The mechanisms by which concrete suffers durability problems and subsequent damage are freeze-thaw; ion flow, absorption and moisture movement within concrete; all of which relate to aspects of durability. Durability is defined within Eurocode 2 (2006), which states: 'A durable structure shall meet the requirements of serviceability, strength and stability throughout its intended working life, without significant loss of utility or excessive maintenance.' The satisfactory durability of CEM 1 (Portland cement) concrete, with or without additives, is a major reason why it is the world's most widely used construction material. Areas of concern that will adversely affect the durabiltiy of concrete are material limitations; design and construction practices; and severe exposure conditions that can cause concrete to deteriorate, which may result in aesthetic, functional or structural problems. Concrete can deteriorate for a variety of reasons, and concrete damage is often the result of a combination of factors, starting with the initiation of cracks which lead to processes that involve deleterious chemical reactions and hydrostatic breakdown, The rate of crack propagation is controlled by ionic/molecular transport systems, producing microstructural changes degrading the physical properties of the concrete. Concrete is subject to deterioration caused by the absorption of moisture and thermal expansion and contraction. Extreme temperature ranges of both hot and cold can cause spalling. Moisture absorbed by the concrete expands and contracts with temperature changes, and the resulting mechanical action can cause fractures and spalling. Airborne pollutants, such as acid rain and carboni dioxide, can cause adverse chemical reactions which can result in surface deterioration. Environmental factors such as seasonal temperature variations, cyclical freezing and thawing, rainfall and relative humidity changes, and the concentration of deletrious chemicals in the atmosphere/water in contact with the concrete, are the main causes of degradation. Geographical location is an important consideration with regard to durability, as are multiple, severe freeze-thaw cycles, which are worse for the destructive stresses applied within the concrete than ann extremely low constant temperature. All processes affecting durabiltiy are reliant upon the ingress of water or ions into the concrete. Therefore, three main areas for durability testing are: - freeze-thaw damage, - ion transfer, - factors affecting diffusion and absorption. Without proper concrete design and production control, deteriorating concrete can compromise structural integrity, pose serious liabiltiy issues, and create significant problems throughout a structure.
|Title of host publication
|Concrete Durability: A practical guide to the design of durable concrete structures
|Place of Publication
|Number of pages
|Published - Feb 2010