one of prototype composite brick/block units that were made
Hanson Brick Ltd and Hanson Block Ltd.
- Prof. Ray Ogden (Department of Architecture), Research Co-ordinator, OISD:Technology
- Dr Bousmaha Baiche (Department of Architecture), Project Manager, OISD:Technology
- Mr Chris Kendrick (Department of Architecture), OISD:Technology
- Additional input provided by: Mr Tim Mander (Mander Structural Design), Mr Paul Rogatzki (Hanson Brick Ltd.), Adrian James (Adrian James Architects), and Dr John Lowry (Oxford Brookes University).
- total grant value: £100,000
- time duration: 2000-2001
The main objective of the project was to develop a prototype prefabricated composite brick/block unit comprised of two brick slips, a concrete block and a specially profiled polyurethane (or polystyrene) core.
The system was expected to provide numerous advantages, including the following:
- Thin walls of low U-value would be made possible by omitting the standard 50mm cavity.
- Construction time would substantially be reduced because all three wall layers should be built at once, and two bricks should be laid at a time.
- The amount of scaffolding would be reduced, since construction can take place from one side only.
- Build quality would be improved, particularly the integration of the insulation layer.
- Airtightness would be improved because the interlocks and the interior sealing system are designed to resist gale force wind pressures.
- Stack bonded brickwork could be achieved for no loss in strength, since the concrete blocks are laid with a half-lap stagger.
Many prototype composite masonry units with different profiles of the insulation core were designed, developed and underwent feasibility studies. Subsequently, several water penetration tests were carried out on wallettes built with prototype composite masonry units. In addition, Buildability tests were conducted as part of the construction of panels to be used for flexural testing, following the 28 days curing process. The structural testing was undertaken at the structures laboratory, School of Architecture, Oxford Brookes University, to optimise the flexural strength of wallettes built with the composite masonry units. Furthermore, a plant was designed that would allow large-scale manufacturing and production of the composite masonry unit.
A prototype composite brick/block unit that was nearly successful. As Hanson was undergoing a restructuring process, funding for the project was stopped. The project, nevertheless, identified issues that needed consideration, notably:
Waterproofing. The continuity of horizontal and vertical joints between units, from the outside face to the inside face, is a potential source of damp problems. Even if waterproof mortar is used, there is a possibility that water could migrate through the structure by capillary action. In more serious cases of cracking, water could flow inwards from the outside face, particularly in areas exposed to high winds.
One of the prototype composite brick/block units that were made.
Building a panel for buildability testing using composite brick/block units.
Condensation of moisture. The plots of temperature gradient and dewpoint temperature through the composite block construction for steady-state condition A (BRE Digest 110) and condition C (BS5250 moist/wet occupancy) showed that interstitial condensation would occur around the insulation/brick interface. Since the moisture was on the outside edge of the insulation, and on the brick facing, it causes no moisture problems on the inside of the construction, and could easily migrate through the brick when the temperatures rise. The predicted moisture would, however, have a small detrimental effect on the overall thermal performance of the block, although this was not considered serious. An area of concern was the effect of possible physical degradation of the outer edge of the insulation, perhaps as a result of freeze/thaw action, upon the insulation/brick bond.
Prof Ray Ogden
Tel: +44 (0)1865 483208
Dr Bousmaha Baiche
Tel: +44 (0)1865 483279
Mr Chris Kendrick
Tel: +44 (0)1865 484286