Building Materials: Timber and Concrete

Timber

• Composed of cellulose fibre, tracheids, and lignin, a natural resin
• Excellent specific strength, but prone to weather damage and pest attacks
• Renewable resource, but many hardwoods are difficult to replace once felled
• Removal can harm fragile ecosystems

Concrete

• Composite of cement, sand, and aggregate
• Sand fills gaps between aggregate particles, cement acts as binder
• Portland cement is a man-made ceramic that reacts with water and sets to a hard, brittle solid
• Stronger and more efficient than cement alone for large structures and paths
• Typical composition: 4 parts aggregate, 2 parts sand, 1 part cement

Fibre Reinforced Polymers

• Polymers with added fibre for improved rigidity and impact resistance
• Examples: glass and carbon fibre in polyester or epoxy resins
• Widely used, with extensive applications in aeronautical fields

Bio-Engineered Materials

• Stainless steels, aluminium alloys, and tungsten alloys are commonly used in bio-engineered products.
• Polymers and ceramics are also important, especially for internal use.

Importance of Biocompatibility

• Biocompatibility is crucial when designing devices that are implanted or in contact with the skin.
• Materials must not react with the body and must remain inert to ensure product integrity and health.

Stainless Steels

• Advantages: creates a stable, thin oxide layer that resists corrosion when exposed to atmosphere or body fluids.
• Conventional steels are prone to corrosion, weakening the material and causing infection or rejection by the body.

Titanium

• Derived from minerals rutile and ilmenite (oxide layers).
• Properties: lightweight, excellent corrosion resistance, high strength-to-weight ratio, and good high-temperature properties.
• Corrosion resistance is provided by an adherent TiO2 film stable until 535°C.
• Uses: hip joints, bone screws, knee joints, bone plates, dental implants, and pacemaker cases.
• Machining properties are comparable to stainless steel.