Freeze-thaw Properties And Experimental Study On Microstructure Of Mixed Aggregate Concrete With Mineral Admixtures

Pumice to replace part of gravel aggregate, can make mixed aggregate concrete get good frost resistance, and in order to further improve the frost resistance of mixed aggregate concrete, try adding mineral admixtures in concrete to replace part of cement. In this way, can not only improve frost resistance of concrete, but also reduce the dosage of cement, and make effective use of industrial waste residue.This paper aims at mixed aggregate concrete which replacement rate of pumice is30%, adding different kinds and dosage of single admixture and addition of mineral admixtures, study the frost resistance properties, and analysis the best combination of mineral admixtures to improve frost resistance of concrete. This experiment adopts the single30%fly ash, double mixing20%fly ash with10%silica fume, double mixing20%fly ash with10%mineral powder, double mixing20%fly ash with10%stone powder to replace cement, then studying the effect of mineral admixtures on frost resistance properties of mixed aggregate concrete.The experimental method is by rapid freeze-thaw method testing the macroscopic expression of concrete, and by scanning electron microscope (SEM) analyzing microstructure and hydration products, thoroughly analyzing the effect of mineral admixture on frost resistance of mixed aggregate concrete through both macroscopic and microscopic methods. Rapid freeze-thaw method uses mass loss rate and relative dynamic elastic modulus loss rate as index to evaluate frost resistance of concrete, SEM analysis is according to microstructure of interfacial transition zone (ITZ) which is the weakest link in concrete to evaluate frost resistance of concrete.Results of rapid freeze-thaw experiment show that:frost resistance properties of concrete added with30%mineral admixtures decrease by different degrees compared with concrete without mineral admixtures. Mixed aggregate concrete containing fly ash and silica fume has the highest frost resistance properties, which is close to concrete without admixtures, followed by fly ash mixed with mineral powder, and then fly ash alone, fly ash mixed with stone powder is the lowest.SEM analysis indicates that:interfacial structure of concrete added with30%mineral admixtures shows degradation by different degrees compared with concrete without mineral admixtures. Mixed aggregate concrete containing fly ash and stone powder shows the most serious degradation, followed by fly ash alone, both fly ash mixed with mineral powder and fly ash mixed with silica fume have a slight degradation, and interfacial structure is dense. In addition, interface structural degradation of gravel-cement is more serious than pumice-cement, showing that pumice aggregate can improve the interfacial transition zone of concrete.Mixed aggregate concrete containing fly ash and silica fume has good interfacial transition zone structure and frost resistance properties, therefore, results of this paper can provide experimental and theoretic basis to application of concrete material in the cold region.