Ch. 15 Coating Concrete and Inspection Flashcards
Some of the properties of concrete are
Inorganic
Hard
Good compresive strength
Improve with age (crystallization)
What is the process by which concrete cures?
hydration
How do ambient conditions and vibration affect poured concrete?
Hot weather causes concrte to cure more rapidly, resulting in a greater possibility for voids, and a dusty, low-strength surface.
Vibration can cause the heavy aggregate to sink to the bottom of the form resulting in a weak, sandy surface, creating a fragile layer of sand and cement known as laitance.
Explain guniting:
Guniting is the process of spraying or slinging shotcrete onto a surface as a coating.
Concrete may be coated for several reasons including:
Asthetics Waterproofing Freeze protection Chemical Resistance Steel Reinforcement Decontamination Abrasion and Erosion Protection Color Coding Contents Protection Improving Cleaning Skid Resistance
Describe the difference between laitance and efflorescence
Laitance is a weak surface layer of water-rich cement mixture on hte 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 is generally performed on concrete by
Abrasive blast clean Hand and power tool clean High-pressure waterjet or blast Acid etch Stone Centrifugal blast Scarify
What is the joint 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
Quickly cuts the surface
Washes dust away
Reduces abrasive and concrete particles in air
What is the difference between sacking and stoning?
Sacking is the technique of 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 the process uses a carborundum brick, or other appropriate abrasive block to smoothe the surface of the concrete
Several generic types of coatings may be used over concrete including
Bituminous cutbacks Chlorinated rubber Vinyl Epoxy Nonvolac epoxy Elastomeric polyurethane Sheet materials (rubber) Glass-fiber-reinforced plastics Furan resins
Tests for the presence of moisture in concrete include
In-situ Probes ASTM F2170-02
Concrete Moisture Meter
ASTM F 1869 Calcium Chloride Test
ASTM D 4263 Plastic Sheet Method
