scholarly journals Influence of Pore Structure on Chloride Penetration in Cement Pastes Subject to Wetting-Drying Cycles

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Honglei Chang ◽  
Zhiwu Zuo ◽  
Mingyue Qu ◽  
Fei Wang ◽  
Zhi Ge ◽  
...  
Keyword(s):  
Pore Structure ◽  
Penetration Rate ◽  
Error Function ◽  
Chloride Concentration ◽  
Total Porosity ◽  
Chloride Penetration ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Cement Pastes ◽  
The Matrix

Copious studies have discovered a phenomenon that a chloride concentration peak appears on the surface of concrete under cyclic drying-wetting environments. In such cases, the chloride diffusion coefficient (D) obtained through directly fitting the standard error function of Fick’s second law is no longer accurate. The more reliable D obtained by the method proposed by Andrade is employed in this research to investigate the influence of pore structure on chloride penetration rate of pastes. The results show that both the effective coefficient (Deff) and the apparent coefficient (Dapp) increase with total porosity, the most probable pore size, and water absorption porosity, suggesting that the increase of the three pore structure parameters accelerates chloride penetration rate under cyclic wetting-drying condition. The increase of the three parameters makes more room available and eases the difficulty for salt solution to enter the matrix and thus leads to the augmentation of chloride transporting in matrix.

Influence of Stone Dust in Manufactured Sand on Resisting Chloride Penetration in Marine Concretes

2012 ◽  
Vol 174-177 ◽  
pp. 1419-1423
Author(s):  
Jian Bo Xiong ◽  
Peng Ping Li ◽  
Sheng Nian Wang
Keyword(s):  
Diffusion Coefficient ◽  
Pore Structure ◽  
Binding Capacity ◽  
Chloride Penetration ◽  
Dust Content ◽  
Chloride Diffusion ◽  
Fine Aggregate ◽  
Chloride Diffusion Coefficient ◽  
Manufactured Sand ◽  
Stone Dust

In China, manufactured sand has been widely used as fine aggregate in concrete. Therefore, it is necessary to investigate the effect of manufactured sand on durability of concrete. This research studies the influence of stone dust content in manufactured sand on resisting chloride penetration in marine concrete by strength and other physical mechanical tests, XRD, TGA and pore structure analysis. Test results have shown that the chloride diffusion coefficient increased with increasing the stone dust content in manufactured sand when the stone dust content increasing from 3% to 13%. The stone dust in fine aggregate was participated in hydration procedure of cementitious, which will promote the hydration degree of cementitious and increase the chloride binding capacity of hydration product. The influence of stone dust in fine aggregate on chloride diffusion coefficient were the combined effects of concrete pore structure and cementitious hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient.

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

2018 ◽  
Vol 875 ◽  
pp. 165-173
Author(s):  
Hong Lei Chang ◽  
Song Mu ◽  
Ya Ya Du ◽  
Li Yang
Keyword(s):  
Surface Layer ◽  
Pore Structure ◽  
Cement Paste ◽  
Pore Diameter ◽  
Total Porosity ◽  
Chloride Content ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Chloride Profiles ◽  
Peak Value

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

Inner Damage and Anti-Chloride Penetration of High-Performance Concrete under Axial Tensile Load

2011 ◽  
Vol 261-263 ◽  
pp. 1210-1214
Author(s):  
Fu Xiang Jiang ◽  
Lei Xin ◽  
Tie Jun Zhao ◽  
Xiao Mei Wan
Keyword(s):  
Diffusion Coefficient ◽  
High Performance ◽  
High Performance Concrete ◽  
Tensile Load ◽  
Total Porosity ◽  
Tensile Loading ◽  
Chloride Penetration ◽  
Chloride Diffusion ◽  
Uniaxial Tensile ◽  
Chloride Diffusion Coefficient

The total porosity of high performance concrete specimens after different level uniaxial tensile loading were measured to reflect the damage degree of mechanical load to the microstructure of the concrete. Meanwhile, considering the environmental characteristics of the ocean tidal zone, chloride penetration tests of the concrete were carried out with salt solution capillary absorption method. Based on the profile of chloride measured from specimens, chloride diffusion coefficients of the concrete under uniaxial tensile load with different levels are determined further by Fick’s second law. Results show that both of total porosity and chloride diffusion coefficient of the concrete are increased significantly after short-term tensile loading. And the evolutions of the porosity and chloride diffusion coefficient are similar with the development of micro-cracks under uniaxial tensile load.

scholarly journals Novel Nano-Precursor Inhibiting Material for Improving Chloride Penetration Resistance of Concrete: Evaluation and Mechanism

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 5929
Author(s):  
Ruixing Chen ◽  
Song Mu ◽  
Jiaping Liu ◽  
Jingshun Cai ◽  
Deqing Xie ◽  
...  
Keyword(s):  
Contact Angle ◽  
Water Absorption ◽  
Chloride Penetration ◽  
Chloride Diffusion ◽  
Hardened Cement ◽  
Slight Reduction ◽  
Chloride Salt ◽  
Chloride Diffusion Coefficient ◽  
Cement Pastes ◽  
Small Pore

Durability improvement is always important for steel–concrete structures exposed to chloride salt environment. The present research investigated the influence of a novel nano-precursor inhibiting material (NPI), organic carboxylic acid ammonium salt, on the mechanical and transport properties of concrete. The NPI caused a slight reduction in the strength of concrete at later ages. NPI significantly decreased water absorption and slowed down the speed of water absorption of concrete. In addition, the NPI decreased the charge passed and the chloride migration coefficient, and the results of the natural chloride diffusion showed that the NPI decreased the chloride concentration and the chloride diffusion coefficient. The NPI effectively improved the resistance of chloride penetration into testing concrete. The improvement in the impermeability of concrete was ascribed to the incorporation with the NPI, which resulted in increasing the contact angle of cement pastes. The contact angle went up from 17.8° to 85.8° for 0% and 1.2% NPI, respectively, and cement pastes became less hydrophilic. Some small pore throats were unconnected. Besides, the NPI also optimized the pore size distribution of hardened cement paste.

Effect of Pore Structure on the Chloride Permeability of Concrete with Mineral Admixture

2013 ◽  
Vol 690-693 ◽  
pp. 835-838 ◽  
Author(s):  
Yan Jun Hu ◽  
Yan Liang Du
Keyword(s):  
Pore Structure ◽  
Total Porosity ◽  
Chloride Ions ◽  
Mineral Admixture ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Chloride Permeability ◽  
Evaporative Water ◽  
Chloride Diffusivity ◽  
Chloride Penetration Resistance

In this paper, the effect of pore structure on the chloride ions ingress into concrete was investigated. The most probable diameter was measured by Mercury intrusion porosimetry (MIP) and the total porosity was measured by evaporative water method (EWM). The results indicate that the most probable diameter by MIP has better linear relationship with chloride diffusion coefficient than the total porosity by EWM, the most probable diameter has significant influence on chloride diffusivity, and the smaller most probable diameter will lead to higher chloride penetration resistance.

Acelerated Test Methods: Determining the Diffusion Coefficient of Concretes in the Saturated Condition

2017 ◽  
Vol 372 ◽  
pp. 91-100
Author(s):  
Tassia Fanton ◽  
João A.M. Bender ◽  
Leandro G. Blois ◽  
Franciele Müller ◽  
André T.C. Guimarães
Keyword(s):  
Diffusion Coefficient ◽  
Standardized Tests ◽  
Chloride Concentration ◽  
Test Methods ◽  
Chloride Penetration ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Reinforced Concrete Structure ◽  
Saturated Condition ◽  
Pozzolanic Cement

The chloride diffusion coefficient indicates the capacity of a particular type of concrete to resist chloride penetration and is therefore used to predict the service life of a particular reinforced concrete structure exposed to environments containing this type of aggressive agent. Its experimental determination is time-dependent and time-consuming. For that reason, our study analyzes the characteristic behavior of the diffusion coefficient (D) of concretes in the saturated condition by testing higher NaCl concentrations and lower contamination ages than those used in standardized tests, in addition, the objective is to analyze the behavior of surface chloride concentration (Cs) over time. Therefore, it was concluded that for concrete dosed with pozzolanic cement, the Cs value varied with increasing tendency at higher ages. In addition, the D value obtained by the proposed method presented values ​​close to those obtained by standardized tests at contamination ages of 21 and 35 days.

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.

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