Diffusion Coefficient Of Concrete Research Articles

Long-Term Sulfate Resistance of Blended Cement Concrete with Waste Glass Powder

This study aimed to evaluate the long-term sulfate resistance of green concrete with blended cement at different waste glass powder contents. The used cement was blended with 10%, 20%, 40%, and 60% of waste glass powder. To benchmark performance, the X-ray diffraction (XRD) test was used to estimate the pozzolanic effect of glass powder, which exhibits a calcium hydroxide decrease. The concrete natural aggregates were replaced by 50%, and 100% with glass at 60% glass powder replacement. There was a direct relation between the concrete diffusion coefficient and the waste glass powder in blended cement. Results of compressive strength loss show a high sulfate resistance with waste glass powder content increasing in cement. Concrete with 50% glass aggregates produced a comparable enhancement in sulfate resistance to that produced with natural aggregates.

Time-varying relationship between pore structures and chloride diffusivity of concrete under the simulated tidal environment

Based on an exposure test of concrete with admixtures under a simulated tidal environment, the free chloride ion concentrations at different exposure times were measured, the apparent chloride diffusion coefficients of test concrete were fitted with Fick’s second law, and the pore structural parameters of concrete at the same time were measured by mercury intrusion porosimetry (MIP). Based on the measured results, the time-varying characteristics of porosity and pore size distribution of test concrete have been analyzed, and the time-varying relationship between the proportion of different pore diameters as well as porosity and apparent chloride diffusion coefficients of concrete have been investigated. Results indicate that, under the simulated tidal environment, the total porosity and apparent chloride diffusion coefficient of test concrete have obvious time-variation, an obvious correlation between porosity and apparent chloride diffusion coefficient can be observed, i.e. both of them decrease with time. It has been found that the time-varying proportion of various pore diameters in concrete is different. Moreover, the correlation coefficients between contribution porosities of different pore diameters and apparent chloride diffusion coefficients show an increasing trend with exposure time.

Numerical modelling of elastic modulus and diffusion coefficient of concrete as a three-phase composite material

Concrete is a complex three-phase composite material at a mesoscale, thus its overall elastic and diffusive properties strongly depend on that of each component. However, the effects of aggregate characteristics are little considered, especially the aggregate shape effect. In this study, a set of numerical methods is employed to evaluate the effects of aggregate characteristics on the elastic and diffusive properties of concrete. Firstly, a concrete representative volume element (RVE) is constructed using a pixel-based method by packing aggregates surrounding a soft interlayer as ITZ in a homogeneous mortar matrix. The different aggregate characteristics including morphology, fineness and type, are respectively considered. Subsequently, a set of the finite element-based and finite difference-based numerical method that is designed for the pixel-based concrete structure, is applied to predict the elastic modulus and the diffusion coefficient of concrete. The simulated results indicate that aggregate characteristics apart from aggregate type play a negligible role in the elastic modulus of concrete, while the effects of aggregate characteristics on the diffusion coefficient of concrete are pronounced. The aggregates with less regularity or coarser size can decrease the diffusion coefficient of concrete. Furthermore, the property of ITZ is another pronounced factor for the elastic and diffusive properties of concrete in addition to aggregate area fraction. The weaker ITZ can significantly decrease the stiffness and increase diffusivity of concrete. The modelling results are expected to guide the design of concrete materials from the perspective of aggregate characteristics.

Statistical analysis of time dependent variation of diffusion coefficient for various binary and ternary based concrete mixtures

The numerical modelling of chloride penetration into concrete requires sound description of input parameters. One of the crucial inputs is the diffusion coefficient of concrete. The concrete is heterogeneous material and its parameters depend on the level of maturity. Therefore, the objective of this work is to describe the time dependent variability of the diffusion coefficient of chlorides into concrete. Computation of the diffusion coefficient is based on the non-destructive testing of bulk electrical resistivity following ASTM C1760 standard and Nernst-Einstein relationship. The presented results show the variation of diffusion coefficient of control OPC mixture and 32 various binary and ternary concrete mixtures where the effect of prolonged aging is even more significant. Two possibilities of the time dependent diffusion coefficient probabilistic model based on coefficient variation (mean value and regression via linear approximation) are proposed. The quality of both approaches is evaluated using Root of Mean Squared Error approach. Overall, this study provides guidance to select proper statistical tool for the assessing the time dependent variation of diffusion coefficient.

Prediction model for carbonation depth of concrete subjected to freezing-thawing cycles

Through the indoor simulation test of the concrete durability under the coupling effect of freezing-thawing and carbonation, the variation regularity of concrete neutralization depth under freezing-thawing and carbonation was obtained. Based on concrete carbonation mechanism, the relationship between the air diffusion coefficient and porosity in concrete was analyzed and the calculation method of porosity in Portland cement concrete and fly ash cement concrete was investigated, considering the influence of the freezing-thawing damage on the concrete diffusion coefficient. Finally, a prediction model of carbonation depth of concrete under freezing-thawing circumstance was established. The results obtained using this prediction model agreed well with the experimental test results, and provided a theoretical reference and basis for the concrete durability analysis under multi-factor environments.

Time-dependent characteristic and similarity of chloride diffusivity in concrete

Corrosion of reinforcing steel due to chloride attack is the main cause of deterioration of reinforced-concrete (RC) structures in a chloride environment. Chloride diffusion in concrete is time-varying and affected by many factors. It is necessary for service life prediction of RC structures to make clear how chloride diffusion coefficients change with time. In addition, the test environment has an obvious effect on the concrete's diffusivity, especially on the chloride diffusion coefficient and the age factor. Therefore, it is advisable to conduct similarity analysis of chloride ingress into concrete between an artificial simulated environment and a field marine environment. Based on the existing field exposure test, an accelerated simulated test with the same concrete mixture proportions as the exposure test under a tidal environment were designed in this paper. The free chloride concentrations in concrete with different exposure times and diffusion coefficients of concrete were obtained, and the relationship between the age factor and water/cement ratio was analysed. Finally, the similarity of the time-dependent characteristic of chloride ions in concrete between the accelerated simulation and field exposure test was investigated.

Prediction of Time-Dependent Chloride Diffusion Coefficients for Slag-Blended Concrete

The chloride diffusion coefficient is considered to be a key factor for evaluating the service life of ground-granulated blast-furnace slag (GGBS) blended concrete. The chloride diffusion coefficient relates to both the concrete mixing proportions and curing ages. Due to the continuous hydration of the binders, the capillary porosity of the concrete decreases and the chloride diffusion coefficient also decreases over time. To date, the dependence of chloride diffusivity on the binder hydration and curing ages of slag-blended concrete has not been considered in detail. To fill this gap, this study presents a numerical procedure to predict time-dependent chloride diffusion coefficients for slag-blended concrete. First, by using a blended cement hydration model, the degree of the binder reaction for hardening concrete can be calculated. The effects of the water to binder ratios and slag replacement ratios on the degree of the binder reaction are considered. Second, by using the degree of the binder reaction, the capillary porosity of the binder paste at different curing ages can be determined. Third, by using the capillary porosity and aggregate volume, the chloride diffusion coefficients of concrete can be calculated. The proposed numerical procedure has been verified using the experimental results of concrete with different water to binder ratios, slag replacement ratios, and curing ages.

The Correlation of Chloride Diffusion Coefficient and Concrete Maturity Value and its Application in Marine Engineering

The correlation of chloride diffusion coefficient and concrete maturity value within 56 days of curing was investigated by the chemically combined water content method, rapid chloride migration (RCM) test and concrete maturity test, respectively. The experimental results showed the chloride diffusion coefficient of concretes decreased not only with increasing curing ages, but also with increasing curing temperature, which can promote the hydration degree of cementitous. There is a significant correlation between the chloride diffusion coefficient of indoor curing specimens and the concrete maturity value when expressed as a power function (R2=0.976), and the calculated values of concrete maturity for outdoor specimens which obtained by using the power function agrees well with the measured values, then it can use the measured concrete maturity value to predict the chloride diffusion coefficient of concrete. And then in this project, when the immersed tube tunnels were placed in seawater, the recommended value and the control value of concrete maturity was 21064°C•h and 13926°C•h, respectively. Furthermore, the ages of the tunnels placed in seawater can be appropriately adjusted by calculation when considering the external curing temperature and heat of hydration of cementious.

Study on Durability of Concrete with Machine-Made Sand Part I: Time-Dependent Chloride Penetration

As part of the studies on the durability of concrete with machine-made sand, this paper introduces the test results and the forecast model of time-dependent chloride penetration of this kind of concrete. Three strength grades of concrete C30, C40 and C50, and the contents of stone powder in machine-made sand of 5%, 9% and 13% in mass were considered in the mix proportion of concrete with machine-made sand. The ordinary concrete with natural river sand in the same strength grade was tested at the same time for comparison. The test was conducted for 360 days, the results showed that the effect of the content of stone powder on the chloride penetration of concrete was obvious at early curing time of 7 days, and tended to be lower with the increase of curing time. When the curing time was longer than 90 days, this effect could be neglected, and the resistance to chloride penetration of concrete with machine-made sand was almost equal to or larger than that of ordinary concrete. The decrement of chloride diffusion coefficient varied from sharp to gentle with the curing time, the resistance of concrete to chloride penetration increased with the increase of concrete strength. Meanwhile, to facilitate the calculation in practice, the forecast model of chloride diffusion coefficient of concrete is proposed.

Experimental Research on Chloride Ingress into Concrete Exposed to Freeze-Thaw Cycles

The most important mechanism of deterioration occurring in concrete in the cold regions are chloride ingress and freeze-thaw cycles. In this paper, the process of chloride ingress into concrete exposed to freeze-thaw cycles is experimentally researched. From the experimental results, it appears that freeze-thaw cycles make the effective diffusion coefficient become bigger. As w/c ratio increasing and fly ash content decreasing, the effective diffusion coefficient increases. The concentration of salt solution has little influence on the effective diffusion coefficient of concrete.

Research on the Concrete Performance in the Marine Environment

This paper mainly studied effects of NaCl,MgSO4 soaking experiments,carbonation and freezing and thawing cycle on concrete intensity.The results show:When the concrete is completely soaked in chloride solution,the concrete of high slump of the same strength grade has high compressive intensity.With the improvement of the concentration of chloride ions solution,the chloride ion diffusion coefficient of concrete is increasing as well;for the structure in marine environment,low water-binder ratio and high mineral admixture can improve most of performances of concrete.

On the Time Dependency of the Chloride Diffusion in High Performance Concrete

The chloride diffusion coefficient of concrete is time dependent. The high performance concrete (HPC) was prepared and the specimens were tested by ASTM C1202 and the durability of HPC in long period is analyzed with the time dependency of diffusion in this paper. The results show that the chloride diffusion coefficients of the HPC with only fly ash are large than those of the HPC with multi-admixtures, but the attenuation of the chloride diffusion coefficients of the formers are faster than the latters. The analysis results show that the chloride concentrations in concrete is over estimated when time-dependence of chloride diffusion is not considered, and the durability of concrete in long period is determined by both chloride diffusion coefficient and age factor.

The Durability Failure of Pre-Damaged Concrete Induced by Mechanical Load

Chloride ion penetration and freezing and thawing damage are the two main factors that affect the durability of concrete structures. Through the chloride ion penetration test and freezing and thawing test of concrete specimens after tensile and compressive loading, the influence of load-induced damage on the long-term durability of concrete was studied. The results showed that the apparent chloride diffusion coefficient of concrete increased by 6.4% and 34%, and the surface chloride concentration increased 10% and 40%, respectively, both of which showed the "negative effect" when the uniaxial tensile load level reached the 65% and 75% of the ultimate capacity. However, with the increasing uniaxial compressive load level, the impact on the frost resistance of concrete experienced a transformation from the "positive effect" to the "negative effect".

EFFECTS OF BLAST FURNACE SLAG ON CHLORIDE PERMEABILITY OF CONCRETE

Chloride-induced corrosion of steel reinforcement is the main cause of deterioration of reinforced concrete structures in marine environments. The penetration of chlodride ions into concrete cover that accelerates corrosion process of steel reinforcement, this affects the bearing capacity of structures. This paper investigates on chloride permeability cheracteristic of concrete using blast furnace slag in terms of chloride diffusion coefficient and chloride binding capacity. The concrete used in this research has grade of 45MPa and the slag content replacement of cement PC50 is in range of 0% - 70%. The chloride diffusion coefficient of concrete is determined by ASTM C1202 and NordTest NT Build 492. Results showed that the blast furnace slag replacement increases (from 0% to 50%), the chloride ion diffusion coeffient decreases and bound chloride content in concrete increases. It is clear to conclude that blast furnace slag can be used to replace cement PC50 in range of 30% to 40% in order to increase the resistance of concrete to chloride penetration without affecting concrete strength.

Comparison of chloride ion penetration and diffusion of high-performance concrete

This paper reports the results of an investigation of chloride ion penetration and diffusion for high performance concrete. Concrete was prepared incorporating pulverised fuel ash and silica fume with various water-binder ratios. Chloride ion penetration was measured at various ages using rapid chloride permeability test in accordance with ASTM C1202-91. Based on experimentally obtained results, isoresponse contours for chloride permeability were developed showing the interactive and optimized effect between the various parameters investigated. Diffusion coefficient of concrete was determined applying Fick’s law of diffusion. The results show that the inclusion of pulverised fuel ash and silica fume reduced both chloride permeability and chloride concentration of concrete. It was found that rapid chloride permeability values were consistent with diffusion coefficient of concrete.

Application of Interpenetrating Silicone Waterproofing Material in the Protection of the Concrete

A cost-effective better performing silicone waterproofing agent interpenetrating polymer network coating for the protection of concrete has been developed. The working mechanism of the silicone polymer on the concrete was revealed and the effect of the material on the water absorption, chloride diffusion coefficient of concrete was analyzed. The results showed that the deep penetration of silicone material formed a hydrophobic layer and provides an effective protection against water corrosion and chloride ingress. A long-term protection can be guaranteed in case the surface of the concrete is waterproofing.

Behavior of Concrete Permeability Considering ITZ

In this paper, concrete was analyzed as a composite consisting of coarse aggregate, mortar matrix and interfacial transition zone (ITZ). Because permeability of each phase are not the same, ITZ will affect the concrete permeability. Effect of ITZ on the concrete permeability was studied by laboratory test and numerical analysis.The diffusion coefficient of ITZ, mortar,and concrete can be caculated by laboratory test. The results indicate that the diffusion coefficient of ITZ is far greater than mortar，which is about 40 times of mortar. The chloride ions diffusion ignoring ITZ and considering ITZ were simulated, the results show that the diffusion coefficient of concrete was bigger when the ITZ was considered, which was closer to the experimental results.

Influence of Permeability of HCSA Expansive Agent on High Volume Fly Ash Concrete

Based on the rapid determination of chloride diffusion coefficient with NEL method and pore structure analysis, the influence of HCSA expansive agent on chloride diffusion coefficient of concrete has been investigated. Besides, the effects of chloride diffusion coefficient of Water-Cement ratio on HCSA expansive concrete have been also analyzed. The results show that on the condition of 55% mixing amount of fly ash, the chloride diffusion coefficient of concrete of no HCSA is 1.96×10－8cm2/s, which is classified moderate. While the concrete mixing HCSA is about 0.62×10－8cm2/s, the permeability belongs to inferior. The effects of permeability of HCSA mixing amount on concrete is not obviously. The Water-Cement ratio affects the concrete permeability. Under the experimental conditions, the water-cement ratio of 0.4 can achieve better effect of the HCSA expansion; Furthermore, the mercury intrusion further verified that incorporating proper amount of HCSA can make the internal structure dense and improve the density and impermeability of concrete.

Impermeability of Wet-Sieving Fine Aggregate Concrete Made from Ordinary Concrete

The research is part of wet-sieving concrete technique for building thermal insulated reinforced concrete composite wall. The fine aggregate concrete is made from ordinary concrete passing sieve with square mash of 15 mm for casting surface concrete layer of the wall, the recomposed concrete is made of residual concrete stayed on sieve and ordinary concrete for casting reinforced concrete structural wall. The impermeability of fine aggregate concrete and recomposed concrete are measured by water permeation method and chloride-ion permeation method, the relative permeability and chloride-ion diffusion coefficients of concrete are determined. Based on the test, the effects of the changes of aggregate series, sand ratio and cement paste on the impermeability of concrete are analyzed.

Influence of Flexural Loading on Permeablility of Chloride Ion and Diffusion Coefficients in RC Beams

The permeability of chloride ion in concrete can be studied using the accelerated aging method in a short period, but the influence of loading characteristic on chloride ion permeability and diffusion coefficients is not considered generally. Three RC beam (120 mm×240 mm×2400 mm) specimens with different flexural loading state are exposed in an artificial corrosion container filled with salt-fog of 5.0 % sodium chloride for 40 days, the chloride ion concentration in different depths of compressive and tensile region are measured, diffusion coefficients of different region concrete are fitted on the basis of Fick’s second law, the effect of flexural loading on chloride ion concentration and diffusion coefficients of concrete are analyzed. The results show that the effect of the flexural load influences permeability of chloride ion and diffusion coefficients of concrete, content of chloride and diffusion coefficients of concrete are controlled by loading level, and the bending load is one of the important factors that can not be ignored in the study of concrete durability.