Research On Application Of Waste Concrete In Cement Stabilized Crushed Stone Base And Subbase

With my country’s large-scale infrastructure construction,tens of thousands of tons of construction waste are generated every year.How to effectively and environmentally treat these construction waste has become a research hotspot.Among these construction wastes,the amount of waste concrete accounts for a large part of the proportion.Compared with other construction wastes,waste concrete has become the focus of many experts at home and abroad due to its high utilization value.On the one hand,waste concrete can be prepared into recycled aggregates to replace natural gravel.On the other hand,since the hydration of cement is a very long process,the waste concrete still contains some cement particles that have not undergone hydration reaction.Taking advantage of the long-term characteristics of cement hydration,the use of waste concrete into fine powder as an auxiliary cementing material has become another way to recycle waste concrete.In highway construction,especially in the construction of the base and subbase,it needs to consume a lot of natural sand and cement.The processing of waste concrete into recycled aggregates and the use of recycled powder in pavement engineering not only solves the shortage of non-renewable resources such as natural sand and gravel,but also solves the problem of disposal of construction waste such as waste concrete.Based on the expansion and reconstruction project of the Laiwu-Taian section of Qinglan Expressway,this research investigated various production processes and preparation processes of recycled concrete powder and recycled aggregates at home and abroad,and studied the use of recycled concrete powder as auxiliary cementing material.The feasibility of use,the process and hydration mechanism of cement production are described.In this paper,different replacement rates are designed,and the mechanical properties of cement paste after the use of recycled powder to replace part of the cement are studied.Use Matlab software to perform regression analysis on the similar compression ratio of cement paste under different replacement rates.With the aid of XRD,SEM,thermogravimetry and other methods,the mineral composition of the regenerated powder,as well as the decomposition,hydration mechanism and gelation ability after low-temperature calcination are analyzed.Various performance indexes of waste concrete recycled aggregates were studied,including apparent density,crush value,water absorption,etc.The mix ratio design of the cement stabilized crushed stone layer is carried out together with the recycled powder of concrete and recycled aggregate.The mix ratio that meets the use intensity of extremely heavy and extremely heavy traffic conditions is determined,including gradation,cement content,replacement rate of recycled powder,maximum dry density,optimal moisture content,etc.Through various compaction tests,a test method that is more suitable for the maximum dry density and optimal moisture content of recycled cement stabilized gravel mixtures is studied.The test results show that the recycled powder prepared from waste concrete can be used as an auxiliary cementing material.Low-temperature calcination can effectively improve the activity of the powder.Part of the hydration products of cement still have the ability to rehydrate and gel after being calcined.The higher the replacement rate of recycled powder,the lower the flexural and compressive strength of the cement paste.When the replacement rate exceeds 30%,it will have a greater impact on the compressive strength in the later stage of the slurry.It is recommended that the best replacement rate of ordinary regenerated powder is 10%,and the best replacement rate of regenerated powder after calcination is 20%.The cement paste mixed with recycled powder has better early strength development,especially the 7d strength activity index is generally higher.Using the Polynomial function to fit the equations about the substitution rate and the analogous compression ratio is more accurate than the Exponential function.The mix ratio of cement stabilized crushed stone base layer and subbase layer designed in this paper can meet the strength requirements for use in extremely heavy and heavy traffic conditions.Under the premise that all recycled aggregates are used,30%recycled fine powder can still be used instead of cement.The higher the replacement rate of recycled powder,the higher the optimal moisture content of the cement stabilized crushed stone mixture and the lower the maximum dry density.The best moisture content and maximum dry density of recycled aggregate measured by static pressure method are more suitable for on-site production mix ratio.It is necessary to make corrections when using the drying method to test the moisture content of recycled concrete aggregates.This research not only uses waste concrete as recycled aggregate,but also prepares it into recycled powder and uses it together with recycled aggregate for the base and subbase of expressways.This greatly improves the utilization efficiency of waste concrete,and at the same time saves a large amount of non-renewable resources and obtains huge economic and environmental benefits.