Concrete Terminology

Concrete
Concrete is an artificial building construction material made from a mixture of portland cement, water, fine and coarse particles, and a small amount of air. Concrete is the most widely used construction material in the world. Concrete is the only major building material that can be delivered to the job site in a soft state. This unique quality makes concrete desirable as a building material because it can be molded to virtually any form or shape. Strong, economical, and durable, concrete also provides a wide choice of surface textures and colors.

Composition
The two major components of concrete are wet cement and inert materials. The inert materials are usually composed of fine particles such as sand and coarse particles such as gravel, crushed stone, or slag. When portland cement is mixed with water, the compounds of the cement react and harden. As the cement hardens, it binds the particles into a solid mass. After exposed surfaces of concrete have hardened sufficiently to resist marring, they should be sprinkled or covered with water or kept moist by using moisture-retaining materials. The longer concrete stays moist, the stronger it becomes. Under normal conditions, concrete grows stronger as it grows older.

Depending on the applications, the proportions of the ingredients in the concrete can be altered to produce specific changes in its properties, particularly strength and durability. Concrete can be made watertight or highly permeable. The correct mixture can produce a heavy product or concrete light enough to float on water.

Construction and Masonry Techniques
Concrete is poured into place in a number of ways. For the footings of small buildings, the wet concrete is poured directly into trenches dug into the earth below frost level. Concrete for foundations and certain types of walls is places between supporting wood or metal forms, which are removed after the concrete has hardened. In lift-slab construction, slabs are cast at ground level, then raised by hydraulic jacks and fastened to columns at the desired elevation. Many other forming techniques have been developed for specific situations.

In air-entrained concrete, tiny air bubbles are intentionally trapped in the cement. These bubbles act as a lubricant in freshly mixed concrete, reduce the need for fine particles, and, when used on roads and streets, limit scaling and provide room for the water in the concrete to expand harmlessly as freezing occurs.

Block and brick building units molded of concrete are used in all types of masonry construction. Masonry units are cored to reduce weight and to provide an insulating air space within the block. Basic block types are fairly well standardized today and are manufactured in virtually any color or texture.

Reinforced Concrete
Concrete in most construction work is reinforced with steel. When concrete structural members must resist extreme stretching forces, steel supplies the necessary strength. It is embedded in the concrete in the form of a mesh, or as roughened or twisted bars. Prestressing concrete with tightly stretched steel has removed many limitations on the spans and loads for which a concrete structure can be economically designed. The strengthening effect of prestressing results from compression. As the steel pulls along its length, the concrete is pressed together and becomes less subject to stretching forces in other directions. Prestressed concrete allows the construction of structures spanning greater widths than would otherwise be possible.

What Does "Slump" Mean?
Slump is an indication of how well the concrete flows. This is important to determine how much water is in the concrete. Usually, the lower the slump, the less water is in the mix and the stronger the concrete will be. The slump is measured by putting concrete in a 12" tall cone with a flat top, then pulling the cone up and allowing the concrete to slump down. The distance the concrete falls from the top of the cone to the top of the slumped concrete is the slump. With today's concrete though, you can achieve a high slump without using much water with the application of superplasticizers or mid-range water reducers.


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