The Strength And Volume Stability Of Chemico-activated CFBC Ash And Slag

Circulating fluidized bed?CFBC?ash is a industrial solid waste.Due to the large amount of II-CaSO₄ and f-CaO,it is easy to expand and crack during hydration.Lower combustion temperature leads to low content of SiO₂ and Al₂O₃ vitreous and poor volcanic activity,which greatly limits their engineering applications.In order to provide theoretical guidance for the resource utilization of CFBC ash,the effects of the content of II-CaSO₄,the type of activator?NaOH,Na₂SiO₃,Na₂CO₃?,slag content,and curing system on the mechanical properties and volume stability of chemico-activated CFBC ash were studied.The results of the project are as follows:?1?Under standard curing,the flexural and compressive strength of CFBC ash stimulated by the three stimulants increased with age.With the increase of anhydrite content,the compressive strength of CFBC ash activated by NaOH increases at first and then decreases,and the compressive strength of CFBC ash activated by Na₂SiO₃,Na₂CO₃ tends to decrease.The linear expansion ratio of hardened bodies in the three activation systems increases with the increase of anhydrite.Under the same alkali equivalent and anhydrite content,the linear expansion ratio of CFBC ash activated by Na₂CO₃ is the largest,the linear expansion ratio of CFBC ash activated by NaOH is the second,and the linear expansion ratio of CFBC ash activated by Na₂SiO₃ is the lowest.The main reason for the volume expansion of CFBC ash activated by NaOH is ettringite and the formation of no ettringite from CFBC ash activated by Na₂SiO₃ is the main cause of the volume expansion of CFBC ash.The expansion of hardened body is mainly caused by C-S-H water absorption expansion,and the volume expansion of CFBC ash activated by Na₂CO₃ is caused by ettringite or carbon thiosilicate.?2?Under dry curing,the flexural and compressive strength of the three activated systems developed stably in the early stage and shrunk in the later stage.The volume stability showed the characteristics of dry shrinkage.The linear shrinkage ratio of CFBC ash activated by NaOH or Na₂CO₃ decreases gradually with the increase of anhydrite.The linear shrinkage ratio of CFBC ash activated by Na₂SiO₃ show a change rule of first decrease and then increases with the increase of anhydrite.The volume change of CFBC ash activated by Na₂SiO₃ is dry shrinkage,and the volume change of CFBC ash activated by NaOH or Na₂CO₃ is caused by dry shrinkage and expansion of ettringite.?3?The linear expansion ratio of CFBC ash and slag activated by the three stimulants decreased with the increase of slag,and the flexural and compressive strength of the NaOH activation system at each age decrease,the flexural and compressive strength of Na₂SiO₃ or Na₂CO₃ excitation system increases.?4?With the increase of the alkali content,the linear expansion rates of the three kinds of stimulants activated CFBC ash and slag show a downward trend.The flexural and compressive strength of CFBC ash and slag activated by NaOH decreased with increase of alkali content.The flexural and compressive strength of CFBC ash and slag activated by Na₂SiO₃ or Na₂CO₃ to increase first and then decrease with increase of alkali content.5%Na₂SiO₃ has the best activation effect.