| Under the external loads and environmental impacts,concrete structures are prone to surface damages.In addition,inappropriate selection of raw materials,incorrect mixture design or irregular construction process can cause quality problems of concrete surface.In these cases,the durability and safety of concrete structures are affected negatively.It is necessary to repair the concrete surface to restore the structure safety and to extend their service life.However,the failures of repairs within a short term are usually attributed to the weak interface between the cement-based repair materials and concrete substrates.To solve these problems,the modified silane/acrylic acid(S/AA-HPEG)with hydrophilicity,reaction activity and water reduction effect was prepared by grafting silane(S)with strong reactivity and acrylic acid(AA)with strong hydrophilicity onto the chain of polyethylene glycol monomethallyl(HPEG)and used to modify ordinary Portland cement-based repair material with low water-cement ratio.S/AAHPEG can migrate into concrete substrate with the water in the fresh paste under the capillary force from the substrate.Moreover,it can react,so the interfacial structure can be improved and the interfacial bond strength can be enhanced.The influences of this organic admixture on cement hydration and microstructure,macro-performance of cement-based repair materials were explored experimentally,as well as the relevant mechanisms.The specific research contents and results in this thesis are described as follow:(1)By using polyethylene glycol monomethallyl(HPEG),which is a raw material of polycarboxylate superplasticizers,as the main chain,three kinds of S/AA-HPEG(P1,P2 and P3)with the silane content of 2.67%,3.82% and 7.50%,respectively,were prepared by grafting3-(Trimethoxysilyl)propyl methacrylate(S)and acrylic acid(AA)onto the main chain.Their relative molecular weight ranged between 48288-77871.Their morphology was wrinkled like,and their adsorption amount on the surface of cement particles increased with the increase of silane content.(2)The effects of the three kinds of S/AA-HPEG at 0.8 wt% of cement on cement hydration,microstructure and macro-performances of cement-based repair material were investigated.When S/AA-HPEG was adsorbed on the surface of cement particles,the early hydration of cement was inhibited,and the hydration degree of cement slurry was reduced,and the setting time of cement repair mortar was prolonged.However,the porosity of cement paste was reduced.In addition the fluidity and the resistance to chloride ion penetration of cement repair mortar were improved,and the dry shrinkage of cement-based repair materials declined.Moreover,the flexural strength of cement repair mortar at late age was increased.(3)The effects of the three kinds of S/AA-HPEG at 0.8 wt% of cement on the interfacial bonding and the interfacial microstructure between the repair and the substrate were investigated.Compared with P3 and P1,P2 had the most significant effect on improving the interfacial bonding property and the interfacial structure.The interfacial bonding property of cement repair mortar with P2 was improved by 25%-47% after 3 d.Moreover,the microhardness of cement-based repair mortar near the interface was increased by 33.3%,compared with that far away from the interface.In addition,the cement repair mortar containing organic admixture with 3.82% silane content had a larger penetration depth than the other two.These S/AA-HPEG penetrating into the substrate can decrease the porosity of the paste in the interfacial region. |
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