Strength of materials

• Strain is the change in length divided by original length.
• Structure and Classification of Building Materials
• All materials, whether solid, liquid, or gas, have spaces between fundamental particles
• Some materials appear to have void spaces, while others do not, depending on how they are formed
• Most building materials are porous due to their method of formation
• Concrete is porous due to the extra water used during production, which later evaporates, leaving void spaces
• Materials like bricks, stones, and timber contain small air pockets or air spaces called pores
• Porous materials have a great influence on mass, density, and relative density
• Porosity
• Building materials are classified based on the quantity of air spaces they contain
• Porous materials contain many voids or air spaces, while non-porous materials have few voids
• Examples of porous materials: concrete, timber, clay products, aggregate; non-porous materials: metals, glass, plastics, bitumen felt
• Relationship of Porosity to Physical Properties
• Porous materials are less dense than non-porous materials
• Density and specific gravity are affected by the presence of voids
• Porous materials have higher solid density and lower bulk density
• Characteristics of Building Materials
• Strength of porous materials is reduced by the presence of air voids
• Porous materials absorb water based on the number of pores and their connectivity
• Porous materials like wood and cork are good heat insulators due to air spaces
• Porous materials trap sound waves in their pores cavities for sound absorption
• Condensation occurs in porous materials when air holding water vapour is cooled below the dew point
• Movement of Moisture in Porous Materials
• Porous materials absorb moisture through capillary action
• Permeable materials allow liquids to pass through, while impermeable materials do not
• Water penetration into materials is facilitated by gravity and the driving force of moving water
• Moisture Content
• Moisture content is the amount of moisture in a material, affecting its strength and heat insulation
• Measurement of moisture content is done by drying a sample to a constant weight in an oven
• Moisture Content of Granular Materials
• Moisture content in granular materials is determined by drying the sample to a constant weight in an oven
• Moisture content exists in granular material in two parts:

  • Absorbed moisture: water absorbed into the particles of the materials
  • Free moisture: water around and between the particles
• Both absorbed and free moisture are expressed as a percentage of the oven-dry weight
• Total moisture content is the sum of the absorbed and free moisture in the material
• Effects of moisture movement
• Flaking or bond failure of plaster or rendering
• Dimensional changes
• Cracks on walls and foundation due to shrinkage of the day of earth material
• Moisture movement or excessive drying shrinkage may cause flaking (bond failure) of plaster or rendering
• Dimensional changes in timber are another effect of moisture movement