Concrete Flashcards
Cement is made with:
Portland cement
Limestone
Clay
other elements including gypsum
How many types of Cement is there and what is the most popular?
5 types
type 1 is the most popular
In cement making, what is the definition of fine aggregate:
Such as sand which passes through a 1/4” sieve
In cement making, what is the definition of coarse aggregate:
Such as pea stone and gravel.
generally the maximum size will be 1 1/2” or less.
Coarse aggregate must be free
of soft stones or cherts which will cause “pop outs” in freezing weather
Each 1 gallon of water added to 1 yard of concrete will
reduce the PSI strength by X PSI.
150 psi
Ready mixed concrete should be totally
discharged from the truck within X hours of being mixed or prior to Y revolutions of the mixer, whichever comes first
1 1/2 hours
300 revolutions
The purpose of Air Entrainment
Reduces internal expansion of hardened concrete and closes off channels during curing time.
What are accelerators:
Help to remove water from the plastic concrete in freezing weather.
Calcium chloride should not be used with reinforcing steel due to the probability of
creating corrosion
What are Superplasticizers:
Reduce the water required in a mix design and
improves flow and workability.
Superplasticizers provide a
high slump of 10” for concrete that would normally have a X
4”
Freezing weather conditions require fresh concrete
to be protected, usually by a blanket
For footings, how do you determine the footing size?
The soil bearing capacity
Types of footings:
1
2
Bearing wall strip footing
Mat, raft, or floating foundation
What type of footing do you use over poor soil load bearing capacity
A mat, raft, or floating foundation
If the soil isn’t strong enough for a footing, what do you use?
Pilings (stilts) are driven down into the ground
Metal reinforcement in footings requires a minimum of X of concrete coverage.
3 inches
Concrete placed in foundation forms should not be dropped more than X feet. ( Use form releasing agents)
5 feet
Concrete should be X after placement
vibrated after placement to avoid cold seams.
Seams created by previous pours
In mild weather conditions, foundation forms generally can be removed X after placement of concrete, in severe weather conditions wait Y.
12 hours
5 to 6 days
Rebar is measured in X
1/8 of inch
Splices in rebar should not be less than X” overlaps
12 inches
Wire fabric requires X” of concrete coverage.
2 inches
New concrete shrinks as it sets. For example X lineal feet of concrete will shrink Y of an inch.
100 lineal feet
3/4 of an inch
Control joints in walls are generally X feet apart
20
What do expansion joints do
permit total freedom of movement
Saw cut control joints should be made within X hours of placement. Completing a slab with a trowel finish should be done when the wet sheen disappears.
4-12 hours
What do you do prior to concrete placement
Moisten sub grade with water prior to concrete placement.
Adding water to the concrete mixer truck requires X revolutions to complete mixing.
30
A test for determining the density of wet concrete is a
“slump test”
darby:
A “darby” is a short handled bull float for finishing high and low spots.
The temperature of concrete should be maintained at X degrees for Y days in cold weather conditions.
50 degrees
5 days
Enclosed spaces heated with fossil fuels must be
vented to reduce carbon monoxide which also causes concrete surface “dusting”
Curing is accomplished by
Curing is accomplished by spraying with a pre-mixed surface curing agent, or using a fog sprayer or other means to keep the top surface damp for a specific period of time.
Concrete testing is accomplished by using X test cylinders of concrete. If concrete is to have a 4000 PSI at 28 days one of the cylinders can be tested at Y days. At Y days the cylinder should resist Z to W% of 4000 PSI.
Concrete testing is accomplished by using 3 test cylinders of concrete. If concrete is to have a 4000 PSI at 28 days one of the cylinders can be tested at 7 days. At 7 days the cylinder should resist 65 to 70% of 4000 PSI.
Air entraiment mix ratio:
Generally 5 to 7 percent in mixes with 3/4” to 1 inch
aggregate when used in severe weather conditions
