Hydraulic lime binders are considered a technological marvel which revolutionized construction techniques in antiquity. The core material is made of a binder that is a mixture of calcite and hydraulic phases, which are amorphous silicate compounds that nanostructurally polymerize into insoluble phases that harden even underwater, formed during the reaction between lime and reactive silicates such as volcanic ash. This is also what makes hydraulic lime so hard to radiocarbon (14C) date. These insoluble phases contain carbonates that may set centuries following their application, resulting in younger ages, which may contaminate the calcite fraction that is favorable for 14C dating. This calcite fraction forms upon the incorporation of atmospheric carbon dioxide during the setting of the hydrated lime. Therefore, different characterization methods are being constantly developed for identifying and characterizing the components of hydraulic lime-binders. In this work, we present a rapid characterization technique based on Fourier transform infrared spectroscopy (FTIR) that characterizes the atomic disorder and chemical environment of the carbonates and silicates fractions in the binder. The atomic disorder of the calcite crystallites was determined by the ν2 and ν4 vibrational modes, and the silicates were characterized by the main peak asymmetry and full width at half maximum (FWHM). Different hydraulic binders from Caesarea Maritima were examined, including Herodian mortars from the underwater breakwater and on-land plasters and mortars from the portʼs warehouse and vaults. Hydraulic binders, in which the calcite fraction in the binder shows atomic disorder that is comparable to modern plaster binders, was associated with silicates that have asymmetry and FWHM of clays and quartz. These materials are considered to be in good preservation state for 14C dating since their carbonates crystallites are disordered and did not interact with the environment chemically to form stable and ordered crystals. Interestingly, the atomic disorder of binders that underwent chemical alterations and recrystallization processes, are associated with reactive silicates aggregates such as volcanic ash (pozzolana). These results suggest a new way to prescreen materials for radiocarbon dating based on the composition of lime-binders and preservation state of the carbonate fraction and hydraulic products.

中文翻译：

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预筛选 Caesarea Maritima 中无序方解石的液压石灰粘合剂：使用 FTIR 表征化学环境

水硬性石灰粘合剂被认为是一项技术奇迹，它彻底改变了古代的建筑技术。芯材由一种粘合剂制成，该粘合剂是方解石和水硬相的混合物，它们是无定形硅酸盐化合物，它们在纳米结构上聚合成不溶相，甚至在水下也会硬化，是在石灰和反应性硅酸盐（如火山灰）反应过程中形成的。这也是使水硬石灰如此难以放射性碳的原因（14C) 日期。这些不溶相含有碳酸盐，在使用后可能会凝固几个世纪，导致年龄更小，这可能会污染有利于14C约会。这种方解石部分是在熟石灰凝固过程中掺入大气中的二氧化碳而形成的。因此，正在不断开发不同的表征方法来识别和表征水硬性石灰粘合剂的成分。在这项工作中，我们提出了一种基于傅里叶变换红外光谱 (FTIR) 的快速表征技术，该技术表征粘合剂中碳酸盐和硅酸盐部分的原子无序和化学环境。方解石微晶的原子无序由 ν 决定2和 ν4振动模式，并且硅酸盐的特征在于主峰不对称和半峰全宽（FWHM）。对来自 Caesarea Maritima 的不同水硬性粘合剂进行了检查，包括来自水下防波堤的 Herdian 迫击炮以及来自港口仓库和拱顶的陆上灰泥和迫击炮。水硬性粘合剂，其中粘合剂中的方解石部分显示出与现代石膏粘合剂相当的原子无序，与粘土和石英的不对称和 FWHM 的硅酸盐有关。这些材料被认为处于良好的保存状态14C测年，因为它们的碳酸盐微晶是无序的，并且不会与环境发生化学相互作用以形成稳定有序的晶体。有趣的是，经历了化学变化和重结晶过程的粘合剂的原子无序与火山灰（火山灰）等反应性硅酸盐聚集体有关。这些结果提出了一种基于石灰粘合剂的组成以及碳酸盐部分和水硬产物的保存状态来预筛选用于放射性碳测年的材料的新方法。