Important properties of civil engineering materials

Properties of a material are its measurable characteristics that decide how it behaves under load, heat, water and weather. They are grouped as physical and mechanical properties.

Physical properties

• Density and specific gravity: mass per unit volume; relates to self weight of the structure.
• Porosity: ratio of void volume to total volume. High porosity lowers strength and durability.
• Permeability: ability to let water or fluid pass through the pores.
• Hygroscopicity: tendency to absorb moisture from air.
• Thermal conductivity: rate at which heat flows through the material. Low conductivity gives good insulation.
• Fire resistance: ability to keep its strength and shape when exposed to fire.
• Durability / weathering resistance: resistance to the action of rain, frost, sun and chemicals.

Mechanical properties

• Strength: capacity to resist load without failure (compressive, tensile, shear, flexural).
• Elasticity: property of regaining original shape after the load is removed. Plasticity is the opposite, permanent deformation.
• Ductility: ability to be drawn into wires or to elongate considerably before fracture (mild steel).
• Malleability: ability to be hammered into thin sheets without cracking (lead, gold).
• Brittleness: fracture without appreciable deformation (cast iron, glass, brick).
• Toughness: energy absorbed up to fracture (area under the stress-strain curve).
• Resilience: energy stored up to the elastic limit.
• Hardness: resistance to scratching, abrasion or indentation.
• Fatigue: failure under repeated or cyclic loading at stress below the ultimate strength.
• Creep: slow, continuous deformation under constant load over a long time.

Why these properties must be studied

1. To select the right material for a given use (steel for tension, concrete and stone for compression).
2. To design safe and economical members using correct permissible stresses.
3. To predict behaviour under load, temperature, moisture and fire so that failures are avoided.
4. To decide testing and quality control methods on site.
5. To compare alternative materials on cost, performance and durability.
6. To plan proper storage, handling and maintenance.