Thaumasite Form Of Sulfate Attack Research Articles

Thaumasite form of sulfate attack in ettringite rich-ternary systems: Effects of limestone filler, etching solutions and exposure temperature

This study aims to investigate the effect of limestone filler, sulfate concentration and temperature on the thaumasite sulfate attack (TSA) in Portland cement (PC)-calcium aluminate cement (CAC)-gypsum ternary system. The compressive strength of mortar was tested, while X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the deteriorated products. The results indicate that the ternary system with limestone filler is susceptible to TSA. The higher the limestone content, the higher the TSA is in systems with MgSO4 solution of less than 5%. When the limestone filler content is 10% or 20%, the sulfate attack is mainly presented as gypsum sulfate attack. When the concentration of MgSO4 solution increases, the corrosion is diminished. The ternary system exposed to low concentration MgSO4 solution of 5% is prone to form thaumasite. The lower the temperature, the more vulnerable the system is to TSA. The mortar at 5 °C under 5% MgSO4 solution is rarely damaged and thaumasite could easily be detected.

Effect of limestone powder and fly ash on the pH evolution coefficient of concrete in a sulfate-freeze–thaw environment

Limestone powder has been widely used in concrete during fly ash shortages and in the green and sustainable development of concrete materials. Because the effect of limestone powder on concrete alkalinity is not well understood, we research the effect of 10% limestone powder concrete, 10% fly ash concrete, and pure cement concrete at different depths on the pH value of the initial state, microstructure and compressive strength, sulfate immersion, and number of sulfate–freeze–thaw cycles at different pH value coefficients of concrete erosion products formed in a sulfate-freeze–thaw environment. Limestone powder has no obvious effect on the pH value of concrete in the initial state, while fly ash reduces the pH value of concrete in the initial state. In the sulfate-freeze–thaw environment, the protective property of limestone powder concrete is slightly stronger than that of pure cement concrete, and the protective property of fly ash concrete is weaker than that of pure cement concrete. The effect of sulfate immersion and the sulfate-freeze–thaw environment on the pH value of the concrete surface layer is greater, which is confirmed by the results of synchronous thermal analysis. TSA (the thaumasite form of sulfate attack)-type damage to limestone powder concrete occurred in the sulfate-freeze–thaw environment, and the C–S–H gel content in 10% limestone powder concrete was significantly less than that in 10% fly ash concrete and pure cement concrete at depths of 0–5 mm, 5–10 mm and 10–15 mm, which reduced the content of C–S–H gel.

Effect of Limestone Powder on Thaumasite Form of Sulfate Attack (TSA) of Cement-Based Materials

Limestone powder can cause the thaumasite form of sulfate attack (TSA) of cement-based materials, but the relationship between the content of limestone powder and the degree of TSA is unclear. Hence, six different contents of limestone powder (0%, 5%, 10%, 15%, 30%, and 45%) were used to study the effect of the limestone powder content on the TSA of cement-based materials according to appearance and Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and chemical analyses. The test results indicated that limestone powder could promote sulfate attack. The formation of ettringite and gypsum was accelerated when the content of the limestone powder was not more than 10%. The degradation degree of the TSA was the most severe when the content of limestone powder was 30%. A new product, hydrated calcium carboaluminate, was found when the content of the limestone powder was 45%, and the degradation of the TSA was also delayed.

Effects of cations in sulfate on the thaumasite form of sulfate attack of cementitious materials

The thaumasite form of sulfate attack (TSA) of cement-based materials is a severe threat. There is little research on the effect of cations in the sulfate on the TSA, especially the mixed cations. The effects of six conditions, namely, Na2SO4 full immersion, MgSO4 full immersion, CaSO4 full immersion, Na2SO4 & MgSO4 full immersion, Na2SO4 & CaSO4 full immersion and MgSO4 & CaSO4 full immersion, on the TSA were studied by the observed degradation grades, mass loss, Raman analysis and X-ray diffraction (XRD). Results show that the degradation grade, degradation rate and degradation products are influenced by cations greatly.

Effect of C3A on Performance of Thaumasite Form of Sulfate Attack of Silica Minerals

AbstractThe effect of tricalcium aluminate (C3A) on the erosion degree and products of silica minerals under the thaumasite form of sulfate attack condition was studied using X-ray diffraction (XRD...

The TSA degradation process of cement-based materials in the electrical field environment

The thaumasite form of sulfate attack (TSA) of cement-based materials is a complex degradation process. However, there is no detailed study on the TSA degradation process in an electrical field environment. X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy (Raman) and chemical analyses were used to study the TSA degradation process based on the present studies. The results indicated that the degradation process of the electrical field cathode Na2SO4 solution-anode MgSO4 solution group was similar to the Na2SO4 and MgSO4 solution full immersion, with the main difference being the degradation rate. The electrical field can obviously accelerate the TSA degradation process. The degradation had progressed to the centre of the sample, and the amount of pulp was found in the electrical field group at 120 days. The degree of degradation of the MgSO4 full immersion affected only the surface of the sample at 360 days. The degree of degradation of the MgSO4 full immersion was the lowest at 360 days. Meanwhile, combining the XRD, chemical analysis data and appearance, the degradation rule was summarized as there being a fixed range to generate the pulp (the representative thaumasite form of sulfate attack), and the pH and the Ca/S need to meet the following conditions: 10.6 < pH < 11.8 and 4.0 < Ca/S < 6.4.

Effect of temperatures on TSA in cement mortars under electrical field

This study was aimed to investigate the effect of temperatures on thaumasite form of sulfate attack (TSA) in cement mortars under electrical field. The mortars were preserved at −5 °C, 5 °C, 20 °C, 5 °C–20 °C cycles, respectively. The damages were visually observed and compressive strengths of specimens were tested on a regular basis. X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were carried out to analyze deteriorated products. The results indicated that the specimens at 20 °C under both full-immersion and electrical field after 150 days were rarely damaged and thaumasite could not be detected. The failure of specimens at −5 °C was mainly due to freezing-thawing and salt scaling, resulting superficial damage. Moreover, an electrical field accelerated the damage induced by sulfate attack in the mortars and the deterioration of specimens at 5 °C was mostly due to the formation of TSA.

Effect of aluminium phases on thaumasite formation in cement slurries containing limestone powder

Under low-temperature conditions with carbonate, sulfate and abundant water, cement-based materials suffer from a severe thaumasite form of sulfate attack. In this study, the effects of aluminium phases on thaumasite formation in tricalcium silicate (C3S) slurries containing limestone powder under gypsum solution conditions was examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, nuclear magnetic resonance, Fourier transform infrared spectroscopy and differential thermal gravity analysis. The results indicate the following: the presence and relative amount of tricalcium aluminate (C3A) are not prerequisites of thaumasite formation; sulfates and carbonates can directly react with the calcium silicate hydrate (C–S–H) gels in cement hydration products, which dissolves the C–S–H gels and produces non-cementitious thaumasite; small amounts of aluminium phases in the reaction are sufficient to accelerate thaumasite formation, and the accelerating effect becomes more noticeable as the aluminium phase content increases. The morphology of erosion products showed that the crystal size become smaller as the C3A dosage increases.

Effect of silica fume on the thaumasite form of sulfate attack on cement-based materials

Thaumasite form of sulfate attack (TSA) can be observed in cement containing limestone under sulfate condition at low temperature. Mixing with suitable mineral admixture could be a good choice to improve the TSA resistance performance of cement-based materials. We investigated the durability performance of limestone-cement mortars reinforced with silica fume (SF) in 5% MgSO4 solution at 5 °C. The mortars, which were immersed in aggressive condition, were prepared with 2%, 4%, 6%, 8%, and 10% cement replacement by SF at a fixed water-to-binder ratio. Appearance, compressive strength, change of length and mass and corrosion products were investigated to evaluate the TSA resistance performance of SF based specimens. The results showed that specimens in the absence of SF almost disintegrated. Increasing SF dosage can reduce the degree of deterioration of SF mortars in TSA environment. Mortar mixtures with more than 6% SF merely show slight degeneration in relation to macroscopic and microscopic tests and characterizations.

Environmental controls and reaction pathways of coupled de-dolomitization and thaumasite formation

Deteriorated concrete and interstitial solutions (IS) were collected from Austrian tunnels to elucidate potential connections between de-dolomitization caused by coupled alkali carbonate reactions (ACR) and thaumasite form of sulfate attack (TSA). A conceptual reaction model for the portlandite–CSH phases–dolomite–calcium sulfate–calcite–brucite–thaumasite system was developed based on experimental data, hydrochemical modelling, IS chemistry and apparent concrete compositions. During the initial stage of sulfate attack, ettringite and gypsum formation weakened the concrete's microstructure and initiated ACR. Leaching of hydrated cement phases resulted in IS with a pH ~ 12-13, which promoted incongruent dolomite dissolution. Infiltration of Ca–SO4–type ground water into the de-dolomitization zone facilitated calcite and brucite neo-formations at 13>pH>10.5 during advanced states of concrete deterioration and subsequently resulted in thaumasite precipitation at pH~8.7. In this contribution, the reaction mechanisms and environmental controls of de-dolomitization are discussed in relation to the durability of concrete under sulfate attack.

Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5°C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.

Influence of curing duration on thaumasite formation of Portland-limestone cement pastes

Extensive researches have been carried out on the conventional sulfate attack, while it has been found that the thaumasite form of sulfate attack (TSA), sulfate attack at low temperature, has just been discovered and its mechanism is not well understood so far. In this study, the sulfate attack of cement paste incorporating 30% mass of limestone powder was investigated. After 20 °C water cured for 7, 14, and 28 days, respectively, 20 mm cube specimens were exposed in a 5% magnesium sulfate solution at (6 ±1) °C for periods up to 240 days. Their appearance change, compressive strength development were examined at different storage time, and selected paste samples were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results indicate that all Portland-limstone cement pastes suffer from appearance deterioration to some extent. The compressive strength of cement paste initially increases and after 120 days decreases with increasing exposed period. In addition, the cement paste with short curing time is more susceptible to sulfate attack, which directly leads to the formation of non-binder thaumasite crystal accompanied by the formation of ettringite, gypsum and brucite, and becomes a white, mushy, and incohesive matrix. Additionally, the extent of sulfate attack is greater and the formation of thaumasite is observed earlier for shorter curing time.

Use of different barium salts to inhibit the thaumasite form of sulfate attack in cement-based materials

We investigated the effects of different barium compounds on the thaumasite form of sulphate attack (TSA) resistance of cement-based materials when they were used as admixtures in mortars. Moreover, we analyzed the inhibition mechanisms within different types of barium salts, namely BaCO3 and Ba(OH)2, on the thaumasite formation. The control cement mortar and mortars with barium salts to cement and limestone weight ratios of 0.5%, 1.0%, and 1.5% were immersed in 5% (by weight) MgSO4 solution at 5 °C to mimic TSA. Appearance, mass, and compressive strength of the mortar samples were monitored and measured to assess the general degradation extent of these samples. The products of sulphate attack were further analyzed by XRD, FTIR, and SEM, respectively. Experimental results show that different degradation extent is evident in all mortars cured in MgSO4 solution. However, barium salts can greatly inhibit such degradation. Barium in hydroxide form has better effectiveness in protection against TSA than carbonate form, which may be due to their solubility difference in alkaline cement pore solution, and the presence of these barium compounds can reduce the degree of TSA by comparison with the almost completely decomposed control samples.

The effect of chloride on cement mortar subjected to sulfate exposure at low temperature

The effect of chloride on the performance of cement mortars made with CEMI and CEMI blended with 10% limestone filler and subjected to sulfate attack was investigated. The specimens were exposed to the combined action of chloride (0%, 0.5%, 1.0% and 2% of Cl−) and sulfate (0.6% SO42−) for 630days at 5±0.5°C. The performance of the mortar cubes was assessed by means of visual inspection and loss of mass. The mineralogy of the deterioration products was determined by infra-red spectroscopy and X-ray diffraction, and scanning electron microscopy was used to examine the microstructure of the specimens. Chemical analysis of the test solutions was also carried out at 540days of immersion in order to assess the end concentrations of calcium, sulfate and magnesium ions. All the specimens suffered from the thaumasite form of sulfate attack, except those stored in the combined sulfate and 2.0% chloride solution, which showed better performance within the 630-day study. The greatest deterioration occurred in mortars made with CEMI blended with 10% limestone filler. Based on visual and mass assessments, it was found that the effect of chloride on thaumasite degradation depended on chloride concentration, accelerating the damage at 0.5% and mitigating it at 2% in the conditions investigated. This is probably related to the reduction in calcite solubility and the increase in Friedel’s salt deposition observed as the chloride level increased in solution.

Effect of Rice Husk Ash on the Thaumasite Form of Sulfate Attack of Cement-Based Materials

The influence of rice husk ash (RHA) on the thaumasite formation of cement pastes containing limestone powder was investigated. The specimens which were cured in 2 % MgSO4 solution were prepared with different ratios of coarse rice husk ash (CRHA) and fine rice husk ash (FRHA) to cement. The visual change of mortars was inspected monthly. Compressive strength, length and mass developments were examined as functions of time. The products of sulfate attack were examined by X-ray diffraction, Fourier transform infrared spectroscopy and Laser-Raman spectroscopy. The results showed that the degree of deterioration was retarded when cement was partially replaced by RHA. The use of FRHA showed better performance than those of the coarser ones. No obvious degeneration was observed in the mortar contains 20 % FRHA after 12 months of immersing in the MgSO4 solution.

The effect of limestone type and nanosilica on the durability of limestone cement mortars

The influence of limestone type and nanosilica on the resistance of cement to the thaumasite form of sulfate attack (TSA) was systematically investigated. The sulfate attack of mortar specimens was evaluated using visual examination and mass, density and strength measurements. Samples were selected from the surface of prisms after 12 months of immersion and examined using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the prisms immersed in magnesium sulfate solution all showed signs of degradation. Limestone cement mortar is susceptible to TSA at 5°C. In mortar with high magnesium limestone, the damage was greater than in mortar with calcareous limestone. Prisms with nanosilica showed better performance than non-nanosilica prisms and this seems to be independent of limestone type. No obvious damage was observed in specimens exposed to sodium sulfate solution.

A modified ASTM C1012 procedure for qualifying blended cements containing limestone and SCMs for use in sulfate-rich environments

Blended Portland cements containing up to 15% limestone have recently been introduced into Canada and the USA. These cements were initially not allowed for use in sulfate environments but this restriction has been lifted in the Canadian cement specification, provided that the “limestone cement” includes sufficient SCM and that it passes a modified version of the CSA A3004-C8 (equivalent to ASTM C1012) test procedure run at a low temperature (5°C). This new procedure is proposed as a means of predicting the risk of the thaumasite form of sulfate attack in concretes containing limestone cements. The goal of the present study was to better understand how this approach works both in practice and in theory. Results from three different laboratories utilizing the CSA A3004-C8 test procedure are compared and analyzed, while also taking into account the results of thermodynamic modeling and of thaumasite formation experiments conducted in dilute suspensions.

Attack of limestone cement-based material exposed to magnesium sulfate solution at low temperature

Limestone in cement could be a source of CO32− needed for thaumasite formation which will result in thaumasite form of sulfate attack (TSA) probably. TSA has more deterioration than ettringite or gypsum form of sulfate attack because it targets the calcium silicate hydrates (C-S-H) which is the main binder phase in all Portland cement-based materials. By means of physical and mechanical property testing as well as erosion phases analysis, magnesium sulfate attack of cement-based material containing 35% limestone powder by mass at 5 ± 2 °C is investigated. The compressive strength and flexural strength of mortar specimen immersed in MgSO4 solution increase firstly, then decrease rapidly with the immersing age. Relative dynamic elastic modulus of mortar specimen changes in a phased process. After immersing in MgSO4 solution for 15 weeks, the main erosion phases in paste specimen change from four phases compounds, three phases compounds to two phases compounds from surface to inside. Deterioration course of limestone cement-based material exposed to magnesium sulfate aggressive environment appears progressive damage layer by layer, and every layer probably suffers four stages, which are property strengthening stage, initial degradation stage, thaumasite formation stage and cementation loss stage, respectively.

Laboratory study of the long-term durability of buried concrete exposed to Lower Lias Clay

This paper describes a long-term investigation into chemical degradation vulnerability of four different types of concrete that were exposed to pyrite rich clay. In this, four 100mm square by 1.2m long concrete columns made from Portland cement (PC), Portland limestone cement (PLC), sulfate resisting Portland cement (SRPC) and Portland cement blended with 25% pulverised fuel ash (PC–PFA) were buried for 9years in slightly weathered Lower Lias Clay of water soluble sulfate class DS-2. One face of each concrete column was coated with bitumen to test the performance of this method of protection. The temperature was controlled at 4.5±0.5°C using a cold water circulation system. The performance of the different concretes was assessed by means of visual observation supported by X-ray diffraction (XRD), Infra-red Scanning (IR) and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX) to identify the deterioration products.It was found that deterioration due to the thaumasite form of sulfate attack occurred in all four concretes with PLC concrete being the worst affected. The thickness of thaumasite deterioration into the concretes over the 9-year exposure was as follows: PLC=47; PC=33; SRPC=22 and PC–PFA=10mm. The study affirmed the susceptibility to Thaumasite Sulfate Attack (TSA) of both PC–25% PFA replacement and SRPC concretes. It was also found that, the amount of concrete deterioration decreased with increasing burial depth, which was probably due to reduced access to air. The bitumen coating, even if damaged, was an effective barrier at preventing deterioration in all concretes.

Resistance to Thaumasite form of Sulphate Attack of Blended Cement Mortars

Resistance to Thaumasite form of Sulphate Attack of Blended Cement Mortars