Influences Of Alkanolamine Accelerators Used In High-Speed Railway On The Mechanical Properties And Microstructure Of Hardened Cement Pastes

Cement concrete is one of the most widely used materials in the ballastless track currently.The performance of cement concrete plays a decisive role in the overall performance of the track structure.Alkanolamine admixtures are often used as early strength agents,grinding aids,etc.to improve the mechanical properties of cement concrete.In this study,hardened cement paste was used as the research object.The addition of triethanolamine,triisopropanolamine,methyldiethanolamine and diisopropylethylamine was used to study effect of different alkanolamines on mechanical properties and microstructure of hardened cement paste.By testing the heat release rate of cement hydration,chemically bonded water content and calcium hydroxide content in the hardened cement paste,the influence of different alkanolamines on the hydration degree of the cement was clarified;The effects of different alkanolamines on the pore structure of hardened cement paste and the morphology of hydration products were studied by means of mercury intrusion and scanning electron microscopy.The mechanism of the influence of different alkanolamines on the mechanical properties of hardened cement paste was revealed Finally.The main results and conclusions of this paper are as follows:(1)The low-dosage of TEA can significantly increase the early strength of hardened cement paste,but reduce its late strength;the high-dosage of TEA significantly reduces the strength of each age.The low-dosage of TEA can effectively prolong the induction period of cement hydration,promote the hydration of silicate phase,and improve the degree of cement hydration at early age.When the TEA content is as high as 1%,the hydration of aluminate phase is greatly advanced,but the hydration of silicate phase is significantly inhibited,so the degree of hydration at early age is significantly reduced.At the same time,due to the complexation of TEA with calcium ions,the content of CH crystals in the hardened cement paste decreased significantly,and a large amount of amorphous CH was found.The change of the degree of hydration and crystal morphology significantly reduced the porosity of the hardened cement paste.(2)The low-dosage of TIPA significantly increased the strength of hardened cement paste at various ages;however,the high-dosage of TIPA had no significant effect on the strength of each age.The low-dosage of TIPA shortens the induction period of cement hydration,but the high-dosage of TIPA prolongs the induction period of cement hydration.TIPA promotes the hydration of the silicate phase,and the amount of chemically bonded water of the hardened cement paste increases at each age,and the degree of cement hydration increases.At the same time,TIPA significantly reduced the CH content in the hardened cement paste,and the morphology of the CH crystal was changed.The degree of hydration and the change of crystal morphology significantly reduced the porosity of the hardened cement paste.(3)The low-dosage of MDEA is beneficial to improve the compressive strength of hardened cement paste and the flexural strength of 1 day old,but reduce the late flexural strength;while the high-dosage of MDEA only increases the early compressive strength and reduces the late strength has no effect on the early flexural strength.The low-dosage of MDEA prolongs the induction period of cement hydration,promotes the hydration of silicate phase,and improves the degree of cement hydration.The high-dosage of MDEA shortened the hydration induction period,the aluminate phase hydration was advanced,the silicate phase hydration was inhibited,and the hydration degree of cement in the 1 day age was slightly reduced,but the hydration degree of cement has increased significantly in 3 days,7 days and 28 days.At the same time,MDEA promotes the transformation of CH crystal from crystalline to amorphous,and the degree of hydration and crystal morphology change significantly reduces the porosity of hardened cement paste.(4)DIPEA has no significant effect on the mechanical properties of the hardened cement paste.DIPEA slightly shortened the induction period of cement hydration,but the hydration degree of cement basically unchanged.At the same time,the microscopic morphology of the hydration product did not change significantly.Resulting in the pore structure of hardened cement paste does not change.(5)The hydroxyl in the molecular structure of the alkanolamine plays an indispensable role in improving the mechanical properties of the hardened cement paste.The amount of hydroxyl groups determines the complexing ability of the alkanolamine admixture to metal ions;The position of the hydroxyl group determines the steric hindrance in the vicinity,which affects the type of complex metal ion of the alkanolamine early strength agent.