Cement Setting Time and Factors

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Questions and Answers

What is the main purpose of understanding the physical properties of Portland cement for a materials specialist?

To understand the chemical composition of Portland cement
To control the quality of civil engineering projects (correct)
To ensure the proper production of Portland cement
To determine the appropriate mix design for concrete

Which of the following is NOT a raw ingredient used in the production of Portland cement?

Limestone
Sand (correct)
Oyster shells
Chalk

What is the primary purpose of adding admixtures to Portland cement concrete?

To improve the setting time (correct)
To increase the compressive strength
To enhance the aesthetic appearance
To reduce the cost of production

Which of the following is a characteristic of the mixing water used in Portland cement concrete?

It should be free from impurities (D) Signup and view all the answers

How does the addition of admixtures influence the setting time of Portland cement concrete?

Admixtures can either increase or decrease the setting time, depending on the type of admixture (A) Signup and view all the answers

What is the primary purpose of understanding the chemical composition of Portland cement for a materials specialist?

To understand the hydration rates of Portland cement (A) Signup and view all the answers

What is the purpose of adding gypsum during cement manufacturing?

To regulate the setting time of the cement (C) Signup and view all the answers

What is a false set in cement?

When the cement stiffens within a few minutes of being mixed, without much heat evolution (C) Signup and view all the answers

How can a false set in cement be resolved?

By vigorously remixing the cement paste without adding water (C) Signup and view all the answers

What does the soundness of cement paste refer to?

The ability of the cement paste to retain its volume after setting (A) Signup and view all the answers

Which test is used to check the soundness of cement paste?

The autoclave expansion test (D) Signup and view all the answers

What factors affect the setting time of cement, apart from the addition of gypsum?

The fineness of the cement, the water-cement ratio, and the use of admixtures (D) Signup and view all the answers

What is the purpose of determining the initial and final set times for cement paste?

To assess the workability and handling characteristics of the concrete mix (C) Signup and view all the answers

Which test method is described for determining the initial set time of cement paste?

The Vicat needle test (B) Signup and view all the answers

How does the Gillmore needle test differ from the Vicat needle test in determining the initial set time?

The Gillmore test uses a lighter needle and measures the indentation depth (C) Signup and view all the answers

What is the criterion for determining the final set time using the Vicat needle test?

When the needle does not penetrate visibly into the paste (D) Signup and view all the answers

What is the significance of the initial set time in concrete construction?

It determines the optimal time for concrete placement and finishing (C) Signup and view all the answers

Which factor can influence the setting times of cement paste?

All of the above (D) Signup and view all the answers

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.