These properties help estimate the quality and condition of a material without applying any external force.
Bulk Density: The ratio of mass to volume, influencing strength, heat, and conductivity.
Porosity: The ratio of void volume to material volume, affecting thermal conductivity, strength, and durability.
Water Absorption: The material’s ability to absorb and retain water.
Hygroscopicity: The ability to absorb water vapor from the air.
Fire Resistance: The ability to withstand fire without changing properties.
Frost Resistance: The ability to resist freezing and thawing.
Mechanical Properties
Mechanical properties are determined by applying external forces.
Strength: The material’s resistance to failure under load.
Hardness: The resistance to scratching, determined using the MOHS scale.
Elasticity: The ability to regain shape after deformation.
Plasticity: The ability to undergo permanent deformation without cracking.
Brittleness: The tendency to fail suddenly under stress.
Fatigue: Weakening of material under repeated loads.
Impact Strength: The ability to absorb sudden loads.
Creep: Slow deformation under constant load over time.
Coefficient of Softening: The effect of water absorption on strength.
Chemical Properties
Chemical Resistance: The ability to resist chemical effects like acids and salts.
Corrosion Resistance: The resistance to rust formation in metals.
Thermal Properties
Thermal Capacity: The ability to absorb heat.
Thermal Conductivity: The rate of heat transfer.
Thermal Resistivity: The ability to resist heat conduction.
Specific Heat: The heat required to raise the temperature of a material.
Building Stone
Classification of Stones
Stones can be classified based on their geological origin, physical properties, and chemical composition.
1. Geological Classification
Igneous Rocks: Formed from the solidification of molten magma (e.g., Granite, Basalt).
Sedimentary Rocks: Formed by the deposition of sediments over time (e.g., Limestone, Sandstone).
Metamorphic Rocks: Formed from the transformation of existing rocks under heat and pressure (e.g., Marble, Slate).
2. Physical Classification
Hard Stones: Highly durable and strong (e.g., Granite, Basalt).
Soft Stones: Easily workable but less durable (e.g., Limestone, Sandstone).
3. Chemical Classification
Siliceous Stones: Contain silica as the main constituent (e.g., Granite, Quartzite).
Argillaceous Stones: Composed of clay minerals (e.g., Slate).
Calcareous Stones: Composed mainly of calcium carbonate (e.g., Limestone, Marble).
Properties of Good Building Stones
A good building stone should possess the following qualities:
Strength: Should be able to withstand loads and stresses.
Durability: Must resist weathering and environmental factors.
Hardness: Should resist wear and abrasion.
Density: Higher density indicates better durability and strength.
Porosity and Absorption: Should have minimal water absorption to prevent deterioration.
Appearance: Should have an appealing texture and color for aesthetic purposes.
Workability: Should be easy to shape and dress without excessive effort.
Resistance to Fire: Should withstand high temperatures without significant degradation.
Toughness: Should resist impact forces effectively.
Specific Gravity: Generally, good stones have a specific gravity of 2.5 to 3.0.
Commonly Used Stones in Construction
Granite: High strength, used for heavy construction.
Basalt: Strong and durable, used for road construction.
Limestone: Used in buildings and concrete production.
Sandstone: Used in decorative works and walls.
Marble: Aesthetic appeal, used in monuments and flooring.
Slate: Used for roofing and flooring.
Quartzite: Used in pavements and decorative works.
Tests on Stones
To ensure quality and durability, stones undergo various tests:
Crushing Strength Test: Determines the load-bearing capacity of stone.
Water Absorption Test: Measures the percentage of water absorbed by stone.
Abrasion Test: Evaluates the resistance to wear and tear.
Impact Test: Assesses toughness by applying sudden loads.
Acid Test: Checks the resistance of stones against chemical weathering.
Quarrying, Dressing, and Seasoning
Quarrying
The process of removing stone from its natural deposit can be done by excavating, wedging, heating, or blasting.
Quarrying by wedging is successful for: Sandstone, Limestone, Marble
For hard stone quarrying, methods used include: Wedging, Channeling machine, Blasting
Dressing
The process of shaping and sizing stones, usually done at the quarry site.
Seasoning
Freshly quarried stones contain quarry sap, which reduces strength and causes issues like efflorescence. Seasoning removes this sap.
Cementing Materials (Lime and Cement)
Lime
Lime is a rigid binding material used since ancient times in construction. It is used for:
Concrete and mortar matrix
Low-cost building joints
Whitewashing and distempering
Timber knotting
Steel manufacturing
Historical preservation
Manufacture of Lime
Lime is produced by burning limestone, a process called calcination. This produces quick lime (CaO), which is then slaked with water to produce slaked lime (Ca(OH)₂).
Sources
Limestone: Used in flooring, mortar, cement manufacturing
Kankar: Used for hydraulic lime in substructures
Sea animal shells: Used for ornamental shell lime
Process of Manufacture
1. Collecting Materials
Pure limestone (impurity <5%) is used for fat lime; Kankar is used for hydraulic lime. Fuel sources include wood, coal, coke, and charcoal.
2. Burning
Clamp Burning
Traditional method, inefficient
Alternative layers of limestone and fuel
Not suitable during rainy seasons
Kiln Burning
Intermittent kiln: Constructed in hills/rivers, limestone stacked over an arch
Continuous kiln: Large-scale production, pure lime, coal-fired
3. Slaking of Lime
The process of converting quick lime into slaked lime:
Air Slaking: Absorbs moisture from air, incomplete process
Basket Slaking: Lime is immersed in water briefly, incomplete process
Platform Slaking: Water is added to lime in controlled conditions
Tank Slaking: Used for making lime paste, ensuring purity
Types of Lime
Fat Lime
Also called rich lime, high calcium lime, pure lime, white lime.
Volume increases by 2.5 times on slaking.
Purest lime > 95% lime.
Made by burning pure limestone, animal shells.
Used for white washing and lime plastering.
Hydraulic Lime
Contains greater than 5% impurity in the form of clay, which imparts hydraulicity (property to dry below water).
With increase in clay content, setting time under water decreases.
Hydraulic Lime Types
Feebly hydraulic: Clay 5-10%, 21 days for drying under water, 5-10 min for slacking.
Moderately hydraulic: Clay 11-20%, 7 days for drying under water, 2 hrs for slacking.
Eminently hydraulic: Clay 21-30%, 24 hours for drying under water, 5 hrs for slacking.
Poor Lime
Contains more than 5% impurity and is of low quality. Not used for engineering work.
Setting and Hardening of Lime Mortar
The process of solidification of lime mortar or concrete involves:
Dehydration: Ca(OH)2 → CaO + H2O
Carbonation: CaO + CO2 → CaCO3
Hydrolysis: Occurs due to Ca(OH)2 being altered by the action of silica and alumina.
Lime Mortar Types
Hydraulic lime mortar: Made by mixing lime and sand in a 1:2 ratio. Used for underwater concrete, plastering, etc.
Gouged mortar: Made by adding a small quantity of cement. Increases strength and decreases setting time.
Surkhi/Pozzolana mortar: Made by mixing lime and surkhi (or pozzolana). Improves strength, reduces shrinkage, and increases resistance.
Cement
Manufacturing of Cement
The raw materials used in cement manufacturing are: