Building Stones and Characteristics

Building Stones: Characteristics and Key Features for Selecting the Right Material

What Are Building Stones?

Building stones are one of the oldest construction materials used by humans to build shelters and tools. Throughout history, stone has been widely used in various structures, from ancient monuments to modern architectural marvels. While materials like brick and concrete have gained popularity due to their ease of use, stone remains a preferred choice for structures requiring durability and resilience, such as bridges, tunnels, retaining walls, avalanche barriers, and load-bearing foundations.

When selecting natural stone for construction, several key properties must be considered, including compressive strength, tensile strength, permeability, weather resistance, and stability. The stone must be free of cracks, pores, fractures, or weak layers that could compromise its structural integrity. Additionally, its color and texture should remain consistent over time.

Classification of Building Stones

Building stones are categorized based on several factors, including their weight, compressive strength, and durability:

1. Classification Based on Density

• Heavy Stones: Stones with a density of more than 1.8 g/cm³, suitable for load-bearing structures.
• Light Stones: Stones with a density of less than 1.8 g/cm³, often used for decorative and non-load-bearing applications.

2. Classification Based on Compressive Strength

• High-Strength Stones: Stones with a compressive strength ranging from 100 MPa to 1000 MPa.
• Low-Strength Stones: Stones with a compressive strength of 4 MPa to 200 MPa, used for non-structural applications.

3. Classification Based on Softening Coefficient

• Usable in Construction: Stones with a softening coefficient between 0.6 and 1 are suitable for structural use.

Applications of Building Stones

1. Foundation and Wall Construction

For foundations and underground structures, igneous and sedimentary stones with a softening coefficient above 0.7 are preferred. These stones should be free of clay minerals, cracks, or any heterogeneous inclusions.

2. Stone Walls and Facades

For exterior walls, suitable stones should meet the following criteria:

• Compressive strength: 0.4 MPa to 50 MPa.
• Density: 0.9 g/cm³ to 2.2 g/cm³.
• Softening coefficient: 0.6 to 0.7.
• Weather resistance: The stone should not be affected by weathering.

3. Flooring Stones

Commonly used flooring stones include:

• Granite (Highly durable, suitable for high-traffic areas)
• Marble (Elegant and luxurious but requires maintenance)
• Travertine (Slip-resistant and widely used in both indoor and outdoor spaces)

4. Stones for Road Construction

Stones used in road construction must possess the following characteristics:

• Compressive strength exceeding 100 MPa.
• Softening coefficient greater than 0.9.
• Water absorption below 1%.
• Density over 2.3 g/cm³.
• Resistant to chemical weathering.

5. Heat and Chemical-Resistant Stones

• Acid-resistant stones: Granite, diabase, diorite, quartzite, and basalt.
• Alkali-resistant stones: Limestone, dolomite, marble, and magnesite.
• High-temperature-resistant stones: Basalt, diabase, and tuff, with compressive strength exceeding 100 MPa and water absorption below 1%.

Factors Leading to Stone Deterioration

1. Effects of Salt Solutions

Salt solutions can penetrate porous stones, causing crystallization and expansion, leading to surface peeling and structural weakening.

2. Environmental Pollution

• Limestone and carbonate-based stones are susceptible to acidic environments.
• Sulfur dioxide (SO₂) reacts with moisture, forming sulfuric acid, which dissolves calcium carbonate and weakens the stone.
• Marble and limestone surfaces lose their polish over time due to acid exposure.

3. Freeze-Thaw Damage

• Porous stones like limestone and dolomite are more vulnerable to freeze-thaw cycles.
• Granite and dense metamorphic rocks are more resistant to frost damage.

4. Metal Corrosion

• Rainwater running over copper or iron can cause staining and discoloration.
• Rusting of embedded metal anchors can lead to structural instability.

5. Fire Resistance

• Granite, marble, and sandstone surfaces can blacken or crack when exposed to fire.
• Limestone is relatively fire-resistant, though its iron content may oxidize, causing a permanent pinkish hue.

Construction Techniques Using Natural Stone

For optimal stone masonry construction, the following principles must be observed:

• Pre-soaking the stone before use to improve mortar adhesion.
• Alternating stone orientations (header and stretcher courses) for stronger interlocking.
• Avoiding continuous vertical joints for better structural integrity.
• Ensuring proper mortar application to prevent direct stone-to-stone contact.
• Placing larger stones at the base for better stability.
• Using metal anchors for stone facades, preferably stainless steel or bronze to prevent corrosion.
• Avoiding construction at temperatures below 5°C to prevent mortar failure.

Key Features for Selecting Building Stones

The ideal building stone should meet the following criteria:

• Homogeneous structure, free from cracks, weak veins, or fractures.
• Low porosity, preventing excessive water absorption.
• Resistance to environmental factors, including moisture, acids, and temperature changes.
• High compressive strength (above 150 kg/cm² for load-bearing structures).
• High abrasion resistance, ensuring longevity in high-traffic areas.

Conclusion

Selecting the right natural stone for construction depends on its mechanical strength, weather resistance, and aesthetic appeal. Stones like granite, marble, and travertine remain top choices for facades, flooring, and structural elements due to their durability and timeless beauty. Proper maintenance and installation techniques further enhance their longevity, making them an excellent investment for modern architecture.