177 / 2022-04-30 15:41:45

Study on hydration mechanism of limestone calcined clay cement (LC3) blended with seawater

Limestone-calcined clay cement hydration,hydration,hydration products,Friedel's salt,Mechanical properties

Abstract



Limestone-calcined clay cement (LC³) is a new type of green cement with less environmental impact than ordinary OPC . The use of seawater for concrete production further contributes to the economic and environmental benefits. This paper aims to investigate the hydration mechanism of limestone-calcined clay cement in pure water and seawater.



It is found that limestone-calcined clay cement and seawater can simultaneously promote the early-age hydration process. The second hydration peak observed in the LC³ system corresponds to the precipitation of hemicarboaluminate and monocarboaluminate owing to the reaction between aluminates,  from cement clinker and calcined clay, and calcium carbonate, from limestone. Dissolved ions in seawater have a non-negligible effect on hydrated phase composition. Monocarboaluminates react with chloride ions in seawater to form the stable phase of Friedel's salts.



In the presence of LC³ and seawater, the reactivity of cement clinker decreases, and the increase in chloride ion content can promote the hydration of aluminates and ferrites, generating other phases such as C-A-S-H, strätlingite and carboaluminate. In both pure water and seawater systems, the amount of CH decreases over time as it is consumed by the pozzolanic reaction of metakaolin. At a given cement content, these phases can improve the engineering properties of the material.



With the addition of LC³ and seawater, the hydrate phase composition and microstructure of the cementitious material changed, which  did not cause deteriorating effect on the physical and mechanical properties of the cementitious material. The samples with limestone calcined clay content of 35% obtained higher compressive strength than other content, and the comprehensive strength activation index had the best effect. The research results can provide a reference for the application of green seawater sea sand concrete in marine infrastructure, which can promote the sustainable development of civil engineering.