that CRC samples showed lower electrical resistivity in the initial days and then resistivity increased at later stages. Chloride ingression test was also conducted on the samples which indicated that crumb rubber concrete showed better resistance to chloride ion penetration. Overall, the result analysis expressed that samples exposed to coastal zone showed lower resistivity, and CRC samples in case of both curing methods and exposure cases showed better resistivity to electrical conduction and chloride ingression than normal concrete samples. So as CRC shows better durability properties than normal concrete, it can be opted as a choice for concrete structures in coastal areas.

Corrosion Behavior in RC Member with Different Cover Depths under Cyclic Chloride Ingress Conditions for 2 Years

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.

Long-term performance of structural concretes in China southeast coastal environments exposed to atmosphere and chlorides

This paper investigates the long-term performance of structural concretes in China southeast coastal area, the city of Shenzhen, exposed to atmosphere and chlorides. The structural concretes, incorporating large quantity of supplementary cementitious materials (SCM), were among the first massive application of such mixtures in construction in China. In both cases, in-field sampling and tests have been conducted during more than 20 years for the resistance of concretes to carbonation and chloride ingress respectively. The synthetic analysis of these results shows that (1) the concretes have substantial strength growth in atmospheric environment with exposure age, but the carbonation rate does not all obey the square root law of exposure time; (2) the protection of silane impregnation of high-performance concrete against chloride ingress maintains its hydrophobic effect after nearly 20 years; (3) Notable “skin” effect of surface concrete was observed for both atmospheric and marine exposures.

Effect of High-Pressure Washing on Chloride Ingress in Concrete – Development of an Accelerated Test Method

Abstract 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.

Transfer Parameter Analysis of Chloride Ingress into Concrete Based on Long-Term Exposure Tests in China’s Coastal Region

Chloride penetration resistance is one of the most important performance measures for the evaluation of the durability of concrete under a chloride environment. Due to differences in theory and experimental conditions, the durability index (chloride diffusion coefficient) obtained from laboratory accelerated migration tests cannot reflect the real process of chloride ingress into concrete in the natural environment. The difference in test methods must be considered and the transfer parameter kt should be introduced into the service life prediction model when the test results of accelerated methods are used. According to the test data of coastal exposure in South China, the attenuation rule of the chloride diffusion coefficient of different cement-based materials changed with time and was analyzed in this paper. Based on the diffusion coefficient-time curve, the theoretical natural diffusion coefficients of 28 d and 56 d were deduced, which were compared with the chloride diffusion coefficients obtained from the non-steady-state rapid migration method (RCM) at the same age. Therefore, the transfer parameter kt that expounds the relationship between concrete resistance to chloride permeability under a non-stationary electrical accelerated state and natural diffusion in the marine environment can be calculated; thus, the RCM testing index can be used to evaluate the long-term performance of the concrete structure in the marine environment. The results show that the value of kt was related to environmental conditions, test methods, and binder systems.

Effect evaluation of microbial mineralization for repairing load-induced crack in concrete with a cyclic injection-immersion process

This study presents the experimental investigations on repairing the load-induced cracks in concrete with microbial mineralization technology. Two groups of load-induced cracked concrete specimens, splitting specimens and bending specimens, with crack widths in range of 0.05–0.10 mm and 0.10–0.30 mm were prepared, respectively. Bacillus pasteurii (DSM 33) was selected to repair these cracks using microbially induced calcium carbonate precipitation (MICP) method. The repair effectiveness on crack healing was evaluated by means of visual observations, ultrasonic measurement tests, rapid chloride migration (RCM) tests and splitting tensile strength tests. The results indicated that after MICP treatment the resistance of repaired cracked specimens to chloride penetration could be effectively improved. Comparison of repair effectiveness between splitting specimens and bending specimens showed that the former had slightly better crack recovery than the latter. For both cracked specimens, the improvement coefficient which can reflect the repair effectiveness decreased from nearly 90–70% with increasing crack width from 0.05 mm to 0.23 mm. Scanning electron microscope (SEM) and energy dispersive spectrum (EDS) tests revealed that the formation of microbial induced CaCO3 precipitation would accumulate and fill the concrete crack, which is believed to be the reason of improving resistance to chloride ingression in the repaired cracked specimens. Besides, for repaired splitting cracked cylinders, their mean splitting tensile strengths could recover around 65.8% and 52.6% for crack width intervals of 0.05–0.10 mm and 0.10–0.30 mm, respectively.

Effect of coarse aggregate size on corrosion of reinforced concrete exposed to carbonation and chloride ingress by electrochemical measurements

This article evaluated the application of electrochemical techniques to assess the degree of corrosion of reinforcement steel in concrete exposed simultaneously to carbonation and chloride ingress. After carbonation accelerated at 3 different levels, the reinforcement corrosion was accelerated by the ionic migration of chlorides. Subsequently, the electrochemical techniques (Rp, cyclic voltammetry, EIS) were applied to the specimens at 40 months of age. Chloride penetrations above 20 mm showed a remarkable drop in steel durability. In this condition, the disappearance of the stability region in the voltammograms and an increase in the capacitive arc of the impedance spectra were identified. The intensification of carbonation reduced the Rp. Concretes with 25 mm coarse aggregate had the worst results in the electrochemical tests since the sharp drop in the phase angle during EIS tests indicates a concrete/reinforcement interface incapable of retaining electrical charges, with a low resistance to corrosion progress. The results of mass loss supported this statement.

Impacts of climate change on long-term reliability of reinforced concrete structures due to chloride ingress

This paper presents the effect of climate change on the long-term reliability of concrete structures due to chloride ingress. The impact has been demonstrated for three regions across the globe for the best and worst-case climate change scenarios. The methodology adopted here can be divided into three main steps. The first one is the development of a machine learning regression model using CatBoost for estimation of surface chloride levels, which is a function of temperature, concrete material properties, exposure conditions, and chloride levels in the seawater. The CatBoost model fitted over the experimental data has a mean absolute error (MAE) and root mean square error (RMSE) value of 0.11 and 0.16, respectively, and a high R2 value of 0.82. The second step is solving the coupled non-linear partial differential equation for temperature, humidity, and chloride ingress in concrete with time. A parametric study considering the effect of external parameters (temperature, humidity, exposure condition, and chloride levels in water) reveals the complexity and the dependencies of the chloride ingress process on external parameters. The final step involves the reliability analysis to estimate the time for chlorides to reach threshold levels at the rebar level using the numerical model. The input for the numerical model is temperature and humidity condition for different representative concentration pathways (RCP) scenarios, the material properties of concrete, and the exposure conditions. The reliability analysis shows that, for the concrete structure located in Dubai, UAE, and Cascais, Portugal, the mean time to corrosion initiation decreases due to climate change and it increases for the structure located in Tasmania, Australia. Further, the structures that are built in the future may have lower service life compared to the structures that were built in the past. Based on the study it concluded that it is necessary to consider the impact of climate change on service life to design resilient structures.

WATER-REPELLANT EFFECT OF REINFORCED CONCRETE (RC) BEAM COATED WITH A SURFACE-PENETRANT

Concrete coated with surface-penetrant is an efficient method to improve durability because it can decrease the ingress of deterioration factors such as water and chloride ions. Our previous study had focused on a silane-based penetrant having high water-repellant effect and examined the freeze-thaw (F-T) durability of the concrete coated with the penetrant. As well as F-T action, the water-repellant effect must decrease the possibility of deterioration related to water and chloride ions ingress. It is well known that water in pore of concrete is a compromising factor to decrease the fatigue durability of RC structures. The effect of surface-penetrant may be significantly varied by microscopic pore structures in concrete. Hence, the study prepared concrete cylinders and RC beam specimens made by wide range of water-cement ratios (w/c) from 0.55 to 1.0. Noting that the low-strength concrete made by the w/c = 1.0 is very unusual for structural concrete. However, such low strength properties are occasionally observed in short-span RC bridges constructed in 1960s or earlier. Hence, the study examined the effect of the surface-penetrant by using various w/c concretes. The paper reports the fundamental investigations of penetration depth and fatigue durability of the coated RC beams.

Chloride Diffusion Prediction in Concrete through Mathematical Models Based on Time–Dependent Diffusion Coefficient and Surface Chloride Concentration

This paper compared several mathematical models predicting chloride penetration in concrete by employing a time-dependent diffusion coefficient for a number of analytical solutions of Fick’s second law. We propose calibrated models that consider a time-dependent build-up of the surface chloride concentration Cs. Predicted values and measured values of chloride profiles from experimental results were compared, which showed that the calibrated models considering a time-dependent surface chloride concentration could significantly improve the correlation compared with the conventional models employing a constant surface chloride concentration. Moreover, we investigated several factors (i.e., skin effect, aging factor m, exposure conditions, curing conditions, water/binder ratio, and fly ash content) that may affect chloride penetration in concrete by adopting the calibrated models. The results showed conclusively that these factors also significantly affected the accuracy of the chloride penetration obtained by these calibrated models. Finally, the results predicted by the calibrated Tang–Gulikers model were proved to be reasonably accurate in concrete with a small water/binder ratio compared with the experimental data. It is concluded that the calibrated Tang–Gulikers model can be applied for predicting chloride penetration and solving relevant service-life problems resulting from chloride ingress in concrete.

Experimental study of the effects of graphene nanoplatelets on microstructure and compressive properties of concrete under chloride ion corrosion

In a marine environment, chloride ingress has the most prominent effect on the durability of concrete. The effect of graphene on the microstructure and compressive properties of concrete subjected to long-term chloride ion corrosion was investigated in this study. The results showed that an increase of up to 20.92 %, 21.97 %, 19.13 %, 19.43 % and 17.81 % is achieved in compressive strength respectively due to the addition of 0.05 wt% graphene nanoplatelets (GNPs) after 0, 40, 80, 120 and 240 days of immersion in sodium chloride solution, compared with ordinary concrete. With an increase in chloride ion deterioration time, the dynamic elastic modulus of graphene concrete gradually increased. The SEM, XRD, compressive performance and chloride ion content test results of the two concretes show that graphene concrete has better and more stable chloride ion resistance than ordinary concrete.

Analytical solution for chloride diffusion in concrete with the consideration of nonlinear chloride binding

An analytical study is presented on the diffusion of chloride in concrete coupled with the effect of nonlinear chloride binding. A double-segment piecewise linear chloride binding isotherm (the DS-PWL isotherm) is proposed that can fit well quite a number of experimentally measured chloride binding isotherms which were reported by many published works. The proposal of the DS-PWL isotherm makes feasible the development of analytical solutions for chloride diffusion in concrete that accommodate nonlinear chloride binding, which is not feasible at present. Based on the proposed isotherm, an analytical solution is obtained for one-dimensional diffusion of chloride in a semi-infinite concrete medium in the context of nonlinear chloride binding. The obtained solution is successfully validated against numerical solution for mathematical correctness while the proposed analytical model is shown to be in tolerably good agreements with a reported chloride diffusion experiment. Moreover, the proposed model is also shown to be in good agreements with the Freundlich-based model, exhibiting a desirable applicability. Parametric study is conducted using the proposed solution to examine the influence of each of the three DS-PWL characterizing parameters on chloride diffusion. Finally, the proposed solution is applied to investigating the influence of nanomaterial addition (the dosage of addition and the type of the nanomaterial added) on the service life of an RC structure member subjected to chloride ingress.

Corrosion‐induced damages and failures of posttensioned bridges: A literature review

AbstractCorrosion of posttensioned bridges raises great concern, since the only way to safely assess the condition of the tendons is through destructive evaluation. In this scenario, this paper presents the results of an extensive literature review on reported cases of corrosion of posttensioned bridges and few prestressed structures. The aim is to increase knowledge about the structural consequences of possible corrosion‐induced failure mechanisms. The cases were rated according to the increasing severity of the observed damage and consequent interventions as follows: ordinary maintenance is effective, extraordinary maintenance is necessary, and maintenance is insufficient or absent. It was found that most corrosion‐sensitive structures were segmental and box section beam bridges. Most cases required extraordinary maintenance. Warning signs were often observed. The damage was mainly ascribed to design and execution mistakes that facilitated the ingress of external chlorides causing corrosion. The paper concludes with a discussion of the consequences for structural safety.