Concrete durability problems in structures can be due to several factors such as temperature variation, moisture, physical and chemical factors, and biological reasons. These factors lead to various damage mechanisms (steel corrosion, concrete delamination, cracking, scaling, spalling, etc.) at different damage levels.
Durability is the ability to withstand weathering action, chemical attack, and abrasion without suffering significant deterioration and maintaining its desired engineering properties.
Different structures require a specific degree of durability based on the environmental exposure and the function of the structure, which dictates the desired properties of materials.
5 Concrete Durability Problems In Structures
1. Concrete Durability Problems Due To Temperature
Contraction and expansion of concrete due to temperature variations lead to durability problems in structures. The detrimental effects of contraction and expansion, such as crack development, occur in restrained concrete elements.
Concrete restraining may occur due to its connection to members such as columns, beams, slabs, foundations. Restraint to volume changes can cause cracking provided that the tensile stresses that develop exceed the tensile strength of the concrete.
Temperatures higher than 90°C (203°F) cause significant changes in concrete. At this temperature, the average value of the concrete expansion is around ten millionth/1C, which amounts to a length change of 5mm per 10m of concrete.
These effects are due to a change in the volume of cement paste and aggregates. Cement paste shrinks at high temperatures due to dehydration while aggregates expand. Therefore, exposure to very high temperatures (i.e., fire) would result in concrete spalling, particularly when the concrete is exposed to high temperatures for a long time.
Factors such as moisture condition of the concrete, types of aggregates and their stability, cement content, duration of exposure to high temperature, rate of change in temperature, age of concrete, and support conditions affect the durability of concrete at high temperature.
Finally, isolation joints and correct detailing lead to the reduction of the detrimental impact of temperature variations.
2. Concrete Durability Problems Due To Moisture
When concrete starts to dry, shrinkage first occurs at the surface of the concrete. This shrinkage of concrete at the surface develops tensile stresses on the concrete surface, which leads to the development of random cracks, especially when concrete element lacks joints.
Problems such as carbonation and moisture cycles are also related to the moisture. The moisture cycles lead to the swelling and shrinkage of concrete. This causes crack formation on concrete surfaces.
3. Physical Factors Affecting Concrete Durability
Sliding of equipment on a concrete surface, scraping, and impacts are physical factors that lead to the abrasion of concrete. In hydraulic structures, factors such as waterborne silt, sand, gravel, rocks, ice, and other debris cause abrasion and erosion. Cavitation in concrete generally occurs when a flow of water with high-velocity) suffers an abrupt change in direction or velocity.
That abrasion resistance is related to the compressive strength of the concrete. That is why strong concrete has more resistance than weak concrete.
Hard aggregates are more abrasion resistant than soft aggregates, and steel-troweled surfaces resist abrasion more than a surface that is not troweled.
Finally, overloading of structures is another physical factor that could cause durability problems since it overstresses structural elements and results in excessive deflection and cracking.
Overloading can occur for a variety of reasons, for example, a change in the use of a structure without proper structural upgrades, unintentional overloading, and other unusual circumstances.
4. Biological Factors Affecting Durability
Concrete gets damaged by live organisms such as sponges, plants, marine borers, or boring shells. Rotting seaweed has been known to produce sulfur which can be easily be converted to sulfuric acid. The presence of sulfuric acid in contact with concrete leads to concrete disintegration.
5. Chemical Factors Affecting Concrete Durability
The durability of concrete is affected by chemical reactions due to chemical interactions between aggressive agents present in the external environment and the constituents of the cement paste.
However, alkali-aggregate reactions occur within the concrete to form a gel that swells. It occurs between the alkalis in cement paste and certain reactive materials when present in aggregate, delayed hydration of crystalline CaO and MgO if present in excessive amounts in Portland cement, and electrochemical corrosion of embedded steel in concrete.
Chemical reactions in concrete result in an increase in porosity and permeability, decrease in strength and cracking, and spalling.
Sulfate attack, alkali-aggregate attack, and corrosion of embedded steel due to chemical reactions in concrete are responsible for the deterioration of a large number of concrete structures.