Cement
Cements are substances, which bind together the particles of
aggregates (sand and gravel) to form a mass of high
compressive strength called concrete. The most common type
of cement in Uganda is Portland Cement.
Portland Cement
• Ordinary Portland cement (Type I)
A general-purpose cement used in many applications, including concrete
mortar and screed.
• Portland Pozzolana Cement
A blend of Portland cement and pozzolanic materials like fly ash or silica
fume, used for general construction and corrosion resistance.
• Low heat Cement (Type IV)
Portland cement that generates less heat while setting
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Other types of cement
• Rapid Hardening Cement: A hydraulic cement that quickly gains
strength, used for precast concrete, repair work and pavement
• High alumina cement: Also known as Calcium Aluminate
cement(CAC) or high Alumina Cement(HAC), this cement is strong, sets
quickly and resists aggressive environments.
• Quick setting cement: Cement that hardens(sets) quickly.
• Sulfate resisting cement: Used in concrete that needs to resist sulfur
salts in soil and groundwater.
• Colored cement: Cement that’s mixed with pigments to create different
colours
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Other types of cement
• White cement: Type 1 white cement is used in architectural concrete
and precast concrete products.
• Type IL: More environmentally friendly than Portland cements.
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Manufacture of cement
There are many kinds of cement each with closely related processes of
manufacture. Portland cement is the most commonly used type of cement with
two processes of manufacture namely the wet process and dry process;
• Wet Process: In this process, substances containing calcium carbonate such as
chalk or limestone are mixed with substances containing silica and alumina
such as clay or shale, to make cement. The two materials are mixed with water
to form a slurry, which is then pumped into the top of steel rotary kiln while
coal is blown in at the bottom end and is fired. This raises the temperature at
the lower end of the kiln such as the slurry passes down it gives up its
moisture to form a white-hot clinker, which is then transferred to cooler
before being ground. 5% gypsum is added to before grinding to prevent a
flash setting off the cement. The grinding is carried out in ball mill.
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Manufacture of cement
• Dry Process: The difference with this process and the wet process is the
reduction of the amount of water that has to be driven off in the kiln. In
this process the two materials chalk or limestone and clay or shale are
ground and blended to form a raw meal of low moisture content. The
meal is granulated in rotating pans with a small amount of water before
being passed to a grate for preheating prior to entering the kiln. After
entering the kiln the process is similar to that in the wet process.
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Manufacturing process visualizer
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Cement Tests
Cement tests determine the quality of cement by assessing its physical, Chemical
and performance characteristics. These tests help ensure that cement meets
standards and performs as intended. Below, we discuss some of the tests carried
out on cement;
• Fineness test: this test is important for evaluating the quality and selecting the
best cement for a specific application. Finer cement particles result in concrete
with earlier compressive strength gain.
1. Ensure the cement sample is free of lumps.
2. Weigh 100 grams of the cement sample.
3. Place the cement in a sieve with a mesh size of 90 microns.
4. Shake the sieve for 15 minutes.
5. Record the weight of the cement that went through the sieve.
6. Calculate the fineness using the formula:
fineness = (W2/W1)*100
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Compressive strength test
• This test measures how much load a concrete or cement specimen can
withstand before breaking(failing).
How its performed;
1. A specimen is placed in a compression testing machine.
2. A load is gradually applied to the specimen until it breaks.
3. The compressive strength is calculated by dividing the maximum load
by the specimen’s cross-sectional area.
What its used for;
1. To ensure concrete meets the required strength for its intended use.
2. To identify problems in the concrete mix or construction process.
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Compressive strength test
What the results mean;
1. Compressive strength is reported in units of pound force per square
inch(psi) or Mega Pascals (MPa).
2. Used to design structures that meet their mechanical & durability
requirements.
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Compressive strength Apparatus
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Consistency test
• A laboratory procedure that determines the amount of water needed to
create a cement paste of a specific consistency. This test is important for
construction because it helps evaluate the cement’s workability and
setting time.
How the test is performed;
1. Mix a sample of dried cement with water to form a paste.
2. Fill a Vicat mold with the paste.
3. Lower a Vicat plunger into the paste until it touches the surface.
4. Release the plunger and note how far it penetrates the paste.
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Consistency test
What do you make of the results;
• The standard consistency of cement is the amount of water that allows a
10mm diameter plunger to penetrate the paste 5-7mm from the bottom
of the mold.
• This test helps determine the amount of water to mix into cement before
testing its setting time, soundness and compressive strength.
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Initial and final setting time test
• This test is conducted using a Vicat
apparatus, where a needle is used to
measure the time it takes for a
cement paste to harden enough to
resist penetration to specific depth,
signifying the initial setting time, and
then further hardening to a point
where a circular attachment can no
longer fully penetrate, indicating the
final setting time. This test is crucial
to ensure proper workability and
setting time for concrete
applications.
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Initial and final setting time test
Procedure.
• Prepare a standard cement paste with a specific water-cement ratio.
• Place the paste in a mold.
• Regularly lower the needle into the paste at set intervals until it can no
longer penetrate beyond a specified depth, marking the initial setting
time.
• Replace the needle with the circular attachment and repeat the process to
determine the setting time.
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Initial and final setting time test
Interpretation.
• Initial setting time: The time taken for the needle to stop penetrating
beyond a specific depth, indicating the point where the cement starts to
harden and lose workability.
• Final setting time: The time taken for the circular attachment to no
longer fully penetrate the paste, signifying full hardening.
Importance of the test.
Workability; Ensures enough time for mixing, transporting , and placing
concrete before it starts to set.
Strength development; Proper setting time is critical for achieving the
desired strength of the concrete structure.
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Soundness test
• Measures how much a cement paste expands when placed in water. The
test helps determine if the cement is likely to crack and cause problems
in construction.
How it’s performed;
1. Fill a small mold with cement paste.
2. Place the mold in water.
3. Measure the distance between indicator points.
4. Boil the water for three hours.
5. Remove the mold from the water and let it cool.
6. Measure the distance between the indicator points again.
7. Calculate the difference between the two measurements.
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Soundness test
• Soundness is an indication of durability. Cement that contains free lime,
magnesia or excess sulfates can expand over time, which can cause
cracks.
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