Three-dimensional computer simulation of cementitious composites incorporating reactive nanomaterials
저자
발행사항
서울 : 세종대학교 대학원, 2024
학위논문사항
학위논문(박사)-- 세종대학교 대학원 : 건설환경공학 2024. 2
발행연도
2024
작성언어
영어
주제어
발행국(도시)
서울
형태사항
269 ; 26 cm
일반주기명
지도교수: Dong Joo KIM
UCI식별코드
I804:11042-200000729849
소장기관
The high costs and time-intensive nature of experimenting for new construction materials underscore the importance of 3D simulations. This thesis aims to enhance the current CEMHYD3D by integrating nanomaterial effects into simulations. Specifically, it focuses on predicting properties and microstructure evolutions in cement-based materials (CBMs), offering an alternative to costly experimental methods. This thesis includes five main contents, which are outlined as follows:
First, comprehensive information on nanomaterials in CBMs was presented. In addition, detailed effects of various nanomaterials on CBMs performance including workability and setting time, heat formation, and strength were provided. Furthermore, several models utilized for simulating the hydration process in cement paste have been outlined. Finally, the most widely used nanomaterials in CBMs and the most well- known cement hydration model were presented.
Second, the influences of cement particle distribution on the hydration process of cement paste were investigated by using a three-dimensional (3D) computer simulation. Pre-hydrated models were created using SEM-based correlation function (CF) and random distribution (RD) methods. The hydration process of cement paste was simulated using the model based on the CEMHYD3D. The RD method, simpler and faster in model generation compared to CF method, showed similar properties to the CF method for cement 133 at a water-to-cement ratio of 0.3. Despite agreement between RD and CF results, the authors suggest larger cement particles (>13 µm) in simulations exhibit multiple crystalline phases while smaller ones show a single phase. Validation with prior experimental data using ordinary Portland cement supported the efficacy of the proposed RD method.
Third, the hydration of nano-silica-incorporated cement paste using multiphase voxels within the CEMHYD3D model was investigated. These voxels, unlike the conventional single-phase ones, contain two phases, enabling a more refined representation of nano particle effects on cement hydration. Various types of multiphase voxels were developed to study the impact of nano-silica on hydration, considering nucleation sites and pozzolanic reactions. The model incorporated dissolution rate equations for major cement phases, allowing simulation of hydration based on quantity of calcium silicate hydrates. Simulation results aligned with experimental data for different nano-silica substitution levels (0.0%, 1.5%, 3.0%, and 5.0% by weight of binder) at a water-to-binder ratio of 0.45. This multiphase voxel approach offers a cost- effective method for micro-level simulation of cement-based materials containing nano particles, benefiting researchers and the construction industry by reducing computational costs.
Fourth, the effect of nano-CaCO3 (NC) agglomeration on cement paste hydration and microstructural evolution were investigated using 3D simulations. Few experimental studies have reported on the effect of NC agglomeration on the properties of CPs because the degree of NC agglomeration is difficult to control in experiments. Herein, NC agglomeration was first investigated in a simulation by assigning different contents of NC in water-filled voxels in CEMHYD3D. CPs containing 3 wt.% NC with a water-to-cement ratio (w/c) of 0.3 were considered in the simulation. Four levels (1, 2, 3, and 4) of NC agglomeration were investigated by assigning 8.5, 13.7, 19.8, and 27 vol.% of NC in a C–H voxel, respectively. Agglomeration level 0 refers to the condition in which no NC particles are deposited in a water-filled voxel. Isothermal calorimetry validated simulation results for plain CPs, showing level 3 agglomeration had the closest match. The influence of NC agglomeration was more pronounced in early hydration stages, impacting hydration rate, degree of hydration (DOH), C–S–H, and CH contents initially. However, despite these effects, ultimate DOH did not increase with the addition of NC particles.
Finally, the elastic modulus and Poisson ratio of hardened cement pastes (HCPs) were predicted by using two methods based on the results of microscale cement- hydration simulations performed using CEMHYD3D. Method 1 employed a continuum micromechanics model whereas Method 2 used finite element analysis. The predicted results were verified through compressive tests and correlation analysis. The elastic moduli and Poisson ratio predicted by both methods were consistent with the experimental results for HCPs with water-to-cement (w/c) ratios of 0.3 and 0.5, especially after 7 d. Furthermore, the integral absolute error values of the elastic moduli obtained via Methods 1 and 2 for HCPs with w/c of 0.3 were 8.67 % and 6.23 %, respectively, and for HCPs with w/c of 0.5 were 9.58 % and 5.67 %, respectively. As Method 1 is straightforward with time and cost efficiency compared to Method 2, it is highly recommended.
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