Building stones: Requirement, Properties and its Classification

 

Building stones

Stone is defined as the natural, hard substance formed from minerals and earth mineral are formed from rocks.

Stones are formed through geological processes and are typically composed of minerals or mineral-like substances.

Technically, the stones are called as rocks. The rocks occur in great variety. All building stones are rocks in nature, all rocks may not be useful as building stones.

Stone is a natural building material that has been used for construction purposes for thousands of years. It is a hard, durable, and strong material that is formed from minerals and rocks found in the earth's crust. Stones are typically quarried from the earth and then cut into various shapes and sizes to be used in construction.

Stones are used in a variety of building applications, including walls, floors, roofs, and decorative features. They are often used in historic and traditional buildings, as well as in modern construction projects. Some common types of stones used in building construction include granite, limestone, sandstone, and marble.

Stone is a popular building material because of its durability, strength, and natural beauty. It is also fire-resistant and provides excellent insulation against heat and cold. Additionally, stone is low maintenance and can last for centuries with proper care.

Red Fort, Taj Mahal, Vidhan Sabha at Bangalore and several palaces of medieval age all over India are the famous stone buildings.

Requirement of good building stone

Good building stones possess specific characteristics that make them suitable for construction purposes. These requirements ensure that the stones can withstand the loads, weathering, and other environmental factors they may encounter in a building. Here are the key requirements for a good building stone:

1. Strength and Durability: 

Building stones should have adequate strength to bear the loads they will be subjected to. The stone should be able to resist compression, bending, and impact forces. Stones with high compressive strength are desirable for structural elements such as foundations, columns, and beams. Durability is also crucial, as the stone should be able to withstand weathering, chemical attacks, and other deterioration factors over time.

2. Hardness: 

A good building stone should be hard to resist abrasion and wear. Stones with high hardness are less susceptible to surface damage and can maintain their appearance and structural integrity over a long period. This is especially important for areas with high foot traffic or where the stone will be exposed to mechanical stress.

3. Density and Weight: 

Density refers to the mass per unit volume of the stone. A higher density indicates a compact and strong structure, which is advantageous for load-bearing purposes. However, excessively dense stones can make construction difficult due to their weight. The weight of the stone should be manageable during transportation, installation, and overall structural support.

4. Porosity and Absorption: 

Porosity refers to the presence of small openings or voids within the stone. Building stones should have low porosity to minimize water absorption. High porosity can lead to water penetration, which can cause deterioration, such as cracking, efflorescence (salt deposits), and freeze-thaw damage. Stones with low water absorption are preferred as they are less prone to these issues.

5. Weathering Resistance: 

Building stones are exposed to various weather conditions, including temperature fluctuations, moisture, wind, and sunlight. Stones with good weathering resistance can withstand these factors without significant deterioration. They should not deteriorate, change color, or lose strength due to environmental exposure.

6. Workability: 

Good building stones should be easy to work with and shape into desired forms. They should allow for cutting, carving, and shaping without excessive effort or risk of damage. Workability is essential for achieving precise dimensions, smooth finishes, and intricate designs.

7. Aesthetics: 

Building stones contribute to the visual appeal of structures. They should have pleasing colors, textures, and patterns that enhance the overall architectural design. Stones with natural beauty and visual interest are often preferred for decorative elements and facades.

8. Availability and Cost: 

While not a physical requirement, availability and cost are practical considerations. Good building stones should be locally available or easily accessible to reduce transportation costs. The cost of the stone should be reasonable and within the project's budget.

Properties and Characteristics of good building stone

To determine the suitability of a stone as a good building material, certain properties and characteristics need to be considered. Here are the specific range requirements for a good building stone:

1. Strength: 

Building stones should possess adequate strength to withstand the loads and stresses they will be subjected to. The compressive strength of a stone is an important parameter and should ideally be in the range of 70 to 140 megapascals (MPa) for most construction purposes. For a good structural stone, the crushing strength should be greater than 100 N/mm². However, the specific strength requirement may vary depending on the type of construction and the intended use of the stone.

2. Durability: 

A good building stone should be durable and capable of withstanding weathering and environmental factors without significant deterioration. Stones with low porosity and low water absorption are generally more durable. The water absorption rate of a stone should be less than 1% for it to be considered suitable for construction.

3. Density: 

The density of a stone affects its strength, durability, and ease of handling. Stones with higher density tend to be stronger and more durable. Denser stones are stronger. Light-weight stones are weak. The specific gravity of a good building stone should ideally be in the range of 2.4 to 2.8. Stones with lower specific gravity may be more porous and less durable.

4. Porosity and Absorption: 

Porosity refers to the presence of open spaces or pores within the stone. Low porosity is desirable in building stones as it reduces water absorption and enhances durability. Ideally, the porosity of a good building stone should be less than 10%.

All stones have pores and hence absorb water. If stones used in building construction are porous then rainwater can easily enter into the pore spaces and cause damage to the stones. Therefore, building stone should not be porous. Water absorption of stone is directly proportional to the porosity of rock. If a stone is more porous then it will absorb more water and cause more damage to stone. The absorption test is specified as the percentage of water absorbed by the stone when it is immersed underwater for 24 hours. For a good stone it should be as small as possible and in no case more than 5.

5. Appearance: 

The appearance of a stone plays a crucial role in its selection for construction purposes. It includes factors such as color, texture, and pattern. The color and texture should be aesthetically pleasing and compatible with the overall design scheme. The stone should also be free from excessive cracks, blemishes, or other defects that may affect its structural integrity or visual appeal.

6. Workability: 

The workability of a stone refers to its ability to be shaped, cut, and dressed into desired forms. A good building stone should be easily workable with standard tools and techniques. It should not be too hard or brittle, as this could lead to difficulties in processing and construction.

7. Availability: 

The availability of the stone in the desired quantity and quality is an essential consideration. It should be accessible locally or from reliable sources to ensure cost-effectiveness and timely construction.

8. Hardness: 

The coefficient of hardness is to be found by conducting a test on a standard specimen in Dory’s testing machine. For road works coefficient of hardness should be at least 17. For building works stones with a coefficient of hardness less than 14 should not be used.

9. Toughness: 

Toughness of stones means it ability to resist impact forces. It is determined by the impact test. Stones with toughness index more than 19 are preferred for road works. The vibrations may be due to the machinery mounted over them or due to the loads moving over them. The stone aggregates used in the road constructions should be tough. Building stones should be tough enough to sustain stresses developed due to vibrations. 

10. Percentage Wear: 

It is measured by the attrition test. It is an important property to be considered in selecting aggregate for road works and railway ballast. A good stone should not show the wear of more than 2%.

11. Fire Resistance: 

Stones should be free from calcium carbonate, oxides of iron, and minerals having different coefficients of thermal expansion.  Igneous rock show marked disintegration principally because of quartz which disintegrates into small particles at a temperature of about 575°C. Limestone, however, can withstand a little higher temperature, i.e. up to 800°C after which they disintegrate. Sand-stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.

12. Ease in Dressing: 

Giving required shape to the stone is called dressing. The cost of dressing contributes to cost of stone masonry to a great extent. The dressing is easy in stones with lesser strength. Hence an engineer should look into sufficient strength rather than high strength while selecting stones for building works. 

13. Cost:

Cost is an important consideration in selecting a building material. The proximity of the quarry to the building site brings down the cost of transportation and hence the cost of stones comes down.

Classification of Building Stones

The building stones are obtained from the rocks which are classified in the following three ways:

Classification of Building Stone: 

1. Physical classification 

• Stratified rocks  
• Unstratified rocks 
• Foliated rocks  

2. Scientific or Engineering classification or Chemical classification  

• Silicious Rocks 
• Argillaceous Rocks 
• Calcareous Rocks

3. Geological classification

• Igneous Rocks 
• Sedimentary Rocks
• Metamorphic Rocks

1. Physical classification: 

This classification is based on general structure of rocks. According to this classification, the rocks are of the following three types:

• Stratified rocks 
• Unstratified rocks 
• Foliated rocks 

Stratified rocks: 

Stratified rocks show distinct layers along which rocks can be split. Their different layers are also called beds. 

Limestone and sandstone are the stratified rocks.

Unstratified rocks: 

Unstratified rocks do not show any types of layers or stratification and cannot be split into thin layers.

Graphite, marble, basalt and trap are the unstratified rocks.

Foliated rocks: 

Foliated rocks have a tendency to be split up in a definite direction only. The Foliated structure is very common in case of metamorphic rocks.

2. Chemical classification:

This classification is known as scientific or engineering classification and according to this classification, the rocks are of the following three types:

• Silicious Rocks
• Argillaceous Rocks
• Calcareous Rocks

Silicious rocks: 

In these rocks, the silica predominates; means, the principal constituent is silica (SO2) i.e., sand. The rocks are hard and durable. They are not easily affected by the weathering agencies. Granite, sandstone, gneiss, basalt, trap syenite are the siliceous rocks.

Argillaceous Rocks: 

In these rocks, the argil or clay predominates; means, these have clay as the principal constituent. These stones are hard and durable but brittle in nature. Slate and laterite are the argillaceous rocks.

Calcareous Rocks: 

In these rocks, the calcium carbonate predominates; means, these have carbonate of lime as the principal constituent. Limestone, marble, kankar, dolomite, and gravel are the calcareous rocks.

3.Geological classification: 

This classification is based on the formation of rocks. According to this classification, the rocks are of the following three types:

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks.

Igneous rocks: 

The molten or pasty rocky material is known as the magma and this magma tries to come out to the earth's surface through cracks or weak portions. The rocks which are formed by cooling of magma are known as the igneous rocks. These rocks are durable, hard, massive and stronger than other stones. Example: Basalt, Trap, Andesite, Rhyolite, Diorite, Granite.

The igneous rocks are recognized in the following three classes:

• Plutonic rocks
• Hypabyssal rocks
• Volcanic rocks 

Sedimentary rocks: 

These rocks are formed by the deposition of products of weathering and erosion on pre-existing rocks. The natural process of rock disintegration are called weathering and erosion. Due to the action of high-speed wind and heavy rain, igneous rocks are disintegrated and deposited in layers, one the earth crust and formed sedimentary rocks. Example: Limestone, Sandstone, Dolomite and Slate are the sedimentary rocks.

Metamorphic rocks: 

These rocks are formed by the change in character of the pre-existing rocks. These rocks are either the sedimentary rocks or the igneous rocks whose physical and chemical properties are changed due to the action of high temperature and pressure.

The resultant mass may have a foliated structure, e.g. slate, gneiss,schist and phyllite or non-foliated structure, e.g. marble, quartzite and serpentine.

Some Common building stones

1. Granite:

It is a deep-seated igneous rock, which is hard, durable and available in various colours. It also having light or dark grey, pink or reddish colour. It can take nice polish.

It has a high value of crushing strength and is capable of bearing high weathering. Its sp. gr. varies from 2.63 to 2.75 and compressive strength varies from 75 to 127 N/mm2. Its weight is about 26 to 27 kN per m³. water absorption in granite is less than 1%. It contains silica 60 to 80%. • Granite is used for bridge components, retaining walls, stone columns, dams, light houses road metal, and ballast for railways, foundation, stonework and for coarse aggregates in concrete. These stones can also be cut into slabs and polished to be used as floor slabs and stone facing slabs, but it is unsuitable for carving. Granite is found in Maharashtra, Rajasthan, Uttar Pradesh, Madhya Pradesh, Punjab, Assam, Tamil Nadu, Karnataka and Kerala.

2. Basalt and Trap: 

They are originated from igneous rocks in the absence of pressure by the rapid cooling of the magma. These are hard, tough and durable and are available in different colours. Hard and tough : difficult to work. 

Its sp. gr. is 3 and compressive strength varies from 150 to 185 N/mm². Its weight varies from 18 to 29 kN per m³.

They have the same uses as granite. It is used as Road metal, for rubble masonry, foundation work, etc.

These are found in Maharashtra, Bihar, Madhya Pradesh, Gujarat and Bengal. Deccan trap is a popular stone of this group in South India.

3. Limestone and Chalk:

These are sedimentary rocks which have been formed of remnants of seaweeds and living organisms consolidated and cemented together. They are easy to work with and contain a high percentage of calcium carbonate.

 

Limestone is used for flooring, roofing, and pavements and as a base material for cement.

Its sp. gr. varies from 2.00 to 2.75 and compressive strength is 54 N/mm2. It is found in Maharashtra, Andhra Pradesh, Punjab, Himachal Pradesh and Tamil Nadu.

Chalk is the pure white limestone. It is soft and easy to form powder. It is used to prepare glazier's putty.

4. Sandstone:

This stone is another form of sedimentary rock formed by the action of mechanical sediments.

It has a sandy structure which is low in strength and easy to dress. This is available in different colours.

Its sp. gr. varies from 2.65 to 2.95 and compressive strength is 64 N/mm2. Its weight is about 20 to 22 kN per m³.

They are used for ornamental works, paving and as road metal. It is available in Madhya Pradesh, Rajasthan, Uttar Pradesh, Himachal Pradesh and Tamil Nadu.

5. Kankar:

Kankar is a sedimentary rock.It is impure limestone.

It is used as road metal, manufacture of hydraulic lime,etc.

It is found in North and Central India.

6. Laterite:

This is a metamorphic rock and is a sandy clayey stone. It is porous and soft. It can be cut easily into blocks and contains a high percentage of iron oxide.

It is decomposed from igneous rocks; occur in soft and hard varieties.The soft variety is used for walls after curing while the hard blocks are used for paving the pathways.

Its comprehensive strength varies from 1.80 to 3.10 N/mm².

7. Gneiss:

It is a metamorphic rock which can be easily split into thin slabs and is easy to work on.  It can be recognized by its elongated platy minerals usually mixed with mica and used in the same way as granite.

Its sp. gr. is 2.69 and compressive strength is 206 N/mm² .  They can be used for flooring, pavement and not for major purposes because of its weakness.  It is found in Karnataka, Andhra Pradesh, Tamil Nadu and Gujarat.

8. Marble:

It is a metamorphic rock which can be easily cut and carved into different shapes. 

It can take good polish and available in different colours. 

Its sp. gr. is 2.65 and comprehensive strength is 71 N/mm². It is used for ornamental purposes, stone facing slabs, flooring, decorative and facing works etc. It is found in Rajasthan, Gujarat and Andhra Pradesh.

9. Slate:

It is a metamorphic rock which can be split easily and available in black colour. 

Its sp. gr. is 2.89 and compressive strength varies from 75 to 207 N/mm². It is used for damp-proofing flooring and roofing.

10. Gravel:

It is available in riverbeds in the form of pebbles and is of different shapes.

it is used to make concrete, to create foundations for new roads, to mix with asphalt, fill construction sites, and even create other construction materials like blocks, pipes, and bricks. 

11.Quartzite:

It is a metamorphic rock which is hard, brittle and crystalline. It is difficult to work with and is very durable.

Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts.