Influence of Pozzolanic Additions and Dewatering on Lime Mortars for Masonry Conservation
: (Alternative Format Thesis)

  • Tugce Busra Su

Student thesis: Doctoral ThesisDoctor of Engineering (EngD)

Abstract

Historic buildings constructed from masonry require conservation due to a range of damage mechanisms caused by various environmental factors over time, including fluctuations in humidity and temperature. Pollution and biological growth also contribute to the degradation processes. To ensure effective conservation, it is important to have a deep understanding the performance and interactions of the historic materials used in masonry, such as stone, brick, mortar. and render, as well as the materials utilized during the conservation process.
The longevity of repairs depends on the compatibility between the original and repair mortar. Since the original and new materials after repair alter the behaviour of the building, the weaker material, typically the original stone or brick, tends to degrade at a faster rate compared to the applied mortar due to the stress changes, leading to more extensive deteriorations. To address this issue, this study aims to identify a weaker mortar, enhanced with additive pozzolans, to achieve more compatible interfaces between the historic masonry and repair materials. By comprehensively understanding the inter-relationship between the historic masonry and repair materials, this research seeks to optimize the repair mortar for improved longevity and performance, ultimately preserving the integrity of the masonry structure.
This research has exploited a wide range of mechanical, physical and chemical characterisation techniques to thoroughly elucidate the underlying processes of lime mortars. The enhancement of the mortar was achieved through dewatering, which led to a reduction in pore volume and an increase in mechanical strength. As a result of this enhancement, the microstructure and mechanical behaviour of the dewatered mortars exhibited remarkable similarities to those of the older non dewatered mortar. This significant achievement highlights the early resistance of the mortar and draws attention to its potential for optimizing the mortar-substrate compatibility in on-site masonry applications. The findings of this study assure for advancing the field of mortar research and facilitating effective preservation and maintenance of historic masonry structures.
Furthermore, pozzolan-lime mortars are widely recognized as one of the most compatible options for masonry conservation, due to their favourable pore structure. Lime mortar containing pozzolans show significant improvements in pore structure, increased resistance to freeze and thaw cycles and enhanced mechanical strength. The evolution of pore structure in the mortar matrix is intimately linked to the physio-chemical properties of pozzolans, which play a crucial role in achieving an optimal transfer sorptivity of the mortar. This study has increased the understanding of the interaction between pozzolan-lime mortar and brick/stone masonry to optimize their compatibility and to promote their cohesive movement mechanisms. In this study, the effects of dewatering and transfer sorptivity on this relationship are studied in detail, considering their influence on the overall performance and durability of the mortar-masonry system. This research contributes to the advancement of knowledge in the field of masonry conservation, providing valuable insights for the development of effective and sustainable preservation practices.
To further strengthen the findings, a comparative pore structure analysis was conducted to 26-year-old trial mortars collected from Corfe Castle. The laboratory mortar samples exhibited similar behaviour, whereas the weathered samples displayed an increased volume of pore structure, resulting in a reduction in the main pore diameter. These results provide additional evidence of the long-term performance of the mortar and highlight the changes in pore characteristics over time, which can have significant implications for the durability and sustainability of masonry structures. This comparative analysis adds a valuable dimension to the study, reinforcing the importance of understanding the evolution of pore structure in historic masonry conservation and contributing to the body of knowledge in this field.
This investigation represents a significant advancement in our understanding of conservation approaches for masonry, providing a basis specifying repair materials that are both sympathetic to the historic fabric of buildings and minimize the risk of damage. Through close collaboration with Historic England, the research methodology encompassed a combination of laboratory-based tests and examination of historic buildings in the field. By integrating both laboratory and real-world observations, this study bridges the gap between theoretical knowledge and practical application, making it a valuable contribution to the field of historic masonry conservation. It is believed that this aids in the selection of appropriate repair materials and techniques that align with best practice and ensure the long-term preservation of our built heritage.
Date of Award13 Sept 2023
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorRichard Ball (Supervisor) & Juliana Calabria-Holley (Supervisor)

Keywords

  • Conservation of masonry, pozzolan-lime mortar, pozzolanic reactivity, historic masonry, repair mortar, mortar-substrate optimisation

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