Construction Materials

Key Properties of Civil Engineering Construction Materials

The properties of construction materials govern how a structure looks, how strong it is, how long it lasts, and how well it serves its purpose. They are grouped as follows:

1. Physical properties — affect appearance and serviceability

• Colour and texture — determine the appearance (finish) of the structure.
• Density and specific gravity — influence self-weight and hence the design load.
• Porosity and water absorption — control permeability, dampness and weathering.
• Thermal conductivity — governs heat insulation and comfort (serviceability).
• Sound absorption — governs acoustic comfort.

2. Mechanical properties — affect strength

• Compressive strength — the main strength criterion for brick, concrete and stone.
• Tensile strength — important for steel and for crack resistance.
• Shear strength — resistance to sliding/racking forces.
• Flexural (bending) strength — governs beams, slabs and pavements.
• Impact strength / toughness — resistance to sudden loads.
• Hardness and abrasion resistance — resistance to wear on floors, roads.
• Modulus of elasticity — governs deformation and deflection.
• Fatigue and creep — long-term behaviour under repeated/sustained load.

3. Durability properties — affect life of the structure

• Weathering resistance — against rain, frost, sun.
• Chemical resistance — against acids, alkalis, sulphates, sea water.
• Permeability — controls ingress of water and harmful salts.
• Resistance to fire, insects and fungi.

4. Workability and other properties — affect construction and serviceability

• Workability — ease of mixing, placing, compacting (e.g. slump of concrete).
• Setting and hardening time — governs construction speed.
• Adhesion and bond with mortar/other materials.
• Dimensional stability — shrinkage, expansion, warping.
• Cost and availability — economy of the structure.

Characteristics of Good Quality Bricks

1. Shape — uniform, rectangular, with sharp, straight, parallel edges and square corners.
2. Size — standard size (Nepali standard modular brick 240 mm × 115 mm × 57 mm) within permissible tolerance.
3. Colour — uniform, deep red or cherry red (copper colour) for burnt clay bricks.
4. Texture — fine, dense and uniform surface, free from cracks, lumps, stones and organic matter.
5. Strength — minimum compressive strength of about 10 N/mm² (10 MPa); a first-class brick should not fail below this.
6. Hardness — sufficiently hard; no impression should remain when scratched with a fingernail or a hard object.
7. Soundness — gives a clear ringing/metallic sound when struck with another brick or a hammer; a dull sound indicates cracks or poor burning.
8. Water absorption — not more than 20% of its dry weight (first-class brick about 12–15%) when soaked in water for 24 hours.
9. Durability — unaffected by weathering, frost and atmospheric agencies; no efflorescence (white salt deposits) on drying.
10. Fire resistance — good fire resistance and low thermal conductivity.
11. Thermal and moisture movement — small, so that cracking and distortion are avoided.
12. Fracture — when broken, shows a homogeneous, compact and fine-grained structure without voids or lumps.
13. Free from soluble salts — no soluble salts that cause efflorescence and disintegration.
14. Cost — reasonably cheap and locally available.