Selection of Materials

• The choice of materials to be used is probably the most important factor affecting the risk of defects & failures .
• The designer must either design to suit the materials available or for a required design , choose materials which may be expected to perform satisfactorily with that design in the given environment .
• The choice of materials will be governed mainly by the following factors :

1. Their ability to fulfill their design function
2. Their ability to withstand the effect of the climate .
3. Their reaction with surrounding materials .
4. Their ease of maintenance and / or replacement .
5. Overall economic acceptability .

• Deterioration Levels of materials
• Materials tend to deteriorate as soon as they are used in a building because of the  following factors :

1. Environment : air temperature , rainfall , wind & atmospheric gases .
2. Design : details to prevent contract between materials & the agents of deterioration .
3. Workmanship : such as faulty assembly
4. Intrinsic properties : determine the physical & chemical changes of the materials during their lifetime use .
5. Problems from incorrect selection of materials

- The incorrect selection & specification of materials by designers will lead to construction & maintenance problems which include :

• Mismatch & misfit problems from the use of different materials having different characteristics , shapes , textures adn fixings .
• Chemical interaction occuring between the materials themselves or as a result of an aggressive environment .
• Construction difficulties particularly when excessive support systems or highly skilled labour are required .
• Premature or accelerated damage due to the use of unsuitable materials .
• Difficulties in repairing or replacing very complex materials if these are used in the original design .
• Structural failure when there is a reduction in the ability of the material to withstand designed load .