Curing of concrete Flashcards
What is the purpose of “moisture curing”?
To ensure that the concrete will have sufficient with water in early age. It prevent cracks due to “plastic shrinkage”
What is the purpose of “heat curing”?
To speed up the development of strength of the concrete. Prevent the concrete from freexing in early age.
What is “plastic shrinkage”? When does it normally happen? Which climatic situation does give the
highest risk? Which kind of binding-agent (sv: bindemedel) shall be avoided in order reduce the
risk? How can plastic shrinkage be prevented?
cracks appear in horizontal surface structures such as slab on ground. The risk of this is especially high when concrete is poured in a dry, hot and windy climate.
The binding agent which should be avoided is silicafume.
What do we mean by “W-methods”? Name advantages and disadvantages!
It will keep the concrete wet by adding water or cover the concrete surface with wet carpets
Advantage: Effective
Dissadvantage:
-Initial moisture inte building
- can not be used in connection with winter concreting
What do we mean by “A-methods”? Name advantages and disadvantages!
Evaporation is prevented by the form-wall. Free concrete surfaces are covered by vapourtight plastic foil or similar.
Advantage:
-less initial moisture into building
-Can be used in connection with winter concreting
Disadvantage:
-Not so effective
-The water within the concrete may not be sufficient for the chemical reaction
What do we mean by “Membrane curing -methods”? Name advantages and disadvantages!
Application of membrane curing liquid as soon as possible after the concrete has been cast or directly after curing with W- or A-method has been completed.
Advantage:
-less initial moisture into building
-can be used in connection with winter concreating
disadvantage:
-Not so effective
-The water within the concrete may not be sufficient for the chemical reaction
There are, in principle, three situations when there can be a need of estimation of concrete strength. Name these!
- time for moisture- curing
- Time for form-stripping
- Time for protection against freezing
The methods for estimation of concrete strength can be divided into two groups. Name these!
- Estimations based on “maturity functions”
- Direct measurement
What is the “equivalent maturity age t20”?
T20= summan(Kti*delta t)
Describe briefly how the strength of concrete can be estimated with the help of maturity functions!
alt 1: 1. Continuous measurement of the temperature in concrete structure
- Calculation of t20 by use of factors
- calculation of strenght with tendency curve
alt. 2 - continous measurement of t20
- calculation of strength with tendency-curve
Describe the BO-test briefly.
help
Describe the LOK-test briefly
helpo
