Chloride Ion Diffusion Coefficient Research Articles

Research on crystalline admixtures for low carbon buildings based on the self-healing properties of concrete

The increasing fascination surrounding low carbon construction materials has propelled self-healing concrete into the realm of vital technologies for attaining low carbon objectives. This investigation through artificial cracking and precompression experiments demonstrates the efficacy of two specific crystalline admixtures (CAs), namely L-aspartic acid (LAA) and Ethylenediaminetetraacetic acid (EDTA), in augmenting the self-healing characteristics of concrete. The flexural and compressive strength as well as chloride ion diffusion coefficient tests, were used to evaluate the mechanical properties and durability, and the microstructures was analyzed by X-ray diffraction (XRD), differential thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), Bruno-Emmett-Teller (BET) and mercury intrusion pore size measurement (MIP). The findings indicate that the optimum dosage for both LAA and EDTA is determined to be 0.5%. At this dosage level, these admixtures effectively fill the pores by stimulating the production of hydrated calcium silicate gel (CSH) and calcium carbonate, leading to a reduction in porosity, enhanced concrete compactness, and successful activation of the self-healing mechanism. Moreover, the incorporation of these admixtures results in improved strength grade and enhanced resistance against chloride ion penetration.

Study on Lifetime Performance Evaluation of a Precast Prestressed Concrete Frame in Chloride Environments.

This study established a comprehensive framework for evaluating the lifetime performance of precast prestressed concrete frames exposed to chloride environments. The proposed analytical framework enabled a scientifically grounded and rational assessment of both the service life and residual load-carrying capacity of precast prestressed concrete frames in chloride environments. It further served as the foundational basis for making informed decisions regarding the repair and maintenance of pertinent structures. Based on Fick's second law, this evaluation framework established the probability distribution of the corrosion initiation time and cracking time of reinforced concrete structures due to corrosion expansion in a chloride environment. Additionally, based on the fragility analysis model and results of a precast prestressed concrete frame in a chloride environment, a practical method for evaluating the time-varying seismic performance of the precast structure considering the influence of corrosion was proposed. Furthermore, by employing the path probability model and reliability theory, time-varying reliability models were proposed to predict the three limit states of the precast prestressed concrete frame. According to the analysis results of a four-story planar frame, it could be seen that the corrosion initiation time and normal service limit state were highly sensitive to the chloride ion diffusion coefficient of the composite layer in precast concrete structures. Compared to cast-in-place structures, the presence of a composite layer in precast concrete structures could lead to more severe degradation of the time-varying seismic performance of the precast prestressed concrete frame.

Multi-scale microstructure quantitative characterization and anti-erosion performance of PHC pipe pile

Pre-stressed high-strength concrete (PHC) pipe pile is widely used in many large-scale projects, thus their durability has attracted more and more attention. However, in most studies, PHC pipe pile is regarded as the same as ordinary reinforced concrete, ignoring the effect of special construction processes and hollow shape on its microstructure and anti-erosion performance. In this paper, the real PHC pipe pile was cored and cut to investigate the multi-scale microstructure and the anti-erosion performance of PHC pipe pile concrete layer. The results shown that pore content first increases and then decreases with PHC pipe pile from the outer layer to the inner layer (5F → 1F) by CT, BSE and LF-NMR results, and the pore content changes most significantly around the rebar in PHC pipe pile. In rebar interfacial transition zone (ITZ), the thickness of the voids in PHC pipe pile is greater than that of normal reinforced concrete under the same water-binder ratio condition. Additionally, the content of un-hydration products in aggregate ITZ is obviously greater than that in rebar ITZ. Furthermore, the chloride ion diffusion coefficient of the concrete on the outside of the PHC pipe pile is slightly larger than that on the inside, which is closely related to the higher pore connectivity of the concrete on the outside of the PHC pipe pile. Moreover, it was found that centrifugation can not only reduce the water-binder ratio of PHC pipe pile but also affect the radial pore structure of PHC pipe pile concrete, including porosity and pore connectivity. This work finally indicated that the microstructure of PHC pipe pile concrete is quite different from that of normal reinforced concrete, providing a theoretical basis for establishing the diffusion model of PHC pipe pile concrete.

Experimental Study and Numerical Analysis of Chloride Ion Diffusion in Hydrotalcite Concrete in Chloride Salt Environment.

Hydrotalcite, known as layered double hydroxides (LDHs), is a new type of admixture used to delay the corrosion of reinforcement. The aim of this study was to investigate the chloride ion diffusion behavior of C30 concrete with varying amounts of calcined hydrotalcite (0%, 2%, 4% and 6%) in a chloride salt environment. The NT-Build 443 test was adopted to characterize the one-dimensional accelerated chloride ion penetration of concrete. The distribution of chloride ion concentration in hydrotalcite concrete with different mix proportions immersed in sodium chloride solution for 30 days and 60 days was determined, and the chloride ion diffusion coefficient and surface chloride ion concentration were fitted based on Fick's second law to establish the chloride ion diffusion model considering the influence of multiple factors. This model was validated using COMSOL Multiphysics finite element software. The results show that concrete mixed with LDHs can meet its compressive strength requirements and that the resistance of concrete with 2% calcined hydrotalcite to chloride ion penetration is the best with a 19.6% increase in the 30-day chloride ion penetration coefficient. The chloride ion diffusion process under chloride salt immersion conditions is in accordance with Fick's second law. The chloride ion concentrations calculated with COMSOL software and the test results are in good agreement, which verifies the reliability of the chloride ion diffusion model.

Development of cementitious capillary crystalline waterproofing agents and durability study of concrete in the presence of chloride with sulfate in aqueous environment

In this study, the chemical composition of cementitious capillary crystalline waterproofing agents (CCCW) was developed by using the water penetration resistance test method. Response to impermeability by first permeability and self-healing properties by second permeability, five effective single components were obtained: Ethylene diamine tetraacetic acid (EDTA), l-aspartic acid, sodium sulfate, sodium silicate and nano-silica. With the help of chloride ion diffusion coefficient measurement and sulfate attack resistance test, it investigates the effect of five components on the durability of the concrete matrix. According to the differential thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis methods, the waterproof mechanism of each component acting in the matrix was proposed. Finally, also combined with the results of macroscopic performance and microscopic analysis designed orthogonal experiments, the results show that the optimal blending of five waterproofing agent components up to 300% increase in substrate impermeability. The optimal amount of each component is 0.5% EDTA, 2% l-aspartic acid, 3% sodium sulfate, 2% sodium silicate, and 2% nano-silica.

Numerical simulation on diffusion–reaction behavior of concrete under sulfate–chloride coupled attack

The transport of sulfate–chloride salts in concrete is the main cause of its structural deterioration. Traditional numerical simulation assumes that the diffusion coefficients of sulfate ions and chloride ions are both constant leading to large deviations in the predicted results. Based on the mass conservation law, Fick’s second law, and the theory of porous media, a variable coefficient transport model of sulfate–chloride salts in concrete is established in this paper. The model fully reflects the adsorption and desorption of chloride ions in the transport process, the reaction-filling process of sulfate ions and hydration products, as well as the most important porosity and tortuosity affecting ion transport. Results show that the prediction results of the two-dimensional variable coefficient model are consistent with experimental and literature results, with maximum error of 23.49%. The analysis of influencing factors shows that the interaction between sulfate ions and chloride ions does not change the transport law of ions in concrete, but delays the rate of ion corrosion within about 700 days. The ability of chloride ions to be adsorbed decreases by about 20% when sulfate ions are present, and the desorption rate is about 40% to 60%. The tortuosity decreases with the increase of water-binder ratio, and increasing the initial porosity from 5% to 12% leads to an early appearance of cracks by about 1400 days.

Chloride penetration resistance and chloride binding capacity under different application environments of ferroaluminate cement

Free chloride is a crucial factor that threatens the long-term performance of marine concrete structures. The resistance of cement to chloride penetration and its capacity to bind chloride are important parameters for assessing the ability of cement-based materials to resist chloride invasion. Ferroaluminate cement (FAC) has considerable application potential in concrete used for marine structures; however, its resistance to chloride invasion and mechanism of chloride binding have not yet been revealed. In this study, the chloride diffusion coefficient and chloride binding capacity of FAC, for both internal and external chloride ions, are experimentally investigated and compared with that of ordinary Portland cement (OPC). The results show that the chloride diffusion coefficient of FAC mortar is approximately 2.5 times lower than that of OPC mortar. FAC exhibits finer overall pore distribution and the number of pores with sizes within 10–100 nm is reduced, which is responsible for its notably lower chloride diffusion coefficient. The chloride binding capacity of FAC to internal chloride ions is slightly lower than that of OPC, and a portion of the chloride ions are chemically bound by reacting with ye'elimite during hydration. The chlorides bound by physical adsorption constitute a dominant portion of the entire bound chloride content. In the case of external chloride ions, the bound chloride content of FAC is lower than that of OPC. The chemical chloride binding capacity of FAC is comparable to that of OPC and the lower physical adsorption capacity for chloride in FAC leads to a weaker chloride binding capacity compared to that of OPC.

Experimental Study on Long-Term Mechanical Properties and Durability of Waste Glass Added to OPC Concrete.

This study aims to achieve the sustainable utilization of waste glass resources through an investigation into the influence of three types of admixtures, namely waste glass powder (WGP) (G), waste glass powder-slag (G-S), and waste glass powder-fly ash (G-F), on the mechanical properties and durability performance of waste glass concrete. The experimental results demonstrate that the exclusive use of WGP as an admixture led to the relatively poor early compressive strength of the concrete, which decreased with an increase in dosage. However, at medium to long curing ages, the strength of the waste glass concrete could equal or even surpass that of ordinary concrete. When dual admixtures were employed, the G-S group exhibited higher compressive strength compared to the G-F group. Specifically, within the G-S group, a glass powder dosage of 15% yielded higher compressive strength, and after 180 days, the dual admixture groups exhibited greater strength than ordinary concrete (G0); the compressive strength of the tG1S1 group was 44.57 MPa, and that of the G0 group was 40.07 MPa. The chloride ion diffusion coefficient showed a varying trend with an increase in WGP dosage, initially decreasing and then increasing. The concrete's resistance to erosion was maximized when the glass powder dosage reached 30%. As the WGP dosage increased, the overall frost resistance decreased. For a total dosage of 30%, the optimal glass powder dosage in both G-S and G-F groups was found to be 15%.

Feasibility of using iron-rich phosphoaluminate cement to prepare anti-corrosive coatings for rebars

The anti-corrosive coating has been taken as an effective measure to keep rebars from corrosion. In this study, the iron-rich phosphoaluminate cement (IR-PAC) based anti-corrosive coating for rebar was prepared. The Cl- diffusion coefficient, strength against abrasion, and impact ductility of IR-PAC mortar were tested, with ordinary Portland cement (OPC) and sulphoaluminate cement (SAC) mortar as controls. The experimental results demonstrated that the chloride ion diffusion coefficient of IR-PAC was the lowest at any age. Compared with OPC and SAC, the strength against abrasion of IR-PAC at 90 d increased by 19.19 % and 14.32 %, respectively. The impact ductility of IR-PAC at 28 d increased by 28.21 % and 17.37 %, respectively. IR-PAC had good resistance to Cl- penetration, excellent strength against abrasion and impact ductility, which assisted the coating in blocking Cl- intrusion and resisting damage. The optimum SCMs based coating for rebar is as follows: 10.08 % Fly ash (FA), 0.1 % nano-silica (NS), and 0.65 % superplasticizer (SP). The coatings prepared with this formulation were used for electrochemical experiments. The rebars coated with IR- PAC had good corrosion resistance, which proved it is feasible to use IR-PAC to prepare anti-corrosive coatings for rebars.

Chloride ion diffusion and distribution characteristics in recycled coarse aggregate concrete under uniaxial and biaxial pressure

Under uniaxial compression, recycled coarse aggregate leads to complex internal stresses (simultaneous uniaxial, biaxial, and multiaxial tensile and compressive stresses at the micro scale) and even micro cracks in concrete, which poses difficulties in accurately predicting the chloride ion diffusion of recycled concrete. By changing the compressive stress level and bi-directional stress ratio of concrete, a self-developed biaxial compression device was used to test the chloride ion diffusion coefficient of recycled concrete under different stress states. In order to analyze the influence of various factors on chloride ion diffusion, DIC digital image technology and microcrack statistics technology were used to analyze the influence of concrete micro deformation on its chloride ion diffusion coefficient under load, and X-ray fluorescence technology was used to accurately analyze the concentration distribution of chloride element in different positions of concrete. The pore structure inside recycled concrete was characterized through experiments, and a real three-dimensional multi-scale model of concrete and the statistical characteristics of porosity at different scales were obtained. Finally, a theoretical model was established to predict the chloride ion diffusion coefficient under biaxial compressive loads, achieving accurate prediction of chloride ion diffusion coefficient close to practical engineering.

Estimation of Durability of HC-550 Floor Slabs Based on Electrochemical Tests of Corrosion Rate of Reinforcement Strings in Concrete

The consequences of the loss of the load-bearing capacity due to the corrosion of prestressing steel can be much more dangerous than in the case of reinforced concrete structures, since failure can occur quite rapidly and without warning. A very important issue, therefore, is to determine the factors affecting the durability of prestressed structures exposed to aggressive agents, especially chloride ions. The aim of this study was to verify the protective properties of concrete of prefabricated HC-type prestressed concrete slabs in order to evaluate the possibility of their application in the ceilings of multilevel garages. In this paper, the corrosion rate of rebar steel in HC-550 floor slabs at a width of 1200 mm was estimated with nondestructive electrochemical methods: linear polarization and impedance spectroscopy. The general and mechanical properties of concrete prepared according to a formula in a laboratory and analogous concrete cut directly from the analyzed floor slabs were also studied. The porosity of concrete from these slabs was determined using X-ray-computed tomography for pore-related characterization. The values of the diffusion coefficient of chloride ions determined in previous works and the previously proposed model for the overexposure of the durability of floor slabs in chloride-containing environments were used to determine the durability of these slabs. Based on the empirical correlations adopted from the literature presenting the relationship of durability/adhesion over time and the corrosion parameters studied, a safe service life was determined at the nominal class of concrete equal to Δtcor.red = 30.48 years. In addition, in the case of discontinuities in the concrete structure, there may be a dangerous reduction in the time of corrosion initiation and a subsequent reduction in service life due to the loss of the adhesion of strut strands for up to 10.68 years of service life.

Time variation law of chlorine diffusion coefficient of marine concrete structures in tidal zone and its influence on service life

Chloride diffusion coefficient (Da) is an important parameter to predict chloride ion concentration in concrete, which is of great significance to the study of durability and service life of concrete structures in the Marine environment. The alternating wet and dry environment in tidal zone has a significant impact on the deterioration of concrete's chloride ion erosion resistance. It is extremely important to study the chloride ion diffusion coefficient in the tidal zone. In this paper, the apparent chloride diffusion coefficient (Da) and its time-dependent constant (m) of concrete were calculated on the basis of a large number of natural exposure test data and engineering data in tidal zone at home and abroad, the time-varying law of chloride diffusion coefficient of marine concrete structures in tidal zone were discussed. The ChaDuraLife Model, DuraCrete model and Life-365 model were utilized to calculate the service life of concrete structures based on the immersed tube tunnel in the north Marine environment of China. The results showed that Da in tidal zone decreases with exposure time and presents a power function relationship. It was found that proper addition of mineral admixtures could improve the chloride ion erosion resistance of concrete structures in tidal zone during long-term service by reducing the chloride ion diffusion coefficient. The type of mineral admixture and the value of m would affect the calculation result of the service life of concrete structures. The addition of mineral admixture would lead to the increase of m, thus prolonging the service life of concrete structures. Service life calculated by different models was changed. The value of m of DuraCrete model was larger, so the calculated service life was longer. Similarly, the calculated service life of Life-365 model was shorter. It was noted that the ChaDuraLife Model was the most economical and safe model to predict the service life of concrete structures.

The durability of basalt-fiber-reinforced cement mortar under exposure to unilateral salt freezing cycles

Basalt fiber and cement-based materials have been widely applied in engineering structures. In this context, the durability of basalt-fiber-reinforced ordinary silicate mortar was systematically studied under exposure to unilateral salt freezing. The mechanical durability, chloride ion diffusion characteristics, and microscopic pore characteristics of cement mortar with basalt fiber content levels in the range of 0 kg/m3–1.5 kg/m3 were tested under exposure to 0–40 freeze–thaw cycles. The relationships of changes in the internal pore structure with mass loss, mechanical damage, and the physical properties of the material were also analyzed under exposure to salt freezing cycles. The results demonstrated that even a small amount of basalt fiber could significantly improve the mechanical properties of cement mortar under unilateral salt freezing and its resistance to salt freezing erosion. In particular, cement mortar with 1.2 kg/m3 basalt fiber content exhibited good durability of compressive and flexural strength, while the specimens with no basalt fibers exhibited a relatively large degree of internal porosity under exposure to unilateral salt freezing. Our work provides concrete evidence for changes in the porosity of mortar under exposure to unilateral salt freezing, with these changes showing an exponential relationship with mortar mass loss and a strong linear correlation with changes in the compressive strength, flexural strength, and chloride ion diffusion coefficient of the material.

Deicing performance of cement pavement concrete mixed with chlorine salt antifreeze material

This study explores a cost-effective and efficient method for snow melting and deicing using a concrete pavement structure with pre-mixed chloride-salt antifreeze material. The mixed design method for road cement concrete with chloride-type antifreeze material is investigated by encapsulating NaCl and CaCl2 in organic resin capsules. The snow melting and deicing efficacy of cement concrete with chloride antifreeze material is evaluated through an automatic tracking measurement system. The results indicate that NaCl-type antifreeze material is more effective in reducing the freezing point of concrete surface solution than CaCl2-type antifreeze material. A composite antifreeze material (4% NaCl + 1% CaCl2) provides the strongest snow melting and deicing ability. An outward migration and diffusion model of chloride ion in cement concrete with antifreeze material is established to calculate the chloride ion diffusion coefficient, surface chloride ion content, and decay rate of concrete. The effective age of snow melting and deicing is analyzed using this model.

Protective Performance of Coated Reinforcement in Coral Concrete under Dry/Wet Cycling.

The actual protective performance of the coated reinforcement in coral concrete was investigated by measuring the chloride ion diffusion coefficient, electrochemical analysis, and numerical simulation. The test results show that the corrosion rate of coated reinforcement in coral concrete under the action of wet and dry cycles is kept at a low level, and the Rp value is always greater than 250 kΩ·cm2 during the test period, which is in the uncorroded state and has good protection performance. Moreover, the chloride ion diffusion coefficient D is in accordance with the power function relationship with the wet and dry cycle time, and a time-varying model of chloride ion concentration on the surface of coral concrete is established. The surface chloride ion concentration of coral concrete reinforcement was modeled as a time-varying model; the cathodic zone of coral concrete members was the most active, increasing from 0 V to 0.14 V from 0 to 20 years, with a large increase in potential difference before the 7th year, and a significant decrease in the increase after the 7th year.

Analysis of the Effect of Protective Properties of Concretes with Similar Composition on the Corrosion Rate of Reinforcing Steel Induced by Chloride Ions.

This study presents a comparison of the protective properties of three concretes of similar composition on the effect of chloride ions. To determine these properties, the values of the diffusion and migration coefficients of chloride ions in concrete were determined using both standard methods and the thermodynamic ion migration model. We tested a comprehensive method for checking the protective properties of concrete against chlorides. This method can not only be used in various concretes, even those with only small differences in composition, but also in concretes with various types of admixtures and additives, such as PVA fibers. The research was carried out to address the needs of a manufacturer of prefabricated concrete foundations. The aim was to find a cheap and effective method of sealing the concrete produced by the manufacturer in order to carry out projects in coastal areas. Earlier diffusion studies showed good performance when replacing ordinary CEM I cement with metallurgical cement. The corrosion rates of the reinforcing steel in these concretes were also compared using the following electrochemical methods: linear polarization and impedance spectroscopy. The porosities of these concretes, determined using X-ray computed tomography for pore-related characterization, were also compared. Changes in the phase composition of corrosion products occurring in the steel-concrete contact zone were compared using scanning electron microscopy with a micro-area chemical analysis capability, in addition to X-ray microdiffraction, to study the microstructure changes. Concrete with CEM III cement was the most resistant to chloride ingress and therefore provided the longest period of protection against chloride-initiated corrosion. The least resistant was concrete with CEM I, for which, after two 7-day cycles of chloride migration in the electric field, steel corrosion started. The additional use of a sealing admixture can cause a local increase in the volume of pores in the concrete, and at the same time, a local weakening of the concrete structure. Concrete with CEM I was characterized as having the highest porosity at 140.537 pores, whereas concrete with CEM III (characterized by lower porosity) had 123.015 pores. Concrete with sealing admixture, with the same open porosity, had the highest number of pores, at 174.880. According to the findings of this study, and using a computed tomography method, concrete with CEM III showed the most uniform distribution of pores of different volumes, and had the lowest total number of pores.

Chloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading

This paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.

Effects of MOFs-derived Ni@NC/CNT nanocomposites on impermeability and microwave absorption of modified epoxy resin coatings on cement-based materials

Human health and information security are harmed by electromagnetic wave (EMW) energy’s constant increase and various reflections. In this study, Metal-organic frameworks (MOFs) derived metal nickel@nitrogen-doped porous carbon/carbon nanotube (Ni@NC/CNT) nanocomposites with excellent EMW absorption performance were utilized to modify epoxy resin coatings on the cement-based materials. Surprisingly, when the dosage is 3 wt%, the cement-based materials coated with the modified epoxy resin coatings show outstanding permeability resistance and EMW absorption properties. The capillary water absorption coefficient and the chloride ion diffusion coefficient are 37.583 and 2.42 × 10-12 m2 s−1, which are 88.05% and 73.2% respectively lower than that of the uncoated specimen. The excellent EMW absorption performance was concretely manifested that the minimum reflection loss (RLmin) value is −45.76 dB, the effective absorption bandwidth (EAB) value is 12.88 GHz, and the effective practical application bandwidth (EPB) value is 15.04 GHz. Additionally, the modified epoxy resin coatings also exhibit exceptional thermal stability and mechanical properties, which are further analyzed with TGA and SEM results. These outstanding properties are attributed to the good compatibility between Ni@NC/CNT nanocomposites and epoxy resin, higher cross-linking densities, favorable nano-size effect, and the excellent EMW performance of Ni@NC/CNT nanocomposites. This work is extremely helpful for improving EMW absorption and other properties of epoxy resin coatings on cement-based materials.

Brownian Motion Simulation for Estimating Chloride Diffusivity of Cement Paste

Chloride ion diffusion properties are important factors that affect the durability of cementitious materials. Researchers have conducted much exploration in this field, both experimentally and theoretically. Numerical simulation techniques have been greatly improved as theoretical methods and testing techniques have been updated. Researchers have modeled cement particles mostly as circular shapes, simulated the diffusion of chloride ions, and derived chloride ion diffusion coefficients in two-dimensional models. In this paper, a three-dimensional random walk method based on Brownian motion is employed to evaluate the chloride ion diffusivity of cement paste with the use of numerical simulation techniques. Unlike previous simplified two-dimensional or three-dimensional models with restricted walks, this is a true three-dimensional simulation technique that can visually represent the cement hydration process and the diffusion behavior of chloride ions in cement paste. During the simulation, the cement particles were reduced to spheres, which were randomly distributed in a simulation cell with periodic boundary conditions. Brownian particles were then dropped into the cell and permanently captured if their initial position in the gel fell. Otherwise, a sphere tangential to the nearest cement particle was constructed, with the initial position as the center. Then, the Brownian particles randomly jumped to the surface of this sphere. The process was repeated to derive the average arrival time. In addition, the diffusion coefficient of chloride ions was deduced. The effectiveness of the method was also tentatively confirmed by the experimental data.

Effect of Cementitious Capillary Crystalline Waterproofing Materials on the Mechanical and Impermeability Properties of Engineered Cementitious Composites with Microscopic Analysis

Building structures are prone to cracking, leakage, and corrosion under complex loads and harsh marine environments, which seriously affect their durability performance. To design cementitious composites with excellent mechanical and impermeability properties, Engineered Cementitious Composites (ECCs) doped with ultrahigh molecular weight polyethylene short-cut fibers (PE-ECCs) were used as the reference group. Different types (XYPEX-type from Canada, SY1000-type from China) and doses (0%, 0.5%, 1.0%, 1.5%, 2.0%) of Cementitious Capillary Crystalline Waterproofing materials (CCCWs) were incorporated. The effect of CCCWs on the mechanical and impermeability properties of PE-ECCs, and the microscopic changes, were investigated to determine the best type of CCCW to use and the best amount of doping. The results showed that with increasing the CCCW dosage, the effects of both CCCWs on the mechanical and impermeability properties of PE-ECC increased and then decreased, and that the best mechanical and impermeability properties of PE-ECC were achieved when the CCCW dosing was 1.0%. The mechanical properties of the PE-ECC were more obviously improved by XYPEX-type CCCW, with a compressive strength of 53.8 MPa, flexural strength of 11.8 MPa, an ultimate tensile stress of 5.56 MPa, and an ultimate tensile strain of 7.53 MPa, which were 37.95%, 53.25%, 14.17%, and 21.65% higher than those of the reference group, respectively. The effects of the two CCCWs on impermeability were comparable. CCCW-PE-ECC(X1.0%) and CCCW-PE-ECC(S1.0%) showed the smallest permeation heights, 2.6 mm and 2.8 mm, respectively. The chloride ion diffusion coefficients of CCCW-PE-ECC(X1.0%) and CCCW-PE-ECC(S1.0%) exhibited the smallest values, 0.15 × 10-12 m2/s and 0.10 × 10-12 m2/s, respectively. Micromorphological tests showed that the particle size of the XYPEX-type CCCW was finer, and the intensity of the diffraction peaks of C-S-H and CaCO3 of PE-ECC increased after doping with two suitable doping amounts of CCCW. The pore structure was improved, the surface of the matrix was smoother, and the degree of erosion of hydration products on the fiber surface was reduced after chloride ion penetration. XYPEX-type CCCW demonstrated a more obvious improvement in the PE-ECC pore structure.