| Compared with the developed countries,the utilization of construction waste resource in China still has more room for improvement.On the one hand,a large number of construction waste landfill and stacking not only occupy and destroy the land,but also lead to serious environmental and groundwater pollution;On the other hand,under the background that the country attaches great importance to ecological civilization and environmental protection,many places have begun to prohibit or limit the exploitation of natural sand,and the resources of construction sand are becoming increasingly tense.The price advantage of cheap sand has disappeared.At the same time,in order to prevent the ground deformation,ensure the stress uniformity of segment lining,prevent floating and improve the impermeability of the tunnel,synchronous grouting behind the wall is necessary.At present,natural sand is one of the raw materials for grouting behind the wall.In order to explore the feasibility of using road concrete recycled fine aggregate to prepare synchronous grouting material behind the wall of subway shield tunnel,this paper selects road concrete recycled coarse sand(RCS),recydled medium sand(RMS)and natural river sand(NRS)as fine aggregate to prepare synchronous grouting material behind the wall,and compares the performance indexes of the prepared materials,The influence of single factor on slurry performance was studied by stepwise regression analysis,and the interaction between various factors was studied by response surface analysis.The mix proportion was optimized by ideal point method combined with MATLAB multi-objective optimization,and the optimization results were analyzed economically.The main research contents and conclusions are as follows:(1)Compared with natural river sand,the aggregate of reclaimed aggregate is characterized by high water absorption rate,fast water absorption rate,hardened cement slurry,more grain edges and angles,rough surface and more micro-cracks,etc.,which leads to the apparent density and compressive strength of the slurry prepared in the same ratio being lower than that of the natural aggregate slurry.The compressive strength of the sample prepared by RMS slurry has little difference with that of NRS slurry.However,the bleeding rate and stone rate of RMS serous fluid at3 h were better than that of NRS serous fluid.(2)Compared with the reclaimed coarse sand,the reclaimed medium sand has better particle size and finer particle size.The apparent density,3-day compressive strength,28-day compressive strength and 28-day compressive strength of the RMS grout prepared with the same ratio are better than those of the RCS grout.However,The 3h bleeding rate and stone rate of RCS grout are better than that of RMS grout,and the setting time is shorter.However,through the optimization of the ratio,it can basically meet the construction performance.(3)According to different construction requirements,there are some differences in the performance of synchronous grouting materials behind the wall.Using single factor analysis and response surface analysis,the numerical trend and variation range trend of slurry performance can be more comprehensively discussed which provides a basis for the actual mix proportion design of the project.(4)After optimization,the recommended mix proportion of NRs slurry is: water binder ratio 0.62,binder sand ratio 0.8,swelling water ratio 0.12,powder cement ratio2.8;The mix proportion of RMS slurry is: water binder ratio 0.64,binder sand ratio0.79,swelling water ratio 0.14,powder cement ratio 2.8;The mix proportion of RCS slurry is: water binder ratio 0.72,cement sand ratio 0.75,swelling water ratio 0.2,powder cement ratio 2.7.The verification test shows that the performance indexes of the grouting material prepared by the optimized mix proportion can meet the construction requirements;The cost analysis shows that according to the current market price,compared with natural river sand,the material cost can be reduced by28.83% and 27.73% respectively by using reclaimed medium sand and coarse sand.It is estimated that the material cost can be saved about 15 million yuan if RMS and the mix proportion are used in Changsha Metro Line 6.The slurry prepared by recycled aggregate can produce good economic and environmental benefits. |
