The Growing Case Against Magnesium Chloride

Several years ago, in light of the wealth of scientific information on the damaging effects of magnesium chloride, Eco Solutions eliminated all usage of the the de-icing chemical magnesium chloride in our formulations. We feel that the case against magnesium chloride is strong enough that we do not feel comfortable recommending it to our customers. The links below are a small collection of the growing scientific data we have found on the subject.

INDEPENDENT STUDIES: Magnesium Chloride – Safety, Corrosion, and the Environment

Here are some studies and additional information from independentsources showing the negative effects caused by magnesium chloride (MgCl2) and calcium chloride (CaCl2 ) with respect to safety, corrosion, and the environment.

 

Safety:

Calcium and magnesium chloride residue on road surfaces can attract moisture at lower relative humidity than salt that may result in dangerous, slippery conditions under certain circumstances.

Source:  The Salt Institute

 

Do not apply CaCl2or MgCl2to a warm road (above 28° F pavement temperature). It can become very slippery and cause crashes.

Source: Minnesota Snow and Ice Control: Field Handbook for Snowplow Operators, Minnesota Local Road Research Board, Manual Number 2005-01, August 2005.

Field Handbook for Snowplow Operators, Minnesota Local Road Research Board, 2005-01

 

  • Bertrand Laplante from the Minister of Transport of Quebec in Montreal said he no longer uses magnesium because it becomes slippery on the road surface.  Denis Plouffe, also from the MTQ, had similar experiences.
  • In 2006, the MTO (Ontario) suspended the use of magnesium after some accidents on the highways during the 2005-06 winter.
  • Many of our clients have experienced similar problems with magnesium and calcium.  Both substances are more susceptible to the formation of black ice at temperatures below -6C since a small change in dilution (which can occur rapidly) will result in a large change in freeze point.

 

Corrosion:

Chloride-based salts are all highly corrosive to motor vehicle components and roadside infrastructure but vary in degree, with the most corrosive being the hydroscopic chlorides (e.g., magnesium chloride and calcium chloride). The hydroscopic chlorides are more corrosive because deposits remain moist and allow corrosion to occur for a much longer period. It has been demonstrated that when acid rain is present, there is a synergistic effect (increase in corrosion rate) with chloride salts (200).

Source:  NCHRP Report 577 – Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts – 2007

 

Environment:

Compared with sodium chloride, magnesium chloride (MgCl2) and calcium chloride (CaCl2) may cause similar effects to vegetation such as growth inhibition, scorched leaves, or even plant death (TRB, 1991; Public Sector Consultants, 1993; Cheng and Guthrie, 1998). Since the chloride ion in salts is what usually causes adverse effects to vegetation, and both MgCl2 and CaCl2 contain a higher concentration of chloride than NaCl by weight, they may be more harmful when applied at the same rates. Magnesium chloride has the highest chloride concentration of 75%, followed by CaCl2 with 64%, and NaCl with 61% (Cheng and Guthrie, 1998). Magnesium and calcium are both crucial for plant growth; however, excess of either nutrient in the soil may result in other deficiencies. For example, excess magnesium may result in calcium deficiencies, and excess calcium may reduce the availability of magnesium and potassium (Cheng and Guthrie, 1998; Bryson and Barker, 2002). Another concern when using magnesium and calcium based products, is that Mg2+ and Ca2+ are soluble in water and can exchange with heavy metals in soil, potentially releasing them into the environment (Public Sector Consultants, 1993).

In another study, the Colorado DOT evaluated three liquid magnesium chloride based products to determine whether such products could be utilized to help reduce the application of salt and sand mixtures, thus, improving air quality and water quality. The products tested included MgCl2, Caliber M1000, and Caliber M2000 (Caliber products are a mix of MgCl2 and bio-based products). The three products were examined in terms of main ingredients, corrosion inhibitors, and contaminants. It was suggested that Caliber M1000 and Caliber M2000 should not be heavily used without strict guidelines and further testing, as both products exceeded environmental background concentrations of phosphorus and ammonia and both contained large quantities of contaminants, while traditional magnesium chloride was approved (Lewis, 2001).

 

Concrete Degradation:

Most recently

Researchers Uncover Hidden Deicer Risks Affecting Bridge Health

 

Iowa State University concluded the following:

In laboratory experiment conditions, magnesium chloride, magnesium acetate, magnesium nitrate, and calcium chloride are much more damaging to concrete under several different environmental conditions than rock salt.

see the complete article:

http://www.ctre.iastate.edu/pubs/semisesq/session1/cody/

 

The Iowa DOT concluded the following in its final report HR-384:

Each deicer salt causes characteristic concrete deterioration by altering dedolomitization rims at the coarse aggregate paste interface, altering cement paste and/or formation of new minerals. Magnesium in deicer solutions causes the most severe paste deterioration by forming non-cementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste and alters ettringite to chloroaluminate. CMA and Mg-acetate produces the most deleterious effects on concrete, with Ca-acetate being much less severe.

see the complete article:

Iowa DOT final report HR-384, Concrete Deterioration and Expansive mineral Growth

 

The Iowa DOT concluded the following in its final report HR-355:

According to this model, magnesium from any source, either from reacting dolomite or from magnesium road deicers, has a major role in highway concrete deterioration. Consequently, magnesium deicers should be used with caution, and long term testing of the effects of magnesium deicers on highway concrete should be implemented to determine their effects on durability.

see the complete article:

Iowa DOT report HR-355, The Role of Magnesium in Concrete Deterioration

 

Peter G. Snow, FACI from Burns Concrete, Inc., Idaho Falls, Idaho wrote the following:

Magnesium chloride comes into contact with the now deiced concrete surface and remains contained in the melt water, and permeates into the concrete. While deicing salts containing sodium, potassium and calcium are chemically innocuous to concrete, this is not true of magnesium.  The magnesium chloride adheres to vehicle tires and to the vehicle itself and is therefore contaminating private property owners’ driveways and sidewalks and causing damage as previously outlined.  This material is extremely corrosive, causing damage to plant and vegetable life, and greatly accelerating the destruction of most metals, primarily automobiles and their accessories.

see the complete article:

Expansive Mineral Growth and Concrete Deterioation hr384

 

David Darwin et al from the International Concrete Research & Information Portal concluded the following:

At lower concentrations, NaCl and CaCl2 have a relatively small negative impact on the properties of concrete. At high concentrations, NaCl has a greater but still relatively small negative effect. At low concentrations, MgCl2 and CMA can cause measurable damage to concrete. At high concentrations, CaCl2, MgCl2, and CMA cause significant changes in concrete that result in loss of material and a reduction in stiffness and strength.

see the complete article:

PCC Pavement Deterioration and Expansive Mineral Growth

 

…Winter maintenance chemicals may chemically react with cement paste or aggregates and cause degradation of the concrete matrix. Laboratory research has shown that MgCl2 reacts with calcium hydroxide, a product of cement hydration, and the “cementitious” calcium-silicate-hydrate (C-S-H) present in the cement paste, to form magnesium hydroxide and “non-cementitious” magnesium-silicate-hydrate (M-S-H). Such reaction degrades concrete strength, and reduces the pore solution pH as well. The latter may result in the loss of passivation of the reinforcing steel and decrease the threshold chloride level to initiate pitting corrosion at the steel surface (Mussato et al., 2004).

A laboratory investigation using concrete samples obtained from existing Iowa highways suggest that magnesium and calcium deicers may accelerate highway concrete deterioration (Cody et al., 1996). Samples were experimentally deteriorated using wet-dry, freeze-thaw, and continuous soak conditions in solutions of magnesium chloride, calcium chloride, sodium chloride, magnesium acetate, magnesium nitrate, and distilled water. Both magnesium and calcium salts were found to severely damage the concrete samples while plain NaCl was the least harmful.

The few complaints from motorists often involve cosmetic corrosion to aluminum parts due to liquid MgCl2. The Salt Pilot Project performed in Washington State found results that would verify this claim, since the corrosion-inhibited MgCl2 product appeared to be more corrosive to sheet and cast aluminum than plain salt (Baroga, 2005).

Source: Montana State University – Western Transportation Institute for PNS and
 Washington State DOT:  Synthesis of information on anti-icing and pre-wetting for winter highway maintenance practices in North America.  August 19,2005

 

As a result of this research, it was determined that there is significant evidence that magnesium chloride and calcium chloride chemically interact with hardened portland cement paste in concrete resulting in expansive cracking, increased permeability, and a significant loss in compressive strength.

Source:  Michigan Tech Transportation Institute for South Dakota Department of Transportation – April 2008 – The Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete

 

Several researchers agree that MgCl2 causes more severe deterioration to concrete than do NaCl or CaCl2, because of the reaction of Mg2+ with components of the cement paste (138, 145, 159–163). The MgCl2 reacts with the cementitious C-S-H in the cement paste to produce non-cementitious magnesium-silicate hydrate (M-S-H) and CaCl2: MgCl2 _ C-S-H ➔M-S-H _ CaCl2

Additionally, MgCl2 reacts with Ca(OH)2 in the cement paste to produce magnesium hydroxide (Mg(OH)2), also known as brucite, and CaCl2: MgCl2 _ Ca(OH)2 ➔Mg(OH)2 _ CaCl2

Both of these reactions are favored because M-S-H and Mg(OH)2 are thermodynamically more stable than C-S-H and Ca(OH)2. The formation of M-S-H is particularly detrimental to the concrete because its lack of binding capacity weakens the cement paste, resulting in loss of strength as it replaces the C-S-H. This, combined with the expansive forces generated through Mg(OH)2 formation, can accelerate concrete deterioration.

Such processes eventually will lead to physical crumbling of the concrete (145, 159, 160). In many of the exposure tests, complete loss of concrete strength was observed (138). The replacement of Ca(OH)2 with Mg(OH)2 will also reduce the pH of the pore solution [pH =12.6 for saturated Ca(OH)2 and pH = 9.0 for saturated Mg(OH)2] which, if occurring at the rebar level, will result in the loss of passivation of the steel and allow the onset of active corrosion, even in the absence of chloride ions (164). This effect, combined with the presence of chloride ions, will further accelerate the corrosion of the rebar. It is not known at what rate Mg(OH)2 will replace Ca(OH)2, specifically at the rebar level. Although most research studying the effects of salts on concrete has used laboratory-prepared concrete specimens, the samples used by Cody et al. (145) were cores removed from “actual” structures in Iowa that were between 8 and 40_years old. These cores were exposed in the laboratory to various salts and subjected to repeated freezing and thawing cycles. Deterioration from MgCl2 appeared to be independent of the concrete quality, which was described as “durable” and “non-durable” service life concrete. “Durable” concrete has had a service record of more than 40 years, whereas “nondurable” concrete has had a service record of less than 15 years. The “non-durable” concrete contained relatively porous, finegrained reactive dolomite coarse aggregate, which contains significant amounts of magnesium. All concrete types contained dolomitic limestone aggregates, because it is common throughout the State of Iowa. The Iowa study concluded that MgCl2 and CaCl2 caused deterioration of the concrete by (1) promoting expansion of the concrete through Mg(OH)2 formation and other mineral growth and (2) chemical reactions with the cement paste, whereas NaCl proved to be less detrimental (145).

Experiments assessing the effects of magnesium products on concrete durability have shown that MgCl2 acts differently than magnesium sulfate (MgSO4) in that MgCl2 causes the cement pore structure to open whereas MgSO4 causes a densification (144). The densification caused by MgSO4 results from sulfate expansion, which results in the pores being filled, before eventually causing disintegration of the cement paste. The opening of the pore structure is attributed to the leaching of Ca(OH)2 during the exchange from Ca2+ to Mg2+ to form Mg(OH)2, as discussed above. This was confirmed by examination using a scanning electron microscope. Similar observations were made by Wakeley et al. (163), although the greater porosity was only observed in the first millimeter near the surface.Magnesium hydroxychloride formed near the surface and the loss in strength was attributed to the formation of M-S-H. The researchers could not identify Mg(OH)2 near the surface of the mortar specimens using energy dispersive X-ray analysis. The absence of Mg(OH)2 was attributed to the Mg(OH)2 phase being more transient than expected and that M-S-H formed more readily.

Helmy et al. (165) also determined MgCl2 to be more detrimental to concrete than NaCl, even when using blended cement. The formation of Mg(OH)2 and loss of strength were observed in samples exposed to MgCl2 after 12 months of exposure. The samples were immersed in 4-percent solutions that were renewed every month. Specimens exposed to NaCl had higher compressive strength values than those exposed to MgCl2, even higher than those exposed to freshwater after 12 months of exposure.

Conversely, Rechenberg and Sylla (166) found that formation of Mg(OH)2 at the concrete surface acts as a protective layer, preventing the ingress of aggressive species. They observed the formation of Mg(OH)2 exclusively near the surface and found no deterioration of concrete specimens (w/c ratios of 0.50 and 0.70) even after 10 years of exposure to 2,500 mg Mg2+/L MgCl2 solution.

Although there is some disagreement about deterioration of the cement paste, there is consensus that magnesium readily reacts with the various cement phases. Some research has found deterioration of cement paste within the concrete matrix; others observed deterioration to be limited to the surface. There also appears to be consensus that Mg(OH)2 and M-S-H are the most predominant reaction products.

Effects of Various Deicing Chemicals on Pavment Concrete Deterioration

 

Power Lines: 

As with railway traffic control signaling, concerns have been raised about the effect of snow and ice control materials on the operation of power distribution lines.Anecdotal information is available; however, formal studies addressing the frequency, mechanism, and magnitude of occurrence are not. Electrical power is most commonly distributed by wires suspended on poles or towers. Insulators, made of a fast drying non-conducting material such as glass, porcelain, or composite materials, are used to hold the wires and to minimize current loss and grounding. Insulator failure because of “natural/ambient” conditions has been a concern and has resulted in loss of current, line shorting, and pole fires. A basis description of the mechanism is as follows (214):

  1. Hot and dry weather conditions allow accumulation of pollutants on the insulators and can dry wooden poles.
  2. Damp conditions bring moisture, allowing the pollutants on the insulators to become slightly conductive.
  3. Current leaks across the insulator and can cause line current losses, shorting, or heating and potential fire of wooden poles.

High ionic salt solutions can exacerbate the process. These solutions have low electrical resistivity (i.e., they can readily conduct electrical current through solution) and, when they coat insulators, can allow transfer of current around the insulator to a greater degree than without salts. Incidents related to snow and ice control materials have included loss of current, shorting of transmission lines, and wooden pole fires resulting from the leak of current across the insulator.

All accounts of effects related to snow and ice control materials involve chloride-based materials. Salts that have been deposited on an insulator and have dried pose little immediate concern. However, these materials can become conductive when moisture is present, such as during damp or foggy conditions. For this reason, it is suggested that CaCl2 and MgCl2 pose the greatest potential concern because they are hygroscopic—these materials can combine with water and maintain a moist conductive coating on the insulator, even during dry conditions.

The degree of aerial deposition plays a defining role in whether or not effects occur.Major multi-lane and high-speed highway traffic can aerially disperse salt aerosols quite extensively. Kelsey and Hootman (29) estimated NaCl aerosols at least 15 meters high within 67 meters of a roadway. Vertical distribution was also found to be distributed more or less exponentially with height from the roadway,with most deposition occurring up to 3 meters (31). Power lines subjected to high levels of aerial dispersion and locations where power lines are exceptionally close to the roadway are of particular concern. Extreme cases include power lines directly next to elevated roadways such as alongside an overpass or bridge.

Source:  NCHRP Report 577 – Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts – 2007