Concrete Mix Proportioning
In this laboratory, two different methods of concrete mixture proportioning, trial batch method
and ACI method, will be explored. The trial batch method is a simple, empirical approach to mixture
design. In the trial batch method, an appropriate water-to-cement ratio (w/c) is selected to obtain the
desired strength and durability, and a mixture is made with that w/c incorporating fine and coarse
aggregate to achieve the desired plastic consistency (i.e., slump and workability). In practice, this is often
an iterative process, where several batches are made to achieve the most economical mixture with the
desired properties. The ACI design method is a standardized design procedure developed by the
American Concrete Institute. Using graphs, charts, and tables provided by ACI and based on
experimental data, proportions of cement, water, SSD aggregate, and air are calculated to achieve the
strength, durability, and workability desired. In this laboratory, a mixture will be prepared using the trial
batch procedure, and the resulting mixture proportions will be compared to proportions generated through
the ACI design procedure.
The objectives of this experiment are: (1) to use the trial batch mix method to determine
optimum proportions of aggregates, cement, and water for concrete to meet specified slump requirements,
(2) to verify the effectiveness of the trial batch method of mix design by comparison with ACI mixture
design (3) to learn concrete mixing practice in a laboratory environment, (4) to observe the characteristic
properties of fresh concrete and (5) to prepare seven 3x6in. concrete cylinders for later evaluation.
Essential Apparatus
Seven 3 in. diameter by 6 in. tall plastic cylinder molds
Two buckets for stocking aggregates
Two small containers for stocking water and cement
Mix equipment: large mixing pan, trowels, slump cone, large and small tamping rods, scoops
12 in. ruler
Scale sensitive to 0.1 lb.
Material Characteristics and Mixture Specifications





Cement:
Slump:
Air content:
w/c:
Coarse Agg:

Fine Agg:
Type I/II; SG = 3.15
3.5  0.5 in.
Non air entrained; assume 1.5% entrapped air.
As stated below
#67 crushed granite, specific gravity (bulk SSD)=2.65;
AC= 0.58%; dry rodded unit weight = 100 pcf; MSA = 3/4”; MC=TBD
-ORrecycled concrete aggregate, specific gravity (bulk SSD)=2.22;
AC= 7.87%; dry rodded unit weight = TBD; MSA = 3/4”; MC=TBD
Natural sand, specific gravity (bulk SSD)=2.63; AC=0.40%;
MC=TBD; as determined in prior lab.
The quantities of the materials listed in Table 1 will be used for each party. The materials should be
sufficient to produce enough concrete for casting seven 3 in. diameter by 6 in. cylinder specimens.
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Table 1. Initial Quantity of Materials for Laboratory Concrete Batching (lb.)
Party No.
Test
Curing
W/C
Initial Wt. Per Batch (lb.)
Age
Cement
Water
C. Agg
Sand
C1-A
14 days1
Fog
0.45
6.7
3.0
202
15
1
2
C1-B
14 days
Fog
0.5
6.0
3.0
20
15
C1-C
14 days1
Fog
0.45
6.7
3.0
20
15
C1-D
14 days1
Fog
0.5
6.0
3.0
20
15
C2-A
C2-B
C2-C
C2-D
7 days
7 days
14 days
14 days
Fog
Fog
Fog
Fog
0.60
0.55
0.5
0.45
5.7
6.0
6.0
6.7
3.4
3.3
3.0
3.0
20
20
20
20
15
15
15
15
C3-A
C3-B
C3-C
C3-D
7 days
7 days
14 days
14 days
Fog
Fog
Fog
Fog
0.45
0.5
0.55
0.60
6.7
6.0
6.0
5.7
3.0
3.0
3.3
3.4
20
20
20
20
15
15
15
15
C4-A
C4-B
C4-C
C4-D
7 days
7 days
14 days
14 days
Ambient
Ambient
Ambient
Ambient
0.60
0.55
0.5
0.45
5.7
6.0
6.0
6.7
3.4
3.3
3.0
3.0
20
20
20
20
15
15
15
15
C5-A
7 days
Ambient
0.45
6.7
3.0
20
15
C5-B
7 days
Ambient
0.5
6.0
3.0
20
15
C5-C
14 days
Ambient
0.55
6.0
3.3
20
15
C5-D
14 days
Ambient
0.60
5.7
3.4
20
15
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All C1 groups test at 14 days, due to fall break. A&B will test at Structures Lab.
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C1A and C1B will use recycled concrete coarse aggregate, while other groups use regular aggregate.
Note: Adjust the amount of coarse aggregate and sand during batching to achieve adequate workability
and the slump for the concrete mix.
Trial Batch Procedure (Detailed information concerning the sample preparation procedures is given in
ASTM C-192.)
1. Weigh quantities of coarse aggregate and fine aggregate and store them in separate containers.
Record the weights on the data sheet. If the aggregate is dry, add water (typically about 0.4% by wt,
of the aggregate) separately to bring the aggregates to about SSD condition.
2. Weigh the quantity of cement given in the table above in a separate container.
3. Weigh the quantity of mixing water given in the table above in a container.
4. Take approximately 2/3 each of the coarse aggregate and the fine aggregate obtained in Step 1 into
the large, just dampened mixing pan. Pour all the cement obtained in Step 2 on top of the aggregates
in the mixing pan. Use a square end shovel to thoroughly mix the aggregates with cement, then
gradually pour all the water obtained in Step 3 into the aggregate-cement mix and thoroughly mix the
dry components with water to form a uniform (but rather soupy) mass. Test the slump (see Step 6 for
slump test). At this point the slump of the mixture should be greater than 4 in. Gradually add small
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quantities of fine or coarse aggregate (or both) and thoroughly remix the concrete and test the slump.
Repeat this process until the mix reaches the desired slump. As the slump is approaching 5 to 6 in.,
the batch should be carefully examined in order to judge which aggregate to add to bring the concrete
to the desired slump. The correct amount of sand is the minimum which will produce enough mortar
to fill the space between pieces of coarse aggregate. In general, too little sand in the mixture creates
harshness (lack of troweling ability) and shows lack of cohesiveness whereas too much sand
decreases "yield".
5. When the batch is judged to be satisfactory by the slump test, weigh the remaining aggregates and
record in the data sheet, and compute the actual amounts of coarse and fine aggregates used in the
concrete mix.
6. In testing the slump, dampen the slump cone and place in the mixing pan. Hold the slump cone down
firmly against the pan. Fill the slump cone with concrete in three layers, each approximately onethird of the volume of the slump cone for each layer. Rod each layer with 25 strokes, distributed
uniformly over the cross-section of the cone. The rod should slightly penetrate into the previous
layer. After the top layer has been rodded, strike off excess concrete with the tamping rod so that the
cone is exactly filled. Immediately remove the cone from the concrete by raising it carefully in a
vertical direction. Measure the "slump" of the concrete by determining the difference between the
height of the mold and the height of the subsided concrete. After the slump measurement is
completed, tap the side of the concrete frustum gently with the tamping rod. The behavior of the
concrete under this treatment is a valuable indication of the cohesiveness. A well-proportioned mix
will gradually slump to lower elevation and retain its original form while a poor mix will crumble,
segregate and fall apart.
7. Before filling the concrete into the cylinder molds, determine the weight of all seven cylinder molds
together and record the weights in the data sheet. Form the cylindrical concrete specimens by placing
the concrete into the cylinder mold in three layers of approximately equal volume. Rod each layer
with 25 strokes using a small tamping rod (1/4 in. diameter rod). Distribute the strokes uniformly
over the cross-section of the mold. Also, gently tap the cylinder mold filled with concrete with the
tamping rod. This treatment will help to consolidate the concrete and to drive out the air bubbles
trapped in the concrete. After the top layer has been rodded, strike off the surface of the concrete
with a trowel. Fill a total of seven concrete cylinder specimens. Measure the weight of all seven
cylinder molds filled with concrete and record the weight on the data sheet. Cover the concrete
cylinders with a plastic bag to prevent the loss of moisture from the concrete.
8. Compute the Unit Weight of concrete, and the weight of materials for making one cubic yard of
concrete. Record these results in the data sheet. Submit the results to the laboratory instructor for
approval.
9. After 24 +8 hours, strip the disposable plastic molds from the concrete cylinder specimens. The
cylinders were then placed in the curing environment prescribed in Table 1. The three curing
regimens specified are: (1) fog room curing at 73.5+3.5oF (23+2oC) and 100% RH, per ASTM C 192
(2) ambient curing outside the lab, and (3) insulated box curing (i.e., cure box). (TAs will do this
step.)
10. Use the ACI absolute volume method to calculate mix proportions for 1 yd3 concrete, using the same
w/c as in the trial batch mixture (i.e. 0.45, 0.50, 0.55, or 0.60). Results of the ACI design should be
included in the laboratory report.
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CONCRETE TRIAL MIX DATA
Name _______________________
Date _____________
Group No. _____ Section _______
Max. Aggregate Size __________
W/C _______________________
Fine Aggregate F.M. __________
CURING ___________________
AGGREGATE TYPE __________
Absorption:
Fine Aggregate _____ %
Coarse Aggregate _____ %
Moisture content:
Fine Aggregate _____ %
Coarse Aggregate _____ %
(A) Material
(B) Initial
weight (lb.)
(C) weight
remaining
(D) weight used
(lb.)
cement
water
coarse aggregate
fine aggregate
other:
Total Batch Weight = ________ (lb.)
Total Wt./ yd3 = _______(lb.)
Measured Slump __________________
(1) Weight of Concrete + containers
(2) Wt. of Containers
(3) Wt. of Concrete = (1)-(2)
= ________
= ________
= ________
(4) total Vol. of Containers
= _________
(5) Unit weight of concrete = (3)/(4)
= ________ (pcf)
(6) Concrete batch volume = (Total Batch Wt.)/ (Unit Wt.) = ___________ (ft3)
Note: (E) = (D) x 27 / (6); Check: Total Wt./ yd3 / 27 = (5)
Comments:
Laboratory Instructor: _____________________
4
(E) weight / yd3
Testing Hardened Concrete Properties:
Compressive Strength and Splitting Tensile Strength
In this experiment, the compressive and tensile strength of the concrete cylinders previously cast will be
assessed to examine the influence of water-to-cement ratio (w/c), curing conditions, age, and coarse
aggregate type on these properties. Five cylinders will be tested in compression, according to ASTM C
39, and two cylinders will be tested by the ASTM C 496 for tensile strength by the splitting tension test.
Essential Apparatus
Compression machine with at least 50,000 lb. capacity
Compressometer
Materials
Steel caps and neoprene pads
Plywood strips
Grinding stones
Rulers and/or micrometers
Marking pen
Compression Test Procedure
1. Remove the concrete cylinders from the curing room and surface dry the cylinders.
2. Select 5 cylinders for this test, choosing those with the smoother end surfaces. Measure the diameter
of the cylinders.
3. Grind the concrete cylinder ends with a mason’s rubbing stone to remove surface irregularities. Place
neoprene end cap on each end.
4. Place one cylinder, with the pad caps and steel end caps, into the testing machine, and apply
compressive load slowly and continuously until the maximum load is reached. Loading rate should
be between 20 psi to 50 psi per second (150 lb. to 300 lb. per second). Failure of the cylinder is
imminent during the test when the load indicator is slowing down, and finally stops. Allow the
compressive load to continue until the cylinder is crushed, and record the maximum load achieved.
Examine the fracture of each sample and identify the type of failure, using Figure 2 where modes (a)
and (b) are considered the normal fracture modes.
5. Determine the compressive strength for each specimen tested.
Figure 2. Fracture modes in concrete cylinders under compression
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Splitting Tension Test Procedure
1.
Measure the dimensions of the remaining two cylinders. Draw diametrical lines on each end of
the specimen which bisect the cylinder.
2.
Center one strip along the center of the lower bearing block of the testing machine. Place the
cylinder on the strip and align so that the lines marked on the ends of the specimen are vertical
and centered over the strip. Place a second strip lengthwise on the cylinder. Lower the upper
loading head of the testing machine until the assembly is secured in the machine, see Figure 3.
3.
Estimate the maximum loading the specimen may take and apply the compressive load slowly
(about 100 psi to 200 psi per min.) and continuously until the specimen fails in split tension.
Record the maximum applied load. Examine the fracture surface, and estimate the percentage of
aggregate that have fractured. Does the failure occur in the matrix or through the aggregate?
Figure 3 Splitting tension test
4. Compute the split tensile strength,t
t = 2Pmax/ (DL)
Where D = Diameter (in.)
L = Length (in.)
Pmax = Maximum Compressive Load (lb.)
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CONCRETE TEST DATA SHEET
Name: ______________________
Date: ______________
Age of concrete: ______________
W/C:______________
Curing: _____________________
Aggregate Type: _______________
Compression Test Results
Specimen
No.
Diameter
(in.)
Max. Load
(lb.)
Compressive
Strength, (psi)
Fracture
Mode
1
2
3
4
5
Average Compressive Strength
= _________ psi
n
Standard Deviation =  
Where xi
xbar
n
(x
i 1
i
 x)2
n 1
= _________ psi
= is a measured value (strength)
= is the average value (average strength)
= number of measurements (5)
Splitting Tension Test Results
Specimen
No.
Diameter
(in.)
Height
(in,)
1
2
Average Tensile Strength =
__________ psi
Laboratory Instructor: _____________________
7
Max. Load
(lb.)
Tensile Strength
(psi)
Results (combined for Concrete Mixing and Testing)
1. Present the calculated mixture proportions using the ACI procedure and those obtained by trial
batching in a table. In this table, also compare the cost of the trial batch mixture prepared by your
group with the cost of the corresponding ACI design mixture. Make sure the quantities compared are
the same – 1 cu. yd. is standard. Assume these prices: cement is $85/ton, #67 crushed granite is
$11/ton, recycled concrete aggregate is $5/ton, natural sand is $13/ton, and water is $0/ton; 1 ton =
2000lbs.
2. Calculate the theoretical % air voids in the concrete batch made in the lab (your party’s data only) and
compare with the % air void assumed for the pre-lab mix calculations. Show the calculations in
Appendix.
3. Calculate compressive strength and tensile strength for each of the cylinders tested. Calculate average
values for each of these and standard deviation for the compressive strength. Present this data in
tabular form.
4. Provide sketches of the failure modes in the compression test, and note the number of your group’s
cylinders to fail in each manner.
5. Using data from all of the mixtures prepared this semester, generate
(1)
a scatter plot comparing the compressive strength of the fog room cured concrete (y-axis) at 7
days and 14 days of age with the w/c of the mixture (x-axis),
(2)
a scatter plot comparing the compressive strength of the ambient cured concrete (y-axis) at 7
days and 14 days of age with the w/c of the mixture (x-axis), and
(3)
one bar chart, comparing the compressive strength (y-axis) of the fog-room cured concrete at
w/c 0.45 and 0.50 with regular and recycled concrete aggregate at 14 days of age
(note: include average strength and standard deviation on each of these plots)
6. Using data from all of the mixtures prepared, generate
(1) a scatter plot comparing tensile strength of the fog room cured concrete (y-axis) at 7 days and 14
days of age with the w/c of the mixture (x-axis),
(2) a scatter plot comparing tensile strength of the ambient cured concrete (y-axis) at 7 days and 14
days of age with the w/c of the mixture (x-axis), and
(3) one bar chart, comparing the tensile strength (y-axis) of the fog-room cured concrete at w/c 0.45
and 0.50 with regular and recycled concrete aggregate at 14 days of age
(note: calculate average strength for these plots)
Discussion (combined for Concrete Mixing and Testing)
1. Discuss any sources of error that may have affected the accuracy of the concrete mixing or testing.
Comment on the standard deviation of the measured compressive strengths.
2. Compare the proportions for the mixture prepared in your group using the trial batch method with the
proportions calculated by ACI mixture design. Discuss differences in proportions of the two mixes
and reasons why they may have differed.
3. Comment on the relative costs of the trial batch and ACI mixture. By how much do they deviate?
Why?
4. Comment on the workability of the mixture prepared by your lab group. Discuss how the target slump
was achieved and the cohesiveness and flow of the mixture.
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5. For the mixture prepared by your lab group, compare the average compressive strength with predicted
or design compressive strength (see Figure 4). Comment on how sources of error or how your party’s
mix design may have affected the strength of the trial batch concrete.
Figure 4. Expected field strengths for
various w/c (source: Design and Control of
Concrete Mixtures, PCA).
6. Using the plots generated in Results (6), discuss the effects of w/c, age (or time of curing), and curing
regimen (i.e., fog vs. ambient), and coarse aggregate type (ordinary vs. recycled concrete) on the
compressive strength of the concrete. What are the expected trends for compressive strength with
each of these variables? Discuss how the collected data fits with or deviates from these trends.
Comment on standard deviation values, when relevant.
7. For the mixture prepared by your lab group, compare the average tensile strength with the average
compressive strength. Compare this relationship to (1) the estimates provided in Figure 11.25 of the
Young text and (2) the values obtained from the equation recommended by the American Concrete
Institute for predicting tensile strength t:
t=kt(fc)0.5
where fc is the average compressive strength in psi and the constant kt is 6.7 for normal strength
concrete.
8. By examining the fracture surface of the splitting tension specimens, comment on primary mode of
failure (i.e. Does the fracture primarily occur through the matrix and around the aggregate or
primarily through the aggregate?) Estimate the percent of aggregate that have fractured. Discuss what
this indicates about the strength of the aggregate relative to the strength of the cement paste and the
role of the interfacial transition zone in fracture of these samples.
9. Using the plot generated in Results (7), discuss the influences of w/c, age (or time of curing), curing
regimen (i.e., fog vs. ambient vs. cure box), and ), and coarse aggregate type (ordinary vs. recycled
concrete) on the tensile strength of the concrete and the effect of any sources of error on the strength.
9