Fertilizer & Sulfate Attack

Time-Tested Performance

Sulphates in solution attack concrete and cause expansion, deterioration, and eventual disintegration. In the early stages of attack there is little visual evidence of any change in the concrete, although there may be some reduction in strength as the chemical action proceeds. This is accompanied by slight expansion, which may not be apparent in the concrete itself, but may cause trouble at points of restraint. As the attack proceeds there is usually some change in color from the normal cement grey, and cracking or spalling occurs, starting from the surface in dense concrete, but penetrating much deeper in more porous 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.

  1. Form in which the sulphate occurs.
    Easily soluble sulphates such as those of sodium, potassium, magnesium, and ammonium, react more vigorously than calcium sulphate or gypsum.
  2. Concentration.
    The higher the concentration of sulphates in solution the more serious the attack. The severity of attack is increased in circumstances in which a flow of sulphate- bearing water brings a continuous supply of the salt into contact with the concrete.
  3. PH value of the soil or groundwater.
    Its temperature may also be a factor at ground level, the activity of sulphate solutions increase with temperature. If the pH value is below 6 in acid soils, the rate of attack is likely to be increased.
  4. Permeability of the concrete.
    Permeable concrete, particularly if one side is in contact with moist soil containing sulphates and the other side is open to the air so that evaporation occurs, is attacked throughout its thickness resulting in an overall expansion and complete disintegration.
  5. Formation of cracks.
    Attack proceeds along the lines of cracks particularly when the movement of moisture along any crack is encouraged by one-sided water pressure of evaporation from a free surface.
  6. Sulphates.
    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 structure causing deterioration of the concrete.

Sulphate salts attack concrete only when they are in solution. It follows that attack is most severe when the soil conditions allow a free movement of ground water.*

Because concrete is porous, and any foreign material can penetrate into the concrete as water-soluble, the solution is to stop the penetration of these chemicals by stopping the capillary action. SEAL-IT Concrete Sealant provides a permanent internal seal, which forms a hydrostatic head, barring the migration of moisture. SEAL-IT Concrete Sealant provides a water barrier so moisture as well as water soluble contaminants sit on the surface instead of penetrating and destroying the concrete.

SEAL-IT Concrete Sealant also increases the strength of the concrete at the surface. This will retard attacks of harmful chemicals at the surface, protecting the vulnerable interior of the concrete, thereby increasing the life-expectancy and safety of the structure.

*ASTM-C-67-Section13. Results: 25% decrease in absorption.
*Compression Strength (surface coat only). Results: +15% at 8 days; +23% at 31 days.
**Concrete Materials and Practice Fifth Edition

Field tests with fertilizers containing primary sources of Nitrogen, Phosphorus, Potassium, and Sulphur have shown that SEAL-IT Concrete Sealant performs exceedingly well in protecting the concrete from the fertilizer attack. The life and integrity of the concrete have been dramatically increased by protecting the surface with SEAL-IT Concrete Sealant.