Study On The Basic Performance Of Composite Limestone Powder-fly Ash-slag-Tailings Mixed Sand Concrete

Auxiliary cementing materials such as slag and fly ash have become an important component of modern commercial concrete,and have achieved good economic and environmental benefits.Using limestone powder as an auxiliary cementing material to replace part of the cement and using tailings-mechanical mixed sand to replace natural river sand can further increase the comprehensive utilization rate of solid waste and reduce energy consumption and pollution.In this paper,through theoretical analysis and experimental research on the working performance,basic mechanical properties,durability and fine microstructure of the composite limestone powder tailings mixed sand concrete,the tailings mixed sand is explored 1.The influence of the amount of limestone powder in the auxiliary cementitious material and the content of limestone powder in the machine-made sand on the basic performance of the concrete,providing a theoretical basis for the comprehensive utilization of the composite limestone powderassisted cementing system and tailings mixed sand in the concrete,the main achievements as follows:(1)The composite limestone powder tailings mixed sand concrete mixture has good workability,and the slump and slump loss basically meet the requirements of pumping concrete.The tailing mixed sand is used instead of natural river sand.The concrete mixture has slight bleeding.After the auxiliary cementing material is added,the initial slump of the mixture is increased by 11.8%,the water retention and cohesion are good,and the slump is lost.Significantly reduced.The initial slump of the mixture increases with the increase of the limestone powder content in the cementitious material,and increases first and then decreases with the increase of the limestone powder content in the machine-made sand.(2)The mixing of tailings mixed sand can improve the compressive strength of concrete at all ages,the increase is about 10%.The addition of auxiliary cementing materials will make the concrete’s early compressive strength drop greatly,but the strength will increase rapidly in the later period.With the increase of the content of limestone powder in the auxiliary cementitious material,the compressive strength of concrete first increased slightly and then decreased,and with the increase of the content of limestone powder in the machine-made sand,the compressive strength of concrete gradually increased.The splitting tensile and flexural strength of concrete also showed similar laws.A two-parameter prediction model for the development of composite limestone powder tailings mixed sand concrete strength with age and limestone powder content(mixing)was established.(3)After replacing natural river sand with tailings mixed sand,the anticarbonization and anti-freezing properties of concrete have been significantly improved,but the carbonation depth of concrete and the quality loss of freeze-thaw cycle at each age increase with the addition of auxiliary cementing materials.When the content of limestone powder in the auxiliary cementing material is 10%,the concrete has the best anti-carbonization and anti-freezing performance.If the amount of limestone powder is increased,the anti-carbonization and anti-freezing performance will decrease.The anticarbonization and anti-freezing properties of concrete increase with the increase of the limestone powder content in the machine-made sand.A two-parameter prediction of the carbonation depth of the composite limestone powder tailings mixed sand concrete with the development of the carbonation age and limestone powder content(doping)is established model.(4)The interface bonding strength between the tailings mixed sand and cement slurry is higher,and the addition of auxiliary cementing material can alleviate the problem of high water-binder ratio in the interface transition zone.With the increase in the amount of limestone powder in the cementitious material,cracks and non-dense pores are more likely to occur at the interface junction,the content of ettringite(AFt)in the hydration product is significantly increased,and the amount of Ca(OH)2 production is significantly reduced.As the content of limestone powder in machinemade sand increases,the actual water-to-binder ratio of concrete decreases,the content of ettringite(AFt)increases,and the density of the cementing system increases.(5)The effect mechanism of microstructure of composite limestone powder tailings mixed sand concrete on macroscopic performance is obtained.The tailings mixed sand strengthens the large central mass effect of concrete and improves the homogeneity of the interface transition zone.The basic mechanical properties of concrete and the anti-carbonization and anti-freezing properties have been improved.The auxiliary cementing material increases the number of negative central mass(pores)in the concrete,and the negative central mass effect reduces the performance of the concrete.When the content of limestone powder is between 5% and 10%,good particle grading optimizes the central network framework of concrete and improves the mechanical properties and durability of concrete.As the amount of limestone powder continues to increase,the interface transition zone becomes a weak link,the porosity of the concrete increases,and the mechanical properties and durability can be significantly reduced.Increasing the content of machine-made sand limestone powder is conducive to strengthening the subcentricity effect and microcentricity effect,and improving the mechanical properties and durability.(6)Verify the feasibility and economic benefits of composite limestone powdertailing mixed sand concrete.The feasibility of composite limestone powder-tailings mixed sand concrete is analyzed from four aspects of raw material acquisition,working performance,mechanical properties and durability.The composite limestone powdertailings mixed sand concrete raw materials are easy to obtain and work performance To meet the requirements of pumping,when the content of limestone powder in the machine-made sand is fixed at 5%,the content of limestone powder in the auxiliary cementing material is 10%,the performance of concrete is close to that of ordinary concrete,and the cost per cubic meter is 19.7% lower than that of ordinary concrete.When the amount of limestone powder in the auxiliary cementing material is fixed at 5%,the content of machined sand limestone powder is 20%.Due to the performance of ordinary concrete,the cost per cubic meter of concrete is reduced by 17.9% compared to ordinary concrete.This paper has 72 figures,36 tables,122 references.