Experimental Study On Mechanical Properties Of Rocklike Material After Freeze-thaw Cycles With Different Moisture Contents

The cold area of China is widely distributed and has rich resources.Rock,as the carrier of most engineering construction,will cause internal structure damage after receiving the freeze-thaw cycles,resulting in the decline of carrying capacity.In addition,in nature,the water content state of most rocks is not the same,and in the process of water and ice phase transition,the volume will increase by about 9%,leading to the further development of internal cracks and pores,and causing certain safety risks to the related engineering construction.Therefore,in order to ensure the stability and safety of the cold area engineering construction,it is very necessary to study the rock mechanical properties after freeze-thaw cycles under different water content conditions.The physical properties of water absorption rate,longitudinal wave velocity,freeze-thaw coefficient and fracture form were analyzed for saturated sandstone and mortar with different water content,the static and dynamic mechanical properties of saturated sandstone and mortar with different moisture content were analyzed,and the damage degradation mechanism of saturated sandstone and mortar with different moisture content was analyzed from macroscopic and microscopic aspects by SEM test and XRD test.The main study content is as follows:(1)Wave velocity of four groups of mortar samples with different moisture content and saturated sandstone samples decreased after freeze-thaw cycles.For dry samples,after the first freeze-thaw cycle,the wave velocity decreases greatly.The wave velocity of each group of samples decreased to varying degrees with the increase of freezing and thawing times,but the decreasing trend became more and more gentle.(2)In uniaxial compression test,the maximum compressive strength decreases with the increase of freeze-thaw cycles.The strength curves of saturated sandstone,dry mortar,mortar with water content of 1% and mortar with water content of 2%have a tendency to slow down.The mortar with water content of 3% has great strength damage in the last stage.After 30 freeze-thaw cycles,the strength decreases most obviously.(3)In the uniaxial impact test,the dynamic stress-strain curve of the specimen after freeze-thaw cycles presents three stages,namely,the elastic stage,the nonlinear deformation stage and the failure stage.Under the same impact pressure,the more freeze-thaw cycles,the smaller the maximum compressive strength of the sample.Under the same moisture content,the peak stress of the sample was positively correlated with the impact pressure.For the peak strain of the sample,with the increase of the impact pressure,the peak strain of the sample is also increasing.The more freeze-thaw cycles under the same moisture content,the more proportion of small particle size after crushing.(4)Under the same freeze-thaw cycles,the energy absorbed by the sample is positively correlated with the impact pressure.The greater the impact pressure,the more the energy absorbed by the sample.In the case of less freeze-thaw cycles,the internal pores of the mortar are less and the mechanical properties are better.Therefore,under the impact load,more energy is absorbed to expand the cracks in the mortar until the specimen is broken.With the increasing number of freeze-thaw cycles,there are more and more cracks in the mortar,and the energy absorbed during crushing is low.(5)It can be seen from the SEM images that the internal structure of mortar is closely arranged in the dry state,and the number of cracks and pores is relatively small.With the increase of water content of mortar,the internal structure becomes more and more loose.After 15 freeze-thaw cycles,it is obvious that the surface of the sample has appeared cracks.After 30 freeze-thaw cycles,the cracks on the mortar surface have formed through,and the bonding force between particles is small.The particles fall off,resulting in the decrease of the bearing capacity.(6)During the freeze-thaw cycles,the proportion of kaolinite,siderite and illite decreased,and the proportion of quartz increased.The kaolinite and illite swell unevenly after absorbing water,resulting in tiny pores.Water enters microcracks and combines with hydrophilic minerals to form hydrated clay.Hydrated clay has the characteristics of expansion,rheology,dispersion or flocculation.Therefore,freeze-thaw cycles accelerates the disintegration of clay minerals,and the porosity of rock further increases..Figure 49 Table 5 Reference 82...