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Development of Bond Strength in Hydraulic Lime Mortared Brickwork

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Development of Bond Strength in Hydraulic Lime Mortared Brickwork Development of Bond Strength in Hydraulic Lime Mortared Brickwork Submitted by ZHAOXIA ZHOU for the degree of Doctor of Philosophy UNIVERSITY OF BATH Department of Architecture and Civil Engineering January 2012 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that they must not copy it or use material from it except as permitted by law or with the consent of the author. This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. Signature of Author........................................................... ii Acknowledgements The work in the thesis was carried out in the Department of Architecture and Civil Engineering at the University of Bath between January 2006 and January 2009. The author would like to thank Professor Pete Walker and Dr Dina D'Ayala, joint supervisors of this study. They have provided continuous support and professional guidance throughout the duration of the research. Their help, patience and time ensured that the project was completed successfully. The author would like to thank Professor Pete Walker in particular, who has been a great supervisor all the way through this long journey, not only contributing considerable expertise to the research, but also providing endless encouragement and support to help me through this most difficult time in my life. Special mention should be made to Dr Andrew Heath for designing the pneumatic loading system on the bond wrench test apparatus, and all of the laboratory staff in the department, Neil, Brian, Will, Sophie, Graham and Paul, who offered a big hand during the large amount of experimental work. Also thanks go to Lawrence, the bricklayer, who had built all the specimens. The author would like to thank EPSRC for the funding to conduct this project, and also the collaborative research partners, the University of Bristol and the University of Bradford, and the associated industrial partners: in particular Lime Technology Ltd and Ibstock Ltd for the building materials provided; Castle Cement (now part of Heidelberger), Network Rail Ltd, BRE Ltd, Lhoist UK and Buro Happold, for their advice and guidance on the steering group. Finally, thanks go to my family for the support and patience during the past few years, and my friends being around to make me smile. iii iv Abstract The first recorded use of hydraulic lime in construction can be traced back to at least two thousand years ago. Hydraulic lime, produced through either adding pozzolanic materials or calcining clay containing limestone, unlike air lime, can set and harden under water, developing strength through initial hydration reaction and subsequent carbonation. After WWII Portland cement mortars had almost completely replaced lime based mortars in modern construction. However, through conservation and specialist construction the benefits of hydraulic lime are becoming increasingly recognised. To support wider usage of these mortars there is a need for systematic study on the mortar properties and structural performance of lime mortared masonry. This thesis presents findings from a research programme conducted to develop understanding of the mechanical properties of natural hydraulic lime (NHL) mortared brickwork. The work focussed on the flexural strength of NHL mortared brickwork. A variety of material and environmental factors, including lime grade and supplier, mix proportion, sand type and age, have been investigated. In addition the research has completed an in-depth study on the influence of brick absorption characteristics on bond development. The two methods of flexural wall panel and bond wrench testing to establish flexural strength have been compared. In addition to flexural strength, initial shear strength and compressive strength of brickwork has also been investigated. A greater understanding of NHL mortared brickwork performance has been developed through this work. Performance of the brickwork has been related to properties of constituent materials and environmental factors. Recommendations for design performance of materials have been provided. v vi Content ACKNOWLEDGEMENTS.......................................................................................................... III ABSTRACT................................................................................................................................. V CONTENT................................................................................................................................. VII LIST OF FIGURES .................................................................................................................... XI LIST OF TABLES ....................................................................................................................XIV 1. INTRODUCTION................................................................................................................ 1 1.1 HISTORY .......................................................................................................................... 1 1.2 MANUFACTURE OF NATURAL HYDRAULIC LIME (NHL).......................................................... 5 1.3 BENEFITS OF NHL MORTARS ............................................................................................. 7 1.4 AIMS AND OBJECTIVES OF STUDY ....................................................................................... 9 1.5 THESIS STRUCTURE ....................................................................................................... 10 2. LITERATURE REVIEW ................................................................................................... 13 2.1 INTRODUCTION ............................................................................................................... 13 2.2 PREVIOUS WORK ON LIME -BASED MORTARS ..................................................................... 15 2.2.1 Introduction.......................................................................................................... 15 2.2.2 Overview of work on lime mortars....................................................................... 15 2.2.3 Influence of constituent materials and mortar workability on mortar performance . ............................................................................................................................. 18 2.2.4 Influence of age on mortar performance ............................................................. 23 2.2.5 Carbonation of lime mortars................................................................................ 27 2.2.6 Other aspects of lime mortar performance.......................................................... 28 2.3 TESTING METHODS USED FOR MASONRY CHARACTERISATION ........................................... 32 2.3.1 Methods used to measure bond strength............................................................ 33 2.3.2 Methods used to measure shear strength........................................................... 38 2.4 PREVIOUS RESEARCH ON MASONRY BOND STRENGTH ...................................................... 43 2.4.1 Introduction.......................................................................................................... 44 2.4.2 Influence of mortar properties on bond performance.......................................... 45 2.4.3 Influence of masonry unit properties on bond performance................................ 49 2.4.4 Influence of moisture content of masonry units at laying on bond strength........ 58 2.4.5 Other studies on bond performance.................................................................... 61 2.4.6 Studies on hydraulic lime mortared masonry ...................................................... 64 2.5 SUMMARY AND CONCLUSIONS ......................................................................................... 68 3. EXPERIMENTAL MATERIALS AND TEST METHODOLOGIES................................... 73 3.1 INTRODUCTION ............................................................................................................... 73 3.2 EXPERIMENTAL BRICKS ................................................................................................... 75 vii 3.2.1 Brick water absorption tests.................................................................................76 3.2.2 Relationships between water absorption parameters..........................................85 3.3 MORTARS .......................................................................................................................91 3.3.1 Binders.................................................................................................................91 3.3.2 Aggregates...........................................................................................................92 3.3.3 Mortar Mixes ........................................................................................................93 3.4 SPECIMEN PREPARATION ................................................................................................94 3.4.1 Programme design...............................................................................................96 3.4.2 Preparation of Constituent Materials ...................................................................97 3.4.3 Fabrication
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