Effects Of Alkalinity,Temperature And Fineness On Dissolution Kinetics Of Blast Furnace Slag,Fly Ash And Metakaolin

Alkali-activated materials(AAMs)are important green low-carbon cementitious materials.The early dissolution of the precursors of AAMs has an important impact on the development of later alkali-activated reactions and mechanical properties of AAMs.Therefore,a deep understanding and characterization of the dissolution activity of different ions at the early stages of the precursors is of great importance for engineering practice.This paper investigated the experimental methods and basic principles of dissolution kinetics of solid particles in different fields.Two important basic kinetic concepts,activation energy and the reaction order are extracted to respectively describe the impact of the two most important variables in engineering,curing temperature and activator alkalinity on the dissolution activity of precursors.The dissolution experiment was conducted with a large solid-liquid ratio(500ml:1g)to eliminate precipitation reaction,and the ion dissolution curve that can be used to characterize the degree of dissolution was obtained.The shrinking core model was used to fit the reaction rate constant of dissolution reaction of Si and Al in blast furnace slag,fly ash and metakaolin with two fineness.According to the calculated reaction rate constant of dissolution reaction,the apparent activation energies of different ions in different precursors and the order of reaction of dissolution with respect to OH~-were calculated.Through the above research,the following conclusions are drawn:(1)The apparent activatiing energy of Al of blast furnace slag and ground blast furnace slag is similar.Grinding does not change the activation energy of blast furnace slag.For every 10℃increase within the range of 20℃-60℃,the Al dissolution activity of blast furnace slag and ground blast furnace slag is increased by about 1.5-1.6 times.(2)The Si and Al of fly ash and ground fly ash have different apparent activation energies.The apparent activation energy of Si is greater than that of Al.Grinding will increase the apparent activation energies of fly ash,with a higher degree of improvement for Si than for Al.(3)The Si and Al of metakaolin with different fineness have different apparent activation energies.Grinding will reduce the apparent activation energy of Al in metakaolin,while having little effect on the apparent activation energy of Si.(4)The apparent reaction order of different ions of the three raw materials is about0.5,and the grinding will not affect the reaction order.The reaction order of the dissolution of armorphous aluminosilicate with respect to OH~-is only related to the ratio of the charge transfer coefficients of anions and cations in armorphous aluminosilicate as well as the dissolution conditions,and has nothing to do with the microstructure of the armorphous phase.(5)Reaction order and activation energy are two different physical and chemical properties of materials.The activation energy is mainly related to the average number of atomic bond constraints inside the armorphous phase.Lower Ca content and higher the degree of polymerization of Si will increase the average number of atomic constraints and the activation energy.