What are the factors of destruction of stones? (Reasons of damage and deterioration of stones)

Despite their high resistance, stones are susceptible to deterioration and damage against many environmental and chemical factors. Even the largest and most famous stone buildings in the world are not spared from decay and destruction; As Herodotus (Greek historian) mentions in his history book that when he saw the Egyptian pyramids for the first time, the stones of the Egyptian pyramids were damaged and were being destroyed.

Several factors cause the destruction of natural stones over time, which endanger the original beauty of the stone and even cause the destruction and disintegration of the stone.

•Rain

           Frostbite or dew in cold weather

           Weathering

•Wind

            Temperature changes and expansion and contraction of rocks

           Mud stones

           Acids

           Microbiological growth

           Contact and human interventions

            Primary construction and mutual decay

            Rain, the first factor that destroys stones

Rainwater affects stones both physically and chemically, therefore, rainwater is an important destructive factor for stones that are used in facades and exteriors. The erosive power of rainwater from a physical point of view and the effect of its chemical compounds causes decomposition, hydration or oxidation of minerals in the rock and leads the rock to destruction. The rate of destruction increases when the rain becomes acidic and chemical reaction occurs between the acid and the minerals in the rock.

Intermittent wetting due to rain and drying due to the sun also causes internal stresses in the stones and as a result the stones disintegrate.

Softer rocks with less resistance (such as sedimentary rocks, limestone, etc.) wear out faster than more resistant rocks (such as metamorphic rocks, granite, etc.) against the weather. More exposure to acid rain leads to faster weathering.

Calcium-based minerals such as marble and limestone are vulnerable to acid rain. This is due to the reaction of calcium with sulfuric acid in acid rain. Due to the ability of acid rain to dissolve marble and limestone, it is not smart to use these stones in open spaces, facades of buildings and historical monuments.

Dew (humidity and cold)

The cause of destruction and loss of stones in cold and wet weather

In cold and humid areas, raindrops or dew seeps into the pores of the rocks and freezes there, expands and creates cracks. Repetition of this phenomenon causes cracking and crushing of stones. Polluted air, including steam and acid particles, can cause the destruction and bursting of rocks with chemical reactions.

Weathering and its relationship with rock erosion

Physical weathering

Physical weathering is the crushing and turning of rock into smaller pieces and particles. In these conditions, as the particles shrink, the surface-to-volume ratio increases and the rate of chemical weathering increases.

Causes of physical weathering:

• Freezing of water in the cracks of rocks
• Rock expansion and contraction due to temperature changes
• Reducing the pressure of the upper layers of rocks
• The formation of crystals in the cracks of rocks
• Expansion of plant roots
• Underground digging by some organisms
• Human interventions

Chemical weathering

Chemical weathering causes weakening and subsequent disintegration of rock due to chemical reactions. These reactions include oxidation, hydrolysis and carbonation. These processes change the nature of the mineral composition of the rock by creating or destroying minerals. Temperature and especially humidity are critical for chemical weathering.

Chemical weathering of rock minerals usually occurs faster in hot and humid climates; And in cold and dry climates, physical weathering is more effective.

Oxidation is the reaction of rock minerals with oxygen, which changes the mineral composition of the rock as a result. When the minerals in the rock are oxidized, they are less resistant to weathering. Iron is a commonly known mineral that turns red or rusty when oxidized. (You may have encountered this reaction and red spots on the stone in some granite stones, which affects the beauty of the granite stone and eventually disintegrates it.) Carbonation, the reaction process of stone minerals with carbonic acid. Is. Carbonic acid is formed from the combination of water with carbon dioxide. Carbonic acid dissolves or decomposes minerals in rock.

CO 2 + H 2 O → H 2 CO 3

(carbon dioxide + water → carbonic acid)

CaCO 3 + H 2 CO 3 → Ca 2 + + 2HCO 3-

(calcite + carbonic acid → calcium + bicarbonate)

Hydrolysis is a chemical reaction caused by water. Water changes the chemical composition and size of the minerals in the rock and makes them less resistant to weathering.

Hydration is the absorption of water in the mineral structure of the rock. Hydration increases the volume and also leads to deformation of the stone. For example, the absorption of water by anhydrite leads to the formation of gypsum.

Any weakness in the rock structure accelerates the attack of weathering agents. Therefore, seam surfaces, layering surfaces, fault surfaces or any type of gap caused by fault or folding (including shear cracks) all create suitable conditions for the effects of weathering and freezing factors. Here, proper stone processing is important to reduce the effects of weathering.

(The strength of metamorphic rocks against weathering is greater because these rocks were formed under high heat and pressure, such as marble, quartzite, and slate)