Test Method On Tensile Creep Of Cement-based Materials At Ultra-early Age

With the continuous deepening of research on the durability of concrete,it is found that cracking of concrete is the main factor that causes the deterioration of concrete durability.Reducing or inhibiting concrete cracking can greatly improve concrete durability.The creep of cement-based materials,especially the tensile creep in early age,plays an important role in suppressing the early cracking of concrete.However,most of the current researches on the tensile creep properties of cement-based materials are 1d or 3d after the preparation of the test piece,and there are few studies on the tensile creep in the super early stage(from initial setting to final setting).In order to measure the ultra-early tensile creep of cement-based materials,a testing device for ultra-early tensile creep of cement-based materials was developed.The device includes a mold,a displacement sensor,an information acquisition and processing device,and a test piece bearing frame.A test method for early creep of cement-based materials is proposed,and based on the characteristics of cement-based materials,by reference to the creep calculation model of concrete,the ultra-early creep calculation model of cement-based materials is determined.Calculation method.Through the ultra-early tensile creep test of cement-based materials mixed with mineral admixtures,it is found that the cement-based materials with different amounts have significant differences in creep,thus verifying the ultra-early tensile creep test method of cement-based materials feasibility.The law of shrinkage and creep of cement stone is comprehensively analyzed,and the low shrinkage and high creep characteristics of cement stone are discussed.The specific work of the thesis is as follows: 1)The calculation model of ultra-early creep of cement-based materials is based on the stepwise calculation method,and the creep coefficient and creep of the cement-based materials are obtained through trapezoidal calculation.2)According to the characteristics of ultra-early deformation of cement-based materials,a polyurethane mold is designed that can be combined with cement-based materials and can produce simultaneous deformation of cement-based materials and molds.3)Designed a cement-based material deformation test device with low cost,stable test data,and a test process consistent with the actual situation of the project.4)Under the environment of temperature(20±2)? and relative humidity of(60±5)%,ultra-early tensile creep test was carried out on cement stone mixed with different proportions of fly ash and slag.It was found that at low water-binder ratio(water-binder ratio 0.3),high mineral admixture content(50-80%),cement stone mixed with ultra-fine fly ash and S95 slag has low shrinkage and high creep characteristic.The cement stone mixed with Grade II fly ash and S115 slag does not have the characteristics of low shrinkage and high creep.5)At 0.25 water-binder ratio,as the amount of mineral admixture increases(60-70%),the creep of cement stone increases and shrinkage decreases,which is the same as that of cement stone with 0.3 water-binder ratio.at 0.35 water-binder In contrast,with the increase of the mineral admixture(60-70%),the creep and shrinkage of cement stone showed an increasing trend.A large amount of mineral admixture and a low water-to-binder ratio are the prerequisites for achieving low shrinkage and high creep of cement-based materials.The research work in this paper puts the ultra-early tensile creep of cement-based materials into a quantitative stage,which has certain value for enriching the theory of ultra-early tensile creep of cement-based materials,and has important engineering significance for the research on the crack resistance of cement-based materials.