Thesis

The effects of nano-titanium dioxide on durability and mechanical properties of cement composite

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Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16446
Person Identifier (Local)
  • 201853242
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Abstract
  • Application of nano-titanium in cement paste to ensure the future competitiveness of concrete as a building material, it is essential to improve the sustainability of concrete infrastructures. Recent developments in nanotechnology show a significant promise in addressing many of the challenges to produce environmentally friendly concrete. In this context and in the scope of this thesis, the environmental impact and sustainability of concrete was improved by the combined use of nano-titanium dioxide and supplementary cementitious materials (SCM). In particular, the effects of SCM such as FA and MK as by product materials and NT as a high surface area additive on the permeability as well as pore structure properties of cementitious materials were investigated and analysed in this PhD thesis. The main properties and characteristics of nano-titanium were obtained using different techniques such as X-ray computed tomography (XCT), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric/derivative thermogravimetric analysis (TG/DTG), and energy-dispersive X-ray spectroscopy (EDAX®). To examine the pore configuration in the matrix, 2D and 3D porosity calculations had been carried out in order to find the pores and their exact sizes, positions and distributions from the pore network using a Nikon XT H 225/320 LC X-ray computed tomography system. In addition, reconstructed tomography images were used to extract the main parameters of porosity. The number of pores in the scanned volume, as well as the volumes and shapes of individual pores were determined and based on these recommendations, design guidelines were suggested. A novel direct tensile were conducted to quantify and characterise the mechanical properties of the NT cement composite. Furthermore, the impact of increasing the amount of NT on the mechanical properties of NT-modified geopolymer were investigated. This test method covers the determination of the fracture energy (Gf) of composites using the disk-shaped compact tension geometry. Numerical results were validated with the existing experimental data specifically on the CMOD responses and von Mises stresses. Finally, we investigated different amounts of nano-TiO2 on the sulfate attack resistance of pure Portland cement pastes. The distributions of internal pore structures of hardened mortars were measured by MIP method. The corrosion progression of a steel bar in concrete was investigated by X-ray computed tomography (i.e., XCT) and accelerated corrosion process of reinforcing steel with impressed current was traced by X-ray micro-computed tomography (μCT) with high accuracy and the mass loss of steel over different accelerated corrosion periods was analysed. This PhD thesis included a significant experimental phase and an associated analytical phase. The experimental phase focused on determining the material behaviours of the NT cement composite from the testing on over 900 individual specimens, with an emphasis toward determining the compressive and tensile behaviours, the long-term stability, and the durability of composite. Many of the material characterization tests were completed according to the British standard test procedures. However, in some instances these tests were modified, or new tests were devised to accurately capture the relevant behaviours of the NT cement. The analytical phase of this research combined, analysed, and explained upon the results from the experimental phase. This results in concrete with better performance, lower costs and improved ecological footprint. The final outcome is a methodology to design concrete and a practical framework which allows the optimum application of NT in concrete, given the available raw materials and the desired properties of the end-product. In summary, it can be concluded that adding a certain amount of NT (around 2.5 wt%) and FA/MK (10 wt%) can modify the pore structure of cement mortars by changing the harmful microscale pores to the nano-sized benign pores, leading to a much stronger durability of cement-based materials. The results demonstrate that the photovoltaic waste can be used as a potential NT-SCM composite to partly replace cement in concrete, thereby decreasing the CO2 footprint of concrete and the environmental impact associated with landfill.
Advisor / supervisor
  • Yang, Shangtong
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