Correct Answer: D. High alumina cement
Solution:
High Alumina Cement is manufactured by fusing or sintering a mixture of bauxite (which is rich in alumina) and limestone. The key characteristic is its high alumina content, which must be at least 32%. This gives it properties like rapid strength gain and high resistance to chemical attack, which are different from Ordinary Portland Cement.
Correct Answer: B. sulphur
Solution:
A small amount of sulphur in the form of sulphur trioxide (SO₃) is beneficial for cement, contributing to its soundness. However, an excess amount of sulphur can lead to unsoundness, causing the cement to expand and disintegrate over time.
List 1 (Property)
P. Soundness Test
Q. Fineness
R. Setting time
S. Tensile strength
List 2 (Method)
1. Vicat's Apparatus test
2. Le-Chatelier Apparatus
3. Briquette test
4. Air permeability method
Correct Answer: D. P-2, Q-4, R-1, S-3
Solution:
The correct matches are:
- P. Soundness Test is conducted using the 2. Le-Chatelier Apparatus.
- Q. Fineness is determined by the 4. Air permeability method (Blaine's apparatus).
- R. Setting time is measured with 1. Vicat's Apparatus test.
- S. Tensile strength is found using the 3. Briquette test.
Correct Answer: A. 30 min
Solution:
As per Indian Standards (IS 8112: 2013), the initial setting time for 43 Grade Ordinary Portland Cement must not be less than 30 minutes. This ensures that there is enough time for mixing, transporting, and placing the concrete before it begins to stiffen.
Correct Answer: A. 3250 cm²/g
Solution:
Rapid hardening cement gets its properties from being more finely ground than ordinary Portland cement. According to IS 8041-1990, the specific surface area, which is a measure of fineness, should not be less than 3250 cm²/g.
Correct Answer: B. Autoclave test
Solution:
The soundness of cement refers to its ability to resist volume change after setting. The Autoclave test and the Le-Chatelier test are both used to determine soundness. The Autoclave test is particularly sensitive to the presence of both excess lime and magnesia.
Correct Answer: A. Equal to (P/4 + 3)% percent of total mass of cement and sand, where P is water required for standard consistency
Solution:
For preparing the cement-sand mortar cubes for the compressive strength test, the amount of water is calculated based on the standard consistency (P) of the cement. The formula specified by IS 4031 (Part 6) is (P/4 + 3.0)% of the combined weight of cement and sand.
Correct Answer: A. C₃A
Solution:
Tricalcium Aluminate (C₃A) is the most reactive of the Bogue's compounds. It hydrates almost instantaneously upon contact with water, releasing a large amount of heat. If its reaction is not controlled (by adding gypsum), it will cause the cement to stiffen immediately, a phenomenon known as "flash set".
Correct Answer: D. 3.15
Solution:
The specific gravity of Ordinary Portland Cement is generally taken as 3.15. This value is important for various mix design calculations. It is determined using a Le-Chatelier flask.
Correct Answer: A. 1% to 2%
Solution:
Sulphur trioxide (SO₃) is present in small quantities in Ordinary Portland Cement, typically ranging from 1% to 3%. Its presence is mainly due to the gypsum added during grinding. While a small amount is necessary to control setting, an excess can cause unsoundness.
Correct Answer: B. Portland pozzolana cement
Solution:
Portland Pozzolana Cement (PPC) is often preferred for lining tube wells due to its higher resistance to chemical attacks from soil and water compared to Ordinary Portland Cement. Oil well cement is a more specialized type used for very deep wells under high temperature and pressure.
Correct Answer: A. expansion
Solution:
The autoclave test is a method for determining the soundness of cement. It measures the potential expansion of a cement sample when subjected to high pressure steam, which accelerates the hydration of free lime and magnesia that could cause long-term expansion and cracking.
Correct Answer: A. 42.5 to 47.5 MPa
Solution:
The older IS 10262:1982 standard used letter grades for concrete mix design. In this classification, Grade C corresponds to concrete with a characteristic compressive strength in the range of 42.5 to 47.5 MPa. Note that this grading system is different from the modern cement grades (33, 43, 53).
Correct Answer: A. Tricalcium silicate
Solution:
Tricalcium silicate (C₃S) is considered the best cementing material among the Bogue's compounds. It is the most abundant compound in well-burnt Portland cement and is primarily responsible for the early strength and hardening of the cement.
Correct Answer: D. Matrix
Solution:
In composite materials like mortar or concrete, the term Matrix refers to the continuous phase that binds the filler (aggregates) together. In mortar, the cement or lime paste serves as the matrix, enveloping the sand particles to create a cohesive and solid mass.
- Admixture: A substance added to modify properties, not the main binder.
- Adulterant: An impurity that degrades quality.
- Paste: While the cement-water mixture is a paste, 'matrix' is the correct technical term for the binding component within the entire composite structure.
Correct Answer: C. Grade 63
Solution:
The Bureau of Indian Standards (BIS) classifies Ordinary Portland Cement (OPC) into three main grades based on their 28-day compressive strength. These are Grade 33, Grade 43, and Grade 53. There is no official "Grade 63" in the standard classification for OPC.
Correct Answer: A. Tricalcium silicate and Dicalcium silicate
Solution:
The strength of cement is primarily due to the hydration of its silicate compounds. Tricalcium silicate (C₃S) provides early strength (within the first 7 days), while Dicalcium silicate (C₂S) contributes to the progressive, long-term strength. Together, they are the most important compounds for the overall strength of cement.
Correct Answer: A. the heat of hydration of pozzolana is higher than that of low heat cement.
Solution:
This statement is incorrect. One of the primary benefits of using pozzolans is that they reduce the heat of hydration. Pozzolanic reactions are slower and generate less heat compared to the hydration of Portland cement. Therefore, the heat of hydration for pozzolanic cement is significantly lower than even low-heat Portland cement, making it ideal for mass concrete structures where thermal cracking is a concern.
Correct Answer: D. Rapid hardening cement
Solution:
Rapid Hardening Cement is specifically manufactured to gain strength more quickly than Ordinary Portland Cement. This is achieved by grinding the cement clinker to a higher fineness and having a higher content of Tricalcium Silicate (C₃S). IS 8041-1990 is the standard for this type of cement, making it the correct choice for applications needing high early strength, such as road repairs or cold weather concreting.
Correct Answer: B. 1300°C to 1500°C
Solution:
During the manufacturing of Portland cement, the raw materials are heated in a rotary kiln to a very high temperature. The crucial stage is reaching the clinkering zone, where the temperature is maintained between 1300°C and 1500°C. At this temperature, the materials sinter (become a coherent mass without melting) and partially fuse to form the small, hard nodules known as cement clinker, which contains the essential cement compounds.