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Last edited 18 Oct 2022
Building related chemical reactions
 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.
 What chemical reactions relate to buildings?
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.
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.
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.
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.
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.
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.
- Admixtures in concrete.
- Alkali-aggregate reaction (AAR).
- Alkali-silica reaction (ASR).
- Decarbonising concrete in the UK.
- Defects in construction.
- Degradation of construction materials.
- Galvanic corrosion.
- Lime concrete.
- Limestone calcined clay cement LC3.
- Marine corrosion.
- Types of concrete.
- Types of materials.
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