Experimental And Theoretical Investigation On The Static And Dynamic Viscoelastic Behavior Of Concrete

Concrete is one of the most widely used materials in modern civil engineering construction, however, there has not been enough attention given to the viscoelastic property of concrete in the past one hundred years. In fact, the viscoelasticity is one of the fundanmental properties of concrete, which considerably influences the static and dynamic macro mechanical properties of concrete, such as creep, energy disspation, etc.The main contents of this thesis are as follows:(1) Based on the tranditional experimental methon on the creep and creep recovery of concrete, a new experimental protocol is proposed and conducted to test the static viscoelasticity of concrete. The deformation performances under loading, duration,unloading and after unloading process are tested in detail. The influences of duration time, load level and age on the short-term creep, hysteretic recovery, residual deformation and elastic modulus are tested and analyzed. In addition, the traditional definition of concrete creep is improved and modified based on the experimental observation.(2) The research achievements of creep mechanism are summarized, foucing on the similarities and differences between short-term creep and long-term creep of concrete.Based on the experimental observation of hysteretic recovery of concrete, the primary mechanisms of short-term creep are proposed. In addition, six frequently-used creep prediction models are calculated and analyzed respectively; the characteristics of different models in predicting long-term and short-term creep of concrete are compared.Based on the experimental data, a predition model for short-term creep of concrete is proposed.(3) The viscoelastic models are employed to describe the static viscoelasticity of concrete. Without any considerable external load applied, the hysteretic recovery of concrete after unloading reflects the viscoelaticity of concrete itself. Firstly, the static viscoelasticity of concrete is analyzed based on the hysteretic recovery. Then the development of residual strain under load duration is obtained from experimental data,and the time-dependent strain of concrete under ]oad duration can be calculated by subtracting the correspondence residual strain from tested creep strain at every moment.Finally, the viscoelastic mechanism of concrete is analyzed based on the experimental observation.(4) According to the uniaxial compressive dynamic modulus experimental method of asphalt mixture, the dynamic viscoelasticity of concrete is tested. The influeces of stress level and loading frequency on the dynamic modulus and hysteretic energy dissipation are analyzed, providing data support for further understanding of the dynamic viscoelasticity of concrete(5) Based on the experimental results of uniaxial compressive hysteretic test, the dynamic viscoelasticity of concrete are further calculated and analyzed. Based on the classical viscoelasticity theory, the theoretical expressions of viscoelastic properties of concrete are deduced, and the relevant parameters are identified based on experimental data. It can be concluded that the viscoelasticity theory is effective for describing the dynamic viscoelastic properties of concrete by comparative verification.