Commercial Concrete sidewalk edmonton

How Long does Concrete Take to Set in Edmonton?

I was out for coffee with a buddy of mine that works for the city and we got talking about some of the different projects that they work on throughout the year.  Larger scale developments, curbs & sidewalks, you know, really interesting stuff!!  We talked about how it is always a point not to disrupt the public as much as possible, especially with sidewalks, etc.  As we discussed this, it made me think, when dealing with Concrete in Edmonton, how long does it actually take to fully cure?

Concrete is typically considered to be one of the most durable and attractive construction materials around, but were you aware that everything you do after pouring has just as much impact on its strength as the mixing process? In fact, the chemical reaction between cement and water that binds sand and gravel together to make concrete takes nearly 28 days to fully complete.  I was very surprised to find out that concrete never really stops curing. That’s right, throughout concrete’s lifespan, there are billions of cement particles within the mix and they constantly react with microscopic water bubbles which continue to form bonds indefinitely. 

Now I think its fair to say that even with the curing process being an ongoing event, for practical purposes, and a timeframe shorter than infinity, here are some general rules of thumb when it comes to concrete curing.

Curing Times for Concrete:

When considering a more industrial concrete application, you can expect its full workable strength at around the 28-day mark. During this timeframe, which is known as hydration, you want to keep moisture in the concrete. Otherwise, water may evaporate too quickly from the surface (which can happen easily outdoors and in direct sun) which can weaken the finished product resulting in stresses and cracking.

During this 28-day period, there are different levels of strength to consider. After about 7 days of curing, the concrete will have reached approximately 70% strength. If you are laying concrete in a residential area, like the driveway or patio, it should be reasonably set within 24-48 hours.  What this means is that your child or pet (or maybe your spouse!!) won’t leave their footprints in the concrete but it does not mean the concrete is ready to be driven over by heavy vehicles. This should be avoided until at least the 28-day period.

Factors that Affect Concrete Setting:

It is important to control the moisture content as well as the temperature of the new concrete for the first several days through curing process. Giving your new concrete some extra attention during this period can increase the structural integrity of the concrete and make it more resistant to future cracking. To ensure the best results, we have put together a “Do’s” and “Don’ts” list for concrete-curing practices.

DO spray new concrete with water.

“Moist Curing” allows moisture in the concrete to evaporate more slowly and is accomplished by hosing the concrete down with water 5 to 10 times per day (or as often as you can) for the first seven days. Moist-cured concrete can be up to 50 percent stronger than concrete that was cured without being dampened! This obviously won’t work all year round, considering Edmonton’s cold weather seasons as spraying is not recommended for concrete poured during cold weather.  For pours in cooler weather, see “Don’t Let Concrete Get Too Cold,” below.

DO cover new concrete.

If you are unable to hose down the concrete as often as needed to do a true moist curing, another option is to use a cover that can trap and slow the evaporation of the moisture in the concrete. We recommend polyethylene sheeting that’s at least 4mm thick or a concrete curing insulating blanket.  Both options are good for this task.  Thoroughly wet the concrete and then cover it with the sheeting of your choice and then keep it in place using bricks, rocks or other heavy items. Remove the covering on a daily basis, wet the concrete again, re-cover it and repeat this for seven days. This technique can also be used for upright concrete columns and walls by wetting them down and wrapping them with a curing blanket or plastic sheeting.

DO pond cure concrete slabs.

Pond curing is another great way to cure concrete.  This is not an easy process as you form temporary berms around a new concrete slab and then flood the area inside them with one foot of water. Three days of pond curing does the work of seven days of moist curing and without daily attention.  It is important to be sure the water level remains above the concrete slab and if it drops, you’ll need to refill a little. As mentioned, this technique may not be for everyone as it takes quite a bit of soil to form berms around a big concrete slab.

DON’T skip control joints in concrete slabs.

The goal of all concrete installation is to produce a high-quality product that resists cracking. While curing concrete will go a long way toward strengthening the finished project, many concrete slabs will crack anyway, despite all precautions.  This is due to concrete shrinkage as water is used up in the hydration process as well as major temperature fluctuations in Edmonton and area. To preserve the integrity of the slab in the face of these challenges, you can place control joints at predetermined locations to guide the inevitable cracks. These joints should be cut in a quarter of the depth of the concrete slab during the very beginning of the curing process, within 24 hours of the initial pour. Using a metal jointing tool, the control joints can be easily and smoothly cut into the concrete surface as the appropriate distances in the slab.

To determine the maximum spacing between joints (in feet), multiply the planned concrete thickness (in inches) by 2.5. For example, if you’re creating a sidewalk that is 4 inches deep, you’d multiply 4 by 2.5 to get a distance of 10 feet between joints. Feel free to place them closer together for added crack protection. On a larger square slab, like a patio, you’ll want to consider breaking the concrete with joints that are perpendicular, too (down as well as across). This way, if your slab patio, driveway, or sidewalk cracks, it will most likely do so along a precut joint and can, therefore, go virtually unnoticed.

DON’T let new concrete get too cold.

Living in Edmonton creates a unique situation for concrete curing based on our seasonal weather.  The best time to pour concrete is when temperatures are expected to remain above 10 degrees Celsius for five to seven days, but plans can change with the arrival of an unexpected cold front. When that happens, the importance shifts from keeping the concrete damp to keeping it warm enough that the chemical hardening process is not interrupted. Concrete’s chemical reaction slows at 10 degrees Celsius and completely stops at 7 degrees Celsius, meaning that it’ll go dormant and it won’t gain strength. If you expect to pour concrete and use it in a couple days, you can’t. When the temperatures drop, new concrete should be covered with concrete insulating blankets (or, in a pinch, old household blankets!). Protect new concrete from the cold for the first two to three days (up to a week, if it’s very cold) after which it should be strong enough to handle it without risk of damage.

DON’T paint or stain concrete in the first month.

Any paint or stain applied to young concrete while it’s still hardening can be negatively affected by residual moisture or the changing chemical content in the concrete. Typically, it takes about a month for all of the water to get used up in the hydration process. If you brush on paint too soon while moisture is still rising to the surface, it can put pressure underneath the hard barrier of paint, causing it to peel away or break the bond. With this, paint may not adhere as well and the final color and appearance of stained concrete may also be affected. To achieve the best results, wait until the 28-day period is over to apply paint or stain.

DON’T subject new concrete to excessive weight.

Although concrete will harden soon after pouring, it’s still susceptible to damage from weight during the first four weeks. Wait at least 24 hours before allowing foot traffic, including pets, on a newly poured sidewalk or slab and don’t drive a vehicle on a new driveway for at least 10 days. After that, you can drive regular passenger cars on the concrete; heavy pickups or RVs can roll onto the driveway once the concrete reaches its full strength, at around 28 days.

If you are looking for professional results are unsure about your concrete skills, it is always best to hire a professional concrete specialist to ensure results that are guaranteed to satisfy.

For any advice related to concrete curing, contact Brett at Garden Concrete Services!

For additional scientific info check HERE!