Study On The Dissolution Behaviors Of Ground Granulated Blast Furnace Slag

Granulated blast furnace slag（GGBS）is produced during the process of ironmaking and its utilization is in accordance with the sustainable development strategy in China.As the main binding material in alkali activated slag binder（AAS）,studying its dissolution behavior in the liquid environment is beneficial to understand the hydration rules of GGBS in AAS,achieving the regulation of AAS hydration and hardening propertiesIn this paper,simulation and experiment methods were applied to study the dissolution kinetics of the GGBS glass structure in pure water and NaOH solution.The effects of hydration temperature（5℃,20℃,40℃）,chemical composition of GGBS and relative humidity（RH）of the storage environment（RH33%,RH59%,RH95%）on the dissolution behaviors of GGBS in pure water and sodium hydroxide solution were investigated.By calculating the thermodynamic parameters of hydration products based on the composition of solution,the thermodynamic stability of hydration products during the slag dissolution process were analyzed.The evolution of vitreous structure of GGBS in liquid phases was characterized by infrared spectroscopy and thermogravimetric analysis.The main results can be summarized as follows:（1）The proposed parameter K_L=（2Ca+2Mg+Na+K）/（4Si+3Al）（atomic percentage）could evaluate the reactivity of the slag（dissolution ability in pure water）.The dissolution concentration of the network former and the network modifier as well as the depolymerization degree of the vitreous network structure in pure water increased with increasing K_L value.Even the silicon-oxygen tetrahedron with low activity and high polymerization degree could dissociate into the silicon-oxygen tetrahedron with low degree of polymerization gradually.（2）The dissolution rate of GGBS in NaOH solution was affected by both K_L value and Al/Si ratio.The higher the Al/Si ratio,the more obvious the improvement of the dissolution ability of the GGBS after activated by NaOH solution,especially the increase of the concentration of Al anion group in the dissociation filtrate,resulting in the rise of the thermal stability of the hydrotalcite phase.Then,a large amount of hydrotalcite phase precipitated from the filtrate.（3）When the hydration temperature was in the range of 5℃-40℃,the dissolution of the GGBS was enhanced by rising temperature and the dissolution concentration of network former as well as the majority of network modifier in GGBS increased with the increasing temperature.The concentration of Na⁺in the solution was mainly controlled by the Na content in the GGBS and it was less affected by temperature.The thermodynamic stability of C-S-H gel,hydrotalcite phase and calcium hydroxide in dissociated filtrate increased with the increase of temperature.（4）Due to the limitation of solution polarity,the promotion effect of temperature increase on the dissolution of GGBS network structure was limited in pure water.The Q⁰～Q³ structure tended to dissociate uniformly.The dissolution of the GGBS glass network structure in NaOH solution was promoted by temperature rise obviously and the dissolution of the Q⁰ structure was preferential.（5）The pre-hydration degree and reactivity loss of GGBS increased with rising relative humidity of the storage environment.The dissolution concentration of Si anion group in dissociated filtrate also decreased with increasing relative humidity and it effects on the inhibition of depolymerization of glass network structure were much more obvious.However,the environmental relative humidity had little effect on the dissolution behaviours of the network modifier and it could only promote the initial dissolution concentration of Ca²⁺.