Study On Interface Bonding Performance And Pressure Sensitivity Of Carbon Fiber Modified Magnesium Phosphate Cement

With the high-quality development of economic construction,the construction of important civil projects such as highways,large bridges and airport runways in my country has achieved significant results.Because of its wide application environment,designable performance and low cost,cement concrete plays a vital role in the construction and reinforcement of major projects.However,in recent years,the building structures of a large number of engineering infrastructures in our country have often been destroyed in advance before reaching the design life,due to the increasing traffic volume and the complexity of the service environment.In view of the requirements of timeliness and functionality of important structural repairs,magnesium phosphate cement with advantages of high early strength,fast setting speed,excellent durability and good adhesion is gradually favored and demanded by the construction market.However,my country's practical application of magnesium phosphate cement(MPC)in the rapid repair of concrete pavement is still in its infancy.Problems such as high brittleness of the MPC,excessive setting speed,and failure to identify the pavement structure frequently occur in the project.In order to solve these problems of MPC in the project,this topic proposes to use carbon fiber to modify MPC to make a quick repair material with good working performance and mechanical properties and certain self-diagnostic function.Working performance and mechanical properties,and research on the bonding performance of the old and new concrete after repair and the pressure-sensitive performance of MPC,make the repair material with the best mechanical and bonding performance,and meet the economic,functional and safety Claim.In this project,the effects of the ratio of magnesium oxide to phosphate(M/P),borax content(B)and fly ash(FA)on the working performance and mechanical properties of MPC materials were firstly studied.On this basis,the influence of different length and content of carbon fiber on the working performance and mechanical properties of MPC sand was further studied.Then,the interfacial bonding performance between the MPC matrix with different length and content of carbon fiber and the old concrete was studied,and the bonding mechanism was revealed by means of microscopic analysis.Finally,the relationship between load,strain and resistivity of MPC material in the process of loading is studied,and a model is established to reveal the rule.The test results show that there is a reasonable range of M/P values.The greater the amount of borax,the greater the loss of MPC strength.The content of fly ash is within 20%,which can moderately prolong the setting time of the slurry.The higher the carbon fiber content and the longer the length,the worse the MPC fluidity and dispersibility At each age,the flexural strength of MPC increases first and then decreases with the carbon fiber content,but the compressive strength may reverse at the early stage.The flexural strength of the length of carbon fiber has obvious effect,but the flexural strength has almost no effect.Carbon fiber had no effect on the bond strength of MPC at the early stage,and the strength increased greatly at the later stage.There are three types of bond interface failure,the location of which is related to the slurry itself.After the addition of carbon fiber,the load-strain-FCR curve of the specimen showed three stages,among which the FCR-strain in the stage of stable cracking showed a linear relationship.The specimen has the best pressure-sensitive performance at the optimum carbon fiber content.