Rocks in Construction: Properties, Types, and Applications

Posted on Aug 10, 2025 in Geology

Rocks: Properties, Types, and Construction Uses

Natural materials extracted from rock masses are fundamental to various construction applications. This document examines their key properties, classifications, and practical uses.

Material Properties and Testing

  • Specimen Testing: Used to determine essential properties such as density, tensile strength, moisture content, and porosity.
  • Granular Sample Testing: Conducted to ascertain particle size distribution, density, moisture content, and abrasion resistance.

Mohs Hardness Scale

The Mohs scale provides a classification of minerals from least hard to hardest:

  1. Talc (laminar)
  2. Gypsum (crystalline)
  3. Calcite
  4. Fluorite
  5. Apatite
  6. Feldspar
  7. Quartz
  8. Topaz
  9. Corundum
  10. Diamond

Alteration of Stone Materials

Stone materials are consistently altered by external agents. These alterations can be categorized as:

  • Physical Changes (Do not cause chemical transformations):
    • Heating-cooling cycles
    • Moisture-dry cycles
    • Freeze-thaw cycles
  • Chemical Transformations (Cause chemical changes):
    • Hydration process
    • Hydrolysis process
    • Ion-exchange process
    • Oxidation-reduction process

Types of Rocks

Igneous Rocks

Formed by the solidification of magma. They are classified based on their formation location:

  • Intrusive (Plutonic): Form from magma solidifying within the Earth’s crust (e.g., granite).
  • Extrusive (Volcanic): Form from lava solidifying on the Earth’s surface (e.g., basalt).

Uses: Igneous rocks are widely used as aggregates for granular layers in road construction, as railway ballast, as aggregates for concrete, and as slabs for building construction.

Sedimentary Rocks

Result from the sedimentation process and the destruction of pre-existing rocks. They are classified into:

  • Detrital Rocks: Formed by the alteration of other rocks. These can in turn be:
    Sheet-like Detrital Rocks:
    • Gravel: Rounded, highly resistant, with variable composition. May be siliceous or calcareous in origin. Used for roads or drainage.
    • Sands: May contain silicon or limestone components.
    • Silts: Formed by fine particles of silica fragments, etc. They possess some plasticity but erode quickly.
    • Clays: Exhibit much greater plasticity.
      • Non-expansive: Examples include chlorite, illite, and kaolinite.
      • Expansive: Expand significantly in the presence of water (e.g., montmorillonite, vermiculite).
    Compact Detrital Rocks:

    These rocks are characterized by a binding compound that compacts them:

    • Silica-source Gravels: E.g., Quartzites.
    • Limestone-origin Gravels: E.g., Limestones.
    • Clay-origin Gravels: E.g., Clay rocks.
    • Limonite: A binding element in clay, which is a material that can disintegrate.
    • Argillite: A compacted form of limonite.
  • Non-detrital Rocks: Formed by the precipitation of substances found in solution, followed by their consolidation.
    • Limestone: Used extensively as aggregate for concrete, asphalt mixtures, cement, lime, and as filler.
    • Dolomite: Similar to limestone but generally harder and scarcer. Uses include aggregates for concrete and as an ornamental rock.
    • Gypsum: A soft material, soluble in water, which can become aggressive to cement and concrete. Uses: raw material for plaster and a percentage as raw material for cement.
  • Intermediate Rocks: Formed by processes intermediate between detrital and non-detrital types.
    • Marl: A detrital clay material with a limestone binder component. Its qualities vary widely depending on composition. It is used as a component in cement.

Metamorphic Rocks

Originate from the metamorphism of pre-existing rocks (igneous, sedimentary, or other metamorphic rocks) due to high pressure and temperatures to which they are subjected.

  • Slates and Schists: Their qualities depend on the degree of metamorphism. They exhibit low strength and distinct cleavage. Aggregates can be obtained from them, and they are used as decorative tiles and stones.
  • Mica Schist: Exhibits more pronounced cleavage and is generally not a good construction material, sometimes used as filler.
  • Gneiss: Possesses characteristics similar to mica schist.
  • Quartzites: Siliceous in origin, they are often flaggy. Their key properties are hardness and strength. Uses: aggregates for concrete and asphalt mixtures for wearing courses, though they may have variable adhesion with binders.