The Effect Of Cement-based Composite Materials Adding Both Fly Ash And Slag Powder

Fly ash and slag powder are widely used in cementitious composites instead of some cement because of their active effect,micro aggregate effect and morphology effect.However,if fly ash or slag powder is added alone,it will have an adverse effect on the performance of cement-based composites.Therefore,it is very important to study the influence of fly ash and slag powder mixing technology on the performance of cement-based composites.In this paper,the particle size,specific surface area and micro morphology of fly ash and slag powder were tested firstly.Then the effects of single mixed fly ash and slag powder on the performance of cement mortar and machine-made sand concrete were discussed respectively.Finally,the effects of fly ash and slag powder mixing and mixing on the composition,morphology and hydration heat of hydration products of cement fly ash slag powder system were discussed by XRD and SEM.From the experimental results of the influence of fly ash and mineral powder on the performance of mortar,it is concluded that both fly ash and mineral powder can help to improve the fluidity of mortar and the strength of 28days and 56 days,but reduce the strength of 3 days,and the extent of fly ash reduction is higher than that of mineral powder.With the increase of the ratio of fly ash,the fluidity of the mortar increases,but it is unfavorable to the development of the 3days strength.The addition of fly ash can reduce the drying shrinkage of cement mortar,but the slag powder increases the shrinkage rate of mortar and mixing them can reduce the dry shrinkage of mortar with increase of fly ash replacing cement ratio.In the machine-made sand concrete,fly ash alone can significantly improve the workability of concrete,but also reduce the early strength and the extent of fly ash reduction is higher than that of mineral powder.However,when the amount of slag powder is too high,the work ability of concrete mixture will become bad.As a result,fly ash and mineral powder should be mixed in a suitable proportion.The durability test results show that slag and fly ash are helpful to improve the penetration resistance to chloride ion of man-made sand concrete whether single or double adding fly ash and slag powder,however,it is unfavorable to the carbonation resistance of concrete.By comparing singleadding fly ash,single adding slag powder and double adding both of them,the carbonation resistance of adding slag powder is better than that of fly ash and double both of them is better than single adding any fly ash or slag powder.The hydration heat of 1days,2days and 3days of the motar is lower than that of the standard cement sample after single or mixing adding fly ash and slag powder.According to the order of reduction of cement hydration heat from high to low.single fly ash>compound>single mineral powder.The XRD results and the SEM results of interface between cement mortar and coarse aggregate showed that the hydration products of cement mortar mixed with fly ash and slag,like Ca?OH?₂reduced and number of rod-shaped ettringite?AFt?increased,while the incorporation of fly ash generated after T obey mullite phase.Therefore,the interface structure,the strength,the resistance to chloride ion permeability etc.were improve.