Concrete may harden enough to walk on in a few hours, but truly curing concrete requires significantly more time -- five to seven days depending on the area of the project. When concrete is fully cured, it reaches it's maximum strength and durability. Not allowing your concrete project to cure properly can cause premature cracking or simply a weak concrete sidewalk, driveway or patio.
Concrete or Cement?
While the concrete and cement are often considered to be the same substance, the truth is concrete is the actual material used to pour your walkway, patio or driveway. Cement is actually only one ingredient in concrete along with sand, crushed stone and gravel. Cement is the paste element that, when watered, allows all the other ingredients to stick together and set up into a hardened substance.
Builders and home improvement enthusiasts will debate their own specific formulae for concrete, but the general rule of thumb for mixing good concrete (per cubic yard) under moderate weather conditions is: - six bags of cement (min) - six gallons of water per bag (max) - six days curing period (min)
If the temperature spikes or drops during the six-day curing period, your concrete could possibly either be significantly weakened or take significantly more time to cure.
Water and cement have a chemical reaction when combined in the right amounts. This process is called "hydration" and causes cement to harden when combined with water under the correct temperature. Very hot outdoor temperatures can cause too much water to evaporate too quickly, while temperatures under 10 degrees Celsius can slow curing precipitously.
It is important to keep the surface of the new concrete moist as it cures to permit proper hydration. Temporary covering layers, like burlap, are often used to delay evaporation of the water so necessary to proper curing. Standard curing time ranges between five and seven days for traditional concrete projects, but can take significantly longer for very deep concrete or concrete sections that require excessive structural support.
Very large construction projects that use large expanses of concrete or very thick layers of concrete can take significantly longer to cure thoroughly. The concrete will set in just a few hours depending on ratio used in the mix, but will take about 28 days to achieve full strength for support structures like anchor bolts to be used without loosening.