Dry Process of Portland Cement

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Questions and Answers

What is the primary reason that alite is considered more reactive than other compounds?

Lower water content

Lower heat of hydration

Higher Fe content

Higher Ca content (correct)

At what time period does the maximum heat evolution typically occur after mixing cement?

24 to 48 hours

1 to 5 hours

5 to 10 hours

10 to 20 hours (correct)

Which type of cement is classified as moderately sulphate resistant?

Type III

Type I

Type II (correct)

Type V

What characteristic is important for the grading of Ordinary Portland Cement (OPC)?

28-day strength Signup and view all the answers

Which type of Portland Cement has the lowest heat of hydration according to ASTM classifications?

Type IV Signup and view all the answers

Which of the following grades of Ordinary Portland Cement was introduced after 1987?

OPC 43 grade Signup and view all the answers

What is a major benefit of using high grade cements in concrete production?

Improved strength of concrete Signup and view all the answers

What is the compound composition range of C3A in Type III cement as classified by ASTM?

8-14% Signup and view all the answers

What is the appropriate method for measuring expansion in cement?

Submerge the assembly for 24 hours at 270C and measure L1. Signup and view all the answers

What is the correct formula to calculate the expansion of cement based on the measurements?

Expansion = L1 – L2 Signup and view all the answers

What is the maximum allowable expansion limit for Super sulphated cement?

5mm Signup and view all the answers

Which of the following types of cement has an expansion limit of 10mm?

Rapid Hardening cement Signup and view all the answers

What is the recommended storage practice for cement bags?

Store in an air tight room, away from moisture and wall contact. Signup and view all the answers

What is the primary hydration product formed from the C3A phase?

Calcium aluminate hydrate Signup and view all the answers

During which stage of hydration does the most significant increase in concrete strength occur?

Stage III - Main hydration period Signup and view all the answers

What effect does the formation of iron hydroxide gel have on the hydration of ferrite?

It reduces the reaction rate. Signup and view all the answers

Which cement constituent is primarily responsible for early strength development?

C3S Signup and view all the answers

What happens during the dormant, or induction, period of hydration for C3A?

There is a relatively low heat evolution. Signup and view all the answers

What is the heat of hydration value for C3S?

502 J/g Signup and view all the answers

Which phase similarly reacts with water as C3A but has a slower hydration rate?

C2S Signup and view all the answers

Over how many days does normal cement generally produce a heat output of 90-100 cal/g?

28 days Signup and view all the answers

What is a distinguishing feature of Rapid Hardening Cement?

It develops higher rates of strength development. Signup and view all the answers

Which condition is NOT recommended for the use of Sulphate Resisting Cement?

Concrete to be used in high-rise buildings. Signup and view all the answers

What undesirable effect does sulphate attack have on concrete?

Causes expansion and cracking. Signup and view all the answers

What is the primary composition of High Alumina Cement?

Calcium aluminates. Signup and view all the answers

What causes the rapid rate of strength development in Rapid Hardening Cement?

Higher fineness of grinding and higher C3S content. Signup and view all the answers

Which hydration product contributes to the high strength of High Alumina Cement?

Calcium aluminate hydrate. Signup and view all the answers

For which application is Rapid Hardening Cement NOT well-suited?

Mass concreting. Signup and view all the answers

What recommendation is crucial to mitigate sulphate attack in concretes?

Use cement with low C3A and low C3AF content. Signup and view all the answers

What is the primary phase of cement manufacturing that involves burning the raw mix to form clinker?

Burning in kiln Signup and view all the answers

What temperature range is typically found in the rotary kiln during the cement manufacturing process?

850 to 1450 °C Signup and view all the answers

Which material is interground with clinker in the final stages of cement production?

Gypsum Signup and view all the answers

What is the typical diameter of clinker produced in the cement manufacturing process?

20 mm Signup and view all the answers

What is the primary calcareous raw material used in cement production?

Limestone Signup and view all the answers

Which quality control parameter indicates the potential presence of free lime in the cement product?

Lime saturation factor (LSF) Signup and view all the answers

What role does gypsum play in the production of Portland cement?

Regulates setting time Signup and view all the answers

Which of the following is NOT a typical weight percentage range for calcium oxide (CaO) in cement composition?

15-20% Signup and view all the answers

What is the typical silica ratio range used in cement quality control?

2.0 - 3.0 Signup and view all the answers

What is the primary argillaceous material used in cement manufacturing?

Clay Signup and view all the answers

Study Notes

Burning Process in Cement Production

Raw mix chemically transforms into clinker through burning.
Burning occurs in a rotary kiln, typically 30-70 m long and 5-6 m in diameter.
Kiln temperatures range from 850°C at the inlet to 1450°C at the outlet.
Cooling reactions may happen outside of the kiln.
The output of the kiln is termed 'clinker'.

Clinker and Gypsum

Clinker, along with gypsum, is ground to produce Portland cement.
Gypsum acts as a sulfate source and set regulator to avoid flash set.
Intergrinding with clinker allows for control over setting time, shrinkage, and strength development.

Raw Materials for Cement

Calcareous materials (CaCO3) - primarily from limestone.
Argillaceous materials (SiO2, Al2O3, Fe2O3) - sourced from clay.
Gypsum is added during the final stages for regulation of the setting process.

Cement Composition

Typical weight percentages in cement:
- CaO (lime): 60-67%
- SiO2 (silica): 17-25%
- Al2O3 (alumina): 3-8%
- Fe2O3 (ferric oxide): 1-6%
- MgO (magnesia): 1-4%
- SO3 (sulfur trioxide): 2-3.5%

Quality Control Parameters

Lime Saturation Factor (LSF) = C / (2.8S + 1.2A + 0.65F) should be 92-98%.
Silica ratio = S / (A + F) generally should be between 2.0 - 3.0.
Alumina ratio = A / F generally should be between 1.0 - 4.0.

Hydration Process

C3A (most reactive phase) hydration produces calcium aluminate hydrate.
The initial exothermic reaction of C3A occurs rapidly, creating ettringite.
Following a dormant period, C3S and C2S phases begin hydration, resulting in strength gain through calcium silicate hydrate and calcium hydroxide formation.

Cement Specifications

Ordinary Portland Cement (OPC) classified as 33, 43, and 53 grades depending on 28-day strength.
Portland-Pozzolana Cement (PPC) and Portland-Slag Cement (PSC) are alternatives for specific applications.
Rapid Hardening Portland Cement focuses on early strength, while Sulphate Resisting Cement (SRC) is resistant to sulphate attacks.

Rapid Hardening Cement (RHC)

High early strength cement, reaching 3-day strength equivalent to 7-day strength of OPC.
Attributed to finer grinding and higher C3S content, while delivering greater heat of hydration.

High Alumina Cement (HAC)

Contains primarily calcium aluminates, providing high strength characteristics.
Raw materials include limestone and bauxite, with hydration products providing strength enhancements.

Packing and Storage Practices

Packed in 50 kg bags for local utilization, stored in airtight conditions to avoid moisture.
Bags should be stacked no more than ten high, with covers to minimize air circulation.

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Description

This quiz covers the burning phase in the dry process manufacture of Portland cement. It details the transformation of raw materials into clinker through rotary kilns, including temperature ranges and necessary reactions. Test your knowledge on the key stages and reactions involved in this essential industrial process.

Dry Process of Portland Cement - Step 3

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