Nothing invites handprints, initials, or other drawings like the surface of concrete recently poured. Before long, those personal touches are literally encased in concrete, left behind for the ages. Timing is important: Too soon and the concrete will level itself out. Wait too long and the concrete will be too hard to work with.
This is the curing process of concrete. Strength development begins immediately as the chemical reaction between water, cement, and aggregate begins. Concrete never really stops gaining strength. The period of time where curing is most important, however, is the first 28 days after the concrete is poured into a mold.
When left alone, the properly mixed curing compounds (water, cement, aggregate) of concrete will do an adequate job of hardening. However, there are additional steps you can take after a pour to expedite and improve the strength of the concrete.
Moist curing is a very common way of curing concrete pads or patios in the field. Once the concrete has been poured, smoothed, or stamped, a contractor mists the whole area down with water every few hours. This is done to prevent the water from evaporating too quickly, which will affect the strength of the concrete.
In Precast, the preferred way of adding moisture to combat evaporation is steam curing. Instead of sprinkling the concrete every few hours, steam is applied to speed up the curing process. In addition, there are ASTM guidelines on how to steam cure products so that it is performing at its max. This process is the preferred method for precast products and has a positive impact on the acceleration of concrete strength.
Extreme temperatures on both ends of the scale have negative impacts on concrete strength. If not properly cured, concrete in either extreme will not be as strong as properly cured concrete. For example, hot weather will make water evaporate too fast and colder weather (less than 35 degrees) may stop the curing process altogether. Ideally, do your best to ensure the ambient temperature is higher than 50 degrees. The targeted concrete curing temperature is between 50 and 60 degrees.
Beyond the decorative aspects of concrete, including stamping, forming, or adding colors, nothing matches the durability of concrete. Used for thousands of years, concrete is the number one building material around the world. The time to gain true concrete strength depends on the thickness of concrete, the size of the product being poured, and the use.
With forces applying pressure from all sides as well as from vehicle traffic above, manholes, catch basins, and panel vaults must meet all the highest strength standards. Each piece has been highly engineered for each job. The amount of rebar, where the rebar is placed, the thickness of the concrete, and the mixture itself are quite regulated.
Concrete is used so often in both public and private applications because of the strength afforded by proper curing. Resistant to rot, rust, and all manners of weather, properly poured and cured concrete is designed to last for nearly a century.
Advantages of Precast Concrete
While it’s true that concrete continues to strengthen throughout its life, after 30 days, the rate of hardening is minute. While there are ways to speed up the initial set and kick start the curing process, once the curing process begins there is little that can be done to affect the concrete’s ultimate strength.
On a job site, waiting for cast in place concrete to cure can affect the project timeline. Those days can mean all the difference in meeting deadlines and sticking to schedules that keep a project on budget. That’s what makes precast products much preferable to pour in place concrete. As we said earlier, time is the best curing agent. But steps taken before and during a pour can make a world of difference, too.
With precast concrete, weather conditions have very little bearing on the final product. Manufactured in a controlled facility, precast concrete can be made 365 days a year. Extreme heat or cold, rain, snow, and even wind affects the concrete pour at the job site. With an uneven mixture, the strengthening of the concrete can be affected, too.
In a facility, all steps of casting concrete are done under a watchful eye. Mixing, pouring, curing, and concrete testing for compressive strengths are overseen to make sure the quality of the concrete is consistent. Once cured for the proper amount of time, the precast piece is ready for delivery and installation.
Have a large infrastructure project that calls for the durability only cured concrete can provide? Contact Columbia Precast Products today. We work with both the Washington and Oregon State departments of transportation, meeting all code requirements to ensure our customers get only the highest quality products.