True or false: Concrete has a very high tensile strength.
List the 4 main components of concrete.
1. Portland cement
2. Fine aggregates (Sand)
3. Coarse aggregates (Gravel)
Concrete sets as the chemical process of ____ begins.
High early strength Portland cement is known as type ___ cement
The ______ possible size of coarse aggregate should always be used
What is a simple test for the mixing water that should be used?
What is the most critical ratio when mixing concrete?
Water to cement
What are the 7 of the many detrimental effects of adding water to the concrete mix at the job site?
1. Increased porosity
3. Increased shrinking
4. Lower resistance to the effects of freeze/thaw cycles
5. Chalky or dusty surface (poor wear resistance)
7. Surface cracking
What are the possible legal outcomes if a concrete truck driver is asked to add water to the mix at the site?
Driver will write down the request and the supplier will NOT be responsible for reduction in quality
How long does it take concrete to attain its designed strength?
The compressive strength of concrete is denoted in _____ in the imperial system and in _______ in the metric system.
psi; MPa (megapascals)
The test for the consistency of concrete is called the _______.
In cold climates the additive _________ must be ordered for all concrete that will be exposed to freeze/thaw cycles
Concrete that is to be pumped should have _____ coarse aggregates and ______ sand content.
The maximum time allowed for the placement of the concrete from the time water is added is _______.
What PPE should a worker wear when working with concrete? (2)
1. Eye protection
2. skin protection
To properly vibrate concrete the vibrator should be....? (2 things)
1. Lowered quickly and
2. Raised slowly
What is the major cause of honeycomb?
Inadequate vibration or segregation (rock pockets) caused by improper placement methods.
What can happen if concrete is vibrated excessively? (3)
1. Settlement of coarse aggregate
2. Increased lateral pressure on the formwork
3. Paste-rich layer at the surface
What are the 2 things that fresh concrete needs to properly cure?
Which type of cement is used for: general concrete construction (floors, foundation wall, sidewalks, high rise office buildings)?
Which type of cement is used when:
-Moderate danger of sulphate attack from ground water.
-Generates less heat while hydrating.
-Used for massive concrete pours or hot weather
Which type of cement has:
-A high compressive strength fast
-Used for columns of a high-rise building
-Used in cold environments
Which type of cement:
-Generates less heat at a slower rate than Type 1
-Used for massive concrete structures (dams, large foundations)
-Where temperature rises and therefore expansion due to hydration of the cement is a critical factor
Which type of cement:
-Exposed to high concentration of sulphates in the soils or ground water
-Gains strength at a lower rate than Type 1
What are the 3 most common types of cement?
1, 3 & 5
There are 2 types of aggregates; ____ and _____. These account for _____- _____% of the total volume of concrete.