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Questions and Answers
What is the main purpose of understanding the physical properties of Portland cement for a materials specialist?
Which of the following is NOT a raw ingredient used in the production of Portland cement?
What is the primary purpose of adding admixtures to Portland cement concrete?
Which of the following is a characteristic of the mixing water used in Portland cement concrete?
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How does the addition of admixtures influence the setting time of Portland cement concrete?
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What is the primary purpose of understanding the chemical composition of Portland cement for a materials specialist?
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What is the purpose of adding gypsum during cement manufacturing?
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What is a false set in cement?
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How can a false set in cement be resolved?
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What does the soundness of cement paste refer to?
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Which test is used to check the soundness of cement paste?
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What factors affect the setting time of cement, apart from the addition of gypsum?
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What is the purpose of determining the initial and final set times for cement paste?
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Which test method is described for determining the initial set time of cement paste?
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How does the Gillmore needle test differ from the Vicat needle test in determining the initial set time?
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What is the criterion for determining the final set time using the Vicat needle test?
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What is the significance of the initial set time in concrete construction?
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Which factor can influence the setting times of cement paste?
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Study Notes
Portland Cement Concrete
- Portland cement concrete is the most widely used manufactured construction material in the world.
- It is used in structures such as buildings, bridges, tunnels, dams, factories, pavements, and playgrounds.
- Portland cement concrete consists of Portland cement, aggregates, water, air voids, and in many cases, admixtures.
History of Portland Cement
- Portland cement was patented by Joseph Aspdin in 1824.
- It was named after the limestone cliffs on the Isle of Portland in England.
Importance of Understanding Portland Cement
- Materials specialists should understand the production, chemical composition, hydration rates, and physical properties of Portland cement.
Portland Cement Production
- Production of Portland Cement starts with two basic raw ingredients: a calcareous material and an argillaceous material.
- The calcareous material is a calcium oxide, such as limestone, chalk, or oyster shells.
Setting of Portland Cement
- The maximum final set time is specified and measured to ensure normal hydration.
- Factors that affect the set time include the fineness of the cement, the water-cement ratio, and the use of admixtures.
- A false set can occur if the cement is exposed to humidity during storage, but it can be remedied by remixing.
Soundness of Portland Cement
- Soundness refers to the ability of the cement paste to retain its volume after setting.
- The autoclave expansion test is used to check the soundness of the cement paste.
- Expansion after setting can result from delayed or slow hydration or other reactions if the cement is unsound.
Setting Tests
- The Vicat test and the Gillmore test are used to determine the initial and final set times of the cement paste.
- The Vicat test involves measuring the penetration of a needle into the cement paste.
- The Gillmore test involves applying a needle to the surface of a molded cement paste pat.
- The initial set time must allow for handling and placing the concrete before stiffening.
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Description
Learn about the factors affecting the setting time of cement, including the addition of gypsum, water-cement ratio, fineness of the cement, and use of admixtures. Understand how exposure to humidity can lead to a false set in cement during storage and how to resolve this issue.