Chloride Migration Test Research Articles

Experimental investigation of the impact of additives in low clinker cementitious materials on multi-ion transference numbers and diffusion coefficients

In this paper, multi-ion transference numbers were determined throughout the chloride migration testing of low clinker cement-based materials. For this purpose, five cement pastes were studied: pure Portland paste (as a reference) and four other pastes, based on limestone filler, fly ash, slag or silica fume. The transference numbers were calculated from the concentration evolution in the three zones of the migration cell (catholyte, anolyte and sample), considering that: (i) ions moved in the catholyte and anolyte; (ii) ions leached from the sample; (iii) ions were generated from the electrode processes, and (iv) the pore solution of the sample evolved during the test. The chloride transference numbers of pastes with pure Portland cement, limestone filler, fly ash, slag or silica fume are almost zero at the beginning of the migration test but 0.23; 0.18; 0.06; 0.05 and 0.20 at the end of the test, respectively. The ion transference numbers obtained were used for the calculation of diffusion coefficients of chlorides, sodium and potassium using the Nernst-Einstein equation.

Mechanical properties and chloride resistance of ultra-high-performance seawater sea-sand concrete with limestone and calcined clay cement (UHPSSC-LC3) under various curing conditions

Although the application of ultra-high performance seawater sea-sand concrete with limestone calcined clay cement (UHPSSC-LC3) provides a promising solution for sustainable marine structures, research on the mechanical properties of UHPSSC-LC3 is quite limited, and no research has been conducted on its chloride resistance performance. In this study, the effect of four curing regimes (i.e. standard curing, 20 °C seawater curing, 40 °C fresh water curing, and 80 °C fresh water curing) on the compressive and flexural strength of UHPSSC-LC3 is experimentally investigated. Rapid chloride migration test and chloride titration test are conducted to determine the chloride diffusion and distribution of UHPSSC-LC3, considering the effects of curing conditions and calcined clay (CC) dosage. In addition, XRD analysis is performed to show the differences in the composition of UHPC, UHPSSC, and UHPSSC-LC3. The obtained results demonstrate that UHPSSC-LC3 attains higher mechanical strength than UHPC and UHPSSC under various curing conditions. The incorporation of LC3 makes the free chloride concentration of UHPSSC-LC3 close to that of UHPC, especially when the heated water curing is applied. The free chloride concentrations of UHPSSC- LC3 cured with 40 °C and 80 °C water are only 10.1 % and 2.9 % higher, respectively, than that of UHPC cured under standard condition. Besides, UHPSSC-LC3 achieves the lowest chloride ion diffusion rate, which is 40.4 % lower than that of UHPSSC, due to the denser matrix resulting from the carboaluminate products and the pozzolanic effects of the calcined clay. Furthermore, the application of heated water curing regimes is recommended for UHPSSC-LC3 when the early strength and chloride resistance are the main concerns.

Multi-scale study of the effect of superabsorbent polymers on microporosity, dimensional stability, and durability of cementitious materials

As internal curing agents, superabsorbent polymers (SAPs) help enhance the degree of hydration of cement particles. In the meantime, however, they affect the dimensional stability and durability of the mixtures that benefit from them. This critical aspect, which is influenced by the type, size, and dosage of SAPs, motivated the current study. To obtain holistic assessments and side-by-side comparisons, six high-performance mortar mixtures were developed based on a control mixture. The referenced mixtures contained two types, two sizes, and two dosages of SAPs. Initially, the performance characteristics of the SAP powders were determined, in terms of water absorption and desorption. Autogenous shrinkage tests were then performed to evaluate how SAPs contribute to controlling this type of shrinkage over time. The microstructures of the developed mixtures were then analyzed using mercury intrusion porosimetry, paired with scanning electron microscope images, providing fundamental insights into to the role of SAPs in both short and long terms. To correlate the findings to the mechanical properties of the developed mixtures, a set of compressive strength and abrasion resistance tests were performed. The results were then complemented with the data obtained from the rapid chloride migration tests. This study’s outcome showed that SAP particles can effectively reduce the development of autogenous shrinkage-induced strains. Additionally, the inclusion of SAPs was found to alter microstructural characteristics, increasing the density of the binding gel, while introducing capillary pores. This was confirmed through enhanced abrasion resistance and reduced chloride resistivity.

Study of corrosion resistance of superhydrophobic hydrotalcite cement mortar in chlorine salt environment

Reinforced concrete structures are susceptible to reduced service life owing to the erosion caused by the of chlorine-containing, external environment and internal chloride. In this paper, a superhydrophobic hydrotalcite cement mortar was studied with internal and external cooperation against chloride ion erosion. The effect of different hydrotalcite substitution amounts on the chlorine corrosion resistance of the mortar was investigated. The mortar exhibited good resistance to chlorine corrosion, and the corrosion resistance rate increased by 91.83 %. The free chloride ion concentration measurement and rapid chloride migration test exhibited that the prepared mortar effectively resisted chloride ion invasion and reduced the content of free chloride ions in the mortar. The proposed anticorrosion method is expected to have potential application prospects for concrete structures under chloride salt environments.

Fresh and hardened properties for a wide range of geopolymer binders – An optimization process

The objective of this study was to identify the optimal geopolymer binder compositions produced from local industrial by-products and compare them with commercially available materials. The first part investigated the optimal binder composition by studying 27 mixtures. In this part of the research, three series of binders were created: the first series of 18 mixtures was Na-based fly ash-slag, the second series consisted of 8 mixtures of K-based fly ash-slag, and the third series were a mixture of metakaolin-slag based geopolymer. The compressive strengths of the mixtures at the age of seven days ranged from 2.18 to 96.23 MPa. The strength development is clearly defined by the components and proportions of the blends. Geopolymers reach about 80% of their 28-day strength in seven days. The 25% water content was optimal for slag-fly ash geopolymers. The strength of the material increased from 68.08 to 96.23 MPa when the Blaine surface area of the slag increased from 3500 to 4500 cm2/g. The optimal proportions of the alkali solution were the intermediate ratios: SiO2/Na2O = 2.0 and SiO2/K2O = 1.5. In the case where Visonta fly ash is prepared for blending, the fly ash content can be maximized by 30%–50% in addition to the blast-furnace slag. In the second part of the research, mortars were prepared from the selected binders: 4 mixtures were prepared with two different binders. In one of these mortars, the solid part of the binder consisted of local raw materials originating from Hungary. This mixture was prepared with 43 m% fine aggregates. The optimal composition of the tested 27 binders tested was selected as the geopolymer matrix for the production of three further mortar mixtures. In these geopolymer mortars, 55, 65, and 75 m% of aggregate applied. The flowtable values of fresh mortars decreased when the proportion of sand increased. The lower the additive content was, the higher the strength of the geopolymer mortar. The 28-day compressive strengths of filtered fly ash-slag mortar sample with 55%, 65%, and 75% of fine aggregate (F–S-a55, F–S-a65, and F–S-a75) made with the selected optimised filtered fly ash-slag geopolymer binder of group A-I.3 (F–S-A-I.3) varied between 11.39 and 40.15 MPa, whereas the Visont fly ash-slag mortar sample with 43% of fine aggregate (V–S-a43) has been 25.05 MPa. For 28 days, the density ranged between 1870 and 2204 kg/m3. The V–S-a43 is found to be the lowest-density blend. The chloride migration test revealed that geopolymer mortars with higher slag content have higher resistance to Cl− ions.

Strength Assessment of RCC Beam With Partial Replacement of Metakaolin and Marble Dust

The most popular and adaptable building material is concrete, which is typically used to withstand compressive stress. A few pozzolanic elements can be added as admixtures to improve the various qualities of concrete. Calcified clay, or metakaolin, is widely accessible in Gujarat, Maharashtra, Bombay, and other places. It is the clay mineral kaolinite in a dehydroxylated state. Metakaolin particles are smaller than cement particles in size. Marble dust is produced by the industries that cut and manufacture marble. Approximately 3500 metric tons of marble dust slurry is produced daily in India. Therefore, marble dust may be found extremely cheaply and simply. Because marble dust has some advantages over cement, it is recommended to utilize it in part. The current study details an experimental program designed to explore the flexural behavior of reinforced concrete beams where river sand was partially replaced with marble powder in preparation for concrete and metakaolin was used in place of some of the cement. In this work, partial cement replacement has been carried out using MK (Metakaolin) at 5% and 10% and MP (Marble Powder) at 5%, 10%, 15%, and 20%. Concrete manufactured with MK-MP has been compared to conventional concrete of grade M30 in terms of both compressive and tensile strength. The Rapid Chloride Migration Test, or RCMT, was also used to examine the durability of concrete.

Understanding the effect of non-carbon-based nanoinclusions on chloride penetration resistance and chloride binding capacity of ultra-high performance cementitious composite

Ultra-high performance cementitious composite (UHPCC) with high durability has been widely employed to prevent the chloride corrosion of reinforced concrete structures exposed to the marine environment. Adding nanoinclusions is expected to fundamentally eliminate the defects (i.e., pores and microcracks) caused by the formulation principle of UHPCC, thereby reducing connected pathways for chloride diffusion. Furthermore, the diffusion resistance of chloride ions largely depends on the chloride binding capacity (CBC) of cement-based composites. Regrettably, the effects of non-carbon-based nanoinclusions on chloride penetration resistance (CPR) and CBC of UHPCC still lack comparison and analysis. This study investigated the effect of non-carbon-based nanoinclusions on the CPR and CBC as well as microstructures of UHPCC, including nano-SiO2 (NS), nano-ZrO2 (NZ), nano-TiO2 (NT), and boron nitride (BN). Correlation between pore structure parameters and CPR of composites was established based on the grey system theory. The results of rapid chloride migration (RCM) tests indicate that due to the incorporation of 1 % NS, 3 % SiO2-coated NT, 1 % NZ, and 0.5 % BN, the CPR of UHPCC is improved by 89.6 %, 66.5 %, 87.5 %, and 73.6 %, respectively. The results of the grey correlation analysis highlight the critical role of harmless and less harmful pores with a diameter below 50 nm in preventing the diffusion of chloride ions. The modifying mechanisms of nanoinclusions can be attributed to the nano-core effects, contributing to reducing chloride diffusion pathways and increasing disconnectivity and tortuosity of the pathways. Firstly, nanoinclusions can reduce pores and microcracks, improving the homogeneity of pore size distribution and inhibiting the growth of CH crystals, thus enhancing the compactness of the cement paste matrix. Secondly, nanoinclusions enriched in the interfacial transition zone (ITZ) can improve the homogeneity of ITZ by optimizing the Ca/Si ratios of C–S–H gels and improving the interfacial bond between cement paste and aggregate. Additionally, Langmuir and Freundlich isotherms can accurately describe the CBC of composites. Only NS among nanoinclusions can significantly improve the CBC of UHPCC. This can be attributed to the involvement of pozzolanic NS in cement hydration, promoting the formation of C–S–H gels for physically adsorbing chloride ions while increasing the diffusion resistance of chloride ions in the pathways.

Suitability of rapid chloride migration tests for determining the migration coefficient in mortars made from different novel binder types

AbstractThe main cause of corrosion of reinforcing steel, especially in infrastructure structures, is the penetration of chlorides, which can lead to high corrosion rates at the reinforcement steel. A frequently used accelerated test method to evaluate the chloride penetration resistance of concrete and mortars is the rapid chloride migration (RCM) test. The test was initially developed for ordinary Portland cement (OPC) based materials and involves spraying an indicator solution onto split test specimens to determine the penetration depth of the chloride ions. The pore solution compositions of new types of binders differ from OPC‐based materials, which can affect the reaction of the indicator solution. To investigate the suitability of the RCM test, the chloride content in the depth of the color change was determined in mortars made from different types of novel binders. The results show that the test provides reliable results for the binder types with partial replacement of OPC by supplementary cementitious materials. For binder types without OPC, there is a deviation in the migration coefficient due to a differing chloride concentration that triggers the color change.

Durability of sodium carbonate alkali-activated slag concrete assessed by a performance-based approach

The study aims to understand the performance and durability of a sodium carbonate alkali-activated slag (AAS) based on a performance-approach. Equivalent performances were obtained between the AAS and CEM III/C-based concretes having a water/binder ratio of 0.4 regarding compressive strength, porosity, resistance to nitric acid, and sodium sulfate. AAS exhibited higher resistivity and better resistance to chloride, assessed by a chloride migration test. The AAS showed similar carbonation resistance to CEM III/C and CEM III/B concretes with w/b ratios of 0.47 and 0.53, respectively. A discussion of durability tests for their application to this type of binder is conducted.

Mechanical performances, chloride permeability, and microstructure of wollastonite microfiber reinforced cement-based composite incorporated with zeolite powder

Wollastonite microfiber (WM) with a unique fiber structure and zeolite powder (ZP) with a high pozzolanic effect can improve the performances of cement-based composite owing to the same calcium silicate system. This study aimed to analyze the effects of WM and ZP on the properties of cement-based composite by compressive test, flexural test, shear test, rapid chloride migration (RCM) test, fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), mercury intrusion porosimetery (MIP) and scanning electron microscopy (SEM). Results showed that utilizing WM and ZP was found to be beneficial for improving mechanical performances and impermeability. WM had a more significant effect on enhancing flexural and shear properties, which can be attributed to the fact that the WM as a fibrous structure could provide skeleton support and bridging crack resistance in the matrix, and an addition of 5% WM (by mass) in the matrix could increase the 60-day flexural strength, shear strength and tensile strength by 24%, 13% and 4%. Additionally, ZP had a more significant impact on improving the late compressive strength and chloride permeability because of the particle filling effect and pozzolanic effect. The pozzolanic ingredient (such as active SiO2 and Al2O3) in ZP can take secondary hydration reaction with Ca(OH)2 to produce C–S(A)-H, this can refine the pore size and reduce the porosity, especially for the large pore.

Resistência à penetração de cloretos em concretos produzidos com agregado miúdo reciclado e sílica ativa

Abstract The use of by-products and recyclable materials in the production of concrete has become an interesting alternative to mitigate environmental impacts, especially those generated by the construction industry, as long as their mechanical and durability properties do not early compromise the service life of the structures. The resistance of concrete to the penetration of harmful agents, such as chloride ions, is an important property since it directly correlates with the performance, integrity, and durability of reinforced concrete structures. This study evaluate four concrete mixes were cast for aggressiveness class III of NBR 6118 [1] produced with 8% of partial replacement of Portland cement with silica fume, resulting of metallurgical production, and with 30% partial replacement of natural fine aggregates by recycled fine aggregate from fresh concrete waste, obtained from the concrete production process in concrete mixer trucks. At 28 days of age, the specimen was submitted to capillarity, mechanical resistance and chloride migration tests, according to the NT BUILD 492 standard [2]. In general, the results indicated that the proposed replacements improved mechanical properties and chloride ion penetration resistance, mainly with the incorporation of silica fume.

Medium transmission property of the interfacial transition zone between MK-GGBFS geopolymer mortar and aggregate

In this study, metakaolin (MK)–ground granulated blast furnace slag (GGBFS) was used to prepare geopolymer mortar, and concrete was prepared using prismatic-shaped basalt or aged cement mortar block as coarse aggregate. The pore structure characterization of the mortar, chloride binding capacity of the corresponding paste and the micro dimension of the interfacial transition zone (ITZ) in concrete were analysed by using a mercury intrusion porosimeter, the chloride adsorption equilibrium method and scanning electron microscopy-energy dispersive spectroscopy, respectively. The medium transmission properties of the concrete and corresponding mortar were analysed through a moisture diffusion test, chloride migration test, and chloride natural diffusion test. On this basis, the permeability resistance of the ITZ in geopolymer concrete was studied by manipulating the parameters for the basalt aggregate. The result shows that the geopolymer mortar exhibits higher porosity compared to cement mortar with similar strength, while the most probable pore size is significantly smaller, with more than 80% of the pores showing a pore size of less than 50 nm. The chloride binding mechanism for geopolymer paste primarily involves physical adsorption, and shows a greater binding capacity than cement paste at a chloride ion concentration greater than 1 mol/L. The medium transmission coefficient for geopolymer concrete is found to be 55.1–79.0% of that of cement concrete for the same parameters of the coarse aggregate. The impermeability of geopolymer concrete and its ITZ is found to be always better than that of cement concrete for varying parameters of the coarse aggregate.

Comparative analysis of three different types of self-healing concrete via permeability testing and a quasi-steady-state chloride migration test

Concrete is the most used construction material in the world and with the growing world population, the demand for housing and infrastructure keeps increasing. Due to its low tensile strength, concrete cracks easily and these cracks have a negative effect on the durability. Different studies have already been conducted on the development of self-healing concrete, which has the ability to heal its own cracks. Unfortunately, due to a lack of standardized test methods, the boundary conditions in these studies are often different, making it difficult to do an accurate comparison. In this research, three different healing agents are tested using the same test methods under the same boundary conditions: a powder of organic/inorganic composite material (WM), solidified calcium sulfoaluminate capsules (SMU) and bacterial pellets (KU). The healing efficiency of the agents is tested with (1) a low-head water flow test on prismatic specimens cracked in a three-point bending test with subsequent active crack width control, (2) a Korean water permeability test on cylindrical specimens cracked by a Brazilian splitting test, (3) a chloride diffusion test and (4) a quasi-steady-state chloride migration test. The results showed that WM performed superior with respect to the reference mix and the other healing agents in the two water permeability tests and the quasi-steady-state chloride migration. The performance of SMU and KU was depending on the healing condition. When fully saturated during healing, the KU specimens had a good behaviour and SMU performed poorly. For the cylindrical specimens, with the specimen partly immersed in water, SMU and KU had a similar performance which was better in comparison to the reference.

Influence of phase change material and nano silica aerogel aggregates on the characteristics of cementitious composite: An experimental and predictive study

This paper studies the influence of two high-performance thermal insulating materials including aerogel and phase change materials (PCM) aggregates, on the key characteristics of cementitious composites in experimental and predictive aspects. Thermal conductivity (ThC), rapid chloride migration test (RCMT), permeable pore volume, compressive strength, dry density, and microstructural analysis were performed for the mechanical properties. Moreover, Least Squares Support Vector Regression (LSSVR) as a machine learning method was introduced to evaluate and provide a proper method for non-destructive evaluation of parameters. The results of experiments indicated that both aerogel and PCM aggregates were highly effective although the aerogel showed more efficiency in enhancing the thermal insulation property of cementitious mixtures. In addition, the compressive strength of the mixtures with PCM composites was higher than the aerogel aggregates, where the compressive strength of the mixture containing 20 % paraffin was 50 % higher than the aerogel mixture with similar incorporation levels. Moreover, the mixtures with PCM aggregates had significantly lower water and chloride permeability compared to those of plain mixtures, and mixtures consisted of aerogel aggregates. The scanning electron microscope (SEM) analyses, also, revealed that the use of the aerogel aggregates led to an open and porous structure of the mixtures; however, PCM aggregates had a weak interfacial transition zone (ITZ) in the vicinity of cement paste. Furthermore, LSSVR model provided a close prediction of the effective parameters with an acceptable accuracy in capturing the influences of important parameters.

An investigation of the durability of ultra-lightweight high-strength geopolymeric composites

As promising and sustainable construction materials, ultra-lightweight high-strength geopolymeric composites (ULHSGCs) may be exposed to harsh corrosive environments. This study is designed to examine the durability of a new ULHSGC with a compressive strength ≥70 MPa and a density ≤1500 kg/m3. In preparing the ULHSGC, ground granulated blast furnace slag (GGBS) and silica fume (SF) were used as the binder, and fly ash cenospheres (FACs) and hollow glass microspheres (HGMs) were used as aggregates. A series of measurements, including accelerated carbonation, rapid chloride migration (RCM), sulfate resistance, X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests, was conducted to determine the effects of the SF content, Na2O content, SiO2/Na2O ratio and fibre type on the durability of the ULHSGC. The results indicated that the proposed ULHSGC with 10–15 % SF content and 6–7% Na2O content exhibited excellent compressive strength, resistance to carbonation, and resistance to chlorine penetration as well as suitable resistance to sulfate attack. Versions of the ULHSGC with lower SiO2/Na2O ratios had better compressive strengths, resistances to chloride penetration and resistances to sulfate attack but lower resistance to carbonation. The addition of polypropylene (PP) fibres and polyethylene (PE) fibres increased the porosity, which reduced the durability of the ULHSGC. However, given the significant contribution of the fibres to the compressive strength, the negative effect of adding 0.5 vol% fibres on the durability was acceptable.

Assessing durability properties of ultra-high performance concrete-class materials

Ultra-high performance concrete (UHPC) is a class of concrete materials that has received significant attention from the infrastructure community due to its favorable mechanical and durability performance. As the use of UHPC in infrastructure projects is becoming more common, there is an increasing interest in identifying appropriate testing techniques to assess the durability properties of UHPC-class materials. The dense microstructure of UHPC-class materials and the presence of a high concentration of fiber reinforcement have made it difficult to rely on existing standard testing approaches for concrete durability assessment. This study explores the application of various conventional-concrete durability test methods to UHPC, including electrical resistivity (American Association of State Highway and Transportation Officials (AASHTO) TP 119-22), freeze–thaw (ASTM C666), water absorption (ASTM C1585), and rapid chloride migration test (NT BUILD 492). The selected tests are meant to qualify and quantify the microstructural penetrability of UHPC to ions and fluids, a surrogate property commonly used as an indicator of durability. The findings from this study indicate that electrical resistivity can be used as a durability indicator for UHPC-class materials. Moreover, strong correlation between electrical resistivity and the chloride migration coefficient is identified, a potential benefit given that chloride migration can be used to estimate service lives of UHPC-class materials. Other tests, including freeze–thaw and water absorption, although identifying the favorable performance of UHPC relative to conventional concrete, were unable to provide insightful information through which the performance of individual UHPCs could be differentiated.

Temperature effect on strength and chloride migration in nuclear power plant concrete

In this study, strength and chloride migration tests were conducted considering nuclear power plant concrete exposed to high temperature and chloride ingress. Two temperature grades (20 ℃ and 50 ℃) were considered for curing and diffusion testing. In the curing at high temperature, cross-over behavior appeared for strength development from 7 to 14 days, however lower migration coefficients were evaluated under high temperature curing conditions. This was because even if cement hydrates were not completely stable, the absorption of chloride was still effective and the pore structure improved due to accelerated hydration. Migration test referred to NT-BUILD 492 method was performed on 40 MPa and 27 MPa concrete of 91 days curing. Activation energy for two strength grades was individually obtained during migration test with chaining temperature to 50 °C. The obtained results were compared with the previous results considering test method (diffusion and migration) and mix proportions.

Modelling of Chloride Transport in the Standard Migration Test including Electrode Processes.

The modelling of chloride transport in concrete under an electrical field requires taking into account the electrode processes. These processes are very rarely introduced into the literature, despite their impact on chloride migration and the electroneutrality of the pore solution of the material. This paper aims to propose a multi-ion model for chloride migration that takes into consideration the electrode processes. The model is applied to simulate the standard chloride migration test. The generation of OH- in the cathode and H+ in the anode allows for the monitoring of the electroneutrality. The model considers all of the ions in the pore solution. Ion fluxes are calculated using the Nernst-Planck equation. The Langmuir model is used to simulate the chloride isotherms. The thermodynamic equilibrium in the material is considered, which reflects the ion-solid interactions during the migration. Measurements of water porosity and the chemical composition of the pore solution are essential to provide input data and the initial and boundary conditions. The numerical results of the ion profiles in the material studied confirm the electroneutrality at any point within the material, in contrast with models that do not take the electrode processes into account. The proposed model allows for the more accurate simulation of the chloride migration test and electrochemical chloride extraction in reinforced concrete structures subjected to NaCl as part of maintenance and repair strategies.

The rapid chloride migration test as a method to determine the chloride penetration resistance of concrete in marine environment

This paper analyses the use of the rapid chloride migration test (RCMT) in assessing the long-term chloride penetration resistance of concrete in real marine environment. Based on extensive experimental data, RCMT results were related to the diffusion and penetration properties of a wide range of normal weight and lightweight aggregate concretes, 5-year exposed under real submerged (XS2) and wetting and drying (XS3) conditions. Most usual structural concrete with different water/binder, types of aggregates and binders were covered. Concretes were ranked in terms of their chloride durability performance in real environment and a new classification was proposed to evaluate the durability of concrete to chloride attack. Classes were established based on service life prediction analysis. Overall, it is shown that the RCMT classification can distinguish the resistance to the chloride penetration of different concretes under distinct exposure environments, allowing for an expeditious method to evaluate the concrete quality.

Improved Rapid Chloride Migration Test for Chloride Diffusion Coefficient of Concrete Based on the Image Processing Technique

Abstract The point average method (PAM) is commonly used in rapid chloride migration (RCM) tests to measure the average depth of chloride migration in concrete specimen. In this article, a spatial average method (SAM) was presented to improve the accuracy and stability of results tested on the basis of an image processing technique. There are 74 groups of concrete specimens prepared with different mix proportions and tested by the RCM technique with varying voltage applied. The area of the chloride migration region on the longitudinal section of the concrete specimens was captured by the image processing technique firstly, and then both the average depth of chloride migration and the diffusion coefficient of concrete were accordingly determined. Furthermore, the spacing of measuring points and the range and amplitude of the edge effect in the RCM test were determined by detailed analysis of the test data, thereby improving results from the PAM and the SAM. It was demonstrated that the edge effect should be taken into consideration in the RCM test for determining the chloride diffusion coefficient of concrete, and the spacing of measuring points for the PAM in current codes and guidance is so large that they should be modified. The general validity, satisfying stability, and high accuracy of the proposed SAM were evidentially proved by comparing it with the test data of the PAM.