This set of Concrete Technology Multiple Choice Questions & Answers (MCQs) focuses on “Hydration of Cement”.
1. What is hydration of cement?
a) Chemical reaction of cement with acid
b) Chemical reaction of cement with water
c) Chemical reaction of cement with base
d) Chemical reaction of cement with salt, and acid
Explanation: As water comes into contact with cement particles, hydration reactions immediately starts at the surface of the particles.
2. As the hydration proceeds the deposits of hydrated products on the original cement grains makes the diffusion of water to unhydrated nucleus ____
b) Very difficult
c) Very easy
Explanation: It is difficult thus the rate of hydration decreases with time & as a result hydration may take several years.
3. The development of first 28 days strength is on account of the hydration of __
Explanation: Higher C3S→higher early strength-higher heat generation (roads, cold environments). Higher C
4. Which compound is liberates higher heat?
Explanation: C3S having a faster rate of reaction accompanied by greater heat generation developes early strength of the paste.
5. Which compound is liberates lower heat?
Explanation: C2S hydrates & hardens slowly so results in less heat generation & developes most of the ultimate strength.
6. Which compound may lead to a rapid stiffening of the paste with a large amount of the heat generation?
Explanation: C3A is characteristically fast reacting with water & may lead to a rapid stiffening of the paste with a large amount of the heat generation (Flash-Set)-(Quick-Set).
7. In order to prevent this rapid reaction ___ is added to the clinker.
d) Extra cement
Explanation: In order to prevent this rapid reaction gypsum is added to the clinker. Gypsum, C3A&water react to form relatively insoluble Calcium-Sulfo-Aluminates.
8. For complete hydration of cement the w/c ratio needed is ____
a) More than 0.25
b) More than 0.25 but less than 0.35
c) More than 0.35 but less than 0.60
d) More than 0.60
Explanation: A mix with a ratio of 0.45 may not mix thoroughly, and may not flow well enough to be placed. More water is therefore used than is technically necessary to react with cement. Water–cement ratios of 0.45 to 0.60 are more typically used.
9. The minimum water to cement ratio for cement concrete to hydrate is ___
Explanation: Minimum water cement ratio is 0.38. It cannot be 35 kg. W/C ratio depends on the exposure condition of concrete but minimum water cement ratio is 0.38 for full hydration of concrete.
10. Approximate percentage range of A2O3 in OPC is ___
c) 3- 10
Explanation: Percentage of A2O3 is 3-8, CaO has 60-67, SiO2 has 17-25, SO3 is 1-3, MgO has .1-4 and soda has .5-1.3.
Sanfoundry Global Education & Learning Series – Concrete Technology.
To practice all areas of Concrete Technology, here is complete set of 1000+ Multiple Choice Questions and Answers.