Penetration Tests And Evolution Studies On Concrete Under The Conditions Of Freezing-thawing Cycle

Permeability is an important index to evaluate and design the frost resistance and permeability of concrete,especially for the hydraulic concrete which affected by the long-term freezing-thawing environment.And the most important form of damage are seepage and erosion damage.The permeability of concrete has an important connection to the strength and durability of concrete under the condition of freezing-thawing,and it can reflect the result that the size and quantity of the internal fissure change with the freezing-thawing environment.The purpose of this paper is to study the permeability evolution of concrete under the condition of freezing-thawing as to reflect the deterioration of concrete material.The purpose of this paper is to study the law of permeability evolution of concrete under the cycle of freezing-thawing,and then the correlation between permeability and conventional freezing-thawing damage of concrete is explored.The main work of this paper is as follows:1)The preparation device of the concrete surface permeation specimen has been invented by improving the concrete specimen preparation device,which solved the problem of poor surface evenness of concrete under the condition of freezing-thawing effectively and the sealing ability that is difficult to meet the requirement of continuous measurement in the test process.Thus,the amount of water infiltration which infiltrated into concrete can be measured quickly,steadily and continuously under different freezing-thawing cycles.2)Based on the three-dimensional seepage finite element method and combined with the Seep3 D modeling treatment,the three-dimensional seepage process of the concrete specimen is simulated and then the relation curve between the permeability coefficient and the permeability is obtained.Through the penetration test,the measured data of the water permeability that change with time can be acquired and the permeability coefficient corresponding to the test data is obtained by interpolation and inverse calculation.According to this method,the permeability coefficient of concrete can be obtained in real time under different freezing-thawing cycles.3)By testing the water permeability of concrete under different water cement ratio and comparing its inverse permeability coefficient,the influence of water cement ratio on concrete permeability is analyzed.The results show that the permeability coefficient of concrete increases slowly with the increase of freezing-thawing times.And then the rate of growth gradually increases,showing an exponential growth overall.The smaller the water cement ratio is,the slower the permeability coefficient of concrete is and the better the permeability is,which is mainly related to the expansion force produced by the volume of ice in the pore water.4)By comparing the results of the permeability test of concrete mixed with fly ash and without it under the environment of freezing-thawing,the variation of permeability coefficient of fly ash concrete is analyzed with freezing thawing times.The results show that the permeability coefficient growth rate of fly ash concrete increases first and then decreases.In the early stage,the permeability coefficient of fly ash concrete is higher than that of non-fly ash.After high freezing-thawing times,the permeability coefficient of fly ash concrete increased slowly and its permeability coefficient is lower than that of non-fly ash.5)The permeability of concrete with double mixing(fly ash and air entraining agent)has little change in the case of the increase of the freezing thawing times,which plays a very good role in the anti-permeability of concrete.6)The correlation between permeability coefficient and compressive strength and mass loss rate of concrete under the condition of freezing-thawing condition is discussed.The research shows that the permeability coefficient can be used to evaluate the freezing-thawing deterioration process of concrete,which has a good correlation with the conventional freezing-thawing deterioration evaluation index of compressive strength and mass loss.In this paper,the relationship model of the compressive strength and permeability coefficient modified by water cement ratio is further developed,and the experimental data are used to verify the deviation of the final model.The results show that the model is satisfied with the range of deviation.