Specialist applications require different types of concrete. Examples of concrete include regular concrete, high strength concrete, high-performance concrete, self-compacting concrete, shotcrete, pervious concrete, cellular concrete, roller-compacted concrete and asphalt concrete. The use of recycled glass as an aggregate is popular these days because of aesthetic appeal.
A great variety of products are made from concrete. Examples include pavements, masonry, pipes and insulating concrete.
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Regular concrete is what you get when you follow the mixing instructions on a packet of cement, using sand or an aggregate. This type of concrete can be made to have a strength of 10MPa to 40MPa depending what it is going to be used for. 10MPa should be sufficient for blinding, for example, but structural concrete should be 40MPa.
High strength concrete has a compressive strength of usually more than 6000 pounds per square inch (40 MPa). You make high strength concrete by lowering the water to cement ratio to 0.35 or lower. Silica fume is often added to prevent the formation of free calcium hydroxide crystals in the cement matrix, because this might reduce the strength at the cement-aggregate bond.
High performance concrete is quite a new term and describes concrete that conforms to a certain set of standards including strength. High strength concrete is also high performance but not all high performance concrete is high strength. Some examples of these standards include density, toughness, volume stability, a long life even in severe environments, long term mechanical properties, compaction without segregation, ease of placement, early age strength, permeability and heat of hydration.
Shotcrete is often used against rock surfaces or vertical soil because formwork is unnecessary. It can be used for rock support, especially when tunneling. There are two application methods for shotcrete - dry mix or wet mix procedures. When using dry mix, the dry mixture of aggregates and cement fill the machine and are conveyed through the hoses with compressed air. The water necessary for hydration gets added at the nozzle. When preparing wet mix, the mixes are made with all the water necessary for hydration and pumped through the hoses. Compressed air is added for spraying, at the nozzle. For both wet mix and dry mix, additives such as fiber reinforcement and accelerators may be used.
To produce uniform, high quality concrete, it is necessary to mix your cement mixture thoroughly. In the process of hydrating and hardening, concrete has to develop certain chemical and physical properties. Among other qualities, low moisture permeability, mechanical strength and chemical and volumetric stability are very important factors.
Types of Concrete
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