Design,Preparation And Mechanism Study Of Waterborne Epoxy-Concrete Composite Repair Materials

In recent years,economy in China has developed rapidly with the amount of concrete has increased sharply.By the extension of service time,the safety and durability of building structures have deteriorated with time.Numerous concrete structures generated cracks,denudation and other damages.If measures are not taken in time,it will cause endless harm.The use of suitable repair materials to repair and strengthen the damaged concrete structure can effectively restore the building function and extend the service life of the concrete structure.Ordinary cement concrete as a repair material has shortcomings such as high brittleness,low tensile strength,and insufficient bonding strength,and it is difficult to meet the needs of repair projects.Therefore,it is urgent to develop new high-performance building repair materials.This thesis takes water-based epoxy-concrete composite repair materials as the core of the research,focusing on the molecular structure design and synthesis of water-based epoxy,organic-inorganic interaction,the preparation and synergistic mechanism of high-efficiency interface agents,and the preparation technology and performance of composite repair materials And so on to carry out a series of basic research.First of all,based on the oil-water partition coefficient and the principle of similar co MPatibility,through chemical grafting and copolymerization,amine groups,polyether and other groups and segments are introduced into the epoxy resin molecule,and two kinds of groups and segments are designed and synthesized with reactive,rigid,flexible and Self-emulsifying water-based epoxy curing agent for water-soluble chain links;using hydrothermal method to disperse nano-silica particles and small molecular siloxanes to prepare multi-scale toughening agents.Based on the above technology,by blending epoxy,curing agent and toughening agent,a water-based epoxy resin with high strength,good ductility,small shrinkage,strong adhesion and synergistic with cement hydration is synthesized.Secondly,according to the characteristics of loose,porous and calcium-rich surface of old concrete,two high-efficiency interface agents that can improve the bonding performance of new and old concrete were prepared,and new methods for improving interface bonding performance and preparation of interface agents were proposed,and the high-efficiency interface agents were clarified.The synergistic mechanism for the bonding performance of the interface.Thirdly,a waterborne epoxy-concrete composite repair material with excellent static and dynamic mechanical properties,bonding properties and durability was prepared,and the interaction mechanism and microstructure evolution law of waterborne epoxy and cement hydration were explained.X-ray diffraction(XRD),gel permeation chromatography(GPC),gas chromatography-mass spectrometry(GCMS),scanning electron microscopy-energy spectroscopy(SEM-EDS),atomic force microscope(AFM),X ray electronic computer tomography(X-CT)and other advanced analytical testing methods and other conventional testing methods,quantitatively characterize the mechanism of cement hydration-waterborne epoxy crosslinking and curing,and reveal the mineral composition,organic-inorganic interaction rules,and hydration products of the repair material.The evolution of fracture morphology and element distribution at different scales.An overview model of water-based epoxy-cement matrix was established to clarify the mechanism of action of water-based epoxy on the improvement of concrete performance.Finally,the application effects of the new organic-inorganic composite repair materials prepared in this thesis were verified in two typical projects,which provided practical and data support for accumulating engineering experience.This thesis provides new materials and new technologies for concrete structure repair,which has important theoretical significance and practical value.The main innovations are as follows:(1)Design,preparation and modification of non-ionic self-emulsifying waterborne epoxy(NEP)There are mainly linear molecules(LHD)and star molecules(SBP)in self-emulsifying waterborne epoxy curing agent(NEP-HD).Each molecule contains three chains:water-soluble,bisphenol A,and reactive.Section.Among them,the water-soluble link is composed of polyether segments;the bisphenol A link is introduced by epoxy resin(E51);the reactive link is composed of amine groups(primary amine,secondary amine,tertiary amine),epoxy,silane Oxy group structure.The LHD molecule is synthesized by the addition of amine-terminated polyether,triethylenetetramine(TETA)and E51;the SBP molecule is synthesized by branched molecules such as polyethylene glycol(PEG)and polyetheramine(D230)in the central molecule 2,4,Chemical grafting and copolymerization of 6-tris(dimethylaminomethyl)phenol(DMP30).This paper found that there are epoxy-modified nano-silica(NS)particles and cyclic and cage-like oligomers in the multi-scale toughening agent(TD),which can participate in the cross-linking and curing of NEP and consolidate NEP.The body has the toughening effect of crack resistance,crack resistance and inducing multi-slit cracking.The hydrothermal method can effectively disperse NS and increase the number of epoxy groups on the surface of NS in TD,thereby improving the toughening and cracking resistance of TD.(2)Epoxy resin curing-cement hydration interactionThe thesis co MPares the effects of NEP and emulsion epoxy(EEP)on the performance of cement stone,reveals the mineral composition,organic-inorganic interaction rules,hydration products,fracture morphology,and element distribution of the repair material at different scales.Evolution.The suitable polymer-cement ratio(P/C)of the water-based epoxy-cement-based composite repair material is 0?0.4.If the P/C continues to increase,the water-based epoxy will hinder the hydration of the cement,and the setting time will be significantly prolonged.The repair material is easy to demulsify and bleed.Waterborne epoxy can induce and promote the formation of CH crystals from cement hydration.EEP mainly exists as filler particles to promote the preferential orientation of CH growth on the{001}crystal plane;NEP mainly exists as a continuous network interpenetrating,and CH crystals are enriched and grown along the surface of the NEP micelles,and the growth direction is mainly{101}The direction of the crystal plane,not the direction of the{001}crystal plane.The failure section of NEPC has the structural failure morphology of NEP and cement stone,the interpenetrating structure of the film network is obvious,and the ductility,crack resistance,and durability are greatly improved.Co MPared with EEP,NEP is more suitable for cement concrete system.(3)Preparation of interfacial agent and bonding enhancement mechanismTwo high-efficiency interface agents that can improve the bonding performance of new and old concrete are prepared,namely,pore plug promoting interface agent(ICA)and surface enhanced interface agent(MF-PSCA),and new methods for improving interface bonding performance and preparing interface agents are proposed.Clarified the synergistic mechanism of the high-efficiency interfacial agent on the bonding properties of the old and new interfaces.ICA has a strong ability to bond CH in cement,and it adsorbs directionally on the{001}and{101}crystal planes of CH crystals.ICA has a depletion effect on CH,crystal refining effect,and forms pore plugs on the surface of CH crystals and the surface of cement matrix.The hole plug is the main difference from the control group.Its microstructure may be a layered composite product composed of NS,oligomers and microcrystalline CH in the ICA during the dissolution-crystallization process.The surface of the old concrete is sprayed with MF and then PSCA,and finally K₂Si F₆,KMg F₃,MF crystals are formed on the surface of the old substrate,and Ca F₂,Mg F₂ and amorphous Si O₂ are formed on the surface of the old substrate within a depth of about 5mm,which improves the hardness of the cement stone.The polycondensation products of ICA and MF-PSCA can chemically bond with old concrete and water-based epoxy-cement-based repair materials to improve the bonding between the old and the new to 2.5MPa,and the form of damage is the cohesive failure of the old concrete.(4)Performance of water-based epoxy-concrete composite repair materialAn overview model of water-based epoxy-cement matrix was established,key performance parameters of water-based epoxy-concrete composite repair materials were obtained,and the effect mechanism of water-based epoxy on concrete performance improvement was clarified.The mechanical test results show that with the increase of P/C,the compressive strength and elastic modulus of the waterborne epoxy-concrete composite repair material show a downward trend,while the flexural strength,tensile strength,bonding strength of new and old concrete,Poisson's ratio,and toughness Than gradually increase.P/C=0.2 is the turning point of the flexural and tensile strength of waterborne epoxy-reinforced concrete,and P/C in the range of 0.2?0.4 is the appropriate dosage of waterborne epoxy in concrete.The bending fatigue resistance and i MPact resistance of waterborne epoxy-concrete composite repair materials are positively correlated with P/C.From the perspective of the gain effect,waterborne epoxy is the main factor to increase the dynamic mechanical properties of concrete,while the fiber component is a secondary factor.The impermeability,frost resistance and volume stability of waterborne epoxy-concrete composite repair materials are positively correlated with P/C.Fiber has a negative effect on the impermeability of concrete,and has no significant effect on frost resistance and volume stability.