The Study Of The Viscoelastic Properties On C-S-H And The Aggregate Of Concrete

Concrete is a kind of construction material,which is composed of cement and aggregate add water mixing.Under the long-team load will be accompanied by the creep phenomenon of concrete,and the creep mechanism comes from two aspects: the creep of material itself and the damage evolution.As well as the damage evolution,material creep will reduce the strength of concrete structure,then shorten its life.Therefore,it is necessary to study the viscoelastic properties of concrete under the continuous load.Generally,the viscoelasticity of concrete comes from its internal product.This study focused on the viscoelastic properties of C-S-H gel and the aggregate of concrete.On the first part of this thesis,the C-S-H gel powder was obtained to study the microstructures and mechanical properties,then used the nanoindentation technique to carry out the creep deformation of C-S-H on samples of cement pastes.The effect of two different kinds of loading history were investigated.Based on the experimental results,the creep deformation of C-S-H always occurred,and it was obvious that the higher loading rate,the greater the creep displacement.As well as the creep load,with the increase of creep load,the displacement became greater.On the second part,the study focused on the micro mechanical properties of the aggregate of concrete.The nanoindentation technique was carried out to investigate the creep deformation of the aggregate of concrete,and two different kinds of loading history methods were used.It was found that the creep deformation always occurred: the higher loading rate,the greater the creep displacement,and the higher creep load,the greater the creep displacement.Because the creep displacement occurred significantly,this implied that viscosity exists in C-S-H and the aggregate of concrete.Based on the experimental results,the elastic-viscoelastic-viscous model was adopted to describe the creep character of C-S-H and the aggregate of concrete.It was seen that the relation between retardation times and loading history approximately obeys a power law.