Shown below are some of the compositions and physical properties of four portlan
ID: 1920896 • Letter: S
Question
Shown below are some of the compositions and physical properties of four portland cements:
A
B
C
D
C3S %
51
46
49
56
C2S %
22
29
25
15
C3A %
10
6
12
12
C4AF %
9
12
8
8
Alkalis
0.73
0.68
0.27
0.84
Specific Surface (cm2/g)
3430
3150
3300
3900
Analysis:
(1) Which cement would have the highest seven-day strength? Why?
(2) Which cement would be most resistant to sulfate attack? Why?
(3) Which cement would be best to use with an aggregate high in reactive silica? Why?
(4) Which cement would probably have the highest ultimate strength (long term)? Why?
A
B
C
D
C3S %
51
46
49
56
C2S %
22
29
25
15
C3A %
10
6
12
12
C4AF %
9
12
8
8
Alkalis
0.73
0.68
0.27
0.84
Specific Surface (cm2/g)
3430
3150
3300
3900
Explanation / Answer
(1) D
reason : C3S is responsible for early strength as D has more value it has high , it has highest early seven day strength
(2) (B)
reason :It liberates a lot of heat during the early stages of hydration, but has little strength contribution. Gypsum slows down the hydration rate of C3A. Cement low in C3A is sulfate resistant. here (B) has low value of C3A
(3) C
reason :
ASR reaction is the same as the pozzolanic reaction, which is a simple acid-base reaction between calcium hydroxide, also known as Portlandite, or (Ca(OH)2), and silicic acid (H4SiO4, or Si(OH)4). this reaction can be schematically represented as following:
Ca(OH)2 + H4SiO4 ? Ca2+ + H2SiO42? + 2 H2O ? CaH2SiO4
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