The problem with dampness and corrosionc

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Factors affecting buildings

Humidity is ubiquitous in our environment, which poses a threat to the durability of buildings. All elements of a building are constantly exposed to it from the outside as well as from the inside.

Walls of buildings are most often affected by humidity in the form of water vapour arising from daily activities or emergency situations such as flooding.

Atmospheric conditions affect the building from the outside, and groundwater acts on the foundations.

An additional problem is the freezing and thawing of water inside the walls.

Causes of problems with dampness

Improper insulation of a building and its foundations, incorrect drainage of rainwater or leaking roof coverings cause water and moisture to enter the walls.

Problems with dampness are mainly due to poor insulation of the walls. In the winter, condensation occurs on the walls from the warmer air indoors. Inadequate ventilation can lead to residual dampness in the walls. This translates into the emergence of an unhealthy microclimate for people.

Groundwater and dampness in buildings

When groundwater or rainwater are badly discharged from a building, it can pass through the leaks in insulation. This can lead to capillary uptake of moisture from the ground.

In the winter, water which got inside the walls freezes, increasing its volume. This inevitably causes the foundations and walls to burst.

Impact of chemical compounds

Water is rarely chemically neutral. Often other substances are dissolved in it (chlorides, sulphates and nitrates), which can be chemically aggressive. Such mixtures, as a result of capillary uptake, can penetrate higher parts of the walls and cause salt efflorescence, discolouration, peeling of coatings or plastering. The substances dissolved in water can even cause chemical corrosion.

Effect of corrosion on health

Equally dangerous is biological corrosion. Damp walls are the perfect breeding ground for fungi and mould, which can be the cause of allergies or respiratory illnesses.

Damp walls are the perfect breeding ground for fungi and moulds. They can cause biodeterioration (the material is destroyed due to its nutritional value - includes things such as wood - or as a result of the action of microbial metabolites. They are also a serious threat to the health of residents.

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Biological corrosion

Biological corrosion in construction is primarily the result of the activity of home fungi, mould, unicellular yeast, algae and lichen. In the case of wood, insects should also be mentioned.

Buildings can be contaminated with many species of the above mentioned organisms. Particularly troublesome is the appearance of mould. Mould is also a threat to human health. Mould required the following to grow:

• substrate containing traces of carbon, nitrogen, phosphorus or many other elements,
• PH value close to neutral,
• increased humidity,
• suitable temperature.

Many fungi release toxic substances that can cause allergies, asthma, rheumatism, hypoxia, and even gastrointestinal diseases.

Causes of biological corrosion

The most common causes of biological corrosion in buildings are:

• lack of ventilation,
• improper insulation,
• improper execution of the drainage system for groundwater and surface water,
• use of high humidity wood in a building,
• use of materials which are unprotected from biological corrosion,
• defects in insulation, installation and other building components,
• use of rooms not in accordance with their purpose,
• design and construction errors of building partitions,
• lack of proper building maintenance.

Chemical corrosion causes concrete to crack and fall apart, in extreme cases leading to the complete destruction of the concrete structure. As a result, salts which are difficult to dissolve are formed which under the influence of crystallisation increase their volume. This in turn leads to the elution of the components of concrete and the formation of readily soluble salts.

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Chemical corrosion

Carbonisation is corrosion that occurs from the outside of a concrete structure. Carbon dioxide from the air reacts with hydration products of clinker phases and forms calcium carbonate. Its presence does not cause damage to the concrete, but it lowers the PH of the walls. As a result, the protective layer (passivation) gradually disappears from the surface of the reinforcing steel.

Carbonisation occurs quickest in conditions which are alternately humid and dry. When an area of concrete with PH lower than 9 reaches the reinforcing bars whilst the moisture content in the concrete is high, the reinforcing steel will corrode rapidly. Rust has a greater volume than steel. The resulting stress leads to the concrete cracking. The reinforcing bars may become completely exposed. When concrete is exposed to chloride ions, the corrosion of steel greatly accelerates.

Chloride corrosion

Chloride ions penetrate the cement matrix the quickest. They cause a reduction in the PH of concrete and corrosion of the reinforcing steel. The course of corrosion is similar to the process of carbonation. Chloride corrosion can be caused by the action of mine or sea water, however, most often it is caused by de-icing agents.

Factors influencing the easier penetration of chlorides are alternating saturation and drying as well as frost action.

Sulphate corrosion

This is one of the most dangerous types of corrosion. It is most commonly found in structures exposed to groundwater, sewage or seawater. Sulphates in groundwater usually occur naturally, although they can also be from fertilisers or industrial waste water. In sea water, sulfate ions are accompanied by large amounts of chloride, sodium and magnesium ions, which intensifies its damaging effects.

Physical effects of sulphate corrosion:

• expansion,
• cracking,
• peeling,
• loss of strength,
• complete destruction of concrete.

Corrosion caused by alkali-aggregate reaction

Two types of aggregates most often react with alkali derived from cement, water, or chemical admixtures:

• aggregates rich in reactive silica (Opal, chalcedony, tridymite) - alkali-silica reaction ASR,
• carbonate aggregates (functional limestone) - ACR-alkali carbonate reaction.

These aggregates can react with alkali present in concrete only in the presence of water. As a result of this reaction an alkaline gel is formed, which absorbs water and swells indefinitely. Around the active grains, gelatinous coatings of even up to 2 mm thickness are formed. Restrictions on the gel through the presence of cement causes internal stress resulting in the cracking and breakdown of concrete.