Effect Of Fly Ash Slag Replacing Fine Aggregate On Strength And Durability Of Mortar Concrete

At present,the annual emission of ash and slag from coal-fired power plants in China has exceeded 800 million tons,of which fly ash lag accounts for about 10%-20% of the total mass of ash and slag.However,the fly ash slag has not been rationally utilized,and most of them are disposed of in landfill,which has great harm to the environment.The particle size distribution of fly ash slag is similar to that of river sand,and it has potential volcanic ash activity.Therefore,the use of fly ash slag to replace the fine aggregate in cement mortar and concrete can not only process and utilize the solid waste,but also reduce the use of fine aggregate resources to some extent and relieve the pressure of the shortage of fine aggregate resources.In this paper,the strength and durability of fly ash mortar and concrete were studied by using fly ash slag to replace fine aggregate.The suitable pre-wetting rate of fly ash slag was explored.The fly ash slag with different particle sizes was obtained by screening and crushing,and the fly ash slag mortars were prepared by replacing the fine aggregate in the corresponding particle size range with equal volume.The influence of fly ash slag on the strength of mortar was analyzed,and the optimal particle size range of fly ash slag was explored.The shrinkage performance of mortar after replacing fine aggregate with fly ash slag was tested.Combined with XRF,XRD,SEM,EDS and other methods,the chemical activity of fly ash slag was explored,and the strength mechanism of fly ash slag on mortar specimens was analyzed.Based on the optimal particle size range of mortar,fly ash slag concrete was prepared,and its strength,frost resistance and impermeability were tested.The results showed that the optimal particle size range of fly ash slag is 0.3 mm-0.6mm;the compressive and flexural strength of mortar specimens can be increased by 10 %and 20 % after the fly ash slag in the optimal particle size range was obtained by screening method to replace the natural river sand in the corresponding particle size range.The optimum particle size range of fly ash slag obtained by screening and crushing methods replaces the corresponding range of manufactured sand respectively,and the strength of mortar specimens was basically consistent with the reference group.After replacing manufactured sand with fly ash slag in the optimal particle size range obtained by screening method,the autogenous shrinkage and drying shrinkage of mortar specimens increased by about 10 % compared with the reference group.After replacing sand making with fly ash slag in the optimal particle size range obtained by screening,the 28 d compressive strength of the prepared C40 fly ash slag concrete specimen can reach 46.3MPa,and the impermeability grade can reach P8.After 50 freeze-thaw cycles,the strength loss rate and mass loss rate are 1.6 % and 0.2 %,respectively,and each index was basically consistent with that of ordinary concrete.The porous structure of fly ash slag makes it have high water absorption.When pre-wetted fly ash slag is used as fine aggregate in mortar and concrete,it can slowly release water and improve the hydration degree of cement.The active silica content of fly ash slag is more than 40 %,which has potential pozzolanic activity,and can be reacted in the calcium hydroxide environment provided by cement.The hydrated calcium silicate gel generated increases the bonding strength of the interface between the two,and the interface area is strengthened.In addition,the uneven surface of fly ash slag and cement slurry interlocking also ensure the strength of the specimen.The research can provide a theoretical basis for the application of fly ash slag as fine aggregate in mortar and concrete,broaden the application field of fly ash slag,and have certain practical significance for saving fine aggregate resources,consuming solid waste of fly ash slag and alleviating environmental pressure.