Chloride Migration Research Articles

Advancements in Geopolymer Concrete for Marine Infrastructure: An Optimization of Performance Considering Workability, Compressive Strength, Capillary Water Absorption, Porosity, and Chloride Migration

Advancements in Geopolymer Concrete for Marine Infrastructure: An Optimization of Performance Considering Workability, Compressive Strength, Capillary Water Absorption, Porosity, and Chloride Migration

The coupling effect of calcined layered double hydroxides and impressed current cathodic protection system on chloride ion binding and migration of sea sand mortar

Chloride introduced by sea sand and sea water leads to steel bar corrosion. Calcined Layered double hydroxides (CLDH) and impressed current cathodic protection (ICCP) system were used to adsorb chloride ion and control steel bar corrosion in chloride abundant environment. In this research, chloride binding effect of two kinds of CLDH were investigated in simulated concrete pore solution. Besides, chloride absorption capacity and steel bar corrosion resistance of Mg-Al CLDH was explored in mortar. Further, hydration degree of mortar installed ICCP system and migration of ions around the anode and cathode were detected. Results show that Mg-Al CLDH exhibits excellent chloride binding capacity and corrosion resistance. After installing the ICCP system, corrosion of steel bars in mortar mixed Mg-Al CLDH was controlled. And ions in mortar specimen around anode or cathode exhibits migration phenomenon in different degree. A two stage-four step model was established to explain the degradation of hydration products and ion migration in CLDH-ICCP system. Under the ICCP system, Cl− in pore solution increased at early stage and then decreased both around anode and cathode, the increment process was controlled by desorption of Mg-Al CLDH and decreased process was controlled by degradation of hydration products. Therefore, the CLDH-ICCP system was recommended to solve the problem of steel bar corrosion introduced by marine environment.

Effects of mix composition on the mechanical, physical and durability properties of alkali-activated calcined clay/slag concrete cured under ambient condition

Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10−12 m2/s) for the non-steady-state migration coefficient (Dnssm). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10−12 m2/s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (Dnssm). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis.

Durability and mechanical properties of concretes with limestone filler with particle packing

This study aims to present alternatives to reduce the demand of cement in concrete production based on particle packing concepts. Physical and mechanical characteristics of concretes, as well as the resistance to chlorides action were analyzed. The tests conducted in this study included compressive strength, chloride migration, capillary absorption tests and wetting and drying cycles in 1M sodium chloride solution. Mixtures containing limestone filler presented satisfactory results compared to the reference mixture with particle packing. Excellent results were obtained for concrete with cement consumption of 253.34 kg.m-3 in terms of compressive strength, binder index, capillary absorption and depassivation time of rebars, thus reinforcing the concept that partial cement replacement by limestone filler yields positive results in these properties. Worse results were obtained for concrete with a cement consumption of 161.86 kg.m-3, because it had a higher proportion of filler than cement. The electrochemical monitoring of the steel bars also shows that the packing of the aggregates was essential to delay the initiation of corrosion.

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.

Chloride permeation resistance of sulphoaluminate cement-based composite characterized by both alternating current section and RCM methods

Sulphoaluminate cement (SAC) was widely used for rapid repair and strengthening of building structures due to its excellent quick hardening and high early strength behavior. This study developed a SAC-based engineering cement composites (ECC) with ultra-high molecular weight polyethylene (UHMWPE) and investigated its mechanical properties. Chloride ion permeability coefficient were evaluated by new alternating-current sectioning and rapid chloride migration (RCM). The mechanism of the SAC-ECC against chloride erosion were quantified using nitrogen isothermal adsorption. The results show that the fracture energy, tensile strength and strain of SAC-ECC samples are higher than that of normal ECC. The polyethylene (PE) fiber could significantly improve the flexural strength and toughness with PE fiber content of 0.75 % by volume. The hydration products generated could react with chloride ion to make it chemically stabilized, leading to reduce the chloride ion diffusion coefficient significantly. Based on microscopic analysis (SEM), the pore structure in SAC-ECC composite improved remarkedly while the volume of harmful pore decreased evidently as well. SAC-ECC developed in this paper could be poetically applied to strengthening and repair of marine concrete structures.

Research on quantitative design methods for the durability of reinforced concrete structures in a hot ocean environment

This paper establishes a quantitative design method for the durability of concrete structures in cross-sea bridges through investigation, rapid chloride migration coefficient method (RCM) and theoretical calculation, considering the impact of temperature on chloride ion diffusion rates in a hot marine salt erosion environment. Combined with the RCM test and bridge service data, a quantitative design method for bridge concrete durability is proposed. Test results show that the growth rate of the chloride ion diffusion coefficient of concrete is approximately 1.028 for every 1 °C increase. For every 5 °C increase, the growth rate of the chloride diffusion coefficient of concrete is about 1.15, and the cover depth of the concrete structure should be multiplied by a coefficient of 1.07. Therefore, the concrete cover depth should be appropriately increased, considering the influence of ambient temperature. Furthermore, fly ash, slag, and stone powder can increase the concrete’s resistance to chloride corrosion. When the influence of temperature on the chloride ion diffusion coefficient is considered, the durability design of the concrete structure of the sea-crossing bridge is conducted, which is beneficial for ensuring their service life.

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.

Calcined Clays as Concrete Additive in Structural Concrete: Workability, Mechanical Properties, Durability, and Sustainability Performance.

Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze-thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production.

Study on the microstructure and impermeability of calcium aluminate cement containing metakaolin for development of high-performance marine engineering materials

To provide a high-performance marine engineering material, the microstructure and impermeability of calcium aluminate cement (CAC) containing metakaolin (MK) were studied. The chloride penetration resistance of the CAC-MK and Portland cement (PC) mortars was assessed based on physical and chemical barrier effects. The results show that the alumina in MK is more easily dissolved than silica, which inhibits the transformation of CAH10 and prevents microstructural deterioration. Adding 7.5% and 15.0% MK reduces the volume of large pores in the 3-day-old CAC paste by 49.8% and 69.1% while increasing the volume of pores smaller than 50 nm by 175.6% and 242.5%, respectively. Moreover, the microstructure of MK-containing CAC pastes becomes denser with age when cured at 40 °C, enhancing the mechanical strength and water penetration resistance. The CAC mortar containing MK exhibits better resistance to chloride attack than PC mortar, due to the stronger chloride binding capacity and migration resistance.

Durability of Alkali activated concrete made using multiple precursors as primary binders

Alkali-activated binders (AABs) have been and continue to be extensively explored as an alternative to ordinary Portland cement (OPC), addressing environmental and sustainability issues. A large number of studies that were conducted earlier focused mainly on the mechanical properties and some durability aspects of industrial waste-based AABs. However, chloride migration and diffusion causing reinforcement corrosion in AAB-based concrete (AAC) have not been thoroughly investigated. The present study focuses on the durability of AAC produced using multiple precursors that included industrial waste materials and natural minerals such as limestone powder (LSP), red mud (RM), silicomanganese fume (SMF), and natural pozzolan (NP) activated by alkali. Firstly, the dosages of all four precursors were optimized through trials and then NP was partially replaced by 10, 20 and 30% OPC to enhance the performance of the AABs. The AAC mixtures were prepared and cured under different conditions and tested for compressive strength and durability characteristics related to chloride permeability, chloride migration, chloride diffusion, and chloride-induced reinforcement corrosion to evaluate the performances of the mixtures. The results show that the composition of the AABs and curing regimes significantly influenced the performance of the AAC. The inclusion of the OPC resulted in a very significant enhancement of the strength and durability characteristics of the AAC. In addition, there is a sharp increase in the performance of the AAC mixtures when the OPC content of the precursor was increased from 10 to 20%, irrespective of the curing method. Therefore, an optimum dosage of the OPC in the precursor can be considered as 20%, allowing utilization of 80% waste materials and natural minerals as the precursor with much higher strength and durability characteristics than traditional OPC concrete, thus saving energy and reducing environmental pollution leading to a cleaner production of concrete. Lastly, electrochemically measured corrosion potential (Ecorr ) and corrosion current density (Icorr ) values for the reinforcing bars (rebars) embedded in AAC mixtures were found to be misleading, as confirmed by visual inspection of the extracted rebars in addition to gravimetric test results. Hence, there is a need for further research to develop corrective measures before the utilization of the electrochemical-reinforced corrosion monitoring methods in the case of AACs.

Prediction and prevention of concrete chloride penetration: machine learning and MICP techniques

The chloride migration coefficient (CMC) of concrete is crucial for evaluating its durability. This study develops ensemble models to predict the CMC of concrete, addressing the limitations of traditional, labor-intensive laboratory tests. We developed three ensemble models: an inverse variance-based model, an Artificial Neural Network (ANN)-based model, and a tree-based model using the random forest regression algorithm. These models were trained on a dataset comprising 843 concrete mix proportions from existing literature. Results indicate that ensemble models outperform single models such as ANN and Support Vector Regression (SVR) in predicting CMC, with the combined random forest and ANN model showing the highest accuracy. Sensitivity analysis using Shapley Additive Explanations (SHAP) reveals that the CMC is most influenced by the water-to-cement ratio and curing age. Additionally, we designed a graphical user interface (GUI) to facilitate the practical application of our models. This research offers a robust methodology for evaluating concrete durability and potential for extending the prediction to other concrete properties.

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.

Investigation on the compressive strength, chloride migration of MK-FA-LS blended cementitious materials with electrochemical techniques

Blended cementitious materials has become an efficient method to reduce the CO2 emission while improving the long-time performance in construction filed, especially for the application of combined supplementary cementitious materials. However, the microstructure and performance evolution of the new materials need further deep investigation. In this study, metakaolin (MK), fly ash (FA) and limestone (LS) was introduced in cementitious materials to form a complicated quaternary system. The compressive strength and chloride migration performance are evaluated, with different MK/FA proportions. Then through the calorimetry test, X-ray Diffraction (XRD)/Rietveld analysis, free water content measurements, and electrochemical impedance spectroscopy (EIS) test, the phase assemblage and microstructure quantification of the blended systems are compared. Finally, to better understand the performance change, the correlation between the compressive strength/chloride migration coefficient and the electrochemical parameters are established. Results showed that the combination of MK, FA and LS is beneficial for the improvement of compressive strength and the chloride resistance in a proper mix design. EIS is a proper nondestructive method to understand the microstructure evolution of blended systems and even predict the chloride resistance of similar systems. This study shields a light for the application of the quaternary system, with a better durability, higher CO2 emission reduction and lower price.

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.

Oxygen-mediated acceleration of chloride capture and migration by copper oxide in PVC-based cable pyrolysis

Oxygen-mediated acceleration of chloride capture and migration by copper oxide in PVC-based cable pyrolysis

Limestone filler as a mineral additive on the compressive strength and durability of self-compacting concrete with limestone manufactured sand

Using limestone filler (LF) as a mineral additive of concrete with manufactured sand (MS) raises concerns about the long-term performance because of the high LF content in mixtures, particularly in high-binder content self-consolidating concrete (SCC). Herein, this paper evaluates the effects of LF as a mineral additive on the compressive strength and durability of SCC incorporating manufactured sand (MS_SCC). Results indicate that LF decreases the compressive strength of MS-SCC akin to that observed with FA, albeit with a more moderate decrease observed at a lower w/b ratio. Both LF and FA contribute to decreasing carbonation resistances, while MS_SCC with LF exhibits a gradual reduction in carbonation rate over time. Furthermore, LF reduces the chloride migration resistance of MS-SCC, unlike FA. However, LF improves the drying shrinkage of MS_SCC, particularly notable at a lower w/b ratio. Microstructure analysis indicates that LF induces a coarsening effect on the pore structure of MS_SCC, with a moderate influence observed for mixtures characterized by a lower w/b ratio.

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.

Microstructure and durability of rapid repair mortar with self-emulsifying waterborne epoxy polymer

Due to the low hydration rate of ordinary Portland cement (OPC), it cannot meet the requirements of rapid repair, especially in negative temperature environments. Simultaneously, facing the harsh marine environment, repair materials urgently need high durability. In this paper, a self-emulsifying waterborne epoxy polymer (WEP) suitable for cement systems was combined with sulfoaluminate cement (SAC) to prepare repair materials. The effect of the WEP on the development of microstructure, auto-drying shrinkage and durability was investigated by nuclear magnetic resonance, XRD and SEM methods. Results showed that a continuous interpenetration polymer network (IPN) was intricately woven within the multiphase composites, using the macromolecular network structure formed by —OH groups in WEP and Ca2+ and Al3+ in cement as a bridge. The resistance to chloride migration and water absorption exhibited an increase followed by a decrease. In particular, the resistance to chloride migration was improved by 45 %. Similar trends were observed for the carbonation resistance. Due to the lower porosity and capillary pressure caused by IPN, leading to a decrease in auto-drying shrinkage. Nevertheless, the larger percentage of capillary pores in a mortar with a P/C of 15 % increased the auto-drying shrinkage. The WEP decreased the availability of pores of critical diameter (14 nm) of mortar exposed to water freezing, leading to an increase in the freeze-thaw resistance. The change in P/C hardly affected the resistance to sulfate attack. Under −10°C, at 2 hours, the compressive strength of CSA-based mortar satisfied the load requirements for vehicular operations. This research provides theoretical and practical implications for the repair work of large-scale projects serving in harsh environments.

Influence of feature-to-feature interactions on chloride migration in type-I cement concrete: A robust modeling approach using extra random forest

Understanding the chloride transport mechanism is crucial for enhancing the durability of structures exposed to chloride-rich environments. This study assessed various machine learning (ML) algorithms for predicting the chloride migration coefficient in type I Portland cement-based concrete. The fine-tuned extra random forest model demonstrated satisfactory predictive capability, with the majority of tested-predicted data points falling within the ±30 % tolerance margin. This calibrated model was employed to explore feature-to-feature interactions affecting concrete resistance to chloride ingress. Examination of partial dependence plots revealed that an increased sensitivity with decreasing water–binder ratio (WB), reaching saturation beyond 0.40 WB, and the increase in curing age substantially reduced chloride diffusion (DN). Further, an augmented dosage of silica fume (SF) decreased DN, with a more pronounced effect of slag (SL) at higher WB, and the impact of superplasticizer (SP) decreased DN at high WB ratios. Concrete incorporating SF showcased optimal resistance to chloride permeability with the highest SF content (20–30 kg/m3). Similarly, high SL content (>150 kg/m3) enhanced resistance. The interactive influence of SF and SP on DN was marginal at low SF dosages (<20 kg/m3) but became complex at higher levels, with potential minimum values observed in the range of 0.5–1.0 kg/m3 SP. For SL-containing concrete, achieving the lowest DN was possible with PC and SL dosages around 200–400 and exceeding 100 kg/m3, respectively. For concrete incorporating Type I PC, an increase in SP content generally had a negligible impact on DN, with a slight tendency to raise values observed at higher cement amounts (exceeding 380 kg/m3). The optimal combination for achieving the minimum DN involved compositions of PC, fine, and coarse aggregate at 200–300, 100–150, and 250–500 kg/m3, respectively.