Fresh mixed concrete

Fresh mixed concrete is the state in which concretes can be mixed and ready for placement in the formwork to settle, also known as green concrete. Freshly mixed concrete material which can be molded into any shape to enable concrete to be fully settle and strengthen; a higher / water/ cement ratio must be calculated by theoretical consideration.

Workability – types of work, thickness of section extent and reinforcement and mode of compaction used.

Fresh mixed concrete is consistent which is the firmness of substance is sometime taken as the degree of wetness, wet concrete are more workable than dry concrete.

It depends on a number of interacting factors.

1. Water content
2. Aggregate type.
3. Cement ratio
4. Presence of admixtures
5. Finess of the cement.

It’s a form of segregation in which some water in the mixer tends to rise to the surface of freshly placed concrete.

It is caused by inability of soil constituent to hold all of the mixing water when they settle downwards

When cement paste has hardened, sufficiently bleeding ceases/stops. If evaporation of water from the surface of concrete is faster than bleeding rate, plastic shrinkage and cracking may occur.

Bleeding is not harmful if it is undisturbed. (water evaporates) the effective water/cement ration maybe lowered with a resulting increase in strength.

1. Water content in the mix
2. Property of cement – bleeding is lower in finer cement
3. Chemical factor in cement – there is less bleeding when cement has higher alkaline content.
4. Temperature – higher temperature within normal increases rate of bleeding.
5. Rich mixes – are less prone to bleeding than lean mixes and reduction in bleeding is obtained by addition of admixtures such as pozzolana or alluminium powder.
6. Air and trainment or entrance – affectively reduce bleeding so that finishing can follow casting without delay.

The method has been universally accepted due to their merit

Slump test

 

If the slump is evenly all around, it is referred to as the true shape.

it happens that one and half of the cone slides down in an included flame a shear slap is said to have taken place and the test should be repeated. If the shear persists as may be the case in the harsh mixes this is an indication of lack of cohesion of the mix.

Mixes of stiff consistence have zero slump so that if the rather dry range no variation can be detected between the mixes of different workability.