Concrete Cure Time Calculator
Cure percent, traffic verdict, and guidance from slab age.
What it does
Fresh concrete looks done long before it is strong: a week old slab carries two thirds of design while full strength waits near day 28. Traffic timing and curing care follow that curve, not the calendar feeling.
The tool above takes days since pour with warm or cold weather. It returns percent of design strength, the traffic verdict, and curing guidance.
The default 7 day warm slab reads 65% with light vehicles OK under a 7 day moist cure. The cold mirror reads 46% cold estimate with blankets ordered.
ACI curing practice sets the 7 day moist cure with 50 F protection, and ASTM cylinder breaks at 7 and 28 days prove the curve. The standard Type I shape behind both runs 16/40/65/85/100 to day 28.
Water cures, cold stalls, and loads punish the young. Keep traffic off early pours, blanket cold ones for 48 hours, and let cylinders rather than optimism open the slab.
How to use
- Type days since the pour.
- Pick warm or cold weather.
- Read strength percent first.
- Read traffic verdict beside it.
- Read curing guidance last.
- Break cylinders to prove big slabs.
Formula
- days
- Days since the pour, 0 to 365.
- temp
- Warm 50 F plus, or cold with blankets.
- pct
- Share of 28 day design strength.
ACI curing guidance centers 7 day moist curing with 50 F protection rules, and ASTM C31 breaks cylinders at 7 and 28 days to verify design strength. The 16/40/65/85/100 curve is the standard Type I shape both bodies assume. Cold multiplies by 0.7 as a planning estimate, flagged in the output.
Worked example
Example: week old slab
Defaults: 7 days, warm (50 F plus).
- Slab: 7 days since pour, warm weather.
- Strength: 7 day table value reads 65% of design.
- Traffic: day 7 sits in light vehicles OK.
- Cure: moist cure 7 days minimum.
- Check: 28 days reaches 100%, full service.
- Tool shows 65% of design, Light vehicles OK, Moist cure 7 days minimum.
Reference table
| Age | Strength | Traffic |
|---|---|---|
| 1 day | 16% | Keep off |
| 3 days | 40% | Foot traffic only |
| 7 days | 65% | Light vehicles OK |
| 14 days | 85% | Light vehicles OK |
| 28 days | 100% | Full service |
Limits
- Type I curve; mixes and admixtures shift it.
- Cold factor is a planning estimate.
- Traffic verdicts assume sound subgrade.
- Cylinders rule on structural pours.
Common mistakes
- Driving at day 3.
- Skipping moist cure in wind.
- Pouring onto frozen ground.
- Reading surface hardness as strength.
- Loading edges before centers.
Try it yourself
Quick checks. Answers sit tucked under each question.
3 days, warm?
40% of design, foot traffic only, moist cure 7 days minimum.
28 days, warm?
100% of design, full service, moist cure 7 days minimum.
7 days, cold?
46% cold estimate with blankets ordered: hold 50 F for 48 h.
Questions
Strength by day?
About 16% at 1 day, 40% at 3, 65% at 7, 85% at 14, and 100% at 28 for moist cured Type I.
Drive on when?
Keep off under 2 days, foot traffic to day 7, light vehicles to day 28, full service after.
Cold weather?
Below 50 F hydration stalls: insulate with blankets and hold 50 F for 48 hours. Never pour on frozen ground.
Moist cure how?
Water, shade, and compound seal the surface so hydration finishes instead of evaporating.
Past 100%?
Strength keeps inching past 28 days toward 110% near 90 days. Design math still uses 28.
Test proof?
Cylinders break at 7 and 28 days per ASTM C31 to prove the curve on real loads.