Kannangara, A M U Thathsarani (2018) The Behaviour of Reactive Powder Geopolymer Concrete at Elevated Temperature. Research Master thesis, Victoria University.

Abstract

Concrete is one of the most widely used materials within the construction industry due to its versatility, durability, superior mechanical properties and excellent resistance to fire. In addition to this, the rapid growth in population and urbanisation has accelerated the demand for high strength concretes. However, high strength concretes suffer a condition called spalling when exposed to elevated temperature levels which is associated with the breaking away or exploding of concrete layers due to the internal stresses. Additionally, concrete is a material having a very high carbon footprint mainly due to its binding material, cement, which is reported to be the second largest emitter of carbon dioxide. These issues have driven researchers to experiment alternative materials which can better benefit the economy and the environment. Studies show that blended concretes, which use supplementary cementitious materials such as slag, fly ash, silica fumes in partial replacement to cement and Geopolymer (GP) concretes, which eliminate cement usage altogether, display a high degree of resistance to fire. Additionally, these materials are further deemed worthy due the reduction or elimination of cement making it a more sustainable material. This study focuses on the fire performance of GP pastes, reactive powder concretes (RPC) and a newly developed GP paste based reactive powder concrete called reactive powder GP concrete (RPGC). RPGC was produced using class F fly ash and sodium-based activators in relation with silica fumes and micrometre aggregate. The study investigates properties such as workability, setting times, density, compressive strength, residual strength, thermal cracking and mass loss under controlled laboratory conditions. The study further investigates the performance of GP paste specimens of varied sizes subjected to different curing conditions. A comparison on the properties of two fly ash materials, namely Gladstone fly ash and Gladstone/Callide fly ash are also presented. Both types of fly ash displayed high early strengths and exceptional fire performance with a maximum strength gain of approximately 45% after an exposure to 400oC. RPC on the other hand exhibited high levels of explosive spalling at a temperature of around 360oC despite initial compressive strengths reaching a maximum of 140.7 MPa at 7-day testing. RPGC displayed good workability conditions with a maximum of 252 mm and a minimum of 187.5 mm, whilst achieving an initial compressive strength of 76.3 MPA at 24-hour testing. Furthermore, RPGC resulted in the lowest degree of thermal cracking with majority of the specimens having no visible cracking even after an exposure of 800oC. Moreover, RPGC recorded the lowest percentage mass loss amongst all experimented specimens.

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