Study On Development Of Long-term Freeze-thaw Resistant Epoxy Resin For Concrete Cracks Repairing

In the arcticalpine and highland areas of China, especially in the northeast, northwest, andNorth China, and so on, which are greatly impacted by various natural factors, such as lowtemperature, large temperature differences between day and night, drying and watering cycle,freeze-thaw cycle, salt alkaline corrosion, and wind erosion, etc., local or large areas foralmost100%projects, suffers from varying degrees of freeze-thaw destroy （main disease isdenudation, cracks, etc.）. Some projects even suffer grave freeze injury during constructionprocess or soon after construction completed. Therefore, freeze-thaw destroy seriously affectthe durability of concrete, and it is quite important of taking appropriate materials andtechnology to repair the concrete cracks in order to ensure the durability of concrete structure.In recent years, epoxy resins have already become an indispensable kind of repair materialsin the concrete crack repairing field. However, the practical use of EP is seriously limitedbecause of the poor impact resistance, toughness and cracking resistance of epoxy resins. Inthis work, it is expected to develop modified epoxy repair materials with high performance byintroducing various reinforcing and toughening ingredients into epoxy resins to repairconcrete cracks which are caused by factors such as wind erosion and freeze-thaw cycles.In this thesis, modified epoxy resin repair materials with high performance are prepared bytoughening with nitrile rubber, asphalt, furfural/acetone and NH2-nano-SiO₂particles graftedby polyurethane, respectively. Better repair material formulas and processes are finallyfiltered out through formula design and experimental study on the mechanical properties,freeze-thaw resistance, water and chemical resistance.（1） Nitrile rubber-modified epoxy resin/LB-B1system: the comprehensive properties of therepair material are the best when the contents of curing agent LB-B1, nitrile rubber, reactivediluents of501#and wollastonite filler reaches20phr,10phr,5phr and100phr one by one.Meanwhile, the performance becomes much better with the increase of freeze-thaw cycles.（2） Nitrile rubber-modified epoxy resin/F system: when the dosage of the epoxy resin ofE-44, curing agent F, nitrile rubber and KH-550is100phr,11phr,5phr, and10phrrespectively, the comprehensive performance of the repair material is optimal. Moreover, theoverall performance of the material will slowly become better with the increment of thefreeze-thaw cycles.（3） Asphalt-modified epoxy resin system: the optimal formula of the repair materials hasbeen seeked out through the integrated analysis on the properties of tensile shear strength,compressive strength, freeze-thaw resistance, water tolerance and chemicals resistance of therepair materials. The comprehensive property of the repair material is much better when theaddition contents of epoxy resin, LB-B1, and asphalt is100phr,15phr, and10phr, respectively. What’s more, the freeze-thaw performance of the repair material is fairly good.（4） Furfural/acetone-modified epoxy resin system. As the dosage of epoxy resin,polyamide/LB-B1, furfural/acetone, and KH-550comes for100phr,25/25phr,10/10phr,and5phr, respectively, the overall performance of the epoxy resin repair material is the best.At the same time, it is a kind of repair material with good toughness. Though the acidresistance is slightly bad and it can not stand long-term freeze-thaw cycles, it can still beapplied in the environments with lower operating requirments.（5） Polyurethane/nano-SiO₂-modified epoxy resin system. Through the orthogonalexperiments, validation test, as well as the toughening analysis of the modified epoxy resinrepair materials, the formula with optimal performance has been located. It is when when thecontent of epoxy resin, curing agent F, PU prepolymer, NH2-nano-SiO₂, and KH-550is100phr,11phr,10phr,3phr, and4phr, respectively. Meanwhile, the compressive strength,tensile shear strength, tensile strength, bending strength and elongation at break of the repairmaterial with optimal performance can reach148.68MPa,23.57MPa,56.08MPa,86.76MPa,and36.33%, respectively. In addition, the repair material also presents excellent freeze-thawresistance, water and chemicals resistance.Additionally, the influence law of the reinforcing and toughening agents content on theproperties and structure of the epoxy repair materials suffered freeze-thaw cycles andchemicals is investigated by freeze-thaw circulating experiment and characterization withFT-IR and SEM techniques. By comparasion with the design requirements （namely, thetensile shear strength, compressive strength, tensile strength, tensile modulus, bendingstrength, and elongation at break need to reach14MPa,70MPa,40MPa,2500MPa,50MPa,and1.5%, respectively）, it can be found that, the basic mechanical properties of nitrilerubber-modified epoxy resin/LB-B1system and asphalt-modified epoxy resin system fail tomeet the design requirements in the early days, however, its shorter curing time and that themechanical properties increase significantly after freeze-thaw cycle make it possible to reachthe design requirements. On the other hand, the performance of the nitrile rubber-modifiedepoxy resin/F, furfural/acetone modified-epoxy resin and polyurethane/nano-SiO₂-modifiedepoxy resin systems can meet or even surpass the design requirements, while the systemsexcept the furfural/acetone modified epoxy resin system have excellent properties offreeze-thaw resistance, water and chemical resistance. These conclusions provide theoreticalbasis and practical guidance for further optimizing the repair materials and the conctere cracksrepairing in the arcticalpine and drought environments.