Fresh concrete has different properties which are required for construction of concrete structures at site. The most important properties of fresh concrete are discussed.
Properties of Fresh Concrete for Construction Works
Workability of ConcreteConcrete workability is the relative ease with which a fresh mix can be handled, placed, compacted, and finished without segregation or separation of the individual ingredients. Good workability is required to produce concrete that is both economical and high in quality. Fresh concrete has good workability if it can be formed, compacted, and finished to its final shape and texture with minimal effort and without segregation of the ingredients. Concrete with poor workability does not flow smoothly into forms or properly envelop reinforcing steel and embedded items, and it is difficult to compact and finish. Depending on the application, a mix that has good workability for one type or size of element may be too stiff or harsh for another, so the term is relative. Each mix must be suitable for its intended use, achieving a balance among required fluidity, strength, and economy Workability is related to the consistency and cohesiveness of the mix and is affected by cement content, aggregates, water content, and admixtures. Concrete workability is increased by air entrainment. Entrained air is different from entrapped air. Entrapped air usually accounts for about 1 to 2% of the volume of fresh concrete and its inclusion is not intentional. Small amounts of air are inadvertently entrapped in the concrete mixing process. Air content can be intentionally increased by a controlled process called air entrainment, which uses either a special cement or a chemical admixture to introduce evenly distributed, microscopic air bubbles. In fresh concrete, the tiny air bubbles act almost like ball bearings or a lubricant in the mix, and in hardened concrete they increase winter durability. Too much air reduces the strength of concrete, though, so air content is generally recommended to be within the ranges shown in table below.
|Sl. No.||Maximum aggregate size, mm||Air content, % by volume|
|1||10||6 to 10|
|2||12.5||5 to 9|
|3||20||4 to 8|
|4||25||3.5 to 6.5|
|5||40||3 to 6|