Experimental Research On Polymer Modified Mortar With Respect To Bridge Reinforcement

At present,many existing concrete bridges in service have a lot of hidden trouble due to the man-made factors such as unreasonable design,improper construction,dysfunctional operation and maintenance and so on,as well as natural disasters and material aging etc.And it has the urgent need of the repair and reinforcement.And enlarging cross-section is the commonly used reinforcement method of prestressed concrete structures.However,the conventional concrete and cement mortar have the disadvantages of low tensile strength and poor adhesion,especially for the prestressed concrete bridges.If conventional concrete or cement mortar with high elastic modulus but low tensile strength is used to enlarge cross-section and increase the reinforcement,the crack resistance of the reinforcement layer will be difficult to meet the requirements and the crack resistance of the original prestressed concrete structure is difficult to match with it.Polymer modified cement-based materials are expected to be important structural reinforcement materials because of their advantages of good workability,high tensile strength,strong toughness and good corrosion resistance.Based on this,this paper has had a further study on using the polymer emulsion to modify the traditional mortar,and the polymer modified mortar in the bridge reinforcement project on the feasibility of the application in two levels of material and structure.the thesis involves mainly the following investigations and corresponding results:(1)For the two types of common polymer modified emulsion:styrene-butadiene emulsion and water-based epoxy emulsion,the properties of the modified mortar with different ash ratio and water-cement ratio were studied.The effects of the two polymers on the mechanical properties(compressive strength,flexural strength,tensile strength,splitting tensile strength,flexural modulus and elastic modulus)of the modified mortar were studied systematically.Based on the experimental results and the analysis that modification mechanism of different polymers to cement mortar,the results showed that the general tendency of SBR emulsion and waterborne epoxy emulsion to improve the modification of cement mortar was coincident while the modification effect was different.With the increase of the content,the compressive strength of the two were both decreasing while the tensile strength had the tendency of increasing.And the tensile strength and elastic modulus of styrene-butadiene mortar are higher than that of water-borne epoxy mortar.In addition,having concluded the conversion formula among the bending-compressive strength,elastic modulus-compressive strength and different tensile strength based on the experimental data.(2)The influences among the surface shape,the anchoring length and the strength of the polymer mortar on the bonding properties between the steel bar and the polymer mortar was studied which based on a pull test of 52 specimens divided by 14 groups of steel bars and polymer mortar bonded and anchored.And the formula for calculating the ultimate bond stress was obtained by statistical regression of the experimental data.The experiment results showed that with the increase of the strength grade of the polymer mortar,the ultimate bond stress increases while the limit slip decreases.When the anchorage length increases,the ultimate load and ultimate slip also increases gradually,but the limit The bond stress decreases a little.(3)Based on the experiment on basic mechanical properties of polymer modified mortar and the experiment on bond and anchoring performance of polymer modified mortar and steel bar,the feasibility of using polymer modified mortar to strengthen the reinforcement of bridge beam at the end of beam was studied.Firstly,the finite element model that considering the force of the reinforced beam is established according to the engineering example.The influence law of the elastic modulus and thickness of the reinforcement layer on the most unfavorable stress of the old and new structures is obtained.In addition,based on the ensurance that there is a reliable bond between the polymer mortar and steel reinforcement,the steel bar limit state equation established,and the polymer mortar required to have the minimum tensile strength and elastic modulus the amount determined from the perspective of reliability.Finally,having summarized the above specific beam stress and bond anchoring requirements for specific engineering examples requires that the appropriate amount of polymer should be controlled in the range of 17%to 20%.