5 Sep 2024

Extending CEMHYD3D to Simulate Hydration of Portland Cement Pastes with High Volumes of Silica Fume

Abstract: Silica fume (SF) influences the hydration rate of Portland cement in differ-ent ways depending on the physical and chemical properties of the SF. This study reports the impact of SiO2 content (%), loss on ignition (%), and Brunauer–Emmett–Teller (BET) specific surface area on the hydration re-action of SF-cement paste mixtures. This study used five types of SFs with varying SiO2 content, loss on ignition (%), and particle morphology. Five SFs were mixed with Class H oil well cement at each of two different re-placement levels (20% or 30% by mass), and the released heat of hydra-tion was measured using isothermal calorimetry. The results were used to improve the pozzolanic reaction simulation feature of the original Virtual Cement and Concrete Testing Laboratory software, which enabled the soft-ware to simulate a higher SF replacement ratio in a cement mixture with higher fidelity. Results showed that a silica fume’s SiO2 content (%), loss on ignition (%), and BET specific surface area significantly influence the heat release rate. The new simulation model agrees well with the measure-ments on all the pastes tested.

5 Sep 2024

Next-Generation Water Quality Monitoring during Dredging Operations: Knowns, Unknowns, and Path Forward

Abstract: Water quality monitoring data are routinely collected during dredging and placement operations to address various state and federal requirements, including water quality standards, with the intention of protecting ecosystem health. However, such efforts may be limited by the lack of a standardized national strategic focus and user-friendly streamlined interfaces to interpret the data. Inconsistencies in how and what data are collected and lack of consensus on scientifically backed biological-effects thresholds make it difficult to quantify potential dredging operations impacts (or lack thereof) both within individual projects over time and across multiple projects of differing characteristics. Summarized herein is an initial effort to define a scientifically backed path forward to improve the value of current and future water quality monitoring and management decisions based on water quality data collected. The provided turbidity data were generally below applicable state thresholds for two case studies but for a third case study did periodically exceed thresholds at depth. This includes providing rationale for strategic focus on the most relevant dredging operations and projects, based on three general site-specific data categorizations: (1) sediment type, (2) dredge type, and (3) ecosystem type.

4 Sep 2024

Comparison of Numerical Simulations of Heat-Induced Stress in Basalt

Abstract: Energy losses due to excessive noise and heat are primary liabilities in traditional mining processes. Some of the currently researched methods to improve these liabilities involve heating the rock to induce internal stress fractures that make it easier to extract or remove rock with traditional mining equipment. Physical experimentation has yielded useful data that have been applied to numerical simulations of the heating and fracturing of rock, and multiple such simulations have been developed in the commercial multiphysics simulator COMSOL. Since COMSOL is not widely available on DoD high-performance computers, the goal of this research is to develop methods of replicating simulations developed in COMSOL as simulations that run in Abaqus FEA, another commercial multiphysics simulator. In this work, a simulated basalt cylinder with a 25 mm radius and a 158 mm height is subjected to a surface heat flux approximating the effects of a laser beam applied to the top of the cylinder. Simulated stress distributions, displacements, and temperatures obtained from both simulators are compared. When comparable results were not obtained using both simulators, the differences in results were investigated using simplified versions of the simulation.