Gypsum dehydration in cement and its impact on air-void structure in air-entrained concrete

Sypek, Maciej; Latawiec, Rafał; Pichór, Waldemar

doi:10.1016/j.conbuildmat.2019.06.011

Cited by 10 publications

(8 citation statements)

References 19 publications

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“…The influence of gypsum dehydration on the structure of the air void system has already been proved in earlier papers [ 45 ]. The same results were obtained in the current study—gypsum dehydration caused a decrease in the A 300 content, while the total air content of the concrete mixtures was unchanged.…”

Section: Discussionmentioning

confidence: 88%

Impact of Surfactant and Calcium Sulfate Type on Air-Entraining Effectiveness in Concrete

Sypek¹,

Latawiec²,

Łaźniewska-Piekarczyk

et al. 2022

Materials

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The paper presents the evaluation of the influence of calcium sulfate on the air void microstructure in concrete and its action mechanism depending on the character of the air-entraining agent. Gypsum dehydration has been previously proven to negatively influence the air void structure of air-entrained concrete. Ettringite, nucleating from tricalcium aluminate and calcium sulfate, influences the adsorption and mode of action of anionic-based polycarboxylate ether admixtures. The authors suspected the admixture’s air-entraining mechanism was also affected by these characteristics. Gypsum dehydration was confirmed to influence the air void structure. In the case of the anionic surfactant, the content of air bubbles smaller than 300 µm was lower compared to cement with gypsum and hemihydrate. On the other hand, the content of air voids with a diameter up to 60 µm, which are the most favorable, was higher. The results obtained led to the conclusion that the mechanism of air entrainment was twofold, and in most cases occurred through the lowering of surface tension and/or through the adsorption of surfactant on cement grains. The adsorptive mechanism was proved to be more effective in terms of the total air content and the structure of the air void system. The results and conclusions of the study provide guidelines to determine the proper surfactant type to reduce the risk of improper air entrainment of concrete, and emphasize the importance of gypsum dehydration of cement in the process of air entrainment.

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Section: Discussionmentioning

confidence: 88%

Impact of Surfactant and Calcium Sulfate Type on Air-Entraining Effectiveness in Concrete

Sypek¹,

Latawiec²,

Łaźniewska-Piekarczyk

et al. 2022

Materials

Self Cite

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“…As mentioned by Sypek, gypsum dehydration in cement results in higher concentrations of sulfate and calcium ions, which has a negative influence for air-entrained concrete. Therefore, gypsum dehydration should be taken into consideration and must be scrupulously avoided.…”

Section: Resultsmentioning

confidence: 95%

“…The synthetic betaine surfactant, although capable of air entrainment, is incompatible with cement solutions because it precipitates when interacting with calcium or sulfate ions . Other researchers , studied the influence of gypsum on the properties of the air void. Due to gypsum dehydration, the amount of Ca 2+ and SO 4 2– releases to pore solution and the performance of air entraining agents are influenced.…”

Section: Introductionmentioning

confidence: 99%

Computational Simulations of Adsorption Behavior of Anionic Surfactants at the Portlandite–Water Interface under Sulfate and Calcium Ions

Zhao,

Yang,

Shu

et al. 2024

Langmuir

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The adsorption behaviors of two kinds of anionic surfactants (called HSO 4 and HPO 4 , respectively) with different negatively charged hydrophilic head groups (sulfate and phosphate groups) under different concentrations of sulfate and calcium ions at the portlandite−water interface are investigated by molecular dynamics simulations. Although the adsorption strength of HPO 4 is much greater than that of HSO 4 , the desorption energy of HSO 4 is slightly greater at an early stage of desorption due to a more perpendicular orientation and denser packing of hydrophobic tail chains. After adding ions, the sulfate ion has a significant weakening effect due to competitive adsorption, and the negative influence of the calcium ion is weaker, and it even slightly promotes the adsorption at low concentration. Due to the stronger electrostatic interaction of phosphate head groups with the portlandite surface, adsorption strength and adsorption stability for HPO 4 are always greater than that of HSO 4 under the interference of sulfate ions. The competitive adsorption of the sulfate ion significantly weakens the interaction of hydrophilic head groups with portlandite and the dense packing of two surfactants. The calcium ion with low concentration approaches the portlandite surface and acts as an ion bridge to slightly enhance the adsorption of the surfactant. The ion bridging effect is stronger in the HPO 4 system than in the HSO 4 system.

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“…An important technical approach to improving the frost resistance of concrete is to entrain numerous steady air bubbles into the concrete using air-entraining agents (AEAs) [3,4]. Entraining many small bubbles into concrete and ensuring their stability are an extremely complex physical-chemical process that is affected by many factors, such as the mixing process [5][6][7], concrete mixture proportioning [8], fine and coarse aggregate characteristics [9], physical and chemical properties of Portland cement [10], other chemical admixtures, and supplementary cementing materials [11,12].…”

Section: Introductionmentioning

confidence: 99%

Effect of Low Atmospheric Pressure on Bubble Stability of Air‐Entrained Concrete

Yang

2021

Advances in Civil Engineering

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The effect of low atmospheric pressure of the environment on the air content and bubble stability of air-entrained concrete was investigated in Beijing and Lhasa. The results indicate that the reduction of atmospheric pressure can weaken the air-entraining capability of air-entraining agents (AEAs). The air content of fresh concrete decreased by 9%–39% when the atmospheric pressure dropped to 64 kPa. The bubble stability of concrete mixed at a low atmospheric pressure becomes worse. Within 50–55 min after mixing, the air content of concrete mixed at a low atmospheric pressure decreases greatly, and the void spacing factor increases obviously. The concrete mixed at a low atmospheric pressure will lose more air content when vibration time increases, leading to the decrease of air content and the increase of the spacing factor, which are more significant than the concrete mixed at normal atmospheric pressure. On the basis of the experiment results in this study, the type of AEAs must be carefully selected, and the vibration time must be strictly controlled to ensure that the air content of concrete will meet the design requirements in low atmospheric pressure areas.

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Gypsum dehydration in cement and its impact on air-void structure in air-entrained concrete

Cited by 10 publications

References 19 publications

Impact of Surfactant and Calcium Sulfate Type on Air-Entraining Effectiveness in Concrete

Impact of Surfactant and Calcium Sulfate Type on Air-Entraining Effectiveness in Concrete

Computational Simulations of Adsorption Behavior of Anionic Surfactants at the Portlandite–Water Interface under Sulfate and Calcium Ions

Effect of Low Atmospheric Pressure on Bubble Stability of Air‐Entrained Concrete

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