Civil Engineering Survey CE-381
Concrete Mixing Lab
Lab Group 14
I pledge my honor that I have abided by the Stevens
Honor System.
Connor Brenna, Nicholas Rose, Vincent Principe, Amedeo
Bove, Ian Staniec, and Brian Williams
Objective:
Preliminary calculations were performed to determine the ratio of water,
cement, coarse aggregates, and fine aggregates necessitated by the
concrete mixture design delegated to Group 1. Following the mixing
process, each group performed a slump test to confirm that the mixture
composition contained the correct amount of water.
GROUP
STRENGTH
14
4000
AIR
ENTRAINED
No
SLUMP
3
Table 1: Strength Requirements
Materials List:
1. Concrete Mix
a. Portland cement
b. Sand
c. Crushed gravel
d. Water
2. Four 5-Gallon Buckets to Weigh Solids and Water
3. One Field Scale
4. One Slump-Test Cone
5. One Board
6. Two Mixing Hoes
7. One Mixing Trough
8. Two 4 X 8 Cylinders for Casting
9. One Towel for Cleaning
10.
One Metal Scoop
11.
One Steel Trowel for Concrete Finish
12.
One 1.25 lb Rubber Mallet for Tapping Concrete Cylinder
13.
One 12-in Ruler to Measure Slump
14.
One Large Rod to Consolidate Concrete During Slump Test
15.
One Small Rod to Consolidate Concrete During Cylinder
Casting
16.
One Brush/Sponge for Cleanup
General Methodology:
Mix Design Development
The objective of this group was to design a concrete mix with a strength of
3000 psi. The design should be suitable for reinforced foundation walls
and footings as well as other substructures and accordingly have no more
than a 3-inch slump (see Appendix A, Table 6.3.1). The mix is non-air
entrained and complies with the material properties below.
Table 2: Material Properties
The team utilised Appendix A, Table 6.3.3 to select the appropriate mixing
water quantity for ½” coarse aggregate. Subsequently, the team used
Table 6.3.4(a) to determine the water-cement ratio and cement component
weight. The team then used Table 6.3.6 to determine the volume of coarse
aggregate needed.
Mix Design Calculations
Table 3 below displays the group’s computations for concrete mix with a
strength of 4000 psi.
Step 1
Step 2
Step 3
Step 4
Step 5
Strength
=
4000.00
psi
Slump
=
3.00
in
Max Aggregate Size
=
0.75
in
Water Content, Table 6.3.3
=
340.00
lb/cy
Air Content, Table 6.3.3
=
2.00%
lb/cy
Water/Cement Ratio, 3000 psi
Weight of Cement
=
=
0.57
596
lb/cy
Step 6
Volume of Coarse Aggregate/Volume of Concrete
=
0.57
cy
Unit Weight, Water
=
62.40
lb/cf
Cubic Feet/Cubic Yard
=
27.00
cf/cy
Dry Weight, Coarse Aggregate
=
1646
lb/cy
Absolute Volume, Coarse Aggregate
=
10.07
cf/cy
Absolute Volume, Water
=
5.45
cf/cy
Absolute Volume, Entrapped Air
=
0.54
cf/cy
Absolute Volume, Cement
Step 7
=
19.09
cf/cy
Absolute Volume, Fine Aggregate
=
7.91
cf/cy
Dry Weight, Fine Aggregate
=
1283.17
lb/cy
Step 8
Coarse Aggregate, Wwet
=
15.41
lbs
Fine Aggregate, Wwet
=
12.04
lbs
Surface Water Contributed by Coarse Aggregate
=
0.10%
Surface Water Contributed by Fine Aggregate
=
0.20%
Estimated Requirement for Added Water
=
335.79
lb/cy
Table 3: Mix Design Calculations
Tables 4 and 5 below display the calculation results per cubic yard and per
0.25 cubic feet, respectively.
Mix Design, per Cubic Yard
Water
=
335.79
lbs/cy
Cement
=
596.5
lbs/cy
Coarse Aggregate, Wet
=
1664.03
lbs/cy
Fine Aggregate, Wet
=
1299.85
lbs/cy
Total Weight
=
3896.16
lbs/cy
Table 4: Final Composition - per Cubic Yard
Mix Design, per 0.25 Cubic Feet
Water
=
3.11
lbs/cf
Cement
=
5.5
lbs/cf
Coarse Aggregate, Wet
=
15.41
lbs/cf
Fine Aggregate, Wet
=
12.04
lbs/cf
Total Weight
=
36.08
lbs/cf
Table 5: Final Composition - per 0.25 Cubic Feet
Slump Test Procedures:
The following steps were taken in order to conduct a slump test on the
concrete mixture:
1. The cone was dampened and placed on a smooth, level surface
2. The concrete mixture was then poured into approximately ⅓ of the
cone by volume.
3. The first layer was evenly tamped 25 times with a 5.8” X 24” tamping
rod
4. The concrete mixture was then poured into approximately ⅔ of the
cone by volume, and was tamped 25 times, as in Step 3. The
tamping rod was not penetrated to the first layer of concrete mixture
below within the cone.
5. The concrete mixture was then poured to the top of the cone and
tamped again 25 times, avoiding penetrating the second layer.
6. Excess concrete from the top of the cone was removed,
7. The cone was lifted vertically and evenly to release the slump
8. The cone was then inverted and placed alongside the slump
9. The tamping rod was placed across the top of the slump cone and
over the slump
10.
Finally, 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 was
measured
Slump Results:
First Test:
Slump was 2.4 inches (too dry)
Second Test:
More water was added. Mix was remixed, yielding a slump of 3.1 inches
Discussion of Results:
The team conducted two slump tests, with the first test acting as more of a
trial run. The only main difficulty stemmed from the team forgetting to
record initial weights, however, this issue was fixed. The team had all of the
different components in separate buckets, so the team simply recorded the
weight of the buckets with the components, then the weight of the bucket
itself. By subtracting the bucket from the bucket and component weight, the
team was able to get the weight of the components, so this issue was
solved with relative ease. The measured weights of each component are
shown below.
 5.52 lbs cement
 15.44 lbs coarse aggregate, wet
 12.10 lbs fine aggregate
These values were all slightly higher than the design values that were
calculated, but due to the shear number of lab groups needing to access
the scales, the team decided that the higher values would be fine. The first
slump test yielded a slump value of 2.4 inches. This mixture was too dry,
which can be attributed to the both the higher amounts of mix components
and simply not having enough water. The team added around 3.05 pounds
of water, which was simply not enough. The team added another 0.2
pounds of water prior to the second slump test, which yielded much better
results. The team achieved a slump value of 3.1 inches.
Conclusions:
From this lab, the team learned that it is incredibly important to be precise
when both recording measurements and weighing out materials. The
importance of both measurement taking and weighing materials was
apparent from the slump test, as the team had to repeat the entire process
due to having too much dry material and not enough water. In the future,
the team will take their time when weighing out their materials, as it is more
important to create a proper mixture while taking their time, instead of
making a bad mixture while working incredibly fast. Luckily, adding the 0.20
pounds of water was sufficient, however, this may not be the case for future
batches of concrete, so it is important that the team takes their time and
records proper measurements.
Appendices:
Figure 1: initial mixture
Figure 2: first mix with incorrect water content is liquified
Figure 3: Slump test 1 with added cement
Figure 4: Slump test 1 fails
Figure 5: Slump test 2 fails after additional aggregate was added
Table 1: Approximate water and air content requirements for different slumps and
nominal
Table 2: Relationships between water-cement or water-cementitious materials ratio and
compressive strength of concrete
Table 3: Volume of coarse aggregate per unit volume of concrete
References:
● Appendix A - Lab manual for concrete mixing and fresh property testing