Quantitative evaluation of segregation behaviors of fresh concrete and influential factors on them

本研究旨在从微观角度定量阐明新拌混凝土的离析行为，并建立一种新拌混凝土抗离析性能试验方法。主要研究成果如下：(1)研制了带有激光照射装置的单面剪切试验机，并利用激光层析成像技术研究了不规则颗粒在剪切力作用下的运动情况。基于Li提出的多相结构模型，从理论上研究了新拌混凝土中颗粒材料的特性和行为，阐明了新拌混凝土在非振动和振动条件下的力学本构关系，并提出了新拌混凝土的非线性变形抗力模型。(3)基于力学本构…研究了粗骨料颗粒在新拌混凝土中的分凝规律，得出了混凝土处于静止、振动、变形和流动状态时的平均沉降率。定量地阐明了平均粒径、新拌混凝土流动度、历时、粗骨料密度与基质砂浆密度之差、法向应力等因素对离析率的影响。(4)建立了新拌混凝土静力和振捣状态下的孔压及其随时间的变化关系，将达西定律应用于新拌混凝土的出水量和出水率的表达，并定量地阐明了影响出水率的因素。(5)推导了可用于评价新拌混凝土离析程度的重心偏移率公式。利用分层剪切箱与γ-射线密度仪相结合的装置进行了一系列剪切试验，验证了新拌混凝土的力学本构关系。该仪器是为测试新拌混凝土的抗离析性能而研制的。较少

This research aims to clarify quantitatively the segregation behaviors of fresh concrete by a microscopic approach, and to develop a segregation resistibility test method. The results of present work can be summarized as follows.(1)One-side shear test apparatus incorporating laser irradiation device was made and used to examine, by means of Laser-Aided-Tomography, the movement of irregular particles under shear force. The observed information such as changes in contact angles and moving distance of the particles were used for later theoretical parts of this work.(2)Characteristics and behavior of granular materials in fresh concrete were theoretically investigated based on the multi-phase structural model, which had been proposed by Li, co-operator of present work, to clarify mechanical constitutive laws of fresh concrete under both non-vibrated and vibrated conditions, and a non-linear deformation resistibility model of fresh concrete was proposed.(3)Using the mechanical constitutive … More laws, segregation behaviors of coarse aggregate particles in fresh concrete were investigated to formulate their mean sedimentation rate for the cases where concrete was in a standstill or vibrated state or in the state of deforming and/or flowing. Also, effects of various factors on the segregation rate, including mean particle size, fluidity of fresh concrete, elapsed time, difference in density between coarse aggregate and matrix mortar, normal stress, and others were quantitatively clarified.(4)After formulating pore water pressure and its change with time for fresh concrete in both static and vibrated states, equations for expressing both amount and rate of bleeding were derived by applying Darcy Law to bleeding of fresh concrete, and factors influencing on the bleeding phenomena were quantitatively clarified.(5)A formula of deviation ratio of gravity center, which could be used to evaluate the degree of segregation of fresh concrete, was deduced, and a segregation resistibility model was suggested for fresh concrete in static state.(6)A series of shear tests were made to verify the mechanical constitutive law of fresh concrete using an apparatus which was a stratified shear box incorporated with an γ-ray density meter. This apparatus was proposed for testing the segregation resistibility of fresh concrete. Less