Transcript Instruction for Concrete Lab

Dr. Sophia Hassiotis
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Laboratory set up
Personal Protective equipment
Directions for mixing
Slump test
Cylinder casting
Cleaning up your station
Mix Design
EQUIPMENT AND
MATERIALS
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Materials (cement, sand,
aggregate, water,
admixtures)
Field scale, slump cone
Four buckets per station
Mixing hoes and trough
Two 4x8 cylinders
Scoops, trowel, mallet,
ruler, rods, cleaning
tools
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Boots or closed leather
shoes
Safety glasses
Apron
Gloves
Respirator mask
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Add 80% of coarse and
fine aggregate, and 80%
of water --- Mix
Add air-entrainment
admixture (use: 1ml for
each pound of cement)
Add ALL cement--- Mix
until cement is blended
in
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Add the rest of the coarse
and fine aggregate
Add the rest of the water.
Mix for a couple minutes,
let it rest for a couple
minutes, mix again and
perform the slump test
Add more water if needed
to obtain a workable
slump.
Record the actual amount
of water used.
Slump
Test
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Dampen inside of cone and place on smooth, moist, non-absorbent level
surface
Fill cone to 1/3 by volume (about 2 ½ inches.)
Rod 25 times with 5/8”x24” tamping rod. Distribute rodding evenly over
entire cross section.
Fill cone to 2/3 by volume (about 6 inches).
Rod the second layer 25 times with rod penetrating into but not through the
first layer. Distribute rodding evenly.
Fill cone to overflow. Rod the third layer 25 times with rod penetrating
into but not through the second layer. Distribute rodding evenly.
Remove the excess concrete from the top of the cone using tamping rod.
Clean overflow from base of cone
Immediately lift cone vertically with slow, even motion. Do not jar the
concrete or tilt the cone during this process.
Invert the withdrawn cone and place next to, but not touching the
slumped concrete
Lay the tamping rod across the top of the slump cone and measure the
slump from the bottom of the rod to the top of the slumped concrete at
the point of the original center of the base
NOTE 1: The slump test should be completed in a maximum of 2 and ½
minutes.
NOTE 2: Do not remove your feet from the sides of the cone till the test
is completed.
NOTE 3: Make sure rod penetrates into the layer below
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Place the 4x8 casting molds on the floor.
Fill the mold to 1/2 full and rod the bottom layer with 25 strokes evenly
spaced.
Consolidate the lift 10 to 15 times with a rubber mallet, your open hand
or the tamping rod.
Fill to the top of the mold and rod the top layer with 25 strokes
penetrating the top of the second layer. Consolidate the lift 10 to 15 times
with a rubber mallet, your open hand or the tamping rod.
Strike off the top surface of the concrete using a sawing action with the
steel trowel. Take special care to smooth the surface.
Mark the cylinders with your group number and date.
Carefully move, using a trowel or hand spade, the cylinders to temporary
storage.
Cover the cylinders with its cover or a plastic bag.
After 20 to 48 hours remove the molds and place them in the water bath.
Transfer your identifying marks from the molds to the top of the
cylinders before placing them in the water bath.
NOTE: Do NOT use sink to wash. Use the minimum water
possible and clean into the TWO COMMON buckets
provided for ALL groups. Use one bucket to dump the
concrete. Use the other as a cleaning bucket.
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Absolute Volume of a Material = Weight of
Material / ( S.G. x 62. 4 lb/cf )
S.G. is the specific gravity of a material and 62.4 lb/cf is
the Unit Weight of water.
A bag of cement (94 lbs.) in a bulk state occupies
approximately 1 cubic foot of volume.
If the cement was without voids it would occupy only
0.48 cubic feet.
Therefore, the volume the cement will actually occupy
in a batch of concrete will be its absolute volume of 0.48
cubic feet.
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Use Table 6.3.1 to find an appropriate value. In
this example, for footings the slump should be
between 1 and 3 inches. Assume a slump of 3
for a mix that is more workable.
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Use the largest that is economically available
and consistent with the dimensions of the
structure.
ACI recommends that maximum aggregate
size be limited to 1/3 of the slab depth and 3/4
of the minimum clear space between
reinforcing bars.
In this example, we will assume a maximum
size of 1.0 inch.
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For our example, for a slump of 3 inches and a
maximum aggregate size of 1 inch, use the airentrained part of the table to find that you will
need 295 lbs of water per cubic yard of concrete.
The fine print under the table specifies that the
water should be reduced by 25 lbs if you are using
well rounded aggregates (ex. Alluvial rock.)
Therefore, in this example we will use 270 lbs of
water.
The same table also shows that the recommended
percent of air content is 6% for severe exposure
In this example, for a 4000psi, airentrained concrete you should pick
w/c = 0.48
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Weight of Water / Weight of Cement = 0.48
Water weight = 295 lbs - 25 lbs = 270 lbs
Therefore,
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Weight of Cement = 270 lbs / 0.48 = 560 lbs
Using the definition of unit weight:
Unit weight=Weight/unit volume
Weight of coarse aggregate =
0.69 cy x (98.5 lbs/cy) x (27 cf/cy) =
1,840 lbs/cy
MATERIAL VOLUMES
VOLUME AND WEIGHT
OF SAND
Remember:
Absolute Volume of a Material =
Weight of Material / ( S.G. x 62. 4 lb/cf )
𝑊𝑤𝑒𝑡 − 𝑊𝑑𝑟𝑦
%𝑀𝐶 =
∗ 100
𝑊𝑑𝑟𝑦
Solving for the Wet Weight
%𝑀𝐶 ∗ 𝑊𝑑𝑟𝑦
𝑊𝑤𝑒𝑡 =
+ 𝑊𝑑𝑟𝑦
100
OR :
%𝑴𝑪
𝑾𝒘𝒆𝒕 = 𝑾𝒅𝒓𝒚 ∗ {𝟏 +
}
𝟏𝟎𝟎
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The weights that we calculate above are dry weights. To create the batch
we will add into the mix wet aggregate weighing:
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Coarse aggregate, Wwet = 1840 lbs x 1.0195 = 1875 lbs
Fine aggregate, Wwet = 1135 lbs x 1.063 = 1206 lbs
Absorbed water does not become part of the mixing water. However, any
free water will add to the water content so we must account for it.
The surface water contributed by the coarse aggregate is 1.95% - 1.0% = 0.95%
The surface water contributed by the fine aggregate is 6.3% - 1.1% = 5.2%
The estimated requirement for added water, therefore, becomes
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270 lbs – 1840 lbs x (0.0095) - 1135 lbs x (0.052) = 193 lbs
Before you come into the lab you
should design your mix for
0.25 cubic feet of concrete.
Use the following materials.
EACH PERSON in the group must calculate the required mix. Then, please check your answer with all
others in the your group. Come to the lab with ONE answer that represents the lab mix that your group will
create in the lab. You will NOT have the time to review this mix while you are in the lab. COME TO THE
LAB PREPARED. CHECK YOUR MIX THE NIGHT BEFORE
MAKE SURE YOU SIGN THE ATTENDANCE SHEET BEFORE YOU LEAVE THE LAB