Effect Of Sand Aggregate Conditioner On Properties Of Machine-made Sand Concrete

From the overall situation of the current sand and gravel industry,there are still many problems in the product quality of machine-made sand.These problems are mainly concentrated in the poor grading of machine-made sand and the high content of stone powder,which makes it present the so-called dumbbell shaped low-quality machine-made sand with a so-called particle size of "large at both ends and small in the middle".Using this kind of machine-made sand with poor grading quality is difficult to ensure good workability of concrete,which undoubtedly brings great challenges to the preparation and production of ready mixed concrete.The poor compatibility between low-quality machine-made sand and water reducing agent brings frequent quality problems,which must be solved in the ready mixed concrete industry.Although China is trying to promote high-quality machine-made sand and gravel aggregate,it will take time,and the above problems will continue in the short term.How to deal with and solve this problem is very important to ensure the workability,strength and durability of machine-made sand concrete.In recent three years,a new type of concrete functional admixture,sand aggregate concrete conditioner,has been increasingly used in the preparation and production of machine-made sand concrete.This functional admixture has effectively improved the workability of concrete caused by the quality of machine-made sand and met the requirements of civil engineering construction for fresh concrete.Now it has become one of the important technical means to solve the poor gradation of machine-made sand.In this paper,the effects of sand aggregate concrete conditioner on the workability,mechanical properties and durability of machine-made sand concrete are systematically studied.Through the use of six kinds of machine-made sand with different fineness modulus and grading for C30 and C50 strength grade concrete,this paper compares the influence of using sand aggregate concrete conditioner and not using sand aggregate concrete conditioner on the relevant performance of concrete,as well as the influence of reducing the amount of cementitious material on the performance of concrete.Sand aggregate concrete conditioner adopts two types of 165 B and 73 B.Through experimental research,it is found that the use of gravel aggregate regulator improves the wrapping of concrete in most cases,the state of bleeding and bottom raking,and the viscosity of concrete in most cases,which obviously improves the workability of concrete and reduces the time loss of concrete;The compressive strength of middle and low strength concrete is obviously improved after using the regulator;The shrinkage rate of concrete will be reduced,reducing the risk of dry shrinkage cracks;Reduce the carbonation depth of concrete and improve the frost resistance of concrete.In general,the use of sand aggregate concrete conditioner can improve the workability,mechanical properties and durability of concrete.This paper puts forward the technical requirements of slump ratio,slump-flow ratio,slump ratio after 1h,slump-flow ratio after 1h,emptying time ratio of slump cylinder,strength ratio(28d),relative dynamic elastic modulus ratio(200 times freeze-thaw cycle),and preliminarily determines the index threshold of these technical requirements through experimental research.Based on the research of sand aggregate concrete regulator in the laboratory,the engineering application test of sand aggregate concrete regulator is also carried out in production enterprises.The engineering application test shows that after using the sand aggregate concrete regulator,the workability of concrete is good and stable,the sensitivity of the impact of sand and gravel quality fluctuation on the workability of concrete is reduced,the collapse loss of concrete is reduced,the pumpability of concrete is guaranteed,and the strength assurance rate is significantly improved;Under the condition of ensuring the concrete quality of production enterprises,reduce the amount of cementitious materials and improve the availability of raw materials.At the same time,it also brings the effect of reducing cost and increasing efficiency to enterprises,which is more green and environment-friendly.