Effect of Gypsum-Contaminated Aggregate on Long Term Properties of Mortar

Li, Bei Xing; Ke, Da; Song, Ji Hong; Fu, Ke Jian

doi:10.4028/scientific5/amr.450-451.205

Cited by 1 publication

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“…CaSO 4 also accelerated C 3 S hydration and enhanced the strength development 11,12 . The sources of sulfate are also from aggregates, groundwater, and seawater, and it reacts with C 4 AF, C 3 A, and its hydration products, causing volume expansion and generating cracks (known as delayed ettringite formation or internal sulfate attack) 13,14 . An optimal sulfate content contributes to the highest mechanical properties and the lowest shrinkage 15 .…”

Section: Introductionmentioning

confidence: 99%

“…11,12 The sources of sulfate are also from aggregates, groundwater, and seawater, and it reacts with C 4 AF, C 3 A, and its hydration products, causing volume expansion and generating cracks (known as delayed ettringite formation or internal sulfate attack). 13,14 An optimal sulfate content contributes to the highest mechanical properties and the lowest shrinkage. 15 It is beneficial to fully understand the differences in hydration mechanisms between C 4 AF and C 3 A to regulate the balance between C 4 AF/C 3 A and CaSO 4 and to ensure the best performance in using cementitious materials.…”

Section: Introductionmentioning

confidence: 99%

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Understanding the adsorption of calcium sulfate on tetracalcium aluminoferrite and tricalcium aluminate surfaces

2023

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Calcium sulfate (CaSO4), an essential retarder in cement, retards the hydration of tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) phases. However, its retarding mechanism remains unclear. This paper focused on the adsorption of CaSO4f on C4AF and C3A surfaces based on isothermal calorimetry, the measurement of the ionic concentrations in a diluted system, and density functional theory to enhance the understanding of the retardation mechanism. The results showed that the retarding effect of CaSO4 on C4AF was stronger than that on C3A due to the slower CaSO4 consumption rate, lower driving force for CaSO4 adsorption, and surface coverage of Fe(OH)3 gel. The adsorption of CaSO4 hindered Ca dissolution more markedly on C4AF than C3A, which was pronounced on Fe‐free C4AF surfaces. The adsorption of CaSO4 weakened the affinity of water on C4AF and C3A surfaces, lowering the driving force for H2O adsorption. The adsorption of H2O and CaSO4 promoted the dissolution of Al on the [AlO6] octahedral surface of C4AF, which may be responsible for the maintenance of a higher Al concentration in the solution. Based on the above results, the adsorption of CaSO4 on initial C4AF and C3A hydration was explained.

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Section: Introductionmentioning

confidence: 99%