Effect Of Curing Temperature And Sulfate Attack On Microstructure Of C₃S-C₃A Paste

The essence of Portland cement hydration is the coupling hydration of different clinker minerals.The composition and microstructure of the C-?A?-S-H gel have a significant effect on the mechanical properties and durability of concrete.C3S and C3A are the main mineral components in Portland cement,which affects the microstructure of C-?A?-S-H gel.The influence mechanism of C₃A content,curing temperature and sulfate attack on the microstructure of C-S-H gel formed by C₃S hydration is still unclear.This paper relies on the National Natural Science Foundation project“Influence Mechanism of Erosive Ions on the Microstructure and Properties of Al-Doped C-S-H Gel in Concrete Materials”?51778513?.The influence of paste composition,curing temperature and Na₂SO₄ corrosion on the composition of hydration products,the formation and evolution of C-?A?-S-H gel microstructure,the transformation of Al-containing products,and the changes of pore structure and chloride ion adsorption were studied.The main research results are as follows:?1?C₃A promoted the early hydration of C₃S,and the degree of hydration increased with the increase of C₃A content.The Al³⁺released by C₃A hydration entered the bridge sites of C-S-H gel silicate chains and formed C-?A?-S-H gel,and at the same time increased the degree of polymerization of the C-S-H gel.The addition of C₃A generated Mesopores with size of below 20 nm in the paste,which reduced the average pore size of the compound paste but increased the porosity of the paste,and at the same time improve the chloride ion adsorption ability of the compound paste.?2?High temperature curing significantly improved the early hydration degree of C₃S-C₃A paste,and promoted the release of Al from C₃A hydration into C-S-H gel.With the increase of curing temperature,Ca/Si of C-S-H gel in C3S-C3A paste decreased,MCL and Al[4]/Si increased.With the increase of curing temperature,the specific surface area,cumulative pores volume and average pore diameter decreased,resulting in a decrease in the chloride ion adsorption amount of the C₃S-C₃A paste.?3?Na₂SO₄ corrosion promoted the hydration process of C₃S-C₃A paste and increased the MCL C-S-H gel.But it hindered the immigration of Al³⁺formed by C₃A hydration into the C-S-H gel bridge site,resulting in decrease of Al[4]/Si.With increase of the hydration age before corrosion,the decrease of Al[4]/Si and Ca/Si in C-?A?-S-H gel was minor.As the corrosion age increased,Al[4]/Si and Ca/Si of C-?A?-S-H gels decreased.Na₂SO₄ corrosion has dealumination and decalcification effects on C-?A?-S-H formed by hydration of C₃S-C₃A,resulting in the evolution of its microstructure.?4?Under Na₂SO₄ corrosion,the specific surface area,cumulative pore volume and average pore size of the composite slurry decreased,and the chloride ion adsorption and solidification ability decreased.The decrease rate of the chloride ion adsorption amount of C₃S-C₃A paste increased with the increase of C₃A content.Compared with the paste corroded after 1 d,the volume of pore below 10 nm was minor in the paste corroded after 28 d,leading to a decrease in the specific surface area and cumulative pore volume but a increase of the average pore diameter in the C₃S-C₃A paste,which further reduced the chlorine ion adsorption amount.The research results can provide references for revealing the formation and evolution mechanism of the microstructure of concrete gelled slurry under sulfate attack environment.