The pitting in the concrete surface was caused by using salt in the winter. Salt (NaCl) is not to be used on concrete, but rather calcium chloride (CaCl) should be used. This problem was complicated by use just several months after the concrete had been poured.
Makes for a nonslip surface😉
Good reminder James!
And, welcome to our forum for the first time. Enjoy and come back!
How do you know that it is true for the slab we are looking at?
Could have been a wet batch of concrete
What do you mean?
Doesn’t have to be wet concrete, it could be weak concrete.
concrete for sidewalks should be at least 4000# PSI or more to withstand the affects of winter salt.
No salt is good for concrete, in or out of it, especially if it is reinforced.
The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch. The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is used to ensure uniformity for different loads of concrete under field conditions.
A separate test, known as the flow table, or slump-flow, test, is used for concrete that is too fluid (non-workable) to be measured using the standard slump test, because the concrete will not retain its shape when the cone is removed.
I’m aware of the test… what I’m not understanding is your pondering of:
It would not have held its shape very well to form the curb, Simon.
If you are aware of the test, it seems like you would consider that, depending on how wet the concrete was, of course.
I have considered, indeed. However, in my area the curbs and sidewalks are made using forms which hold the concrete in place until it sets & cures. Without the forms the concrete would never hold its proper shape regardless of its water content.
How is it done in your area?
This was a picture of the walkway at the office space I was renting. The concrete looked good until the first winter when the landlord spread some salt on the surface. The dimpling was pretty quick. After pointing it out to the landlord he only uses calcium chloride products on the concrete now.
Will do, thanks.
There would be a form on the outside flat vertical area but the curb itself would be shaped by hand, especially in a tapered shape that the picture shows. Hence, the importance of the amount of water mixed into the concrete.
That won’t matter, it is not the salt that does the damage.
Salt is hygroscopic, meaning that salt attracts and retains water. When salts are applied to concrete, they attract up to 10% more water into the pore structure of the concrete. This process leaves less room for expansion in the pore structure which, in turn, creates more pressure inside the concrete when it freezes, causing the surface to chip, flake, and pop (typically called “spalling”).
Many times the cause is improper finishing. The surface is hard troweled too soon before the water has a chance to escape. Did you ever notice that some very old concrete drives still show no signs of spalling? The old time finishers did not rush the finishing.
rock salt finish is an intentional common finishing technique
unless significant structural concrete paving or slab failure was evident
i’d advise of this possibly being intentional for aesthetic purposes
James, you might try Magnesium Chloride. I have have very good performance using it down to about -5F. It is a little more costly but for my use it has been worth it. IMHO
" Shoveling built up snow on homes and driveways is a strenuous task. Areas that experience freezing temperatures during winter use treatments to remove snow from their homes. Magnesium chloride ice melt is one popular choice that is considered smarter, safer and efficient compared to other types of rock salt.
But What Exactly is Magnesium Chloride?
Magnesium chloride is a salt made up of magnesium and chlorine. It is commercially available in different hydrate forms including anhydrous, hexahydrate, and brine. Anhydrous magnesium chloride is extremely exothermic and too dangerous to use as snow and ice melt, while its hexahydrate form is less exothermic when diluted or brined.
Benefits of These Ice Melts
Magnesium chloride ice melt is available in flake form and resembles other deicers. However, it has numerous positive attributes that make it the preferable choice for melting ice. These include:
- Slow Attack Rate
Standard ice melts can corrode pavements and other surfaces when over-applied or misused. Therefore, it is important to select an ice melt that causes the least amount of damage to both property and vegetation. Magnesium chloride is widely known to be a less corrosive ice melt.
- Leaves Minimal Damage
Magnesium chloride ice melt is less harmful to vegetation and concrete when used as directed. It melts ice slowly and leaves minimal damage to surfaces. Since it is a naturally occurring mineral, the ice melt is recognized nationally as environmentally friendly. It delivers safe surfaces for residential and commercial building owners without causing damage to natural stone (like tile entrances, granite steps, natural flogging or bluestone walkways).
- Minimal Residue
Magnesium chloride melts ice just as fast as calcium chloride. It is hygroscopic (ability to absorb moisture), which allows it to quickly dissolve into brine and start the process of melting ice. Furthermore, compared to other ice melt products, magnesium chloride leaves behind little to no residue making it easy to clean up after.
- Coldest Temperatures
Magnesium chloride works in freezing temperatures of up to negative five degrees Fahrenheit (-5°F). This temperature is much lower than that of traditional rock salt products, which makes the ice melt suitable for use in both commercial and residential areas. But this does have limitations (see below).
But Please Use with Caution
As any other salt product, magnesium chloride has some cautions and limitations that should be pointed out before making a purchase.
It’s 48 percent active - what does this mean? Magnesium chloride has more water molecules and may be quickly diluted hence ineffective after a long time. Since it dissolves quickly once applied on the ice, it loses its melting ability after a relatively short period, which may require the use of more of the product for excessive amounts of ice and snow.
Due to this shorter active state compared to other products like rock salt, magnesium chloride may prove more expensive for excessive amounts of snow and ice. It can get pricey if you have to keep reapplying more and more product.
Magnesium chloride also offers reduced results when used in really low freezing temperature scenario. Since it works best up to temperatures of negative five degrees Fahrenheit, one risks reduced results if they use the product in an area with extremely low temperatures.
Surfaces like pavements and roads covered with snow and ice pose a serious public safety hazard because they can lead to accidents, loss of life, as well as the destruction of property. Magnesium chloride ice melt offers dependable snow removal qualities. Furthermore, it leaves minimal damage to surfaces, infrastructure and surrounding areas."
Good one Marcel!