Materials Chemistry

Materials Chemistry

Civil engineers work with a vast array of materials. Understanding their chemical composition and reactions is essential for durability, strength, and sustainability.

Polymers and Plastics

Polymers are large molecules made of repeating structural units (monomers).

• Thermoplastics: Soften when heated and harden when cooled (e.g., PVC pipes, Polyethylene). Can be recycled.
• Thermosets: Chemical cross-linking prevents melting; they decompose at high heat (e.g., Epoxies, Polyurethanes). Stronger but brittle.
• Elastomers: Highly elastic polymers (e.g., Rubber, Neoprene bridge bearings).

Nanomaterials

Materials with structures at the nanoscale (1-100 nm).

• Carbon Nanotubes (CNTs): Extremely high tensile strength and conductivity. Added to concrete for reinforcement.
• Titanium Dioxide ($TiO_2$): Used in self-cleaning concrete (photocatalysis breaks down pollutants).

Cement and Concrete Chemistry

Portland cement is the most common binder.

• Major Compounds:
  • Tricalcium Silicate ($C_3S$): Early strength.
  • Dicalcium Silicate ($C_2S$): Long-term strength.
  • Tricalcium Aluminate ($C_3A$): Flash set, high heat.
  • Tetracalcium Aluminoferrite ($C_4AF$): Color (grey).

Crystal Structures in Metals

Metals have crystalline structures that determine their mechanical properties.

• Body-Centered Cubic (BCC): Iron (alpha), Chromium. Strong but less ductile.
• Face-Centered Cubic (FCC): Aluminum, Copper, Iron (gamma). More ductile.
• Hexagonal Close-Packed (HCP): Magnesium, Zinc, Titanium. Brittle.