Concrete – proper handling of a modern building material
mixing water gives rise to crystalline hydrate phases (including calcium silicate hydrates etc.) and calcium hydroxide, resulting in an alkaline environment with a pH value of 12 to 13. In a stable, highly alkaline concrete, a passivation layer forms on the surface of the reinforcing bars which, despi- te exposure to oxygen and moisture, protects the steel from corrosion. When made properly, high-quality concrete does not suffer decay other than normal surface weathering. Decay is almost always attributable to errors made in manufacturing, planning or during use and to the fact that in previous decades the mechanisms underlying decay were insufficient- ly well understood. It is normal for alkalinity to fall in concrete exposed to a central European atmosphere. The calcium hydroxide of the cement reacts with atmospheric carbon dioxide to form calcium carbonate, which incre-
Concrete as we know it today has been in existence for more than 100 years. It was the idea of the gardener Josef Monier to make flower pots of cement mortar lighter and more durable by embedding wire netting, so laying the foundations for the development of the composite material steel-reinforced concrete. The combination of the compressive strength properties of concrete with the tensile strength of steel has proved outstandingly successful in all areas of construction. Reinforced concrete is made on site or in a facto- ry using manual methods. As a result, quality and durability are more high- ly dependent on the care taken during processing than is the case with a »finished« building material. This, together with environmental exposure, is the reason for the issues surrounding concrete decay.
Structural influences
Long-term behaviour of concrete
Concrete hardens chemically. The reaction between the clinker and the
Concrete hardening
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