Sulfate Attack In Concrete Research Articles

Key inhibitory mechanism of external chloride ions on concrete sulfate attack

To explore the key inhibitory mechanism of external chloride ions on concrete sulfate attack, long-term partial- and full-immersion experiments of concrete in chloride solutions and chloride and sulfate composite solutions were performed. As corrosion time begins, visual inspection, compressive strength, and ultrasonic velocity were periodically observed or tested. Moreover, the micro-morphology, the contents of Cl and S elements in concrete, and the transport speeds of Cl− and SO42− ions through concrete were investigated by using scanning electron microscope, X-ray fluorescence spectrum, and chemical analysis. Chloride ions neither have corrosive effects on concrete nor effects on concrete physical and mechanical properties, which is the prerequisite for chloride ions in inhibiting concrete sulfate attack. In the case of combined solutions, the transport speed of Cl− ions into concrete is evidently higher than that of SO42− ions. Then, chloride ions enter concrete early and form Friedel's salt with AFm or with C3A and Ca(OH)2 in concrete, which inhibits the transport of SO42− ions into concrete and reduces the formation of expansive corrosion products of ettringite or gypsum. Thus, the sulfate attack on plain concrete is alleviated. Based on the inhibitory mechanism of Cl− ions on concrete sulfate attack, the presence of Cl− ions cannot completely avoid concrete sulfate attack but can partially reduce sulfate risk on concrete.

An effective transport model of sulfate attack in concrete

Abstract This paper presents both an experimental and theoretical investigation of the consumed and accumulated rates of sulfate ions in concrete. The authors analyze the effects of sulfate solution concentration and the water-cement ratio on the sulfate ions distribution. Based on the diffusion theory, a sulfate transport model for concrete was established considering the effect of surface sulfate concentration. On this basis, an effective transport model of sulfate attack is presented, which relies on effective diffusivity. This model can be applied to predict the sulfate ions distribution; moreover, its predicted values are in good agreement with the experimental ones.

Effects of internally introduced sulfate on early age concrete properties: Active acoustic monitoring and molecular dynamics simulation

Sulfate attack of concrete is still a “confused world” that deserves further study. An active acoustic method is employed to monitor the early-age evolution of fresh concrete mixed with soluble sulfate ions. The effects of introduced sulfate salt at different dosages on the setting and hardening process of fresh concrete as well as mechanical properties of hardened concrete up to the age of 28 days are examined and analyzed. The experimental results from the active acoustic monitoring clearly reveal the acceleration effect of introduced sulfate salt on the solid skeleton formation process of fresh concrete. Introduced sulfate salt leads to higher values of mechanical property indices at early ages (e.g., 1 day), but poorer mechanical properties of hardened concrete at the age of 28 days. The corresponding mechanism has been studied in the light of molecular dynamics simulation, scanning electron microscopy and X-ray diffraction, and it is concluded that introduced sulfate ions not only damage the cement matrix due to the overexpansion of ettringite formation, but also weaken the loading resistance of the ionic-covalent bonds in the C-S-H gel.

MODELO DE EVOLUCIÓN DEL DAÑO SOBRE HORMIGÓN, AFECTADO TEMPRANAMENTE POR ATAQUE DE SULFATO Y SU VERIFICACIÓN EXPERIMENTAL

The disturbance during the early age of the setting and hardening stage of concrete usually creates microcracks in the concrete matrix and thus decreases its strength and durability. Among the factors that affect the durability of concrete, sulfate attack is one of the important factors that cause damage. To analyze the damage development of early disturbed concrete under sulfate attack environment, the residual coefficient of flexural strength of concrete was tested by the perturbation of horizontal vibrating table. Using erosion damage factor to characterize the degree of erosion deterioration of concrete, the sulfate attack tests were carried out on the disturbed concrete. Starting from the crack initiation condition of sulfate attack, and based on the theory of microcrack nucleation and growth in the process of erosion, the statistical evolution equation of sulfate corrosion damage of concrete was obtained by using micro crack propagation to characterize the mechanical behavior of concrete after corrosion damage. Considering the influence of early disturbance on the critical stress of concrete microcrack nucleation, the damage evolution model of concrete with different disturbed conditions under sulfate attack was established, and the corrosion degree of disturbed concrete at different erosion ages was predicted. Based on the experimental data of damage factors, the damage evolution equation was fitted and the model was validated. Results demonstrate that the damage model curve fits well with the test curve of damage factor, and the correlation coefficients are above 0.98, which can reflect the damage evolution law of disturbed concrete sulfate attack. This method provides a good reference for evaluating the effect of early disturbance on the sulfate resistance of concrete. Keywords: Concrete, Disturbance, Sulfate attack, Microcrack nucleation, Damage evolution

Chemo-mechanical modelling of the external sulfate attack in concrete

This paper is focused on the modelling of the mechanical consequences of external sulfate attack in concrete structures under partially or fully saturated conditions. To this purpose a weakly coupled approach is developed: first the moisture content is computed through a simplified diffusion model, then a reactive-diffusion model allows for the computation of the expansive products of the reaction occurring between the aluminates of the cement paste and the incoming sulfate ions, finally the solution of a nonlinear mechanical problem gives the expansion, the stress state and the degradation induced by the reaction. The mechanical problem makes use of a multiphase elasto-damage model, developed in this work and accounting for both chemical and mechanical damage. The model is validated by simulating various experimental tests on concrete specimens subject to external sulfate attack and then applied to the simulation of a reduced scale structure of a tunnel lining.

Experimental study on physical sulfate salt attack

Sulfate attack can cause severe damage to concrete structures. The most common mitigation strategy against chemical sulfate attack in concrete is reduction of water to cementitious materials ratio, use of low-C3A Portland cements, and/or use of supplementary cementitious materials. However, physical salt attack from sodium sulfate exposure may still cause damage to concrete with low water to cementitious materials ratio, and supplementary cementitious materials have been reported to even reduce resistance to physical salt attack. The purpose of the current research is to study the effect of water to cementitious materials ratio and supplementary cementitious materials on the ability of mortar to resist physical salt attack. Mortars, made with water to cementitious materials ratios between 0.35 and 0.50, and with two levels of cement replacement by either fly ash or ground granulated blast-furnace slag, were exposed to physical sulfate attack. Mass loss due to physical sulfate salt attack and its relationship with pore structure and transport properties were studied. The results show a good correlation between the resistance to physical salt attack and the pore threshold radius using mercury intrusion porosimetry, as well as the chloride migration coefficient. For the curing conditions used, ground granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect.

Inhibitory effects of chloride ions on concrete sulfate attack in the marine adsorption environment

ABSTRACTTo study the inhibitory effects of chloride ions on concrete sulfate attack in the marine adsorption environment, a series of cubic concrete specimens was fabricated. These specimens were totally submerged or partially submerged in 10% Na2SO4 solutions with 0, 0.5, 2, and 5% NaCl concentration. Three specific aspects, namely, superficial phenomenon, compressive strength degradation, and X-ray fluorescence spectrometry analysis, were studied during 450 days of long-term exposure. Results showed that Na2SO4 solution had a strong corrosive effect on concrete in both the adsorption and submersion zones, especially in the adsorption zone. Chloride ions exerted inhibitory effects on concrete sulfate attack in both the submersion and adsorption zones, and higher concentration of chloride ions will produce stronger inhibitory effects. However, given the different inhibitory effects of chloride ions on concrete sulfate attack with different corrosion mechanisms, the inhibitory effect of the same chloride concentration on concrete sulfate attack was a little lower in the adsorption zone than in the submersion zone.

Diffusion–reaction model for the internal sulfate attack in concrete

In the analysis of the behavior of concrete structures affected by expansive problems, it is often necessary to use kinetics models of the reactions involved to assess and predict the magnitude, distribution, and evolution over the time of expansion. In this study, a diffusion–reaction model is developed for the internal sulfate attack (ISA) problem due to the oxidation of the pyrrhotite into the aggregates. The model takes into account the kinetics of the pyrrhotite oxidation under the two main oxidizers and the oxygen transport in the concrete. The dependence of the water content of the concrete is included in the analysis, which affects the reaction kinetics and oxygen diffusion. The developed model is applied to two real dams affected by the ISA. The results obtained validate the model and demonstrate its potential for evaluating and predicting the behavior of structures affected by the ISA.

Mass Change Prediction Model of Concrete Subjected to Sulfate Attack

The present study suggested a mass change prediction model for sulfate attack of concrete containing mineral admixtures through an immersion test in sulfate solutions. For this, 100% OPC as well as binary and ternary blended cement concrete specimens were manufactured by changing the types and amount of mineral admixture. The concrete specimens were immersed in fresh water, 10% sodium sulfate solution, and 10% magnesium sulfate solution, respectively, and mass change of the specimens was measured at 28, 56, 91, 182, and 365 days. The experimental results indicated that resistance of concrete containing mineral admixture against sodium sulfate attack was far greater than that of 100% OPC concrete. However, in terms of resistance against magnesium sulfate attack, concrete containing mineral admixture was lower than 100% OPC concrete due to the formation of magnesium silicate hydrate (M-S-H), the noncementitious material. Ultimately, based on the experimental results, a mass change prediction model was suggested and it was found that the prediction values using the model corresponded relatively well with the experimental results.

Monitoring of Sulfate Attack in Concrete by Al27 and Si29 MAS NMR Spectroscopy

Si29 and Al27 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy techniques were employed towards evaluation of hydrated cement paste and concrete subjected to accelerated sulfate attack. Quantitative analyses of the Si29 NMR spectra of specimens subjected to different periods of sulfate attack indicated that the chain length CL of SiO4/AlO4 tetrahedra was lowered by sulfate attack. Al27 NMR spectra indicated that sulfate attack produced a significant rise in the intensity of ettringite and a sharp drop in the concentration of monosulfate hydrate, which are some primary indications of sulfate attack on concrete. Fourier-transform infrared (FTIR) spectroscopy method was employed in order to verify the result of NMR spectroscopy.

Electrochemical impedance behavior of mortar subjected to a sulfate environment – A comparison with chloride exposure models

Samples of reinforced mortar specimens (Sps) were studied over 300days of exposure in reference, sulfate, and chloride environments. Electrochemical impedance spectroscopy (EIS) was used to investigate external sulfate attack (ESA) in comparison with known chloride models. The study, based on the mortar behavior and its measured electrical properties, highlighted the mechanisms that occur under the pores during the aging. The sulfate samples presented a capacitive behavior at lower frequencies, and the mortar resistance shifted. It was confirmed that EIS is a qualified technique to identify the sulfate attack in concrete by non-destructive methods.

Experimental Study on Improving Concrete Sulfate Attack Resistance Ability with Silane Impregnation

Silane impregnation effects on concrete sulfate attack resistance ability are systemic researched, through forming different cementitious material system and different water cement ratio mortar specimens, treating with silane impregnation and then curing to 14d age naturally, and doing sulfate solution wetting-drying test. Results shows that silane impregnation effect is poor when fly ash amount is large or water gel is relatively low. Through XRD microscopic, the improving sulfate attack resistance ability mechanisms are analyzed from aspect of cementations material hydration product; water-binder ratio effect on silane impregnation is explained by water absorption test.

New kinetic model to quantify the internal sulfate attack in concrete

Kinetic and quantitative predictions of the internal sulfate attack (ISA) of concrete containing aggregates with iron sulfides have become a challenge, especially in the diagnosis of dams subject to expansive phenomenon. The present study proposes equations to quantify the expansion due to the iron sulfide oxidation and due to the secondary ettringite formation in the concrete. A simplified model to assess the evolution of the concrete expansion with time is outlined and validated with experimental results. Unlike others in the literature, this model allows a direct prediction of the expansions generated by the ISA taking into account the physical and chemical characteristics of the concrete and of the aggregate. The concrete volumetric expansion calculated with this model is then used to estimate the movements of a real dam affected by the ISA. The result obtained fits the measurements and serves to the prediction of future movements of the structure.

Experimental Study on Accelerated Speed of Concrete Sulfate Attack

Through test on compressive strength of concrete and mass changes, the effects of solution concentration and temperature on speed of concrete sulfate attack were investigated. The results show that, the speed of attack is accelerated with increasing concentration and temperature, as well as the decreasing of the size of the specimen, sulfate attack speed at 45 °C sodium sulfate solution soak with wet and dry cycle is insignificant difference with at 20 °C.It is suitable to adopt compressive strength as the assessing criterion of the sodium sulfate attack.

Evolution of viscosity of concrete under sulfate attack

This paper presents a theoretical and experimental study on the attenuation coefficient of the ultrasonic expansion wave in concrete specimens made of different mixes and suffering from sulfate attack. The relationships between the attenuation coefficient, relaxation time, and the wave velocity of the elastic expansion wave were derived. By using simple ultrasonic techniques, the variation of the attenuation coefficient with time during the process of sulfate attack was determined experimentally. The results showed that the magnitude of the attenuation coefficient of concrete increased with time, reflecting damage evolution in the material caused by sulfate attack. This suggested that the damage caused by sulfate attack in concrete can be determined by using simple ultrasonic testing methods. Also, it was found that the concrete specimens with added fly ash had a better performance (reduced sulfate attack) than those with added fine ground slag.

The Changes of the Micro Structure by Deterioration Factors for LILW Waste Disposal Facility Concrete

One of the most important deterioration mechanisms of concrete is that caused by the changes of the cement matrix. For this reason, the Freezing and Thawing and Sulfate attack of concrete has been considered for years a subject of interest in researches of cement chemistry. The concrete deterioration process is a complex physicochemical process that slowly modifies the structures of the concrete in the course of time and induces changes into its chemical and physical properties

Foundation of Service Life Prediction Model of Sulfate Attack in Concrete

Sulfate attack of cementitious materials is closely related to the essential properties of cementitious materials and erosive environments. Therefore, the foundation of service life prediction model becomes very difficult and complicated. In this paper, the temperature and concentration of an erosive solution were taken into account in lab accelerating test, the service life prediction model of sulfate attack based on equivalent time and damage variable was founded by using Arrhenius equation, the concept of maturity, Fick’s law and the theory of damage mechanics. Dynamic elastic modulus value change, and/or mass change, and/or compressive or flexural strength change, et al. can be used as damage variable to show the evolving process of sulfate attack in concrete in this prediction model, and certain changed rate was considered as the damage critical value in concrete in terms of the standard or references or test results. To estimate the possible service life of concrete structures in sulfate attacking condition by lab accelerating test according to this prediction model, it will be benefit to guide the selection of raw materials and design of durability in concrete.

Recovery from Sulfate Attack in Concrete via Electrokinetic Nanoparticle Treatment

Microstructural damage induced by sulfate attack in concrete is a cause of primary concern in building foundations and other structures. Most research focuses on prevention. In contrast, the concept of damage recovery has not received significant attention. Studies were conducted using alumina-coated-silica nanoparticles to facilitate an electrochemical recovery of strength. Treatments were applied to extract sulfates while the nanoparticles were being injected. Initial sodium sulfate exposure on cylindrical concrete specimens was conducted for a period of 30 days. This exposure induced body cracking and microstructural damage. The specimens were subjected to electrokinetic treatment using a constant current density of 1 A/m2 for 7 days. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis revealed significant sulfate content in the sulfate-exposed specimens that was not detected in the treated cases. Raman spectroscopy also indicated a higher C-S-H among the treated specimens, ...

The thaumasite form of sulfate attack in concrete of Yongan Dam

According to microanalytical investigations, it is shown that the concrete of Yongan Dam is deteriorated due to the thaumasite form of sulfate attack (TSA). Analysis results of scanning electron microscopy (SEM), Energy Disperse X-ray (EDX) and X-ray Diffraction (XRD) are supported by the analysis of the concrete composition and the geographical conditions of the dam.

Developing a More Rapid Test to Assess Sulfate Resistance of Hydraulic Cements.

External sulfate attack of concrete is a major problem that can appear in regions where concrete is exposed to soil or water containing sulfates, leading to softening and cracking of the concrete. Therefore, it is important that materials selection and proportioning of concrete in susceptible regions be carefully considered to resist sulfate attack. American Society for Testing Materials (ASTM) limits the tricalcium aluminate phase in cements when sulfate exposure is of concern. The hydration products of tricalcium aluminate react with the sulfates resulting in expansion and cracking. While ASTM standard tests are available to determine the susceptibility of cements to sulfate attack, these tests require at least 6 months and often up to a year to perform; a delay that hinders development of new cements. This paper presents a new method for testing cement resistance to sulfate attack that is three to five times faster than the current ASTM tests. Development of the procedure was based upon insights on the degradation process by petrographic examination of sulfate-exposed specimens over time. Also key to the development was the use of smaller samples and tighter environmental control.