Abstract
In recent years, there has been growing interest in the research and development of Compressed Earth Blocks (CEBs), driven by the demand for low-cost and sustainable building materials. Although there have been advances in the technical understanding of CEBs, there remain significant gaps in knowledge regarding the use of jute fibre reinforcement, the influence of aspect ratio on the results of direct compression tests, and the application of Finite Element Analysis (FEA).This compilation-style thesis contains a series of published research articles and publishable research articles (under review) produced as part of this PhD study. The overall aim of the project was to investigate the mechanical properties of fibre-reinforced, unstabilised compressed earth composites and understand the influence of geometry and aspect ratio on compressive strength. A combination of experimental analysis and numerical FEA modelling was employed to achieve this aim. The design and fabrication of the bespoke UoP-CEB Machine were central to the experimental programme and enabled the manufacture and testing of full-scale compressed earth blocks. Other specimen sizes, including half-scale blocks and compressed earth cylinders, were investigated to examine the influence of aspect ratio.
Throughout the study, two main soil types were investigated, including Kent Brick Earth (KBE) and a BS6801 compliant subsoil. Jute was selected as the natural fibre reinforcement as it is one of the most affordable, versatile, and widely available fibres, and it remains relatively unexplored in existing literature. The influence of fibre length (10mm, 20mm and 30mm) and fibre content (0.125%, 0.25% and 0.50% by weight), and fibre moisture content (ambient, soaked and dried) was assessed. The results show that the addition of 10, 20 or 30 mm jute fibres at 0.25–0.50% by weight provided a statistically significant increase in the compressive and tensile splitting strength of compressed earth composites. The incorporation of 20mm jute fibres at 0.25% by weight was found to provide the optimal performance, achieving a 100% and 85% increase in compressive and tensile splitting strength compared to an un-reinforced sample. The results also showed that jute fibres should be incorporated into the earth mixture at its natural ambient moisture content. Soaking or drying of fibres should be avoided to prevent the degradation of the fibre and the composite.
The primary focus of the study was to determine the influence of geometry and aspect ratio on un-stabilised and fibre-reinforced compressed earth composites. This aimed to address a significant gap in knowledge regarding the effects of confinement caused by platen restraint during direct compression tests. To assess the influence of geometry, three un-stabilised block
types were manufactured and tested including solid blocks, hollow blocks and blocks with frogs. The experimental investigation and numerical modelling found that solid blocks exhibited the greatest compressive and flexural strength, while blocks with frogs exhibited the lowest compressive strength. This is due to the effective area available to transfer load throughout the specimen. To assess the influence of aspect ratio, un-stabilised and fibre- reinforced cylindrical samples were manufactured and tested with an aspect ratio ranging from 0.5 to 2.0. The results showed that specimens with a lower aspect ratio displayed higher compressive strength due to confinement caused by platen restraint. Furthermore, the effects of confinement are compounded by the influence of fibre reinforcement, resulting in a disproportionately large increase in apparent compressive strength. From the results, novel aspect ratio correction factors were produced which enabled the samples with alternative aspect ratios to be converted to the unconfined compressive strength. The study addresses a key gap in knowledge and seeks to improve the current production and testing methods of un- stabilised and fibre-reinforced compressed earth composites.
The study demonstrates the successful use of FEA to model the behaviour of compressed earth composites, including individual masonry units and masonry assemblages. The numerical models were created and verified using results obtained from experimental analysis. Several novel techniques were adopted, including the use of cohesive zone modelling to simulate the mortar-block interface. In summary, this research demonstrates the potential of jute fibre reinforcement as a low-cost and sustainable building material. The research addressed significant gaps in knowledge and encourages continued research and development of CE composites.
This thesis also presents an extended application of CEB technology by examining compressed blocks produced from Construction, Demolition and Excavation (CD&E) waste, known as Trommel Fines. Through mechanical testing, durability assessment and chemical analysis, the viability of Compressed Trommel Fine Blocks (CTFBs) was demonstrated. This research highlights the potential to divert waste from landfills, promote a circular economy, and develop new markets for innovative CD&E waste-based building materials. This extended application establishes a foundation for future research and development into waste-derived building materials created using CEB technology.
| Date of Award | 10 Oct 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Muhammad Ali (Supervisor), Alireza Tatari (Supervisor) & Brett Martinson (Supervisor) |