civ2043..properties of fresh concrete Flashcards
what is consistence ?
Measure of the stiffness / sloppiness or fluidity of a concrete
- consistence is tested by slump test
what is cohesiveness?
tendency to resist segregation and bleeding
What is workability
The ease with which a concrete mix can be placed ,compacted and finished without segregation of the individual components
“User friendly of concrete “
factors affecting workability
-Mixed proportion (water,paste,cement content)
-aggregates characteristics (shape and surface texture,average particle size)
-Binder types(GGBS and FA improves workability , CFS reduces workability)
-Admixtures (plasticizers improve workability at a fixed water content
What is plastic shrinkage ?
-Reduction of concrete volume due to removal of water from compacted concrete before setting
How to control plastic shrinkage ?
–Reduce water loss from concrete
* pre-wet soil before placing concrete
* curing concrete after finishing
what is settlement and bleeding ?
and why is it happening ?
- upwards movement of mixing water (bleeding) and downward movement of aggregates and cement (settlement).
-Because of difference in density
Why Bleed water can reduce plastic shrinkage cracking
film of Bleed water prevents premature drying
Why bleeding weakens the concrete surface?
-Increase water content
-Increased water cement ratio
- reduce strength
Why bleed water creates voids in concrete
Bleed water is trapped under aggregates Particles and reinforcement
How to control settlement and bleeding
- increase fine material
- reduce water content
- use air-etraining agent
What is loss of slump
Loss of consistence from time of mixing
