ACI 306R-16 Table 7.2
Table 7.2 gives the minimum protection period, in days, for concrete kept at the Table 5.1 Line 1 minimum temperature. It depends on the load the concrete will carry, whether it is exposed to the weather, and whether the mix is normal set or accelerated set.
- No load, not exposed: 2 days normal set, 1 day accelerated set.
- No load, exposed: 3 days normal set, 2 days accelerated set.
- Partial load, exposed: 6 days normal set, 4 days accelerated set.
- Full load: refer to Chapter 8.
Reading the right cell
Most errors come from reading the neighbouring cell:
- Normal-set, no load, exposed is 3 days. 2 days belongs to no load, not exposed (normal set) or to no load, exposed (accelerated set).
- Accelerated-set, partial load, exposed is 4 days. 6 days is the normal-set figure for the same row.
Check three things before reading a number: the load, the exposure, and the set.
Converting to hours
The table notes that a day is a 24-hour period. Multiply days by 24:
- Partial load, exposed, accelerated set: 4 × 24 = 96 hours.
- Using the normal-set 6 days gives 144 hours, the wrong row.
- 48 hours is the 2-day no-load, exposed, accelerated-set figure; 72 hours is the 3-day no-load, exposed, normal-set figure.
Protection is not stripping time
ACI 306R-16 §8.1 says the Table 7.2 protection periods do not provide enough strength for removing forms or shores. Using them as stripping times is the common error.
- Forms and shores do not come off as soon as the Table 7.2 period ends.
- There is no rule to pull shores at the end of the period and keep forms 24 hours more.
- 500 psi is the freeze-protection strength, not a form or shore removal criterion.
Table 7.2 answers one question only: how long to keep the concrete protected from the cold.