Degradation of stone materials

Question 1

Which are the three types of weathering that can occur?

Answer 1

Weathering = degradation strictly related to environmental conditions

PHYSICAL WEATHERING
Carbon expansion, gelivity

CHEMICAL WEATHERING
The material dissolves by the effect of rain, acids

BIOLOGICAL WEATHERING
The material is damages due to the effects of biological things, fungal etc.

Question 2

What are the boundary conditions?

Answer 2

The boundary conditions are the environment and climat that the stone is subjected to. It is important to consider these to forecast teh possible weathering mechanisms.

Question 3

Some considerations about natural weathering of stones

Answer 3

• Alteration does NOT necessarily involve weathering
• Natural weathering can be formation of sedimentary rocks
• Rocks in quarries are not exposed to weathering pollutants as much
• Rocks in cold environments are exposed to physical weathering the most (gelivity, thermal changes)
• Rocks in tropical environments is exposed to chemical weathering the most (water)

Question 4

What are some different alterations?

Answer 4

• Fractures
• Deformation (swelling)
• Chromatic alteriations
• Formation of surface coatings and crusts
• Loss of materials
• Loss of smoothness, surface roughness

Question 5

Explain the physical weathering of stone materials

Answer 5

There are several mechanisms for physical weathering and they are the following:
Micro-traumas during processing
Coupling or contact with other stone materials
Too high loads/mechanical stresses
Thermal shock effects
Light effect
Wind and water effects

Question 6

Explain the consequences of physical weathering

Answer 6

The consequences of physical weathering can be tremendous, like the following:
Flaking
Disintegration or detachment
Exfoliation
Swelling
Fracture or cracks

Question 7

Explain the mechanisms of chemical weathering for carbonatic stones

Answer 7

There are three mechanisms:
bi carbonation
Nitrification
Sulfation

Question 8

Explain sulfation

Answer 8

Sulfation occurs when a stone is carbonatic based adn is exposed to the atmosphere and the pollutants in the air form industrial emissions. They can form sulfuric oxide and react with acid water. This comes in contact with the carbonatic rock and the acids reacts with it and forms calcium sulfate. Then dark crusts can form which increases due to the salt since the salt has a 5 times higher thermal expansion coefficient than the stone which induces stresses and swelling.

Question 9

Explain the chemical weathering os silicate-based rocks

Answer 9

Ex granite: contains feldspader, quartz and mica. The chemical weathering of granite primarily involves the hydrolysis of feldspar, oxidation of biotite and other ferromagnesian minerals, hydration, and carbonation. These processes lead to the breakdown of the original minerals in granite, forming clay minerals, oxides, and hydroxides, as well as dissolved ions. This results in increased porosity, weakening of the rock structure, and the gradual disintegration of granite over time.

Question 10

What is the effect of temperature?

Answer 10

Temperature changes can induce mechanical stresses, and if two materials are in contact and have different thermal expansion coefficients, they will expand differently and there will be an increase of the internal stresses.

Question 11

What is the effect of water?

Answer 11

Water can wash away material in a slow way, erosion. Water is very dangerous for porous materials since they can enter and crystallization of soluble salts can occur when the water evaporates in the pores and the salt creates crystals that expands and creates pressure on the pore walls. A consequence of crystallization of soluble salts is alveolarization, which is a disintegration action due to the high pressure inside the pores.

Question 12

which are the biological organisms?

Answer 12

Heterotrophic bacteria: can develop and grow only on the material there are organic residua or in consequences of restorative, conservative or presentative actions.
Chemoautotroph Bacteria exploit the energy derived from the oxidation of ammonia- or sulphate-derived salts
Fungi can cause:
Physical weathering: the hyphae can deeply penetrate inside the material → rock disintegration
Chemical weathering: fungi released acids that dissolve the rock due to pH decrease and can form salts by reacting with metal ions in the stone material
Lichens: symbiosis between fungus and alga
Moss: they cause:
Physical weathering
Chemical weathering
Superior plants: weathering caused by roots. Effects:
Formation of new cracks
Increment and enlargement of pre-existing cracks
Water entrance into these cracks and pits → washing away, rocks dissolution
Animal: birds
Human