Study On Controllable Low-strength Materials Made From Subway Shield Muck

In recent years,the increasing amount of industrial waste in cities has caused serious environmental pollution,and the shortage of natural gravel has caused the continuous rise in the price of building materials,which has become a hot topic in society and academia.While,as the urbanization process continues to accelerate,subway construction has sprung up in major cities,and the resulting shield muck is not only huge in volume but also has a flow plastic state compared with other solid wastes,which is not suitable for traditional extensive treatment.At the same time,the characteristics of wide source,strong region,complex composition and difficulty in natural drainage consolidation lead to its single utilization path,small utilization amount,high energy consumption and complicated preparation process.In addition,the survey found that there are relatively few relevant studies on the utilization of subway shield muck resources.In response to the policy call for energy conservation and emission reduction,this paper relies on the subway construction of zhengzhou city and draws on the definition of controllable low-strength materials from abroad.The new filling materials with low strength,self-compaction and self-leveling are prepared by directly utilizing the Subway shield muck into controllable low-strength materials,which are mainly used for backfilling in narrow Spaces such as pipe trench excavation,inspection well and highway back.It will open up a new way for the utilization of shield muck and realize the multi-win situation of saving resources,protecting environment and improving economic benefit.This paper mainly discusses and analyzes the workability,mechanical properties,durability and performance optimization of controllable lowstrength materials.The main research contents are as follows:(1)Based on the principle of convenient construction and utilization,the influences of water cement ratio,fly ash content and shield slag content on the fluidity,bleeding rate and time-lapse fluidity loss of controllable low-strength materials are analyzed,and the test mix ratio is determined.(2)By testing the unconfined compressive strength,flexural strength and CBR value of controllable low-strength materials at various mixing ratios,the effects of different water-cement ratios,fly ash content and Shield residue content on mechanical properties are analyzed,meanwile the regularity and mechanism are also analyzed,and combined with the changing rules of fluidity,gives the recommended mix ratio.(3)Carrying out durability test research,including dry-wet cycle and freeze-thaw cycle.The relationship between the 28-day unconfined compressive strength,the compressive strength loss rate,and the relative strength change amount and the number of cycles is mainly studied under different mix ratios.The test results show that the controllable low-strength materials have strong resistance to dry and wet cycling,it can reach more than 16 cycles;however,it has weak anti-freezing and thawing cycle ability,up to 12 cycles.The higher the compressive strength of the controllable low-strength material,the stronger the damage resistance.(4)The performance of high-content controllable low-strength materials are optimized with a combination of water-reducing agent and bentonite.The test results show that the proper addition of water-reducing agent and bentonite can significantly increase the fluidity of the mixture while the bleeding rate could be controlled below 5%,the loss of fluidity over time is reduced;both the compressive strength and flexural strength have been improved,and the 28-day compressive strength can reach about 3.5 MPa and the flexural strength above 1 MPa;furthermore the durability also improved slightly.Through experimental analysis,it is feasible to directly use the subway shield muck as a raw material for preparing controllable low-strength materials.By adjusting the water-cement ratio,the amount of fly ash,and the admixture,a new type of fluidity of 180 mm ~ 260 mm,a bleeding rate of about 5%,and the 28-day unconfined compressive strength of 1.5MPa ~ 3.5MPa can be obtained.While CBR value meets the requirements of the new type of filling materials.