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Problems Related to Workability
Problems Related to Workability
The analysis of this is based on the concept in physics call “Rehology”
“Which are the science of dealing with the deformation and the flow of material under stress”
1) Segregation
Segregation of the component in the mix resulting in a non uniform mix.
E.g. if a mix is subjected to excessive vibrations the coarse aggregates settle to bottom and paste will rise to the top.
2) Bleeding
“Appearance of the water of the surface of concrete after it has been consolidate before it has set this is a special form of segregation it can lead to a weak pours surface.”
3) Setting
Setting is the on set of rigidity in fresh concrete”
It can be desiccant from hardening. Setting proceeds hardening
(Hardening: This is the change in measurable strength)
i. Initial Setting:
When paste begins to stiffen considerable define by vicat needle, time of penetration 25 mm in to paste.
Generally the typical value of initial setting time is 2 to 4 hours.
ii. Final Setting:
When paste has harden to the point at which it can sustain some load define by vicat needle time of zero penetration into the paste
Typical values of final setting time are 5 to 8 hours.
iii. False Setting:
False setting is the rapid stiffening of the concrete shortly after the mixing with out evaluation of much heat. Fluidity can be stored by remixing with no water addition after which the concrete mat set normally
iv. Flash setting:
Flash setting is the rapid development of rigidity with evaluation of considerable heat.
Rigidity can not be over come only by mixing and plasticity can not be regained with out addition of water.
