Chloride Ion Penetration Depth Research Articles

Mechanical Properties and Chloride Salt Corrosion Resistance of All-Lightweight Shale Ceramsite Concrete

In investigating the mechanical properties and chloride corrosion resistance of all-light shale ceramsite concrete (ALSCC), samples of ALSCC20–ALSCC45 with a compressive strength of C20–C45 were individually prepared. The compressive strength, split tensile strength, and elastic modulus of ALSCC were analyzed. Additionally, the chloride salt corrosion resistance of ALSCC was assessed by examining chloride ion penetration depth, steel corrosion rate, and compressive strength after ALSCC30 corrosion. Furthermore, the microstructure of ALSCC hydration products was observed using scanning electron microscopy (SEM). Results indicate that as the strength grade increases, the water–cement ratio decreases, and the internal structure becomes denser, thereby improving the mechanical and corrosion resistance properties of ALSCC. Notably, the chloride corrosion resistance of ALSCC surpasses that of ordinary concrete. SEM images reveal that the hydration of ceramsite with Ca(OH)2 in concrete generates Ca[Al(OH)4]2 precipitation and C–S–H gel, which enhances internal filling and improves chloride corrosion resistance. Furthermore, based on the results of the ALSCC30 corrosion test, a calculation model for predicting compressive strength in a chloride environment was proposed. This model effectively predicts the compressive strength of ALSCC under chloride exposure conditions.

Chloride Corrosion Process of Concrete with Different Water-Binder Ratios under Variable Temperature Drying-Wetting Cycles.

In this paper, four water-binder ratios (w/b) of 0.29, 0.33, 0.39, and 0.46 were designed. A variable test temperature was implemented in the drying-wetting cycle test according to the temperature fluctuations in the actual service environment, and the constant temperature test was established as the control group. The mechanical properties and chloride corrosion resistance of concrete with different w/b ratios under variable temperature drying-wetting cycles, as well as the microstructure changes, phase composition, and damage mechanism inside the concrete, were investigated. The results showed that the mechanical properties of concrete increased first and then decreased with drying-wetting cycles increasing, whereas the chloride corrosion resistance continued to decline. A higher w/b exacerbated the deterioration of the concrete performance. A higher w/b increased the porosity, chloride diffusion depth, and chloride content, thus reducing the resistance of chloride corrosion. Compared with w/b = 0.29, the compressive strength, splitting tensile strength, mass, and relative dynamic elasticity modulus of w/b = 0.46 exposed to 60 drying-wetting cycles decreased by 54.50%, 52.44%, 0.96%, and 6.50%, respectively, while the porosity, peak chloride content, and erosion depth increased by 45.12%, 70.45%, and 45.00%. Compared with the drying-wetting cycle with a constant temperature, the cumulative damage caused by the drying-wetting cycle with a variable temperature was greater, resulting in more severe deterioration of concrete performance. The increase in the test temperature significantly accelerated the diffusion rate, penetration depth, and chemical binding capacity of chloride ions. After 60 drying-wetting cycles, the peak chlorine content and erosion depth of w/b = 0.46 under variable temperature cycles were 15.38% and 10.32% higher than those under a constant temperature, while the compressive strength, splitting tensile strength, mass, and relative dynamic elastic modulus were reduced by 7.76%, 14.81%, 0.33%, and 2.40%, respectively. Microscopic analysis confirmed that higher w/b and variable temperature cycles accelerated the decay of mechanical properties and the decline of chloride corrosion resistance. According to the numerical fitting analysis, the w/b should be 0.29~0.39 under the condition that the mechanical properties and chloride corrosion resistance of concrete are met.

Effects of induction furnace slag on the durability properties of concrete

In this study, three major properties of concrete were compared, viz: water absorption, compressive strength and chloride ion penetration. The percentage amounts of Induction furnace slag (IFS) varied in concrete to replace cement were 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% and 60%. These specimens were made to undergo curing for 7, 14, 28, 56 and 90 days following which the aforementioned tests took place. The results of the three tests (i.e. compressive strength test, water absorption test and chloride ion penetration test) showed an optimal performance of concrete at 25% IFS replacement. Some of the specimens containing varying amounts of slag (i.e. 0%, 25% and 45%) were subjected to microstructural and phase identification tests in other to establish their distinguishing properties. These tests include Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Meanwhile the IFS was also examined for its composition through X-ray Fluorescence (XRF). Predictive models were generated from all the results obtained. The models developed can predict the compressive strength of concrete (Y) if information on the percentage of IFS replaced (X1), the depth of chloride ion penetration into concrete (X2) and the amount of void left in concrete after water is absorbed (X3) are all known. There existed a high correlation; strong relationship between compressive strength and the depth of chloride ion penetration; and between compressive strength and the percentage volume of void.

Research on the Strength Damage and Permeability Characteristics of Cemented Paste Backfill under Chlorine Salt Erosion and Dry–Wet Cycles

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry–wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry–wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry–wet cycle conditions. The results showed that the strength and Young’s modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry–wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 × 10−10 m2/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry–wet cycle, the CPB structure was severely damaged.

Coating technology on mortar surface for extending service life of on-site building construction

The superhydrophobic, self-cleaning and anti-corrosion surface was successfully coated on mortar using an effective one-step spray coating technique. A coating solution was prepared by mixing methyltrichlorosilane-modified SiO2/TiO2 nanoparticles at different ratios to enhance the super-hydrophobicity and reduce water absorption of the mortar. The sample prepared using a SiO2/TiO2 with the ratio of 75/25 was found to be optimal, exhibiting a high water contact angle and low sliding angle, which resulted in a reduction of water absorption more than 97.5 % and chloride ion penetration depth. Furthermore, the robustness of the superhydrophobic coating was analyzed against various tests including water drop impact, sand abrasion impact, tape peeling and sandpaper abrasion tests, with each test conducted over 10000 drops, 300 g, 60 cycles, and 5 cycles, respectively. Notably, the coating showed excellent water absorption reduction of 82.6 % after sandpaper abrasion for a length of 200 cm (20 cycles), even though the water contact angle was reduced to 118?. Thus, the fabrication of superhydrophobic mortar surface offers a novel, alternative approach that is simple, efficient, cost-effective and provides multifunction protection surface to increase the service life of on-site building construction with enhanced mechanical durability and anti-corrosion properties.

On effects of freezing and thawing cycles of concrete containing nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathbf {SiO_2}$$\\end{document}: experimental study of material properties and crack simulation

Construction during cold weather can lead to freezing accidents in concrete, causing significant hidden threats to the project’s performance and safety by affecting the mechanical properties and durability reduction. This study aims to deduce the compressive strength and durability of the concrete containing nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} under freezing-thawing cycles with the Caspian seawater curing condition. The specimens were subjected to freezing-thawing cycles according to ASTM C666. Furthermore, crack propagation in the concrete after freezing-thawing cycles is simulated. The results reveal that adding until nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} until 6% improved compressive strength before and after freezing-thaw cycles. The water permeability experiences a substantial reduction as the amount of nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} increases. Furthermore, the water permeability exhibits a positive correlation with the number of cycles, resulting in significantly higher values after 150 cycles compared to the initial sample. Moreover, adding 8% nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} reduced the depth of water permeability and chloride ion penetration after 150 cycles by 57% and 86%, respectively. The crack simulation results indicate that concrete containing 6% nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} shows an optimal resistance against crack formation. Concrete with 6% nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} requires 13.88% less force for crack initialization after 150 freezing and thawing cycles. Among different nano-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{SiO}_2$$\\end{document} percentages, 6% shows the best crack resistance and 8% the minimum water permeability and chloride ion penetration.

Multidimensional Transport Experiment and Simulation of Chloride Ions in Concrete Subject to Simulated Dry and Wet Cycles in a Marine Environment.

Chloride ion erosion is an important factor affecting the durability of marine engineering concrete. In particular, concrete structures in wave splash and tidal zones are subjected to dry and wet cycles and multidimensional diffusion of chloride ions. To investigate the intricate diffusion of chloride ions within concrete under these dynamic conditions, we devised a comprehensive experiment. This experiment encompasses multiple dimensions, involving dry and wet cycles, as well as static immersion. The experiment intends to reveal how chloride ions are distributed in the concrete and clarify the changes that occur in its microstructure. Based on Fick's second law, the multidimensional diffusion model of chloride ions in concrete under the dry and wet cycles and static immersion was established by comprehensively considering the effects of chloride ion exposure time, environment temperature, relative humidity, and the action of dry and wet cycles. The results show that, under the same conditions, the chloride content in concrete decreases with the increase in penetration depth but increases with the increase in the chloride diffusion dimension and exposure time. Dry and wet cycles and multidimensional diffusion of chloride ions increase the development of cracks and pores in the concrete structure and generate large quantities of C3A·CaCl2·10H2O, which will exacerbate the chloride ion transport rate and penetration depth of concrete. Under the same exposure time and penetration depth, the chloride ion content in concrete under two-dimensional (2D) and three-dimensional (3D) diffusion under dry and wet cycles was 1.09~4.08 times higher than that under one-dimensional (1D) diffusion. The correlation coefficients between the simulation results of the multidimensional transport model of chloride ions in concrete under multi-factor coupling and the experimental results were all greater than 0.95, and the model can be utilized to predict the distribution of chloride ion concentration in concrete.

Exploring the Detection of Cl- Penetration in Portland Cement Mortars via Surface Electrical Resistivity.

Surface electrical resistivity is a non-destructive technique that is sensitive to the microstructure of hydrated cement paste and the chemical composition of the pore solution in cement-based materials. In this study, a Wenner array was used to measure changes in mortar resistivity due to chloride ion diffusion as a function of electrode separation. Specimens were made from four mortar mixtures: 100% Ordinary Portland cement and 60% cement + 40% fly ash at two water/binder ratios of 0.55 and 0.40. The specimens were subjected to unidirectional chloride ion diffusion in a 2.8 M NaCl solution for 175 days. To determine the chloride penetration depth, three methods were used: silver nitrate spraying, chloride concentration profiles via potentiometric titration, and chloride concentration profiles via inversion of the resistivity data using the RES1D software (version 1.00.09 Beta). The results showed a linear relationship between the chloride ion penetration depth obtained via inversion of the surface electrical resistivity data versus the penetration depth from colorimetry and from chloride concentration profiling (both with R2 = 0.8612). Chloride penetration changed the conductivity of the pore solution; therefore, the resistivity decreased when increasing both the chloride concentration and the penetration depth. Inversion of surface resistivity data obtained with a Wenner array permitted non-destructive determination of chloride penetration. However, these results were obtained under laboratory environmental conditions and other scenarios must be addressed for wider applications.

Effect of seawater dry-wet cycling on the durability of concrete repair materials

In order to investigate the durability of concrete repair materials in marine environments, this research selected four typical repair materials commonly used on the market to carry out indoor seawater dry and wet cycling tests and real marine environment exposure tests. The research results show that: the compressive strength and abrasion loss variations of these four repair materials under indoor seawater dry-wet cycling are closely related. Among them, magnesium phosphate mortar demonstrates better resistance to seawater erosion in both environments. The chloride ion penetration depth of four repair materials increases with seawater dry and wet cycling time. Its law of change is closely related to the law of change of the most probable pore size inside the material, while the epoxy resin mortar and acrylic-modified mortar have a high depth of chloride ion penetration under the real marine environment due to the microcracks and porous phenomena appearing on the surface of the material. In addition, the results of the tests in the real marine environment differed somewhat from those in the indoor environment, highlighting the need to conduct real marine environment tests. The results provide theoretical support for selecting and evaluating concrete repair materials in the marine environment.

Chloride ion transport in unsaturated ultra-high performance concrete cracks under high hydraulic pressures

The high strength, durability, and impermeability of ultra-high performance concrete (UHPC) make it a vital material for the construction of deep underground facilities, such as tunnels, nuclear waste repositories, and research laboratories. However, the presence of cracks and high hydraulic pressure in deep underground greatly accelerates the transport of chloride ions, which can shorten the service life of UHPC. Unfortunately, the underlying mechanism for this is still unclear. Here, we investigated the influence of hydraulic pressure and capillary force on chloride ion transport in cracked UHPC using a self-designed testing module. It was found that the presence of trapped gas creates a gas–liquid two-phase state within the cracks. Theoretical models were established using the Laplace equation, which effectively describe the hindrance of gas within cracks on the transport of chloride ions. Contrary to current understanding, the primary driving force for chloride ion transport within the crack is the capillary pores along the crack walls, rather than the capillary forces associated with the crack itself. In addition, the unhydrated regions within the UHPC interior expedite the adsorption of water molecules compared to ordinary concrete. Hydraulic pressure significantly accelerates the depth of chloride ion penetration. Subsequently, the visualization of the solution within cracks was carried out through the application of X-ray computed tomography (X-CT) and capillary tests, thereby providing a means to validate the accuracy of the model. This study contributes to the advancement of our knowledge regarding the influence of capillary force and high hydraulic pressure on the transport of chloride ions. The findings have important implications for the analysis of the durability of UHPC structures situated in deep underground environments.

Chloride penetration of concrete exposed to dry-wet cycle with various dry-wet ratios and temperature

Numerous factors influence the concrete performance in dry-wet cycle environment, with dry-wet ratio and temperature being particularly significant. In this paper, the effect of dry-wet ratios (1:3, 1:1, and 3:1) on the chloride corrosion resistance of concrete was studied, and the variable test temperature and constant test temperature were implemented in the dry-wet cycle. The deterioration law of chloride corrosion resistance of concrete was investigated, and the microstructure, phase composition, and pore structure were examined. The results showed that the deterioration degree of concrete performance was intensified by a higher dry-wet ratio. Compared with D1W3 (the dry-wet ratio is 1:3), the compressive strength, splitting tensile strength, flexural strength, mass, and relative dynamic elasticity modulus (RDEM) of D3W1 (the dry-wet ratio is 3:1) exposed to 72 dry-wet cycles decreased by 11.05%, 19.40%, 8.33%, 1.09%, and 6.14%, respectively, while the peak chloride content and erosion depth increased by 40.98% and 22.75%. Compared to the dry-wet cycle with constant temperature, the cumulative damage caused by the dry-wet cycle with variable temperature was greater, resulting in more severe deterioration of concrete performance. Variable temperature accelerated the diffusion rate and penetration depth of chloride ions. The peak chloride content and erosion depth of D1W3 were 27.08% and 18.44% higher than those of control group after 72 dry-wet cycles. Microscopic analysis confirmed that higher dry-wet ratio and variable temperature cycles accelerated the decay of mechanical strength and the decline of chloride erosion resistance.

Mesoscale numerical simulation of chloride ion penetration in geopolymer concrete under the externally applied electric field

This paper presents a numerical investigation on the penetration of chloride ions in a saturated geopolymer concrete under the action of externally applied electric field. The chloride ion transport model in geopolymer concrete is established, and the interactions between different ionic species such as potassium ions, sodium ions, hydroxide ions, and chloride ions are considered. By solving the modified mass conservation equation and the Poisson equation of individual ionic species, the concentration and electrostatic potential of different ions at any position and at any time are obtained. Results show that under the action of externally applied electric field, the ion electromigration plays a leading role, which is characterized by a rectangular wave in the concentration distribution curve. In addition, the average chloride ion penetration depth obtained from the numerical simulations agrees well with that measured from the experiment in the cited literature. Moreover, the transmission speed of the two positively charged ions (or the two negatively charged ions) are almost the same. While there is a striking difference in the transmission speed between the positively charged ions and the negatively charged ions, indicating that the electrostatic potential gradient is not constant, and is region related.

Evaluation of crack self-sealing in flexural concrete members with SAPs by chloride ion penetration resistance

Self-sealing concrete is a technology to repair cracks using swelling properties of superabsorbent polymers (SAPs) without external work. Many studies have been conducted on SAPs as self-sealing materials that fill cracks in concrete. However, because each study evaluated self-sealing performance using different experimental methods, each study reported different results. Therefore, a standardized test method to evaluate the self-sealing performance of SAPs is needed. This study evaluated the self-sealing performance of cementitious materials with SAPs through water absorption, chloride ion penetration, and water flow tests and analyzed the correlations between the results. Two SAPs with different particle sizes were used, and their contents were set to 0.3%, 0.5%, and 0.7% depending on the binder weight. The experimental results revealed that the self-sealing performance improved with increasing particle size and SAP content. In the water absorption test, the amount of water absorbed by the surface of the original specimen and that absorbed through cracks were measured. However, the influence of the self-sealing ability of the SAPs on the total water absorption rate could not be clarified. A chloride ion penetration test was conducted to measure the chloride ion penetration depth directly, and the corresponding results indicated that the self-healing ability of the SAPs enhanced the resistance of the cementitious materials against the penetration of harmful ions. Finally, a water flow test was performed, and the results revealed that the short-term self-sealing performance of SAPs can be evaluated relatively independently.

Enhanced fracture and durability resilience using bio-intriggered sisal fibers in concrete

Biomimetic agents and natural fibers are the promising combo to enhance the strength and self-healing efficacy of concrete infrastructures. However, their contribution in durability and fracture attributes of the host concrete matrix is still questionable. This study explores the use of sisal fiber reinforcement and Bacillus Subtilis to modify the fracture, shrinkage, and durability performance of concrete. Fracture response was analyzed in compression, tension and flexural followed by durability tests conducted for chloride penetration, water absorption, and acid resistance. Results revealed that the addition of Bacillus Subtilis increases stiffness, while sisal fiber imparts ductility to the concrete. The resulting mixture exhibited significant improvements in compressive strength (14.0%), split tensile strength (36.8%), flexural strength (30.9%), and bi-surface shear strength (25.4%) as compared to the control mixture. Additionally, the toughness indices of the resulting concrete improved under compressive, split tensile, and flexural loadings. Incorporating sisal fiber and Bacillus Subtilis into concrete mixtures also led to a notable reduction in linear shrinkage (58.9%), attributed primarily to the fiber-reinforcing effect. When sisal fiber and Bacillus Subtilis are combined in the concrete mix, there is a net improvement in the concrete's durability. The resulting blend exhibited an increase of 18.3%, 24%, and 14.1% in resistance to water absorption, chloride ion penetration depth, and acid attack, respectively, as compared to the control mixture. Micro-forensics endorsed the signatures of microbially-induced calcite precipitation in the concrete mixture, which contributed to add in the durability of the resulting matrix. The study demonstrated that the conjunctive use of Bacillus Subtilis and sisal fiber can yield durable and ductile concrete. The findings provide valuable insights into the use of biomimetic agents and natural fibers to enhance concrete fracture and durability attributes, with significant potential for practical applications in the construction industry.

Electrochemical characterization of chloride ion transport in rubber concrete

Chloride-induced corrosion of steel in concrete structures is a significant issue. As an environmentally-friendly building material, rubber concrete has been proven to have the potential to resist chloride-induced permeation. In this paper, the transport behavior of chloride ion in rubber concrete was investigated by electrochemical impedance spectroscopy (EIS) approach. A novel electrochemical equivalent circuit Rs(Q1(Rct1W1)) (Q2(Rct2W2)) was used to study the electrochemical properties of rubber concrete systems and compare with other equivalent circuits by evaluation indicator. The results demonstrate that Rs(Q1(Rct1W1)) (Q2(Rct2W2)) is more suitable for the study of rubber concrete system and the increase of rubber will enhance the resistance to chloride ion transmission. The equation was established by the relation between the equivalent circuit parameter (Rct1) and the migration depth of chloride ion. On this basis, the EIS method can be utilized to predict the depth of chloride ion penetration in rubber concrete.

Effect of carbonation curing on distribution and binding capacity of chloride ions in cement pastes

Carbonation curing of concrete is an effective measure to reduce CO2 emissions, but it can adversely affect chloride binding capacity of cement pastes and its durability. In this study, the chloride ion content and phase assemblages of cement pastes under three curing conditions: standard curing, carbonation curing, and mixed curing (7-day carbonation curing and 21-day standard curing) were investigated based on combined macroscopic and microscopic methods. The chloride ions were introduced into cement pastes either through internal incorporation during the mixing process or from external penetration during its immersion in chloride contained solutions. Experimental results show that a large number of internally incorporated chloride ions were accumulated in the surface layer of pastes due to moisture evaporation during carbonation curing process. The transport of internally incorporated chloride ions in the paste under the mixed curing process was affected by the coupling effects of carbonation and capillary suction, resulting in inward migration of chloride ions. The external chloride ions from the solution penetrated into paste through initial diffusion and subsequent capillary suction during carbonation curing and mixed curing processes. Neither internally-incorporated nor externally-penetrated chloride ions could be bound in the carbonated zone, and the Friedel's salt could not be formed either. Due to the decrease of carbonation effect along the penetration depth and inward migration of chloride ions, the bound chloride ion content increased and formed a peak value in the inner layer.

Multifunctional Concrete with Graphene-Based Nanomaterials and Superabsorbent Polymer

This study reports on the development of a multifunctional concrete using graphene nanoplatelet (GnP) and sodium polyacrylate (SP) superabsorbent polymer. A combination of concrete functionalities was convened to improve, i.e., high strength and durability along with smart properties such as self-healing and self-sensing. GnP (0.05% by weight of cement) and SP (0.11% by weight of cement) were dispersed in concrete. Compared to the control concrete mix (no GnP and SP), the compressive strength increased 14% by GnP and decreased 9% by SP, and their combination resulted in a 6% enhancement in strength. The durability performance of concrete samples under coupled degradation mechanisms of freeze-thaw and chloride ion ingress suggested that SP in concrete has a better performance than GnP in concrete. SP in concrete shows self-sealing abilities resulting in less chloride ion penetration. However, the combined effect of both GnP and SP in concrete resulted in the maximum reduction in chloride ion penetration depth under freeze-thaw, a 42% reduction compared to the control mix. Microstructural analysis was conducted and found to resist the effects of freeze-thaw and reduce chloride ion penetration in modified concrete compared to the control concrete mix. GnP developed self-sensing abilities in concrete, resulting in about 12.7% fractional change of electrical resistance under 10 KN of cyclic compressive loading. The synergic impact of GnP and SP possesses a new prospect for developing highly efficient multifunctional concrete.

Performance Degradation of Fiber-Reinforced Concrete under Freeze–Thaw Cycles and Its Resistance to Chloride Ion Penetration

This study investigated the frost resistance of fiber-reinforced concrete with different contents of polyvinyl alcohol (PVA) fiber under freeze–thaw cycles, and the resistance to chloride penetration. The freeze–thaw cycle experiment was carried out using the rapid freeze–thaw method. Mass loss, relative dynamic modulus of elasticity, compressive strength, and flexural strength were investigated, and the influence of chloride ion content and the chloride ion diffusion coefficient after freeze–thaw cycles was analyzed. The results showed that under freeze–thaw cycles, PVA fiber can effectively reduce mass and dynamic elastic modulus loss and improve compressive and flexural strength. The contributions of fiber to mass loss, relative dynamic elastic modulus, and compressive strength gradually decreased with the addition of PVA fiber (>0.12 vol. %), while the contribution to flexural strength increased. The penetration depth of chloride ions positively correlated with the number of freeze–thaw cycles. The PVA fiber-reinforced concrete exhibited better chloride ion penetration resistance compared with that of the control concrete after freeze–thaw cycles. The concrete mixed with 0.12 vol. % PVA fiber exhibited the best chloride ion penetration resistance.

Effects of pipe diameter, curing age and exposure temperature on chloride diffusion of concrete with embedded PVC pipe

Concrete structures are often embedded with pipe opening for the installation of pipelines which tends to weaken the integrity and durability. The effects of pipe diameter, curing age, and exposure temperature, on the chloride ion resistance of concrete with embedded PVC pipe (CEPP) were investigated in this paper. The testing parameters include compressive strength, electric flux density, chloride ion diffusion coefficient, chloride ion penetration depth, and chloride ion content. The results showed that electric flux density and chloride ion diffusion coefficient of CEPP increased with the diameter of PVC pipes following a second-degree parabola and a linear relation respectively, while the chloride ion diffusion coefficient decreased with the prolonging curing age. The chloride ion resistance and compressive strength of CEPP were decreased with the increase of pipe diameters, because the weak areas formed in the transition interfaces between the PVC pipes and concrete matrices and expanded with increased diameter. The chloride ion penetration depth and chloride ion content were relatively higher in the testing points near the PVC pipes than the ones far away from the PVC pipes. In addition, the rate of chloride ion penetration of CEPP could be accelerated by the higher exposure temperatures, leading to severer chloride ion penetration of CEPP. Finally, a novel modified Fick's second law diffusion model considering the effects of pipe diameters and curing age was proposed to predict the chloride ion resistance of CEPP.

Study on the penetration and diffusion of chloride ions in interface transition zone of recycled concrete prepared by modified recycled coarse aggregates

This work aims at exploring the penetration and diffusion behavior of chloride ions in interfacial transition zones (ITZs) of modified recycled aggregate concrete (RAC). For this purpose, RAC were prepared by using nano-SiO2 and carbonation treated recycled coarse aggregates (RCA, with different strength grades of C30 and C60) and immersed in 3.5% NaCl solution for 45 days and 90 days. The mechanical properties and free chloride ion content of the modified RAC were investigated and the topographic characteristics and element distribution patterns of Ca, Si, and Cl in ITZs of RAC were detailed characterized. The results show that the chloride ion will permeate into the interface in ITZs of RAC in the first instance, and then intrude into mortar matrix through the pores and fractures. In contrast, the internal microscopic structure of ITZs become more compact and the number of the cracks are decreased obviously after nano-SiO2 treatment, which can provide effective barrier and significantly reduce the penetration depth of chloride ions. In addition, the high strength RCA can also effectively reduce the penetration and diffusion of chloride ions to concrete matrix due to the compact and uniform microstructure. This work provides a certain theoretical guidance for further improving the chloride erosion resistance of RAC.