【作者】 孟德亮；

【导师】 李慧剑；

【作者基本信息】 燕山大学 ， 工程力学， 2014， 博士

【摘要】 混凝土是由水泥砂浆和石子等粗骨料组成的非均匀、各向异性的工程复合材料。由于其成本低廉，便于运输、施工和容易浇筑成任何形状，又具有良好的抗冻性、耐腐蚀性和较强的抗压强度，所以混凝土材料被广泛的应用在工业和民用等建筑中。但是，在一些重大的事故如地震中房屋的倒塌、一些堤坝的过早破坏等事件中，人们发现除去个别因施工质量等因素外，混凝土材料均没有达到设计时的强度就已发生破坏。后来经过研究发现，之所以混凝土结构的构筑物远低于设计值便发生灾变破坏，是因为人们没有考虑尺寸效应的影响。以往各国学者对混凝土的各种尺寸效应研究了很多，本文主要从混凝土试件的不同表面状态、不同骨料粒径这两种尺寸效应来研究它们对混凝土试件破坏的影响。本文研究手段主要是借助试验的方法。不同表面状态的试件分为浇筑表面的试件和切割表面的试件，浇筑表面试件为在试模里直接浇筑形成，试件外层主要为砂浆层。切割表面试件为由一大块混凝土试件切割而成，试件外层露出很多粗骨料。不同骨料粒径的试件为混凝土试件中骨料粒径分别为5-10mm、5-15mm、5-20mm。先对不同的试件进行了静压试验，对静压试验后试件的强度值、应变值进行了对比，并计算出了各个试件的吸收能。通过这些数值的对比，发现浇筑表面的试件无论是在强度值、应变值还是在吸收能上均大于切割表面状态的试件。不同表面状态下不同骨料粒径的试件在这三个参数的对比上也得到了一致的规律，即最大骨料粒径较小的试件均大于最大骨料粒径较大的试件。接下来用白光散斑法分析了试件表面变形场的不同。文中用应变场涨落来定量分析混凝土试件应变场的局部化程度。试验后对比发现，不同的表面状态和不同的骨料粒径对试验后试件的应变涨落有着明显的影响，试件的局部化程度也不同，最终试件发生破坏的方式也不同。又对不同种类的试件进行了疲劳加载的试验。试验采集中分别借助了白光散斑法、超声法、声发射和低场核磁共振扫描的方法。通过白光散斑法的采集计算，得到了不同试件加载过程中的应变场。通过对比发现，这两种尺寸效应对混凝土试件的位移场及应变场的演化、剪切应变场的演化也有明显的影响，不同试件会有不同的破坏。用超声波法对疲劳后的试件进行了内部探伤，发现试件表面状态不同，骨料粒径不同，试件内部的损伤量是不一样的，即尺寸效应对试件的内部损伤产生了不同的影响。用声发射法分别对静压加载和疲劳加载的试件进行了采集。试验发现在这两种加载形式下，得到了与前述试验方法大致相同的尺寸效应影响试件破坏的规律。为了进一步分析不同试件内部的孔隙破坏情况，对疲劳后的试件进行了核磁扫描。通过核磁扫描后分析得到的T2谱图、孔径分布图、孔隙度以及成像图等，发现不同骨料大小以及不同表面状态的试件疲劳后，内部所表现出的孔隙破坏特征与之前所用试验方法总结得到的规律一致。这也进一步验证了本文总结的两种尺寸效应对混凝土灾变破坏影响规律的准确性。更多还原

【Abstract】 Concrete is a kind of nonhomogeneous and anisotropic engineering compositematerial which is composed of cement mortar and coarse aggregate such as gravel.Because of its low cost, convenient transportation and construction and easy pouring intoany shape, but also has good frost resistance, corrosion resistance and high compressivestrength, so the concrete materials are widely used in industrial and civil buildings.However, in some major accidents such as housing collapse in earthquake, and prematurefailure events in some dam, people found that removal of individual factors suchas construction quality, concrete materials are not reached the design strength but theyhave been destroyed. Later, after the research people discovered that why the catastrophicfailure occurred when the buildings of the concrete structure are far lower than thedesign value, because people do not consider the influence of size effect.The previous scholars have studied a lot about concrete’s various size effects. Thispaper is mainly to study the effects on the specimens from the concrete specimensof different surfaces and different aggregate sizes these two kinds of size effects. Thisstudy is mainly by experiments. Different surfaces of specimens were dividedinto pouring surface specimens and the cut surface specimens.Pouring surface specimens are formed in test moulds. The outer of the specimensare mainly mortar layer. The cut surface specimens are cut by a chunk of concretespecimens. The outer of specimen revealed many coarse aggregate. In different aggregatesize of concrete samples, aggregate diameters were5-10mm,5-15mm,5-20mm.In this paper, we did the hydrostatic pressure test to the different specimens first. Wecompared the strength value and the strain values and we calculated the absorption energyof each specimen. By comparing these values, we found that both in strength value andstrain value or in the absorbed energy pouring surface specimens were higher than cutsurface specimen. In different surface states, different aggregate size specimens in thethree parameters have been consistent, namely the smaller maximum aggregatediameter specimens were greater than the larger maximum aggregate size specimens. Next we used white light speckle method to analysis the deformation field of the specimens’surface. We use strain field fluctuations to quantitative analysis the localization degree ofconcrete specimen strain field in this paper. After the test comparison, we found thatdifferent surface states and different aggregate size have obvious different effect onthe specimen’s strain fluctuation. The localization degrees are different andthe failure modes are different at last.In this paper, we made fatigue loading to the different types of specimens. In the test,we respectively used the white light speckle method, ultrasonic method, acousticemission and low field nuclear magnetic scanning method. By using the white lightspeckle method to collect and calculate, we obtained the different strain field duringloading process. By contrast, these two kinds of size effect also have evident influence onthe concrete displacement field, strain field and shear strain field evolution. Differentsamples have different failure. We use ultrasonic to conduct internal inspection forspecimens after fatigue. Then we found that if specimens’ surface states and aggregatesizes were different, damage amount of specimens were different. That is, size effectsproduce different effect to the internal damage of the specimen.In this paper, we used acoustic emission technique to collect the dates of staticloading and fatigue loading specimens. The test found that in the two kindsof load forms, the influence of size effect is roughly the same as the front tests’ laws.Finally, in order to further analyze the internal pore destruction of the differentspecimens, we conducted MRI scanning on the fatigue specimens. By analyzing T2spectra, pore size distribution, porosity and MRI imaging, we found that when differentsurface states and different aggregate sizes specimens were fatigue loaded,internal pore destruction features of concrete specimens are same as the front tests. Thisalso further confirmed the accuracy of influence law summarized in this paper about howtwo kinds of size effect affect the concrete destruction.更多还原