Chapter 7 - Concrete Production Flashcards
Describe the properties of normal weight concrete
140-160 lb/cu*ft for design purposes 150 lb/cu ft
Describe the properties of structural lightweight concrete
less than 120 lb/cu*ft. Aggregates used: Shale, Clay, etc.
Describe the properties of insulating concrete
15 to 90 lb/cu ft used for thermal insulation with perlite as aggregate
Describe the properties of heavy-weight concrete
180 to 400 lb/cu ft is mainly used for nuclear radiation shielding with barite as a heavy aggregate.
Concrete components.
Describe concrete type 1
Used for general purposes
Concrete components.
Describe concrete type 2
Good for piers or drainage systems due to its resistance to alkali attack
Concrete components.
Describe concrete type 3
High early strength, used in cold weather. 150% heat hydration compare to normal cement
Concrete components.
Describe concrete type 4
Low heat (40-60^ heat hydration compare to type 1). 55% cured in 7 days, good for dams.
Concrete components.
Describe concrete type 5
Max resistance to alkali attacks.
What are aggregates used in cement?
- 60% to 80% of concrete
- Ideally rounded or cubical in shape
- Strong & resistant to freeze and thaw
- Fine & coarse aggregates
Why is water used in cement?
- water quality: drinking water
- water cement ratio - 40% to 70%
- used for cement hydration, the ratio defines the concrete strength
Why do we use air-entering agents in cement?
Increase resistance to freezing and thawing
Why do we use water-reducing agents in cement?
Increase slump or workability
Why do we use retarders/accelerators in cement?
To slow down or speed up the setting time
Mixer classification: what does 34E stand for? what would the letters S and M stand for?
A number indicates capacity: 34 cu.ft
E = paving, S= construction , M= mortar
What is batching?
The process of proportioning cement, water, aggregates, and additives with an accuracy of 1% to 3% prior to mixing concrete
Match the following moisture conditions of aggregate with the following terms:
Over dry, air dry, SSD, wet
More/equal/ less than potential absorption
oven-dry & air dry = less than
SSD = equal to
wet = more than
What is the concrete paving process?
Haul trucks -> Slipform paver -> texture/tine -> curing -> Sawing joints
What is a Slipform paver?
Used in airfields and highways to spread, consolidate and finish a concrete slab without conventional forms. Can also be used in canals, concrete gutters, concrete curbs and drainage systems.
What is the max duration for hauling the concrete from the introduction of water?
What is the pace of the initial mixing in drum and the drum speed while travelling to the job,
90 minutes or 400 drum revolutions.
Initial: 20-22 from for 100 revolutions
Travelling speed: =< 2 rpm
what is a consolidation?
The process of removing air voids as concrete is placed happens by shaking the concrete.
Can be done by using immersion-type vibrators (very common)
Describe the finishing process.
It is done to make the concrete smooth.
Screeding -> floating -> troweling - > brooming
