Research On Freeze-thaw Damage Model Of Nano-concrete Based On Fatigue Cumulative Damage Theory

Freezing and thawing damage is one of the main failure types of concrete structures in cold regions.Almost all concrete structures in cold regions have suffered different degrees of freeze-thaw damage.The service life of concrete significantly decreased,which because the ordinary cement concrete frost resistance is relatively poor under the effect of freeze-thaw cycles and meet the durability requirements of concrete in severe cold area is difficult.As a new material in the 21 st century,a ano-materials have some excellent properties that traditional materials do not have,such as micro-aggregate filling effect,nucleation effect,surface effect and interface effect.Configuring the high performance and strength nano-concrete by adding the appropriate amount of nano-materials to concrete will significantly improve the frost resistance of concrete.Therefore,it is very important that quantitatively analyze the actual freeze-thaw damage through establishing freeze-thaw damage models based on damage theory and experiment.Firstly,based on the theory of fatigue cumulative damage,the macroscopic variable of measurability is adopted,which the relative dynamic elastic modulus is used as the damage variable to describe the damage state of concrete material's internal structure under freeze-thaw action and the effect of the damage state on the mechanical properties,durability and appearance of concrete material,the micro-defect of the materials are reflected in the macroscopic properties to quantitatively evaluate the deterioration degree of freeze-thaw damage of concrete structures.Furthermore,based on the existing fatigue damage accumulation model of concrete,an attempt was made to establish a nano-concrete freeze-thaw damage model to quantify the actual freeze-thaw damage.Combined with the experimental data,data processing software is used for regression analysis to determine the parameters of the freeze-thaw damage model.The freeze-thaw damage models of nano-concrete of different nano-materials under different nanometer contents was established to reveal the degradation law of freeze-thaw damage inside nano-concrete materials under freeze-thaw cycles,and implemented quantitative analysis of concrete freeze-thaw damage;Finally,the reliability of the freeze-thaw damage models are verified by experimental data and theoretical validation,in order to verify the correctness and rationality of the nano-concrete freeze-thaw damage models.Based on the freeze-thaw damage models,a method for predicting the actual safe service life of nano-concrete is established.The research shows that the actual freeze-thaw damage characteristics reflected by the theoretical models of nano-concrete freeze-thaw damage in this paper are in good agreement with the actual freeze-thaw damage situation,and the fitting accuracy is high,and the theoretical value of freeze-thaw damage is close to the experimental value.Therefore,the freeze-thaw damage models constructed in this paper can better characterize the law of freeze-thaw damage degradation of nano-concrete materials under freeze-thaw cycles,and can effectively quantitatively analyze and accurately predict the freeze-thaw damage of nano-concrete and determine the freeze-thaw fatigue life of nano-concrete.