| Because of the complex environment in which the rocks exist and are often subjected to chemical and freeze-thaw cycles,which cause numerous engineering disasters,so the study of physical and mechanical properties of rocks under chemical corrosion,freeze-thaw cycles and their combined effects are of great theoretical and practical value.From the microscopic composition,granite is a complex composed of various minerals such as quartz,feldspar and mica,and its macroscopic damage mechanism is determined by the microscopic damage mechanism of the minerals that compose the rock.However,the conventional test methods used in the past to study the mechanical properties of granite cannot obtain the micro-mcchanical properties of mineral particles in granite,and fail to reveal the micro·mechanical mechanism of granite well.Therefore,this paper investigates the micro-mechanical properties of granite under chemical corrosion,frcezethaw cycles and their combined effects based on nano-indentation test technology to reveal the micro-damage mechanism of granite under the conditions of chemical corrosion and freeze-thaw cycles.First of all,through multiple cycles of loading and unloading and single loading and unloading modes nano-indentation test,the mechanical parameters such as elasticity modulus,hardness and fr cture toughness of quartz,feldspar and mica,the main rnincrals of granite,were invcstigated.the effects laws of diffcrent holding time,indentation depth and loading rate on the nano-indentation test results were analyzed.And combination with the residual indentation morphology under the scannting electron microscope(SHM),fracture toughness of diffcrent minerals at the nano-scale was analyzed in comparison by fracture toughness analysis methods such as the crack length method,the synthesis method and the energy method.The content of the main minerals of granite was quantified with the help of X-ray diffraction test(XRD).The upgrading of granite mechanical parameters from microscopic scale to macroscopic scale was achieved by four mechanical index upgrading methods,including comprehensive weighting method,self-consistent method,sparse method and Mori-Tanaka method.The creep properties of the loading sections of the three main minerals of granite were studied by using nano-indentation test technique,and the influence laws of different holding times,stable loads and loading rates on the nano-indentation test results of granite minerals were obtained respectively.The test curves of quartz,feldspar and mica in granite were fitted by generalized Kelvin body,Burgos body and double Kelvin body creep models respectively,and the variation law of nano-indentation creep parameters with load and the variation law of nano-indentation creep parameters with loading rate were obtained.Finally,the nano-indentation creep parameters obtained from the three creep models were upgraded to macroscopic creep parameters.Secondly,by preparing chemical solutions with different pH value,and the granite is soaked in chemical solutions with different pH value for different times,then the nano-indentation mechanical properties of quartz,feldspar and mica in the corroded granite were measured and the damage deterioration analysis was carried out.The change laws of the different mechanical properties damage characteristics and mechanical properties of granite minerals with corrosion time after soaking in different pH value solutions were studied.The influence laws of chemical solution on elastic modulus damage variable and hardness damage variable of different minerals of granite was quantitatively analyzed.At the same time,the surface mineral characteristics and morphology of granite after corrosion were observed by scanning electron microscope test,the deterioration mechanism of chemical corrosion damage of granite was analyzed from the microscopic perspective,and the damage evolution equations of elastic modulus and hardness with the change of pH value and time were established,and the microscopic parameters were scaled up.Finally,through the freeze-thaw cycle test was carried out on granite after 120 days of corrosion,the mechanical properties of quartz,feldspar and mica in granite undergoing different freeze-thaw cycles were measured.The damage characteristics and time effects of elastic modulus,hardness and fracture toughness of granite minerals under different pH value solutions and freezethaw cycle combined effect were studied.The damage variables of elastic modulus and hardness of different granite minerals were quantitatively analyzed,and the damage evolution equations of elastic modulus and hardness with the change of pH value and the number of freeze-thaw cycles were established.At the same time,scanning electron microscopy(SEM)test was used to observe the mineral characteristics and morphology of the granite surface after treatment,and the scale upgrade of the meso parameters was carried out to reveal the deterioration mechanism of the mechanical properties of granite under the combined effects of chemical solution and freeze-thaw cycle from the mesoscopic. |
