Accelerated Chloride Migration Test Research Articles

Identification of chloride diffusion coefficient in concrete using physics-informed neural networks

The corrosion of steel caused by chloride is one of the important causes of the deterioration of reinforced concrete structures. In order to describe the transport behavior of chlorides in concrete and to make quantitative durability designs based on it, it is necessary to determine the chloride diffusion coefficient correctly. However, the commonly used analytical method is not suitable for the free chloride diffusion coefficient considering the nonlinear chloride binding capacity of concrete. In this study, by comparing the results of solving forward problems involving chloride transport equations using finite element method (FEM) and solving corresponding inverse problems using physics-informed neural networks (PINNs), it is verified that PINNs can be applied to identify the chloride diffusion coefficient in non-steady-state immersion tests and accelerated chloride migration tests considering no chloride binding, Langmuir binding, or Freundlich binding. The robustness of PINNs is verified by training with 5% and 10% noise data as observed data. The results of interpolation and extrapolation using PINNs trained successfully show its excellent generalization performance.

Effect of recycled aggregate and supplementary cementitious material on the chloride threshold for steel bar corrosion in concrete

Under marine environment, the passive film on the surface of steel bar embedded in reinforced concrete structures will be broken once a threshold value of chloride, i.e., chloride threshold (Cth), is reached at the rebar-concrete interface by diffusing through the concrete cover. The value of Cth is essential for determining service life of concrete structures. In this investigation, the effect of recycled aggregate (RA, i.e., recycled coarse aggregate) and supplementary cementitious material (SCM), including ground granulated blast furnace slag, red mud and glass powder, on the value of Cth was investigated. A chloride threshold test method for accurate determination of Cth was proposed by the alternation of accelerated chloride migration test and artificial-natural diffusion test, which can simulate the marine environment and accelerate the diffusion of chloride. The corrosion activity of steel bar was monitored using two electrochemical methods, including linear polarization resistance method and macro-cell corrosion method, to detect the initiation of corrosion. Immediately after the corrosion initiation, corresponding specimen was taken out to measure the chloride content of concrete adjacent to the surface of steel bar. A calculating method of chloride threshold Cth was presented considering the actual distribution of coarse aggregate in concrete adjacent to the surface of steel bar. The results of the chloride threshold tests show that RA and SCM have a significant influence on the protective properties of passive films, and it is worth noting that the positive effect of RA on the quality of passive film has been observed. For concrete with the same substitution level of SCM, the chloride threshold Cth increases linearly with RA content. Subsequently, the suggested values of Cth for natural aggregate concrete (NAC) with different substitution level of SCM are given, and the suggested values of Cth for corresponding recycled aggregate concrete can be given by an amplified factor kRA multiplied by Cth for NAC with ± 10% relative error.

Engineering Properties of Ternary Cementless Blended Materials

A new non-cement blended materials is developed as a full replacement of cement without alkali activator. This study was conducted to explore a suitable method for activating new ternary green materials with desulfurization gypsum, water-quenched blast-furnace slag and co-fired fly ash from circulating fluidized bed combustion as non-cement inorganic binder. Test subject was included flowability, compressive strength, absorption, total charge-passed from rapid chloride permeability test, chloride diffusion coefficient from accelerated chloride migration test and SEM observation. Test results indicate that a ternary mixture containing 1% desulfurization gypsum, 60% water-quenched blast-furnace slag and 39% co-fired fly ash was a suitable development in compressive strength. The new non-cement blended materials were performed a well compressive strength, lower absorption, and lower chloride diffusion coefficient. In addition, the compressive strength decreased as the inclusion of desulfurization gypsum increased. It was concluded that using desulfurization gypsum alone decreased the setting time and compressive strength. SEM micrographs were verified the development in compressive strength originated from the C-S-H and C-A-S-H gel produced by Ca(OH)2, SiO2, and Al2O3.

Semi-empirical prediction model of chloride-induced corrosion rate in uncracked reinforced concrete exposed to a marine environment

Chloride-induced corrosion of reinforcement in uncracked concrete was simulated by a test method combining an artificial-natural diffusion test (ANDT) and an accelerated chloride migration test (ACMT). The electrochemical kinetics of the corrosion process were evaluated by linear polarization resistance (LPR), weak polarization technology (WPT) and Tafel test, which indicates that the corrosion process is mainly under anodic control. Based on the hypothesis of anodic diffusion control, a semi-empirical prediction model for the corrosion rate in reinforced concrete has been proposed. This model reflects the effects of concrete resistivity, chloride content, chloride diffusion coefficient and concrete cover thickness on the corrosion rate. It also provides a non-destructive method to evaluate the corrosion rate of steel bars in uncracked concrete, which makes it convenient and available to the engineering community.

Investigation on chloride threshold for reinforced concrete by a test method combining ANDT and ACMT

Abstract Chloride threshold (Cth) of reinforced concrete structures in tidal zone of marine environment has been experimentally investigated. A new test method combining artificial-natural diffusion test (ANDT) and accelerated chloride migration test (ACMT) was proposed to simulate the marine environment and accelerate the chloride diffusion. Different definitions and expressions of Cth were discussed and Cth was defined as the chloride content required for activating the depassivation of steel bar and maintaining the aggressive pitting corrosion in present work. The effects of concrete cover thickness and steel type were then investigated. The results show that Cth decreases as concrete cover thickness increases and then remains steady. Moreover, ribbed bars can survive in a higher chloride concentration than plain ones. In view of the design parameters of reinforced concrete structures in tidal zone, Cth for hooping bar (plain bar) and longitudinal tensile bar (ribbed bar) is suggested to be 0.2% and 0.3% (total chloride content by weight of concrete), respectively. Also, a concept of critical pH was mentioned and a value of 11.0 may indicate a high risk of steel bar corrosion. Compared to the results in other field studies, this test method can be expected to be convincing and time-saving.

A modified accelerated chloride migration tests for UHPC and UHPFRC with PVA and steel fibers

Accelerated migration tests which are commonly used to measure chloride diffusion in ordinary cement-based materials cannot be directly applied to composite with very low permeability, such as Ultra High-Performance Fiber Reinforced concretes (UHPFRC). In order to assess the UHPFRC enhancement on the structural durability, there is a critical need to accurately assess the permeability level of the material to chloride ions. The objective of this work is to adapt an existing set-up of accelerated chloride migration test in order to (i) better characterize the resistance of chloride ion penetration in UHPFRC; and (ii) to compare the resistance of chloride ion penetration between UHPC and UHPFRC. The material characterization, the set-up modifications of the existing accelerated migration test, the results are presented. In conclusion, the modification of the test-set-up allowed to accurately measure chloride transport of very low permeability UHPFRC and to shed light on the effect of the fiber reinforcement.

Differences in Gradient Variations (ΔMs/ΔT) of the Chloride Ion Diffusion Coefficients between Mortar and Concrete at Different Temperatures

This paper reports differences in gradient variations (ΔMs/ΔT) of chloride ion transport behavior of mortar and concrete, as determined using the accelerated chloride migration test (ACMT). with a water/cement ratio of 0.45 and fine aggregate volume fractions of 60%, under different environment temperatures (25, 40, 60 and 80C) were evaluated according to the passage of chloride ions through the specimens using ACMT. The Nernest-Planck equation and a modification of Fick’s second law were used to calculate the steady-state chloride migration coefficients. For the temperature at different levels of 25 C to 80 C, the chloride ion diffusion coefficients (Ms) in order of magnitude were M45>C45>SF45.

Properties of Cement-based Composite Materials under Different Storing Environment Temperature

This study reports on the properties of cement-based composite materials (mortars) under different storing environment temperature, as determined using the accelerated chloride migration test (ACMT). Mortars with a water/cement ratio of 0.45 and five fine aggregate volume fractions (0%, 15%, 30%, 50% and 60%) under various environment temperatures (25, 40, 60 and 80°C) were evaluated according to the passage of chloride ions through the specimens using ACMT. Calculate chloride migration coefficients on the steady-state. Cement-based composite materials with 60 % fine aggregate presented a migration coefficient higher than that of other specimens, whereas mortar with 30 % fine aggregate was lower, due to the effects of dilution and tortuosity.

Chloride migration in structural lightweight aggregate concrete produced with different binders

This paper characterizes the chloride penetration resistance of structural lightweight aggregate concrete (SLWAC) produced with different types of aggregates and binders, for usual compressive strengths of about 20–65MPa. Concrete is characterized by means of capillary absorption, electrical resistivity and accelerated chloride migration tests. In general, it was found that the chloride penetration resistance can be substantially affected by the type of binder. Besides the microstructural refinement effect, the mineral admixtures should also affect the ionic composition of the pore solution. The type of aggregate had a little influence on the chloride penetration resistance. Chloride penetration resistance should not be related to the compression strength of concrete. However, chloride diffusion is exponentially related to the w/c ratio, regardless the type of aggregate. The capillarity and resistivity results did not correlate well with those from the chloride migration test. It is concluded that SLWAC with less porous aggregate can be at least as resistant as normal weight concrete.

A three-phase, multi-component ionic transport model for simulation of chloride penetration in concrete

Chloride-induced corrosion of reinforcing steel in concrete is a serious problem in the durability of structures. In order to predict how chlorides penetrate in concrete, unlike most existing models which consider the penetration of only a single species or in a single phase medium, this paper presents a numerical model considering the transport of multiple species in a multi-phase medium. The 2-D, 3-phase, multi-component ionic transport model proposed in the paper also considers ionic binding and the model is used to simulate the rapid chloride migration (RCM) test of concrete. The effects of aggregates, ITZs and ionic binding on chloride penetration in concrete are examined and discussed. The obtained result is also validated against experimental data obtained in an accelerated chloride migration test.

Determining the steady-state chloride migration coefficient of ITZ in mortar by using the accelerated chloride migration test

In this study, an electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. The steady-state chloride migration coefficient of mortar was determined experimentally as a function of the aggregate volume fraction to investigate the effect of aggregate content. The influence of the aggregate–cement paste interfacial transition zone (ITZ) on the steady-state chloride migration behavior in mortar was investigated using a three-phase model. The three-phase material was composed of cement paste matrix, aggregate, and ITZ. The chloride diffusion is considered to take place in the cement paste and the ITZ phases. The chloride flow is controlled by dilution in the cement paste, and the chloride flow is controlled by the combining effects of tortuosity and dilution in the ITZ. The experimental results are fitted with the three-phase model. Based on the experimental and regression analytical results, the approximate chloride migration coefficient of ITZ with different assumed thicknesses of ITZ is determined.

Evaluation of the sulfate resistance of fly ash and slag concrete by using modified ACMT

Pozzolanic concrete has been widely used in various projects. In this study, fly ash and slag concretes were placed in the solution of 5% sodium sulfate under drying–wetting and temperature change cycles and long-term immersion, to simulate the effect of structures in tidal zones and seawater, respectively. The durability of concrete is assessing by using modified Accelerated Chloride Migration Test (ACMT). The results indicate that adding 20% fly ash and 40% slag concrete curing at 23°C and 100% R.H. for 4months, the chloride ion non-steady state migration coefficient (Mn) were 69% and 28% that of ordinary concrete, respectively. Ordinary and fly ash concrete were placed in the solution of 5% sodium sulfate under drying–wetting and temperature change cycles for 12weeks, Mn were reduced to 82% and 33% of the initial value, respectively. This result represented that after the cycle procedure the ability of resisting chloride ion penetration increased. However, Mn of slag concrete became 2times of the initial value, it represented that slag concrete was deteriorated under drying–wetting and temperature change cycles. In addition, results showed that Mn was approximately 3–10times against steady state migration coefficient (Ms), and it is higher than the predicted value of the NIST program. This result indicating the modified ACMT will underestimate the durability of concrete, but it still can be a method for comparing durability of different kinds of concrete.

THE STUDY OF CHLORIDE ION TRANSPORT BEHAVIOR OF MORTAR UNDER DIFFERENT STORING ENVIRONMENT TEMPERATURES

This study presents the chloride ion transport behavior of mortar from accelerated chloride migration test (ACMT). The water/cement ratio of mortars is 0.45, and the five volume fractions of fine aggregates (0%, 15%, 30%, 50% and 60%) were evaluated. After stored under different environment temperatures (25°C, 40°C, 60°Cand 80°C), the chloride ion passing through specimens was carried out with ACMT. From the Nernest-Planck equation and modified Fick’s second law, test data could be calculate the chloride migration coefficient of non-steady-state and steady-state. For mortar structure, dilution and tortuosity effects are positive effect to resist the penetration of Chloride ion. On the contrary, ITZ and percolation effects are negative effect to resist the penetration of Chloride ion. Thus the migration coefficients of mortar at 60% volume fractions of fine aggregates is higher than other mixes because of ITZ and percolation effects.

THE RELATIONSHIP BETWEEN ACCELERATED MIGRATION TIME IN ACMT AND PONDING TIME IN PONDING TEST FOR CEMENT-BASED MATERIALS

The salt ponding test has been widely used in recent year to evaluate the durability of cement-based materials. However, the duration of more than 90 days salt ponding is considered as time-consuming. In this study, the electrochemical technique (ACMT; Accelerated Chloride Migration Test) is applied to accelerate the movement of chloride ion in the cement-based materials to reduce the duration of testing time. The chloride profiles are obtained from ponding test with various ponding times and ACMT with different accelerated migration times. The total amount of chloride in specimens are calculated from the profiles and compared. Based on the total amount of chloride, the equivalent accelerated chloride migration time to the ponding time is obtained. The experimental result shows that the total amount of chloride for the 9-, 10-, 11-, and 12-h accelerated migration time in ACMT is close to the 60-, 90-, 120-, and 150-days ponding time in ponding test, respectively.

Application of High Performance Concrete with Compound Admixtures of Fly Ash and Perlite Powder in Pavement of Highway

Based on former experimental achievement in laboratory, application and construction of high performance concrete (HPC) in pavement of highway were introduced to the paper. The HPC was proportioned with compound admixtures of 12% fly ash and 12% perlite powder replacing cement in equal mass. Perlite powder of both is a new mineral admixture, originated natural volcanic rock perlite composed of mainly aluminosilicate glass, was ground to mostly under 45 μm so as to possess pozzolanic activity, and then added to concrete as a supplementary cementitious material to substitute for partial cement. Multiplex of the two admixtures is profitable to increase workability, mechanical properties and durability during post-stage for concrete in varying degrees. The testing slump and construction fit of the fresh concrete in situ were shown that both of admixtures improved workability of the concrete. HPC samples remained in field and drilled from pavement were determined and investigated on mechanical properties and durability by means of test. It has been observed by inspected result of that flexural strength of these concrete are above 5 MPa at 28 cured days and compression strength about 40 MPa. The indexes of their abrasion resistance distribute throughout 1.94—2.63 kilo-rotation/mm at 90 days. These measured mechanical characteristics are so large enough to the technical specification of heavy traffic grade highway on mechanical property. To investigate durability of the HPC, the charge passed and the chloride diffusion coefficient in concrete at 90 cured days obtained from the accelerated chloride migration test were determined with RCM experimental equipment. The values of charge passed in the concrete were lower and ranged in 449—928 Coulomb, which revealed that the HPC are also better permeability resistance of chloride ion and be able to sustain in environment of chloride salt for 100 years. The chloride diffusion coefficients of the HPC were scattered in 1.4—4.7×10-12m2s-1. These parameters exhibited completely the HPC better or excellent for electrical indication of concrete’s ability to resist chloride ion penetration referent to relevant standards and information.

A rapid method to determine the chloride profile in cement-based materials by using electrical field

In this study, the electrochemical technique is applied to accelerate chloride-ion migration in cement-based material to estimate its permeability. This article presents a simplified procedure to obtain the chloride profile in cement-based materials after the accelerated chloride migration test. The chloride profile can be obtained from the total amount of chloride and the surface chloride content. A good correlation is observed between the charge passed and the total amount of chloride during the non-steady-state condition, and the approximate surface chloride content can be obtained from the chloride content at the first slice (about 5 mm thickness). A simplified procedure using the charge passed and the near surface chloride content is developed to obtain the chloride profile. The chloride penetration depth is determined from the profile and the depth can be used to determine the non-steady-state chloride migration coefficient.

Influence of initial curing conditions and exposure environments on chloride migration in concrete using electrochemical method

To investigate the influence of initial curing conditions and exposure environments on chloride ions’ migration in concrete, the specimens that were cured in different conditions and placed in several marine environments were studied. The amount of chloride ions passing through the specimen’s section was monitored in the accelerated chloride migration test. The effective chloride diffusion coefficients (D e) were calculated from the steady-state on the basis of Nernst-Planck’s equation. The results indicated that the initial curing conditions and the wet-dry interval of external environments have coupling influence on effective diffusion coefficient of chloride ion significantly. D e reflected the density and pore connectivity of concrete. The co-effects of the initial curing condition and following exposure environment should be taken into account in durability design for concrete structure located in marine environment.

Relation between the chloride migration coefficients of concrete from the colourimetric method and the chloride profile method

In this study the electrochemical technique is applied to accelerate chloride ion migration in concrete to determine its transport property. After the accelerated chloride migration test (ACMT; the electrochemical technique is applied to accelerate chloride ion migration), the penetration depths of the colourimetric method were detected by 0.1 N AgNO3 and the chloride penetration profiles of the profile method were obtained from the chloride content of each depth. The chloride migration coefficients were calculated from the modified Fick's second law based on the colourimetric method and the chloride profile method. In order to develop a better understanding of the relationship between the migration coefficient obtained from the colourimetric method and the chloride profile method, the migration coefficient obtained from those two methods are compared. The experimental result shows that the migration coefficients obtained from the colourimetric method and the chloride profile method are linearly correlated, and the concentration of color change boundary, Cd = 0.07 mol/L, can be used to determine the migration coefficient regardless of the concrete type.

The influence of medium–high temperature on the transport properties of concrete by using accelerated chloride migration test

The effect of medium temperature on the transport properties of concrete was investigated. The transport properties, the non-steady-state migration coefficient and the steady-state migration coefficient, were investigated after the specimens were heated to the temperature of 95 °C. In this study the electrochemical technique was applied to accelerate chloride ion migration in concrete to estimate the breakthrough time and the chloride flux. The non-steady-state chloride migration coefficient and the steady-state chloride migration coefficient of concrete were calculated from the modified Fick’s second law based on measurements of the breakthrough time and the chloride flux. The results show that the non-steady-state migration coefficient and the steady-state migration coefficient increase by 4.6–14.6 times and by 2.3–7.1 times, respectively, when the temperature is raised from room temperature to 95 °C.

Strength and durability of high-volume fly ash concrete

The effects of replacing 10, 40 or 60% of the cement content by low-calcium fly ash on the compressive strength and durability of the concrete were investigated. An appropriate amount of (super)plasticiser was added to the mix to obtain good workability. At an early age the compressive strength decreases with increasing level of cement replacement. After 28 days the compressive strength increased relatively more for high-volume fly ash concrete than for the control concrete. Concrete with fly ash performed better in lactic/acetic and sulphuric acid during accelerated experiments. The chloride diffusion coefficients resulting from accelerated chloride migration tests were significantly lower for concrete with fly ash than for the control concrete, except for the mixture with 60% replacement of the cement content. The resistance to frost/thaw cycles was similar for all concrete mixtures. The carbonation depth after 9 weeks in a 10% carbon dioxide (CO2) environment increased with increasing fly ash content. High volumes of fly ash also decreased significantly the resistance against the combined action of frost and de-icing salts (3% sodium chloride (NaCl) solution). From these results it can be concluded that high-volume fly ash concrete has a potential for commercial use in particular applications.