Concrete Technology Multiple Choice Questions on “Chemical Composition Test”.
1. Portland cement is composed of four major oxides (CaO, SiO2, Al2O3, Fe2O3 ≥90%).
a) True
b) False
Answer: a
Clarification: Portland cement is composed of four major oxides ((CaO, SiO2, Al2O3, Fe2O3≥90%) & some minor oxides. Minor refers to the quantity not importance.[/expand]
2. What is the approx amount of lime is present in cement?
a) 60-67%
b) 70%
c) 75%
d) 60%
[expand title=”View Answer”]Answer: a
Clarification: Deficiency in lime reduces the strength of cement. Deficiency in lime causes cement to set quickly.[/expand]
3. What is the approx amount of silica is present in cement?
a) 17-25%
b) 3-8%
c) 60-67%
d) .1-4%
[expand title=”View Answer”]Answer: a
Clarification: Sufficient quantity of silica should be present in cement to di calcium and tri calcium silicate.[/expand]
4. What is the amount of Na2O & K2O in P.C.?
a) =.6%
b) >6%
c) <6%
d) 0
View AnswerAnswer: c
Clarification: Alkalies (Na2O & K2O) may cause some dificulties if the cement is used with certain types of reactive aggregates in making concrete.
5. Insoluble Residue mainly comes from which compound?
a) Lime
b) Soda
c) Silica
d) Alumina
Answer: c
Clarification: Insoluble Residue is that fraction of cement which is insoluble in HCl. It comes mainly from the silica which has not reacted to form compounds during the burning process in the kiln.
6. Loss on Ignition (L.O.I.) is the loss in weight of cement after being heated to _____________
a) 1000°C
b) 100°C
c) 500°C
d) 1500°C
Answer: a
Clarification: It indicates the prehydration or carbonation due to prolonged or improper storage of cement & clinker.
7. C4AF is not a true compound.
a) True
b) False
Answer: a
Clarification: C4AF is not a true compound. The ferrite phase ranges from C2AF to C6AF. *C4AF represents an average.
8. On cooling below 1250oC, C3S decomposes ____________
a) Fast
b) Slowly
c) Never
d) Depends on the conditions
Answer: b
Clarification: On cooling below 1250oC, C3S decomposes slowly but, if cooling is not too slow, C3S remains unchanged and is relatively stable at ordinary temperatures.
9. Gypsum reacts with ____________ to form calcium sulfo aluminates and calcium sulfo ferrite.
a) C4AF
b) CF4
c) SO3
d) CaO
Answer: a
Clarification: C4AF work as flux material and also it accelerates the hydration of silicates. C4AF hydrates to tricalcium aluminate hydrate and calcium ferrite CaO.Fe2O3 in amorphous form.
10. C3 S and C2S require approximately the _____________ amount of water for hydration.
a) Same
b) More
c) Less
d) Depends on the paste
Answer: a
Clarification: C3S and C2S require approximately the same amount of water for hydration, but C3S produces more than twice as much Ca(OH)2 as is formed by the hydration of C2S.