Huang, Bo and Saafi, Mohamed and Ye, Jianqiao (2021) Characterisation of cementitious composites with green two-dimensional (2D) nanomaterial produced from sugar industry waste. PhD thesis, Lancaster University.
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Abstract
In recent years, nanomaterials have been used to engineering cementitious composites to have improved performance. In particular, two-dimensional (2D) nanomaterials such as graphene, graphene oxide (GO) and boron nitride (BN) are considered as ideal candidates for cementitious materials admixtures, due to their high surface area and excellent mechanical properties. However, the applications of these 2D nanomaterials in those mixtures have been hindered by several roadblocks including high costs, incompatibility with the cementitious materials, health and environmental issues associated with their processing. The objective of this thesis is to study the properties of the cementitious composites, incorporating a newly developed 2D bio nanomaterial. The 2D bio nanomaterial is in the form of sugar beet pulp nanosheets (SNSs) synthesised from sugar industry waste. The SNSs incorporation has two functions. One is amplifying the effect of the hydration products and the other is reinforcing the hydration phases of the cementitious composites. An extensive experimental programme was carried out to characterise the cementitious composites, the hydration mechanism and the mechanical and fracture properties. First, the 2D SNSs were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), x-ray energy dispersive x-ray spectrometer (EDS), fourier-transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), nitrogen adsorption and desorption isotherm. Second, the effect of SNSs on the hydration mechanism of OPC was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), TGA and DSC. The thermal behaviour of the cementitious composites was examined, relationship between the degree of hydration (DOH) and the SNS concentration was established and the mechanism of hydration was elucidated using CV and EIS-equivalent circuit. Third, the compressive, flexural and tensile strength, and fracture properties of the cementitious composites was obtained through mechanical testing. Fourth, the influence of SNSs on the microstructure, types of hydration product and porosity were determined using SEM, EDS, BET, XRD and TEM. The development of the hydration phases, pore size and crack propagation in the matrix as a result of SNSs are elucidated. In addition, a hydration mechanism of the cementitious composites is proposed. The obtained results from the experiments show that the SNS is an excellent nanomaterial to reinforce the cementitious composites. The SNS addition can substantially develop the cementitious composites DOH and promote the microstructure quality. The flexural, tensile and the fracture properties of SNS-cement pastes were significantly improved at different w/c ratios and in different SNS dispersion states. The mechanical performance and the microstructure changes indicates that the SNS can bridge fibre within the cementitious composites, accelerate the hydration and promote the chemical bonding.