Bounce Reduction of Pre-treated Salt vs. on Board Pre-wetting

Original Message: Benjamin J. Jordan, P.E.

Program Director
University of Wisconsin - Madison
College of Engineering

Department of Engineering Professional Development

Phone:  (608) 265-4478

E-mail:  bjordan@wisc.edu

September 16, 2011

In the facilities arena we see many salt materials that are treated with a liquid, bagged and marketed as being pre-wetted salt. In the bulk salt arena we see salt treated with a liquid and stockpiled. There has been previous discussion on this list about leaching of moisture from treated stockpiles. It seems intuitive to me that if a stockpile or a bagged product experiences moisture loss between the time of treatment and the time of application that it would be less effective at reducing salt "bounce" than a material that was wetted at the time of application. Can anyone point me to research that has looked at the effectiveness of stockpile pretreatment vs. on board pre-wetting for bounce reduction?

Response Messages

Max Perchanok

Research Coordinator
Design and Contract Standards Office
Ontario Ministry of Transportation

Phone: (416) 235-4680

September 16, 2011
There is an Ontario paper from the 5th International Conference on Snow Removal and Ice Control Technology, 2000, a TRB paper from a couple of years earlier and a more recent paper Denmark, that demonstrate the benefits of pre-wetting vs dry granular salt in retention on the pavement.  I don't know of any similar comparisons between pre-wetted and stockpile-wetted salt.

Ontario had some experience in the 1980's with stockpile treatment leaching out of the stockpile.  Jim Young and our Huntsville patrol staff did some informal testing last winter where he observed no leaching out and that the pre-wetted and stockpile-treated salt worked about the same.  Moisture content was not measured.




Bill Sadar, B.Sc.
President
Can-Am Infrastructure Services Ltd.
Phone: 604 309 2635
E-mail: info@cisl.ca

September 29, 2011

After some 20 some odd years of participating in both methodologies, there is several factors which affect stockpile leaching. The obvious one is the application rate and the strength of the brine [water brines have higher water contents]... if you just want freeze proofing the rates are lower than if you want to make a "hot" salt where the application rates are higher. Other variables are the moisture content of the salt, particle shape and how you build the stockpile.

Question: The newer anti-corrosion products which are out there today, particularly the corn based products; are they not 'designed' to reduce leaching because of their viscosity?

With regards to stockpile pre-treat vs. on-board units, my experience is stockpile treating creates a much more homogeneous material than on-board spray units. This experience is based on over 20 years of observing both methods. Just my opinion with no real scientific data to back it up but certainly a worth while study for one to initiate.




Monty Mills
WSDOT Maintenance Operations Branch Manager
M&O Division
Phone: 360-705-7803
E-mail: millsm@wsdot.wa.gov

September, 29 2011

With respect to your last point; having practically no experience with stockpile treatments, but much experience with on-board units, a subjective analysis would indicate that the design and quality of the on-board unit would have much to do with the homogenous nature of the end product. For example, a simple chute mounted spray system will not provide a very well-blended product when compared to the full blown slurry generating systems which are currently on the market. Kind of like comparing mixing concrete by spraying dry Portland Cement with a hose while it is dumped from a wheelbarrow, versus mixing it in a concrete mixing truck from the batch plant.

Secondly, while stockpile mixing may effectively blend product, it adds a step (or steps) which could more effectively be accomplished on the truck, if it is so equipped. That technology pays off quickly in most cases.

As for the corrosion inhibitor products which are being added to chlorides, most or all are viscous, but my understanding is that the unintended benefit of that viscosity is actually to provide staying power to the application rather than to prevent leaching in the stockpile. The only stockpile leaching research I’m aware of is the recently completed study on Inhibitor Longevity done by WTI.




Michael (Mike) T Mattison, P.E.
Maintenance Engineer
Nebraska Dept. of Roads
Phone: 402-479-4878
E-mail: mike.mattison@nebraska.gov

September, 29 2011

We have had stockpile leaching in the past and have reduced the application rate to 6-8 gal/ton which seems to work fairly well with the products we use (mostly MgCl2). I just got some literature from Envirotech at a meeting with them this morning for a product called SOS that they claim will not leach at application rates as high as 40 gal/ton. The recommended application range is 6-10 gal/ton of salt.




Mark Cornwell
Sustainable Salting Solutions, LLC
Phone: 248/634-0820 (office), 248/895-2888 (cell)
Website: www.sustainablesaltingsolutions.com

October 4, 2011

Excellent comments. I am most definitely in the "wetter is better" camp but even saying that I have some serious doubts about the whole salt loss from bounce and scatter. A few years back I observed what appeared to be a fairly high rate of bounce off the intended target with high liquid application rates of 60-80 gallons per ton. After sieving some standard ASTM spec salt through a 1/2" and 1/4" hardware cloth it became obvious to me that the large particles in the mix would require a 1/2" of Gorilla Glue around them to get them to stick on the pavement when dropped from a spreader at 30+ mph on relatively clear pavement. Too large a mass in motion! The test I observed was using sodium chloride brine alone with only a coloring dye added. The Danish study indicated that significant additional applied materials were lost off target with vehicle traffic. My conjecture then becomes that we are losing 50% of applied materials, dry or even potentially pre-wetted. In this test we checked the salt that was thrown out 30+ feet to see if it was uniformly coated and, with the addition of the colorant, we found it was fairly well covered.

Your analogy of the concrete mixer is very good. I have had serious doubts about how well some on-board pre-wet systems(fan sprayers on the spinner) were actually coating the salt considering the turbulence behind a vehicle.

Bill, Max, and Ben's comments about stockpile treatment are on target. I would add that I have wondered if stockpile treatments with hygroscopic treatments might be inducing some "sweating" which might lead to leaching during periods of higher humidity. This is only again my conjecture.




Phillip Anderle
E-mail: Phillip.Anderle@dot.state.co.us

October 4, 2011

In Region 4 of CDOT, we worked with our sand vendor and one of our liquid vendors and we now have our wet sand delivered to us. This works great for those patrols that don’t have combo units. The liquid vendor ran some lab tests and came up with 4 gallons of Caliber M-2000 per ton of clean sand. More liquid burned through and less liquid didn’t burn in. I believe that in the end, it depends on what you are trying to do with your pre-wet material. I am always concerned about the amount of chlorides we introduce back into the environment. I am always encouraging my crews to use only the amount of chloride they need to and get the desired level of service. Our wet sand has shown that we are reducing the amount of aggregates we put back into the environment too. We don’t have to apply as much wet sand as we have had to apply dry sand and we don’t have to reapply as often. Happy plowing.




Tom Byle
Ass’t. Director of Engineering
Kent County Road Commission
Grand Rapids, MI
E-mail: tbyle@kentcountyroads.net

October 5, 2011

Just a few comments to follow up on Mark’s comments (although you have heard them from me several times) and we are getting off the original topic but I feel this is one of the most important aspects of sensible salting.

I’ve long been a believer that the benefit of pre-wetting is getting the liquid melting action on the roadway quicker. The reduced bounce might be a side benefit but certainly is not the reason to pre-wet. Our agency has been pre-wetting since the mid 60’s. We have gone full circle, on-board initially, switching to a spray bar over the loaded truck at the stockpile due to the issues with the early on board systems to today utilizing a spray bar over the load at the stockpile and then adding more liquid at the discharge chute. The wetter the better.

The only real way to reduce the scatter is to NOT use a spinner and SLOW down. When I used to supervise our Maintenance Division (I have since returned to our Engineering Division) I used to tell our drivers to use the spinner like they always have for a couple miles / a few intersections, then use just a left hand discharge chute for the next few miles / intersections. Then I encouraged them to go back 20-30 minutes later, look at the results and decide for themselves which was the best way. To this day, we have drivers that have not used the spinner on their truck in over 15 years (old habits die really hard). I’d encourage each and every one of you to try the chute, no spinner method. See for yourself how it works, I think you will like it.

Drivers need to SLOW down when salting. Use the left hand chute and go slow enough lay a sloppy wet “bead” of salt on the centerline or high side of the lane without a lot of scatter. On a multilane highway, traffic can go around if they are in a hurry. On a 2-lane highway the driver does need to be aware of significant traffic backups. Yes, it will take 14 minutes to cover 6 miles at 25 mph vs. 8 minutes at 45 mph, but when the salt stays on the centerline, keeps melting the roadway and the truck doesn’t need to return to make a second application, you have reduced salt usage and saved the time required for a second application.




Monty Mills
WSDOT Maintenance Operations Branch Manager
M&O Division
Phone: 360-705-7803
Email: millsm@wsdot.wa.gov

October 5, 2011

Tom & Mark,

Great comments from you both on the issues associated with material scatter and loss. I have heard from several of our region personnel about their concerns with the loss of large salt particles either through traffic displacement, spinner speed, truck speed or all of the above. The primary culprit is the size of the salt particles which are lost. They are noticing the “shoulder boulders” at a increased rate regardless of the liquid content of those particles. Some of this salt is actually being distributed out of slurry generating equipment, so saturation is not necessarily a guarantee of product staying where it is supposed to.

As a state transportation agency, we don’t have the luxury of keeping our application speeds at 25mph or lower due to the lengths of our plow routes and the higher relative traffic speeds, especially on the interstates. We have previously used zero velocity spinners with mixed results, but I personally feel that the best answer is evenly graded product with a high liquid content, placed (or plopped) at regular intervals where it can benefit from traffic spread – similar to what Tom describes below.

Unfortunately, most of our solid salt is a wide gradation product with a lot of large particles. We would pay substantially more ($5 + per ton) for a more consistent grade, but it might be worth it considering the percentage of loss we see currently. There is one slurry generator currently on the market which incorporates a roller/crusher assembly in the process. We will have at least one of these this coming winter and it will be interesting to note if this is effective in preventing material loss compared to other styles of similar equipment.




Stan Hudecki
Training & Development
Ground Force Training Inc.
Email: shudecki@gfti.ca

October 5, 2011

Tom,

It was great to read your method of delivery for salt. It is something we have been teaching for years but have faced a lot of kickback because the current use of the spinner “is the way we have always done it”. I remember the first time I suggested the use of a chute down the crown, centerline or high point it was considered outrageous. This is one of the best applications in the event of freezing rain. We know that whatever you put down is going to be diluted quickly but if the concentration can prevent the bond and allow traction at least on part of the road you have achieved success. Your other comment about the bounce vs the melting action was right on the money. It is the reaction time that is the most important … of course it can’t react if it is scattered off the road, but your suggestion to slow down and not use the spinner is correct. I have heard of several organizations that have put in a block so that the material does not travel as far. Another issue is the “blast” button…and the old saying of “when in doubt, put it out”. I would like to come and see your set up sometime, and talk to someone on the “same page”.