CONST MTRL & TESTING: CONCRETE

Concrete is the combination of cement with coarse aggregates, fine aggregates and water. When most structures have already been built using concrete, one has to always remember that concrete is low on tensile strength but strong in compression. Other advantages of using concrete in structures are easy to cast, fire resistant, can be fabricated on site, reusable and recyclable, has low maintenance and carries different aesthetic properties.

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The two kinds of concrete mixes are:

1. Nominal mix, which are the proportion of the materials to reach a desired strength usually low until 30N/mm2. The arbitrary proportions can be used to attain the strength required without any doubt or recalculations needed.

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2. Design mix, on the other hand, is the proportion of materials to make concrete for high-rise buildings. These buildings require stronger concrete, thus design mix would require the computation for the desired strength of the structure.

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The study of concrete would also need to discuss workability of concrete besides its strength. Workability is the rate at which concrete can be transported and placed without segreration of the materials, especially the coarse aggregates. Workability is in direct proportionality with the amount of water introduced in the concrete. The balance between workability and strength of the concrete can be measured with the concrete slump test.

While the concrete is setting from inside the structure, proper curing is also needed to help maintain the moisture of the concrete while it hardens. Improper curing usually is shown from the cracks on the concrete surface. Curing of concrete can be employed in various methods where ponding is the most commonly used. 

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Pre-cast concrete is a kind of concrete structure which was fabricated at the factory and not on site. Pre-cast concrete usually carry high strength wherein most often pre-tensioning of the reinforcing cables inside the concrete structure is adopted to lift the strength of the member.

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Pumped concrete is also a kind of concrete whereby it is pumped from the truck barrel to the structure. This kind of concrete would need to be high in water to be easily pumped out. Pumped concrete is used in high rise structures where pouring of concrete will be impossible to be done in any other method.