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12. Carbonation of 20-year-old blended cement pastes

Author

Li, Shuangxin

Subjects
628.74
Abstract

This PhD study aims to understand the carbonation mechanism of slag-rich waste forms and consequently benefits assessing the long term efficiency of immobilising waste materials with cementitious disposals. Three phases of experiments had been managed to achieve the aim. The first was an examination of three 20-year-old alkali-activated neat slag pastes. This section supplied the information about the immobilisation mechanism of alkaline metal cations within a cement system. The second was a characterisation of four 20-year-old water- activated slag-bearing pastes with curing at 40°C for the initial five years. This part concerned the effects of aging and heating treatment in cement hydration. The third was the accelerated and gentle testing of the water-activated pastes. The carbonation mechanism was mainly drawn by the micro-structural and nano- structural features of carbonated pastes and comparison to those of hydrated pastes. The obtained experimental data for the alkali-activated pastes confirmed the outstanding suitability of slag for fixing metal cations. It was because the formed C- S-H gel had been verified to be entirely tobermorite-based and possess a high substitution degree of bridging Si tetrahedra by Al tetrahedra. Meanwhile, the main fixation mechanism has been proved to be the incorporation of metal cations into the structure of the C-S-H through balancing the charges caused by the substitution. Thus, the significant incorporation of Ae+ within the structure of the C-S-H could be advantageous of immobilising alkaline cations through charge-balancing. The collapse of the C-S-H structure during carbonation has been observed due to not only decalcification, but also dealumination. Thus, according to the above findings, the carbonation is very likely to negatively affect the fixation of waste materials within cement systems. It was because, along with the extraction of the bridging Al tetrahedra, the charge-balancing cations were not needed and possibly would eventually be released. A conceptual model of carbonation occurring in hardened cement pastes has been proposed at the end of the chapter conclusion. More findings about the efficiency of different activators on hydration and the effects of curing temperature and aging on hydration have been discussed in details in the following chapters.

Published
2012

18. An investigation into the thermal conductivity of hydrating sprayed concrete

Author

Li, Shuangxin, Jones, Benoit, Thorpe, Roger, and Davis, Martin

Subjects
Concrete -- Investigations -- Analysis -- Mechanical properties, Business, Construction and materials industries
Abstract

ABSTRACT Information about the thermal conductivity of sprayed concrete is useful for calibration exercises using sprayed panels, where heat flows need to be estimated, and future enhancements to the method [...]

Published
2016
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19. Microstructure and composition characterisation of three 20-year-old GGBS-OPC blended pastes

Author

Li, Shuangxin

Subjects
Temperature -- Analysis, Portland cement -- Thermal properties -- Chemical properties -- Composition -- Analysis, Microstructure -- Analysis, Business, Construction and materials industries
Abstract

ABSTRACT It has become a common practice to use composite cement instead of pure Portland cement in many construction applications, then acknowledging the long-term microstructures and compositions of the composites, [...]

Published
2016
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25. Preparation, morphology and properties of natural rubber/carbon black/multi-walled carbon nanotubes conductive composites

Author

Xuefeng Ta, Li Yu, Jun Xu, and Li Shuangxin

Subjects
Materials science, 02 engineering and technology, Carbon nanotube, 010402 general chemistry, 01 natural sciences, law.invention, chemistry.chemical_compound, Natural rubber, law, Electrical and Electronic Engineering, Composite material, Tear resistance, Vulcanization, Dynamic mechanical analysis, Carbon black, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Atomic and Molecular Physics, and Optics, 0104 chemical sciences, Electronic, Optical and Magnetic Materials, chemistry, visual_art, Masterbatch, visual_art.visual_art_medium, 0210 nano-technology, Glass transition
Abstract

Nature rubber (NR)/carbon black (CB)/multi-walled carbon nanotubes (MWNTs) electrical conductive composites were prepared through latex compounding technique assisted by anionic surfactants containing phenyl ring moieties, NR/MWNTs masterbatch treated with silane coupling agent containing polysulphide bond and mixed with commercial NR, CB, sulphur and other ingredients and vulcanization. When MWNTs were dispersed in sodium dodecylbenzene sulfonate (SDBS) water solution, SDBS assembly on the surface of MWNTs prevent aggregation of MWNTs in water forming a stable MWNTs suspension. After MWNTs suspension mixed with NR latex, NR-MWNTs latex compound was co-coagulated to obtain the well dispersed NR/MWNTs masterbatch. In order to strengthen interface bonding between MWNTs and NR matrix, MWNTs in the masterbatch were treated with silane coupling agent by melt mixing process. During rubber mixing process, MWNTs dispersed in masterbatch thoroughly mixed with all the components and MWNTs homogenously embedded in NR matrix. Owing to homogenous dispersion of MWNTs, interfacial bonding between MWNTs and NR matrix as well as synergistic reinforcing effect between MWNTs and CB, NR/CB/MWNTs composites exhibited improved mechanical properties, dynamical storage modulus, glass transition temperature, electrical and thermal conductivity. Tensile strength, stress at 300 % strain, tear strength and steady state thermal conductivity of NR/CB/MWNTs composite with 4 phr MWNTs loading were increased by 12.36, 26.02, 16.95 and 102 %, respectively, and volume resistivity at room temperature of the composite was decreased by four orders of magnitude compared with NR/CB composite.

Published
2016

26. Design of high-efficient and universally applicable blades of tidal stream turbine

Author

Guangzhe Li, Chen Jianmei, Mingqi Xu, Wu Baigong, Xueming Zhang, and Li Shuangxin

Subjects
Airfoil, Engineering, Turbine blade, business.industry, Mechanical Engineering, Mechanical engineering, Control engineering, Stall (fluid mechanics), Building and Construction, Kinetic energy, Pollution, Turbine, Industrial and Manufacturing Engineering, law.invention, General Energy, law, Torque, Electrical and Electronic Engineering, business, Wells turbine, Mechanical energy, Civil and Structural Engineering
Abstract

The tidal stream turbine is the major device we use to obtain the kinetic energy of tides. The blades of the rotor are one of the essential parts which can convert tidal current energy into mechanical energy. Now most horizontal-axis turbine blade design theories are mostly based on the BEM (blade element momentum) theory and Glauert theory (e.g., WTperf, GHbladed). This paper comes up with a new method – Schmitz design. This method is easier, but they have the same physical philosophy. Also we change the chord length distribution to adapt the low stream velocity. This new hydrofoil increases the startup torque, improves the total performance of the turbine and decreases the thrust coefficient. At the same time we consider the incipient cavitations, tip loss and airfoil loss. We compare the design results with the experimental data in the literature. This method can satisfy the requirement of the design.

Published
2013

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