STONES
- All the structures are composed of different types of materials.
- For a good civil engineer, a thorough knowledge with regard to the use of these building materials is necessary.
- An engineer must be able to choose the suitable type of material as per the conditions of the environment, strength requirement, and availability, simultaneously also be able to compare the economics of construction between different alternatives.
Building stones are obtained from rocks.
Rocks are majorly classified on the basis of the mode of their occurrence, also referred to as Geological classification.
Geological Classification of Rocks
Igneous rocks:
- Rocks that are formed by the cooling of Magama or lava (molten or pasty rocky material) are known as igneous rocks. Eg: Granite, Basalt and Dolerite etc.
Sedimentary rocks:
- These rocks are formed by the consolidation of the products of weathering obtained from the pre-existing rocks. Examples: gravel, sandstone, limestone, gypsum, lignite, etc.
Metamorphic rocks:
- These rocks are formed by the change in the character of the pre-existing rocks when subjected to great heat and pressure.
- The process of their transformation is called metamorphism.
- Examples: Quartzite, Schist, Slate, Marble, and Gneisses.
The rocks can be further classified on a physical and chemical basis.
Physical Classification can be done as
1. Stratified rocks:
- These rocks possess planes of cleavage or stratification along which they can be split.
- Sedimentary rocks usually possess this property.
2. Un-stratified rocks:
- The structure may be crystalline granular or compact granular. Examples: Igneous rocks.
3. Foliated rocks:
- These rocks have a tendency to split up in a definite direction only. Ex: Metamorphic rocks.
Chemical Classification of Rocks
It is useful to predict the behavior of rock under harsh environmental conditions.
1. Siliceous rocks:
- In these rocks, silica is predominating.
- These rocks are hard; durable and not easily affected by weathering agencies.
- Example: Granite, Quartzite, etc.
2. Argillaceous Rocks:
- In these rocks, clay predominates. These rocks may be dense and compact or maybe soft.
- Example: Slates, Laterites, etc.
3. Calcareous rocks:
- Calcium carbonate is the main constituent of these rocks.
- The durability of these rocks will depend upon the constituents present in the surrounding atmosphere.
- Ex: Lime Stone, marble, etc.