Internal Humidity Migration Of Concrete And Environmental Humidity Influence On Mechanical Properties Of Hydraulic Concrete

The humidity of concrete and environmental humidity are important factors affecting the mechanical properties of concrete.The internal relative humidity of concrete is not only related to its hydration reaction,but also to the external environment humidity.When concrete causes internal relative humidity to decrease because of its hydration reaction,it will produce self drying in concrete.It can easily cause internal tensile stress and produce cracks from inside and outside.When concrete is affected by ambient humidity,concrete moisture is lost through surface and will produce dry shrinkage deformation and dry on the surface of concrete.Shrinkage stress can easily cause cracks on the surface of concrete.Although there are many reports about the relative humidity of high performance concrete,there are few reports about the relative humidity test of hydraulic concrete.In addition,the existing concrete test specification stipulates that the performance test of concrete material is carried out in the standard maintenance state,but the actual condition of concrete engineering is far from the standard maintenance state,which leads to the great difference between the mechanical properties and the actual conditions of the concrete material obtained under the condition of indoor standard maintenance.In view of the above problems,this paper first carried out the experiment on the internal humidity distribution law of concrete under different water glue ratio,and then carried out the experiment on the influence of different curing temperature and humidity on the mechanical properties of concrete material.The specific research contents are as follows(1)Experimental study on internal relative humidity of hydraulic concrete.The internal relative humidity test of hydraulic concrete with different dampness under the real environment was carried out,and the self drying test of different water cement concrete and high performance concrete was compared,and the effect of dry and wet cycle on the relative humidity of high performance concrete was explored.The research shows that the relative humidity inside the hydraulic concrete can be divided into two stages: the internal relative humidity is maintained at the 100% stage and the slow decline stage.The decrease of the relative humidity in the hydraulic concrete is mainly caused by the diffusion of water to the outside world,and the self drying of the cement hydration reaction is very small,and the water binder ratio is less than 0.41.The self drying phenomenon of the soil is existing,which will cause the slow self shrinkage deformation of the concrete inside,and then analyze the mechanism of the long-term instability of the non stress meter which deducts the temperature component of the southwest special high dam project,and the self drying phenomenon of the high performance concrete with the water to rubber ratio less than 0.5is obvious,and with the decrease of the water glue ratio,it is self drying.The greater the degree of dryness,the addition of fly ash to a certain extent reduces the self drying of low water cement concrete,and the rate of relative humidity rising in the wet process is obviously greater than that of the relative humidity in the drying process,and with the increasing number of dry and wet cycles,the internal humidity of the concrete is relatively wet.The rate of increase gradually slows down.(2)Experimental research on the influence of curing humidity on the compressive strength of hydraulic concrete.The test of concrete compression strength under standard curing,parcel maintenance,natural curing and water curing is carried out.The study shows that the environmental temperature and humidity have great influence on the compressive strength of concrete,the compressive strength of the standard curing is the largest,thecompressive strength of the package curing is the second,the second is the compressive strength of natural curing,because of the softening effect,The compressive strength of water curing is the least,and a double exponential compression strength model is established considering the coupling of temperature and humidity with the theory of hydration.At the same time,based on the fractional calculus theory,a fractional order compression strength model considering the coupling of temperature and humidity is proposed and established for the first time.The analysis shows that the 2 compressive strength models established in this paper have been analyzed.The model can better fit the development law of compressive strength under different curing temperature and humidity,and the fitting effect of the fractional compression strength model is better than the double exponential compression strength model.(3)Experimental study on influence of curing humidity on tensile creep of hydraulic concrete.First,the measured strain of the compensable specimen is analyzed,and then a statistical model of the measured strain is set up to obtain the temperature strain,the autogenous volume deformation,the dry shrinkage strain and the wet expansion strain under different curing conditions.Then the creep values of concrete under different humidity conditions are analyzed and the creep values of concrete under different humidity conditions are obtained.Based on this,the concept of wet swelling and creep is proposed for the first time,and the creep theory is further perfected,and the total creep,basic creep,shrinkage and creep and wetness are obtained.Swelling and creep.Finally,based on the hydration degree theory,the 8 parameter creep model and the fractional order creep model,which consider the coupling of temperature and humidity,are set up.The parameters of the new creep model are estimated by the actual measured values of concrete creep under different curing humidity.The analysis shows that the creep model considering the coupling of temperature and humidity can reflect the difference better.The rule of creep and change of concrete under curing humidity,Based on the superposition principle,the elastic aftereffect under different curing humidity agrees well with the measured elastic aftereffect.