Factors to consider when choosing construction materials

• The choice of building material depends mainly on the properties of the materials and
• The purpose of the structure which is being constructed
• For example concrete is used to make large buildings
• Fiberglass is used to make cars and water tanks
• Wood is used to make roofing trusses
• Stone is used to make walls
• Some of the properties of materials that have to be considered are:

The strength of the material

• The table above was adapted from Focus on Science
• It shows the strength of various construction materials
• The strength of a material can be found by finding the amount of force required to break it
• As shown different materials have different breaking strengths as shown by the table
• Engineers must know the strength of materials when they design structures such as bridge
• Steel is strong in both tension and compression
• Wood is weak in compression and strong in tension
• Concrete is weak in tension but strong in compression
• it can be combined with steel to make reinforced concrete which is strong in tension and compression
• Civil engineers should use the strongest material after considering the forces involved in that part of the structure

Flexibility

• Flexibility is another factor that engineers need to consider
• Flexibility is the ability of a material to bend without breaking
• Rubber is an example of a flexible material
• It is used where flexibility is required for example rubber soles of shoes
• Materials that are not flexible are known as rigid
• Examples of rigid structures include steel and concrete
• Some structures e.g. walls of building require rigid materials
• Wood is slightly flexible but it has low shear strength
• Twisting forces will easily break it making it unsuitable for structures that experience shear forces

Corrosion

• Materials are constantly being weakened, corroded and decay due to
• sunlight, water, pollution, living organisms such as termites and bacteria as well as fire
• When materials are erected they are immediately attacked by water and oxygen
• Iron which is commonly used as a construction material rusts when subjected to water/moisture and oxygen
• It can be protected by electroplating, painting and alloying
• Copper is low on the reactivity series which makes it less susceptible to corrosion
• Aluminum is protected from corrosion by a thin layer of aluminum oxide that forms a protective covering
• So even though it is higher in the series it does not react
• Steel is more resistant to corrosion than iron
• Where corrosion is undesirable such as on bridges steel or materials that do  not corrode easily are to be preferred

Corrosion by pollutants

• Where corrosive pollutants are found materials that are resistant to these pollutants must be considered
• For example sulphur dioxide is produced when coal is burnt
• The gas combines with water and oxygen in the atmosphere to form sulphuric acid
• This falls as acid rain and attacks most materials and corrodes them
• Nitrate factories  e.g Sable Chemicals also produce nitrates
• which are expelled via chimneys and combine with rain water to form
• acids that are even corrosive than sulphuric acid

Destruction by living organisms

• For example wood is attacked by living organisms
• Such as termites, fungi etc
• This destroys and weakens many wooden structures especially given Zimbabwe’s warm moist climate
• Wood can be protected by
• Painting it or dipping it in creosote
• which protects the wood and makes it last longer

Other factors

• Other factors to consider include:
• Cost
• Weight of material
• Or even the physical  appearance of the material
• Environmental impact of using that material i.e. is it Eco friendly
• Durability
• How easy is it to maintain

To access more topics go to the Combined Science Notes page