Ptychographic X-ray computed tomography data for three Portland cement pastes

Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO₂ footprints, a sound description of their (spatially-resolved) mineralogy is compulsory. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium-silicate-hydrate (C-S-H gel). Furthermore, other poorly crystalline phases (e.g. iron-siliceous hydrogarnet or silica oxide) may coexist which are even more difficult to characterise. Traditional spatially-resolved techniques like electron microscopies involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, we have used synchrotron ptychographic tomography for obtaining spatially-resolved information on three unaltered representative samples: neat Portland paste, Portland-calcite and Portland-fly ash blend pastes with spatial resolution below 100 nm in samples of up to 5×10⁴ mm³ of volume. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 gcm^-3 and contents of 41.1 and 6.4 vol% for nanocrystalline C-S-H gel and poorly crystalline iron-siliceous hydrogarnet, respectively. Furthermore, the spatially-resolved volumetric mass density information has allowed to characterise inner product and outer product C-S-H gels. The average density of inner product C-S-H is smaller than that of outer product and its variability larger. Full characterisation of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamical modelling. Ptychographic X-ray computed tomography provides 3D electron mass density and attenuation coefficient distributions of unaltered cement pastes with an isotropic resolution below 100 nm. This imaging technique allows quantitatively distinguishing between different components with very similar absorption contrast. Samples were measured at the cSAXS beamline: i) a neat Portland Cement (PC); ii) a PC-CC blend: 80 wt% of PC and 20 wt% of CaCO₃, and iii) a PC-FA blend: 70 wt% of PC and 30 wt% of fly ash. The main aim of this study is to have a better insight of the microstructure of the amorphous/nanocrystalline gels with submicrometer spatial resolution. It is worth noting that it is possible to determine the gel mass density and water content within the attained 3D resolution (about 100 nm). Here, we focused on the spatial distribution of the different components and in the variation of the electron density values which are very related to the mass density values. Special attention is paid to the density values of the amorphous (or nanocrystalline) components. The electron and mass density values of the C-S-H gel for three pastes are thoroughly analyzed. The density values range from 2.05-2.10 g·cm^-3 for high density C-S-H gel for neat PC and PC-CC pastes to 1.80 g^.cm^-3 for low density C-S-H gel in PC-FA paste. The density value of poorly crystalline iron-siliceous hydrogarnet component, r=2.52 g·cm^-3, has also been determined. A summary of our ongoing research focused on the analyses of cement pastes by synchrotron PXCT is reported and discussed. <strong>PC sample:</strong> tomo_beta_S02536_to_S03341_Hann_freqscl_0.35_0xxx tomo_delta_S02536_to_S03341_Hann_freqscl_1.00_0xxx <strong>PC-CC sample:</strong> tomo_beta_S04692_to_S06001_Hann_freqscl_0.35_0xxx tomo_delta_S04692_to_S06001_Hann_freqscl_1.00_0xxx <strong>PC-FA sample:</strong> tomo_beta_S03351_to_S04661_Hann_freqscl_0.35_0xxx tomo_delta_S03351_to_S04661_Hann_freqscl_1.00_0xxx砂浆与混凝土是无处不在的工程材料，拥有极为复杂的层级微观结构。为全面掌握其核心性能并降低二氧化碳足迹，对其空间分辨（spatially-resolved）矿物学特征进行准确描述是必要前提。获取该认知极具挑战性，因为水化水泥约有一半体积属于纳米晶组分——钙硅酸盐水合物（calcium-silicate-hydrate, C-S-H凝胶）。此外，其他低结晶度相（例如铁硅水榴石（iron-siliceous hydrogarnet）或氧化硅）可能共存，其表征难度更高。传统空间分辨技术（如电子显微技术）需经过复杂的样品制备步骤，这往往会引入人为伪影（例如脱水与微观结构改变）。 本研究采用同步辐射叠层成像断层扫描（synchrotron ptychographic tomography），对三种未受干扰的代表性浆体开展空间分辨信息采集：纯硅酸盐水泥浆体、硅酸盐水泥-碳酸钙复合浆体以及硅酸盐水泥-粉煤灰复合浆体。上述样品的体积可达5×10⁴ mm³，空间分辨率低于100 nm。针对纯硅酸盐水泥浆体，叠层断层扫描研究测得其纳米晶C-S-H凝胶与低结晶度铁硅水榴石的密度分别为2.11 g·cm⁻³与2.52 g·cm⁻³，体积占比分别为41.1%与6.4%。此外，借助空间分辨体积质量密度信息，可实现内产物与外产物C-S-H凝胶的表征。内产物C-S-H的平均密度低于外产物，且其密度变异性更高。本研究报道了所有浆体的完整表征结果，包括不同组分的分割结果，并将组分占比与热力学模拟得到的结果进行了对比。 叠层X射线计算机断层扫描（ptychographic X-ray computed tomography, PXCT）可在各向同性分辨率低于100 nm的条件下，获取未受干扰水泥浆体的三维电子质量密度与衰减系数分布。该成像技术可对吸收对比度极为相近的不同组分进行定量区分。 样品在cSAXS光束线进行测试：① 纯硅酸盐水泥（Portland Cement, PC）试样；② PC-CC复合试样：含80 wt% PC与20 wt%碳酸钙；③ PC-FA复合试样：含70 wt% PC与30 wt%粉煤灰。本研究的核心目标是借助亚微米空间分辨率，更深入地解析无定形/纳米晶凝胶的微观结构。值得注意的是，在本次研究达到的3D分辨率（约100 nm）范围内，可实现凝胶质量密度与含水率的测定。 本研究聚焦于不同组分的空间分布，以及与质量密度密切相关的电子密度值的变化规律。研究重点关注无定形（或纳米晶）组分的密度值。本研究对三种浆体中C-S-H凝胶的电子密度与质量密度值开展了详尽分析。纯PC与PC-CC浆体中的高密度C-S-H凝胶密度范围为2.05~2.10 g·cm⁻³，而PC-FA浆体中的低密度C-S-H凝胶密度为1.80 g·cm⁻³。低结晶度铁硅水榴石组分的密度值为2.52 g·cm⁻³，该结果也已测得。 本研究总结并讨论了当前正在开展的基于同步辐射PXCT的水泥浆体分析相关研究。 <strong>PC试样：</strong> tomo_beta_S02536_to_S03341_Hann_freqscl_0.35_0xxx tomo_delta_S02536_to_S03341_Hann_freqscl_1.00_0xxx <strong>PC-CC试样：</strong> tomo_beta_S04692_to_S06001_Hann_freqscl_0.35_0xxx tomo_delta_S04692_to_S06001_Hann_freqscl_1.00_0xxx <strong>PC-FA试样：</strong> tomo_beta_S03351_to_S04661_Hann_freqscl_0.35_0xxx tomo_delta_S03351_to_S04661_Hann_freqscl_1.00_0xxx