Experimental Study On The Interaction Mechanism Between Very Early-age Concrete And Structures

Concrete is one of building materials which is largest and most widely used in the world.And the interaction between very early-age concrete and structures has been one of the important research subjects of civil engineering.Using the interaction between very early-age concrete and structures as the research subject,two model tests are carried out by developing new test equipment,focus on the effect of different water cement ratio on the lateral pressure between very early-age concrete and structures,and the effect of different mixture ratio,different hydration time and different release rate on tangential force between very early-age concrete and structures.Analyze the influence rule and explore the influence mechanism.The main content and results of the research are given as follows:On the basis of summing up other researchers' results,a new apparatus which is used to measure lateral pressure and tangential force between very early-age concrete and structures is designed,the relevant test plan is proposed.The apparatus is made up with four parts which are the casting mould,power control equipment,data acquisition equipment and the external frame.The test plan includes the design of effect of water cement ratio on the lateral pressure,relative moving speed between very early-age concrete and structures,the design of contact pressure and effect of different contact surface roughness on tangential force.The experimental results show that the influence of different water cement ratio on the lateral pressure between very early-age concrete and structures can be observed by using this new apparatus and corresponding experimental methods.And the influence of different ratio,different hydration time,different release rate on the tangential force can be measured too.The lateral pressure and temperature of two groups of the very early-age concrete with different water-cement ratio are determined starting from the time of after pouring.The experimental results indicate that immediately after filling the formwork,the concrete is shown to act as a fluid exerting almost hydrostatic head.With the development of time,the difference of the lateral pressure distribution becomes larger,and the linear distribution of the vertical distribution is close to the nonlinear distribution,and this difference is more obvious in the later stage;The lateral interaction between very early-age concrete and structures is influenced by concrete mix proportion.The higher the concrete water cement ratio is,the closer lateral pressure is to the hydrostatic pressure and the faster the rate of decline of the lateral pressures;The decline of the lateral pressures mainly occurs in the hydration reaction stage,at this stage,the hydration product accelerates the formation of the material with the self bearing capacity,so the lateral pressure decreases rapidly and eventually disappears;In order to study the influence of shear rate,contact pressure,contact surface roughness on the tangential action,casting three groups of specimens as the contrast tests.The experimental results indicate that the tangential interaction between very early-age concrete and structures is mainly composed of bond stress and friction stress,and the initial tangential stress is mainly derived from the bond of cement mortar.Once the initial adhesion is destroyed,the friction effect will increase in the proportion of tangential effect.The bond force originates from the yield stress and viscous flow of the contact surface,and the friction force is proportional to the lateral pressure.The lower the concrete water cement ratio,the closer the relationship between tangential force and time,which is due to the increasing proportion of friction.With the development of concrete hydration,the initial tangential force is obviously increased,and the relationship between tangential force and time is more closely related.Test results show that the increase in drawing rate can lead to the increase in initial tangential force,,the relativity of tangential force in the middle and later stage and time is relatively flat;Lubricant can significantly reduce the initial tangential force,and the tangential force in the middle and later period is basically unchanged;A microscopic model of the interaction between the early concrete and the structure is established.From the perspective of meso level,the tangential force between very early-age concrete and structures is controlled by the interface layer,and the change of the interface layer properties,such as the thickness,viscosity,roughness,are the main reasons causing the change of tangential force.