Initial set, as defined by ACI 116R, is a degree of stiffening of a mixture of cement less than final set, generally stated as an empirical value indicating the time in hours and minutes required for the cement paste to stiffen sufficiently to resist to an established degree, the penetration of a weighted test needle. The concrete setting time at various temperatures is given at table below:
Table 1 Setting Time of Concrete at Various Temperature
| Temperature | Approximate Setting Time (hours) |
| 100oF (38oC) | 1-2/3 |
| 90oF (32oC) | 2-2/3 |
| 80oF (27oC) | 4 |
| 70oF (21oC) | 6 |
| 60oF (16oC) | 8 |
| 50oF (10oC) | 11 |
| 40oF (4oC) | 14 |
| 30oF (-1oC) | 19 |
| 20oF (-7oC) | Set will not occur |
The retardation of initial setting time by the use of admixture is affected by three factors, that is, the ambient temperature, the dosage used, and the time of adding to the batch.
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