Concrete Curing Time
Strength gain day by day, when the slab tolerates foot traffic and vehicles, and what heat, cold and drying do to the schedule.
Quick answer
Strength gain by day
| Age | % of 28-day strength | On a 3,000 psi mix | What you can do |
|---|---|---|---|
| 1 day | 16% | 480 psi | Forms can often come off vertical faces; no traffic |
| 3 days | 40% | 1,200 psi | Foot traffic usually acceptable |
| 7 days | 65% | 1,950 psi | Light loads; keep curing wet or covered |
| 14 days | 90% | 2,700 psi | Most residential loading is fine |
| 28 days | 100% | 3,000 psi | Design strength reached; vehicles OK |
| 90 days | 110% | 3,300 psi | Continued slow gain beyond design strength |
Setting versus curing
Setting is concrete stiffening, and it happens in hours. Curing is cement hydrating with water, and it continues for weeks as long as water is present. Concrete does not dry to get hard — it reacts. Let the surface dry out in the first week and the reaction stops there, which is exactly where the dusting, crazing and shallow spalling come from.
Temperature scales the reaction. Between 50 and 90°F the timeline above holds. Above that, cover and wet-cure aggressively; below 50°F expect strength gain to stretch out, and below 40°F protect the pour with blankets — freezing fresh concrete permanently damages it.
Cut or tool control joints within the first 6 to 12 hours, at a depth of one quarter of the slab thickness and a spacing in feet of no more than two to three times the thickness in inches. A 4 inch slab wants joints every 8 to 12 feet — concrete will crack, and joints decide where.
Source & method: The strength-gain fractions are the widely published hydration curve for moist-cured normal-weight concrete referenced to 28-day design strength, and the psi column is arithmetic on a 3,000 psi mix. Presented as guidance, not as a code table.
Frequently asked questions
- How long before you can walk on concrete?
- About 24 to 48 hours for foot traffic, once the surface no longer marks. At three days concrete has reached roughly 40 percent of its 28-day strength.
- How long before you can drive on new concrete?
- Seven days for a passenger car on a properly designed slab, and 28 days before heavy vehicles or loaded trailers. At seven days concrete is near 65 percent of design strength.
- Why is 28 days the standard for concrete strength?
- Cement hydration is fast at first and then slows sharply. By 28 days a moist-cured mix has reached the strength used for design, and gains after that are small — which is why specifications and cylinder breaks are referenced to 28 days.
- Does concrete cure faster in hot weather?
- It sets faster but does not end up stronger — hot, dry, windy conditions pull water out before hydration finishes, which weakens the surface and causes plastic shrinkage cracks. Keep it wet or covered. Below 50°F the reaction slows dramatically and below 40°F it can effectively stop.
- How long should you keep concrete wet?
- Seven days of moist curing is the standard target: wet burlap, plastic sheeting, a curing compound or periodic sprinkling. Those first seven days buy most of the strength you will ever have.
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