Components used in construction

• Bricks


  • 215mm long, 102.5mm wide and 65mm high
  • Up to 337.5mm long, up to 225mm wide and 112.5mm high
• Nominal size of brick

  225mm x 112mm x 75mm (includes mortar joint)
• The size of bricks is extremely important to give a predictable product with a low failure rate in manufacture
• One effect of brick standardisation is that extension and maintenance are easy
• Mortar joint width


  Normal is 10mm, modified slightly depending on brick tolerance
• Strength of brickwork


  Depends on designed strength, type of mortar and pointing used
• Frost resistance of bricks

  Grade must be used below damp-proof course (DPC) or ground level and in areas susceptible to frost
• Brick colour


  Depends on impurities in the clay or pigments added to the mix
• Overall colour of a wall

  Determined by brick colour, mortar colour, pointing and brick texture
• Clay bricks


  Constructed of clay and fired in a kiln, commonest external finish for domestic buildings in Britain today
• Types of clay bricks


  • Stocks (self-coloured through the brick)
  • Commons or flettons (colour and texture applied to the surface)
• Thermal expansion of clay bricks


  Very similar to concrete and steel
• Expansion joints should be provided at 6—8m intervals vertically and horizontally, unless movement has been accommodated using lime mortar or similar
• Sand lime bricks


  Produced by autoclaving or 'pressure cooking' a mixture of sand and calcium silicate for approximately 24 hours
• Thermal expansion of sand lime bricks

  Similar to clay, but moisture movement is 5% greater
• Sand lime products require movement joints at 4m intervals or less to prevent uncontrolled cracking
• Bricks


  Can be made to special shapes and in a wide variety of strengths, textures, colours and types
• Blocks


  Precast concrete blocks, larger than bricks, size determined by weight a bricklayer can lift with two hands and need to keep to a multiple of the brick module for bonding
• Common block sizes


  440mm × wall width × 215mm, wall width commonly 65mm to 225mm
• Dense solid concrete block weight

  100mm thick block is 22kg, at the lifting limits for manual lifting
• Lightweight blocks


  Made from foamed slag or pulverised fuel ash (PFA), provide good thermal insulation
• Strength of concrete blocks

  Varies and must be checked for each type, many insulating blocks provide only minimal support
• Thermal and moisture movement of concrete blocks

  Vary considerably with the material used and are unlikely to match brick products
• Concrete products require a significant amount of water in their manufacture and tend to shrink slightly over time, while clay products are more likely to expand slightly when saturated and have different coefficients of thermal expansion
• Many blocks have a scratched finish to provide a key for plaster and joints between the blocks are usually similar to those of brickwork, although it is possible to lay blocks using a 'thin joint' system
• Clay blocks


  Hollow clay blocks or pots used extensively in the London area in the interwar period for partition work in multi-storey buildings to reduce weight, difficult to repair or modify and presents problems when heavy fixings are required
• Concrete


  Used as a component in many elements of a simple building — mainly the foundations, the ground floor slab and sometimes the first floor — and can be used for the complete structure of a house or a low-rise building due to its high thermal mass
• Concrete constituents


  • Cement
  • Fine aggregate (sand)
  • Coarse aggregate
  • Water
• Coarse aggregate


  Natural (such as stone and gravel) and artificial (such as clinker and slag)
• There is a growing use of recycled aggregates, particularly in large cities such as London, to avoid the need to quarry fresh material and reduce lorry movements
• Most common size of coarse aggregate for reinforced concrete

  20mm, larger aggregates have smaller surface area (relative to volume) so require less cement
• Cement


  Gains its strength from the reaction between the cement particles and water (hydration), the sand and aggregates are inert and act as fillers
• Main reactive compounds in cement

  • Tricalcium silicate (alite)
  • Dicalcium silicate (belite)
• Alite


  Reacts quickly with water and gives concrete an early strength gain
• Belite


  Reacts more slowly and helps the concrete to develop late strength
• Cement production has been estimated to produce around 4% of the world's CO2 emissions
• Cement replacement materials


  • PFA (in its fine particle form)
  • Ground granulated blast furnace slag (GGBFS)
• PFA and GGBFS


  Can replace a proportion of the cement in a concrete mix while maintaining strength, tend to slow down the strength gain of hardening concrete which can be advantageous
• Water-cement ratio


  Relationship between the weight of water and the weight of cement used, a lower ratio increases concrete strength
• Typical water-cement ratios are generally 0.4 or 0.45, with a minimum of around 0.2 to completely hydrate the cement