Study On Effects Of Activator Mix Proportions On Hydration Process And Shrinkage Behavior Of Alkali-activated Slag Binder

Alkali-activated slag binder,which is a low carbon and environmental friendly cementious material,offers a range of high performance characteristics,including excellent mechanical strength and resistance to chemical attack.The widely application of AAS is restricted by its rapid setting and high shrinkage.To slove this challenge,one of the most significant ways is to find effective methods to control and regulate the hydration process of AAS.The influence of four different activators?water glass,Na₂CO₃,NaOH,Ca?OH?₂?and their proportions on initial fluidity,compressive strength and hydration process of alkali-activated slag binder was studied by mixture design under the condition of fixed water to binder ratio?0.4?and alkali concentration?4%Na₂O?.The main effects and interaction effects of four activators with different ages and the quality of slag were analysed.Isothermal calorimetry method,X-Ray diffraction,Thermogravimetric analyses and Mercury intrusion porosimetry were carried out to explain the mechanism.Activator mix proportions were proposed based on reults above to investigate their effects on autogenous shrinkage of AAS.Chemical shrinkage,internal relative humidity test and Thermogravimetric analysis were also performed to understand the shrinkage mechanism.The main results can be summarized as follows:?1?The compressive strength development and hydration process of AAS cement samples were strongly affected by the activator mix proportions.Compared with AAS activated by water glass,the addition of Na₂CO₃ retarded the hydration process of AAS,while the early hydration process was accelerated by adding NaOH and Ca?OH?₂,though reducing the hydration degree of AAS at 28d.Furthermore,equations derived from ANOVA regression analysis offered approaches to optimize the AAS hydration process through varying activator types and their proportions.?2?When the alkali concentration and water to binder ratio kept constant,the effect of water glass and Ca?OH?₂ on slag changed little with slags of varying chemical composition,while the effect of Na₂CO₃ and NaOH on slag changed little in the early stage,but was greatly affected by the chemical composition of slag in the later stage.In addition,the significant age of interaction between different activators on the compressive strength of AAS is related to the chemical composition of slag.?3?Comparable levels of hydration progress and compressive strength development of AAS prepared by different chemical composition of slag could be achieved through varying activator mix proportions,but adjustment methods were strongly depend on slag chemistry,due to the selectivity of slags to different activator.?4?The content of Ca?OH?₂ in activator mix and slag quality had a significant influence on the autogenous and chemical shrinkage of alkali-activated slag binder.When the dosage of Ca?OH?₂ in the activator mix was low,its effect on the autogenous shrinkage of AAS strongly depended upon the slag type,while higher content of Ca?OH?₂ reduced autogenous shrinkage.The influene of Ca?OH?₂ content on chemical shrinkage of AAS also depended heavily on slag origin.The shrinkage caused by self-desiccation accounted for a large proportion in the autogenous shrinkage,which led to the situation that the content of Ca?OH?₂ in the activator had opposite effect on the autogenous shrinkage and chemical shrinkage of AAS.