Features Profiles
Chemical effects in de-icing pavers

Interlocking concrete pavements are a flexible and durable system that performs successfully in the most demanding applications, conditions and climates. One of the more extreme conditions is the application of de-icing chemicals to prevent or reduce ice buildup that can contribute to slips, falls and loss of vehicular control.

This technical note outlines factors that contribute to a low risk of damage from de-icing materials on concrete pavers.

Unit properties impacting paver durability
Ice that may form and expand inside the paver can cause stresses that may lead to degradation. De-icing materials mixed with the ice can increase the damage potential. Properly manufactured concrete pavers, however, are very durable and resistant to degradation because the high density of a paver limits de-icing materials from entering. In addition, high cement content helps a paver resist damage from the stress of expanding ice. Research and experience have highlighted factors affecting the winter durability of concrete pavers, including the utilization of:

• Aggregates with low absorption that will not degrade when subject to freezing and thawing and de-icing materials;
• Proper aggregate gradation that allows for high-density compaction;
• Sufficient cement paste to coat the aggregate and reduce capillary pores; and
• Sufficient compaction during manufacturing to ensure maximum density and uniformity.

Units manufactured with these characteristics typically yield a high density, low absorption, high compressive strength, resulting in a durable paver.

ASTM C936 standard specification for solid concrete interlocking paving units includes freeze-thaw durability criteria for assessing the freeze-thaw durability and resistance to de-icing salts. C936 references the test method ASTM C1645 standard test method for freeze-thaw and de-icing salt durability of solid concrete interlocking paving units.

C936 includes an optional lower freezing temperature for regions of the United States that experience severe freezing conditions based on a climatic zone map. The optional testing in three per cent saline for these regions is equivalent to the testing required in the Canadian concrete paver standard, CSA A231.2 precast concrete pavers. To obtain a copy of ASTM C936 or ASTM C1645, visit www.astm.org (link is external). The CSA standard is available from
www.csagroup.org (link is external).

Comparison to ready mixed concrete
Properly air-entrained and finished ready-mix concrete can resist freeze-thaw degradation, although over-finished, cast-in-place slabs or those made with re-tempered concrete with too much water can be susceptible to surface scaling. Compared to ready-mixed concrete, concrete pavers have the following advantages when exposed to freeze-thaw conditions and deicing agents:

• Stronger aggregate bonding from higher cement content than typically used in pavement quality ready-mix concrete;
• Smaller aggregates (more surface area for the cement to bond);
• Lower water/cement ratio as well as vibration and compaction during the manufacturing process to increase aggregate-cement contact and to eliminate the possibility of over-watering;
• Produced in a highly controlled manufacturing plant leading to lower variation in material properties with elimination on over-finished surface; and
• Can be successfully installed in cold weather because they are properly cured before they leave the manufacturing plant.

Research prepared for the Utah Department of Transportation* in 2013 found that concrete exposed to sodium chloride experienced only minor, if any, adverse effects, while specimens exposed to calcium chloride, magnesium chloride, or calcium magnesium acetate (CMA) experienced significant deterioration, including scaling, cracking, mass loss, and compressive strength loss. While the literature review did not specifically address unit pavers, the findings are directly related to cured unit concrete properties. The report recommends that engineers responsible for winter maintenance of concrete pavements should utilize sodium chloride whenever possible, instead of calcium chloride, magnesium chloride, or CMA, and apply only the amount absolutely necessary to ensure safety of the traveling public. These findings support ICPI’s guidelines for de-icing salt exposure.

*Physical and Chemical effects on De-icers on Concrete Pavement: Literature Review, Report No. UT-13.09 Prepared for Utah Department of Transportation Research Division by Brigham Young University, July, 2013

Guidelines for limiting de-icing chemical exposure
A key to successfully using de-icing materials on unit concrete pavers is using only as much as needed to do the job. This will maximize their benefits while minimizing any damage to the concrete pavers and surrounding environment. The following guidelines can help limit the exposure of de-icing chemicals while maintaining a safe environment:

• Apply sand first to increase traction, then apply de-icers as needed. Sand should not be applied to permeable interlocking concrete pavements.
• Rock salt (sodium chloride [NaCl]) is the least damaging to concrete materials and should be used whenever possible.
• If a more effective, quicker acting de-icer is necessary, consider the judicial use of calcium chloride.
• The use of magnesium chloride or CMA is not recommended because they can chemically degrade all types of concrete, significantly increasing potential damage. The potential for damage from CMA increases with the amount of magnesium in the formulation.
• Do not over apply de-icing chemicals; follow the recommended dosage.
• Do not use de-icing chemicals in place of snow removal but reserve them for melting ice formed by freezing precipitation or freezing snow melt.
• Once loosened, snow, ice and excess de-icing salts should be promptly removed by plow or shovel to avoid a buildup in concentration of the de-icing chemical(s).
• Protect vegetation and metal from contact with de-icing chemicals as most can impair vegetation and corrode metals.

In addition, use ICPI-recommended jointing and bedding sand materials to minimize water penetration into the pavers. This can also help reduce salts from entering and accumulating in the jointing and bedding sand that may eventually degrade the pavers. ICPI also recommends adequate pavement slopes (typically a minimum of two per cent) to facilitate surface water drainage and help remove de-icing materials. While not essential, reduction of water entering jointing sand can be further enhanced with joint sand stabilization materials and/or sealers.

Reprinted with permission by the Interlocking Concrete Pavement Institute.