This set of Concrete Technology Multiple Choice Questions & Answers (MCQs) focuses on “Accelerators and Retarders”.
1. What is accelerator?
a) Which speed up the initial set of concrete
b) Which delays the initial set of concrete
c) Which speed up the final set of concrete
d) Which delays the final set of concrete
View Answer
Explanation: An admixture used to speed up the initial set of concrete is called accelerator.
2. What is retender?
a) Which speed up the initial set of concrete
b) Which delays the initial set of concrete
c) Which speed up the final set of concrete
d) Which delays the final set of concrete
View Answer
Explanation: An admixture used to delay the initial set of concrete is called retender.
3. NaOH is the example of retenders.
a) True
b) False
View Answer
Explanation: NaOH speed up the initial rate of hydration of cement and also speed up the initial set of concrete.
4. Zinc is the example of retenders.
a) True
b) False
View Answer
Explanation: Zinc delays the initial rate of hydration of cement and also delays the initial set of concrete.
5. Retarders are used to ___________
a) Offset the accelerating effect of cold weather on the setting of concrete
b) Offset the accelerating effect of hot weather on the setting of concrete
c) Offset the Retarding effect of cold weather on the setting of concrete
d) Offset the Retarding effect of hot weather on the setting of concrete
View Answer
Explanation: Retarders are used to offset the accelerating effect of hot weather on the setting of concrete.
6. At normal temperatures addition of sugar _____________ per cent have little effect on the rate of hydration.
a) .5-1
b) 1-2
c) .05-.1
d) .1-.2
View Answer
Explanation: At normal temperatures addition of sugar .05-.1% have little effect on the rate of hydration, but if the quantity is increased to 0.2 percent, hydration can be retarded to such an extent that final set may not take place for 72 hrs.
7. Pick up the correct statement from the following.
a) Calcium fluosilicates act as a retarders
b) CaCl2 acts as a retarders
c) Gypsum acts as a retarders
d) Gypsum acts as an accelerators
View Answer
Explanation: Gypsum is well known retarders helps to accelerating effect of high temperature on setting properties.
8. Setting time of cement increases by adding ____________
a) Gypsum
b) CaCl2
c) NaOH
d) Hydrogen peroxide
View Answer
Explanation: Gypsum is often added to cement and concrete to slow down the drying time. Cement dries quickly. If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.
9. Retarders used at grouting oil wells, where temperature is about _____________ oC.
a) 100
b) 150
c) 200
d) 250
View Answer
Explanation: Retarders used at grouting oil wells, where temperature is about 200 °C, at a depth of 6000 meters.
10. Minute spherical bubbles of size ranging from ______________ microns.
a) 1-100
b) 5-80
c) 15-20
d) 50-60
View Answer
Explanation: Minute spherical bubbles of size ranging from 5-80 microns distributed evenly in the entire mass of concrete.
Sanfoundry Global Education & Learning Series – Concrete Technology.
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