Metals (Leaving Cert Construction Studies): Revision Notes
Building materials - Metals
Steel - the primary construction metal
Steel stands as the most widely used metal in the construction industry. Understanding its properties and applications is essential for construction work.
Composition and properties
Steel contains high iron content with low carbon content, typically less than 2%. The iron provides steel with its remarkable strength, making it ideal for structural applications. However, this strength comes with an important trade-off.
Strength vs. Ductility Trade-off
As strength increases, ductility decreases. This means steel becomes less malleable and harder to shape compared to softer metals. This is a fundamental property that affects how steel can be worked with on construction sites.
Main construction applications
Steel serves multiple purposes in building construction:
- Structural elements: Steel beams support internal and external balconies, providing the framework for buildings
- Lintels: These horizontal supports span openings like doors and windows
- Fittings and hardware: Socket boxes, hinges, taps, and various connecting components
- Concrete reinforcement: Steel rods strengthen concrete structures, creating reinforced concrete
Reinforced concrete combines the compressive strength of concrete with the tensile strength of steel, creating a composite material that's stronger than either component alone.
Structural steel sections
When steel is used for structural purposes, it comes in standardised cross-sectional shapes. These components are manufactured by rolling hot steel through moulds that create the desired cross-section shape. The technical term for these structural steel components is RSJ (rolled steel joist).
Common steel section types include:
- Angles and tees for corner connections
- Channels for edge support
- Columns for vertical load-bearing
- Beams for horizontal spanning
- Hollow sections (square, rectangular, and circular) for various structural needs
Rust prevention methods
Steel's main weakness is its susceptibility to rust when exposed to air and moisture. Two primary methods prevent this deterioration:
Galvanising Process
Galvanising involves coating the steel with zinc. This can be done through dipping the steel in molten zinc or electro-plating zinc onto the surface. The zinc layer acts as a barrier, preventing moisture and oxygen from reaching the steel underneath.
Protective Painting
Painting provides another protective barrier. The key is selecting appropriate paint types that effectively seal the steel surface. The paint prevents air and moisture from penetrating through to the metal, stopping rust formation before it starts.
Stainless steel - the premium option
Stainless steel represents a more expensive steel variant created by adding chromium to the metal composition. This chromium addition makes the steel highly resistant to corrosion and staining. Due to its cost, stainless steel isn't used for structural purposes. Instead, it's commonly found in kitchens and bathrooms where the chromium provides essential protection against moisture and humidity.
Cost vs. Application
While stainless steel offers superior corrosion resistance, its high cost limits its use to specific applications where this property is essential, rather than general structural work.
Key Points to Remember:
- Steel combines high iron content with low carbon content (under 2%) for maximum strength
- Greater strength means reduced ductility - steel is strong but harder to shape
- RSJ refers to rolled steel joists used in structural applications
- Galvanising (zinc coating) and proper painting prevent rust formation
- Stainless steel contains chromium for corrosion resistance but costs too much for structural use