scholarly journals Deterioration Regularity of Sodium Sulfate Solution Attack on Cemented Coal Gangue-Fly Ash Backfill under Drying-Wetting Cycles

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shaojie Chen ◽  
Zhen Zhang ◽  
Dawei Yin ◽  
Junbiao Ma
Keyword(s):  
Fly Ash ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Coal Gangue ◽  
Salt Crystallization ◽  
Sodium Sulfate Solution ◽  
Sulfate Ion ◽  
Sulfate Ions ◽  
Ion Contents ◽  
The Masses

To research the properties of cemented coal gangue-fly ash backfill (CGFB) exposed to different concentrations of sodium sulfate solutions under drying-wetting cycles, the mass changes, uniaxial compressive strengths, sulfate ion contents at different depths, and microstructures of CGFB samples were measured in this study. The results show that the CGFB samples were damaged by salt crystallization in the dry state and attacked by the expansive products in the wet state. The sulfate ion contents in CGFB samples increased with the sulfate concentrations and drying-wetting cycles and decreased from the surface to the inside of the samples. The damage process of CGFB samples evolved from the surface to the inside. In the early stage of corrosion, sulfate ions adsorbed to the surface of CGFB samples and consumed nonhydrated particles to form acicular ettringite and other products that filled the material pores. For this stage, the driving force of sulfate ions to enter into the CGFB samples was the highest for the samples immersed in 15% sodium sulfate solution, and the masses and strengths increased the fastest. As the drying-wetting cycles continued, the nonhydrated particles inside the samples were nearly completely hydrated, and the samples were constantly damaged by salt crystallization and dissolution. The corrosion ions entered into the samples and consumed portlandite to produce a large amount of prismatic ettringite and aggravated the internal corrosion of CGFB samples. At the fifteenth drying-wetting cycle, the higher the salt concentration of the immersion solution was, the faster the masses and the strengths of CGFB samples decreased. Moreover, the surface spalling and failure of CGFB samples were more severe.

scholarly journals Experimental Study on the Durability of Fly Ash-Based Filling Paste in Environments with Different Concentrations of Sulfates

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Boqiang Cui ◽  
Yin Liu ◽  
Hao Guo ◽  
Zhanxin Liu ◽  
Yao Lu
Keyword(s):  
Fly Ash ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Mechanical Analysis ◽  
Test Block ◽  
Sodium Sulfate Solution ◽  
Stress Strain ◽  
Hydrated Calcium Silicate ◽  
Soaking Time ◽  
Hydrated Products

In order to study the effects of different concentrations of sulfate on the strength of fly ash-based coal mine filling paste, using variable control, mechanical analysis, and other means, the changes in the uniaxial compressive strengths of filling paste blocks soaked in different concentrations of sodium sulfate solution for different durations are studied, and their stress-strain curves are discussed. The hydrated products of each block are analyzed at different stages by XRD, and the results indicate that different concentrations of sodium sulfate solution have different effects on the strength of the filling paste after soaking for different durations. A sodium sulfate solution with a concentration of 5% had an activator effect on the fly ash-based filling paste and enhanced the strength of the filling paste. A sodium sulfate solution with a concentration of 10% and 15% increased the early strength of the paste test block faster, but after 60 d, the strength decreased. The stress-strain curves for these blocks show that the elastic moduli of the filling paste test blocks change irregularly, and it was found that with the increase in soaking time, the blocks soaked in the 10% and 15% sodium sulfate solutions developed fissures in the later stage that adversely affected the strength of the filling paste. The XRD results show that the filling paste test block hydration products are hydrated calcium silicate (C-S-H) based and that ettringite (AFt), beneficial to strength of the filling paste in proper quantities, appeared in the main product of the filling paste test blocks that were soaked in the sodium sulfate solution. With the increase in the concentration of the sodium sulfate solution, the AFt is generated in larger quantities, and gypsum crystals begin to appear, which is not conducive to the filling paste block strength.

scholarly journals Damage and Degradation of Concrete under Coupling Action of Freeze-Thaw Cycle and Sulfate Attack

2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
Wei Tian ◽  
Fangfang Gao
Keyword(s):  
Fly Ash ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Sodium Sulfate Solution ◽  
Failure Characteristics ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Two Stages

In this study, the mechanical behaviors, failure characteristics, and microstructure of concrete containing fly ash (FA) against combined freeze-thaw cycles and sulfate attack were studied compared with normal concrete, and the formation rates of corrosion products during coupling cycles were investigated. Results showed that, during the coupling action of freeze-thaw cycles and sodium sulfate solution, concrete containing 10% fly ash exposed in 5% sodium sulfate solution exhibited better freeze-thaw resistance. Meanwhile, the variation of compressive strength of concrete during the coupling cycles could be divided into two stages, including the strength enhancement stage and the strength reduction stage. Moreover, the proportion of micropores and capillary pores decreased obviously during combined freeze-thaw cycles and sulfate attack, and excessive concentration of sodium sulfate solution led to more macropores after high-frequency freeze-thaw cycles.

Effect of Fly Ash on Resistance to Sulfate Attack of Cement-Based Materials

2013 ◽  
Vol 539 ◽  
pp. 124-129 ◽  
Author(s):  
Kai Wei Liu ◽  
Min Deng ◽  
Li Wu Mo
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Length Change ◽  
Sulfate Attack ◽  
Sodium Sulfate Solution ◽  
Reaction Products ◽  
Visual Appearance ◽  
Cement Based Materials

The resistance to sulfate attack of mortars containing 0%, 20%, and 40% of fly ash cured in 5 wt. % sodium sulfate solution at 20°C was investigated in this paper. Visual appearance, cracking analysis, velocity of ultrasonic wave and length change were applied to evaluate the sulfate resistance of mortars. The phases and microstructure of the reaction products due to sulfate attack were examined by XRD and SEM, and the pore structure of the mortars was analyzed by MIP. The effects of fly ash on the sulfate attack of mortars were analyzed. Results indicated that the addition of fly ash improved the resistance of sulfate attack significantly, this probably contributed to the pozzonlanic reaction of fly ash.

Impact of sodium sulfate solution on mechanical properties and structure of fly ash based geopolymers

2014 ◽  
Vol 48 (3) ◽  
pp. 683-697 ◽  
Author(s):  
Zvezdana Baščarević ◽  
Miroslav Komljenović ◽  
Zoran Miladinović ◽  
Violeta Nikolić ◽  
Nataša Marjanović ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fly Ash ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Sodium Sulfate Solution

Research on Stress Corrosion of Concrete in Sodium Sulfate Solution

2011 ◽  
Vol 94-96 ◽  
pp. 1243-1246 ◽  
Author(s):  
Yong Ning Liang ◽  
Tao Ji ◽  
Yi Zhou Zhuang ◽  
Xu Jian Lin
Keyword(s):  
Fly Ash ◽  
Sodium Sulfate ◽  
Bending Strength ◽  
Concrete Strength ◽  
Corrosion Damage ◽  
Sulfate Solution ◽  
Hydration Product ◽  
Sodium Sulfate Solution ◽  
Time Intervals ◽  
Initial Strength

An investigation was carried out on the behavior of concrete under both sulfate attack and mechanical stress. The specimens of concrete with/without fly ash were subjected to flexural load with a level of 0.2 and 0.4 of their initial strength and also immersed into a 10% sodium sulfate solution or water respectively. The bending strength of the concrete was tested at certain time intervals. The results indicate that fly ash could effectively relieve the deterioration of the concrete in corrosive environment; flexural load could accelerate the corrosion damage and that the development of concrete strength is related to the internal structure, hydration product and the interface between coarse aggregate and cement paste.

scholarly journals Durability of Mortars with Fly Ash Subject to Freezing and Thawing Cycles and Sulfate Attack

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 220
Author(s):  
Monika Jaworska-Wędzińska ◽  
Iga Jasińska
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Sodium Sulfate ◽  
Sulfate Solution ◽  
Physical Factors ◽  
Sodium Sulfate Solution ◽  
Freezing And Thawing ◽  
High Calcium ◽  
High Calcium Fly Ash ◽  
Freezing And Thawing Cycles

Destruction of cement composites occurs due to the alternate or simultaneous effects of aggressive media, resulting in the destruction of concrete under the influence of chemical and physical factors. This article presents the results of changes in the measurement of linear strains of samples and changes in the microstructure of cement after 30 freezing and thawing cycles and immersed in 5% sodium sulfate solution. The compressive strengths ratios were carried out at the moment when the samples were moved to the sulfate solution after 30 cycles and at the end of the study when the samples showed visual signs of damage caused by the effect of 5% Na2SO4. The composition of the mixtures was selected based on the Gibbs triangle covering the area up to 40% replacement of Portland cement with low and high-calcium fly ashes or their mixture. Air-entrained and non-air entrained mortars were made of OPC, in which 20%, 26.6%, and 40% of Portland cement were replaced with low and/or high-calcium fly ash. Initial, freezing and thawing cycles accelerated the destruction of non- air-entrained cement mortars immersed in 5% sodium sulfate solution. The sulfate resistance, after the preceding frost damage, decreased along with the increase in the amount of replaced fly ash in the binder. Air-entrained mortars in which 20% of cement was replaced with high-calcium fly ash showed the best resistance to the action of sodium sulfate after 30 freezing and thawing cycles.

Properties of MSFAC Long-Term Exposure to Sodium Sulfate Solution

2013 ◽  
Vol 438-439 ◽  
pp. 25-29
Author(s):  
Li Yun Pan ◽  
Jian Dong Liu ◽  
Lun Li ◽  
Xiao Ke Li
Keyword(s):  
Fly Ash ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Ion Concentration ◽  
Capillary Absorption ◽  
Sulfate Ion ◽  
Ion Content ◽  
Powder Samples ◽  
Ion Contents ◽  
Different Depths

Experiments were conducted to study sulfate attack on concrete made machine-made sand and fly ash (MSFAC). The cubes with dimensions of 100 mm were cast and immersed in sodium solution with sulfate-ion concentration of 50000mg/L and tested after exposed for 30, 90, 180, 270, 360 and 540 days. The powder samples were made by steps of drilling, cutting and grinding. The sulfate-ion contents of concrete at different depths were measured by the chemical titration method. The results show that the sulfate-ion content of concrete decreased with depth, the sulfate-ion entered concrete by diffusion, permeation and capillary absorption. The sulfate-ion content of concrete decreased with the increasing replacement of cement by fly ash, and also decreased with the increase of exposure time when 30% of cement is replaced by fly ash. There are some advantages of using fly ash for concrete with machine-made sand to resist sulfate attack.

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