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Transcript of Materials Lab 6
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CONCRETE STRENGTH LAB AND MIX DESIGN TEST LAB
Course: CIE 622
Lab Section: 3
Subject: Engineering Materials
Lab Number: 6
Lab Instructor: Rebekah Briggs
Date of Experiment: November 14 2006
Date Due: December 11 2006
Date Submitted: December 11 2006
Names: Ryan L. Clay
Jeffrey M. CliftonMichael P. McGurlHeather N. Newton (Party Chief)Matthew J. ValleJohn Westover
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Abstract
Previous to this lab the group mixed a batch of concrete, with a water
cement ratio of 0.4, and made 15 concrete cylinders and a beam. These concrete
specimens were evenly split up to be cured in different conditions ( outside, inside, and
wet). In this lab the group tested the concrete for a one day, seven day, and 28 day curing
period. The specimens were tested with the use of two different Young’s Machines, an
Instron device, and a compressometer. The Young’s machines tested the strength of the
concrete, for each curing environment, by measuring the failure load. The Instron
measured the elastic properties of the specimens, and the compressometer measured the
deflections in the cylinders and beam. With these measurements it was possible to
determine the strength of the concrete, compare the strengths of the different curing
environments and compare the strength between different water cement ratios. It was
found that concrete with a lower water cement ratio had a higher strength, specimens
cured inside and in a wet bath were the strongest, and as the curing period increased so
did the strength of the concrete.
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Table of Contents
Title Page ....................................................................................................... i
Abstract ......................................................................................................... ii
Table of Contents ........................................................................................... iii
List of Tables ................................................................................................. iv
List of Figures ................................................................................................v
Introduction & Background ...........................................................................1
Description of Apparatus ...............................................................................4
Procedure .......................................................................................................8
Results ............................................................................................................10
Discussion& Analysis ....................................................................................15
References ......................................................................................................21
Appendix A: Raw Data .................................................................................22
Appendix B: Sample Calculations ................................................................23
Appendix C: Lab Sheets ...............................................................................27
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List of Tables
Table 1: Final Data.........................................................................................10
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List of Figures
Figure 1: Small Young’s Machine .................................................................4
Figure 2: Large Young’s Machine .................................................................5
Figure3: Instron Testing Device ....................................................................6
Figure 4: Compressometer .............................................................................7
Figure 5: Wet Cured Compressive Chart .......................................................10
Figure 6: Inside Cured Compressive Chart ....................................................11
Figure7: Outside Cured Compressive Chart .................................................11
Figure 8: Cylinder Tensile Chart ...................................................................12
Figure 9: Modulus Chart ................................................................................12
Figure 10: Tensile Vs. Compressive ..............................................................13
Figure 11 Modulus of Rupture Vs. Compressive ..........................................13
Figure 12: Modulus of Rupture Vs. Water Cement Ratio .............................14
Figure 13: Inside Specimen Trends ...............................................................16
Figure 14: Outside Specimen Trends ............................................................18
Figure 15: Wet Specimen Trends .................................................................19
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Introduction & Background
The purpose of this lab was to perform destructive tests on the concrete cylinders
and beam constructed previously in lab #3. The tests performed should yield results
similar to those expected for the specific mix design. Some of the tests included
compression, flexural, and a cylinder splitting tensile strength test. It will be beneficial to
analyze the different results from the three different types of methods for curing. The
cylinders were wet dried for up to 28 days, dried indoors at room temperature, and
allowed to dry outdoors sheltered from the elements.
Portland cement was named after the Isle of Portland in England when engineer
Joseph Aspdin patented the product in 1824. Portland cement is a part of the paste in a
concrete mixture that helps hold the aggregates together. A typical concrete mixture will
consist of Portland cement, water, aggregates, and possibly admixtures. The ratio of
water to cement in a mix design helps determine the strength of the concrete. A concrete
with a low water to cement ratio will have a higher strength than a mixture with a higher
water to cement ratio. Admixtures may be added to the mix design for numerous
reasons. Accelerators for the hydration process, retarders that slow the hydration process,
air entrainers, plasticizers, superplasticizers, and pigments may be added to the mix
design in order to achieve certain desired results or workability of the concrete. In all
cases, curing the concrete in the correct conditions is essential to obtain the desired
results.
An ideal environment for concrete curing is one in which the concrete is kept
hydrated until the process of hydration is complete. Good hydration will decrease the
permeability of the concrete and will ultimately increase the strength of the concrete.
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Poor hydration may cause tensile cracking on the exterior portions of the extremely dry
concrete, due to the inner portions still undergoing the process of hydration. This type of
cracking may indicate a structurally inadequate concrete due to improper curing methods.
Concrete will typically have a tensile strength that is 1/10 th that of its compressive
strength. This typically causes concrete to fail only in the form of tensile cracking. To
prevent such cracking, reinforcement is often added to the concrete. Metal bars, known
as rebar, may be added into the structure to aid in the concrete’s tensile strength. Fibers
may also be added to concrete mixtures to help improve the tensile strength. The type of
aggregate used in the mix design also must be carefully observed. A soft aggregate maylower the strength of the concrete. Examples of this can be seen when a concrete
cylinder is split and the aggregate is split right down the middle. This may indicate
failure due to weak aggregate. If the cylinder is split down the middle but the aggregate
is completely intact then it is most likely is a failure in the paste that holds the cylinder
together.
To meet the needs of certain environments, different types of concrete have
been developed. These different types allow for the highest quality of concrete that
would be appropriate for the specific job site or location that the concrete is to be placed.
Types of concrete are classified from type 1 to type 5, with or without air-entrainment.
These different types of concrete range from that which meets general construction
needs, to those in which the concrete will be placed in the ocean, and has high needs for
protection against such elements within its environment.
Overall, a concrete will be designed and tested, then classified according to its
ultimate strength. The ultimate strength may be considered the pressure at which the
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concrete fails. In this lab, the ultimate strengths of the concrete cylinders and beams will
be tested for. Once the ultimate strength of a mix design is known, it is then
determinable whether or not a specific type of concrete will be sufficient for an
application. Ultimately, the ultimate strength highly depends on the water to cement ratio
and can be altered by such things as admixtures and curing techniques.
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Description of Apparatus
Testing Machines
Figure 1- Small Young's Machine
Small Young’s Machine: This Young’s machine was used on the one day, seven day,
and 28 day cured concrete specimens. For each test day, the cylinders were placed in the
loading apparatus, and the load was actuated at a controlled loading rate. Once the
specimen reached its critical load, one of the load indication needles recorded the exact
failure point.
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Figure 2- Large Young's Machine
Large Young’s Machine: The large Young’s machine served the same purpose as the
smaller one, but the load applied by the larger machine was much greater. This machine
was used on the 28 day cure length cylindrical specimens. A protective shield was used
to alleviate safety concerns associated with concrete shrapnel.
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Figure 3- Instron Testing Device
Instron Testing Device: The Instron was used in the procedure which required precise
load control. With the maximum compressive strength known from the Young’s
Machine, the Instron was able to load the cylinder to 40% of the maximum load. This
precise level of control allowed the Instron computer to measure the elastic properties of
the specimen.
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Figure 4- Compressometer
Compressometer: The compressometer uses two yokes securely attached to a
cylindrical concrete specimen. A rod is located opposite of a digital measurement device
capable of measuring deflection much more precisely than the Instron. The rod acts as a
pivot point, and the deflection read at the measurement device is a magnified version of
the actual reading, which was translated into an actual deflection.
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Procedure
The twenty eight day concrete cylinders and beam were collected from their
curing location (water bath, inside, and outside). Each of the cylinder diameters and
lengths, as well as the beam dimensions, were measured with a dial caliper and tape
measurer. Two separate measurements were taken of each of the specimens dimensions
to remove any measurement bias. The measurements were recorded, and an average
value was taken for use in later calculations. The specimens, which were removed from
the water bath, were replaced to avoid surface drying until they were ready for testing.
Two cylinder specimens from each of the three cure locations were used for initial
testing of the 28 day concrete strength. One of each of the cure location specimens was
tested in the Young’s machine. The Young’s machine applied an operator controlled
load to the concrete specimen until a failure occurred. At the point of failure, the
Young’s machine indicator needle was located at the reading which indicated failure.
The maximum compressive load was taken in the same way for all of the three cure
location specimens. Once the maximum load was known, 40% of the value was taken
and used for further testing.
With the 40% strength value, the second set of concrete specimens were tested
with the Instron loading apparatus. Each of the different cure location specimens were
placed into a device known as a compressometer. The compressometer allowed for more
accurate readings of deformation in the concrete cylinder, than the Instron was capable of
measuring. The compressometer in principle acted like a pair of scissors. The
compressometer had a fixed rod around which the deforming concrete pivoted, allowing
for a magnified deformation reading which was normalized for calculations.
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The concrete beam was removed from its water bath and placed on two
semicircular supports which allowed for point loading. The load arm was placed on a
load apparatus that allowed the beam to be point loaded one-third of the way from each
end. The Young’s machine was used to produce a uniform loading rate until beam failure
was reached. Once the failure point was reached, the maximum load was recorded for
further analysis.
The final analysis of the concrete cylinders was to find the splitting tensile
strength of the specimens. One of each of the cure location specimens was placed in the
Young’s machine, so that the circular cross section was vertical. The specimen wasplaced on a semicircular support to allow for point loading. The load arm was brought
into contact with a top point loading device. The specimens were then loaded at a
constant rate and the maximum splitting tension was recorded for calculations.
After all of the specimens were loaded and their failure points were recorded, the
failure pattern was noted as well as the mode of failure. The failure pattern was either
shear or cone and the mode of failure was whether or not the specimen split through
aggregate and paste, or just the paste.
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Wet Cured Strength v. Time
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30
Time (days)
S t r ( p s
i )w/c=.4w/c=.45w/c=.50w/c=.55w/c=.60
Results
Table 1- Final Data
Figure 5-Wet Cured Compressive Chart
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Outside Cured Str v Time
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 5 10 15 20 25 30
Time (days)
S t r ( p s
i ) w/c=.40w/c=.45w/c=.50w/c=.55w/c=.60
Inside Cured Str v. Time
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25 30
Time (days)
S t r ( p s
i ) w/c=.40w/c=.45w/c=.50w/c=.55w/c=.60
Figure 6- Inside Cured compressive Chart
Figure 7- Outside Cured Compressive Chart
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Modulus of Elasticity v. Water-Cement Ratio
0.E+00
1.E+06
2.E+06
3.E+06
4.E+06
5.E+06
6.E+06
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
W/C
M o
d u
l u s o
f E l a s
t i c i t y
Wet Cured
Inside Cured
Outside Cured
Cylinder Splitting Tensile Str v. Water-Cement Ratio
0
100
200
300
400
500
600
700
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
W/C
S t r ( p s
i ) Cylinder Wet Cured
Cylinder Inside Cured
Cylinder Outside Cured
Beam
Figure 8- Cylinder Tensile Chart
Figure 9- Modulus Chart
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Modulus of Rupture v Compressive Str
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
0 1000 2000 3000 4000 5000 6000
Compressive Str (psi)
R
w/c=.4w/c=.45w/c=.50w/c=.55w/c=.60
Tensile Str v Compressive Str
0
100
200
300
400
500
600
700
0 1000 2000 3000 4000 5000 6000
Compressive Str
T e n s
i l e S t r w/c=.4
w/c=.45w/c=.50w/c=.55w/c=.60
Figure 10- Tensile Vs. Compressive
Figure 11- Modulus of Rupture Vs. Compressive
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Modulus of Rupture v Water-Cement Ratio
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
w/c
RWet CureInside CuOutside C
Figure 12- Modulus of Rupture Vs. Water Cement Ratio
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Discussion and Analysis
First of all, it is important to comment on the group’s design of the concrete,
which is consistent with the previous report, but is still important when talking about the
final concrete properties. The properties for the concrete obtained in the lab from testing
varied from the originally intended properties described in the last report. In some
circumstances, the air-content and slump were both lower than expected and designed
for. There were several possibilities of error that might have resulted in the low results.
One, while filling up the bucket of water to use in the mix, a significant amount of water
and air-entrainment agent was splashed out of the bucket. This may have caused the drop
in air-content. Secondly, the slump obtained was much lower than designed for in some
cases. Again the loss of water may have had some affect on this, as it affected the water
cement ratio. The water cement ratio was also affected by the percent saturation of the
fine aggregate. If the fine aggregate was less saturated than thought then the water
cement ratio would have been lowered due to the lack of water. A lower water cement
ratio would cause a lower slump. The lack of the desired air-entrainment would also
cause a reduction in the slump. For every 2% air there is a 1 inch change in slump. The
group mixed the concrete very carefully, and with the intent of keeping any and all error
minimized. The cylinders were then allowed to cure.
The cylinders completed were placed both outside and inside for curing. This
helped the group to compare the differences in strength and determine which curing
method was the best. A third method, the concrete water bath solution, was introduced
into the experiment for this same reason. The way concrete is cured can have a great
effect on the strength of the concrete. The group compiled information on concrete
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specimens with water-cement ratios of 0.4, 0.45, 0.5, 0.55, and 0.6. A total of fifteen
cylinders were created for each individual water cement ratio. Then the fifteen cylinders
were divided into three groups. Five were allowed to cure outside, five inside, and five
were placed in a wet calcium hydroxide solution. Tests were then conducted after one
day, seven days, and twenty-eight days. The results were compiled in a table for
analysis. First, the group analyzed the inside specimen testing results and then compiled
a graph of strength vs. water-cement ratio:
Inside Specimen
0
1000
2000
3000
4000
5000
6000
w/c (0.4/0.45/0.5/0.55/0.6)
p s
i 1 day28 days7 days
Figure 13- Inside Specimen Trends
This plot helped the group make conclusions about the compiled results. The 28
day test yielded the highest strength on the whole, regardless of water cement ratio. It is
interesting to notice that for the water cement ratio of 0.45, the seven day specimen was
stronger than the 28 day specimen. This is assumed to be because of experimental error,
because it does not follow the expected trend seen on the other two plots displayed later
in this section of the report. Notice that the water cement ratio of 0.4 yielded the highest
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strength regardless of when the actual testing occurred. The strength of each specimen
took a large decline when the water cement ratio was 0.45. There seemed to be an
increase in strength when there was a 0.5 water cement ratio. This was not true for the
seven day test, which hints at more potential experimental error. This error may have
originated from something as simple as some cylinders not having a uniform height,
which would cause an uneven loading. The strength of the concrete after the one day test
was significantly lower than the seven day and twenty-eight day tests. Most experts
would agree that the compressive strength of concrete is inversely related to the water-
cement ratio. The data collected did not follow this trend. It is important to note thatthere are other factors which contribute to compressive strength such as aggregate size,
grading, surface texture, shape, entrained air, and the presence of admixtures. The two
properties that could have been influenced by experimental error in our samples are air
entrainment and admixture concentrations. This may or may not have affected the data.
Next, the group examined the specimens that were left in an outdoor curing
environment. An outdoor curing setting relinquishes all control the group had over the
temperature of the specimen and the relative humidity of the air. The outdoor samples
were located under sufficient protection that would shield them from rain but nothing
else. The following chart was plotted to summarize the group’s findings:
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Outside Specimen
0
1000
2000
3000
4000
5000
w/c (0.4/0.45/0.5/0.55/0.6)
p s
i1 day7 days28 days
Figure 14- Outside Specimen Trends
This plot follows many of the same trends as the indoor plot. Notice that the
strengths of the samples have declined from being outside under temperatures that were
not ideal. The ideal temperature for concrete curing is between 50° and 60°F. The
samples left outside cured under a much lower temperature which must have affected
their curing process greatly. The twenty-eight day testing still yielded the highest overall
strength regardless of water cement ratio. The same decline is seen at the 0.45 water
cement ratio. The strength begins to rise again at a 0.5 ratio which is also seen in the
inside curing plot. Then there is another drop in strength when the water cement ratio is
at 0.6.
Next, the group examined the results from the testing of the material which was
allowed to cure inside the wet bath. Calcium hydroxide was added to the bath because of
its reputation for increasing the quality of the concrete curing process. The compiled
results from the testing yielded this plot:
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Wet Specimen
0
1000
2000
3000
40005000
6000
w/c (0.4/0.45/0.5/0.55/0.6)
p s
i 1 day7 days28 days
Figure 15- Wet Specimen Trends
Again, this graph shows the same trends which have been visible for both the
indoor and outdoor sample cylinders. Notice that the strength of the concrete in general
is higher than the strengths of the concrete in the other two curing environments. This
demonstrates that calcium hydroxide is in fact a very useful additive to the curing
process, aiding the hydration of the concrete and thus increasing its strength. Again it
shows the highest strengths at a water cement ratio of 0.4, a decline at 0.45, followed by
an increase at 0.55, and the final decline at 0.6. The wet samples were clearly the most
structurally sufficient samples mixed.
Next, the group looked at all the data on the whole, neglecting any previous
assumptions about the water-cement ratio’s relationship to compressive strength. Fromexamining the data, the water cement ratio of 0.4 clearly was the strongest of all. This
might not always coincide with the workability needed for the Kingsbury Hall project.
The 0.45 ratio samples were the least structurally sound in any of the curing
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REFERENCES:
• Smith, Hashimi. Foundations of materials science and Engineering: FourthEdition, McGraw-Hill Companies Inc. 2006
• ASTM C 39/C 39M – 01 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
• ASTM Designation: C 469 – 02 Standard Test Method for Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression
• ASTM Designation: C 78 – 02 Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
• ASTM C 496 – 96 Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens
• Lab manual
• Manual for the criteria of the lab report
• Professor Gress, CIE 622.03: Materials class notes
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APPENDIX A:RAW DATA
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APPENDIX B:SAMPLE CALCULATIONS
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SAMPLE CALCULATION:
1-day, 7-day, 28-day StrengthsThis calculation was used to determine the compressive strength of the concrete
specimens based on different cure locations. The value that is in bold and underlined is
for the first wet bath cylinder cured for 28 days.
σ = compressive strength = P/AP = 74,500 lbA = ( π /4) X (4.01in) 2 = 12.63 in 2
σ = 5,899psi
Cylinder Splitting Tensile StressThis calculation was used to determine the splitting tensile strength of cylindrical
concrete specimens. The value that is in bold and underlined should be the value in the
results for the wet bath curing.
T = cylindrical splitting tensile stress = 2P/ π LDP = 20,750lbL = 8 inD = 4.01 in
T = 411.78psi
Beam Splitting Tensile StressThis calculation was used to determine the splitting tensile strength of concrete
beam specimens.
T = beam splitting tensile stress = 2P/ π a2 P = 6,430lba = (3in X 3in) = 9in
T = 50.54psi
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Flexural StrengthThis calculation was used to determine the flexural strength of concrete beam
specimens.
σ = MY/IM = (P/2) X (L/3)
P = 2,810lbL = 3.25in
= 1522.083inlbY = 1.5inI = 1/12BH 3
B = 3inH = 3in
= 6.75in 4
σ = 338.24psi
Modulus of ElasticityThis calculation was used to determine the modulus of elasticity of cylindrical
concrete specimens. The value that is in bold and underlined is for outside curing.
E = chord modulus of elasticity = (S 1-S2)/(ε 1-ε 2)S1 = stress corresponding to 40% of ultimate load = P/A
P = 30,000 lbA = ( π /4) X (4.01) 2 = 12.63 in 2
= 2375.48psiS2 = stress less than 40% of ultimate load = P/A
P = 10,000 lbA = ( π /4) X (4.01) 2 = 12.63 in 2
= 791.83psiε 1 = longitudinal strain produced by stress S 1
= DGR(3.875/7.75)/5.25inDGR = 0.0063in
= 6E-4in/in
ε 2 = longitudinal strain produced by stress S 2 = DGR(3.875/7.75)/5.25in
DGR = 0.002in= 1.905E-4in/in
= 3.86E6psi
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Chord Modulus of ElasticityThis calculation was used to determine the chord modulus of elasticity based upon
the compressive strengths of concrete specimens. The value that is in bold and
underlined is close to the value in the results.
E = chord modulus of elasticity = (S 1-S2)/(ε 1-0.000050)S1 = stress corresponding to 40% of ultimate load = P/A
P = 30,000 lbA = ( π /4) X (4.01) 2 = 12.63 in 2
= 2375.48psiS2 = stress corresponding to a longitudinal strain of 50 μ in/in = E ε
E = 3.86E6psiε = 50 μ in/in
= 193.5psiε 1 = longitudinal strain produced by stress S 1
= DGR(3.875/7.75)/5.25inDGR = 0.0063in
= 6E-4in/in= 3.96E3ksi
Modulus of RuptureThis calculation was used to determine the modulus of rupture based upon the
compressive strength of concrete specimens. The value that is in bold and underlined is
for the wet bath curing.
R = modulus of rupture = ( σ2)/2E
σ = P/AP = 30,000lbA = ( π /4) X (4.01) 2 = 12.63 in 2
= 2375.48psiE = 3.86E6psi
= 0.73