Apparent Chloride Diffusion Coefficient Research Articles

Randomness and time-varying characteristics of chloride ion transport in existing harbor concrete structures

This paper presents a study on the durability testing of a concrete facility located within the North Bay Port region, which has been in service for 200 months. Based on the results of 20 sets of concrete samples, an improved Kolmogorov-Smirnov (K-S) test method and gross error discrimination method are proposed to analyze the random distribution functions of the apparent chloride diffusion coefficient (Dapp) and the apparent surface chloride concentration (Cs), and further explore the time-varying characteristics of chloride ion transmission in concrete. The research shows that the improved K-S method presented in this paper can effectively reduce the probability of type II errors by selecting a rational sample size, which can also improve detection efficiency. When the sample size does not exceed 10, the 2σ criterion proposed in this paper can effectively identify and eliminate gross errors. In general, Dapp and Cs follow the log-normal distribution, while the time factor (m) follows a normal distribution parameter. The value of Cs basically stabilized after exposure to 80 months, whereas Dapp tended to stabilize after exposure to 100 months. The value of m obtained through fitting short-term experimental data is typically overestimated, and its value decreases as the exposure time prolongs. Therefore, m should also be considered a time-varying parameter that decreases with time. The tested RC structure will begin to experience rebar corrosion after 48.5-60 years of exposure to the marine environment based on the probabilistic assessment.

Time-depth dependent chloride diffusion coefficients of self-compacting concrete

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentrations (CICs) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCMs) - fly ash (FA), blast furnace slag (BS), and silica fume (SF) – were measured through the accelerated salt immersion tests. The apparent chloride diffusion coefficients (CDCs) at any exposure time and erosion depth were calculated using the Boltzmann-Matano method. The influence of the type and content of SCMs, the water-binder ratio (W/B), and the type of salt solution on CICs and CDCs were investigated. Both introducing SCMs and reducing W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CICs were reduced to a greater degree than total CICs in FA and BS concrete, but the opposite was true for SF concrete. Presence of calcium chloride in salt solution increased total CICs while reducing free CICs. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilized. A model of apparent free CDC considering the time-depth dependence was created, which shows that time reduction factors of CDC is larger in SCM-containing SCC than in control SCC.

Chloride Transport Characteristics of Concrete Exposed to Coastal Dredger Fill Silty Soil Environment

In contrast to the marine environment, coastal regions encompass substantial saline soils characterized by complex corrosive chemical compositions. This poses notable challenges to the durability of concrete structures erected in coastal dredger fill silty soil environments. This research undertook concrete chloride corrosion assessments in both a dredger fill silty soil environment and a simulated solution environment. The findings demonstrated a progressive escalation in the free chloride concentration within concrete specimens, as the exposure duration was extended from 60 to 120 d, and discernible convection zones were observed with depths ranging from 6 to 8 mm. The investigation revealed a diminishing trend in the apparent chloride diffusion coefficient, corresponding to the elongation of exposure time and the augmentation of burial depth. Paradoxically, the burial depth and exposure duration exhibited converse effects on the apparent surface chloride concentration. Empirical formulations were derived to express the apparent surface chloride concentrations and apparent chloride diffusion coefficients as dependent on the exposure time and burial depth variables. These models exhibited an excellent goodness of fit, reaching up to 0.96. Notably, concrete specimens interred at a depth of 0.0 m displayed a favorable likeness to the simulated solution environment throughout the 60 d exposure period.

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.

Effect of Magnesium Sulfate in Chloride Solution on Variation in Microstructure, Chloride Diffusion, and Chloride-Binding Behavior of Concrete

In this study, variation in microstructure, diffusion of chloride (Cl−) ions, and binding of chloride in concrete exposed to solutions containing MgSO4 (MS) in NaCl (NC) under the wetting-drying cycle are analyzed and reported. The results reveal that the amount of compounds such as ettringite (E), calcium hydroxide (CH), gypsum (G), calcite (CC), and calcium chloroaluminate (CCA) varies with the depth of concrete from the exposure face. Among exposure solutions, the amount of E was higher in NC + MS solutions compared with NC solutions and with increased MS content. The amount of CCA was higher in NC solutions compared with NC + MS solutions with an increase in NC content. The amount of CH was higher in concrete subjected to NC + MS solutions than to NC solutions and decreased with an increase in NC content. The amount of CCA was mostly higher in ordinary portland cement (OPC) with 20% fly ash concrete (O20FA-C) than in OPC concrete (OPC-C) followed by portland pozzolana cement (PPC) concrete (PPC-C). The amount of E was higher in O20FA-C than in PPC-C followed by OPC-C. Free chloride content (Cf) and apparent chloride diffusion coefficient (D) were reduced in the presence of MgSO4 mainly due to the effect of filling of pores with E. PPC-C exhibited better performance against ingress of chloride (Cl−) ions than that of O20FA-C followed by OPC-C. MS in exposure solutions reduced chloride binding. The concrete made with OPC exhibited higher chloride binding than O20FA followed by PPC.

Chloride diffusion modeling of concrete using tree‐based forest models

AbstractReinforced concrete structures can experience various harsh environments during their service life, among which chloride ion exposure, especially in marine environments, can cause the durability reduction and deterioration of concrete structures. Artificial intelligence (AI)‐based modeling of the non‐steady‐state apparent chloride diffusion coefficient (DC) of concrete for a long exposure time using the experimental field results can assist in identifying the influential factors and better estimating the service life of a concrete structure. In this study, two novel extensions of ensemble AI algorithms, including genetic programming forest (GPF) and linear genetic programming forest (LGPF) algorithms, were proposed to model the DC of concrete. The experimental field data were gathered from the literature. Different structures of the proposed ensemble methods were developed and examined, and the best‐developed model was selected for further analysis, including sensitivity analysis and parametric study. In addition, the random forest (RF) method was used as the control ensemble technique to have a comparison. The results show that the best LGPF model possesses superior performance than the best‐developed GPF and RF models. In addition, the results show that silica fume‐to‐binder ratio, exposure time, and exposure conditions have the most significant impacts on the DC of concrete. This study contributes to the civil engineering practice by developing a new tool to model the DC of concrete that facilitates the durability assessment of concrete structures.

A time-variant model of chloride diffusion in prestressed concrete cylinder pipe (PCCP) considering the effects of curing age

Chloride penetration is considered as the most responsibility to steel corrosion for PCCP during service. Compared with ordinary concrete structures, the curing method of PCCP is generally steam-curing. Despite numerous contributions have shown that curing age has significant effect on the resistance to chloride penetration of concrete. There is still a lack of critical understanding of the curing age effect on the chloride migration in steam-cured concrete. For this reason, this paper aims to establish a chloride diffusion model suitable for PCCP. In this study, the non-steady-state chloride diffusion coefficient and chloride concentration of steam-cured concrete are measured through RCM test and chloride diffusion simulated test, respectively. The apparent chloride diffusion coefficient and surface chloride concentration are calculated based on Fick’s second law. Moreover, the instantaneous chloride diffusion coefficient was estimated. It is found that the steam-cured concrete cannot ignore the influence of curing age on the chloride penetration resistance, according to RCM test results, the non-steady-state chloride diffusion coefficient of 28 days decreased by 33 % compared with that of 3 days, while the chloride diffusion coefficient of 90 days decreased by 15 % compared with 28 days under steam curing. The larger the curing age, the smaller the chloride concentration at each depth, as well as the chloride diffusion coefficient and surface chloride concentration. In addition, it can be concluded that with the increase of exposure time, the chloride diffusion coefficient decreases gradually, while the surface chloride concentration increases gradually. Thus, the two kinds of test results and theoretical analysis were combined to establish the time-variant models of instantaneous chloride diffusion coefficient and surface chloride concentration of steam-cured concrete considering the effects of curing age and exposure time. On this basis, a new chloride diffusion model considering the effects of curing age, exposure time, the time-variant chloride diffusion coefficient and time dependence surface chloride concentration was established, which plays an important role in durability evaluation of PCCP.

Chloride ion permeability of Ultra-high-performance fiber-reinforced concrete under sustained load

This work aims at investigating the effect of multiple microcracks in Ultra-High Performance Reinforced Concrete (UHPFRC) occurring in service conditions on the apparent chloride diffusion which is critical to guarantee the design lifetime. First, series of preliminary static bending tests were carried out on three UHPFRC beams to characterize their flexural response as well as their microcrack distribution measured by Digital Image Correlation (DIC). Then, a special test set-up was designed to apply and maintain a sustained bending moment on the UHPFRC beams. Finally, some accelerated migration tests were carried out on the micro-cracked UHPFRC beams under sustained bending load. The results showed different chloride penetration rates and profiles in tested UHPFRC beams under different loading levels, and the influence of the microcrack's width on the apparent chloride diffusion coefficient of the considered UHPFRC was clearly identified, which is a precious information for better predicting the service lifetime of a UHPFRC structure.

Experimental study of chloride transport law in concrete considering the coupling effects of dry-wet ratio and freeze–thaw damage

In marine environment, dry-wet ratio (D/W) in the dry-wet cycling zone of coastal structures and freeze–thaw (FT) damage can both affect the chloride transport characteristics in concrete. In this paper, FT cycling tests of concrete specimens were conducted by the FT cycles testing machine to establish the relationship between the number of FT cycles and FT damage. Then, the chloride natural diffusion tests of concrete specimens with different FT damage under the dry-wet cycling zone were carried out to investigate the chloride transport law considering the coupling effects of D/W and FT damage on the condition of the dry-wet cycling period = 24 h. Under the influence of dry-wet cycles, there is a convection zone in the transmission of chloride in concrete specimens. Based on the Fick's second law, the convection zone peak concentration, the convection zone depth and the apparent chloride diffusion coefficient considering the coupling effects of D/W and FT damage were determined by fitting the chloride concentration distributions at various exposure time. The results show that the effect laws of D/W on unfrozen and frozen concrete specimens are basically the same. The convection zone peak concentration, the convection zone depth and the apparent chloride diffusion coefficient increase with the increase of FT damage in concrete specimens. The influences of FT damage on the convection zone peak concentration, the convection zone depth and the apparent chloride diffusion coefficient were quantified by introducing the impact coefficients of FT damage. Finally, a prediction model of chloride transport in concrete considering the coupling effects of D/W and FT damage was proposed, and the accuracy and reasonability of the prediction model were validated by comparing the predictive results of the model and the measured values of the tests.

Effect of exposure temperatures on chloride penetration resistance of concrete incorporating polypropylene Fibers, silica fume and metakaolin

• The diffusion resistance of silica fume (SF) concrete was 1.4–7.3 less than OPC concrete. • The diffusion resistance of metakaolin (MK) concrete was 1.2–3.9 less than OPC concrete. • The effect of 10% SF on migration resistance was almost similar to that of 15% MK. • Models to predict the service life of RC structures in hot environments were developed. Rapid degradation of reinforced concrete (RC) has become a serious concern due to its reduction of life span and high unexpected maintenance cost. Chloride penetration and subsequent corrosion are the primary causes of such concrete deterioration. This study investigated the effects of polypropylene fibers, metakaolin and silica fume on chloride diffusion and migration resistance of concrete at different exposure temperatures. Eight concrete mixes were prepared using a water/binder ratio of 0.38, cement replacement of 0, 5, 10, and 15 % by either silica fume (SF) or metakaolin (MK) with zero or 0.6 kg/m 3 polypropylene fibers (PPFs). Furthermore, concrete resistance to chloride diffusion at four different exposure temperatures (23, 38, 53 and 68 °C) and chloride migration at 23 °C was evaluated. The results showed that both pozzolanic admixtures, SF and MK, significantly reduced apparent chloride diffusion coefficient (D a ) and chloride migration coefficient (D nssm ). However, PPFs concretes incorporating MK showed inferior chloride diffusion than those containing SF. D a for PPFs concretes incorporating SF and MK were 1.4–7.3 and 1.2–3.9 times less than Type I cement concrete, respectively. While D nssm for PPFs concretes incorporating SF and MK were 1.7–6.3 and 1.5–3.2 times less than Type I cement concrete, respectively. The results also showed that the effect of 15 % MK on D nssm and D a was almost similar to that of 10 % SF. The D a increased slightly at exposure temperatures of 23 and 38 °C. However, at higher exposure temperatures of 53 and 68 °C, a significant increase in D a was noted. Eight models were developed using regression analysis and were validated by comparing the predicted apparent chloride diffusion coefficient values with the measured ones. The validation of the developed models showed that the predicted D a values were within ± 7 % error margin. The developed chloride diffusion models in the current study allow us to predict and quantify the long life of future realizations of RC structures in marine hot environments.

Experimental and analytical investigation on chloride ions transport in concrete considering the effect of dry-exposure ratio under diurnal tidal environment

For reinforced concrete structures in tidal zone, the dry-wet ratio (the ratio of drying time to wetting time in one cycle) of member varies with the elevation. Chloride ions transport in concrete is affected by coupling action of diffusion and convection under dry-wet cycle environment. The erosion of concrete corresponding elevation of the most unfavorable dry-wet ratio is the most intense, in which invade the most chloride ions. In existing studies, the most unfavorable dry-wet ratio determined by different scholars is not consistent, and there is a lack of quantitative indexes to describe the impact of convection action on chloride concentration distribution. In this research, a series of natural exposure experiments were carried out in submarine environment and dry-wet cycle environment using the indoor tidal automatic circulation device independently invented by the laboratory. A new index, dry-exposure ratio (the ratio of drying time to exposure time in a cycle), was proposed to quantify the dry-wet cycle environment. The mechanism of convection and the influence of different dry-exposure ratios on chloride ions transport in concrete were discussed, and the most unfavorable dry-exposure ratio was determined. Under the condition of diurnal tide (dry-wet cycle period is 24 h), while wetting time is 10 min, shallow part of concrete is the most seriously corroded by chloride ions due to the coupling action of convection and diffusion, while wetting time is 45 min, deep part of concrete is the most seriously corroded by chloride ions diffusion. The variations of peak chloride concentration, depth of convection zone and apparent chloride diffusion coefficient with the dry-exposure ratio and exposure duration were analyzed. The results show that the peak chloride concentration and depth of convection zone can be used as the indexes of quantitative convection. By introducing the depth of convection zone and modifying the peak chloride concentration and apparent chloride diffusion coefficient, a time-dependent model of chloride ions transport in concrete considering the effect of dry-exposure ratio was established. The proposed empirical model is expected to be useful in realistically predicting chloride ions transport in concrete under dry-wet cycle environment.

Chloride diffusion behavior and microstructure of basalt-polypropylene hybrid fiber reinforced concrete in salt spray environment

The chloride diffusion performances of basalt-polypropylene hybrid fiber reinforced concrete (BPHFRC) in salt spray environment were investigated. The effects of concrete strength, fiber addition form and content on the pore solution pH and chloride concentration were evaluated. The results showed that the stable depth of pore solution pH of BPHFRC increased with the increase of exposure time.The greater the strength of concrete, the slower the decrease rate of pore solution pH with exposure time. The effects of addition form and content of basalt fiber (BF) and polypropylene fiber (PF) on chloride concentration were different. When the fiber content was 0.1%, the addition of BF, PF or hybrid BF-PF could improve the chloride corrosion resistance of concrete.However, addition of 0.2% hybrid BF-PF increased the chloride concentration in the concrete. The apparent chloride diffusion coefficient of BPHFRC decreased with an increase of salt spray erosion time, and exhibited a power function with erosion time. The calculation model of BPHFRC apparent chloride diffusion coefficient was established, and its effectiveness was verified. In addition, the pore structure, phase composition and micromorphology of BPHFRC before and after erosion were performed using RapidAir-457 porosity analyzer, X-ray diffraction and field emission scanning electron microscope, and the influence rules of BF and PF on chloride diffusion properties of concrete was discussed.

Durability of eco-friendly blended cements incorporating ceramic waste from different sources

Environmental conservation is mandatory for the sustainable development of the construction industry. A large amount of ceramic waste results from construction and demolition waste (C&DW). In addition, the extended service life of the structure is essential. This paper assesses the effectiveness of powder ceramic wastes (PCWs) from C&DW to improve the durable performance (chloride diffusion, sulfate resistance, and alkali–silica reaction) of blended cement (replacement 24% by mass). The suitability of blended cement is supported by the proven pozzolanicity (Frattini test, XRD, FTIR, and nonevaporable water content). Additionally, PCWs incorporation effect on the life cycle analysis of concrete is included. All samples containing ceramic waste show pozzolanic activity at 28 days, significantly reduce the apparent chloride diffusion coefficient, present good performance against the sulfate attack and reduce the expansion caused by ASR. In addition, PCWs reduce CO2 emissions. Results reveal a comparable performance of PCWs, indicating the unnecessary classification of them.

Effect of Ammonia-Soda Residue on the Strength and Chloride-Resistance Performance of Steel Slag-Granulated Blast Furnace Slag-Based Concrete after Immersion in Artificial Seawater.

Ammonia-soda residue (ASR) is the main solid waste generated from soda manufacturing and is hard to reuse due to its complex chemical composition. This study investigated the influence of ASR content on the strength and chloride-resistance capacity of concrete based on basic oxygen furnace slag and ground blast furnace slag. The hydration and chloride resistance mechanisms were analysed by comparing the hydrate products and pore structural changes. The results showed that adding ASR had the greatest impact on early strength. ASR-introduced chloride ions may participate in the hydration process to generate Friedel’s salt and decrease ettringite. The optimum pore distribution appeared when the ASR-to-desulphurisation gypsum ratio was 2:3 because of the introduction of nucleation sites and the decrease of C–S–H gels. The two chloride resistance-capacity measurements were affected differently by the ASR content. The apparent chloride diffusion coefficient was mainly affected by the percentage of pores that were larger than 10 nm. However, electric flux increased when ASR increased due to the influence of introduced chloride. The crystallisation pressure of Friedel’s salt decreases the strength of concrete with ASR content after high-concentration artificial-seawater immersion. The significant chloride-resistance property provided an alternative use for the concrete containing ASR.

Influence of non-linear chloride binding on the determination of apparent chloride diffusion coefficient for cement paste with mineral additives

The determination of apparent chloride diffusion coefficients (Da) in standard codes employs the linear chloride binding assumption. However, this assumption is too simplified as chloride binding is actually non-linear. This paper intends to investigate the influence of non-linear chloride binding on the determination of Da values in the bulk diffusion test. To achieve this aim, a semi-analytical method for the semi-infinite diffusion problem was firstly established. This method can be used in data fitting to obtain the Da values considering non-linear chloride binding. Then, bulk diffusion test and mercury intrusion porosimetry were conducted on four different cement pastes with fly ash and blast furnace slag. Based on chloride profiles, the chloride binding isotherms were obtained through data fitting. Meanwhile, the Da values considering the linear and non-linear chloride binding assumption were calculated respectively and compared. The results show that the chloride binding isotherms in the bulk diffusion test fit well with the Freundlich isotherm but are not so non-linear as expected. The proposed method can calculate the effective diffusion coefficient which cannot be obtained in standard codes. Da values will vary along the chloride ion diffusion direction rather than be a constant once the non-linear chloride binding is considered. The comparison between different cement paste mixtures indicates that both the apparent diffusion coefficient calculated from free chloride profiles or total chloride profiles can only be regarded as a qualitative description of resistance to chloride diffusion for a certain mixture. The comparison between different mixtures based on these values is not reliable.

Chloride Transport Performance of Basalt-Polypropylene Fiber Reinforced Concrete under Drying-Wetting Cycles

This study investigated the chloride transport performance of basalt-polypropylene fiber reinforced concrete (BPFRC) subjected to drying-wetting cycles. The effects of the strength grade, basalt fiber (BF), polypropylene fiber (PF), and hybrid BF-PF on the pore solution pH, chloride concentration distribution, chloride peak concentration (Cmax), and apparent chloride diffusion coefficient (Da) of the BPFRC were analyzed, and a multifactor model of Da was established. Moreover, the microstructures of BPFRC were studied to explore the effect of fibers on chloride transport performance of concrete in terms of theoretical pore volume, fiber-matrix interface, fiber bonding properties, and corrosion morphology. The results showed that the chloride concentration of the BPFRC increased and the pore solution pH of the BPFRC decreased with the increase in the exposure time. The chloride concentration and Da of the BPFRC decreased with the increase in the strength grade. At a fiber volume content of 0.1%, the addition of BF and PF reduced the chloride concentration and Da of the BPFRC; at a fiber volume content of 0.2%, the addition of hybrid BF-PF increased the chloride concentration and Da of the concrete. The chloride peak concentration appeared at the depth of 2 mm inside the concrete, and the change of the chloride peak concentration with exposure time followed the power function model. The theoretical pore volume of the BPFRC specimens decreased initially and then increased with the increase in the exposure time. FE-SEM observed that the bonding property between BF and matrix was better than that of PF, which could effectively control the development of microcracks.

Prediction of chloride concentration with elevation in concrete exposed to cyclic drying-wetting conditions in marine environments

Chloride ions are generally considered one of the most significant factors in the corrosion of steel bars in reinforced concrete (RC) structures exposed to alternate drying-wetting marine environments. When RC structures are exposed to cyclic drying-wetting conditions, such as in the marine tidal zone, the chloride concentration distributions in RC structures along the elevation direction changes due to the influence of various drying-wetting ratios. In the study presented here, an indoor exposure experiment for chloride transport in concrete specimens under different conditions of drying-wetting ratios is employed to explore the chloride concentration distributions along the elevation of an RC structure. The elevation related to the peak value of the chloride concentration, which corresponds to the most unfavourable drying-wetting ratio for the RC structure, is determined. On the basis of the tested chloride concentration results, the variation of the time-dependent models of surface chloride concentration and apparent chloride diffusion coefficient with elevation are established for an RC structure. Furthermore, an empirical model of chloride diffusion based on Fick’s second law is developed and adopted to predict the chloride concentrations in concrete at an arbitrary elevation and exposure time. The accuracy of this prediction model of chloride diffusion is validated in terms of the experimental chloride measurements.

Experimental Study on Chloride Ion Diffusion in Concrete under Uniaxial and Biaxial Sustained Stress.

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride solution erosion. The influence of different sustained compressive stress states on chloride ion diffusivity is evaluated by testing chloride concentration in concrete. The experiment results show that the existence of sustained compressive stress does not always inhibit the diffusion of chloride ions in concrete, and the numerical value of sustained compressive stress level can affect the diffusion law of chloride ions in concrete. It is found that the chloride concentration decreases most when the lateral compressive stress level is close to 0.15 times the compressive strength of concrete. In addition, the sustained compressive stress has a significant effect on chloride ion diffusion of concrete with high water/cement ratio. Then, the chloride diffusion coefficient model under uniaxial and biaxial sustained compressive stress is established based on the apparent chloride diffusion coefficient. Finally, the results demonstrate that the chloride diffusion coefficient model is reasonable and feasible by comparing the experimental data in the opening literature with the calculated values from the developed model.

Experimental investigation on chloride-ion penetration resistance of slag containing fiber-reinforced concrete under drying-wetting cycles

The corrosion of reinforcing steel is a major problem of concrete structures, particularly those exposed to chloride environment. In this study, slag was incorporated as cement replacement in various types of fiber-reinforced concrete, and the chloride penetration resistance of the concrete was investigated. The specimens were exposed to drying-wetting conditions and the chloride ion content was determined via potentiometric titration. The results show that the apparent chloride diffusion coefficient decreases with an increase in exposure time, following an exponential relationship. Slag has a positive effect on the chloride penetration resistance of the concrete, and an optimal dosage of slag exists. The effect of macrofibers on the resistance of concrete to chloride ion penetration depends on the macrofiber material; steel fibers can improve the chloride ion penetration resistance of concrete, whereas macrofibers made of polypropylene exacerbate chloride ion penetration. The effects of microfibers are related to its type and volume fraction: A lower volume fraction is favorable, whereas a higher volume fraction weakens the resistance of concrete against chloride-ion penetration.

Durability health monitoring during construction of concrete structures in marine environment

A new methodology for durability health monitoring for a bridge structure during construction was developed by monitoring concrete's saturated electrical resistivity (ρS), rapid chloride permeability (RCP), and the apparent chloride diffusion coefficient (DAP) indices. Results were compared with same durability indices collected previously from in-service bridges located along the Gulf of Mexico (Florida, USA, and Yucatan, Mexico). Excellent correlations were found between ρS versus RCP, ρS versus DAP, and RCP versus DAP from present and previous investigation data. Empirical models obtained corroborate that ρS test is feasible to use, instead of more complicated and expensive testing, for structural health monitoring for quality control/assurance during construction.