Did You Know?

The life of concrete is limited by a number of disintegrating effects:

WeatheringVoidsGasesCrackingSewageMoisture

Weathering by rain and frost action is chiefly a function of water-tightness or impermeability, since leach and attack by the carbonic and other acids present in rainwater, and disruption by frost action, depend on the penetration of water into the surface. Chemical attack such as industrial chemicals and wastes; sewage; animal and vegetable oils, fats, grease; milk; and sugars. Wear by abrasion from foot and vehicular traffic, by wave actions, and by water-borne and wind-borne particles.

Concrete has the tendency to be porous due to the presence of voids formed during or after placing. It is usually necessary in order to obtain workable mixes, to use far more water than is actually necessary for chemical combination with the cement. This water occupies space, and when it later dries out, it leaves behind air voids.

Gases such as sulphur dioxide and carbon dioxide in damp situations, attack concrete. Sulphuric acid also attacks concrete, but the attack from sulphuric acid is likely to be accompanied by abrasion. Sulphates of sodium potassium, magnesium and ammonium may cause serious damage to Portland cement concrete in the presence of moisture. This begins by expansion within the concrete, which may be enough to cause general expansion in the member.

Cracking and disruption follow. Cracks provide a path for soluble chemicals to migrate into the interior of the “Generally, inorganic acids are destructive to concrete… may also be released from some salts…” structure causing deterioration of the concrete. Fertilizers often contain ammonium, potassium and magnesium sulphates. Generally, inorganic acids are destructive to concrete. These may also be released from some salts such as ammonium chloride and ammonium nitrate by interaction with lime. Leaching then follows. A number of fertilizers are soluble in water, enabling the chemical easy pathway to the interior of the concrete. Although petroleum oils, are not known to cause extensive damage to concrete, they do penetrate into the pores and cause unsightly staining, with subsequent high maintenance cleaning as well as possible contamination of the soil below leading to environmental issues. Organic acids such as stearic, oleic, lactic and tannic all attack concrete. Lactic substances which are derived from dairy product have a most destructive effect. Vegetable oils attack, molasses, sugar, syrup, glucose have a fair degree of attack, acetic acid which occurs in vinegar and tartaric acid which occurs in some fruit juices all attack concrete.

Sewage normally has an alkaline tip reaction and is harmless, but it may become acid by contamination with factory wastes and will then attack concrete. The concrete along the top of sewers can be severely attacked as the result of hydrogen sulphide gas being evolved from the stale sewage. The hydrogen sulphide is oxidized by anaerobic bacteria to form sulphuric acid which condenses on the walls of the structure. The attack may be rapid particularly in warm conditions and where ventilation is poor.

Excess moisture in concrete can be fatal to a floor covering installation. Moisture migration through concrete can cause wet, curled, lose or blistered floor coatings that have lost the bond to the substrate.

Water vapor from the floor can make rooms more humid, which can be a concern when installing carpeting or other floor coverings or coatings. Wet floors can promote mold growth. Also, a stained slab that has excessive moisture movement can blacken or discolor.

The biggest problem for decorative concrete with a lot of moisture moving through a slab is the pressure it exerts at the surface. If there is too much moisture in the concrete, and an impermeable layer is placed over it the moisture migration can delaminate the coating (sealer) or overlay. Sealers that allow some vapor passage can be used, but most topical membrane sealers require a moisture vapor emission rate (MVER) of 3 or 5 pounds/1000 square feet/24 hours.

In commercial applications, when carpet, wood, or vinyl flooring is installed over damp concrete, moisture creates real havoc, since the dampness and high alkalinity will lead to mold, emulsified adhesives, and warped flooring. This very expensive problem has led to a lot of research in recent years, and the simple answers that have emerged are to use a low water-cement ratio concrete (0.5 or less) and to install a vapor barrier under slabs on ground.

Recent advances in both available raw materials and formulating have given Johnson & Sons the opportunity to control moisture migration to eliminate these problems. We provide a concrete curing agent that cures, seals, hardens, increases the density and moisture proofs concrete.