Coating Concrete Flashcards
Some of the properties of concrete are?
Extremely durable Inorganic Hard 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?
Decoration Waterproofing Enhancing chemical resistance Protection from freeze thaw cycles Protection of reinforcing steel Decontamination 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 Stoning Centrifugal blasting Scarifying
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 Vinyl Epoxy 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
