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Flashcards in Coating Concrete Deck (12):

Some of the properties of concrete are?

Extremely durable
Has good compressive strength
Improves with age


How does concrete cure?

A process called hydration


Poured concrete can be affected by?

Ambient conditions - Hot weather causes concrete to cure more rapidly than otherwise, resulting in a greater possibility of voids, and a dusty low strength surface. Curing compounds or wet burlap curing blankets can be used to prevent this 'drying out'
Vibration - This is done to remove air pockets, and can cause heavy aggregate to sink to the bottom. This results in a weak, sandy surface creating a fragile surface known as laitance.


What is guniting?

Guniting is the process of spraying or slinging shotcrete onto a surface as a coating to restore concrete to its original grade.


Concrete may be coated for several reasons including?

Enhancing chemical resistance
Protection from freeze thaw cycles
Protection of reinforcing steel
Surface sealer
Protection against abrasion and erosion
Colour coding
Protecting purity of water or other products contained
Improving/simplifying cleaning
Skid resistance


Describe the difference between laitance and efflorecence?

Laitance - is a weak surface layer of water rich cement mix on the surface of fresh concrete caused by the upward movement of water
Efflorescence - is caused by moisture passing through the concrete and carrying soluble concrete salts with it to the surface. The salts react with carbon dioxide in the atmosphere creating a fluffy white crystalline deposit on the surface


Surface preparation on concrete is generally performed by?

Abrasive blast cleaning
Hand and power tool cleaning
High-pressure water-jetting or blasting
Acid etching
Centrifugal blasting


What is the joing NACE/SSPC blast standard for surface preparation of concrete?

NACE no.6/SSPC-SP 13 Joint surface preparation standard for surface preparation of concrete


The advantages of waterjetting and wet abrasive blasting on concrete include?

Fast cutting of the surface
Washing dust away
Reducing abrasive and concrete particles in air


What is the difference between sacking and stoning?

Sacking - Scrubbing a mixture of cement mortar over the concrete surface using a cement sack, gunny sack or sponge rubber float
Stoning- Is similar to sacking, except that a carborundum brick, or other appropriate abrasive block is used to smooth the surface of the concrete


Several generic types of coatings may be used over concrete including?

Bituminous cutbacks
Chlorinated rubber
Novalac Epoxy
Elastomeric Polyurethane
Sheet Materials (e.g rubber)
Glass-fibre reinforced plastics
Furan Resins


Tests for the presence of moisture include?

ASTM D 4263 Standard test method for indicating moisture in concrete by the plastic sheet method
ASTM F 1869, Calcium chloride test
Electronic testing: Concrete moisture meter