Concrete: The Material for Infrastructure

The Material for Infrastructure

 

By

Subhash C. Bhatia, Morehouse College

Natarajan Ravi, Spelman College


 

Table of Content

 

  1. History and usage of concrete
  2. Cement

a)     History

b)     Production

c)      Physical properties

d)     Chemical properties

e)     Composition

f)        Role in concrete

  1. Physical Properties

a)     Density

b)     Density and composition

c)      Density, strength and stiffness

  1. Processing and Properties
  2. Building materials, privacy and communication
  3. Degradation and Improvement of concrete
  4. Design Projects

a)     tiles

b)     translucent tiles

c)      environmentally friendly concrete

d)     glowing tile

 

 

 

Flow Chart for Concrete Module

Ceramics Flow Chart

 

  1. States of matter
  2. Physical and Chemical Properties
    1. Density
    2. Strength
    3. Porosity
    4. Environmental deterioration

(sea breeze, sea water, sand and salt mixture, and simulated acid rain)

3.      Physical and Chemical changes during formation of concrete.

a.      pH

b.      temperature

c.      hydration

4.      Design Activity

a.      Fabrication of boat

b.      Changing of Physical appearance

c.      Changing color

d.      Environmental improvement

 

Supplementary Material

 

Different states of matter and classification of matter; density, different types of strength, porosity, effect of salt on concrete, acids, bases, pH, temperature, hydration, pollution, color, floating, catalysis, chemical reactions, chemical structure.  Differences between clay, marble, cement, concrete, and calcium carbonate.

�Calcium Carbonate�

Egg shells

Sea shells

Structure of CaCO3 crystal

Cement � biological source

Electromagnetic spectra, wireless

Communication

 

  

Activities

 

1.      States of Matter

2.      Physical Properties

a.  density

b.  strength

c.  porosity

3.  What is going on when you mix different components together?

4.  Testing for porosity making it colorful and with different compounds.

5.  Design activity.

 

 

Activity I

 

Purpose:        The purpose of this activity is to introduce the physical and chemical properties of matter.

 

Objectives:    

a.      to identify different types of matter based on physical properties.

b.      to differentiate between homogeneous and heterogeneous mixtures.

c.      to differentiate between physical and chemical change.

d.      to introduce the key components of cement and concrete.

 

Background:

 

All materials are made up of matter.  Matter has four basic physical states:  solid, liquid, gas, and plasma.  Matter can have different components or can be made of pure substance.  Matter is identified by its characteristic physical properties.  Physical properties are those that can be determined without altering the composition of the substance, such as, color, odor, density, strength, elasticity, magnetism, and solubility.  Chemical properties are descriptions of the substance and its reactions with other substances to create new substances with new properties.  These chemical properties are identified through chemical reactions.  Evidence of a chemical reaction possibly occurring can be seen through a color change, temperature change, evolution of a gas, and the formation of a new substance.  This activity focuses on the physical and chemical properties.

 

Materials:

 

Chalk, clay, marble, sea shells, egg shells, cement, concrete, calcium carbonate.  Test tubes, magnifying glass, water, vinegar, and Bunsen burner.

 

Procedure:

 

1.          Examine each sample.  Record color, odor, and relative particle size in the data table.  Use a magnifying glass if necessary.

2.          With a magnet, test each sample for magnetic properties.  Record whether the sample is magnetic or not.

3.          Place small amount of each sample in a test tube.  Add approximately 5 milliliters of water to each test tube.  Record your observations.

4.          Place small amount of each sample in new test tubes and heat the test tubes with Bunsen burner.  Record your observations.

5.          Place small amount of each sample in new test tubes and add 5 milliliters of vinegar.  Record your observations.

 

 

Analysis of data:

 

Organize your observations in a table format.  The table should have the name of the sample, physical properties, and changes (if any) the sample underwent in steps 3-5.

  

Answer the following questions (based on your observations)

 

  1. What physical properties of materials (samples) you observed?
  2. Which of the samples you will clarify as mixtures?
  3. Which of the samples you will classify as pure substance?
  4. Which of the samples had chemical change when heated?
  5. Which of the samples changed when water was added?
  6. Which of the samples changed when vinegar was added?

 

N.B.  You can use web to find the chemical composition of each sample.

 

 

Supplementary Material

 

 

 

 

Activity II

 

Purpose:        The purpose of this activity is to demonstrate to students that a physical property of a material depends on composition.

 

Objection:       a) to determine the density of a concrete sample.

                        b) to relate the density of concrete to various types of aggregates

                        c) to understand the concepts of density and buoyancy.

 

Background:

 

You have observed in daily life that some objects float in water while other objects sink in water.  In day to day language, you will say that the objects which sink in water are heavier than water and the objects which float are lighter than water.  For scientists and engineers the words �heavier and lighter� mean that some objects have more amount of matter than others. Thus, heavier and lighter indicate the relative amount of mass of different objects.  To explain why some objects sink while other floats, the scientists compare the amount of mass for the same amount of space occupied by the object.  This is defined as density. Now we can say that objects which float in water are less dense than water while the objects that sink are denser than water.  In this activity you will first predict the density of different mixtures and than will determine their densities.

 

Predictions

 

You are given water, cement, sand, sea gravel and dry vermiculite.  Arrange them from low density to high density materials.

 

Experiment

 

  1. Take 6 100 mL graduated cylinders
  2. Pour each of material (water, cement, sand, pea gravel, and dry vermiculite) in different graduated cylinder to have 25 mL of each in respective graduated cylinders.  Record your observations.
  3. Which samples are closely packed and which one are not closely packed?
  4. Tap each cylinder gently on the table top to pack each sample and make sure the total volume is 25 mL.  If not, add more of the sample or remove the sample.
  5. Which one of the samples, you predict to have the maximum mass and which one has minimum mass?
  6. Determine the mass of each sample, record the mass and volume.  Compare the determined masses to your predictions in #5.  Calculate the density and compare it to predictions.
  7. In a beaker, make 50 mixed-aggregate sample by combining coarse aggregate and fine aggregate.  Choose the relative amounts of coarse aggregate and fine aggregate that you think will produce the densest mixed sample.  Record the masses of coarse aggregate and fine aggregate you used, as well as the total mass of the mixed-aggregate sample.  Then calculate and record the ratio of coarse aggregate to total aggregates in the sample.
  8. Use a stirrer to mix thoroughly the mixed-aggregate sample.  Pour the sample into a graduated cylinder.  Tap the cylinder gently on the tabletop to pack the aggregates.  Not the sizes of the spaces between the particles and compare them to the spaces in the coarse-aggregate sample and in the fine-aggregate sample.  Record your observations.
  9. Record the volume of the mixed-aggregate sample.  Then calculate and record its density.
  10. Share your data for the mixed-aggregate sample with other groups.  In a class data table, record the names of the groups in your class, the ratio of coarse aggregate to total aggregates each group used to make their mixed-aggregate sample, and the density of that sample.

 

Analysis of Data

 

  1. Which type of aggregate sample had the least empty space between its particles?  How do you know? 
  2. What is the relationship between the density of an aggregate sample and the amount of space between its particles?
  3. Compare the density of your mixed-aggregate sample with that of other groups.  What ratio of coarse aggregate to total aggregates would you use to make the densest concrete?  Give evidence to support your answer.
  4. Did the cement and concrete samples differ as you expected they would?  In what ways do you think these differences might be significant when building different parts of the infrastructure?
  5. After you calculate the densities of the different aggregate samples, were you surprised by the results?  What did you learn about aggregate packing and density from doing this part of the activity?

 

 

Activity III

 

Purpose:        The purpose of this activity is to relate two physical properties of concrete.

 

Objective:       a) to learn how to make concrete

                  b) to relate density, strength, and composition

 

Background:

 

Concrete is a mixture of cement, aggregates (rocks of different sizes and shapes), and water.  The Physical properties of the concrete formed depends on the relative amount of each component, how they are mixed, and for how long.  Concrete when poured into mold, eventually hardens and takes the shape of the mold.  Cement is very brittle.  Aggregates are added to improve the strength and they make up as much as 80% by volume of the total concrete.  The size and shape of aggregate determines the density of concrete.  High density concrete has different usage than low density concrete.  The amount of water in cement and concrete also affects the density of concrete.  In this activity, you will formulate concrete with different composition and test the properties.

 

A. Predictions:

The chart given below shows the cement formulation and the different concrete formulations that the groups in your class will be assigned.  How will the density of the cement formulation compare with the densities of the concrete formulations?  Which concrete formulation in the chart do you think will be densest?  Record your predictions and your reasons for making them.

 

Assigned Formulation

Coarse Aggregate

(g)

Fine

Aggregate

(g)

Portland

Cement

(g)

Water

(mL)

A

0

0

200

90

B

0

240

60

33

C

0

240

60

45

D

120

120

60

27

E

120

120

60

33

F

120

120

60

39

G

120

120

60

45

H

240

0

60

33

I

240

0

60

45

 

 

Materials:

 

Rubber gloves, dust mask, safety glasses, and apron

3 molds

Masking tape

Permanent marker

Fine aggregate (sand)

Coarse aggregate (pea gravel)

Portland cement

Balance

Weighing trays

3 Petri dishes

Sturdy disposable stirrers, such as craft sticks, dowels, or paint stirrers

Graduated cylinder water

Magnifying glass

Centimeter ruler

 

Procedure:

 

  1. Your group will be assigned one of the formulations listed in the chart above.  Using masking tape and a marker, label the molds provided by your teacher with your group�s name and your assigned formulation.  Calculate the water-to-cement ratio and the coarse-aggregate-to-total aggregates ratio of your formulation, using the amounts listed in the chart.  Record the formulation and the ratios in a group data table.
  2. Measure out the dry ingredients of your formulation, and using a disposable stirrer, mix them vigorously in disposable cur for about one minute.  Then add the correct amount of water to the mix.  Stir the mixture vigorously once again for one minute, making sure it is uniform.
  3. Pour the mixture into one of the molds, up to the top of the mold.  Use the stirrer to smooth the exposed surface of the mixture in the mold.  Dispose of the stirrer, the mixing cup, and any excess mixture in the garbage.  CAUTION:  Do not pour even tiny residues of cement down a drain because cement can clog the plumbing.
  4. Repeat steps 2 and 3 twice to make two other samples of the same formulation.
  5. If you are using milk-carton molds, place the molds right net to each other and against a wall, with books placed up against them.  This will prevent the samples form bulging at the sides.  Allow the samples to harden overnight.  The next day, label the hardened samples with your group�s name and samples� formulation.  The remove the samples form the molds.  Look at the samples with magnifying glass and record your observations.
  6. Measure and record the mass and volume of each sample.  Calculate and record their densities, using your mass and volume data.  Then calculate and record the average density of the formulation, using the densities of your three samples.  Save your samples for Activity 4.
  7. Share with other groups the ratios and the average density of your formulation.  In a class data table, record the names of the groups in your class, the formulation that each group made, and the ratios and average density they calculated for their formulation.

 

Analysis of data

 

Make a group data table with space to record:

         prediction about the densities of cement and concrete

         prediction about which concrete formulation will be the densest

         your assigned formulation

         formulation�s ratio of water to cement

         formulation�s ration of coarse aggregate to total aggregates

         observations of each sample you made

         mass of each sample

         volume of each sample

         density of each sample

         average density of the formulation

 

Make a class data table with space to record:

         names of the groups in your class

         the different formulations made by the groups in your class

For each formulation:

    ratio of water to cement

    ratio of coarse aggregate to total aggregates

    average density of the formulation

 

Based on the observations recorded in the table, answer the following questions.

 

  1. Did any of the samples your group made vary in density?  If so, give possible reasons why.
  2. How does the density of cement compare with that of concrete?  Why do you think this is so?

3.      How does the water-to-cement ratio affect the density of concrete?  How does the coarse-aggregate-to-total-aggregates ratio affect the density of concrete?  Give possible reasons why the ratios have these effects.

4.      How does the class results compare with your predictions?  Did any of the results surprise you?  Explain.

5.      Did the reasons you gave for your predications turn out to be valid? If so, what evidence do you have that your reasons were correct?  If not, what other ideas do you have and how do the data from this activity support these ideas?

6.      Do you think the proportions of the components of concrete might affect other properties of concrete, besides density?  If so, what properties might be affected?

 

N.B.  Save the sample for next activity.

 

B.     Testing for Strength

 

Predictions:

 

Of all the formulations made by your class, which do you think will be the strongest?  Give reason(s) for your predictions.  Construct a plausible explanation (hypothesis) based on your reasons.  How will you test your hypothesis?

 

            Procedure:

 

1.      In order to compare the relative strengths of your concrete samples, you can place a short length of PVC pipe on top of the concrete disk and drop a small ball bearing through the pipe.  Continue this process using longer pipe, and/or heavier ball bearings until the sample breaks.  Record carefully the conditions under which each sample breaks.

 

2.      Make a table of observations for the entire class.  Based on the class results, what can you conclude regarding the composition and density for making the strongest concrete sample?

 

3.      Do your results agree or disagree with your hypothesis?  If your results disagree than how will you modify and test your new hypothesis.

 

 

Activity IV

 

Purpose

 

The purpose of this activity, is to relate the composition to the observed physical property of a mixture.

 

 

Objectives:

 

1.      to relate composition of the mixture to the porosity of the sample.

2.      to understand that the electric resistance is indirect measure for the porosity.

3.      to understand the concepts of resistance and conductivity.

4.      to understand how a physical property changes  as a function of time.

 

Background

 

The electric current is due to the motion of electrons and/or ions through the matter.  This means that the good conductor such as copper has almost free electrons and the element copper does not hinder the flow of electrons.  The scientists refer to the hindrance of the flow of electrons or ions as electrical resistance.  The 100% pure water does not conduct electricity but the electricity.  The salt when added dissociates into ions which carrying the current .  The ability to flow of the electric current in concrete will depend on the presence of ions and how easily these ions can move through the concrete.

Predictions:

 

Look over the water-to-cement ratios of the concrete formulations listed in the chart below.  Which concrete formulation do you think will be the most porous?  The least?  To help you make your predictions, think back on what you learned about the density of concrete in Activity 3.  Record your predictions and your basis for making them.

 

Formulation

Coarse Aggregate

(g)

Fine

Aggregate

(g)

Portland

Cement

(g)

Water

(mL)

Water-to-

Cement

Ration

 

A

184

184

92

37

0.4

 

B

184

184

92

46

0.5

 

C

184

184

92

55

0.6

 

 

Materials:

 

Rubber gloves, dust mask, safety glasses, and apron

3 molds

Masking tape

Permanent marker

Fine aggregate (sand)

Coarse aggregate (pea gravel)

Portland cement

Balance

Weighing trays

3 large disposable cups

Sturdy disposable stirrers

Graduated cylinder

water

6 �penny� electrodes

Centimeter ruler

Ohmmeter

Plastic wrap

 

Procedure:

 

  1. Your group will be assigned one of the concrete formulations listed in the chart.  Record the formulation and its water-to-cement ratio in a data table.  Using masking tape and a marker, label the molds provided by your teacher with you group�s name and the water-to-cement ratio of your formulation.
  2. Measure out the dry ingredients of your formulation and, using a disposable stirrer, mix them vigorously in a disposable cup for about one minute.  Then add the correct amount of water to the mix.  Stir the concrete mixture vigorously once again for one minute.
  3. Pour the concrete into one of the molds, up to the top.  Us the stirrer to smooth the exposed surface of the concrete in the mold.  Place tow penny electrodes in the concrete, about 8 cm apart, as shown on the next page.  Position each electrode so that the side with the wire faces the side of the mold.  Dispose of the stirrer, the mixing cup, and any excess concrete in the garbage.  CAUTION:  Do not pour even tiny residues of cement down a drain because cement can clog the plumbing.
  4. Repeat steps 2 and 3 twice to make two other concrete samples with the same formulation.
  5. Measure the electrical resistance of each sample by connecting its two electrodes to an ohmmeter.  Try not to disturb the electrodes as you take the measurement.  Record the electrical resistance of the samples in ohms.  The record the electrical resistance of each sample every hour until the end of the school day.  After you take each measurement, cover the sample with plastic wrap.
  6. Early the next day, measure and record the electrical resistance of each sample again.  (You can leave the samples in the molds.) Measure the samples� electrical resistance once again, as late in the day as possible.  Continue measuring the samples� electrical resistance twice each day for the next six days.  Remember to cover the samples with plastic wrap each time you have finished taking measurements.
  7. Using the data from your three samples, calculate the average electrical resistance of your formulation at each time period you too measurements.  Share your averages with other groups.  Make a graph that compares the average electrical resistance of the different concrete formulations over time.

 

 

Analysis of Data:

 

  1. How does the electrical resistance of concrete change as it hardens with time?  What does this tell you about the porosity of concrete?
  2. What is the effect of the water-to-cement ratio of concrete on its porosity?  How do your data support your answer?
  3. How do the class results compare with your predictions?  What were your reasons for making your predications valid?  Explain.

 

 

Part B:

Background:

Many bridges and buildings are constructed from concrete and iron bars.  The addition of iron or steel bars improves the tensils strength of the concrete.  During winter months, the sand/salt mixture is used to deice the roads.  Bridges and roads on the oceanfront are also exposed to seawater and sea breeze.  The environmental pollutants such as acid rain and carbon dioxide can lead to the degradation of the concrete and steel bars used in the construction business.  The ability of these pollutants or naturally occurring chemicals in the environment to react with concrete or their ability to migrate in the concrete leads to the degradation.

 

 

Predictions:

 

Look over the concrete formulations in Part A.  Which formulation do you think will be the most resistant to the sea water?  Record your predictions and your reasons.

 

 

New Materials:

 

5% salt solution in water

Other colored salts.

Organic dye that will glow when current is applied.

 

 

Procedure:

 

  1. Pour 20 mL of salt solution on one of your concrete samples in Part A.
  2. Measure and record the resistance of each sample.
  3. Add the solution of colored salt to the new sample of the concrete.  Measure the resistance and record other observations.
  4. Add the dye given to you and make a new concrete sample.  Measure the resistance and record other observations.

 

Data Analysis:

 

  1. Which of your samples with salt solution gave the least resistance?
  2. Relate the composition of your concrete to the resistance you measured.
  3. Did the colored salts change the appearance and the resistance of the concrete?
  4. What effect did the dye have on the concrete sample?

 

 

Activity 5

Purpose:        The purpose of this activity is to design and construct a product using concrete.

 

 

Objective:       Students will design.

a.      Floor tile

b.      Translucent concrete

c.      Concrete which can be used in environmental remediation.

Background:  The concrete is not aesthetically pleasing and has drab color.  The concrete turns black from the pollutants in the atmosphere.


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