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Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time.Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as ciment fondu.However, asphalt concrete, which is frequently used for road surfaces, is also a type of concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.When aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape.It has been demonstrated that a total sand content of about 50% of total aggregate is favorable in designing for SCC.The major breakthrough in SCC technology came with the advent of third generation Poly-Carboxylic Ether based Polymers, used as admixtures.
Additionally some complex forms cannot easily be vibrated.
Ordinarily, concrete is a dense, vicous material when mixed, and when used in construction, requires the use of vibration or other techniques (known as compaction) to remove air bubbles (cavitation), and honeycomb-like holes, especially at the surfaces, where air has been trapped during pouring.
This kind of air content (unlike that in aerated concrete) is not desired and weakens the concrete if left.
The incorporation of powder, including supplementary cementitious materials and filler, can increase the volume of the paste, hence enhancing deformability, and can also increase the cohesiveness of the paste and stability of the concrete.
The reduction in cement content and increase in packing density of materials finer than 80 µm, like Fly Ash etc.