Feasibility Study Of Pulverized Coal Ash Residue Replacing Fine Aggregate

With the rapid development of China’s industry,a series of environmental problems have been arisen.On the one hand,a large number of industrial waste discharged and accumulated,polluted the environment,occupied a large number of land resources.On the other hand,with the rapid development of China’s infrastructure,natural river sand resources are becoming more and more valuable.As a kind of fine aggregate,apply pulverized coal ash residue in mortar and concrete.If it is feasible,it can relieve environmental pressure and save natural river sand resources.With the development of modern materials,concrete is developing towards high strength and high performance.The concept of concrete internal curing has been put forward.At present,the typical internal curing materials are super absorbent resin(SAP),light aggregate,etc.According to the characteristics of pulverized coal ash residue,loose porous and high water absorption,it is another idea of this experiment to use it as a new type of internal curing material in concrete.In this experiment,pre-wet the solid waste utilization and then replace the fine aggregate according to the equal volume method.The replacement rates in the mortar are: 20%,35%,50%,65%,80%;the replacement rates in concrete are: 20%,35%,50%.Control curing time are: 3 d,7 d,28 d.Explore the effect of different replacement rates of solid waste utilization on the performance of mortar and concrete,including: compressive strength and flexural strength of mortar and concrete,elastic modulus and Poisson’s ratio of concrete;shrinkage of mortar,resistance to carbonization.In terms of mechanism analysis,the change of ultrasonic wave velocity of concrete was measured,the transition zone of fine aggregate interface was observed by SEM,and the microhardness was measured by dotting.The feasibility of replacing fine aggregate with solid waste utilization was analyzed from various aspects.The experimental results show that: in terms of mechanical properties,for the mortar,after the dry fly ash residue replaces the sand,regardless of the curing time,the flexural strength can be increased by 20%,and the compressive strength can be increased by 10%;After the wet fly ash residue replaces the fine aggregate,when the curing time is sufficient(28 d),the replacement rate of the fly ash residue is 20%,the flexural strength is increased by 10%,and the compressive strength is increased by 5%;the curing time When it is insufficient(3 d,7 d),the replacement rate of fly ash residue is 50%,the flexural strength is increased by 25%,and the compressive strength is increased by 5%.For concrete,the replacement rate of 20% is the best,the increase in flexural strength is about 10%,and the decrease in compressive strength is about 5%.In terms of durability,the shrinkage of mortar is the best when the replacement rate of fly ash and slag is 20%,which is 9% larger than the shrinkage value of the unreplaced group;when the mortar is resistant to carbonization,when the replacement rate of fly ash and slag is 50%,The carbonization resistance of the mortar is not much different from the unreplaced group.Through mechanism analysis,scanning electron microscopy and microhardness,it is shown that the cement slurry near the fly ash hydrates better than the cement slurry around the sand.It can be seen that the fly ash residue has played a certain role in internal maintenance.Therefore,the feasibility of replacing fine aggregate with fly ash is not only related to the replacement rate,but also related to the maintenance time and the application object.If used in mortar,the replacement rate of fly ash residue is 50% is better;if used in concrete,the replacement rate of fly ash residue to fine aggregate is more suitable 20%.When the replacement rate of fly ash and slag is 35%,it is unfavorable for the compressive strength of mortar and the flexural strength of concrete,and should be selected carefully.Hope to provide a certain reference for the application of solid waste utilization in the project.