The Properties and Requirements of Good Building Stones for Construction

Properties of Stones

The following properties of the stones should be looked into before selecting them for engineering works:

1. Structure.
2. Texture.
3. Density.
4. Appearance.
5. Strength.
6. Hardness.
7. Percentage Wear.
8. Porosity and Absorption.
9. Weathering.
10. Toughness.
11. Resistance to Fire.
12. Ease in Dressing.
13. Seasoning.

1. Properties of Stone: Structure

The structure of the stone may be stratified (layered) or unstratified. Structured stones should be easily dressed and suitable for super-structure. Unstratified stones are hard and difficult to dress. They are preferred for the foundation works.

2. Properties of Stones: Texture

Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable.

3. Properties of Stones: Density

Denser stones are stronger. Light-weight stones are weak. Hence stones with a specific gravity less than 2.4 are considered unsuitable for buildings.

4. Properties of Stones: Appearance

A stone with uniform and attractive colour is durable if grains are compact. Marble and granite get a very good appearance, when polished. Hence they are used for face works in buildings.

4. Properties of Stones: Strength

Strength is an important property to be looked into before selecting stone as a building block. Indian standard code recommends, a minimum crushing strength of 3.5 N/mm² for any building block. Table 1 shows the crushing strength of various stones. Due to the non-uniformity of the material, usually, a factor of safety of 10 is used to find the permissible stress in a stone.

Hence even laterite can be used safely for a single storey building because in such structures expected load can hardly give stress of 0.15 N/mm². However in stone masonry buildings care should be taken to check the stresses when the beams (Concentrated Loads) are placed on laterite wall.

Table 1. Crushing Strength of Common Building Stones

5. Properties of Stones: Hardness

It is an important property to be considered when a stone is used for flooring and pavement. 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.

6. Properties of Stones 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%.

7. Properties of Stones: Porosity and Absorption

All stones have pores and hence absorb water. The reaction of water with a material of stone cause disintegration. 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.

8. Properties of Stones: Weathering

Rain and wind cause loss of the good appearance of stones. Hence stones with good weather resistance should be used for face works.

9. Properties of Stones: Toughness

The resistance to impact is called toughness. It is determined by the impact test. Stones with toughness index more than 19 are preferred for road works. Toughness index 13 to 19 are considered medium tough and stones with toughness index less than 13 are poor stones.

10. Properties of Stones: Resistance to Fire

Sand-stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.

11. Properties of Stones: Ease in 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.

12. Properties of Stones: Seasoning

The stones obtained from the quarry contain moisture in the pores. The strength of the stone improves if this moisture is removed before using the stone. The process of removing moisture from pores is called seasoning. The best way of seasoning is to allow it to the action of nature for 6 to 12 months. This is very much required in the case of laterite stones.

Requirements of Good Building Stones

The following are the requirements of good building stones:

1. Strength
2. Durability
3. Hardness
4. Toughness
5. Specific Gravity
6. Porosity and Absorption
7. Dressing
8. Appearance
9. Seasoning
10. Cost

1. Strength : The stone should be able to resist the load coming on it. Ordinarily this is not of primary concern since all stones are having good strength. However in case of a large structure, it may be necessary to check the strength.

2. Durability: Stones selected should be capable of resisting adverse effects of natural forces like wind, rain, and heat.

3. Hardness: The stone used in floors and pavements should be able to resist abrasive forces caused by the movement of men and materials over them.

4. Toughness: Building stones should be tough enough to sustain stresses developed due to vibrations. 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 construction should be tough.

5. Specific Gravity: Heavier variety of stones should be used for the construction of dams, retaining walls, docks, and harbors. The specific gravity of good building stone is between 2.4 and 2.8.

6. Porosity and Absorption: Building stone should not be porous. If it is porous rainwater enters the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of water in pores takes place and it results in the disintegration of the stone.

7. Dressing: Giving the required shape to the stone is called dressing. It should be easy to dress so that the cost of dressing is reduced. However the care should be taken so that, this is not at the cost of the required strength and the durability.

8. Appearance: In case of the stones to be used for face works, where appearance is a primary requirement, its colour and ability to receive polish is an important factor.

9. Seasoning: Good stones should be free from the quarry sap. Laterite stones should not be used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning.

10. 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.

FAQ

What are the key properties to consider when selecting stones for engineering works?

When selecting stones for engineering works, you should consider the following properties: structure, texture, density, appearance, strength, hardness, percentage wear, porosity and absorption, weathering, toughness, resistance to fire, ease in dressing, and seasoning.

How does the structure of a stone affect its use in construction?

The structure of a stone, whether stratified or unstratified, impacts its suitability for different applications. Stratified stones are easier to dress and are suitable for super-structures, while unstratified stones are typically harder and used for foundations due to their durability.

Why is density important when choosing building stones?

Density indicates the strength of a stone. Denser stones are generally stronger and more suitable for construction purposes, while stones with a specific gravity less than 2.4 are considered unsuitable for buildings due to their lower strength.

How does texture influence the use of stones in construction?

Fine-grained stones with a homogeneous texture are more attractive and suitable for carving and decorative purposes. These stones are often strong and durable, making them ideal for aesthetic applications.

What is the significance of a stone’s strength in construction?

The strength of a stone determines its ability to withstand loads. The Indian standard code recommends a minimum crushing strength of 3.5 N/mm² for building blocks. Stones with higher strength are preferred for structural elements, while weaker stones may be used in less load-bearing applications.

How is hardness measured and why is it important?

Hardness is measured using Dory’s testing machine. Stones with a higher coefficient of hardness are more suitable for flooring and pavement as they can resist abrasion. Stones with a hardness coefficient less than 14 are generally not recommended for building works.

What does percentage wear indicate about a stone’s suitability?

Percentage wear, measured by the attrition test, indicates how much a stone will wear over time. For road works and railway ballast, a good stone should not have more than 2% wear, as high wear rates can affect the stone’s performance and longevity.

Why is porosity and absorption important for building stones?

Porosity and absorption affect a stone’s durability and resistance to weathering. Stones with high porosity absorb more water, which can lead to disintegration and damage. A good building stone should have low absorption, ideally less than 5%.

How does weathering affect stones used in construction?

Weathering, caused by rain and wind, can deteriorate the appearance and integrity of stones. Stones with good weather resistance are preferred for face works to ensure they maintain their appearance and performance over time.

What is toughness and why is it significant?

Toughness refers to a stone’s resistance to impact. Stones with a toughness index greater than 19 are preferred for road works due to their ability to withstand impact stresses. Stones with lower toughness may be unsuitable for such applications.

How does resistance to fire vary among different types of stones?

Different stones have varying levels of fire resistance. Sandstones generally resist fire better, while argillaceous materials, though weaker, are good at resisting fire. This property is crucial for ensuring the safety and durability of structures exposed to high temperatures.

What is the importance of ease in dressing stones?

Ease in dressing affects the cost of stone masonry. Stones that are easy to dress reduce labor costs, but it is important to balance ease of dressing with maintaining sufficient strength and durability for the intended application.

What does seasoning involve and why is it necessary?

Seasoning involves removing moisture from stones before use. This process improves the stone’s strength and durability. Stones, particularly laterite, should be seasoned for 6 to 12 months to remove quarry sap and enhance performance.

What are the requirements for good building stones?

Good building stones should possess strength, durability, hardness, toughness, specific gravity, low porosity and absorption, ease of dressing, and attractive appearance. Seasoning and cost are also important considerations in selecting stones.

How does the cost of building stones affect the overall project?

The cost of building stones is influenced by factors such as transportation and quarry proximity. Selecting stones from nearby quarries can reduce transportation costs and overall project expenses.