| Due to its low added value,large resource consumption,poor performance stability and other deficiencies,it is difficult to be utilized and popularized efficiently.In order to accelerate the construction of ecological civilization and build an environment-friendly society,it is an inevitable trend to efficiently apply waste concrete in civil engineering field,which has attracted the attention of researchers at home and abroad.Replacing natural aggregate with recycled aggregate obtained by the component separation technology of waste concrete can relieve the consumption of traditional building raw materials in civil engineering,and is one of the main research directions of waste concrete resource utilization at present.In the process of separation of used concrete components,a large amount of used cement stone powder will be produced.Because of its high water demand,poor cementitious activity and other shortcomings,it has been unable to be used efficiently.Recycled concrete technology is the realization of building one of the main measures for the sustainable development of resources and environment,the development and application of recycled concrete technology,can effectively reduce the usage of traditional cement,alleviate the pressure of the CO2 emissions,reduce the dependence on clay,limestone and other non-renewable resources,solve a lot of old cement powder processing difficulty and the resulting adverse problems such as resources and environment worsening.Characteristics of sand strata grouting materials,the author of this paper,through the grouting material research and development test,indoor model test and numerical simulation analysis method,using waste cement as main raw materials,developed a renewable cement sand strata grouting material,and dehydration again-waste cement hydration behavior mechanism of grouting materials,the physical and mechanical performance and working performance of the system research.The main research contents and results are as follows:(1)Using synchronous thermal analysis,XRD,Fourier infrared spectrum and SEM method,systematically studied the waste cement dehydration and rehydration process realized the phase composition and mineralogical characteristics and the changing rule of the hydration products of morphology,regeneration active substance determines the heat treatment temperature and dehydration-the relationship between the rehydration behavior.The feasibility of thermal activation technology was studied and theoretical support was provided for the selection of heat treatment mechanism.(2)The reclaimed cement was adjusted by adding gypsum to improve its physical and mechanical properties.Combined with the influence of phosphogypsum,desulfurized gypsum and natural gypsum on the physical and mechanical properties and setting time of reclaimed cement-based stones,the optimal type of phosphogypsum was selected,and 10%was the optimal dosage of gypsum.The regenerated cement with thermal activation at 750℃ and adding 10%phosphogypsum can reach 6.33 MPa for 3 d and 12.26 MPa for 28 d at 1.0 water-cement ratio,respectively,and the setting time is prolonged from 5 min to 27.5 min.Combined with hydration heat,pore size distribution and fractal dimension analysis,the effects of phosphogypsum on hydration process and microscopic pore structure of recycled cement were studied,and the retarding mechanism and mechanical property improvement mechanism of phosphogypsum on recycled cement were revealed from microscopic perspective.(3)Based on the collaborative complementary use of theory,put forward the recycled cement-phosphorus gypsum-slag ternary system,through a large number of matching test,studied the thermal activation temperature and ash content of recycled cement grouting material fluidity,setting time,the effect of the physical and mechanical performance,750℃ heat treatment temperature of recycled concrete is determined,as recycled cement dosage of phosphogypsum and 10%of the total phosphorus gypsum,mineral content accounted for 30%of total powder as the optimal ratio of the ternary system.(4)Adjust the water-cement ratio,the type and dosage of water reducer,and study the influence rule of water reducer and water-cement ratio on the working performance of grouting materials.The results showed that the water reducing effect of polycarboxylic acid superplasticizer was the most obvious.When the content of polycarboxylic acid superplasticizer was 0.3%and 1.2%,the fluidity reached 40 cm and 46 cm,increased by 48.1%and 70.3%respectively.The water cement ratio has a great influence on the setting time of the slurry.When the water cement ratio is 0.6,the setting time is only 8 min,and when the water cement ratio is 1.2,the setting time can reach 56 min.Among the three types of superplasticizer,polycarboxylic acid superplasticizer is more suitable for regulating the setting time of grout.When the content is 1.2%,the setting time of 1.0 water-cement ratio grout can be extended to 68 min.With the increase of water-cement ratio,the mechanical strength of the recycled cement stone decreases continuously.When the water-cement ratio is 0.6,0.9 and 1.2,the 28-day strength of the stone body is 16.22 MPa,11.47 MPa and 7.04 MPa,respectively.Polycarboxylic acid superplasticizer and aliphatic superplasticizer have little effect on the mechanical properties of calculi,while naphthalene superplasticizer can effectively improve the mechanical strength of calculi.(5)The engineering applicability of recycled cement-based grouting materials was verified through visual sand media grouting model experiment.The effects of water-cement ratio,polycarboxylic acid superplasticizer content on slurry diffusion distance,slurry filling rate,reinforcement physical strength,macroscopic failure characteristics and microstructure of slurry-rock interface were studied.The PFC particle flow discrete element numerical simulation software is used to predict the physical and mechanical properties and macroscopic failure characteristics of grouting and solid under different sand particle fineness,which has certain reference significance for the engineering application of reclaimed cement-based sand grouting materials. |
PDF Full Text Request