Geocomposites: Next generation natural fibre reinforced geopolymers

Lead Research Organisation: University of Bath
Department Name: Architecture and Civil Engineering

Abstract

The proposed research will attempt to develop geocomposite materials, consisting of a geopolymer matrix and reinforcing fibres acquired from natural sources. A multitude of possible matrix compositions incorporating different combinations of precursors and alkaline activators, and numerous natural fibres available each with equally varied constituents and structures are available. Therefore, a detailed investigation into such components and their compatibility in geocomposite form will be carried out. Compatibility level will be determined based on chemical cohesion and interfacial bond between fibre and matrix.
Upon gaining a greater understanding of compatibility, appropriate treatments and processing methods for both fibre and matrix that possess the ability to enhance the material properties and characteristics will be studied and analysed. Such methods will also aim to improve the compatibility between fibre and matrix, including the reduction in alkalinity and initial viscosity of the geopolymer, as well as fibre surface properties to form strong interfacial bonds and aid resistance to such harsh environments.
In addition to microstructure investigation, manufacturing techniques of the resulting composites will be developed and optimised. The response under possible corrosive and degrading conditions, such as fire, and the long-term durability of the material will be assessed.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R512424/1 01/10/2017 30/09/2021
2112312 Studentship EP/R512424/1 01/10/2017 30/09/2021 James BRADFORD
 
Description The first objective, determining suitable geopolymer compositions for use as composite matrices, required the utilisation of various raw materials in differing quantities to form the desired chemical combinations. To improving sustainability and reduce carbon dioxide emissions - a fundamental aspect of the project - industrial by-products were applied which possess inherently complex compositions that differ drastically between material sources. It was discovered that in application of one industrial by-product, the silica containing precursor, the resulting geopolymer material exhibited significant expansion upon curing due to unexpected pore growth.
The porosity was later found to result from impurities - traces of free silicon present in the raw material - resulting from by-product procurement, which reacted aggressively with the alkaline component of the geopolymer to yield hydrogen gas ergo expansion. This highlights the complexities involved with producing sustainable, low-carbon construction materials when using non-standardised raw materials of industrial origin. That being said, despite not being directly applicable to this project, such an occurrence poses the possibility of a new form of lightweight, strong and porous construction material.
To prevent further difficulties to the project, a purer non-expansive source material was used, allowing for more controlled and repeatable material production and testing. It was found that, in testing the fluid and mechanical properties of a wide range of desirable geopolymer compositions, the properties critical to material manufacture and performance were largely dependent upon two factors, the water and alkali content. These factors dictated the rate of geopolymer reaction kinetics, in turn influencing the rate of change of viscosity and eventual material strength - associated with manufacturability and performance, respectively. Of the two, alkali content is deemed to be the critical component due to optimal workability and strength occurring in compositions containing greatest alkali content, with additional water further improving workability, but reducing relative strength.
As reference, with a controlled chemical composition varying only in alkali content, compressive strengths of 10MPa to 70MPa were achieved, at the lowest and highest alkali content, respectively. Such strength is comparable to those of non-sustainable, carbon-emitting polyester resins commonly applied in fibre-reinforced polymers, at around 80-110MPa. Similarly, when varying only water content, viscosity ranged from 0.2Pa.s to 2.5Pa.s - less than the 0.5Pa.s minimum of conventional polymers - with the former also exhibiting optimal strengths of 70MPa where high alkali content was utilised. It can be said that of the 24 compositions tested, around 8 possess the necessary combination of suitable workability and strength.
In relation to fibres, although untested as of now, the low viscosity will provide good impregnation and in turn yield a fibre-reinforced composite of adequate density and mechanical strength. One major concern to be addressed is the corrosive effect that such high alkalinity will have on the natural fibres - which is to be investigate extensively throughout the remainder of the project.
Lastly, regarding the failure of geoplymeric matrices and the sudden catastrophic manor in which it occurs, when manufacturing fibre-reinforced composites, the brittle failure mode may be tailored through utilisation of the porous geopolymer type previously discussed. Adding a porous interlayer around the reinforcement, in bulk combination with the dense and strong geopolymer provides a cheap and simple method to control material failure mode - an otherwise elusive control factor when considering conventional fibre-reinforced polymers.
Exploitation Route The findings provide a strong basis for other research and development centres on the geopolymer compositions and raw materials most suited to the application of fibre-reinforced composite matrices, and the performance that may be exhibited, as well as highlighting the difficulties and unexpected benefits that industrial by-products provide.
Sectors Aerospace, Defence and Marine,Construction,Environment