Fundamental Understanding of NOx Sequestration Capacity And Pathways in Nano-TiO2 Engineered Cementitious Materials

The ubiquity of concrete in the urban environment and the upscaling of nanomaterial production have prompted interest in the incorporation of titania (TiO2) nanoparticles into cementitious materials. Air purification by TiO2-based cementitious materials occurs by photocatalysts that capture nitrogen oxide species (NOx) from the atmosphere, then oxidizing them into nitrite and nitrate species. Because nitrite- and nitrate-based corrosion inhibitors are effective in improving corrosion resistance in reinforced concrete, there is potential to develop nano-TiO2 engineered cementitious materials that transform atmospheric NOx into corrosion inhibitors. To provide guidelines for engineers and scientists to design such materials, a fundamental understanding of the NOx sequestration capacity and pathways in cementitious materials is needed. This dissertation first examines the effects of TiO2 nanoparticles on cement hydration. The inclusion of TiO2 nanoparticles accelerates the early age hydration of TiO2-modified OPC pastes due to nucleation and growth effects induced by the addition of TiO2. However, TiO2 retards the early age hydration of CAC samples possibly due to the presence of sulfate ions on the surface of the TiO2 nanoparticles. TGA and XRD results reveals that the early age hydration, which is affected by TiO2 inclusion, does not affect the hydrated cementitious phase composition or proportionality after 28 days of curing. The SEM/EDS analyses show that the TiO2 nanoparticles are uniformly distributed in the cementitious hydrates and exhibit no preference to binding with any particular hydrated phases, ensuring a consistent photocatalytic performance of the TiO2-modified cementitious materials. The photocatalytic performances of both TiO2-doped and TiO2-coated cementitious materials are examined in this research. Ordinary portland cement (OPC) samples exhibit higher NOx and methylene blue photodegradation efficiencies than calcium aluminate cement (CAC) samples. The difference indicates that different NOx sequestration pathways occurred in these cements and are likely due to differences in chemical composition and hydrated cementitious phases. For TiO2-coated cementitious materials, the inclusion of a hydrophobic SiO2 layer improves the bonding between the TiO2 coating and the cementitious substrates but compromises the photocatalytic efficiency. Therefore, it is important to consider the bond strength, the desired interactions between the coated surface and water, and the photocatalytic performance when selecting and designing TiO2-coated cementitious materials. This research also develops a novel experimental approach that combines water-based wet chemical extraction, UV-visible spectrophotometry, and ion chromatography to quantify the NOx sequestration capacity in both plain and TiO2-modified cementitious pastes. Compared to plain cement pastes, TiO2-modified cement pastes exhibit higher NOx uptake (in terms of nitrite and nitrate detected in the material) due to the activation of photocatalytic reactions, a greater surface area, and an increased amount of micropores from the addition of TiO2. The detection of nitrite and nitrate ions in unmodified cement paste demonstrate these cementitious materials’ intrinsic NOx sequestration capacities, which are related to the surface-related catalyzed heterogeneous reactions and the alkaline environment.Ph.D

The applications of combined use of fiber reinforced cementitious composites (FRCC) and fiber reinforced polymers (FRP)

In this thesis, the combined use of Fiber Reinforced Cenmentitious Composite (FRCC) and Fiber Reinforced Plastic (FRP) in two applications is studied. First, the FRCC plate has been investigated as an anchor to improve the performance of FRP sheets on concrete members. Second, the high-strength fiber reinforced cementitious composites (HSFRCC) has been studied as a joining material for permanent formwork elements with protruding GFRP that will be embedded in the joint. For the first application, to increase the bond and deformation capabilities of FRP sheets employed in the strengthening of concrete members, the precast FRCC plate is glued on top of the FRP sheets. In order to measure the improvement in terms of ultimate load and deformation capacity and to study the failure mechanisms around the anchored area, the direct shear bond test is performed on concrete prisms with bonded FRP. Several sets of tests have been carried out with anchoring plates of different FRCC compositions and lengths. Comparison with the control sample shows that the installation of FRCC plate can significantly increase both the bond and deformation capacities (by up to 100%). Based on the shear bond test, two types of FRCC plate materials were found to be particularly effective and selected for strengthening of beam members to be tested under four point bending. Comparison with control members (without anchor) and those with conventional U-shape FRP anchors indicates that both the ultimate load and central deflection can be improved by the new anchoring method. The second application is related to the development of permanent formwork for durable concrete structures., Formwork elements, fabricated with pseudo-ductile cementitious composites (PDCC) and embedded glass fiber reinforced polymer (GFRP) reinforcement, need to be effectively joined together. A novel jointing method, involving the embedment of GFRP in high-strength fiber reinforced cementitious composites (HSFRCC), is proposed. Direct pull-out test is carried out to investigate the bonding capacity between the HSFRCC and GFRP reinforcement. From the experimental data, interfacial parameters are extracted for calculating the required embedded length of GFRP bars to ensure sufficient bonding capacity. According to the test results, the required embedded length of GFRP bars is about 21d (where d is the diameter of GFRP bar). Beam members with joined and monolithic PDCC formwork are prepared and tested under four point bending. In the presence of the joint in the formwork, the load capacity decreases by only 5%. Also, the ultimate load is higher than the value obtained from conventional reinforced concrete design calculations. The feasibility of the joining method for practical applications is hence verified

Nano TiO2-Engineered Cementitious Materials with Self-Cleaning Properties

Due to the Ubiquity of Concrete in the Urban Environment and the Upscaling of Nanomaterial Production, the Incorporation of Nanoparticles into Cementitious Materials Has Gained Increased Attention. This Chapter Focuses on Understanding the Self-Cleaning Properties of Nano TiO2-Engineered Cementitious Materials, Including Self-Cleaning Mechanism and Types (Section 8.2), Effect of Nano-TiO2 on Cementitious Substrates (Section 8.3), and Self-Cleaning Performance and Application (Section 8.4). Two Attributes Are Studied to Understand the Self-Cleaning Capacity of These Materials: TiO2-Induced Photocatalysis and Surface Superhydrophilicity. Future Study Should Focus on the Expanding Use of Visible-Light-Responsive Nano Photocatalysis in Cementitious Materials

An efficient algorithm for online management of 2D area of partially reconfigurable FPGAs

Partially Runtime-Reconfigurable (PRTR) FPGAs allow hardware tasks to be placed and removed dynamically at runtime. We present an efficient algorithm for finding the complete set of maximal empty rectangles on a 2D PRTR FPGA, which is useful for online placement and scheduling of HW tasks. The algorithm is incremental and only updates the local region affected by each task addition or removal event. We use simulation experiments to evaluate its performance and compare to related work. © 2007 EDAA

Joint Management of Energy Harvesting, Storage, and Usage for Green Wireless Sensor Networks

Recently, energy harvesting has been emerging as a promising technique to prolong the lifetime for wireless sensor nodes. Most existing efforts address the design of energy harvesting and sensor node subsystem separately or ignore some real-world constraints. In this paper, we study how to codesign the two subsystems and how to jointly manage energy harvesting, storage, and usage. We first propose a novel system architecture for energy harvesting which employs several supercapacitors to eliminate the conflicts on charging and discharging among different system components. Then, we present a method to schedule their charging and discharging, which is proved to be able to guarantee zero waste of the harvested energy if the battery is not full. Third, we propose an optimal algorithm to minimize different components’ capacity and two heuristic algorithms to maximize the system reward. We conduct extensive experiments based on real-life data traces. Results show that the proposed system architecture can harvest more energy compared to the state of the art, and the capacity optimization algorithm can choose the most suitable size for each system component

Efficient algorithms for 2D area management and online task placement on runtime reconfigurable FPGAs

Partial Runtime Reconfigurable (PRTR) FPGAs allow HW tasks to be placed and removed dynamically at runtime. We make two contributions in this paper. First, we present an efficient algorithm for finding the complete set of Maximal Empty Rectangles on a 2D PRTR FPGA. We also present a HW implementation of the algorithm with negligible runtime overhead. Second, we present an efficient online deadline-constrained task placement algorithm for minimizing area fragmentation on the FPGA by using an area fragmentation metric that takes into account probability distribution of sizes of future task arrivals as well as the time axis. The techniques presented in this paper are useful in an operating system for runtime reconfigurable FPGAs to manage the HW resources on the FPGA when HW tasks that arrive and finish dynamically at runtime. (C) 2009 Elsevier B.V. All rights reserved

Wetland Evolution and Driving Force Analysis in the Qingtongxia Reservoir Area

In recent years, the combination of river disruption and irrational human activities has caused serious damage to wetlands. Based on long-time-series remote-sensing images, this study applied the land use transfer matrix and landscape index method to investigate the dynamic evolution and driving forces of the Qingtongxia wetland in the upper reaches of the Yellow River from 1999 to 2020. The results show that the land use types of Qingtongxia wetland changed insignificantly from 1999 to 2020, with the area of water and grassland decreasing and the area of reed wetland, beach, farmland and forest increasing. The spatial changes in the watershed changed the distribution of other land uses within the wetland, with the watershed concentrating in a southwest–northeast direction and shrinking in the southwestern part of the wetland area between years. From 1999 to 2011, the wetlands were restored, the landscape became less fragmented and simpler in shape and the dominant species developed significantly. From 2010 to 2020, the wetlands were disturbed and, as a new tourist destination, the planning and renovation work increased fragmentation and the complexity of the patches. The complexity of the patch shape increased, and, at the same time, with the implementation of various conservation measures, the development of the dominant species within recovered. The drivers of change in the different land use areas within the wetlands of the Qingtongxia reservoir are dominated by flow, and the drivers of the evolution of landscape patterns within the wetlands are closely related to the population and gross regional product, in addition to being influenced by flow. In recent years, increased fragmentation has been the main reason for the decline in bird habitat quality. Maintaining bird diversity in the wetlands of the Qingtongxia reservoir can be based on rational planning of the proportion of different land uses within the wetlands, reducing landscape fragmentation by limiting human activities in the corresponding areas, as well as appropriate flow control measures. This study provides some reference for biodiversity conservation within wetlands