Studying On Mechanism Of Complexation Effect In Hydration Of Steel Slag

Lower activity, lower hydration velocity as well as inferior stability are the main reasons, restraining the wide application of steel slag?SS? in concrete as supplementary cementing material from the way of rapidly consumed. Dense structure, higher formation temperature and fewer defects are the main factors giving rise to the lower Solubility of SS, ultimately, bring negative impacts on its activity. In this project, SS was chosen as the research object in order to improve its early hydration activity. The impacts of complexing agents on properties and hydration process of SS-cement system were investigated. Furthermore, the mechanism of complexing effect between complexing agents and metal ions that promotes the dissolution of SS was discussed.The effects of four kinds of complexing agents?triethanolamine?TEA?, triisopropanolamine?TIPA?, diethanol-isopropanolamine?DEIPA? and methyldiethanolamine?MDEA?? on hydration process and cementing property of SS-cement systems were investigated. At the dosage of 0.03%, the mortar strengths of blend systems were enhanced by these complexing agents. The compressive strengths were enhanced about 10%-12% at 3d, 13-15% at 7d, 12-13% at 28 d. X-ray diffraction?XRD? analysis, Differential scanning calorimetry-thermogravimetric?DSC-TG? analysis, Mercruy intrusion pore size distribution?MIP? analysis and Scanning electron microscopy analysis were used to study hydrate structures of hardend pastes. Studies had shown that the non-evaporable water contents of hydrated pastes in 3d, 7d and 28 d, the formation of AFt and AFm were promoted by four types of complexing agents; CH contents and porosity of hydrates were reduced by these complexing agents.The effects of four kinds of complexing agents on dissolution properties of SS were studied. XRD, p H meter, conductivity meter, isothermal calorimetry and inductively coupled plasma atomic emission spectroscopy?ICP-AES? were used to investigate the changes of each ion concentration in liquid phase, mineral contents and solution heat, which represented the dissolution property of SS. The results showed that the value of p H and conductivity, heat of solution, ionic concentration of SS paste solution are increased by four types of complex agents and the main mineral contents are reduced by complex agents; The effect of TEA and DEIPA are better than TIPA and MDEA.The effects of complexing agents on the complexing abilities and mechanism were investigated, and the existence of the complexing effect was confirmed. The complexing ability of the complexing agents for different mental ions was quantified by precipitation reaction and the chelate value of TEA, TIPA, DEIPA and MDEA for Ca²⁺, Fe³⁺ and Al³⁺ was determined, revealing that the chelating abilities of the DEIPA is superior, and MDEA is interior. Relatively, the complexing capacity of TEA and TIPA is between DEIPA and MDEA. From the 1HNMR result, it can be concluded that hydroxyl complexation is the main binding mode between TEA and mental ions. Furthermore, studies have shown that TEA was complexed with the central atom by the O and N atoms forming five rings chelate structure with Ca²⁺, Fe³⁺ and Al³⁺ ions.