Civil Engineering Reference
In-Depth Information
Table 4.
Setting Times of Concrete Containing Calcium Chloride and
Calcium Nitrite
Cement Brand
Admixture
Setting Time (hr: min)
Initial
Final
A
-----
8:45
12:21
A
Calcium Chloride
4:20
7:30
A
Calcium Nitrite
6:00
10:20
B
-----
8:38
---
B
Calcium Chloride
3:16
5:00
B
Calcium Nitrite
5:24
9:04
(Reprinted with permission from ASTM.)
Table 5.
Effect of Calcium Nitrite on Strength Development
Compressive Strength (lbs/in
2
)
1 Day
Admixture %
7 Days
28 Days
-----
1299
3401
5032
2
1615
4538
5732
3
1959
4964
5907
4
2294
5337
6383
5
2367
5324
6493
(Reprinted with permission from ASTM.)
The relative acceleratory effects of calcium chloride, calcium
nitrate, and sodium thiocyanate on cement have been studied.
[61]
The total
heat is higher in the presence of all accelerators. Calcium chloride addition
results in the maximum amount of heat. Sodium thiocyanate accelerates
better than calcium nitrate. Calcium nitrate works well at early stages, but
sodium thiocyanate is more effective at later ages. Sodium molybdate and
trioxide also have an acceleratory effect.
[62][63]
Generally, the
hydroxycarboxylic acids are regarded as retard-
ers, but lactic acid behaves differently.
[64]
In dosages of 0.1 to 0.4%, it
reduces both the initial and final setting times of cement. The compres-
sive strength at 28 days is higher than the reference by about 10-15%.
α
