KC

Week 1 - Principle Properties of Building Materials

Introduction to Building Materials

  • Building materials are fundamental in modern technology and engineering fields.
  • Their primary use is in construction, which affects both quantity and quality of work.
  • The building materials industry significantly contributes to national economy.

Factors Influencing Material Choice

  • Climatic Background: Different regions develop varying materials based on climate.
  • Economic Aspects: Advances in construction methods and tools affect material choices.
  • The diversity in building usage requires materials to have a wide range of properties (e.g., strength, resistance to elements).
  • Standardization of material quality is crucial and requires continual improvement.
  • Understanding properties allows optimal choices for specific service conditions.

Physical Properties

Density

  • Density formula:
    p = M/V
  • M = mass (g)
  • V = volume (mm³)
  • Example densities of materials:
  • Brick: 2.5-2.8 g/mm³
  • Granite: 2.6-2.9 g/mm³
  • Wood: 1.5-1.6 g/mm³
  • Steel: 7.8-7.9 g/mm³

Bulk Density

  • Bulk density formula:
    Pb = M/V
  • Indicates natural state density, usually less than density for solids and liquids.
  • Example bulk densities:
  • Brick: 1.60 - 1.80 g/mm³
  • Granite: 2.50 - 2.70 g/mm³
  • Steel: 7.85 g/mm³

Porosity

  • Defined as the ratio of volume of pores to the volume of material.
  • Indicates other properties such as bulk density and durability.
  • Materials with low porosity are used for high mechanical strength constructions.

Hygroscopicity

  • Ability to absorb water vapor from the air, influenced by temperature and humidity.

Water Absorption

  • Expressed as a percentage of weight or volume:
  • Computation formulas for weight and volume absorption.
  • Absorption affects strength properties when saturated.

Weathering Resistance

  • Ability to withstand alternating wet and dry conditions without significant change in properties.

Frost Resistance

  • Endurance to freezing and thawing, crucial for water-saturated materials.

Heat Conductivity

  • Influenced by material type, structure, and porosity.
  • Important for materials used in heated buildings.

Thermal Capacity

  • Ability of a material to absorb heat, relevant for thermal stability in buildings.

Fire Resistance

  • Resistance to high temperatures without significant loss of strength; includes classifications of materials (e.g., non-combustible).

Refractoriness

  • Ability to withstand high temperatures (>1580°C) without melting.

Chemical Resistance

  • Ability to resist action from acids and other chemicals; important for durability.

Durability

  • Overall ability to withstand environmental factors over time.

Mechanical Properties

  • Key mechanical properties include strength (compressive, tensile, etc.), hardness, elasticity, plasticity, and abrasion resistance.

Strength

  • Resistance to failure under stress from loads, varies significantly by material type.
  • Compressive Strength: tested via standards with cylinders, prisms, or cubes.

Hardness

  • Measured by ability to resist penetration; using Mohs scale for minerals and ball indentation for metals.

Elasticity

  • Ability to return to original shape after load removal; defined by modulus of elasticity.

Plasticity

  • Ability to change shape under load without rupture and retain that shape afterwards.

Characteristic Behavior Under Stress

  • Ductility: Ability to be drawn into wires without breaking.
  • Brittleness: Lack of plasticity resulting in sudden failure; seen in materials like concrete.
  • Stiffness: High modulus leading to minimal deformation with load.
  • Flexibility: Materials that bend considerably under load.
  • Toughness: Ability to withstand heavy shocks combined with strength and flexibility.
  • Malleability: Ability to be hammered into sheets.
  • Hardness and Abrasion Resistance: Critical for durable materials in construction.