Freeze-Thaw
Effect
Concrete is very strong in compression but relatively weak in
tension. It can and often does crack. Concrete is also fairly porous and subject
to forces that absorb and release water. Absorbed water can freeze within the
concrete and cause spalling and cracking.
Chemical Attack
Chemical attack can occur because concrete is alkaline and
chemically reactive. It can be attacked by acids; some alkalis; numerous salt
solutions; and organics such as fermenting liquids, sugars, and animal oils,
especially if they contain free acids. Seawater will attack concrete. Corrosive
solutions penetrating to the steel reinforcing rods may be particularly
destructive because the large displacement of the corrosion products of the
steel can cause cracking and spalling of the concrete. In addition to the
general physical and chemical properties of concrete that make it subject to
physical and chemical attack, several other factors influence the makeup of
concrete and therefore must be considered before selecting a method of surface
preparation. How the concrete will be used (e.g., as structural concrete or for
floors), the method used to place the concrete, and the additives that may be
present either on the concrete surface or incorporated into it all will affect
the strength and the surface condition of the concrete. A discussion of
structural concrete, concrete for flooring, and the surface conditions that
accompany each follows.
Crazing
This is a network of very small surface cracks usually
spreading out over large areas or the entire surface. Crazing is caused by
finishing the concrete with bleed water on top. The bleed water is forced down
into the surface by the finisher’s trowel. This increases the ratio of water to
cement, creating a weak surface layer.
Scalling
Thin flakes of concrete come loose and flake or peel off the
surface. The sizes of the flakes vary, but they usually increase over time and
with traffic. Conditions that cause scaling and include freeze/thaw cycles,
deicing agents with calcium or sodium chloride, fertilizers containing nitrates,
working in bleed water, or improper curing. Any one of the can cause scalling,
but it’s usually a combination of two or more that lead to severe scaling.
Blisters
These are typically about ¼ to 1-inch diameter, but it’s not
impossible to get 3 to 4 inch blisters. They are not easily seen until they are
broken by traffic. Blisters are caused by working and finishing the surface
while water or air is still working its way up through the mix to the surface.
Spalling
Spalling is similar to scalling except large chunks instead of
just flakes break loose. This indicates a severe weakness in some parts or the
entire project. It is more likely to happen during freeze thaw conditions.
Dusting
Also known as chalking, this is a fine loose powder caused by
the deterioration of a weak surface. Causes of dusting include working in bleed
water, improper curing, a bad sand-to-cement ratio, or exposure to carbon
monoxide caused by using an unvented heat source to keep a project warm.
Foreign Objects
Foreign objects can often slip into the form prior to pouring
and may not become evident until after the forms are stripped. If fully
embedded, the foreign object does not create a coating problem. But a piece of
rope on the surface disappearing into the concrete is a problem. It must be
removed, usually by chipping, and the concrete must be restored.
Efflorescence
Efflorescence is more likely to be found on concrete that has
been in place for a while. Concrete contains water-soluble salts. As water from
the interior of the concrete migrates to the surface and evaporates, salts are
deposited on the surface, usually as a white stain. Efflorescence can occur with
concrete, brick, or concrete block construction. It can be removed with acid
etching. The best way to prevent its recurrence is with adequate waterproofing.
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Vanguard Concrete Coating
229 Crescent NE
Grand Rapids, Michigan 49503
Phone: 616-742-1540
Fax: 616-742-3793
Ian@vanguardconcretecoating.com
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rights reserved by Vanguard Concrete Coating of Grand Rapids, MI. For residential floors our service area includes the Central, Southwest, & West
Michigan cities of Grand Rapids, Muskegon, Traverse City, Mount Pleasant, Midland, Bay City, Saginaw, Flint, Howell, Jackson, Lansing, Kalamazoo, South
Haven, Holland, Grand Haven and small cites in-between. For industrial &
commercial clients we service a larger area including Detroit & Ann Arbor, Ohio / OH,
Northern Indiana / IN, and Northeastern Illinois / IL cities.
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