| Summary: | Concrete is responsible for 8% of the world’s CO2 emission, 9% of the global industrial water withdrawal, and 68% of sand and gravel mining, and the use of concrete is expected to continue increasing. With such a significant environmental impact, research on sustainable construction materials is essential. In particular, characterizing the chemo-mechanical properties could lead to the development and evaluation of sustainable materials. However, the spatial and temporal complexity of cementitious materials makes it challenging to characterize these materials. Here, a time-space-resolved Raman characterization framework was developed by combining confocal Raman spectroscopy and two-point correlation analysis. In addition, other chemical, mechanical, and crystallographic characterization tools were correlated with the Raman maps to link the structural features to the chemo-mechanical properties.
First, the space-resolved Raman analysis framework is established in order to study the structureproperty relationships in nacre material. The crystallographic texture of the nacre is correlated with its energy absorption capacity to study the toughening mechanism. A corporative movement of co-oriented stacks of aragonite platelets is observed, which defined the platelet stacks as another hierarchical structure contributing to the material’s toughness. Furthermore, the mechanical contributions of the microtexture in drumfish teeth were studied through a correlative chemo-mechanical characterization.
Next, the time component is added to the framework. Using the time-space-resolved Raman analysis framework, the molecular structure of C-S-H is analyzed, and the real-time hydration process of cementitious materials is visualized. The Raman spectrum of C-S-H obtained from insitu underwater Raman spectroscopy corroborates Gartner’s C-S-H model. Moreover, the earlystage cement hydration dynamics are visualized for the first time. The setting process is explained by the crystallization of calcium hydroxide and the percolation process, where the hydration products construct a network.
This framework can be applied to studying other chemical reactions in cementitious materials. Future applications include studying the hardening or deterioration process and identifying the effects of admixtures in cementitious materials. In addition, understanding the hydration kinetics in real-world conditions could lead to the advancement of sustainable construction techniques, such as carbonation curing or 3D concrete printing.
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