Improving Icy Sidewalks during Winter at
Minnesota State University Moorhead
Introduction to the Problem
7,695 students, 347 faculty members, additional staff, and the public walk daily the 15 miles of sidewalk on campus. In the winter months, the snow and ice can cause safety concerns and slower walking conditions. The grounds crew at MSUM supplied with sand, salt and their equipment typically are able to handle the conditions. However, the grounds crew would benefit from having better supplies to combat winter conditions.
Background Information
The grounds crew at MSUM has committed removing snow and ice down to bare pavement as it accumulates. They begin by focusing on high traffic areas and the more affected areas, such as sidewalks north of most buildings and driving approaches. Once snowfall has ceased and major sidewalks are cleared, the crew can focus on clearing the remaining snow-covered sidewalks. Last year due to the thaw/refreeze process in the fall as well as an ice storm in December, the grounds crew was forced to use salt for the first time in seven years, in addition to 38 tons of sand. The salt that the grounds crew used last winter was turf friendly and similar to what can be found at a local hardware store. The equipment that is used to disperse the sand/salt is all less than ten years old. In the last five years, through rising fuel costs, equipment purchases and annual costs for sand, salt and other operation expenses the grounds crew has stayed under budget.
Research Methods
In studying the feasibility of improving ice removal at MSUM, we used several research methods. These research methods included: internet searches about deicers and heated sidewalks, interviews with members of the grounds crew, and student surveys. We were able to find excellent information from these sources.
Possible Solutions
Deicing chemicals
The most easily accomplished solution to improving the sidewalks is using higher quality deicing chemicals. Our research produced extensive results on deicers of pellet, rock and liquid forms. The following chart provides information concerning four of the most widely used forms of deicers. Less commonly used forms of deicer include: calcium magnesium acetate with a lowest temperature of -15 degrees Fahrenheit, sodium acetate witch is active at lower temperatures below 0 degrees Fahrenheit, potassium acetate and calcium hydroxide.
How Deicers Work
The freeze temperature of the deicer is lower then that of the surrounding ice which results in the ice melting. This water/chemical solution is called brine, which penetrates down through the snow until it reaches pavement, where it breaks the ice/pavement bond loosening the ice for mechanical removal.
Important Deicer Qualities
In determining important qualities for a deicing agent Peters Chemical Company conducted a survey of their two thousand biggest buyers of deicing products and found how often each of these factors were rated as most important.
Figure 1
Effective temperatures
The first measure of deicers effectiveness is the range of temperatures in which it can provide deicing action (in a reasonable period of time). The "practical" lowest temperature limits for these materials are defined as effective within 15-20 minutes of application and is listed next to the material.
Figure 2
Deicing Speed
The speed at which a deicing agent can melt is the most important factor listed by major users of deicing agents. It is important because the faster the agent can penetrate through the ice and form brine underneath the faster the ice can be removed. Unlike other deicing chemicals, calcium chloride is the fastest working. Calcium chloride can absorb the moisture it needs from its surroundings; in addition, it releases heat when it changes to a liquid form, which in turn melts more ice. In twenty minutes, at fifteen degrees Fahrenheit, calcium chloride can melt approximately two times the volume of snow compared to rock salt.
Effect on Concrete
Some Deicing agents have a chemical effect on concrete that lead to erosion. The most common cause of damage is repeated freeze thaw cycles. Water seeps into cracks in the concrete; the water expands as it freezes producing larger cracks in the concrete. The freeze/thaw cycle occurs more often when using deicers. To reduce the effects of repeated freezing remove snow and ice as soon as possible, and brush away additional deicing agents.
Effect on Vegetation
It is crucial that a deicing agent does not have any negative impacts for vegetation. When using deicers it is important not to use too much in order to reduce the negative impact on vegetation.
Residues
Most deicers dry to a white powdery residue. Magnesium chloride and calcium chloride leave a clear brine solution; however, calcium chloride is the hardest to clean from carpets.
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Deicer Comparisons
HALITE – ROCK SALT / CALCIUM CHLORIDE / POTASSIUM CHLORIDE / MAGNESIUM CHLORIDEDescription / Irregularly shaped sodium chloride crystals. / Small, white pellets processed from naturally occurring material / Irregular shaped, off white or white crystals. / Large, flat, clear to off-white flakes containing over 51% water of hydration
Relative deicing speed / Slower than calcium chloride. / Fast acting deicer at all temperatures. / Slower than calcium chloride / Starts about as fast as calcium chloride, but may become diluted and ineffective.
Lowest practical temperature / Down to 20° F. / Down to -25° F. / Down to 12° F. / Down to 5° F.
Effect on concrete / Does not chemically attack concrete. Can cause damage from freeze-induced expansion pressures by increasing number of freeze/thaw cycles. / Does not chemically attach concrete. Poses least threat of damage from freeze induced expansion pressure. / Does not chemically attack concrete. Can cause damage from freeze-induced expansion pressures by increasing number of freeze/thaw cycles. / Chemical attacks concrete at a “slow rate”. Can cause damage from freeze-induced expansion pressures by increasing number of freeze/thaw cycles.
Effect on vegetation / Sodium ion is toxic to vegetation. / Used as recommended, will not harm vegetation. Calcium Chloride is used as a calcium source for certain fruits and vegetables / Will not harm vegetation. / Used as recommended, will not harm vegetation.
Residue / Leaves a white, powdery residue when it dries. / Leaves no powdery residue / Slight, white residue / Leaves no powdery residue.
Manufacturer’s recommended
application rate / 8 oz/yd / 2 -4 oz/yd. / 8 oz/yd. / NA
Table 1
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Heated Sidewalks
The rising cost of labor and equipment, the lack of room for storage of snow, and an increasing demand for better and more rapid snow and ice removal has been a major reason to use snow melting systems for building entrances, driveways, sidewalks, and parking areas.
There has been an increase in the use of snow melting systems but it is only recommended for areas where benefits would justify the high cost of its installation and operation.
How does Snow Melting System Works?
Ice melting systems must provide enough heat to melt snow as well as offset surface heat loss by evaporation and heat loss from the slab into the ground. The system must be designed in order to melt hourly rate of snow at an anticipated site. To keep areas free of snow completely, some melting systems are designed to melt snow as it falls. Table 1 provides amounts of heat required to melt snow.
Average Rate of Snowfall / Estimated Maximum Hourly Rate of Snowfall(in/hr) / Heat Required(Watts/ sq ft)0.25 / 0.5-0.9 / 12-20
0.5 / 1.1–1.8 / 24-40
1.0 / 2.2-3.6 / 48-80
Table 2
< http://irc.nrc-cnrrc.gc.ca/cbd/cbd160e.html >Accessed April 18th
Design Standards
A most important requirement in designing a system is to establish the standard of operation required. Research has shown that it is neither necessary nor economical to design systems that maintain bare pavement conditions at all times. Designing for 25 to 50 percent, snow cover is a reasonable choice for most situations. If a heated surface becomes snow, covered surface heat losses are reduced and more heat becomes available for melting snow, creating a “built-in” safety factor. Designing for complete snow coverage of a heated area may be satisfactory for residential requirements.
Cost Analysis
It is extremely difficult to give reliable cost figures for snow melting systems because they vary a great deal with local conditions.
In case of snow melting systems, cost will vary with:
· Design Criteria – bare or snow-covered pavement
· Power rates
· Location and availability of power transformers and power sources
· Method of operation – continuous, on and off, or automatic
· Climatic conditions
· Amount of snow to be melted
· Area of pavement to be heated and
· Complexity of installation
The annual cost of melting snow by electrical systems is estimated to be 30 to 40 times that of removing it by mechanical or chemical methods. Pit melting system, where snow is transported to a pit or tank, are comparatively cheaper because the system need to operate only when snow is to be melted and heat losses to the surroundings can be reduced to a minimum.
Recommendations
Snow melting systems are recommended only for sites where the benefits will justify the high cost of installation and operation, where mechanical methods would be difficult, where use of chemicals would damage structures, where traffic delays at critical locations and safety is a factor.
Underground Tunnels/Skyways
Our research of underground tunnels was unsatisfying. The cost of constructing underground tunnels would be expensive; however, our research provided no cost estimates. To acquire a cost analysis a professional estimator would need to be consulted. In terms of the long run expenditures, this alternative to outdoor sidewalks could prove to be more cost effective.
Improving Sidewalk Construction
To improve the sidewalks themselves we suggest that some of them be widened or built up to improve drainage. The cost of building a new sidewalk is $3.50 per sq/ft. In order to remove existing sidewalks and replace with new sidewalks it would cost $4.50 per sq/ft and $5.25 per sq/ft to raise the levels of low spots.
Continue Use of Current Methods
Of course, continuing all current methods always an option. Current ice removal methods have proven adequate to MSUM standards. There would obviously no additional costs associated with this method and there would also be no change in current conditions. Our recommendation is to avoid this method as it would to nothing to improve current conditions.
Feasibility of Solutions
The use of higher quality deicing chemicals would greatly improve the efficiency of ice removal at MSUM. Of the chemicals that we discussed in the report, calcium chloride is a standout product when accounting for lowest practical temperature, melting time, environmental effects, and residue. It performs at temperatures 45 degrees colder than MSUM’s current deicer. Also, it melts ice quicker, is the less harmful to concrete and vegetation, and leaves no residue. The cost is approximately five times more expensive than the current rock salt, but requires only 25% as much product per usage.
The cost of heated sidewalks would be incredibly high in comparison with the costs of added deicing chemicals. These costs would increase as the Fargo-Moorhead climate presses on frigid temperatures through the middle of winter. And while the overall product is very desirable the cost is likely more than MSUM needs to spend to improve its sidewalks.
The costs of installing a system of underground tunnels and skyways would also be very great. This also proves to be more of an alternative to icy sidewalks than a solution. Some students would still choose to use the sidewalks and they would be subject to unimproved conditions.
Sidewalk reconstruction is both necessary and cost effective. Low spots around campus that create ponded, freezing water on the sidewalk are a major issue for a crew trying to remove the ice. Raising the few areas that are problematically low would greatly help removing ice. Also some sidewalks are too narrow to handle the equipment used by the grounds crew. These sidewalks also need updates.
Recommendations
Having discussed these possible solutions for icy sidewalks, we have decided upon the best plan for MSUM. We feel that MSUM needs to begin with building up low spots around campus to keep water from pooling and freezing on the sidewalks. We have identified these areas and placed them in blue on this map, see Figure 3.
Figure 3
Also, we suggest that MSUM purchases calcium chloride. Calcium chloride is more cost effective than other major deicers and will outperform all of them. The use of this deicer will help keep the sidewalks clear even when the grounds crew is not out working. To cut down on the costs of using a deicer everywhere on campus we have identified the most used walkways around campus and suggest that deicer be limited to those areas, see the yellow sidewalks in figure 4.
Figure 4
Spreading calcium chloride on these areas on a regular basis should only require 8-12 tons per year in contrast with the average of 38 tons of sand they spread over all the sidewalks each year. This would cost MSUM $1700-$2600 per year.
A survey of students showed that MSUM students would be willing to pay a $2 per semester fee to help bare the added costs. This $2 fee would provide and extra $30,780 per year, based on current student enrollment. Thirty thousand dollars would pay for more than 100 tons of calcium chloride, which is well above the 8-12 tons we projected would be needed.
We are confident that if MSUM employs our suggestions, the sidewalks will be safer, easier to use, and will take less time for maintenance crews to keep clear of ice and debris.
Work Cited
Helmenstine, Anne Marie. “Melting Snow & Ice with Salt”. <http://chemistry.about.com/cs/howthingswork/a/aa120703a.htm>. Accessed 2005 April 11.
SMRC. “Pollution Prevention Fact Sheet: Bridge and Roadway Maintenance”. <http://www.stormwatercenter.net/Pollution_Prevention_Factsheets/BridgeandRoadwayMaintenance>. Accessed 2005 April 11.
Rindels, Sherry. 1998 January 13. “Deicing Materials for Slick Sidewalks and Roads”. <http://www.ipm.iastate.edu/ipm/hortnews/1996/12-13-1996/deice.html>. Accessed 2005 April 12