scholarly journals Investigation on Numerical Simulation of Chloride Transport in Unsaturated Concrete

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Qingzhang Zhang ◽  
Feng Wang ◽  
Yifeng Ling ◽  
Hui Chen ◽  
Zhongyuan Li
Keyword(s):  
Diffusion Coefficient ◽  
Relative Humidity ◽  
Moisture Absorption ◽  
Chloride Transport ◽  
Salt Spray ◽  
Chloride Diffusion ◽  
Transfer Model ◽  
Chloride Diffusion Coefficient ◽  
Desorption Process ◽  
Water Equilibrium

Marine atmosphere environment accelerates the process of chloride penetration into concrete under the coupling effect of ambient temperature and relative humidity, thereby reducing the durability and service life of concrete. This paper aims to investigate the change of water equilibrium saturation and the chloride transport properties of concrete materials in different environments. The water equilibrium saturation tests at three temperatures and five relative humidity (RH) and salt spray erosion tests at three temperatures were performed. The influence of RH and temperature on the equilibrium saturation of concrete and the influence of temperature and time on the chloride diffusion coefficient are investigated. The results show that, in the process of moisture absorption and desorption, the equilibrium saturation of concrete gradually decreases as temperature rises. At the same depth of concrete, the chloride content gradually increases with temperature increasing, as well as the chloride diffusion coefficient. However, as the corrosion time of salt spray increases, the altering of chloride diffusion coefficient becomes less. Based on the Kelvin equation, a relationship between capillary pressure and water saturation in concrete was established, and a moisture transfer model for concrete in the process of moisture absorption and desorption was derived. Further, based on the established chloride diffusion equation and heat balance equation, a model of temperature-wet-chloride coupling chloride transfer was derived. Theory model simulation results show the transfer speed of chloride under the coupling of diffusion and capillary is higher than pure diffusion in moisture in the absorption process. However, the opposite is true in the desorption process. Moreover, with the increment of saturation rate, the capillary effect on chloride transport is enhanced.

scholarly journals Chloride intrusion into thermally damaged self-compacting concrete

2015 ◽  
Vol 42 (10) ◽  
pp. 720-727 ◽  
Author(s):  
Rami H. Haddad ◽  
Ayat Hinawi
Keyword(s):  
Diffusion Coefficient ◽  
Relative Humidity ◽  
Ultrasonic Pulse Velocity ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Chloride Diffusion ◽  
Percentage Increase ◽  
Chloride Diffusion Coefficient ◽  
Self Compacting Concrete ◽  
Damage Indices

The post-heating resistance of limestone self-compacting concrete (SCC) against chloride intrusion is investigated considering key parameters such as water-to-cement ratio (0.4, 0.45, and 0.5), relative humidity, and elevated temperature (300 °C and 400 °C). The SCC mixtures were proportioned to conform to universal specification with regard to different workability requirements. Chloride profiles were determined for post-heated and companion prismatic (100 mm × 100 mm × 250 mm) specimens, kept at room temperature. Consequently, diffusion coefficients were determined based on Fick’s steady state formula. Post-heating damage was quantified, as well, using various techniques such as ultrasonic pulse velocity waves, resonant frequency, compression test measurements. The results indicated significant reductions in compressive strength and estimated dynamic modulus ranging from 20 to 60% and 10 to 40%, respectively, with a corresponding increase in chloride diffusion coefficient reaching 80%. Both temperature and relative humidity levels had tangible impact on post-heating damage of SCC, hence percentage increase in chloride diffusion coefficient. The empirical models developed in this work showed excellent correlation between various damage indices and the percentage increase in diffusion coefficient. Furthermore, the electrical charge passing through SCC compared very well with the percentage increase in diffusion coefficient.

scholarly journals Model for the Patterns of Salt-Spray-Induced Chloride Corrosion in Concretes under Coupling Action of Cyclic Loading and Salt Spray Corrosion

Processes ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 84 ◽  
Author(s):  
Ruixue Liu ◽  
Huiguang Yin ◽  
Lianying Zhang ◽  
Bing Li ◽  
Xianbiao Mao
Keyword(s):  
Diffusion Coefficient ◽  
Gas Flow ◽  
Salt Spray ◽  
Chloride Ion ◽  
Flow Equation ◽  
Chloride Diffusion ◽  
Second Law ◽  
Chloride Diffusion Coefficient ◽  
Salt Spray Corrosion ◽  
Convection Diffusion

In this study, the patterns of chloride ion erosion of unsaturated concrete subjected to the coupling action of cyclic loading and salt spray corrosion were experimentally studied, and Fick’s Second Law was used to fit the variation patterns of chloride concentration to obtain the chloride diffusion coefficient. Accordingly, we have established a mathematical model that describes chloride transport in unsaturated concrete and accounts for the effects of gas flow, water migration, convection diffusion, and capillary action. This model is composed of three equations—the gas flow equation, the solution flow equation, and the solute convection–diffusion equation. The COMSOL numerical analysis software was subsequently used to obtain solutions for this model, based on parameters such as porosity and the chloride diffusion coefficient. Subsequently, the saturation, relative permeability, and the chloride ion concentration during the first corrosion cycle were analyzed. The numerical results were consistent with the experimental values and were therefore superior to the values obtained using Fick’s Second Law.

A Probabilistic-Based Durability Analysis of Concrete Structures Exposed to Chloride Containing Environment

2012 ◽  
Vol 204-208 ◽  
pp. 3282-3286
Author(s):  
Wei Hua Shi ◽  
Zhi Wu Yu ◽  
Ya Chuan Kuang
Keyword(s):  
Diffusion Coefficient ◽  
Life Prediction ◽  
Chloride Transport ◽  
Concrete Structures ◽  
Chloride Diffusion ◽  
Chloride Ingress ◽  
Chloride Diffusion Coefficient ◽  
Time Dependency ◽  
Durability Analysis

Time dependency of chloride transport has been studied and an improving model for predicting the apparent chloride diffusion coefficient has been proposed. A probabilistic-based durability analysis to estimate failure probability on the chloride ingress into concrete has been carried out. Results of the analysis demonstrate that the improving model in this paper is appropriate for long term service life prediction of concrete structures exposed to chloride containing environment.

Chloride Diffusion Characteristics of the New Interface Transition Zone in Recycled Aggregate Concrete

2011 ◽  
Vol 261-263 ◽  
pp. 104-110
Author(s):  
Hai Long Wang ◽  
Jun Jie Wang ◽  
Xiao Yan Sun ◽  
Juan Cheng
Keyword(s):  
Diffusion Coefficient ◽  
Steady State ◽  
Transition Zone ◽  
Chloride Transport ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Aggregate Concrete ◽  
Phosphorous Slag

A three-part model (mortar, original concrete and ITZ) was established in this study to analyze the chloride coefficient of the new interfacial transition zone (ITZ) in recycled aggregate concrete (RAC). Based on this model, a formula for calculation was derived from the chloride transport characteristics in the steady state. Two types of RAC were used to study the properties of ITZ by steady-state migration test and Scanning Electron Microscope (SEM) method. The results indicate that the chloride diffusion coefficient of new ITZ in RAC is about 1 to 4 cm2/year, and that the addition of superfine phosphorous slag (PHS) not only reduces the chloride diffusion coefficient of mortar but also decreases the thickness and the chloride diffusion coefficient of new ITZ in RAC due to its pozzolanic reaction effect. The chloride permeability of mortar containing 20% PHS is only 1/5 of that in normal RAC. The chloride diffusion coefficient of ITZ in normal RAC is about 10 times greater than that of ordinary mortar. When modified with PHS and superplasticizer, the permeability of chloride in new ITZ is 3 to 7 times greater than that in the ordinary bulk cement paste. Furthermore, the mechanism and the effects of superfine phosphorous slag (PHS) on the resistivity of chloride permeation were discussed on basis of the experimental results and the images of SEM.

scholarly journals Experimental Study on Effective Chloride Diffusion Coefficient of Cement Mortar by Different Electrical Accelerated Measurements

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 240
Author(s):  
Jianlan Chen ◽  
Jiandong Wang ◽  
Rui He ◽  
Huaizhu Shu ◽  
Chuanqing Fu
Keyword(s):  
Diffusion Coefficient ◽  
Cement Mortar ◽  
Early Stage ◽  
Chloride Concentration ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Cement Ratio ◽  
Water To Cement Ratio ◽  
Good Consistency ◽  
Determination Methods

This study investigated the effective chloride diffusion coefficient of cement mortar with different water-to-cement ratio (w/c) under electrical accelerated migration measurement. The cumulative chloride concentration in anode cell solution and the cumulative chloride concentration drop in the cathode cell solution was measured by RCT measurement and the results were further used to calculate the chloride diffusion coefficient by Nordtest Build 355 method and Truc method. The influence of w/c on cement mortar’s chloride coefficient was investigated and the chloride diffusion coefficient under different determination methods were compared with other researchers’ work, a good consistency between this work’s results and literatures’ results was obtained. The results indicated that the increased w/c of cement mortar samples will have a higher chloride diffusion coefficient. The cumulative chloride concentration drop in the cathode cell solution will have deviation in early stage measurement (before 60 h) which will result in overestimation of the effective chloride diffusion coefficient.

scholarly journals Numerical Simulation of Non-Uniformly Distributed Corrosion in Reinforced Concrete Cross-Section

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3975
Author(s):  
Magdalena German ◽  
Jerzy Pamin
Keyword(s):  
Reinforced Concrete ◽  
Cross Section ◽  
Chloride Transport ◽  
Chloride Concentration ◽  
Corrosion Current ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Initiation Phase ◽  
Chloride Corrosion ◽  
Cover Thickness

Reinforced concrete structures can be strongly damaged by chloride corrosion of reinforcement. Rust accumulated around rebars involves a volumetric expansion, causing cracking of the surrounding concrete. To simulate the corrosion progress, the initiation phase of the corrosion process is first examined, taking into account the phenomena of oxygen and chloride transport as well as the corrosion current flow. This makes it possible to estimate the mass of produced rust, whereby a corrosion level is defined. A combination of three numerical methods is used to solve the coupled problem. The example object of the research is a beam cross-section with four reinforcement bars. The proposed methodology allows one to predict evolving chloride concentration and time to reinforcement depassivation, depending on the reinforcement position and on the location of a point on the bar surface. Moreover, the dependence of the corrosion initiation time on the chloride diffusion coefficient, chloride threshold, and reinforcement cover thickness is examined.

scholarly journals Effects after 1500 Hardening Days on the Microstructure and Durability-Related Parameters of Mortars Produced by the Incorporation of Waste Glass Powder as a Clinker Replacement

2021 ◽  
Vol 13 (7) ◽  
pp. 3979
Author(s):  
Rosa María Tremiño ◽  
Teresa Real-Herraiz ◽  
Viviana Letelier ◽  
Fernando G. Branco ◽  
José Marcos Ortega
Keyword(s):  
Diffusion Coefficient ◽  
Water Absorption ◽  
Glass Powder ◽  
Cementitious Materials ◽  
Cement Industry ◽  
Waste Glass ◽  
Supplementary Cementitious Materials ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Waste Glass Powder

One of the ways of lessening the CO2 emissions of cement industry consists of replacing clinkers with supplementary cementitious materials. The required service life of real construction elements is long, so it is useful to characterize the performance of these materials in the very long term. Here, the influence of incorporating waste glass powder as a supplementary cementitious material, regarding the microstructure and durability of mortars after 1500 hardening days (approximately 4 years), compared with reference mortars without additions, was studied. The percentages of clinker replacement by glass powder were 10% and 20%. The microstructure was studied using impedance spectroscopy and mercury intrusion porosimetry. Differential thermal and X-ray diffraction analyses were performed for assessing the pozzolanic activity of glass powder at the end of the time period studied. Water absorption after immersion, the steady-state diffusion coefficient, and length change were also determined. In view of the results obtained, the microstructure of mortars that incorporated waste glass powder was more refined compared with the reference specimens. The global solid fraction and pores volume were very similar for all of the studied series. The addition of waste glass powder reduced the chloride diffusion coefficient of the mortars, without worsening their behaviour regarding water absorption after immersion.

scholarly journals Influence of Hydrostatic Pressure and Cationic Type on the Diffusion Behavior of Chloride in Concrete

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2851
Author(s):  
Huanqiang Liu ◽  
Linhua Jiang
Keyword(s):  
Diffusion Coefficient ◽  
Hydrostatic Pressure ◽  
Diffusion Model ◽  
Coupling Effect ◽  
Experimental Results ◽  
Chloride Diffusion ◽  
Concrete Durability ◽  
Chloride Diffusion Coefficient ◽  
Diffusion Behavior ◽  
Diffusion Source

The durability of the concrete in underground and marine engineering is affected by the underground and ocean environment. Chloride diffusion coefficient under hydrostatic pressure is a key parameter of concrete durability design under corresponding conditions. Therefore, this paper studies the diffusion behavior of chloride in different diffusion source solutions by experiment and simulation. Based on the experimental results, this paper proposes a new chloride diffusion model under the coupling effect of diffusion and convection. The interaction of ions and compounds in the diffusion source solutions, concrete pore fluid, and concrete material are considered in the new chloride diffusion model. The experimental results show that chloride diffusion rate is significantly affected by hydrostatic pressure, which increases with the increase of hydrostatic pressure. The chloride diffusion coefficient shows a certain difference in difference diffusion source solutions. The chloride diffusion coefficient in divalent cationic diffusion source solutions is the largest, the chloride diffusion coefficient in the divalent and monovalent cationic compound ones is in the middle, and the chloride diffusion coefficient in the monovalent cationic ones is the smallest. There is a linear relationship between the chloride diffusion coefficient and the hydrostatic pressure whether in single or combined cationic diffusion source solutions.

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