Rapid Chloride Migration Test Research Articles

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.

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.

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.

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.

Improved chloride transport resistance of cement mortar using quartz sands modified with MgAl-LDH

The chloride transport into concrete is responsible for the durability deterioration of concrete under chloride-laden conditions. This paper aims to restrict the chloride transport into mortar by the partial replacement of fine aggregates with the quartz sands modified by MgAl-LDH, which were prepared by the co-precipitation method. The microstructures of modified sands and mortars were characterized. Besides, the chloride transport properties in mortar were evaluated by the rapid chloride migration test and long-term chloride diffusion test. The results indicate that quartz sands with in-situ-growth MgAl-LDH have improved specific surface area and chloride binding capacity. With the replacement ratio of modified sands increasing, the resistance of mortar against chloride penetration is significantly improved. The reason for the improved chloride transport resistance may be due in part to the improvement of the microstructure of ITZ, but more importantly, to the chloride ions immobilization of the modified quartz sand.

Properties of Self-Compacting Concrete Produced with Optimized Volumes of Calcined Clay and Rice Husk Ash-Emphasis on Rheology, Flowability Retention and Durability.

The durability of concrete requires a dense microstructure which can be achieved by using self-compacting concrete (SCC). Both calcined clay (CC) and rice husk ash (RHA) are promising supplementary cementitious materials (SCMs) that can partially replace cement, but their use in SCC is critical due to their higher water demand (WD) and specific surface area (SSA) compared to cement. The effect of partial substitution of cement at 20 vol-% with binary and ternary blends of CC and RHA on flowability retention and durability of SCC was investigated. The empirical method of SCC design was adopted considering the physical properties of both CC and RHA. The deformability of the SCC was evaluated using the slump flow and J-ring tests. The T500 time and the V-funnel test were used to assess the viscosity of the SCC. The flowability retention was monitored by the plunger method, and flow resistance was determined based on the rheological measurements of SCC. The evolution of the hydrate phases of the binder in SCC was determined by thermogravimetric analysis, while the durability was evaluated by a rapid chloride migration test. Cement partial replacement with 20 vol-% CC has no significant effect on fresh SCC, flowability retention, compressive strength and durability properties. On the other hand, 20 vol-% RHA requires a higher dosage of SP to achieve self-compactability and increase the viscosity of SCC. Its flowability retention is only up to 30 min after mixing and exhibited higher flow resistance. It consumes more calcium hydroxide (CH) and improves the compressive strength and chloride resistance of SCC. The ternary blending with CC and RHA yielded better fresh SCC properties compared to the binary blend with RHA, while an improved chloride penetration resistance could be achieved compared to the binary CC blend.

Pre-treated corn straw fiber for fiber-reinforced concrete preparation with high resistance to chloride ions corrosion

Chloride ions erosion is a negative factor for concrete sustainable usage. Fiber addition is a potential solution, which promotes a tight concrete structure formation resulting in the resistance of chloride ions. Corn straw is a kind of crop waste widely sourced that can be used as sustainable concrete reinforcement material. The traditional recycling method of corn straw including burnt as straw ash is not environment friendly. This work aims to pre-treat corn straw fiber (CSF) by some convenient methods (untreated, water-treated, alkali-treated) and add treated CSFs directly into concrete to prepare fiber-reinforced concrete with excellent mechanical properties and high resistance ability to chloride ions. The component content of different treated CSFs was tested to study the fibers composition and microstructure changes. The heat of hydration, compressive strength, and flexural strength were tested to study the hydration degree and the effect of different treated CSFs on the concrete mechanical performance. The rapid chloride permeability (RCPT) and chloride migration (RCM) tests were designed to study the reinforced concretes chloride ions resistance ability change. In addition, to further explore the mechanism of mechanical performance and chloride ions resistance ability change, water absorption rate (WAR) and mercury intrusion porosity (MIP) were tested to provide more supporting information from the micro-level. It is concluded that CSF treated by Na2SiO3 has the least impurities and a rougher surface with a larger specific surface area bonding with the cement substrate. Compared to the original concrete, the compressive strength of CSF concrete, WT-CSF concrete, and NT-CSF concrete increased by 15.7 %, 17.8 %, and 33.4 % respectively. The results of RCM and RCPT show a decreasing trend with different treated CSFs addition, the NT-CSF concrete shows the greatest decrease with 20.1 %, and 17.5 %, respectively. Except for the rougher surface and less impurities of CSF, the improvement of mechanical performance and chloride ions resistance ability is mainly due to treated CSF, especially the NT-CSF contributes to a denser structure formation based on the MIP and WAR test results. The viscosity of Na2SiO3 solution acts as a binder that helps to tighten the bonding between substrate and CSF. The water adsorbed by CSF and the alkaline environment provided by Na2SiO3 facilitates hydration decreasing the chloride ions migration. At the same time, the cellulose in CSF containing many hydroxyl and carboxyl groups further contributes to the concrete chloride ion resistance improvement due to its weak conductivity and the binding force of ions exchange.

Reinforced anticorrosive composite coating with mesh-brick structures and excellent air permeability on concrete

The commonly used resin coatings have excellent anti-corrosion properties, but cannot meet demanding performance requirements in marine environment, such as high mechanical stability and water vapor permeability. Water vapor permeability is important for concrete coating, which will discharge the residual water in the process of cement hydration. In this work, regulated poly(methyl methacrylate) (PMMA) porous and reticulated membrane (“mesh”) and two-dimensional modified zirconium phosphate (S–ZrP, “brick”) were used to form a novel “mesh-brick” structure, constructing organic-inorganic coating (S–ZrP/PMMA coating). Then, the microscopic structure of composite coatings was detailed studied, and the performance were characterized by the capillary water absorption, rapid chloride migration, abrasion resistance, and water vapor permeability (WVP) test. The results show that the coating with “mesh-brick” structures can significantly improve the hydrophobicity, impermeability, and chloride ion penetration resistance of the concrete mortar. The effect of S–ZrP concentration on the properties of composite coatings was studied, with the best impermeability performance at a concentration of S–ZrP of about 9 wt%. Benefit from the “mesh-brick” structures, the abrasion resistance of the coating has been improved, the contact angle of S–ZrP/PMMA coating did not decrease significantly, showing better stability, which reached 123.8° ± 3° even after rubbing 1000 cm. And it also greatly improved the mortar's WVP, keeping the cement-based materials air permeable. It is promising to provide long-lasting and stable protection for concrete.

Production of eco-friendly UHPC with high durability and resistance to harsh environmental conditions using copper mine tailings

In recent years, constructing environmentally friendly buildings, also known as green buildings, has become a crucial aspect of sustainable development principles. This experimental study investigates the partial replacement of Portland cement with Sungun copper mine tailings (SCMT) for the production of eco-friendly UHPC. The research includes resistance testing against sulfate attack at a 5% Na2SO4 concentration at 30, 90, and 180 days, with SCMT replacement ratios ranging from 5% to 30%. Furthermore, the mechanical properties of eco-friendly UHPC are examined. The study also assesses the mass loss and compressive resistance of UHPC after exposure to an HCl acid solution for 30 and 90 days. The resistance of UHPC to chloride penetration is evaluated using the rapid chloride migration test (RCMT). Additionally, capillary water absorption and microstructural properties of eco-friendly UHPC are studied through SEM analysis. The results indicate that UHPC with partial cement replacement by SCMT had improved mechanical properties, durability, and microstructure. The compressive strength reduction in eco-friendly UHPC mixtures due to acid attack was minimal when 10% SCMT was used as a replacement for cement after being immersed in HCl acid for 90 days. Furthermore, the mixture that contained 10% SCMT demonstrated lower penetration for chloride ions, Which referred to an improvement of 17.6%, compared to the control mixture. In addition, the results of the tests demonstrated that the incorporation of SCMT in UHPC at a rate of 5%–15% had a beneficial impact on the resistance of UHPC to sulfate attack when exposed to a 5% Na2SO4 concentration. This study demonstrates the potential of sustainable UHPC production with SCMT as a suitable alternative to cement in aggressive environments containing acids, sulfates, chlorides, and similar compounds.

Efficacy of high-volume fly ash and slag on the physicomechanical, durability, and analytical characteristics of high-strength mass concrete

In the last decade, the use of high-strength mass concrete has increased for the building of various high-impact infrastructure projects. Due to the larger size of sections and greater volume of Portland cement, the reduction of core strength and durability is often witnessed in these concrete sections. In this study, an attempt has been made to minimize the above issues by substituting ordinary Portland cement (OPC) with high-volume fly ash (FA) and ground granulated blast furnace slag (GGBFS). For this purpose, six types of samples viz. S1 (100% OPC), S2 (20% FA + 80% OPC), S3 (35% FA + 65% OPC), S4 (50% GGBFS + 50% OPC), S5 (70% GGBFS + 30% OPC), and S6 (33% FA + 33% GGBFS + 34% OPC) were prepared. The performances on the actual core concrete were evaluated by analyzing the peak temperature, compressive strength of cylindrical cores, rapid chloride migration test (RCMT), X-ray diffraction (XRD), thermogravimetry (TG), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM). Additionally, the bulk densities (wet and dry), water absorption, apparent porosity, and compressive strength of cube samples are also reported. Analyzing the results critically, it was observed that the use of high-volume FA and GGBFS (S5 and S6 samples) lowered the peak core temperature by 11–13 °C, increased the compressive strength of cores by 8–10 MPa, and lowered the RCMT values of cores by 12 × 10−12 - 13 × 10−12 m2/s as compared to the S1 (control) sample. Additionally, the increase in the ratio of the core-to-cube strength for the S5 and S6 samples is noted to be 24% and 29%, respectively, more than the control sample at 56 days of curing. The enhanced performance of the high-volume FA and GGBFS-based samples is due to the less core temperature rise due to less hydration reaction at the early ages and more secondary hydration reaction at the later ages, which has been justified by the XRD, FTIR, TG, and FESEM analyses. Finally, the sustainability and cost analysis revealed that the use of high-volume FA and GGBFS can significantly reduce embodied energy by 39–42%, embodied carbon by 53–58%, and production costs by 16–17%. The approach proposed in the article regarding the use of high-volume FA and GGBFS results in more green, durable, sustainable, and cost-effective high-strength mass concrete.

Mechanical properties, durability and environmental assessment of low-carbon cementitious composite with natural fibrous wollastonite

Cementitious composite is one of the most widely used construction materials around the world, but cement production is accompanied by energy waste and CO2 emission. Wollastonite, a natural fibrous silicate mineral, can be a potential supplementary cementing materials (SCMs) for cementitious composite owing to its similar calcium silicate system, and it has an eco-friendly and convenient production process. Furthermore, its unique fibrous structure can possibly act as reinforcement for the cement matrix. In view of this, this study aimed to investigate the effects of different sizes (the median diameter of 3 μm, 6 μm, 9 μm and 12 μm) and contents (0%, 5%, 10%, 15% and 20% by mass) of wollastonite combined with 5% silica fume on the mechanical strength, durability and microstructure of cementitious composite by compressive test, flexural test, shear test, rapid chloride migration test, sulfate corrosion test, X-ray diffraction(XRD), scanning electron microscope (SEM) and fourier transform infrared spectrometer (FTIR). The results showed that the strength and durability of samples increased and then decreased as wollastonite content increased. An addition of 10% wollastonite into the cement matrix increased compressive strength, flexural strength and shear strength by 6.22%, 29.3% and 18.4%, respectively. However, an addition of 5% wollastonite was found to be more beneficial for improving resistance to chloride and sulfate corrosion. Additionally, samples prepared with 3 μm wollastonite performed better, which can be attributed to the fact that the small size of wollastonite contributed to both the filling effect and the skeletal support and bridging effect of microfibers. The CO2 emissions of cementitious composites decreased as the wollastonite percentage increased. The findings confirm that natural wollastonite as SCMs for cementitious composite has performance enhancement and environmental benefits, however, it is recommended that the wollastonite content should not exceed 15%.

Experimental studies on durability performances of ultra-lightweight low-carbon LC3 cement composites against chloride ingression and carbonation

This study aims to experimentally evaluate the durability performances of a novel ultra-lightweight low-carbon calcined clay cement composite (ULCC-LC3) for use in sustainable concrete. The durability performances of ULCC-LC3 were characterized by conducting rapid chloride migration tests, accelerated carbonation tests, MIP and TGA tests. Results indicate that using LC3 is beneficial for improving chloride resistance of ULCC-LC3 due to refined pore structure while the carbonation resistance performance can be reduced due to less content of cement and pozzolanic reaction. The MIP tests showed the effect of using LC3 on microstructure of ULCC without carbonation was reducing the volume of porosity coarser than gel pores while increasing the volume of gel pores. The cementitious matrix of mixes with LC3 was significantly densified by carbonation. The carbon emission and energy consumption were significantly decreased by 41.9% and 26.7% respectively by replacing cement with calcined clay and limestone. However, it was noted that the use of superplasticizer increased the energy consumption especially for the mix with LC3.

Strength, durability and appearance of low-carbon fair-faced concrete containing multiple mineral admixtures

The feasibility of using fly ash, blast furnace slag, silica fume, and CaCO3-TiO2 composite and seashell powders as mineral admixtures in fair-faced concrete is investigated. A series of mix proportions were designed based on an orthogonal method. The effects of different mineral admixtures on the strength, durability and appearance properties were assessed by compressive strength, rapid chloride migration and grey-scale value tests, respectively. The results have shown that compressive strength is affected most by the content of seashell powder. Regarding chloride migration coefficient, blast furnace slag presents the most robust effect. Fly ash has the greatest influence on the grey-scale values at 180 d. Excessive seashell powder would lead to substantial decline in overall performance of fair-faced concrete.

Chloride penetration and binding behavior in unsaturated alkali-activated slag mortars

A comprehensive study from detailed microstructure analyses to mass transport investigations was implemented to explore chloride penetration of unsaturated alkali-activated slag (AAS) mortars accounting for chloride binding behaviors. Unsaturated chloride penetrations reflected from diffusion cases of instantaneous plane source and sorption cases of wetting-drying exposure were elaborated in relation to solid hydrates and pore structure features. It is found that the specimen with lower saturation has a slower chloride diffusion but a larger chloride penetration under wetting-drying cycles. Slag mortars with sodium hydroxide activation exhibit higher chloride binding capacity owing to more hydrotalcite-like phases and higher Ca/Si ratio of C-(N-)A-S-H gels in the outer product zones as compared to sodium silicate activated slag mortars, regardless of the saturation. Accelerations of the chloride penetration under the wetting-drying exposure are limited in saturated AAS specimens while for unsaturated AAS specimens more wetting-drying cycles result in the inner layers to be gradually diffusion-controlled. The chloride binding capacity of AAS specimens follows Langmuir's isotherm and clearly decreases with a lower saturation. It is advised to consider the electrical double layer effect within narrow pores when applying rapid chloride migration tests for AAS systems.

Modeling the chloride migration of recycled aggregate concrete using ensemble learners for sustainable building construction

The use of supplementary cementitious materials such as slag and recycled aggregate in concrete can mitigate some of the negative environmental impacts of using virgin materials. However, the durability of recycled aggregate concrete (RAC) and its resistance to harsh environmental conditions such as chloride penetration must be investigated before practical applications. The rapid chloride migration test (RCMT) is one of the well-established tests that can provide valuable estimations of the concrete quality against chloride penetration. RCMT coupled with machine learning techniques can lead to authentic models, which could save in time, cost, materials, and the need for skilled technicians. In this study, five homogeneous ensemble learners, including two types of bagging and three types of boosting techniques, were developed to model the RCMT output using a comprehensive database collected from the literature. Different types of analysis, including statistical measures, SHapley Additive exPlanations (SHAP) sensitivity analysis, SHAP parametric study, and comparison study, were conducted to examine the performance of the developed models and the effects of the input features on predictions. The results show that the developed extreme gradient boosting learner with the mean absolute percentage errors of about 9% possesses excellent capability for modeling the RCMT of RAC. Besides, the RCMT testing age is the most influential factor affecting the RCMT output, and the amounts of natural fine aggregate and superplasticizer are in the following orders. Finally, a graphical user interface (GUI) was designed, which allows the users to insert the input features and obtain the RCMT output in a user-friendly environment.

On the Chloride Distribution in Concrete and Mortar Samples after an RCM Test.

It is of essential need to face the challenges of CO2 reduction in industrial cement and concrete production reliable test methods in order to evaluate the performance of concretes, especially with regard to the service life of our infrastructure. The rapid chloride migration test (RCM test) is a standard method to assess the resistance against chloride ingress of concrete. However, during our study, certain critical questions arose with regard to the chloride distribution. The sharp chloride ingress front based on the model assumptions contradicted the shallow gradient of the experimental data. For this reason, investigations on chloride distribution in concrete and mortar samples after RCM tests were performed. The focus was on the factors influencing the extraction, e.g., time after RCM test and the location on sample. Furthermore, differences between concrete and mortar samples were investigated. The investigations showed that no sharp gradient on concrete samples was found due to the extremely uneven chloride front. In contrast, the theoretical profile shape was instead demonstrated on mortar specimens. The prerequisite for this result is that the drill powder must be taken directly after the completion of the RCM test from very uniform penetration areas. Thus, the model assumptions on the chloride distribution via the RCM test could be confirmed.

Applicability of the Formation Factor for Different Alternative Binder Types Investigated on Mortars

The high energy demand and associated CO2 emissions to produce ordinary Portland cement (OPC) create the need for alternative types of binders that can be produced in a more environmentally friendly manner. These alternative binders either have a reduced OPC content or can be produced entirely without the use of OPC clinker. To allow their widespread use also in reinforced concrete components, these binders must meet the same durability requirements as types of cement that have already been standardized. This requires a thorough characterization of the materials and, in addition, a verification of the applicability of the evaluation criteria known from the traditional binders. One of the most important factors influencing the transport processes in the material and therefore the durability is the penetration resistance of the pore structure for aggressive species, such as chloride ions. One key parameter for describing the pore structure is the formation factor (FF), which is used for various applications to evaluate durability. It is determined based on the ratio of the electrical resistivity of the concrete and of the pore solution. A high resistivity also influences the corrosion process of depassivated steel reinforcement in concrete or mortar: by inhibiting ion transport, the corrosion rate may be limited. In this study, mortars produced with different alternative binders are characterized in terms of their FF and pore size distribution. In addition, chloride migration coefficients determined by the rapid chloride migration test are related to the FF. The test program includes nine different alternative binders and two reference cements. In addition to a CEM I and CEM III/B, two calcined clays and a modified steel mill slag were investigated as supplementary cementitious materials, as well as a calcium sulfoaluminate () cement and a calcium silicate hydrate (C-S-H) binder. Four materials belong to the group of alkali-activated mortars: Two geopolymers and two alkali-activated slags were investigated here. It is shown that the AC resistances and the conductivities of the pore solutions differ greatly among the mortars investigated. The FF is a suitable parameter for a simplified estimation of the chloride penetration resistance of the investigated alternative binders, provided that realistic values of the pore solution conductivities are determined and used for the calculations.