Experimental Study On Mechanical Properties Of Magnesium Phosphate Inorganic Adhesive At High Temperature And In-plane Shear Properties Of Carbon Fiber Cloth Bonded To I

Carbon fiber sheet reinforced concrete structure has the advantages of light additional weight,easy construction,good corrosion resistance,etc.,which is widely used in reinforcement engineering.While the epoxy resin organic adhesive matching with the carbon fiber sheet reaches the glass state at 65～82℃and has low high temperature resistance performance,which is the technical weakness affecting the fire resistance of the reinforced structure.Therefore,it is urgent to develop inorganic cementing materials suitable for the pasting carbon fiber sheet with good high temperature resistance and bonding performance.Compared with other inorganic cementing materials,magnesium-phosphate inorganic adhesive has the advantages of high early strength,strong adaptability to ambient temperature,high bonding strength,good wear resistance and frost resistance,etc.In this thesis,the inorganic adhesive suitable for pasting carbon fiber sheet is developed,and the high temperature mechanical properties and bonding properties of magnesium-phosphate inorganic adhesive are studied as follows:（1）In view of the key problems that ordinary magnesium-phosphate inorganic glue is easy to lose water and its high temperature resistance declines significantly after high temperature at 400℃,the water-binder ratio,the thickness of potassium dihydrogen phosphate,wolash powder and glass powder are used as test variables.The compressive and flexural tests of 180 40mm×40mm×40mm cube blocks and 90 40mm×40mm×160mm prismatic blocks were carried out at room temperature and 400℃,and the influence of each test variable on compressive strength and flexural strength was analyzed.The results show that proper dosage of wollastonite powder and glass powder is helpful to inhibit high temperature cracks.Reducing water-binder ratio and crude potassium dihydrogen phosphate can effectively control cracks at 400℃.At 400℃,magnesium-phosphate inorganic adhesive block showed a trend of significant increase in bending strength as potassium dihydrogen phosphate coarser and water-binder ratio decreased.The remaining bending strength and compressive strength of10%glass powder at 400℃were 88.92%and 50.3%,respectively.The optimum composition and mixing ratio of magnesium-phosphate inorganic adhesive block were crude potassium dihydrogen phosphate,water-binder ratio 0.16 and glass powder content 10%.（2）The basic mechanical properties and microstructure of the modified magnesium-phosphate inorganic adhesive at 20～600℃were analyzed by SEM scanning electron microscopy.At high temperature,the compressive strength and tensile strength of the modified magnesium-phosphate inorganic adhesive decreased significantly at 100℃,which was about33%and 65%of that at room temperature,respectively.The strength at 200℃was 35%and73%higher than that at 100℃,respectively.The strength decreases slowly at 200℃and decreases to 18%and 51%of that at 600℃.According to SEM scanning electron microscopy and EDS analysis,the main hydration product of magnesium-phosphate inorganic adhesive at room temperature is petal-shaped potassium magnesium-phosphate hexahydrate（KMg PO₄·6H₂O）,which is connected with each other in a closed network structure,forming a dense internal structure.At 400℃,most of the products changed into well-crystallized and arranged flat magnesium pyrophosphate（Mg₂P₂O₇）.（3）With anchorage length as the test variable,the double shear test was carried out on 18samples of high temperature modified magnesium-phosphate inorganic adhesive carbon fiber sheet at normal temperature;with temperature and adhesive type as the test variables,the double shear test was carried out on 36 samples of high temperature modified magnesium-phosphate inorganic adhesive carbon fiber sheet at 20～600℃.The shear strength of the high temperature resistant modified magnesium-phosphate inorganic adhesive carbon fiber sheet at room temperature decreased gradually with the increase of the length of the carbon fiber sheet,and the optimal bond length was 10cm.At 600℃,the tensile strength of the concrete base is lower than the in-plane shear strength between the magnesium-phosphate inorganic adhesive and the carbon fiber sheet,which results in the tearing failure of the concrete base.At room temperature,there is little difference between epoxy organic adhesive and magnesium-phosphate inorganic adhesive in surface shear performance of carbon fiber sheet.At 200℃,magnesium-phosphate inorganic adhesive in surface shear performance of carbon fiber sheet is significantly better than that of epoxy organic adhesive.