The study then investigated the suitability of fly ash geopolymer for the production of concrete. Geopolymer concrete possesses strength comparable to concrete made with OPC. High early age strength is attributed to excellent aggregate-paste bond and reduction of porosity when aggregates are introduced. However, thermal incompatibility between aggregate and paste is an issue at elevated temperatures. At elevated temperatures, the aggregates expand while the geopolymer paste shrinks, leading to strength deterioration. Subsequent study identified specimen geometry and aggregate sizing are two key parameters that govern geopolymer concrete behaviour at elevated temperatures. These parameters determine how efficiently the geopolymer is able to expel moisture during heating, as well as the magnitude of its thermal gradient. High thermal gradients were recorded during the initial stages of temperature exposures. This effect was investigated by temperature-profiling geopolymer at various depths from the heated surface. Further, hydrocarbon fire tests were carried out to compare the spalling performance of geopolymer and OPC. Spalling was observed in one of the four geopolymer slabs tested, which was attributed to the build-up of strain energy due to the thermal mismatch between paste and aggregate. Subsequently, the larger specimens were more likely to experience spalling due to their higher insulating capacity - a behaviour which is consistent to observations made regarding OPC concrete from existing literature. This led to higher thermal gradients that negatively impacted the spalling resistance.
This project carried out fire testing of geopolymer concrete specimens and associated laboratory testing. This report focuses on the outcomes of the series of pilot-scale tests on geopolymer concrete panels, which were conducted on a single geopolymer concrete formulation. Geopolymer concrete is derived from coal fly ash and metallurgical slag, which are reacted together with an alkaline "activating solution" (sodium silicate in this case), blended with fine and coarse aggregate (quartz sand and crushed granite in this case) to generate a product which is similar in mechanical properties and general appearance to Portland cement concrete.
Portland cement concrete is a world-wide used construction material. However, when Portland cement concrete is exposed to fire, its mechanical properties are deteriorated. The deterioration of concrete is generally caused by the decomposition of the Portland cement hydrate or the thermal incompatibility between cement paste and aggregate. Spalling, which is a violent or non-violent breaking off of layers or pieces of concrete from the surface of a structural element, may also occur when the concrete is exposed to rapidly rising temperatures. It is generally believed that spalling is influenced by the build-up of pore water pressure and thermal gradient in the concrete when exposed to elevated temperatures.Geopolymer is an alternative cementitious material which has ceramic-like properties. Geopolymer belongs to the family of inorganic polymers. The chemical composition of geopolymer is similar to natural zeolite, but the microstructure is amorphous. It is suggested that geopolymer processes a potential superior fire resistance due to its amorphous and ceramic-like properties. The objective of this thesis is to study the fire resistance of geopolymer material and to explore the spalling behaviour of geopolymer material when exposed to elevated temperatures.In this thesis, a method was presented to carry out spalling test in small scale specimen with exposure to rapid temperature rise using a commonly available electric furnace. Hydrocarbon fire and standard fire exposure can be simulated by manipulating the exposure location of the surface of the concrete cylinder. Ordinary Portland cement concrete cylinders with different strengths were tested. The results demonstrated that this method was an effective and convenient technique to predict the spalling risk of a concrete. The spalling behaviour of geopolymer concrete by using the surface exposure test and standard gas furnace fire test was studied. It was shown that 100% fly ash based geopolymer concrete had a better spalling resistance to rapidly rising temperature exposure than that of Portland cement concrete.The study of sorptivity test of geopolymer concretes results showed that the geopolymer concrete specimen's structure is more porous and more continuous pore structure than Portland cement concrete specimen. The more porous structure of geopolymer than OPC concrete facilitates the release of the internal steam pressure during heating. Hence, less tensile stress is imposed in the geopolymer concrete than Portland cement concrete during heating, reducing the geopolymer's risk of spalling. When slag was used as a replacement to fly ash in the geopolymer binder, geopolymer paste and concrete specimens developed considerably high strength at room temperature. It was showed that the magnitude of shrinkage of fly ash and slag based geopolymer is significantly higher than that of 100% fly ash based geopolymer and Portland cement concrete. The residual strength of fly ash based geopolymer concrete with slag replacement after exposure to elevated temperature was studied. It was found that the residual strength of 100% fly ash based geopolymer concrete after elevated temperature exposure increased in the temperature range of 200~500°C compared with OPC concretes. Fly ash based geopolymer concrete with slag replacement experienced a strength loss at the temperature range of 200~300°C, then followed by a strength gain at 300~400°C, and another strength loss after 500°C. When slag was used as an additive to fly ash based geopolymer concrete, the overall strength loss of geopolymer concretes with slag replacement after exposure to elevated temperatures ranging from 200~800°C was higher compared with 100% fly ash based geopolymer concrete, however, it was significantly lower than that of the Portland cement concrete specimens. The investigation of fire resistance property of fly ash and slag based geopolymer material when exposed to hydrocarbon fire was followed. After hydrocarbon fire, no spalling was observed on geopolymer concretes when using varying factors as binder, slag replacement, cation type of alkaline liquid activator, room temperature and elevated temperature curing. Residual strength testing of geopolymer concretes after hydrocarbon fire exposure showed a similar residual strength percentage compared with the result of Portland cement concrete. However, it is noted that high strength Portland cement concrete spalled, while high strength geopolymer concrete still had a considerably high residual strength after fire exposure.
The book covers the topic of geopolymers, in particular it highlights the relationship between structural differences as a result of variations during the geopolymer synthesis and its physical and chemical properties. In particular, the book describes the optimization of the thermal properties of geopolymers by adding micro-structural modifiers such as fibres and/or fillers into the geopolymer matrix. The range of fibres and fillers used in geopolymers, their impact on the microstructure and thermal properties is described in great detail. The book content will appeal to researchers, scientists, or engineers who are interested in geopolymer science and technology and its industrial applications.
A geopolymer is a solid aluminosilicate material usually formed by alkali hydroxide or alkali silicate activation of a solid precursor such as coal fly ash, calcined clay and/or metallurgical slag. Today the primary application of geopolymer technology is in the development of reduced-CO2 construction materials as an alternative to Portland-based cements. Geopolymers: structure, processing, properties and industrial applications reviews the latest research on and applications of these highly important materials.Part one discusses the synthesis and characterisation of geopolymers with chapters on topics such as fly ash chemistry and inorganic polymer cements, geopolymer precursor design, nanostructure/microstructure of metakaolin and fly ash geopolymers, and geopolymer synthesis kinetics. Part two reviews the manufacture and properties of geopolymers including accelerated ageing of geopolymers, chemical durability, engineering properties of geopolymer concrete, producing fire and heat-resistant geopolymers, utilisation of mining wastes and thermal properties of geopolymers. Part three covers applications of geopolymers with coverage of topics such as commercialisation of geopolymers for construction, as well as applications in waste management.With its distinguished editors and international team of contributors, Geopolymers: structure, processing, properties and industrial applications is a standard reference for scientists and engineers in industry and the academic sector, including practitioners in the cement and concrete industry as well as those involved in waste reduction and disposal. Discusses the synthesis and characterisation of geopolymers with chapters covering fly ash chemistry and inorganic polymer cements Assesses the application and commercialisation of geopolymers with particular focus on applications in waste management Reviews the latest research on and applications of these highly important materials
This volume represents the current knowledge on the effect of SCMs (slag, fly ash, silica fume, limestone powder, metakaolin, natural pozzolans, rice husk ash, special SCMs, ternary blends) on the properties of fresh and hardened concrete (e.g. early strength development, workability, shrinkage) and curing requirements. Other topics treated in the book are postblending vs preblending, implications of SCM variability, interaction between SCM and commonly used admixtures (e.g. superplasticizers, air entrainers).
The Concrete Construction Engineering Handbook, Second Edition provides in depth coverage of concrete construction engineering and technology. It features state-of-the-art discussions on what design engineers and constructors need to know about concrete, focusing on - The latest advances in engineered concrete materials Reinforced concrete construction Specialized construction techniques Design recommendations for high performance With the newly revised edition of this essential handbook, designers, constructors, educators, and field personnel will learn how to produce the best and most durably engineered constructed facilities.
Geopolymer is an amorphous aluminosilicate binder which is produced by hydrothermal synthesis of aluminosilicates in the presence of concentrated alkaline or alkaline silicate solutions. It is an emerging construction material purported to provide an environmentally-friendly alternative to ordinary Portland cement (OPC) based concrete. Owing to its ceramic-like properties, geopolymer has been touted to be a highly fire resistant material. This claim is further supported by results from investigations of residual strength after thermal exposure. Some studies have found that geopolymers increase in strength after exposure to temperatures of 800°C. In contrast, several recent studies have shown a decrease in residual strength of geopolymers after a similar exposure. These contradictory observations are explored here. The study shows that two opposing processes are occurring simultaneously in geopolymers at elevated temperatures. Process (1) is further geopolymerization, and has the effect of increasing the strength. Process (2) is the damage due to thermal incompatibility which arises because of (i) the temperature gradient and (ii) different movements between matrix and inclusions. Process (2) is also a function of the brittleness level of the material. Whether the strength increases or decreases is dependent on which of the two processes is dominant in the specimen and the test conditions.The detailed examination of process (2) reveals a strong correlation between the degree of strength loss and the brittleness of geopolymers. This correlation suggests that geopolymers are quite brittle. For the first time, the brittleness of geopolymer concrete has been quantitatively determined and compared with OPC concrete. The comparatively high brittleness of geopolymer concrete is important for its fire resistance properties. The high brittleness will also require special structural design measures, similar to the design requirements for high strength concrete. With regard to the fire resistance of geopolymers, most research to date has investigated only residual strength, but the properties of geopolymer while hot have received less attention. Therefore, a number of tests to determine stress-strain curve, ultimate strength, elastic modulus and creep were undertaken in steady and transient heating conditions. In these tests, several critical features of the material's performance were observed: (1) geopolymers exhibit glass transition behaviour at elevated temperatures; (2) glass transition temperature is improved by the substitution of a sodium-based activator for the potassium-based activator; (3) below glass transition temperature there is a significant increase in hot strength and hot elastic modulus; (4) in the range of 250-550°C thermal transitional creep is absent as compared to OPC concrete. Data obtained from these measurements can serve as input for the development of constitutive models which are essential to predict the response of geopolymer concrete elements in fire. In addition to its deteriorating properties at high temperatures, concrete can also be damaged in fire by a phenomenon called spalling, which is particularly severe in high strength concrete. Since geopolymer is comparatively more brittle than high strength concrete, the issue of spalling in fire is further explored in the last part of this study. It was found that the spalling resistance of geopolymer concrete increases as maximum aggregate size increases. The increasing aggregate size results in an increase in fracture zone length (lp); this in turn reduces the flux of kinetic energy (due to pore pressure) that is released into the fracture front and thereby improves spalling resistance. This theory is further validated by the observation of a good correlation between lp and spalling resistance in this thesis. This study is the first to propose such a hypothesis on the effect of aggregate size on the spalling of concrete, both OPC and geopolymer, and contributes to a better understanding of spalling of concrete in fire.
Portland cement is the main component of traditional concrete used for construction; hence it is widely used. The production of Portland cement produces a high amount of CO2 what makes it harmful for the environment. Therefore, geopolymer concrete has been of interest since it serves the same utilities as Portland cement concrete by using a different type of raw material. This material is coming from waste therefore do not cause environmental damage. This binder is created using materials rich in alumina and silica with addition of an activating solution known as the alkali solution. Fly ash coming from the burning of coal is used in this study along with an activating solution composed of sodium hydroxide and sodium silicate to produce an alternative binder for concrete. Fly-ash will be partially substituted by Glass Powder which is also a waste material to see its effect on geopolymer concrete. Moreover, the durability of geopolymer concrete will be checked and compared to that of ordinary Portland cement concrete in terms of acid attack and fire resistance. Therefore, mixtures with different percentages of glass powder (0%, 5%, 10% and 20%) were carried out and different molarities of NaOH (10M and 14M) to generate a geopolymer concrete that has workability, strength and durability properties. Compressive strength, acid attack, and fire resistance are the tests that are respectively done for the previously mentioned properties. Results showed that 5% glass powder replacement of fly-ash in geopolymer concrete with 14M as NaOH concentration gives a similar fc of 48.32 MPa compared to the reference GPC without glass that gives 47.73 MPa. Also, up to 10% substitution of fly-ash with glass powder do not have a major effect on the strength (45.8 MPa). In addition, geopolymer concrete gives better durability properties than ordinary Portland cement concrete.
