Research On Creep And Creep Recovery Performance Of Fly Ash Concrete

Deformation has an important impact on the long-term performance of concrete structures.Creep may increase the deformation and the additional eccentricity of structures,especially in high rise and mass concrete structure.At the same time,during the construction and service period of concrete structure,it is difficult to keep the stress of the building structure unchanged.With the progress of construction,the stress of the bottom structure increases continuously.However,with the reinforcement and transformation of the building structure in the later period of structural service,the stress at the bottom of the structure will be shared by the strengthened structure,and the reduction of the stress at the bottom will lead to the creep recovery.In water conservancy construction,the change of water level causes the structure to be stressed and unloaded periodically,so it is necessary to study the creep and creep recovery of the structure.The addition of fly ash will affect the microstructure and mechanical properties of concrete.The creep mechanism of fly ash concrete is very important to analyze its time-dependent deformation performance.Through the summary and analysis of concrete creep mechanism,it is found that single creep mechanism can not make a reasonable explanation for concrete creep phenomenon.The microstructure of fly ash concrete and pozzolanic effect of fly ash are analyzed.The effect of micro aggregate effect and pozzolanic reaction on creep of fly ash concrete is discussed.According to the time-dependent development law of concrete creep,the creep rheological model of concrete is proposed,and the constitutive equation and creep equation are established according to different stress states.The existing research shows that fly ash has a great influence on the development of concrete strength.By considering the influence of fly ash on concrete creep,the method of considering fly ash content,water binder ratio,environmental relative humidity and other factors is used to modify B4 model.Based on the development law of concrete creep recovery,and considering the factors affecting creep recovery,such as load holding time and loading age,a creep recovery model of benchmark concrete is established.The influence of fly ash on creep recovery is analyzed.The prediction model is modified by using the influence coefficient.The creep and creep recovery data of fly ash concrete are collected to fit the model.Finally,the creep and creep recovery model are compared with the test data to verify the accuracy and law of the model.The model prediction results are in good agreement with the test results and the development law is consistent.