KC

Week 1 - Properties Generally

Properties Generally

Overview of Properties

  • Properties pertinent to specific materials are discussed in other chapters.

  • This chapter covers general properties of building materials:

  • Density and specific gravity

  • Strength

  • Optical properties

  • Electrical properties

  • Thermal properties

  • Acoustic properties

  • Deformations

  • Deterioration

  • Appearance

1. Density and Specific Gravity

  • Density: Mass per unit volume, important for assessing material weight and loading.

  • Specific Gravity: Ratio of the density of a substance to the density of water at 4°C, used for various calculations.

  • Reference table of densities for common materials provided for practical use.

2. Strength

  • Definition: Ability of materials to support their own weight and applied loads without distortion.

  • Key readings include:

  • The New Science of Strong Materials by J E Gordon.

  • Strength Types:

  • Tensile Strength: Resistance against being pulled apart.

  • Compressive Strength: Resistance against being compressed.

  • Shear Strength: Resistance against forces causing sliding.

  • Behaviour of materials changes based on:

  • Moisture content (particularly in timber).

  • Load rates and frequencies.

  • Temperature impacts on materials (e.g., plastics).

  • Elastic vs. Plastic Failure:

  • Elastic materials revert to original shape post-load; plastic materials do not.

  • Ductility versus Brittleness:

  • Ductile materials can deform significantly before fracturing.

  • Brittleness: material fractures without significant deformation.

  • Creep: Gradual deformation under constant load over time.

3. Optical Properties

  • Reference materials related to optical properties are discussed under specific chapters (e.g. Glass).

4. Electrical Properties

  • For detailed information, refer to relevant sections in the chapters.

5. Thermal Properties

  • Thermal Conductivity (k): Measure of heat transfer through materials.

  • Defined as Watts (J/s) per unit thickness (m) over unit area (m²).

  • Thermal Resistivity (1/k): Opposition to heat flow, calculated from conductivity.

  • Effective insulation characteristics vary with thickness and surface types:

  • Optimum insulation achieved with sealed cavities.

  • Humidity Impact: Moisture materially alters thermal conductance (20% moisture can triple heat transmission).

6. Acoustic Properties

  • Sound insulation is achieved through mass and natural barriers.

  • Types of sound absorption properties:

  • Porous Materials: Absorb at higher frequencies.

  • Resonant Panels: Absorb at lower frequencies (specific designs).

  • Use of fallen materials is important for sound insulation and fire resistance considerations.

7. Deformations

  • Deformation types include:

  • Movements from applied loads.

  • Changes in moisture and temperature.

  • Restraint can lead to additional stresses and deformities in building materials.

8. Deterioration

  • Common deteriorating factors include:

  • Corrosion, sunlight, biological factors, and water.

  • Solutions for prevention include using resistant materials and appropriate design strategies.

9. Appearance

  • Factors influencing the appearance of buildings incorporate structural forms and chosen materials.

  • Economic considerations often guide the choice of materials with lower maintenance needs.