Study On Physical And Mechanical Properies Of Unclassified Tailings Consolidation Under Freeze-thaw Cycles

Tailings are solid waste that can not be utilized temporarily after beneficiation.Simply discharging tailings into tailings pond can not satisfy people's increasing awareness of safety and environmental protection.In order to solve this problem,unclassified tailings consolidation discharge technology(UTCDT)emerges as the time required.Based on the application of UTCDT in seasonal cold region,this paper has studied the physical and mechanical properties of unclassified tailings-cemented body(UTB)under freeze-thaw cycles.Around the problem of unclassified tailings-cemented body under freeze-thaw cycles,a large number of systematic laboratory tests have been carried out in this paper,including research and test of a new cementitious material,uniaxial compressive strength(UCS),XRD test,thermogravimetric analysis test,SEM test,mercury injection test,freeze-thaw cycle test at different temperatures,ultrasonic test,resistivity test and so on.The physical and mechanical properties of UTB under freeze-thaw cycles are comprehensively understood.The mechanism of freeze-thaw damage deterioration and its influencing factors are deeply analyzed.The THM multi-field coupling model of the UTB under freeze-thaw cycles is constructed and numerically simulated.The main results are as follows:(1)This paper has researched a new cementitious material to cement unclassified tailings.Orthogonal test was carried out to study a new cementitious material,which use granulated blast furnace slag as its main component.According to range analysis and variance analysis of the date of the uniaxial compressive strength test,the proportion of the new cementitious material was obtained.The variety and quantity of hydration products and the morphology difference of hydration products were studied when the new cementitious materials and 42.5#ordinary silicon cement were added to UTB for 3,7 and 28 days of standard curing time,and the influence of the new cementitious materials on UCS was analyzed.With the increasing of curing age,the change of pore volume and the most probable pore size of UTB with new cementitious materials and ordinary silicon cement were analyzed.(2)The influence of' freeze-thaw cycles on the strength failure characteristics of UTB is studied.Freeze-thaw tests with different cycles at freezing temperatures of-5?,10? and-15?,as well as uniaxial compression tests,XRD tests,thermogravimetric analysis tests and SEM tests after freezing-thawing cycles were carried out for UTB with curing ages of 3 days.7 days and 28 days,respectively.The effects of freezing-thawing cycles on the mechanical damage and the macroscopic and microscopic failure forms of UTB were studied.The function relationship between damage amount and freeze-thaw times was established,and the relationship between damage rate and freeze-thaw times was obtained.(3)The influence of freeze-thaw cycles on the micro-pore structure of UTB is studied.The freezing-thawing tests of UTB with Standard curing time for 7 and 28 days were carried out under freezing temperatures of-5?,-10? and-15?,and mercury intrusion tests were carried out respectively.The pore size distribution,freezing temperature and freeze-thaw cycle times of UTB under different curing ages and freezing temperatures were studied.The function relationship between pore volume and porosity on the damage of UTB was established.(4)Nondestructive testing of UTB under freeze-thaw cycle is studied.The freeze-thaw cycling test,ultrasonic testing test and resistivity testing test of UTB under the freezing temperature of-5?,-10? and-15? were carried out under the standard curing conditions of 3,7 and 28 days.The effects of curing age,freezing temperature and freezing-thawing times on the ultrasonic wave velocity and resistivity of the UTB during freeze-thaw cycles were studied.The functional relationship between ultrasonic wave velocity and freeze-thaw cycles and between resistivity and freeze-thaw cycles was established.The applicability and conditions of nondestructive testing in engineering application are studied by linking ultrasonic testing,resistivity testing and uniaxial compressive strength testing.(5)The coupling relationship of temperature field,seepage field and stress field in the freeze-thaw process of UTB is analyzed.A multi-field coupling model of temperature-seepage-stress is established.The mathematical model is embedded in COMSOL Multiphysics software.The coupling behavior of UTB under different freeze-thaw times is simulated.The correctness of the model is verified by comparing laboratory tests.