Curing Exterior Concrete – The What & The Why, To Do It Correctly

Curing Exterior Concrete – The What & The Why, To Do It Correctly

As we approach the fall season, many people are anxious to finally see the dreaded orange cones disappear. Contractors have been hard at work all summer on highways, bridges, sidewalks & driveways. All these projects have one thing in common, and in many cases of residential work, it is completely ignored. That one thing is proper curing of concrete.

On most highways you will see contractors spraying a white chemical after they have tined the concrete to its final finish. On bridges, contractors will saturate burlap with water and then cover the burlap in plastic for moisture retention. Very rarely do you see either of these methods used in residential or commercial construction. Why are these methods used in some cases, but not in others? What is the difference between each method? Let us take a deeper dive into concrete curing and find out.

First off, what is concrete curing and why is it important? Curing is the process of allowing the concrete to sustain hydration. Hydration is the reaction of the dry mix materials in concrete, combining with water. The longer the hydration process continues, the longer the materials in the concrete will have to combine and bind with each other. In turn, the longer this process continues, the more resilient and less porous your concrete will be. If the concrete has only a short amount of time to hydrate, excess materials are left in the concrete that do not bind with the materials around it. If you are making the investment in concrete, wouldn’t you want to get a better, longer lasting product in the end? Often time on private projects, this process is skipped as some do not see the value in the extra cost for the curing chemical or increase labor costs of wet curing.

What kind of costs are we looking at for each method? For example, three methods were used on a bridge project in Oklahoma: common curing compound, premium curing compound and burlap wet curing. The common curing compound cost was estimated at 0.07% of the total project cost, the premium compound was estimated at 0.19% and the burlap wet cure was estimated at 0.47%. As you can see, all three of the options were a small portion of the total project costs.

Any of the options are an improvement over no curing at all. You may be saying to yourself that you still do not see the value in curing, even at such a low overall cost. Does it really increase the durability & longevity of my concrete enough to justify the cost? A 2018 Construction and Building Materials journal entry (162 (2018) 306-313) tackled this exact question.

Living in the upper Midwest, our harsh winters and road chemicals wreak havoc on our concrete. The intrusion of these chemicals into pores near the surface of our concrete, causes degradation long before its typical service life. How can proper curing help us increase the life on our concrete? Let us go back to the hydration of our concrete. Any excess materials in the concrete that were not able to bond to each other due to lack of hydration, create even more pores in the concrete. Lack of hydration equals more pores for chemical intrusion. More chemical intrusion equals shorter life of your concrete. In the 2018 study, 3 days of wet curing reduced chloride intrusion by 60%. You read that correct. You can double the life of your concrete against outside chemicals just by properly curing it.

This image shows chloride intrusion in "good" cured concrete and "not as good" cured concrete. Notice how much deeper the chloride penetrates when curing isn't as good.

If you have new concrete in your future or concrete that was not properly cured, that desperately needs some help, contact your local Bierschbach Equipment & Supply. We have the products and the knowledge to help extend the life of your investment.