THESIS
2018
xvii, 136 pages : illustrations (some color) ; 30 cm
Abstract
Cementitious materials are the most consumed materials in the word. In nanoscale and mesoscale, calcium silicate hydrate (C-S-H) contributes significantly to the cohesiveness and durability, determining the engineering properties in the macroscale. In the microscale, cement paste becomes the research concentration due to its typical performance in both chemical and mechanical aspects, acting as a bridge to link the mesoscale and macroscale. Considering its hierarchical characteristics, modelling the cementitious materials from nanoscale into microscale would pave the way in both understanding the properties and uniting the methodology.
In the study of this thesis, first of all, an upscaling numerical mesoscale model of C-S-H for the investigation of transportation properties is propose...[
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Cementitious materials are the most consumed materials in the word. In nanoscale and mesoscale, calcium silicate hydrate (C-S-H) contributes significantly to the cohesiveness and durability, determining the engineering properties in the macroscale. In the microscale, cement paste becomes the research concentration due to its typical performance in both chemical and mechanical aspects, acting as a bridge to link the mesoscale and macroscale. Considering its hierarchical characteristics, modelling the cementitious materials from nanoscale into microscale would pave the way in both understanding the properties and uniting the methodology.
In the study of this thesis, first of all, an upscaling numerical mesoscale model of C-S-H for the investigation of transportation properties is proposed through molecular dynamic (MD) method. In order to enlarge the simulation scale, the generally accepted MD model for C-S-H and water is simplified by the coarse-grained (CG) method. Firstly, the modified Lucas-Washburn equation is introduced in the paralleled nano walls. Then, the effects of dynamic contact angle and inertia force, slip length and viscosity modification are taken into consideration with a pore size of 8 nm (paralleled walls), of which the theoretical modification matches the imbibition trends generally. The similar modification rule matches other pore sizes such as 12 nm, 16 nm and predicted 20 nm, proving both the feasibility of the upscaling transportation model for C-S-H and the reliability of the numerical modification during the transportation process.
Secondly, an upscaled mesoscale model for hydrated cement in simulating the hydration process is proposed with MD. The hydration process in this scale is modelled through the grand canonical Monte Carlo (GCMC) process. Then, the dynamic, structural and mechanical properties are explored through mean square displacement (MSD), radial distribution function (RDF), pore systems and uniaxial tension test based on the constructed C-S-H gel model. The structural and mechanical performance confirm the consistency with both experiments and other modelling works.
At last, the microscale model is constructed based on the existing microstructure of cement paste. Uniaxial tension are utilized for the investigation of mechanical properties and failure mechanism analysis. Besides, experimental comparison proves the feasibility of MD in modelling the micro-scale cementitious materials.
The major contribution of the thesis is to realize the multiscale simulation of cementitious material bridging the nanoscale into microscale. The details are as follows:
1. A sub-mesoscale model of C-S-H, utilizing the molecular dynamic (MD) method, was established to investigate the nanopores transportation of water. The corresponding theoretical modifications are considered to improve the traditional transportation model. (Chapter 3)
2. A mesoscale model in modelling the hydration and precipitation process of C-S-H is proposed. Both the system properties and mechanical properties are converted well from the nanoscale. (Chapter 4)
3. The construction of microscale model is based on the existed microstructure. Uniaxial tension results indicate the consistency between the mechanical properties and degree of hydration. In addition, the discrete element method, molecular dynamic simulation, proves the feasibility in the microscale application of cement paste. (Chapter 5)
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