Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO2 footprint, a sound description of their spatially resolved mineralogy is necessary. 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 characterize. Traditional spatially resolved techniques such as electron microscopy involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, synchrotron ptychographic tomography has been used to obtain spatially resolved information on three unaltered representative samples: neat Portland paste, Portland–calcite and Portland–fly-ash blend pastes with a spatial resolution below 100 nm in samples with a volume of up to 5 × 104 µm3. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 g cm−3 and a content 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 characterization of inner-product and outer-product C-S-H gels. The average density of the inner-product C-S-H is smaller than that of the outer product and its variability is larger. Full characterization of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamic modelling.
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机译:砂浆和混凝土是无处不在的材料,具有非常复杂的分层微观结构。为了充分了解它们的主要特性并减少其二氧化碳足迹,有必要对其空间分辨的矿物学进行合理的描述。发展这一知识非常具有挑战性,因为大约一半的水合水泥体积是纳米晶体成分水合硅酸钙(C-S-H)凝胶。此外,可能共存其他较差的结晶相(例如硅铁水石榴石或氧化硅铁),这甚至更难以表征。传统的空间分辨技术(例如电子显微镜)涉及复杂的样品制备步骤,这些步骤通常会导致伪影(例如脱水和微观结构变化)。在这里,同步加速器层析层析技术已用于获取三个未改变的代表性样品的空间分辨信息:纯净的波特兰糊,波特兰-方解石和波特兰-粉煤灰混合糊,样品中的空间分辨率低于100 nm,体积最多为5 ×10 4 sup> µm 3 sup>。对于纯净的波特兰糊剂,分光光度法研究的密度分别为2.11和2.52 g cm −3 sup>,纳米晶C-S-H凝胶和弱晶铁硅质水石榴石的含量分别为41.1和6.4 vol%。此外,通过空间分辨的体积质量密度信息可以表征内部产品和外部产品C-S-H凝胶。内部产品C-S-H的平均密度小于外部产品的平均密度,并且其变异性较大。报告了糊剂的全部特性,包括不同成分的细分,并将其含量与通过热力学建模获得的结果进行了比较。
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