Study And Development Of Polyurethane-Epoxy Resin Materials Used For Concrete Protection And Repair

Cement concrete is one of the most important construction materials used in civilengineering. However, influenced by some natural factors, such as the low temperature, largetemperature differences, wind erosion, freeze-thaw cycle, etc., concrete structure in somealpine plateau area faces insufficient durability. Consequently, cracks and damages will leadin concrete structure, which seriously affect the normal use of concrete building structure.Therefore, effective measures should be taken to protect and repair the concrete structure soas to improve the durability of concrete structure and prolong the service life. Thus, thenormal use of concrete structure can be ensured.In this thesis, aiming at the problem of insufficient durability of concrete structures,moisture-curable one-component polyurethane coatings and polyurethane-modified epoxyresin are developed, and which can be used as concrete structure protection and concretecrack repair, respectively. Consequently, it is expected that the durability of concretestructures can be prolonged.(1) Polyurethane prepolymer was synthesized through the formula design and experimental research, and then one-component moisture-curable polyurethane coating withexcellent freeze-thaw resistance was developed successfully through the curing of moisture air. Finally, the effects of the ratio of raw materials and reaction process parameters (such as R value, polyether mass ratio of N220:N330, catalyst content, reaction temperature, and reaction time, etc.) on the tensile properties, thermal properties, and freeze-thaw resistance of one component polyurethane coatings were investigated.Results show that, the tensile strength of the coatings increases firstly and then decreases,and the elongation at break decreases while Shao(A) hardness increases gradually with theincrease of the R value. Meanwhile, the tensile strength and Shao(A) hardness of the coatingsdecrease gradually while the elongation at break increases be degrees with the increase ofpolyether mass ratio. Additionally, the surface drying time and hard drying time of thecoatings decrease gradually with the catalyst content increased. Finally, the optimal processparameters and the best ratios among raw materials for preparation of one-componentmoisture-curable polyurethane coating are determined as follows: the initial reactiontemperature is50℃, and the optimal temperature for synthesis of the polyurethane is75℃while the reaction time is in1.5~2.5h under the stirring speed of150~200r/min. In additional,the polyether mass ratio between N220and N330is8:1and R value is controlled as4:1whilethe content of dibutyltin dilaurate is0.5~1%. Consequently, the one-componentmoisture-curable polyurethane coating with best properties is prepared under these parameters.For instance, the tensile strength and elongation at break can reach6.46MPa and518%, respectively, while Shao(A) hardness is72. Meanwhile, the tensile properties of the coatingcan be further improved significantly after freeze-thaw cycles.(2) Through the modification and toughening by polyurethane, the polyurethane-modified epoxy resin was synthesized, and which can be used for repairing of concretecracks. The chemical structure of polyurethane-modified epoxy resin was characterizedand analyzed by techniques as FT-IR. Additionally, the influence law of the polyurethane content on the mechanical properties, thermal property, and the chemical resistanceof the polyurethane-modified epoxy resin was investigated.Results show that with the increase of the polyurethane content, the tensile strength,bending strength, and impact strength of the polyurethane-modified epoxy resin increasefirstly and then decrease, and the elongation at break increases while the compressive strengthdecreases gradually. Meanwhile, the weight of polyurethane-modified epoxy resin increasesafter soaked by10wt%of the sulfuric acid solution while which decreases after soaked by10wt%of sodium hydroxide and sodium chloride solution, respectively. In addition, the weightchange ratios gradually enhance with the increase of polyurethane content.It can be determined from the above research results that when the content ofpolyurethane added in the epoxy resin is20%, the optimal performance of the modified epoxyresin can be resulted, and the tensile strength, bending strength, elongation at break, andcompressive strength of the polyurethane modified epoxy resin can reach45.2MPa,78.4MPa,5.8%, and36.0MPa one by one. Meanwhile, the weight increase after soaked by10wt%of sulfuric acid solution is4.8%while weight decrease ratios after soaked by10wt%ofsodium hydroxide and sodium chloride solution are0.98%and0.89%, respectively. Moreover,the glass transition temperature (Tg) enhances while the mechanical properties and chemicalresistance of the repair materials improve distinctly with the increase of freeze-thaw cycles.Finally, the splited concrete cracks were repaired using the polyurethane-modified epoxyresin, results show that it has good mechanical properties, and repair materials has excellentadhesive for concrete.