ME31B: CHAPTER TWO

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ME31B CHAPTER TWO

• BUILDING MATERIALS

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2.1 INTRODUCTION

• A wide range of building materials is available
  for rural building construction.
• The proper selection of materials to be used in
  a particular building can influence the original
  cost, maintenance ease of cleaning, durability
  and of course, appearance.
• Proper selection of material is very important
  and the following factors are to be considered.

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Properties of Building Materials

• a) Strength and Durability This includes
  tensile and compressive strength, hardness,
  toughness, shear strength etc.
• The materials should also be durable ie. able
  to retain strength and other properties over a
  considerable period of time.
• b) Workability Ease of working with the
  material eg. Cutting and shaping.
• This should be considered hand in hand with
  skilled labour or otherwise available.

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Properties of Building Materials Contd.

• c) Cost Cheaper materials should be preferred
  without sacrificing other characteristics.
• d) Availability Local materials should be
  preferred, all other things being equal over
  imported or transported materials.

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Other Properties of Building Materials

• Other properties to consider include
• Esthetics,
• Resistance to corrosion and to fire,
• Easy transportability and ease of cleaning,
• Resistance to environmental changes, and to
  insect attack as well as imperviousness.

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2.2 Soil(Earth)

• This is one of the oldest materials for building
  especially in rural areas. Advantages of earth
  as a building material are
• i) It is resistant to fire
• (ii) It is cheap and readily available
• (iii)It has a high thermal capacity which enables
  it keep the inside of the building cool when the
  outside is hot and vice versa.
• (iv) It is a good noise absorbent

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Soil (Earth) Contd.

• (v) It is easy to work using simple tools and
  skills.
• The following properties of earth need
  improvement for it to be a good building
  material
• Look,
• Crackness,
• Weakness,
• Lack of water proofness.

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2.2.1 Methods of Improving Soil Properties

• Soil can be improved by compaction. Adobe
  bricks(made from soil) can be used to build.
  This improves the looks and reduces cracking.
• a) Cracks Soil particles range from clay to
  sand.
• Clay is strong but cracks, while sand does not
  crack but is weak.
• A mixture of clay and sand can be used to avoid
  cracking.

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Improving the Soil Contd.

• This is the principle of brick making. Cracks
  can also be controlled by using fibres of certain
  plants e.g. straw. The fibre reinforces the soil
  particles by bridging the gap between them.
• b) Weakness Soil strength can be improved by
  adding clay or chemicals eg. cement. Other
  stabilizers include lime, bitumen, rice husk ash,
  natural fibres e.g. grass, straw, sisal, saw
  dust, resins, cow dung and gypsum.

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Improving Earth Contd.

• c) Water Proof-ness The soil's waterproof
  qualities can be improved by adding some
  chemicals e.g. benzene.
• Emulsified asphalt can also be added but it is
  very expensive.
• The earth wall should be protected from rain by
  extending the roof.

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2.3 MASONRY

• Masonry is an art of building with stones, bricks
  or concrete blocks.
• 2.3.1 Stones Soft stones are preferred for
  building to ease reshaping.
• Stones generally show good strength, high
  durability, low cost(especially if available in
  site), resistance to fire, insects and
  environmental changes.
• Stones have high compressive strength and hence
  good for walls, columns, foundations etc. 

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2.3.2 Clay Bricks

• Bricks are made from clay the clay paste is
  placed in proper moulds, hardened and burnt in
  kilns (oven) in high heat.
• Bricks are generally strong, durable, resistant
  to environmental changes, fire and insects.

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2.3.3 Mortar

• Used to put stone materials together. It is a
  mixture of sand, water and a binding material
  like clay, cement or lime.
• Cement is more expensive that lime which is more
  costly than clay.
• Lime is produced by burning calcareous stone
  (Caco3) in water.
• CaCo3 H 2O Ca(OH)2 CO2
• Cement is a mixture of lime and clay.

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2.3.4 Cement or Concrete Blocks

• Made using mortar of cement and sand with
  necessary quantity of water.
• The blocks can also contain low sized gravel
  also.
• The blocks are generally made hollow with the
  core making about 25 of the gross area. These
  blocks are quite strong, durable and have most
  other characteristics of a good building
  material.
• The core of the block increases the acoustical
  and thermal properties and reduces the
  self-weight. 

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2.4 CONCRETE

• Concrete is probably the most important
  structural material today.
• It has the following ingredients
• i) Cement Portland cement
• ii) Fine aggregate Sand, granite granules etc.
• iii) Coarse aggregate Gravel, crushed stone,
  broken bricks etc.
• iv) Water.

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2.4.1 Ratio of Concrete

• Normal ratio of concrete is 1 2 4 (by volume).
• This means 1 part cement, 2 parts fine
  aggregates and 4 parts coarse aggregates.
• Fine aggregates fill the pores of coarse
  aggregates, cement fills the pores of fine
  aggregates.
• Cement with water forms a very good binding
  material which binds the concrete into a
  homogeneous mass.

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2.4.2 Water-Cement Ratio (w/c ratio)

• The best w/c ratio is 0.45 to 0.65 by weight.
• Too high w/c ratio increases workability of
  concrete but reduces strength of the paste while
• Very low values reduce workability and binding
  ability leading to cracking of concrete.

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2.4.3 Processes in Concreting

• a) Batching This involves bringing all the
  ingredients together in a proper ratio. It is
  normally done by volume but better results are
  obtained if the ration is taken by weight.
• For 1 m of concrete, take approximately 1 m3
  of coarse aggregate.
• With 1 2 4 ratio, 0.5 m3 of sand and 0.25 m 3
  of cement are used.
• Water is normally added by experience.

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Processes in Concreting Batching Contd.

• With these mixtures, a little more than 1 m3
  of concrete is obtained.
• For more accurate results, for 1 m3 of
  concrete, take 0.96 m3 of coarse aggregate and
  others accordingly using the mixing ratio.

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Processes in Concreting Mixing

• Mixing can be done manually or mechanically.
• In manual mixing, cement and sand are mixed
  thoroughly and then mixed with the coarse
  aggregate, and then water is added and mixed
  thoroughly.
• In mechanical mixers, all aggregates and water
  are added in the rotating mixer and rotated to
  mix them thoroughly.

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Other Processes in Concreting

• c) Conveyance or Transport Done using barrows
  or mechanical dumpers. Should be done quickly.
• d) Placing Before placing concrete in sites,
  the formwork is to be checked, cleaned and oiled.
• e) Compaction Concrete must be compacted
  adequately to secure maximum density.
• This is done either manually or using rods or
  mechanical vibrators.

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Processes in Concreting Curing

• f) Curing The setting of cement and hardening
  of concrete depends on the water content.
• The placed concrete has to be protected against
  evaporation.
• Curing is done by keeping the exposed surface of
  concrete wet continuosly.
• It is done by flooding in case of slabs or by
  continuous spraying in other cases.
• Curing is done for 7 to 10 days, but 21 days of
  curing gives maximum strength.

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2.4.4 Reinforcement of Concrete

• Concrete is strong in compression but weak in
  tension.
• Reinforcement involves inserting steel bars into
  concrete to make it resist tension.
• Beams, slabs etc. need reinforcement in order to
  make them resist bending which produces tension.

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Example

• Find the required quantities of cement, sand and
  coarse aggregate required to concrete a slab 10 m
  long, 5 m wide and 12 cm thick. Calculate the
  quantity of water required also. Specific
  gravity of cement is 1.5 ratio of ingredients is
  1 2 4 and water cement ratio is 0.5.

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Solution

• Total volume of concrete needed 10 m x 5 m
  x 12/100 m 6 m3
• Assume 0.96 m of coarse aggregates per m3 of
  concrete
• Coarse aggregate required is 6 x 0.96 5.76 m3
• Fine aggregate required is 5.76 x 2/4 2.88
  m3
• Cement required 5.76 x 1/4 1.44 m3

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Solution Concluded

• Note Bulk density of water is 1000kg/m3
  with specific gravity of 1.5 bulk density of
  cement is 1.5 x 1000 1500 kg/m3
• Wt. of cement 1.44 m3 x 1500 kg/m 3
  2160 kg.
• Assuming 1 bag of cement weighs 40 kg,
• Cement required 2160/40 54 bags.
• w/c ratio is 0.5, water required 0.5 x wt.
  of cement 0.5 x 2160 1080 kg 1080 litres
• Note 1 litre of water weighs 1 kg.

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2.5 WOOD

• Wood is a traditional building material. The
  quality of wood varies widely.
• Wood is generally durable, strong, dependable,
  workable and possesses many other
  characteristics.
• It is, however, highly inflammable and liable to
  insect attacks if not properly protected. Wood
  is mainly used for roof skeleton, doors and
  windows, walls and partitions in small
  buildings.

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Properties of Wood Contd.

• Wood may be hard or soft.
• Hard ones include ebony, mahogany, etc. while
  soft ones include Douglas fur, palm tree etc.
• Strength of wood increases with decreasing
  moisture content.
• By seasoning (drying), the strength can be
  improved. Wood is highly workable.

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Plywood

• Produced by gluing many layers of split wood
  together.
• The grains are arranged alternatively to
  eliminate distortion.
• The plywood is a very good modern construction
  material whose quality depends on type of wood
  used, glue used and pressure of steam used in
  gluing.

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Shapes of Wood Contd Block

• c) Blocks Very thick eg. 25 x 25
  mm(width-depth) or 20 x 25 mm or 30 x 30 mm
•   BLOCK
•  
•  
•  
• Many grades of wood exist depending on the
  strength.

BLOCK
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2.6 METALS

• These are man-made materials whose properties are
  known. The most widely used metal is steel.
• 2.6.1 Steel Steel is very strong, highly
  durable, resistant against weather, fire and
  insects and possesses almost all good
  characteristics.
• Steel is used in reinforcement in concrete,
  gates, windows, roof trusses, steel sheets for
  partitions and tanks etc.

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2.7 Other Building Materials (Synthetic
Materials)

• a) Asbestos Cement Used for making roof
  sheets, drain pipes and accessories. It is also
  used for partitions and ceilings.
• b) Plastics used in water supply and sanitary
  systems. Also electric fittings.
• c) Ceramics, fibre glass etc. are new materials
  used in some restricted areas.

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2.8 PROTECTION OF BUILDING MATERIALS

• Plastering with cement mortar, lime mortar etc.
  is common to protect the super structure.
• Painting is used to protect steel from rusting,
  timber from insect attack and shrinkage etc.
• Painting of walls, ceilings etc. are done for
  light control and beauty.
• Galvanizing and other protective coverings of
  certain materials especially metals are common.