What is Concrete scaling?
Before knowing what causes concrete scaling you have to know some basics of concrete scaling. So, let’s start.
When the finished surface gets exposure to the freezing or thawing, local flaking or peeling occurs known as concrete scaling.
It is mainly occurred due to the physical activity between the hydraulic pressure due to water freezing and the concrete surface. Generally, it starts in small patches, later if not cured may extent and merge to large patches and areas.
Concrete scaling may cause the loss of up to 2.5 to 10mm of surface mortar and when it occurs severely it makes the aggregates exposed clearly, sometimes it may pop out too.
We all know, in line with ACI, “scaling of concrete is that the local flaking or peeling away of the near-surface portion of hardened concrete or mortar can differ from light to very severe with fall of coarse particles size larger than 20mm (7/8”).”
Stage of Concrete Scaling As classified by the ACI
|Scaling stage||Effects||Surface loss|
|Light||without exposure of coarse aggregates.||Loss of surface mortar|
|Medium||Exposure of coarse aggregates||0.2 to 0.4 inches loss in depth.|
|Severe||Loss of mortar surrounding aggregates particles.||0.4 to 0.8 inches loss in depth.|
|Very severe||Loss of coarse aggregates particles as well as surface mortar.||Loss of depth greater than 0.8 inches.|
Effects of salt on the scaling of concrete
Salt directly does not react with the hardened concrete but salt can lower the freezing point of water, attract moisture, and can increase the pressure of frozen water.
Salt boosts the freeze-thaw cycle if the temperature differs between 15°F and 25°F and scaling can occur in the absence of salts too.
What causes concrete scaling?
The general causes of the concrete scaling are as follows.
Use of low strength or improper mix designed concrete with high water-cement ratio concrete which allows the water and the declining solutions to penetrate deeper.
Use of non-air entering agents which results in poor air void system which causes the scaling at the surface
Improper finishing which leads to trapping of water at the slab top resulting in a low strength concrete layer.
Choosing improper curing methods.
Fewer days of curing timing which results in the strength, permeability resistance, and durability of the concrete to reduce.
Improper protection after laying out the concrete.
Exposing the new concrete to freezing and thawing before the concrete achieves its desired compressive strength of 4000 psi because of inadequate curing.
Use of deicing chemicals at the new concrete increases the amount of scaling
Accelerated drying of concrete results in weak surface development due to inadequate strength development.
Exposure of corrosive fertilizers to the surface of the concrete
We have studied causes of concrete scaling now let us discuss somewhat on Initial precaution to prevent concrete scaling
Initial precaution to prevent concrete scaling
The following precaution should be applied on concrete for avoiding scaling.
The concrete should be mixed in a proper mix at the desired water-cement ratio. Proper concrete mix with durable and well-graded aggregates should be done.
The use of a non-air entering agent should be kept to a minimum as it decreases the strength of the concrete due to which the scaling occurs.
But, must use air-entrained concrete having low water cementing ratio. Here, Portland cement containing 300 kg/m3 and moderate slump (up to 125mm can help in producing a strong wear-resistant surface.
Should not perform any finishing operation with water present on the surface and also initial screeding should be done followed by bull-floating.
Curing should be done properly and it should be done at least for 7 of days and done according to the no of days required. Provide curing using a liquid membrane compound which increases the strength of the concrete.
Exposure to corrosive fertilizers should be prohibited. Avoid using salts such as calcium, magnesium, or sodium chloride on newly placed concrete. Use of clean sand should be done for traction whereas the use of ammonium sulfate or ammonium nitrate should be avoided as they are aggressive chemical which can destroy the concrete surface.
Concrete should be protected from the harsh winter environment as it is necessary to protect the young concrete from becoming saturated with water prior to the freeze and thaw cycle in winter.
Before the application of sealer, concrete should be dry and for late summer concrete, a minimum one month of drying post-curing preceding should be applied before using a sealer.
Finishing should be done properly. Scale occurs if the water is added when concrete is prematurely floated or troweled.
Also finishing concrete before the bleed water comes to surface results in scaling, so proper finishing practice should be done.
How to fix concrete scaling?
The repaired surface will not be much strong but will be effective as the base surface to which it bonded. The surface which is to be repaired should be free from dirt, oil, or paint and should be sound and can make it by using a hammer, chisel, shot blasting, or jack-hammer.
Application of sealer to create a moisture barrier for preventing the water to penetrate into the concrete is the most commonly used treatment for lightly scaled concrete.
This can be done by a light powder washing of surface to remove all the loose materials and debris. After drying, treat the surface with high quality penetrating sealer. They react with alkaline materials and moisture to form a barrier for limiting water and deicer penetrating.
Some of other common method for repairing concrete scaling are:
Portland cement concrete resurfacing
Firstly, mix three parts of sand to one part of Portland cement and add enough water to make the consistency of the mix similar to bricklayer mortar.
If some amount of gravel is to be mixed then the ratio is three-part of gravel, two-part of sand, and 1.5 part of Portland cement.
- Loose concrete should be removed.
- the concrete surface should be cleaned well.
- Good to work when the temp is in the 50-60 F range.
- Don’t work on a windy day.
- Should damp the old concrete and apply a thin layer of cement paste before the installation of concrete resurfacing material.
- Latex modified concrete resurfacing
Latex is poured into the mixture and sand and cement are added along with diethylene glycol and the amount of water depends on the moisture content of sand. Mixing should not exceed more than 5 minutes and the load should be dumped as soon as completion of the mixture. The mixture should be shut off if circumstances prevent immediate discharging.
Placing and finishing
- The surface should be kept damp before placing of resurfacing material.
- Thoroughly brush a portion of mortar into the substrate and complete the pour in order to bring up the concrete to the desired level.
- The area may be re-wet with a 50,50 latex-water.
- Little pressure should be given for efficient troweling of latex modified concrete.
- Epoxy resin sealer should be used for covering all the construction joints.
- Can be reopened after 5 days.
Disadvantages of concrete scaling
- Lower the tensile strength
- Lower the specific strength
- Decrease the durability
- If scaling goes on increasing can cause spalling,
- Increase maintenance cost
- Spoil the appearance of the surface
- Change the property of concrete
The concrete scaling is one of the faults on the concrete slab. The concrete scaling not only degrades the concrete but also influences its property like strength toughness.
Also, when it gets to a more extent it causes spalling. The degradation of concrete scaling also decreases the life of the buildings. So, the scaling should be cured initially by an appropriate technique.
I hope this article on “What causes concrete scaling, their effects and repairs” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Shreya Parajuli