DEPARTMENT OFCIVIL & ENVIRONMENTAL ENGINEERING

LABORATORY REPORT COVER

Concrete Mixture Lab Report

CEGR 3255Structural Materials Laboratory

Submitted By: Date Performed:Sara Keranakis February 25, 2015

I, Sara Keranakis, have committed no violations of the UNC Charlotte Code of Student Academic Integrity in preparing and submitting this report.

Signature: Sara Keranakis Date: February 25, 2015

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Executive Summary

This lab had to do with mixing concrete and testing the wet concrete mixture. During this

lab the amount of mixture was found, the concrete was mixed, and the mixture was tested

according to the ASTM standards. The tests were done in a controlled environment under the

supervision of a lab instructor and lab assistant. The test were done as a whole and only one

sample was used.

The previous lab provided the mixture amounts that were used in the lab. The materials

were collected then mixed together. After the mixing was completed, the testing of the mixture

was carried out.

Three tests were done. These test were the slump test, pressure test and volumetric test.

The slump test calculated the amount of workability for the concrete mixture. For this lab a value

of 1.75 inches was recorded for this mixture. This is a low workability measurement meaning the

concrete mixture is slightly stiff. The other two tests allowed for the amount of air content to be

calculated. Each of these tests directly gave off the air content reading. For both test a value of

0.5 was recorded.

Along with these tests a gravimetric test was to be performed. During the time of this lab

the final weight of the concrete mixture in the bowl was not calculated. This did not allow for the

yield to be solved.

The following report is the procedures for the lab along with the results and analysis of

the concrete mixture.

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Table of Content

Title Page...............................................................................................................................i

Executive Summary..............................................................................................................ii

Table of Contents..................................................................................................................iii

Introduction ..........................................................................................................................1

Procedures.............................................................................................................................3

Mixing Mixture................................................................................................................3

Slump Test.......................................................................................................................4

Volumetric Test...............................................................................................................4

Pressure Test....................................................................................................................5

Results....................................................................................................................................7

Mixing Mixture................................................................................................................7

Slump Test.......................................................................................................................7

Volumetric Test...............................................................................................................7

Pressure Test....................................................................................................................8

Conclusions............................................................................................................................9

Slump Test.......................................................................................................................9

Volumetric Test...............................................................................................................9

Pressure Test....................................................................................................................9

Reference……………………………………………………………………………………10

Appendix.……………………………………………………………………………………11

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Introduction

Today most structures are composed with some type of concrete material. Concrete is

used in anything from highways to beams. Concrete is a mixture of water, admixtures,

cement and aggregates. In the first lab fine and coarse aggregates were studied to predict the

amount of each that should be used in the mixture of wet concrete.

The mixture of concrete was made with portland cement. This cement is made up of three

main components; Lime, Silica and Alumina. This cement is a type of hydraulic cement,

which means the cement does not disintegrate in water. Water helps the cement set and

harden throughout its span of lifetime. This process is done by hydration, which is a chemical

reaction of water and cement. A chemical reaction between water and cement during this

process yields the binding properties that allow the mixture to harden. The aggregates are

essentially rocks or fragments of rocks that combined with the cement paste make the

concrete mixture. The cement acts like a glue and fills all of the void spaces.

The previous lab was used to find the correct combination of aggregates, water and

cement. A sieve analysis was conducted on the fine and coarse aggregates that were used in

the concrete mixture. The particle sizes were discovered by the sieve analysis, along with the

specific gravity, weight, and the absorption of the fine and coarse aggregate. These properties

were used to find the correct ratio of each aggregate, water and air content that was need to

make the optimum mixture of cement.

The lab tested the concrete in its fresh or “wet” form. There were many test that were

conducted on the “wet” concrete. The concrete properties that were tested were the slump, air

content, yield, density and specific gravity.

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The slump test of the concrete represents the workability of the concrete. This is the

ability for concrete to be flexible. In order to build with concrete it needs the ability to be

shaped and not deform from its shape once formed. Usually if there is too much water the

slump will be high. If there is less water there will be little to no slump. Normal slump can

range from three to four inches, which can mean that the concrete was mixed well.

There were three tests that measured the amount of air content in the concrete. The

volumetric test, the pressure test, and the gravimetric test gave data needed to calculate the

air content of the mixture. Wet concrete usually has around two or three percent of air

content. A high amount of air bubbles can lead to weaker concrete because it allows void

space, which can cause the concrete to have a lower compressive stress. The mixture had to

be mixed carefully to insure air bubbles were present. Air bubbles are important to have in

the concrete because of the freeze-thaw issues. Concrete needs to have room to expand and

contract in the colder temperatures. The last wet concrete test was the gravimetric test, which

gave data that will be used to calculate the yield, air content and density. This test determines

the density of the mixture that when combined with air content can calculate yield. Yield is

the volume of concrete produced from a mixture when the components are known. This

allows one to see if the mixture was over yield, producing more concrete than expected, or

under yield, producing less concrete than expected.

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Procedures

The follow lab procedures all called for the wet mixture of water, cement, coarse

aggregate, and fine aggregate. The previous lab assisted in determining the amounts of these

components. The weight of each component was 17.6 pounds of water, 48.4 pounds of cement,

102.2 pounds of coarse aggregate, and 46.7 pounds of fine aggregate. Members of the lab

collected the materials and began mixing and testing the concrete by the following procedures.

Mixing Mixture: (ASTM C192)

Materials Used: Concrete Mixture, Aggregate, Water, Cement and Timer

1. Wash out/wet mixer with water

2. Add all of the coarse aggregate to the mixer and a little water (This starts the combining

process)

3. Add half of the cement and fine aggregate and a little water

4. Add second half of cement and fine aggregate and a little water

5. Mix for 3 minutes, rest for 3 minutes then mix again for 2 minutes

Image One: Concrete Mixture

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Slump Test: (ASTM C143)

Materials Used: Slump Cone and Base, Wet Concrete, Scoop or Trowel, Tamping Rod and Ruler

1. Wet slump cone

2. Place slump cone on top of platform and lock into place

3. Place the concrete in the cone using a scoop or trowel

4. Fill the slump cone in three equal layers, rodding each layer 25 times using a tamping rod

5. Remove slump cone from the base for 5 seconds and place beside the concrete

6. Measure the distance from the top of the concrete to the top of the cone

Figure Two: Slump Test Results

Volumetric Test: (ASTM C173)

Materials Used: Bowl, Wet Concrete, Scoop or Trowel, Tamping Rod, Soft Head Hammer, Water, Alcohol, Cap for bowl, and Timer

1. Weigh the empty bowl

2. Calculate the volume of the bowl

3. Wet the bowl

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4. Place the concrete in the bowl using a scoop or trowel

5. Fill the bowl in two equal layers, rodding each layer 25 times using a tamping rod

6. Tamp the bowl 15 times with a soft head hammer (this helps remove air bubbles)

7. Wet bowl lid and lock in place on top of bowl

8. Add 1 pint of water to the bowl

9. Add ½ pint of alcohol to the bowl

10. Add water until the water level reaches zero

11. Place cap on the lid

12. Turn bowl upside down and shake for 5 seconds

13. Turn bowl right side up and rest for 5 seconds

14. Repeat steps 12 and 13 for a total of 5 times

15. Set bowl at 45 degree angle and rock for 1 minute (aggressively)

16. Remove cap and record level of water

17. Wait 2 minutes

18. Record new level of water

Figure Three: Volumetric Test

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Pressure Test: (ASTM C231)

Materials Used: Bucket, Wet Concrete, Scoop or Trowel, Tamping Rod, Funnel Lid, Water and Soft Head Hammer

1. Wet bucket

2. Place the concrete in the bucket using a scoop or trowel

3. Fill the bucket in two equal layers, rodding each layer 25 times using a tamping rod

4. Place and lock funnel lid on top of the bucket

5. Pump and flip the funnel lid 5 times

6. Rock bucket for 4 minutes

7. Seal the bucket

8. Add water into one side until water comes out of the sides

9. Add pressure until the gage reads zero

10. Tamp the bucket (this removes air)

11. Record the pressure

Figure Four: Pressure Test

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Results

The results below include the data that was collected from the lab and all of the

calculations used to find the ending values.

Mixing Mixture: (ASTM C192)

Given the information from the sieve analysis, specific gravity, weight, and the

absorption of the fine and coarse aggregate, the correct percentage of each item was able to be

found. Different values were calculated, so an average value was agree upon. These amounts are

located the table below.

Table One: Mixing Amounts

Material Amount

Water 17.6 lbs

Cement 48.4lbs

Coarse Aggregate 102.2 lbs.

Fine Aggregate 46.7 lbs.

Slump Test: (ASTM C143)

The slump was calculated by finding the amount of deformation of the concrete after the

cone was lifted. After lifting the cone it was set beside the pile of wet concrete and a distance

was measured from the top of the cone to the top of the pile. The distance measured directly

correlates to the slump. This value was measured to be 1.75 inches.

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Volumetric Test: (ASTM C173)

The volumetric test was done with the bowl and lid after shaking the bowl and adding the

last round of water and alcohol, the lid read a level of water. This is the initial level of water and

after two minutes the ending water level is recorded. These two numbers are subtracted to get the

percent of air in the mixture. For this mixture of concrete the initial water level was 1.5 and 2

was the ending water level. The percent air content was 0.5% for this mixture of concrete. The

calculation for this in shown in the equation below.

% Air=Final height of water−Initial height of water(1)

Pressure Test: (ASTM C231)

Pumping pressure into the bucket until the gage read zero performed the pressure test.

After this point the bucket was tamped on the side and the pressure difference from zero on the

gage would represent the amount of air content. The gage read 0.5 and this is the amount of air

content in the concrete mixture.

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Analysis and Conclusion

Many tests were done throughout this lab on the wet concrete. These test allowed

us to tell many things about the concrete. The following section goes into detail explaining the

meanings of the result found in the lab.

Slump Test:

The slump test is done to find the degree of workability in the concrete mixture. The

tested wet concrete mixture had a slump of 1.75 inches. According to aboutcivil.com this amount

of slump is considered low workability. This means that there was not enough water. This error

could have come from a bad measurement of water or water could have been lost when pouring.

At the beginning of the test a small portion of water spilled out of the mixer. This may have led

to the low slump recorded in the lab.

Volumetric Test and Pressure Test:

The volumetric test and the pressure test gave the value of 0.5% for the air content in the

mixture of wet concrete. Each of these test allowed for the air content to simply be read off

without any major calculations. The information of these two tests would allow one to solve for

yield using the gravimetric method. Unfortunately a miscommunication occurred and the final

weight of the known volume mold combined with the concrete was not weighed. This left off

crucial information needed to find this value.

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References

"Concrete Slump Test." - Procedure, Applications & Types of Slump. 1 Jan. 2014. Web. 24

Feb. 2015. <http://www.aboutcivil.org/concrete-slump-test.html>.

ASTM C143 (2009). “Standard Test Method for Slump of Hydraulic-Cement Concrete.”

American Society for Testing and Materials, West Conshocken, PA

ASTM C173 (2009). “Standard Test Method for Air Content of Freshly Mixed Concrete by

Volumetric Method.” American Society for Testing and Materials, West Conshocken,

PA

ASTM C192 (2009). “Standard Practice for Making and Curing Concrete Test Specimens in

the Laboratory.” American Society for Testing and Materials, West Conshocken, PA

ASTM C143 (2009). “Standard Test Method for Air Content of Freshly Mixed Concrete by

the Pressure Method.” American Society for Testing and Materials, West

Conshocken, PA

Somayaji, Shan. Civil Engineering Materials, Second Edition. New Jersey: Prentice Hall,

2001.

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Appendix

% Air=2−1.5=0.5(2)

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