Why do concrete surfaces flake and spall?
Concrete surfaces can flake or spall for one or more of the following reasons:
How do you remove stains from concrete?
When can I walk on my new concrete?
You may walk on your new concrete the next day.
When can I drive on my new concrete?
You may drive across your new concrete after 7 days.
When can I park on my new concrete?
You may park your car on your new concrete after 10 days.
Why is my concrete different colors/shades?
Concrete takes months until it is cured. This will cause the concrete to look spotty because there are different amounts of moisture evaporating from each section of your concrete. Please do not be alarmed…this is very normal.
What should I do if I see a crack?
Due to the shrinkage that occurs in concrete, it is normal for cracks to form. We are very skilled at what type of concrete mix we use and where we design our control joints to minimize and control where cracks occur. Hairline cracks do not affect the structural integrity of your new concrete.
Can I use salt on my new concrete?
Salts or any other deicers claiming to be safe for concrete should not be used because they can damage your new concrete. The best way to keep your concrete safe in the winter is to keep it clean with a plastic shovel and to use kitty litter or sand for traction.
Will stamped and/or colored concrete fade?
Decorative concrete will fade if it is not properly maintained. We recommend your new decorative concrete be re-sealed every few years, however in high traffic areas it may need to be re-sealed more often.
How often do I need to seal my new concrete?
We recommend concrete to be pressure-washed and sealed with a commercial grade penetrating sealer every 5-10 years to maximize longevity and esthetics. Read about our Clean & Seal service.
What is concrete made from?
Concrete is a mixture of gray powder called “Portland Cement”, sand and gravel or crushed stone. The “Portland Cement” reacts chemically with water and hardens over time – a process called “hydration,” Concrete doesn’t “dry;” it “cures.” Additives are generally included in the mixture to improve its suitability for driveways. The most common are water-reducers that improve strength, and air-entraining mixtures that make the concrete resistant to cycles of freezing and thawing. Air-entrained concrete additives, containing billions of microscopic air bubbles, and reduce expansion and contraction. This helps concrete withstand Illinois’s large temperature range over our four seasons.
How Strong Is Concrete?
The compression strength (resistance to downward force) of concrete is determined by a number of factors. The most important is the ratio of water to cement in the mixture – the lower the ratio the stronger the concrete. Another way to increase the strength of concrete is to increase the amount of cement used. The strength of concrete is measured in pounds per square inch (PSI) Concrete used in driveways is generally 3,000 – 4,000 PSI, this strength is the result of using 5 bags of cement per cubic yard in the mix. If you increase the cement to 6.5 bags per cubic yard, the strength goes to 4000 PSI. At Catalano Concrete, we use 4,000 PSI for our concrete projects.
If Concrete Is So Strong, Why Does It Crack?
There are two kinds of concrete: the kind that is cracked and the kind that is going to crack. If a driveway contractor tells you his concrete driveways won’t crack, be skeptical, because it’s just not true. Although concrete has very high compression strength, it has very little tensile strength (resistance to being pulled apart). Because concrete shrinks as it cures, at a rate of about 1/16th of an inch for every 10 feet, there is strong tension pulling the cement slab. Because the whole slab can’t move over the ground, it can pull apart in the middle, causing a crack. Proper steel grid and micro-fiber reinforcement can help reduce this cracking tendency.
Control joints help control cracking. Control joints, as they are called, weaken the concrete slightly at the surface, so that when the concrete cracks it will likely follow the control joint and not be noticed. These control joints can be created in two ways. The concrete can be cut in straight lines, roughly ¼ of the depth of the slab. Hand-troweled control joints are another option, also often seen on sidewalks. The number and spacing of these control joints depends on the specific installation.
What Other Factors Cause Cracks?
In addition to shrinkage, there are four other main causes that contribute to cracking:
- Expansion and contraction due to temperature changes
- Concentrated heavy loads
- Poor un-compacted sub-base conditions
- Rapid water loss prior to finishing the concrete after it is poured.
All of these causes can be minimized with proper care and installation. A properly compacted sub-base of the proper thickness under the concrete is crucial. In Illinois’s cold winter climate, only air-entrained concrete should be used. Heavy vehicles, such as garbage trucks should be kept off the slab, especially near the edges. Finally, an experienced concrete paving company will properly manage the curing process after the concrete is poured.