Chloride Penetration In Concrete Research Articles

Numerical modelling on coupled behavior of calcium leaching and chloride transport in cement-based materials by considering ion desorption

Concrete structures serving in water environment with rich chloride ions are subjected to the coupling action of calcium leaching and chloride corrosion. In this paper, a transport model of calcium and chloride ions coupled with the calcium solid-liquid equilibrium equation is proposed to simulate the behavior of calcium leaching and chloride penetration in concrete. In the model, the effect of free chloride ions bound by solid calcium and the release of bound chloride ions caused by the dissolution of solid calcium is considered. Secondly, the model is numerically solved by using the finite difference method of Crank-Nicolson scheme. Then, the experimental data of porosity and calcium silicon ratio, chloride concentration are compared to the calculated results to validate the model. Finally, a numerical simulation is conducted to analyze the evolution of ion concentration, solid calcium content and porosity of cement paste slice exposed to deionized water and accelerated dissolution solution. The results show that, the concentration of calcium ion decreases with corrosion time, while that of chloride ion increases. There are concentration gradient distributions of calcium and chloride ions in the slice. The higher the concentration of accelerated dissolution solution, the larger the porosity of cement paste and the higher the concentration of chloride ions in the paste. It indicates that, the calcium leaching accelerates the chloride penetration into concrete. In addition, the dissolution process of solid calcium, i.e. calcium hydroxide first dissolves followed by C-S-H gel, are presented.

Theoretical model for the coupling effect of moisture transport on chloride penetration in concrete

Concrete's internal pore structure crucially influences the rate at which moisture and chemicals, e.g., chloride, move through concrete. This paper explores the coupling effect of moisture transport on the chloride penetration in both saturated and non-saturated concrete, which arises because moisture carries chloride ions as it moves through the pores. To characterize simultaneous moisture and chloride movement in general, a modified Fick's first law can be used for the flux of chloride ions as well as the flux of moisture. A mathematical model is developed based on a multiscale approach for the effective humidity diffusion coefficient, accounting for different moisture diffusion mechanisms in different sizes of pores: Molecular, Knudsen, and Surface diffusions. Based on the results for humidity diffusion coefficient, a material model for the coupling parameter was developed. Validation based on available experimental results demonstrated excellent agreement in predicting pore relative humidity and chloride content profiles.

Durability of concrete incorporating recycled coarse aggregates: carbonation and service life prediction under chloride-induced corrosion

The use of recycled aggregates (RA) is growing due to the environmental problems associated with extracting natural aggregates (NA) and the disposal of construction and demolition waste (CDW). However, the service-life prediction of recycled coarse aggregate concretes remains incipient. Thus, this study aimed to evaluate the effects of different replacement contents of NA by RA (25, 50, and 75 wt%) on physical (water absorption, porosity, and bulk density), mechanical properties (compressive strength and modulus of elasticity), microstructure (evaluated by X-ray microtomography), accelerated carbonation, and chloride penetration of concrete. A service life prediction analysis of RA concretes was conducted based on the chloride profile obtained and considering the application of different concrete surface treatments. The RA contents evaluated increased the carbonation and chloride diffusion coefficients by 75.7% and 43.0%, respectively, compared to the reference concrete. Nevertheless, reductions of approximately 50% on the critical chloride concentration depth of RA concretes are estimated considering the application of acrylic-based surface treatment. Therefore, applying surface treatments is promising to increase RA concretes' durability and service life, contributing to its wide use and dissemination feasibility.

Deep learning-based prediction for time-dependent chloride penetration in concrete exposed to coastal environment

The application of deep learning methods in civil engineering has gained significant attention, but its usage in studying chloride penetration in concrete is still in its early stages. This research paper focuses on predicting and analyzing chloride profiles using deep learning methods based on measured data from concrete exposed for 600 days in a coastal environment. The study reveals that Bidirectional Long Short-Term Memory (Bi-LSTM) and Convolutional Neural Network (CNN) models exhibit rapid convergence during the training stage, but fail to achieve satisfactory accuracy when predicting chloride profiles. Additionally, the Gate Recurrent Unit (GRU) model proves to be more efficient than the Long Short-Term Memory (LSTM) model, but its prediction accuracy falls short compared to LSTM for further predictions. However, by optimizing the LSTM model through parameters such as the dropout layer, hidden units, iteration times, and initial learning rate, significant improvements are achieved. The mean absolute error (MAE), determinable coefficient (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE) values are reported as 0.0271, 0.9752, 0.0357, and 5.41%, respectively. Furthermore, the study successfully predicts desirable chloride profiles of concrete specimens at 720 days using the optimized LSTM model.

Multi-scale modelling and statistical analysis of heterogeneous characteristics effect on chloride transport properties in concrete

The transport properties of concrete are closely related to its heterogeneous features. In this study, by considering the multi-scale microstructural characteristics, the chloride transport properties of concrete are comprehensively analysed. Based on the selected representative elementary volumes from bulk cement paste to concrete, a multi-scale predictive model was first proposed for diffusivity prediction of bulk cement paste, mortar and concrete. By taking the hydration process, the presence of sand/interfacial transition zones (ITZs) and the aggregate shape into account, the predicted diffusivities of each scale were validated against the experimental results. To further analyse the weights of different heterogeneous characteristics on chloride transport properties of cementitious materials, a statistical analysis method (principal component analysis) was then adopted based on the modelled results. The analysed results indicated that the capillary pore and C-S-H parts dominate the diffusivity estimation of bulk cement paste, and the consideration of ITZ and multi-species ions interaction can enhance the prediction accuracy for diffusivities of mortars and chloride penetration depths in concrete, respectively. The proposed multi-scale framework provides a novel perspective to study the chloride penetration in concrete by considering the effects of both the multi-scale microstructural characteristics and multi-species interactions, which can also enhance the understanding of deterioration mechanisms for reinforced concrete structures serving in a complex or marine environment.

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.

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.

All-solid-state chloride sensor for in-situ monitoring of chloride penetration in concrete

In this study, an all-solid-state chloride sensor constituted with Ag/AgCl working electrode and Mn/MnO2 reference electrode was developed. The Ag/AgCl electrode fabricated with galvanostatic anodization method and Mn/MnO2 fabricated with powder compaction method exhibited homogeneous micro-structures. The as-prepared chloride sensor showed good ability of polarization resistance, long-term stability, perfect Nernst response, and low hysteresis effect in solutions. The influence of pH, temperature, and interfering ions on the chloride response of the sensor was also systematically investigated. Furthermore, the chloride sensor was embedded in the mortar specimen and used to monitor the chloride penetration process during the capillary absorption test. The results indicate that the chloride sensor can provide accurate chloride content variations of the mortar specimens, and it has great potential for non-destructively monitoring the chloride penetration in concrete structures.

Effect of Carbonation on Chloride Maximum Phenomena of Concrete Subjected to Cyclic Wetting-Drying Conditions: A Numerical and Experimental Study.

The combined action of chloride and carbonation generally accelerates chloride penetration in concrete. Plenty of studies have revealed a chloride maximum phenomenon in the chloride profiles of concrete under wetting and drying cycles, which affects the accuracy of the service life prediction of concrete structures. Carbonation is probably one of crucial factors inducing chloride maximum phenomena. To investigate the influence of carbonation on chloride distribution of concrete subjected to cyclic wetting–drying conditions, this study established a numerical model coupling carbonation effect, simulated chloride distribution at different carbonation degrees, and verified the simulation results with experimental results. The results show that a chloride peak appears in all predicted chloride profiles when carbonation effect is taken into account, and the higher the carbonation degree is, the more significant the chloride peak is. This demonstrates that carbonation can enhance the forming of chloride maximum phenomenon under cyclic wetting and drying. Moreover, the calculated results are highly consistent with the experimental results under different carbonation conditions, especially in terms of the peak chloride concentration and the corresponding depth. Furthermore, the significance degree of the chloride maximum phenomenon is closely related to some key parameters, such as CO2 concentration, environmental humidity, and temperature.

Chloride Ingress into High-Performance Concrete Containing Graphene Oxide Nanoplatelets and Ground Granulated Blast Furnace Slag under Different Conditions of Water Pressure and Temperature

In this study concrete samples were made by addition of 0.1wt.% Graphene Oxide (GO) and 50wt.% Ground Granulated Blast Furnace Slag (GGBFS). Tests on mechanical and chloride permeation properties were conducted. Concrete samples exposed to pressurized 3.5% NaCl aqueous solution under time and temperatures. The water pressure was at 0.1, 0.3 and 0.7 MPa. The chloride concentration profiles at different conditions were measured. The results show that the addition of 0.1 wt.% GO and 50wt.% GGBFS increased the compressive strength of concrete sample by 19.9% during 28 days and 17.6% during 90 days compared to ordinary concrete sample. Concrete with a combination of 0.1wt.% graphene oxide and 50wt.% granular slag had an increase in flexural strength of 15% during 28 days and 13.6% during 90 days. A high reduction in electrical conductivity from 4012C to 1200C was observed for 90-days cured concrete containing GGBFS and GO compared to the ordinary concrete. Chloride ion content was substantially enhanced by increase in water pressure and exposure time. The convection-diffusion coupling is the main mechanism of the transfer of chloride ion in concrete in this research. The mix with 0.1wt.% GO and 50wt.% GGBFS was shown considerable performance on chloride penetration in concrete. This admixure reduced the chloride penetration by up to 17.6% in 90 days compared to ordinary concrete. Chloride ion penetration is curtailed when GO and GGBFS are added to ordinary concrete. Pozolanic reaction effects in concrete leading to the filling of the pores are factors in the proposed curtailment mechanism.

Influence of Salt Type and Seasonal Variation on Chloride Penetration in Concrete with Deicer Salt

Influence of Salt Type and Seasonal Variation on Chloride Penetration in Concrete with Deicer Salt

Enhanced concrete performance in cracking resistance and chloride penetration using hybrid fiber blends

The fracture response and resistance to chloride penetration of concrete reinforced with discrete steel fibers (SF) and hybrid blend of steel and macro polypropylene fibers (HyFRC) are evaluated. A significant improvement in fracture response is obtained in HyFRC compared to SF. Cohesive stress-crack opening (σ-w) relationships are obtained for the concrete with and without discrete reinforcement from the measured fracture test responses. The hybrid fiber blend has a higher tensile strength and a significantly higher stress resistance to crack opening when compared to an identical volume fraction of steel fibers. HyFRC also exhibit a lower chloride penetration when compared to control and SF concrete mixtures. The hybrid blend of steel and polypropylene fibers provides improved structural performance due to enhanced resistance to crack opening and an improvement in the durability by reducing the chloride penetration in concrete.

Application of ferronickel slag as fine aggregate in recycled aggregate concrete and the effects on transport properties

Industrial and construction solid waste regarded as a hazardous material has given rise to the potential threats of environmental pollution. The ferronickel slag (FNS) as an industrial by-product and recycled concrete aggregates (RCAs) derived from construction and demolition wastes have potential for sustainable use as the fine and coarse aggregate in concrete, respectively. However, less information regarding the re-utilization of FNS as fine aggregate in recycled aggregate concrete (RAC) and the effects on transport properties can be found in the previous literature. The aim of this study is to investigate the compressive strength and transport behavior of RAC incorporating FNS as fine aggregate. In this study, several groups of specimens with different replacement ratios of FNS as fine aggregate (0, 20%, 40% and 50%) and RCAs (0, 50% and 100%) as coarse aggregate were prepared. The compressive strengths of FNS-RAC specimens at curing age of 3, 7 and 28 days were measured. The coupled effects of FNS and RCAs on the resistance to water absorption and chloride penetration of concrete were discussed. To explore the effect of microstructure on transport behavior, the tests of scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were further conducted. Overall, the sorptivity and chloride diffusion coefficient increase as the RCA replacement ratio increases, but they generally decrease with increasing of FNS content. The mixtures containing 40%–50% FNS fine aggregate in RAC exhibit the greater compressive strength and better resistance to transport behavior.

Evaluation of chloride diffusion in concrete using PSO-BP and BP neural network

Chloride diffusion is the major causes of deterioration of concrete structures in engineering. Because chloride diffusion experiments are time consuming, it is desired to develop a model to predict the chloride diffusion in concrete. In this paper, the optimizing of particle swarm algorithm (PSO) on BP neural network is adopted to predict the chloride penetration in concrete. For purpose of building these models, training and testing pattern is gathered from the technical literature. PSO-BP neural network can improve BP disadvantage. PSO-BP neural network is better precision than BP neural network through the results of PSO-BP, BP and experiments. The research results demonstrate that PSO-BP neural network is an effective tool in the prediction of chloride diffusion.

Chloride penetration in concrete under wave impact action

In this paper, a washing-machine-shaped experimental device is presented to investigate the effect of marine environments on the penetration of chlorides in concrete. The proposed experiment is used to simulate different flow speeds and wave patterns surrounding the concrete and examine their effects on the penetration of chlorides in the concrete. The obtained experimental results show that there is a significant difference in chloride profiles between the specimens exposed to a marine environment with flow and wave actions and those immersed in a stationary solution. The difference is found to increase with exposure time, suggesting the importance of considering the marine environment when predicting the long-term durability of concrete exposed in a marine environment.

Lattice Mesoscale modelling of Chloride Penetration in Concrete: Effect of aggregate volume fraction and fly ash

ABSTRACT Chloride ions penetrated into reinforced concrete member causes rebar corrosion and induces the volume expansion of the rebar and cracks of concrete cover. This study aims to predict the chloride ingress in the reinforced concrete member and its operational service life by using a lattice model. Concrete is considered at the mesoscale, which constitutes three phases: aggregates, cement matrix and interfacial transition zones (ITZ). Fick’s second law was implemented into the lattice model to describe the diffusion of the chloride ions within concrete. The diffusivity coefficient of aggregates is almost null, whereas those of cement paste and of ITZ are deduced from macroscopic diffusivity measure. Numerical solutions is validated against the test data and the analytical solution. The effect of the aggregate volume fraction is discussed. Curves, which help to determine the service life of the reinforced concrete structure from the cover thickness, is resulted from the lattice modelling for concrete with different aggregate volume fractions.

Influence of Crack Width on Chloride Penetration in Concrete Subjected to Alternating Wetting-Drying Cycles.

To investigate the durability of reinforced concrete (RC) beams under the combined actions of transverse cracks and corrosion, corrosion tests were conducted on a total of eight RC beams with different water–cement ratios and cracking states. The effects of the transverse crack width, water–cement ratio, and the length of the wetting–drying cycle on the distribution of the free chloride concentration, the cross-sectional loss of the tensile steel bars, and the chloride diffusion coefficient are analyzed. The results show that the widths of the transverse crack and the water–cement ratio of concrete greatly affected the chloride profile and content of the RC beam specimens. Specifically, the chloride contents in all the cracked RC beams at the depth of the steel bar exceeded the threshold value of 0.15%. As the width of the cracks increased, the chloride concentration and penetration of the cracked concrete beam increased. However, the chloride concentration at the reinforcement position did not seem to be obviously affected by increasing the wetting–drying cycles from 182 days to 364 days. Moreover, the decrease of the water–cement ratio effectively inhibited the penetration of chloride ions in the RC beam specimens. In terms of the cross-sectional loss of the steel bars, the average loss of the steel bar increases with increasing crack width for the beams with 182-day cycles, while the effect of crack width on the average loss is not as noticeable for the beams with 364-day cycles. Finally, a model is proposed to predict the relationship between the crack width influence coefficient, μ, and the crack width, w, and this model shows good agreement with the experimental results.

An alternating experimental study on the combined effect of freeze-thaw and chloride penetration in concrete

Abstract For the reinforced concrete structure in high latitude marine environment, the influence of freeze-thaw on chloride ion transport has been paid more and more attention. This paper intends to explore whether there is any other unknown coupling mode, by an alternating experiment of rapid freeze-thaw and chloride diffusion. For the purpose of data comparison, the tests of pure immersion diffusion are also carried out. It is found that the transport rate of chloride ions in the alternating test is significantly higher than that in the control groups; and the boundary concentration increases with the number of freeze-thaw cycles. The result indicates that there exists another influence mechanism of freeze-thaw on the transport of chloride ions, in addition to increasing the diffusion coefficient. Then, a new hypothesis mode is proposed and its mechanism is explained from the micro scale, i.e. the phase transition of pore solution during the freeze-thaw process can drive the migration of chloride ions dissolved in it.

Study of the environment factor from Fick’s and electrical resistivity models by simulation of chloride diffusivity prediction

The penetration of chlorides in concrete is the main reason for the beginning of corrosion in reinforced concrete structures exposed to a marine environment, reducing their service life. This article proposes correlations between the surface chloride content ( Cs) of Fick’s model and the ambient factor ( kCl) of a resistivity model. Literature data for three types of cement were used to simulate chloride diffusivity: (1) CEM I 52.5 R; (2) CEM II/A-P 42.5 R (with 6%–20% of pozzolans); and (3) CEM type II (with 12% of pozzolans and 8% of silica fume). Concretes containing these cements were analyzed for different environmental conditions: atmosphere zone, seawater immersion, and tidal/splash zones. The surface chloride contents were determined by a combination of Fick’s and resistivity models. In this article, it was noticed that the estimated Cs value varies with the exposure class from 0.484% to 0.644% (total chloride concentration by weight of cement). An equation has been proposed to correlate Cs with the ambient factor kCl of the resistivity model.

A mechanical-diffusive peridynamics coupling model for meso-scale simulation of chloride penetration in concrete under loadings

A coupled mechanical-diffusive peridynamics (PD) model is developed to simulate chloride penetration in saturated concrete under various loadings at meso-scale. PD is implemented in the architecture of finite element method (FEM) and truss elements are used to substitute for the PD bonds. In the coupled model, damage evolution and crack growth in concrete under loadings and chloride penetration into concrete with updated diffusivity caused by cracks can be investigated simultaneously. At each coupling step, the quasi-static mechanical analysis is conducted by solving the equilibrium equations, while the forward differencing method is adopted for chloride diffusion. Several numerical examples are carried out to validate the proposed PD models in terms of addressing mechanical-diffusive problems. The numerical results coincide with the test findings and clearly indicate that the width and depth of cracks can influence the chloride diffusivity when “threshold crack width” is reached. Additionally, the chloride diffusivity increases with the increase of stress level under high compressive, tensile and flexural stress levels.