Building related chemical reactions

[edit] What is a chemical reaction?

A chemical reaction describes a process of transformation from one or a number of chemical substances, which are known as the reactants, in to one or a number of other substances, which are known as the products.The phrase is commonly use in the field of chemistry but is also relevant to numerous other fields from energy to the environment and biology to buildings.

[edit] What chemical reactions relate to buildings?

There are many many different chemical reactions that relate to buildings, below are some common ones.

[edit] Degradation

Degradation is a complex slow process by which substances might be deformed or broken down into smaller molecules by external factors such as UV light or chemical reactions.

[edit] Biotic degradation

Biotic degradation (or biodegradation) is where natural microorganisms such as fungi and bacteria degrade chemicals to obtain energy. Hydro-biodegradation is a breaking down process caused by hydrolysis, and then oxidation, whilst oxo-biodegradation occurs just in the presence of oxygen (accelerated by heat and light). Biodeterioration is the first primarily surface related stage, bio-fragmentation the second, where polymer bonds are broken down forming oligomers and monomers and assimilation is considered the final stage of biodegradation.

[edit] Abiotic degradation

Abiotic degradation similarly occurs via hydrolysis, photolysis or oxidisation. The chemical reaction that causes rust in metals is called is an oxidation reaction. This is where iron reacts with water and oxygen to form hydrated iron oxide, which we see as rust. Iron and steel rust when they come into contact with water and oxygen. Similarly a common abiotic degradation issue in ceramics involves soluble salts that enter the boy of a ceramic material from the environment.

[edit] Lime

Lime is a white caustic alkaline substance consisting of calcium oxide, which is obtained by heating limestone and which combines with water with the production of much heat; quicklime.

[edit] Hydraulic lime

Hydraulic lime (HL) is a general term for calcium oxide, a variety of lime also called quicklime, that sets by hydration. The more hydraulic a lime is, the faster it sets and the higher its final strength, but this means that it is less breathable and flexible it is.

For more information see: Hydraulic lime.

[edit] Non-hydraulic lime

Non-hydraulic lime is made from a pure limestone, pure calcium carbonate, and tends to be in the form of a putty. Non-hydraulic lime sets by carbonation Non-hydraulic lime is sold as either hydrated lime or putty lime; they set and harden through drying out and absorbing carbon dioxide from the air.

For more information see: Non-hydraulic lime.

[edit] Cement

Cement is a powdery substance made by calcining lime and clay, mixed with water to form mortar or mixed with sand, gravel, and water to make concrete.

For more information see: Cement.

[edit] Hydraulic cement

Hydraulic cement, limestone, clay and gypsum, are combined to form what is known as Portland cement, which is subject to the chemical reaction of hydration. Firstly Limestone (calcium carbonate) is converted to a water-soluble material, lime (calcium oxide) which then in turns converts back to a water-insoluble material when cement hardens and cures (calcium hydroxide). Over time the electrochemical reaction between carbon dioxide, moisture and calcium hydroxide which produces calcium carbonate is called carbonation.

[edit] Non-hydraulic cement

Non-hydraulic cement is made up of lime, gypsum plaster and oxychloride it is not subject to hydration but the chemical carbonation with the carbon dioxide present in the air as such unlike hydraulic cement, which should be kept wet, non-hydraulic cement should be kept dry as it cures in the air. The chemical reaction of oxidation can cause concrete damage and normally occurs when certain materials present in the mix are exposed such as iron in the aggregates or reinforcement.

[edit] Paint

The drying of wet paint is subject to the chemical reaction of oxidation, in gloss paints, the alkyd polymer cross-links react with oxygen, evaporating the solvent to dry and harden.

For more information see: Paint.

[edit] Related articles on Designing Buildings

• Admixtures in concrete.
• Alkali-aggregate reaction (AAR).
• Alkali-silica reaction (ASR).
• Corrosion.
• Decarbonising concrete in the UK.
• Defects in construction.
• Degradation of construction materials.
• Galvanic corrosion.
• Lime concrete.
• Limestone calcined clay cement LC3.
• Marine corrosion.
• Rust.
• Types of concrete.
• Types of materials.