Research Idea Details
Benefits of Salt vs. Non-chloride Alternative Deicers: Twenty Years of Learning
- Focus Area: Sustainability
- Status: Archived
- Subcommittee: Air Quality, Environmental Process
- Cost: $100k-$249k
- Timeframe: 1-2 years
Research Idea Scope
TRB Special Report 235 was published in 1991 to evaluate
the potential for widespread use of non-chloride deicers. The focus was on Calcium Magnesium Acetate
(CMA) due to its recent introduction into the market and the relative lack of
other non-chloride deicers available at the time. The report was divided into individual
chapters focused on examining the effects of deicers on motor vehicles and
infrastructure, the environment, and drinking water. Non-chloride deicers have significant
advantages in all of these areas.
However, at that time, primarily due to the significantly higher cost of
CMA, it was concluded that widespread use of CMA as a general replacement for
salt was unlikely and unwarranted. It is
now proposed to reopen Report 235 to reevaluate whether its conclusions still
hold some 22 years later.
In 1991, field experience with alternative non-chloride
deicers was quite limited. Several
decades of experience with CMA and the development of many new non-chloride
deicing chemicals, including bio-derived, allow for a much clearer
understanding today of how these deicers work, which is, in some cases, by very
different means, but as much or more effectively than traditional chloride
deicers. Some, for example, do not generate a flowing brine like rock salt, but
instead modify the snow/ice crystal morphology to prevent packing. The result is a dryer, oatmeal-like
consistency easily moved by traffic action so that a high degree of friction is
maintained without actually melting all of the snow away. The past twenty years have seen great changes
in many other areas of highway deicing including improvements in application
equipment and techniques such as anti-icing and prewetting, advancements in
weather forecasting and monitoring through roadside systems, and changing
national economic conditions. But most
significantly, there has been a growing public awareness of environmental issues
such as:
• sustainability
of current deicing practices and how they affect things such as air and water
quality for future generations
• how
higher travel demand by the public changes the assumptions upon which pollution
decisions were based 22 years ago
• life
cycle analysis (from both an economic and environmental standpoint)
Therefore, it seems prudent at this time to reevaluate
some of the assumptions made in Report 235 to determine if they are still valid
particularly in light of a renewed focus on sustainability of deicing to ensure
that safe roads today do not endanger the ability of future generations to
enjoy clean drinking water and healthy landscapes. For example, the authors noted that, after
salt use had doubled every five years during the 1950s and 1960s, it had
leveled off in the 20 years preceding the 1991 report, and this was expected to
hold due to improvements in practical experience and the increasing use of
formal salt management policies implemented by highway agencies. This did not turn out to be the case. Contrary to the assumptions made in the
report, the subsequent decades saw a great increase in US highway salt use,
with USGS data indicating that highway deicing accounted for 38% of the
estimated 44,000,000 metric tons of salt produced in 2011 in the United
States, an unexpected increase of more
than 60% over the average yearly use at the time of Report 235.
This proposal is to request a further, more detailed
breakdown of the secondary costs of salt vs. alternatives. Rather than looking at infrastructure,
vehicular corrosion, and environment in broad terms, it may be very beneficial
to look at particular types of infrastructure (e.g., the effect of salt on a
particular bridge may be very different from its effect on a stretch of
highway), and particular environmental areas with various concerns (e.g., rural
vs. urban, mountainous areas vs. marshland, etc.) with the goal being the
development of a targeted deicer application program based on cost/benefit
ratios in specific types of areas with a focus on the long-term preservation of
these areas for generations to come.
Urgency and Payoff
The benefits of the use of chloride-based products for
winter maintenance are widely known in terms of highway safety, mobility, and
productivity. So, however, are the
hazards—particularly in corrosivity and environmental effects. Not only the cost of repairs to salt damaged
transportation infrastructure, estimated to be over five billion dollars each
year. In addition, the indirect costs to
the public for detours, impedance of traffic flow, etc. during the corrosion
maintenance, repair, and rehabilitation, are currently estimated to be as high
as ten times that amount. While there
have been more recent studies focused on the “hidden” costs of salt, these have
focused on broad areas—infrastructure, vehicular corrosion, and
environment. However, not all
infrastructure is equally affected. For
example, bridges may be more susceptible to chloride damage than normal spans
of highway. And, it has been found that
some areas are much more environmentally sensitive than others.
The environmental effects of salt, in particular, have
received much more attention in recent years.
Recent environmental studies have shown that salinity in aquatic systems
of the rural northeastern United States is quickly advancing toward thresholds
beyond which many rural streams will become toxic to sensitive freshwater life
and no longer potable for human consumption.
This was not as much of a concern in 1991, but is certainly of
increasing relevance today. Sodium
chloride can accumulate as it is not biodegradable and is not naturally removed
from water as it migrates through soil.
Deicing salt has been linked to contamination of drinking water wells to
the extent that remediation programs, such as in Massachusetts, have been
required. It is also well established
that deicing salt use is damaging to roadside vegetation including protected
species.
This growing environmental concern is evident in
increased government attention to this issue.
The US Congress has determined that low corrosive and environmentally
preferred anti-icing/deicing products are deserving of matching Federal Funds
under the Moving Ahead for Progress in the 21st Century (MAP-21) Act signed into
law in July 2012. This legislation
allows for matching funds for minimally corrosive, environmentally acceptable
deicers, such as acetates and formates, to provide for better stewardship of
the environment and long-term preservation of the highway infrastructure. This funding challenges the cost assumptions
upon which the original report was largely based.
Experience from the past several years indicates that not
only was the adverse environmental impact of chloride salt deicing been
underestimated in the original Report 235, some assumptions about the possible
detrimental effect of alternative deicers may have been overestimated. It was assumed that organic alternative
deicers may themselves be harmful to the environment by possibly depleting
oxygen in receiving waters. New
information may shed more light on this.
A recent report sponsored by the New Zealand Transport Agency of
long-term direct field monitoring of CMA under normal operational use in New
Zealand indicates that the alternative deicer poses negligible risk to most, if
not all, receiving environments.
The fact remains that the cost of alternative deicers is
significantly higher than traditional chloride salts. However, while it may be that Report 235’s
original conclusion that widespread complete replacement of road salt with
other more recently developed non-chloride deicers may not be warranted due to
this cost differential, improvements in deicing operations over the years
suggest that alternative approaches such as blending of non-chloride deicers
with chloride salts, or the use of such techniques as compartmentalized trucks
capable of delivering salt in some areas and other deicers in more sensitive
areas (such as salt-sensitive bridges or areas where salt can threaten drinking
water supplies) without a major upset in normal routes and operations may now
deserve a further look to balance cost with salt loading. It is these targeted application techniques
that may be most promising and it is here particularly, that more research is
needed.
http://minerals.usgs.gov/minerals/pubs/commodity/salt/mcs-2013-salt.pdf
Shi, X.,
Veneziano, D., Xie, N., Gong, J., 2012. Use of chloride-based ice control
products for sustainable winter maintenance: A balanced perspective., Cold
Regions Science and Technology Volume 86 (2013), February 2013, pages 104-112
Kaushal, S, et.
al.. Increased Salinization of Fresh Water in the Northeastern United States,
Proceedings of the National Academy of Sciences, 2005 102 (38) 13517-13520 http://www.pnas.org/content/102/38/13517.full
http://www.mhd.state.ma.us/default.asp?pgid=content/environ/salt_rem&sid=about
Turner, J..
Calcium Magnesium Acetate Deicing Agent: A review of environmental effects
monitoring in New Zealand 1998-2009, 2010 Report prepared for the New Zealand
Transport Agency by Opus International Consultants Ltd.
Ms. Kimberly Engle Cryotech Deicing Technology
10/09/2013