| Hydraulic conventional concrete(the following is a abbreviated description of hydraulic concrete)will be subjected to water regularly or periodically.When the concrete is placed in a humid environment or water,the cement gel will absorb water cause the concrete to develop wet expansion strain and thus change the strain and even the stress state of the concrete.There are many factors affecting the wet expansion characteristics of concrete,which can be divided into internal and external factors.However,only a few studies about wet expansion characteristics of hydraulic concrete test have been reported so far,and the existing test code for hydraulic concrete(SL352-2006,DL/T 5150-2001)recommend the dry shrink and wet expansion test of concrete under no external load and constant temperature(20°C ± 2°C)conditions,but it is difficult to reasonably reflect the influence of different internal and external factors on the wet expansion strain characteristics of hydraulic concrete.To this end,the test of the wet expansion characteristics of hydraulic concrete under the influence of different factors,such as water-to-binder ratio,curing state,first immersion age,curing temperature,specimen size and historical stress state,are designed and developed in this paper,and then the wet expansion strain model of hydraulic concrete is established under the influence of different factors,to excavate the evolution law of wet expansion strain characteristics of actual concrete water engineering under the influence of different internal and external factors,and provide the reference analysis of the stress state of the hydraulic concrete structure.The main research contents are as follows:(1)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of water-to-binder ratios.The wet expansion characteristics tests of four different water-to-binder ratio hydraulic concretes,ie 0.33,0.41,0.50,and 0.60,are designed and carried out.A statistical model for the measured strains is established to separate wet expansion strain about four groups of different water-to-binder ratio hydraulic concrete after water immersion,at the same time,based on the change of water content and wet expansion strain of concrete specimens in the water-immersed stage,the coefficient of wet expansion of the water-immersed stage is calculated.The results show that with the increase of water-to-binder ratio,the wet expansion strain decreases gradually after water immersion,and the evolution regular pattern of the wet expansion coefficient is similar;based on the combination index expression,the water-to-binder ratio influence factor is introduced,and the water immersion wet expansion strain model of different water-to-binder ratio hydraulic concrete is established.Then combined with the results of multiple dry and wet cycle tests under laboratory environmental conditions,a dry-wet cyclic strain model is established with a concrete specimen of 0.5 water-to-binder ratio as an example.The new model parameters are identified by the optimization algorithm.The analysis shows that the calculated values of the new model are well fitted to the measured values.(2)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of different curing states.A total of four different curing state hydraulic concrete wet expansion characteristics tests,ie indoor exposure,indoor wrapping,standard maintenance,low temperature maintenance are designed and carried out.A statistical model for the experimental measured strain is established to separate wet expansion strain about four groups of different maintenance state hydraulic concrete after water immersion.The results show that the wet expansion strain of the indoor exposed specimen is larger than that of the indoor wrapped specimen,because the large dry shrinkage strain is generated of the indoor wrapping specimen before the water immersion,so the gel absorbs more water and large wet expansion strain will be generated;and the wet expansion strain of the low temperature curing specimen is larger than that of the standard curing specimen,because the cement hydration reaction is inhibited due to low temperature,and there are many pores around the gel,after water immersion,the water absorbs more and the wet expansion strain is larger.(3)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of first immersion ages.The wet expansion characteristics tests of five different first immersion age hydraulic concrete,ie 7d,14 d,28d,60 d and 90 d are designed and carried out.The statistical model is established for the measured strains to separate wet expansion strain of five groups of test concrete after water immersion,then based on the change of water content and wet expansion strain of concrete specimens in the water-immersed stage,the coefficient of wet expansion of the water-immersed stage is calculated.The results show that with the increase of the first immersion age,the wet expansion strain decreases gradually after immersion,when the first immersion age is greater than 28 d,the stability value of concrete wet expansion strain basically no longer changes with the increase of the first immersion age,and the evolution regular pattern of the wet expansion coefficient is similar;analog variation law of concrete creep,the 8-parameter and fractional order wet expansion strain models about immersion age and the duration tine of immersion are established respectively.Combined with the measured strain,the new model parameters were identified by the optimization algorithm.The analysis shows that the calculated values of the new model are well fitted to the measured values.(4)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of curing temperatures.The wet expansion characteristics test of hydraulic concrete with different curing temperatures of 5 °C,20 °C and 40 °C are designed and carried out.The statistical model is established for the measured strain after water immersion test to separate wet expansion strain of three groups of test concrete,then based on the change of water content and wet expansion strain of concrete specimens in the water-immersed stage,the coefficient of wet expansion of the water-immersed stage is calculated.The results show that with the increase of curing temperature,the wet expansion strain increases gradually after water immersion,and the evolution regular pattern of the wet expansion coefficient is similar;based on the combination index expression,the temperature influence factor is introduced to establish the wet expansion strain model of hydraulic concrete with different curing temperatures,and the fitting effect is good.(5)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of specimen sizes.The wet expansion characteristics test of three different sizes of hydraulic concrete,ie 100mm×100mm×500mm,150mm×150mm ×500mm and 200mm×200mm×500mm are designed and carried out.The statistical model is established for the measured strain,and wet expansion strain after immersion in water about three sets of test concrete are separated,then based on the change of water content and wet expansion strain of concrete specimens in the water-immersed stage,the coefficient of wet expansion of the water-immersed stage is calculated.The results show that with the increase of the size of the test specimen,the wet expansion strain increase after with water immersion,and the evolution regular pattern of the wet expansion coefficient is similar;and based on the combination index expression,the size effect influence factor is introduced to establish the wet expansion strain model of hydraulic concrete test with different specimen size.The new model parameters are identified by the optimization algorithm.The analysis shows that the calculated values of the new model are well fitted to the measured values.(6)Experimental study on the wet expansion characteristics of hydraulic concrete with the factor of history stress states.Firstly,the uniaxial tensile and uniaxial compressive loading and unloading creep test are designed and carried out,and then the test of the wet expansion characteristics of the tensile creep specimen,the compression creep specimen and the compensation specimen after unloading are carried out,and finally the measurement strain statistical model is established.According to the strain statistical model,the wet expansion strain of three groups of test concrete after water immersion was obtained,and the wet expansion coefficient of the water immersion stage was calculated based on the wet expansion strain and water content data of the concrete specimen in the water immersion stage.The results show that the wet expansion strain of tensile creep specimen and compressive creep specimen have little difference,and the tensile creep specimen is slightly larger,while the compensation specimen is only about 1/2 of the first two.The law of wet expansion coefficient after water immersion is similar. |
PDF Full Text Request