Modification of Magnesium Oxysulfate Cement by Incorporating Weak Acids

Modification of Magnesium Oxysulfate Cement by Incorporating Weak Acids

AbstractThis paper investigates the effects of weak acids (citric acid, boric acid, and trisodium citrate) with dosages of 0.5, 1.5, and 2.5% of MgO weight on compressive strength, water resistance, and drying shrinkage of magnesium oxysulfate (MOS) cement. Hydration products and microstructure of t...

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Bibliographic Details
Published in:Journal of materials in civil engineering Vol. 30; no. 9
Main Authors: Qin, Ling, Gao, Xiaojian, Li, Wengui, Ye, Huan
Format: Journal Article
Language:English
Published: New York American Society of Civil Engineers 01-09-2018
Subjects:
Acids
Building materials
Cement
Cements
Citric acid
Civil engineering
Compressive strength
Differential thermal analysis
Differential thermogravimetric analysis
Drying
Fourier transforms
Infrared analysis
Magnesium oxide
Microcracks
Shrinkage
Sodium citrate
Technical Papers
Thermogravimetry
Water resistance
X-ray diffraction
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Summary:AbstractThis paper investigates the effects of weak acids (citric acid, boric acid, and trisodium citrate) with dosages of 0.5, 1.5, and 2.5% of MgO weight on compressive strength, water resistance, and drying shrinkage of magnesium oxysulfate (MOS) cement. Hydration products and microstructure of typical samples are studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis-thermogravimetry (DTA-TG), and scanning electron microscope (SEM) facilities. The results show that compressive strength of MOS cement increases with an increasing MgO/MgSO4 molar ratio and decreasing H2O/MgSO4 molar ratio. The addition of citric acid, boric acid, or trisodium citrate significantly enhances compressive strength and water resistance and alleviates drying shrinkage of MOS cement paste. With the incorporation of weak acid, 5·1·7 [5Mg(OH)2·MgSO4·7H2O] phase, which is a new magnesium subsulfate crystalline product with a needlelike crystal whisker shape, forms in cement paste. This substance behaves in a criss-crossing manner and fills in pores and microcracks, inducing the improved performance of MOS cement paste. With optimum dosages of 0.5, 2.5, and 0.5%, respectively, citric acid, trisodium citrate, and boric acid exhibit decreasing improvement effect.
ISSN:0899-1561
1943-5533
DOI:10.1061/(ASCE)MT.1943-5533.0002418