【作者】 高翔；

【导师】 黄卫；

【作者基本信息】 东南大学 ， 道路与铁道工程， 2018， 博士

【摘要】 水泥基材料是一种典型的多尺度、多物相的材料,其宏观表现是由微观尺度的性质决定的。研究水泥基材料的微观性质,有助于掌握材料本质、预测宏观行为。当下用于表征水泥基材料微观性质的测试技术纷繁多样、优缺点明显。本文围绕水泥基材料的微观表征展开,使用了包括基于扫描探针显微镜的形貌成像与模量成像;基于仪器化压入的点阵纳米压痕、原位纳米压痕和微米压痕;基于扫描电镜观测的背散射电镜成像及附带的能谱点探测和线扫描;光镜观测成像;X-ray断层扫描成像;压汞;热重分析等在内的技术手段。基于对这些表征技术应用现状的调研,分析这些试验手段在测试水泥基材料性质时的适用性和影响因素,讨论试验数据的提取方法处理方法。在实测微观性质的基础上,探索试验数据的深入应用,包括多尺度建模和验证、多种试验数据联合分析、以及这些微观研究手段在其他材料上的应用。以期联合运用这些试验技术和数据处理方法,相互补充,实现高效、合理地表征水泥基材料的微观性质。第一,提出了基于扫描探针显微镜的动态模量成像技术在水泥基材料微观表征中的应用。该技术具有精度高的优势,有助于捕捉材料性质变化的细节。提出动态模量成像试验结果中线数据和面数据的提取方法,讨论了样品表面粗糙度、预设数据点间距和荷载大小对试验结果的影响。得出试验结果对表面粗糙度和预设数据点间距不敏感,但荷载大小会决定实测数据的有效性。推荐使用准静态荷载为4μN、动态荷载为3.5μN的加载模式,在此设置下,不同物相的储能模量之间差异明显,而同一物相的储能模量值波动程度相对较小,有利于对水泥基材料的微观物相进行识别;第二,针对水泥基材料微观力学性质分析和微观形貌观测试验中对试件表面平整度的高要求,提出使用环氧树脂真空镶嵌试件后进行打磨抛光的方法和步骤。环氧树脂的填充有助于支撑孔隙结构,减缓或避免磨抛环节对样品的侵蚀,从而减小样品表面的粗糙度。在力学性质测试环节,一般情况下树脂镶嵌对实测值的影响不大,但对于材料孔隙率较大的情况,如水灰比较高的净浆、或骨料和浆体基质之间的界面过渡区,树脂镶嵌会高估其力学性质;第三,提出了联合使用光镜、电镜观测和动态模量成像技术识别水泥基材料中微观物相的方法,并基于动态模量成像实现微观形貌和微观力学性质的表征。利用动态模量成像数据点间距小、分辨率高的优势,识别并表征了水泥颗粒和矿渣颗粒内部水化产物层的厚度和力学性质,发现了未水化C₃S颗粒与水化产物之间存在1μm²μm的界面过渡区,这些信息在其他试验方法中容易被忽略或无法被量化;第四,联合使用仪器化压入、动态模量成像、能谱探测和扫描技术识别了水泥基材料中的微观物相并表征了其力学、化学性质。基于原位纳米压痕和能谱点探测,得到水泥-矿渣复合体系中的内部或外部水化产物的力学性质不随其化学成分而变化,根据各种水化产物典型的模量值和化学元素占比可以实现物相的识别;基于动态模量成像和能谱线扫描,印证了未水化C₃S颗粒与水化产物之间界面过渡区的存在;基于原位纳米压痕和动态模量成像,得到压痕模量和储能模量呈较好的线性关系,且二者基本相等;基于点阵纳米压痕,研究了大样本数据的解卷积方法,得到了与原位压痕结果相近的不同水化产物的力学性质结果;基于微米压痕实测了材料净浆尺度的力学性质,得出被测区域力学性质的大小由区域内各微观物相的含量变化而决定;第五,基于不同微观物相实测的力学性质和体积含量,使用基于连续介质力学的模型预测了净浆尺度的力学性质,讨论孔隙、水化产物和未水化物的模量和体积含量取值对模型结果的影响,并使用微米压痕的结果对计算得到的净浆等效模量进行了验证;第六,在研究和讨论水泥基材料的微观表征手段和数据处理方法的基础上,尝试联合使用多种试验手段对同一待测指标进行表征和量化。如联合使用热重分析、背散射电镜图像分析和点阵纳米压痕数据计算水泥-矿渣复合体系的水化程度;联合使用压汞、背散射电镜图像分析和CT图像分析研究经历冻融循环的净浆试件的孔径分布特征,并基于孔径分布参数计算不同水灰比净浆受冻后的渗透性变化。综合来讲,本文提出、应用并深入讨论了多种水泥基材料的微观表征技术和数据处理方法,对各种方法的优劣势和适用场合进行了评述,对多种试验方法的联合使用进行了实施,尝试合理、高效地使用这些表征技术,实现对水泥基材料的微观性质进行多方位的表征,并为多尺度建模提供基础参数。更多还原

【Abstract】 Cementitious materials are characterized with multi-scales and multi phases.Many macroscopic behaviors originate from the nano-scale properties of cementitious materials.It is fundamental requirement to understand the mechanism at the nano-scale level for further material tailoring to achieve better concrete.In this study,the characterized methods for the micro mechanical properties,microstructure and morphology of cementitious materials are investigated.The coupled techniques of the modulus mapping of scanning probe microscope（SPM）,the in-situ and discrete nanoindentation（NI）,the discrete microindentation（MI）,the back-scattered eletron microscope image analysis（BSE-IA）,energy-dispersive X-ray spectroscopy（EDS）,optical image analysis,X-ray computed tomography（CT）,mercury intrusion porosimetry（MIP）,thermal gravity analysis（TGA）,etc.are adopted to characterize the cementitious materials at nano-and micro-scales.The following aspects are discussed:Firstly,the application of SPM-modulus mapping in cementitious materials is proposed.The SPM-modulus mapping allows to measure the mechanical properties without causing plastic deformation to the materials and with much higher spatial resolution compared to NI technique.For better utilizing SPM-modulus mapping to identify and quantify the microstructure morphology of individual phases in cementitious materials,this study explored several critical aspects related to the experimental protocol and the data processing during SPM measuring for both ordinary Portland cement paste and slag-blended cement paste.Two data processing methods are proposed to extract the line data and the area data from the mapping images.The effects of the pixel spacing,the surface roughness of sample and the magnitude of loads on the measured mechanical properties are discussed.The results of this study will help to select the proper testing parameters for identifying different phases and quantifying their sizes under a nondestructive testing condition at a much higher resolution.Secondly,the vacuum impregnation method is adopted to prepare the epoxy impregnated concrete and paste samples.The aspects of microscopic properties of impregnated and non-impregnated samples are evaluated and compared in terms of the surface elevation,the indentation modulus,and the thickness of the interfacial transition zone between the aggregate and the paste matrix(ITZ_agg-paste)as well as that between the residual C₃S clinker and the hydration product(ITZ_C3S-HP).The results show that the epoxy impregnation is favored in the microscope image analysis,nanoindentation measurement and characterizing the ITZ_C3S-HP by SPM modulus mapping.It is not recommended for characterizing the thickness of ITZ_agg-pastegg-paste by SPM modulus mapping and for measuring the micromechanical properties at the paste scale by MI.Thirdly,the comprehensive investigation on the chemical-mechanical-morphological properties of CSH gel in both ordinary Portland cement paste and slag-blended cement paste is conducted by using the coupled techniques of SPM-modulus mapping,NI and EDS.The thickness of the inner C-S-H（IP）layer is precisely measured for the first time by modulus mapping,it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials.An interface transition zone（ITZ）is found between the unreacted C₃S grain and the surrounding inner C-S-H layer.Fourthly,the mechanical properties of the five types of C-S-H in OPC and slag-blended pastes are measured,and they are not significantly affected by their chemical compositions.A good correlation between the storage modulus and the indentation modulus of the individual phases is found.Moreover,the modulus at paste scale is measured by MI.And the differences between the measured paste modulus are found to be decided by the varied volume fractions of different phases at CSH scale.Fifthly,the effect of individual phases including the CSH,the residual clinker and the capillary pore on calculating the homogenized modulus of the hardened cement paste is quantified.It is found that the effective modulus of pore needs to be set as 12 GPa rather than0 GPa as the input for homogenization.As for the solid phases,the variation of the clinker modulus has limited influence on the homogenized modulus of the hardened cement paste.Whereas,the homogenized paste modulus increases significantly with the increasing fraction of high density CSH and the decreasing fraction of low density CSH.The results of this study can help to select appropriate input parameters for multiscale modeling the mechanical properties of cementitious materials.Finally,the coupled methods of TGA,BSE and NI are conducted to quantify the hydration degree of cement-slag system;the couple methods of MIP,BSE and CT are conducted to measure the distribution of pore in the paste sample influenced by the freezing and thawing.更多还原