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High-strength concrete has a compressive strength greater than 40 MPa (6000 psi). In the UK, BS EN 206-1 [2] defines High strength concrete as concrete with a compressive strength class higher than C50/60. High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower.
A lower ratio leads to higher strength and durability, but may make the mix more difficult to work with and form. Workability can be resolved with the use of plasticizers or super-plasticizers. A higher ratio gives a too fluid concrete mix resulting in a too porous hardened concrete of poor quality.
The law states the strength of a concrete mix is inversely related to the mass ratio of water to cement. [1] [2] As the water content increases, the strength of concrete decreases. Abrams’ law is a special case of a general rule formulated empirically by Feret: = / where S is the strength of concrete
Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete. A 25% strength gain between 7 and 28 days is often observed with 100% OPC (ordinary Portland cement) mixtures, and between 25% and 40 ...
IS: 516BXB JWJJS– methods of test for strength of concrete. IS: 13311 – ultrasonic testing of concrete structures. IS: 4925 – specifications for concrete batching plant. IS: 3025 – tests on water samples; IS: 4990 – specifications for plywood formwork for concrete. IS: 9103 – specifications for concrete admixtures.
Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. [69] The paste is generally mixed in a high-speed , shear-type mixer at a w/c (water to cement ratio) of 0.30 to 0.45 by mass.
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Their addition allows to decrease the water-to-cement ratio of concrete or mortar without negatively affecting the workability of the mixture. It enables the production of self-consolidating concrete and high-performance concrete. The water–cement ratio is the main factor determining the concrete strength and its durability. Superplasticizers ...