The gradual hardening of concrete after pouring is mainly the result of the hydration of cement, which requires appropriate temperature and humidity conditions, so that the concrete must be cured in order to ensure suitable conditions for hardening and growing strength.

For concrete that has been poured, natural curing should begin before the concrete is finalised (usually within 8-12h after the concrete has been poured). Curing should be carried out immediately after the final setting of waterproof concrete and should not be less than 14d.Timing of concrete curing

Ordinary concrete is cured before final setting, but waterproof concrete is cured afterwards. Why is this?

This is because a layer of hydrophobic membrane is formed after the hydration reaction of the waterproof concrete, and it is thanks to this layer of hydrophobic membrane that the waterproof concrete plays the role of a water repellent. So it is necessary to wait until the hydration reaction of waterproof concrete is complete, and then sprinkle water to maintain it, so as not to destroy the hydrophobic membrane, to ensure that the waterproof concrete plays a waterproof role.

One thing must be noted about waterproof concrete: it should be cured immediately after final setting. This is because if curing is not carried out in time, the water inside the concrete will evaporate quickly, making the hydration of the cement incomplete. The evaporation of water will cause the capillary network connected to each other, forming seepage channels, while concrete shrinkage increases, cracking, a sharp decline in impermeability, or even complete loss of impermeability.

Concrete curing time summary

Ordinary concrete

(1). For poured concrete, natural curing should begin before the final setting of the concrete (usually within 8 to 12h after the concrete is poured).

(2). The standard curing age of concrete specimens is 28d, and their compressive strength should be tested.

(3). After concrete has been poured: ① Cover and moisturise the concrete within 12h. For concrete mixed with Portland cement, PuSi cement and slag cement, the curing time shall not be less than 7d, and for concrete mixed with slow-setting admixture or with anti-seepage requirements, the curing time shall not be less than 14d.

(4). After construction of the whole surface, the curing time shall be not less than 7d, and the compressive strength shall reach 5MPa before people are allowed to walk on it.Timing of concrete curing

Waterproof concrete

The maintenance should be carried out immediately after final setting and should last no less than 14d.

Post-pouring zone

(1). The concrete should be covered for moisture conservation within 12h after it has been poured.

(2). The back-cast zone should be kept for at least 28d and maintained for at least 15d of wet maintenance.

(3). Waterproofing of the back-cast zone: (1) The age of the concrete on both sides should be 42d; (4). The curing time should be not less than 28d.Timing of concrete curing

Large volume concrete

(1). For large-volume concrete, the duration of moisture conservation curing shall not be less than 14d.

(2). For large-volume concrete: when ordinary Portland cement is used, the curing time shall be not less than 14d; when slag cement is used, the volcanic ash cement curing time shall be not less than 21d; waterproof concrete shall be cured immediately after final setting, the curing time shall be not less than 14d.

Shotcrete

(1). Curing after 2h after final setting of shotcrete, with curing time not less than 14d.

(2). When the temperature is below 5°C, no water spray curing is allowed.