Research On The Influence Of Vibro Compaction On Heterogeneity Of Hardened Concrete

Vibro compaction is the most common method of compacting concrete in construction,but it's easy to cause segregation of the concrete,which influences homogeneity and durability of hardened concrete.Analyzing the mechanism of segregation caused by vibration and researching on the influence of vibration method and rheology of fresh concrete on segregation have great significance for reducing segregation and ensuring the consistency of macro properties such as strength and durability.This paper includes three parts:First,this paper analyses the mechanism of segregation caused by vibration and builds its data model.The fresh concrete is simplified as solid-liquid two-phase system in which aggregates suspend in mortar.The rheology of mortar is simplified as Bingham model and the shape of an aggregate is simplified as a sphere.The settling distance during vibration of a single aggregate in mortar is deducted on the basis of previous study in which the mortar is approximated as Newtonian fluid under low shear rate.Next,this paper designs experiments to compare with the conclusions from the mechanism analysis by researching on the influence of vibration method and rheology on homogeneity of aggregates distribution of hardened concrete.The aggregates distribution along direction of height is get by two methods,apparent density of different sections and cross section images.The difference ratio is used to evaluate the degree of segregation,which verifies the influence of vibration method and rheology on segregation.It can be concluded that plastic viscosity plays the main role in decreasing segregation,and the increase of vibration duration causes more segregation increment in concrete which has lower yield stress and plastic viscosity.But it doesn't agree with the mechanism analysis that the increase of vibration amplitude causes more segregation increment in concrete which has higher yield stress and plastic viscosity.So the mortar under low shear rate during vibration should be corrected as Bingham fluid with low yield stress,which can agree well with the experiment result.Finally,this paper studies the difference of strength and permeability of different height after different methods of vibration and analyzes its mechanism from microcosmic.Rebound method,electric flux and microhardness of interface transition zone are methods chosen.It can be concluded that the conjugation condition of lower interface transition zone of aggregates on top will be worse if the vibration amplitude is higher,duration is longer,and the yield stress and plastic viscosity of fresh concrete are lower.The relationships of the width of transition zone with the difference ratio of rebound value and electric flux can both be fit as linear ones.