Properties and hydrates of seawater-mixed magnesium potassium phosphate cements with high magnesium-to-phosphate ratio. (November 2022)

• Record Type: Journal Article
• Authors: Xu, Biwan; Lothenbach, Barbara; Li, Zongjin
• Is Part Of: Cement & concrete composites. Volume 134(2022)
• Publication Date: 2022-11
• Subjects: Magnesium potassium phosphate cement -- Seawater -- Compressive strength -- Hydration -- Thermodynamic modelling; Composite-reinforced concrete -- Periodicals; Concrete -- Periodicals; Composite materials -- Periodicals; Composites de ciment -- Périodiques; Béton -- Périodiques; Composites -- Périodiques; Béton léger -- Périodiques; Cement composites; Composite materials; Composite-reinforced concrete; Concrete; Lightweight concrete; Periodicals; Electronic journals; 620.135
• DOI: 10.1016/j.cemconcomp.2022.104807
• Languages: English
• ISSNs: 0958-9465

Abstract

Abstract: Seawater can be used as an alternative to freshwater for preparing cement-based materials. The effect of seawater on properties and hydrates of the magnesium potassium phosphate (MKP) cement pastes with Mg/PO4 molar ratio of 8 and low w/c ratio of 0.15 were investigated in this study. Compared with freshwater, seawater prolongs the MKP cement setting, slows down the heat release, increases the compressive strength in air, but slightly decreases the water resistance. K-struvite is the main hydrate in both pastes together with a minor amount of bobierrite and traces of Mg2 KH(PO4 )2 ⋅15H2 O in seawater. Seawater leads to less K-struvite, which agrees well with thermodynamic modelling predictions, but it also leads to partial elongated K-struvite needle crystals, which could contribute to the increased compressive strength. Water exposure has little changes on the main hydrates, but caused minor additional potassium chloride in the seawater-mixed paste, which partially explains the higher strength loss.