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



v

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



APPENDIX C:LAB SHEETS

Documents

Materials Lab 6