Study On Performance Of Alkali-activated Fly Ash-slag(AAFS) Mortar At Room Temperature And Degradation Mechanism After High Temperature

Alkali-activated fly ash-slag（AAFS）mortar is produced using fly ash and slag as raw materials,which are alkali activated to forms C-A-S-H and N-A-S-H gel structures through a series of depolymerization and polycondensation reactions.AAFS mortar has the advantages of low energy consumption,low CO₂ emission and high strength.Therefore,it is a promising low-carbon cementitious material by scholars at home and abroad.It is hoped that AAFS mortar can partially or even fully replace ordinary Portland cement mortar.The available research regarding the post-fire properties of the AAFS is very limited,which restrained its wide application.Therefore,in this thesis,the author focuses on the properties of AAFS at both room temperature and after high-temperature exposure.In this study,the NaOH,Na₂CO₃ and Na₂Si O₃ are used as alkali activators,while fly ash and slag are used as the precursor in production of AAFS mortar.The effects of Na₂CO₃content,Na₂O content,silica modulus of alkali activator,slag content,steel fiber and basalt fiber on the setting time,fluidity,drying shrinkage,strengths at room temperature and high temperature resistance were systematically investigated.The main findings results are summarized as follows:（1）Adding Na₂CO₃ can significantly extend the setting time,inhibit the drying shrinkage,and reduce the fluidity of mortar.Meanwhile,the higher content of Na₂CO₃reduces the compressive and flexural strengths of AAFS mortar after shorter curing period,however,promote the strength development after 56 days curing.In addition,after 200°C exposure,the compressive and residual flexural strength of AAFS mortar improve at higher Na₂CO₃ content.But when the temperature reaches 800°C,the high temperature resistance of AAFS mortar is quite close at different Na₂CO₃ content.（2）The higher Na₂O content and larger alkali activator modulus have positive effects on the setting time,fluidity,compressive strength and flexural strength of AAFS mortar.However,further increase in Na₂O content and alkali activator modulus will hinder the later strength development.In addition,increasing the Na₂O content and the modulus of the alkaline activator will aggravate the drying shrinkage.Furthermore,the high-temperature resistance of AAFS mortar is not relevant to the Na₂O content and the modulus of alkali activator.（3）Although higher slag content can improve the compressive and flexural strength of AAFS mortar at room temperature,it will shorten the setting time,reduce the fluidity,and aggravate the drying shrinkage.In addition,,increasinge the slag content will significantly reduce the residual compressive and flexural strength of AAFS mortar after high-temperature exposure.（4）Adding steel and basalt fibers can effectively reduce the drying shrinkage,increase the compressive and flexural strengths of the AAFS at room temperature.But they higher content of fibers causes adverse effects on both setting time and fluidity.In addition,the higher fiber volume content temperature resistance of mortar,and even when the fiber volume content deteriorates the high temperature resistance.Figure[43]table[5]reference[154]...