Chloride Diffusion Coefficient Research Articles

Formation Factor Concept for Non-Destructive Evaluation of Concrete's chloride diffusion coefficients

Estimation of chloride diffusion coefficient (Drcm) is an integral part of service life assessment of vulnerable concrete structures due to chloride induced corrosion. This study focuses on the suitability of an alternate non-destructive, low-cost approach of estimating diffusion coefficients through electrical resistivity and formation factor as a replacement of conventional destructive migration tests. The variation in formation factor for 60 concrete mixes with different Supplementary Cementitious Materials (SCM) types (fly-ash, slag) and proportions (0–40%) along with multiple mix parameters (w/cm ratio and target slump) were studied after 365 days of curing. Drcm values predicted from formation factor approach were found to be in close proximity to the coefficients obtained from migration test but however, required certain modifications to ensure conservative estimations. Tentative modification factors were developed for each binder separately as well as for all blended mixes. Based on the obtained factored Drcm values using the modification factor, it was demonstrated that it is possible to ensure reliable and conservative estimation of corrosion initiation time of any mixes without the requirement of destructive testing.

Chloride diffusion behavior and microstructure of basalt-polypropylene hybrid fiber reinforced concrete in salt spray environment

The chloride diffusion performances of basalt-polypropylene hybrid fiber reinforced concrete (BPHFRC) in salt spray environment were investigated. The effects of concrete strength, fiber addition form and content on the pore solution pH and chloride concentration were evaluated. The results showed that the stable depth of pore solution pH of BPHFRC increased with the increase of exposure time.The greater the strength of concrete, the slower the decrease rate of pore solution pH with exposure time. The effects of addition form and content of basalt fiber (BF) and polypropylene fiber (PF) on chloride concentration were different. When the fiber content was 0.1%, the addition of BF, PF or hybrid BF-PF could improve the chloride corrosion resistance of concrete.However, addition of 0.2% hybrid BF-PF increased the chloride concentration in the concrete. The apparent chloride diffusion coefficient of BPHFRC decreased with an increase of salt spray erosion time, and exhibited a power function with erosion time. The calculation model of BPHFRC apparent chloride diffusion coefficient was established, and its effectiveness was verified. In addition, the pore structure, phase composition and micromorphology of BPHFRC before and after erosion were performed using RapidAir-457 porosity analyzer, X-ray diffraction and field emission scanning electron microscope, and the influence rules of BF and PF on chloride diffusion properties of concrete was discussed.

Microstructure and Chloride Diffusion Properties of Hardened Fly Ash Cement Paste with Three-dimensional Graphene

In this paper, the influence of three-dimensional graphene (3DG) on the microstructure and chloride diffusion properties of fly ash cement paste was investigated. 3DG accounting for 0.0–0.2% of cement mass was evenly dispersed in hardened cement paste containing fly ash by using ultrasonic and polycarboxylate superplasticizer. The microstructure of the cement paste was characterized by mercury intrusion test (MIP), X-ray diffraction (XRD), and scanning electron microscope (SEM). The results indicate that an appropriate amount of 3DG accelerates the secondary hydration of fly ash and provides a platform for the growth of cement hydration crystals. Moreover, the hydrated crystal fills the pores, reduces the harmful porosity, and refines the pore structure. The enhanced microstructure significantly improved mechanical properties and chloride diffusion resistance of hardened fly ash cement. With the addition of 0.1% 3DG, the compressive strength increased by 31.33%, and the chloride diffusion coefficient was reduced by 49.44%. The findings are beneficial to promote the generalized application of 3DG in cement in the marine environment.

Test and theoretical prediction of chloride ion diffusion in recycled fine aggregate mortar under uniaxial compression

A combined test device was developed to investigate the effect of microcracks on rapid chloride ion diffusion in mortar with recycled fine aggregate under uniaxial compression loading. Deformation and microcrack growth were statistically evaluated using the digital image correlation (DIC) method. The chloride ion distribution and porosity in mortar with different proportions of natural and recycled fine aggregates were investigated by micro X-ray fluorescence (μXRF) and mercury intrusion porosimetry (MIP), respectively. Chloride ion transportation was affected by pore structure and natural fine aggregate content. The diffusion coefficient decreased and then increased with increasing compression load and reached the minimum at stress of 0.4 fc-0.5 fc. A statistical specific crack area method based on DIC is proposed for the first time, based on which the chloride diffusion coefficient in mortar with recycled fine aggregate can be predicted.

Chloride ion penetration resistance and microstructural modification of concrete with the addition of calcium stearate

Hydrophobic modification is a conventional method of promoting the durability of cementitious materials located in ion erosion environments. In this study, calcium stearate was used to modify the hydrophilicity of concrete. The mechanical strengths, chloride diffusion coefficient, contact angle and pore structures of concrete with different amounts of calcium stearate addition were investigated and the underlying mechanism of calcium stearate on the resistance of concrete to chloride penetration was discussed. The results revealed that the water absorption of concrete decreased with increasing calcium stearate content, the compressive strength was substantially reduced with increasing calcium stearate, and the rapid chloride migration coefficient, electric flux and natural chloride diffusion coefficient first increased and then decreased with the addition of calcium stearate. The optimal amount of calcium stearate was 4% because the concrete with 4% calcium stearate had the strongest resistance to chloride penetration. The improvement in the resistance of concrete to chloride penetration by calcium stearate was indicated by an increased in the contact angles, and then the rise in hydrophobicity hindered the connection of capillary water channels in the mortar matrix. Additionally, the water absorption and connected chloride ion transport channels were both reduced, and finally, the chloride concentration in the concrete decreased.

Ageing factor for fly ash cement concrete (FACC).

Durability performance of concrete is enhanced by adding supplementary cementitious materials such as fly ash. The concrete made with addition of fly ash with Portland cement is called fly ash cement concrete (FACC). Generally, modelling approach is applied to predict the service time of concrete in aggressive environment. Most degradation of concrete is found in marine environment, due to the exposure of concrete to chlorides. Service life modelling is performed using diffusion equation (Eq.1) with diffusion coefficient (D) equation (Eq.2), and to get the diffusion coefficient (D) over time, ageing factor is used for analysis. During modelling stage, as this phase of study is started well before construction, concrete for its durability performance is checked. As well, service life modelling is performed for the existing structures, so that the time to failure may be obtained. In recent times, failure of Miami Building, USA, June 2021, has raised the importance of service life modelling (SLM) of reinforced concrete structures (RCC) in chloride environment. So, in such environments, a more need of more reliable results is raised. Presence of a number of ageing factors in literature raises a question which ageing factor is more approximate. Dependency of performance of modelling approach is on the selection of more approximate values. So, in present study, performance of ageing factors for fly ash cement concrete (FACC) is checked. So, literature was surveyed and the long-term chloride diffusion coefficient (D) values were obtained for fly ash cement concrete (FACC). It was found that a significant difference is present in the predicted values with different available ageing factors. Since results obtained from modelling depend on the parameters, so it can be assumed that the variation of chloride diffusion coefficient (D) will vary the results. So, in present study, a new ageing factor was developed. Service life modelling for durability with fly ash cement concrete (FCC) may be relied on the newly developed ageing factors, as this will give better results, which will be more reliable.

Time dependent correlation of permeability of fly ash concrete under natural tidal environment

Based on the long-term exposure test of fly ash concrete under natural tidal environment, the gas permeability coefficient, water permeability coefficient, chloride concentration and microstructure parameters of fly ash concrete were tracked and tested. Relationships between permeability and exposure time as well as fly ash content were analysed. Time dependent models for permeability of concrete were established, and time dependent relationships among water/gas permeability, and chloride diffusivity were discussed. Based on the results of mercury intrusion porosimetry (MIP), the influence of fly ash content on time dependent porosity and pore size distribution (PSD) of concrete were analysed. Results show that fly ash can significantly reduce the porosity, instantaneous chloride diffusion coefficients, water and intrinsic gas permeability coefficients after the same exposure time. A time dependent chloride diffusivity model is established based on the time dependent intrinsic gas permeability coefficients. With the increasing exposure time and fly ash content, the proportions and contributive porosity (100 nm < d < 1000 nm) decrease gradually. Water and intrinsic gas permeability as well as chloride diffusivity of concrete are more closely related to the contributive porosity of large capillary pores (100-1000 nm).

Attenuation behavior of pavement concrete under rolling load and hydrodynamic pressure coupling

In addition to rolling vehicle load, the damage of hydrodynamic pressure to pavement concrete cannot be ignored. To investigate the attenuation behavior of pavement concrete under the coupling effect of rolling load and hydrodynamic pressure, an indoor-accelerated loading test was conducted. The decay rules of strength, dynamic elastic modulus, and impermeability were studied, and the correlation between pore structure and macro-properties was analyzed. The results show that hydrodynamic pressure has significant additional degradation effect on strength and dynamic elastic modulus at the later stage of loading (more than 100 thousand times). The chloride permeability coefficient increases in parabolic shape under rolling load, whereas it amplifies exponentially under the coupling of load and hydrodynamic pressure. The pore structure of pavement concrete presents a “coarsening - refining” trend under the coupling effect. The attenuation of flexural strength and dynamic elastic modulus has great correlation with the total aperture area, mean pore diameter, and area median aperture, and the chloride diffusion coefficient is greatly affected by porosity and total aperture area.

Effects of additives on water permeability and chloride diffusivity of concrete under marine tidal environment

The influences of fly ash (FA), slag (SG), silica fume (SF) and basalt fiber (BF) on time dependent water permeability, chloride diffusivity and microstructure of concrete were studied. Time dependent models for water permeability coefficient (Kw) and instantaneous chloride diffusion coefficient (Dins) were established. Time dependent porosity, pore size distribution (PSD) and contributive porosity (ρc) were determined by MIP. Results show that SF and FA have the best effects on reducing Kw before 240 d. The effects of SF and SG on reducing Dins are relatively poor, due to their small dosage. Kw and Dins are increased by adding BF at early exposure period, but decreased after 240 d. Time dependent Dins and Kw is basically consistent with time dependent porosity. The stable reduced proportion of pores with size greater than 100 nm and corresponding ρc are the leading factors to the decreasing porosity. The correlation between ρc with pore size of 100 nm-1000 nm has a higher correlation with Kw than Dins.

Chloride diffusion models for plain and blended cement concretes exposed to laboratory and atmospheric marine conditions

Chloride-induced corrosion of steel in a reinforced concrete structure compromises its safety and may decrease the designed service-life. The initiation and the rate of reinforcement corrosion mainly depends on the diffusion of chloride ions to the surface of the steel bars. As such, it is important to determine the coefficient of apparent chloride diffusion (Da) for the type of concrete to be used in a structure, which is time-consuming. Therefore, the development of a short-term and simple procedure to predict Da is highly desirable. This study was conducted to develop a correlation between the short-term chloride migration coefficient (Dnssm) and long-term Da for Type I, Type V and pozzolanic cement concretes. Two groups of concrete specimens, each consisting of five concrete mixtures designed with a w/b ratio of 0.4, were prepared. The first group was exposed to a marine exposure site for 10 years and Da was evaluated after 1, 2, 5 and 10 years. The second group was tested according to NT BUILD 492 under laboratory conditions to determine the short-term Dnssm. Correlation models between the field and laboratory results were developed and statistically validated by comparing the predicted values with the measured ones. The predicted Da values are within ±7% of the measured values. Further, the Dnssm of pozzolanic cement concretes is 2.20–4.40 and 3.55 to 7.30 times less than that of Type I and Type V cement concretes, respectively. The developed models can be utilized to assess the long-term Da by determining the short-term Dnssm.

Effects of Mineral Admixtures on Chloride Diffusion in Environment-Friendly Coral Aggregate Concrete

Coral materials can replace concrete aggregates and achieve material self-sufficiency for reducing the construction costs of island projects. This paper studies the effects of different mineral admixtures on the properties of coral aggregate concrete (CAC). The chloride concentration of CAC after different erosion times is measured using the potentiometric method, and the porosity of the CAC is calculated using thermogravimetric and drying methods. The chloride concentration of the CAC presents a two-phases distribution. The peak chloride concentration followed a power function, increasing with the erosion time. The chloride diffusion coefficient of CAC is 7.9%– 37.5% larger than that of ordinary aggregate concrete, and the addition of 15% fly ash and 5% silica fume can significantly reduce the chloride diffusion coefficient, with a maximum reduction of 45.0%. The porosity obtained via the thermogravimetric and drying methods is well correlated. The porosity has a strong negative correlation with the compressive strength and a strong positive correlation with the chloride diffusion coefficient.

A Two-Step Approach for Calculating Chloride Diffusion Coefficient in Concrete with Both Natural and Recycled Concrete Aggregates

A Two-Step Approach for Calculating Chloride Diffusion Coefficient in Concrete with Both Natural and Recycled Concrete Aggregates

Exploration of hydration and durability properties of ferroaluminate cement with compare to Portland cement

This study investigated the hydration process and durability properties of ferroaluminate cement (FAC). Hydration heat, hydration products, compressive strength, gas permeability and chloride diffusion coefficient were investigated experimentally for FAC mortar samples with different water-to-cement ratio (0.5, 0.45 and 0.4) and were compared with OPC mortar samples with the same mixing proportion. The mechanism of the difference in the durability of two cements was revealed from the perspective of pore size distribution and hydration products. The results show that FAC has a relatively fast hydration rate and the compressive strength at early age is larger than OPC. The gas permeability and chloride diffusion coefficient of FAC mortar samples are approximately 3–4 times lower than that of OPC mortar samples. The permeability and diffusivity of both FAC and OPC decrease significantly when the w/c decreases from 0.5 to 0.4. The main hydration products of FAC are ettringite, ferric hydroxide and aluminum hydroxide gel, large amounts of ettringite make FAC to form a dense structure, the proportion of the pores with pore size of 10–100 nm in FAC sample decreases greatly with compare to the OPC sample, which endows FAC superior impermeability properties.

Reinforced Concrete Structure Performance in Marine Structures: Analyzing Durability Indexes to Obtain More Accurate Corrosion Initiation Time Predictions.

This paper presents a comparison of six index properties collected during durability inspections of five Mexican seaports. Typical durability indicators such as compressive strength, saturated electrical resistivity, ultrasonic pulse velocity, percent total void content, capillary porosity, and chloride concentration profiles were analyzed to obtain empirical correlations with the non-steady-state chloride diffusion coefficient. These indices were compared to determine correlation coefficients that are the most important for obtaining better corrosion initiation forecasting. Two models of corrosion initiation time (ti) were used: Fick’s second law of diffusion and the reported UNE-83994-2 (Spanish Association for Standardization, UNE) in which electrical resistivity was used to calculate concrete service life. The data from both models were cleaned using correlated variables, and the initial variables were compared with ti. The main result achieved was the verification of the feasibility of using correlations of variables to clean unnecessary data in order to calculate ti. Additionally, electrical resistivity was identified as one of the main durability indexes for in-service concrete structures exposed to marine environments. This is important because electrical resistivity is a non-destructive and reliable test that can be measured both in the laboratory and in the field very easily.

Chloride Diffusion by Build Orientation of Cementitious Material-Based Binder Jetting 3D Printing Mortar.

Binder jetting 3D printing (BJ3DP) is used to create geometrical and topology-optimized building structures via architectural geometric design owing to its high degree of freedom in geometry implementation. However, building structures require high mechanical and durability performance. Because of the recent trend of using 3D printing concrete as a structural component in reinforcing bars, its durability with respect to chloride penetration needs to be reviewed. Therefore, in this study, the compressive strength and durability of the chloride diffusion of cement-based 3D-printed output were evaluated. In addition, to confirm the performance difference based on the build orientation, the compressive strength and chloride diffusion were evaluated with respect to the build direction and transverse direction. The experimental results show that the compressive strength was approximately 22.1–26.5% lower in the transverse direction than in the build direction and that the chloride diffusion coefficient was approximately 186.1–407.1% higher in the transverse direction. Consequently, when a structure that requires long-term durability is produced using BJ3DP, it is necessary to examine the design and manufacturing methods in relation to the build orientation in advance.

Iodide and chloride ions diffusivity, pore characterization and microstructures of concrete incorporating ground granulated blast furnace slag

Innovative approaches are under research to study the resistance of chloride ion penetration in concrete containing chloride ions, to minimize the impact of chloride ion penetration test errors in coastal reinforced concrete (RC), which is helpful to the design of coastal RC structures. In this study, the diffusion depth, free ion concentration and diffusion coefficient of chloride, iodide ions with different curing ages and GGBFS content were measured by the Rapid Chloride Migration Test (RCM) and Rapid Iodide Migration tests (RIM). The SEM-EDS and MIP were used to analyze the microstructures, pore size distribution and the hydrated products. The results show that the performance of GGBFS concrete against the diffusion of corrosive ions is affected by the curing age and the content of GGBFS. With the increase of GGBFS content, especially concrete with 60% GGBFS, the influence of chloride, iodide ion penetrating into concrete gradually becomes smaller. The long-age curing system is more conducive to the concrete resistance to the migration and diffusion of chloride, iodine ions. Compared with the ordinary concrete, the total porosity of concrete mixed with GGBFS is lower, the internal microstructures have fewer cracks and defects, the density is better, and the diffusion coefficient of chloride and iodide ions is also lower. In addition, using the concept of corrosive ion adjustment coefficient (conversion coefficient of diffusion between chloride ion and iodide ion) and applying the data regression analysis (DRA), it is found that there is a good quadratic parabolic function relationship between the GGBFS content and the ions adjustment coefficient.

Diffusion behavior of chloride in coral aggregate concrete in marine salt-spray environment

In this study, the chloride diffusion behavior of coral aggregate concrete (CAC) in a salt-spray environment was investigated. Ten concrete groups were designed using different mix proportions, and the concrete samples were exposed to a salt-spray environment for 180 days. The effects of the aggregate type, CAC strength grade, fly ash (FA) content, and basalt fiber (BF) content on chloride ion diffusion were analyzed. The results showed that the chloride concentration of CAC was higher than that of ordinary aggregate concrete. The chloride corrosion resistance of CAC could be effectively improved by adding 30% FA or 0.1% BF to the concrete mix, and the peak chloride concentration decreases by 15.9% and 16.3%, respectively. The peak chloride concentration of concrete appeared at 3–5 mm in the concrete and exhibited a power function increase with the exposure time. In addition, a model for calculating the peak chloride concentration was established. The chloride diffusion coefficient decreased with an increase in exposure time. When the BF content was 0.1%, the chloride diffusion coefficient was the smallest. X-ray diffraction and thermogravimetric analysis were performed to analyze the erosion products, and the deterioration mechanism of the CAC in the salt-spray environment was determined.

Durability of eco-friendly blended cements incorporating ceramic waste from different sources

Environmental conservation is mandatory for the sustainable development of the construction industry. A large amount of ceramic waste results from construction and demolition waste (C&DW). In addition, the extended service life of the structure is essential. This paper assesses the effectiveness of powder ceramic wastes (PCWs) from C&DW to improve the durable performance (chloride diffusion, sulfate resistance, and alkali–silica reaction) of blended cement (replacement 24% by mass). The suitability of blended cement is supported by the proven pozzolanicity (Frattini test, XRD, FTIR, and nonevaporable water content). Additionally, PCWs incorporation effect on the life cycle analysis of concrete is included. All samples containing ceramic waste show pozzolanic activity at 28 days, significantly reduce the apparent chloride diffusion coefficient, present good performance against the sulfate attack and reduce the expansion caused by ASR. In addition, PCWs reduce CO2 emissions. Results reveal a comparable performance of PCWs, indicating the unnecessary classification of them.

The role of chloride binding mechanism in the interpretation of chloride profiles in concrete containing limestone powder

The effect of limestone powder addition on the chloride binding capacity of concrete was evaluated. The results indicate that the chloride binding capacity becomes weaker as the limestone content increases due to decreased physical adsorption and chemical binding. XRD patterns indicate that adding limestone restrains the formation of monosulfate (AFm), thereby undermining the chemical binding. Thermogravimetric analyses (TGA) validate that despite limited participation of calcite in the hydration reaction, it is significant enough to change the stoichiometry of the cementitious systems and restrain the formation of Friedel's salt. The ratio between the apparent and effective chloride diffusion coefficients increases with decreasing chloride binding. A modified diffusion model was proposed based on Fick’s second law coupled with Freundlich adsorption isotherm on water-accessible pore surfaces to predict the chloride profile. The model exhibits a consistent trend that an enhanced chloride binding, higher tortuosity and lower porosity contribute to a lower chloride content.

Effect of Manufactured Sand with Different Quality on Chloride Penetration Resistance of High-Strength Recycled Concrete.

High–strength manufactured sand recycled aggregate concrete (MSRAC) prepared with manufactured sand (MS) and recycled coarse aggregate (RCA) is an effective way to reduce the consumption of natural aggregate resources and environmental impact of concrete industry. In this study, high–, medium– and low–quality MS, which were commercial MS local to Changzhou and 100% by volume of recycled coarse aggregate, were used to prepare MSRAC. The quality of MS was determined based on stone powder content, methylene blue value (MBV), crushing value and soundness as quality characteristic parameters. The variation laws of compressive strength and chloride penetration resistance of high–strength MSRAC with different rates of replacement and different qualities of MS were explored. The results showed that for medium– and low–quality MS, the compressive strength of the MSRAC increased first and then decreased with increasing rate of replacement. Conversely, for high–quality MS, the compressive strength gradually increased with increasing rate of replacement. The chloride diffusion coefficient of MSRAC increased with decreasing MS quality and increasing rate of replacement. The chloride diffusion coefficient of MSRAC basically met the specifications for 50–year and 100–year design working life when the chloride environmental action was D and E. To prepare high–strength MSRAC, high–quality MS can 100% replace RS (river sand), while rates of replacement of 50–75% for medium–quality MS or 25–50% for low–quality MS are proposed. Scanning Electron Microscope (SEM) images indicated that an appropriate amount of stone powder is able to improve the compressive strength of RAC, but excessive stone powder content and MBV are unfavorable to the compressive strength and chloride penetration resistance of RAC.