1. 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
Explanation: Retarders are used to offset the accelerating effect of hot weather on the setting of concrete.
2. 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
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
3. 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
Explanation: Gypsum is well known retarders helps to accelerating effect of high temperature on setting properties.
4. Setting time of cement increases by adding ____________
a) Gypsum
b) CaCl2
c) NaOH
d) Hydrogen peroxide
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.
5. Retarders used at grouting oil wells, where temperature is about _____________ oC.
a) 100
b) 150
c) 200
d) 250
Explanation: Retarders used at grouting oil wells, where temperature is about 200 °C, at a depth of 6000 meters.
6. Minute spherical bubbles of size ranging from ______________ microns.
a) 1-100
b) 5-80
c) 15-20
d) 50-60
Explanation: Minute spherical bubbles of size ranging from 5-80 microns distributed evenly in the entire mass of concrete.
7. What is Silica Fume?
a) Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys
b) Silica fume is a mono product of producing silicon metal or ferrosilicon alloys
c) Most commonly found in nature as quartz and in various living organisms
d) Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide
Explanation: Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys.
8. Silica fume is ______________
a) Less reactive
b) Neutral
c) More reactive
d) Absent in concrete
Explanation: One of the most beneficial uses for silica fume is in concrete, because of its both properties, it is a very reactive pozzolana.
9. Concrete containing silica fume can have very __________ strength and can be very __________
a) Low, Durable
b) High, Durable
c) Low, brittle
d) High, brittle
Explanation: Concrete containing silica fume can have very high strength and can be very durable.
10. Content of SiO2 in silica fume is ___________
a) 52%
b) 35%
c) 21.9%
d) 85-97%
Explanation: The content of SiO2 in silica fume is 85-97%. 35% is the content of SiO2 in Calcareous (ASTM C618 Class C) Fly Ash.