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Title: New concept in fire resistant concrete
Other Titles: Fang huo hun ning tu de xin gai nian
Authors: Chan, Wai Wing (陳偉榮)
Department: Dept. of Physics and Materials Science
Degree: Doctor of Philosophy
Issue Date: 2005
Publisher: City University of Hong Kong
Subjects: Concrete -- Fire-testing
Notes: CityU Call Number: TH1087.C45 2005
Includes bibliographical references (leaves 181-188)
Thesis (Ph.D.)--City University of Hong Kong, 2005
v, 219 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: It has been reported that concrete engineering is over one hundred years old. Although certain concretes are required to work in high temperature environments or posses adequate fire protection, most researches were mainly directed to investigate the severity of fire damage and the decomposition of the cement paste. In particular, the study of the development of fire resistant concrete is rare, not to mention details such as the effects of using different forms of formwork panel materials. This study aims to develop concrete with cement replacement with pulverized fuel ash (PFA) or silts and clays to achieve the equivalent strength and durability, and to study their fire resistance performance. Further, the effects of the different formwork panel materials during concrete forming on fire resistance were also studied. The compressive strength, workability, sorptivity, and water permeability of the concrete formed with various non-reactive waste materials, i.e. carbon black, silts and clays were studied. Further, the resulting change in the microstructure and cement hydration in these concretes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. It was found that the critical problem of maintaining or increasing the designed workability could be solved by using a high specific surface area material and with a superplasticizer admixture. The study also indicated that an alternative durable concrete could be made with 25 vol.% of cement replaced with silts and clays / waste / recyclable material using a water/cement (w/c) ratio of 0.5. The use of this type of new formulation will be environmentally friendly. In order to analyse the reason behind the low early strength of PFA concrete and to verify the practical application of newly discovered formulation to mix design, the compressive strength, workability and sorptivity of the existing and new formulated PFA concrete were compared. The resulting change in the microstructure and cement hydration was studied by XRD, SEM and EDX. Grouting mixes without superplasticizer and aggregates were also evaluated by Fourier transform infrared (FT-IR) spectrometry. The study indicated that superior strength concrete could be made with 35 vol.% of cement replaced with PFA using a water/OPC ratio 0.52. A fire test as stipulated in BS 476 Part 20: 1992 to 2 hours was carried out to the samples developed in the earlier part of the study, at a fire temperature of about 1200oC. The resulting change in the microstructure and cementitious hydration was studied by visual inspection, SEM, FT-IR spectrometry and compressive strength tests. The study indicated that the newly-developed concrete with cement replacement materials improved the fire resistance. The chemical changes in the concrete due to fire were also classified, such that the calcium silicate hydrate was confirmed to be an important compound affecting the strength of concrete before and after fire. The effects of formwork panel materials to a fire resistance mix were then studied. As titanium oxide (TiO2) may be applied on the surface of concrete for certain applications, this type of concrete was also studied as to its fire resistance performance. It was concluded that samples cast on wooden fibre lining + TiO2 powder provided concrete with the best fire resistance. Conversely, samples formed with metal casting with the use of release agent and TiO2 powder would induce an adverse effect to strength after fire.
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