| With the continuous development and progress of civil engineering equipment and technology,the existing concrete structure repair materials have gradually been unable to meet the high difficulty,high performance and high efficiency requirements of structural engineering repair.In addition,the traditional construction methods are complex,inefficient and costeffective,which have been gradually eliminated in the engineering operations with time-limited requirements or poor construction environment.Therefore,it is urgent to develop a new type of engineering repair material with excellent early mechanical properties,high toughness,low shrinkage,low cost and controllable setting time.Based on the characteristics of rapid opening,excellent performance and efficient construction,a new type of engineering repair material-Injectable Ultra High ToughnessStrength Cementitious Composite(ITSCC)was prepared in this paper.On this basis,the working performance of ITSCC was studied,including fluidity,setting time,rheological property,pumping model and outdoor spraying test.Secondly,the mechanical properties of ITSCC were studied,including compressive and flexural strength,flexural properties,tensile properties,failure modes and analysis of key influencing factors.Finally,the interfacial bonding properties of ITSCC are studied,including mix design of new and old concrete and its deformation matching.The effects of strength grade,interfacial roughness,curing age and interfacial treatment on interfacial bonding properties are also studied.Based on the above experimental study,the following conclusions can be drawn:(1)Working Performance of ITSCCWater-binder ratio,water reducer and retarder can improve the working performance of ITSCC synergistically.The increase of water-binder ratio and water reducing agent content can obviously improve the flowability of ITSCC and prolong its first rheological stage;the retarder has no substantial effect on the flowability of the system,but can prolong the first rheological stage;the introduction of PVA fibers will greatly reduce the flowability of the system and shorten the first rheological stage,so the introduction of fibers will greatly reduce the working performance of the system.Secondly,with the increase of water-binder ratio,water reducer and retarder,the setting time of the system increases.However,from the analysis of retarding effect,changing the water-binder ratio and retarder dosage can improve the retarding effect better than changing the water reducer.Considering that the introduction of retarder in the system will not have other chemical effects and thus affect hydration,changing the retarder dosage is the most effective way to control the setting time of the system.Thirdly,ITSCC is a Bingham fluid with positive thixotropy.From the analysis of the area of hysteresis ring,the thixotropic energy of the system decreases with the increase of water-binder ratio;and the thixotropic energy of the system increases with the increase of water reducer and thickener.From the rheological parameters analysis: the increase of water-binder ratio will reduce the yield stress and plastic viscosity of the system;the increase of water reducer content will reduce the yield stress of the system,but its plastic viscosity will increase accordingly;after the introduction of 0.1% HPMC into the system,the plastic viscosity will increase by 321.1%,and the yield stress will increase by 92.0%.Fourthly,the outdoor spray test results show that the mechanical properties and interfacial bonding properties of Spray-Formed ITSCC are consistent with those of indoor Spray-Formed ITSCC,and even exceed those of indoor SprayFormed ITSCC.(2)Mechanical Properties of ITSCCThe use of early strength cementitious system and the introduction of PVA fibers in matrix increases the 24-hour compressive strength of ITSCC,up to 50 MPa or more.Compared with the ordinary fast-hardening sulphoaluminate cement system,the 24-hour flexural strength of ITSCC reaches 14.80-19.35 MPa and the flexural performance increases by 64.4%-115.0%,but the 28-day flexural strength of ITSCC shows different degrees of retraction.Secondly,ITSCC has obvious strain hardening and multi-slit cracking under bending and tension loads.Compared with the ultimate strain of ordinary concrete,the ultimate strain of ITSCC is two orders of magnitude higher,showing much higher toughness and ductility than that of ordinary cement-based materials.Thirdly,by range analysis,the R values of tensile and flexural properties of the fiber content are both the maximum,while the R values of tensile and flexural properties of the other three factors are less or far less than the R values of the fiber content.Therefore,fiber content is the most important factor affecting the tensile and bending properties of ITSCC materials.The other three factors are secondary or auxiliary factors.The increase of fiber content can improve the tensile and bending properties of ITSCC materials at the same time.However,the effects of water-binder ratio,water reducer and fly ash on the tensile and bending properties of ITSCC materials are mixed.(3)Interfacial Bonding Properties of ITSCCThe shrinkage of ITSCC is 292?? and 475?? in 7d and 28 d respectively.When ITSCC is combined with existing concrete without other measures,shrinkage stress will result in cracks.By adding 3.0% shrinkage reducing agent,the shrinkage of the system can be reduced obviously.The shrinkage of the system is only 75?? and 155?? in 7d and 28 d respectively.Continuing to increase the content of shrinkage reducer will change the setting time of the system.However,when 3.0%~6.0% expansive agent and 3.0% shrinkage reducing agent are used together,the shrinkage of the system will be further reduced and the setting time of the system will not be greatly changed.Secondly,the interfacial bonding performance between ITSCC and existing concrete structures is directly affected by the strength grade of existing concrete,interfacial roughness,curing age and interfacial treatment methods.When other casting conditions are the same,the bond splitting tensile strength of composite specimens is approximately linear with interface roughness and the strength grade of existing concrete;the bond splitting tensile strength of composite specimens is approximately logarithmic function relationship with curing age.The bond splitting tensile strength of composite specimens can reach 3.20~3.63 MPa in one day,which is about 90% of the bond splitting tensile strength in 28 days.In addition,different interface treatments have great influence on bond splitting tensile strength of composite specimens.The bond splitting tensile strength of ITSCC composite specimens treated with interfacial adhesive increases by about 30% compared with that of blank group and 20% compared with that of composite specimens treated with paste. |
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