Questions and Answers- Road Resurfacing.docx

Questions and Answers Road Resurfacing

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1. Can a contractor substitute Magnesium Chloride or Calcium Chloride @ 77% concentrated salt?

Answer: NO, the project solicitation calls for 121 tons Calcium Chloride solid @94% pure salt. The Pay Item is in tons for this product. No liquid concentration substitutions will be allowed.

A conversion factor of 200% for solid Magnesium Chloride, and 122% would be needed to put these concentrations in “same or equal” category. The bid schedule states 121 tons. It does not allow for one of these other products in a different amount.

For example, if Mag Chloride solid @ 47% pure salt or Calcium Chloride solid @ 77% was substituted our 121 tons Calcium Chloride solid @94% pure salt, then 242 tons of Mag Chloride or 150 tons Calcium Chloride @77% would be required.

2. Are there any known suppliers for the solid Calcium Chloride (calcium chloride flake/pellets)?

Answer: Tom Oxford in Moyie Springs, ID is probably the closest known supplier.

Here is a list of other known suppliers:

Calcium Chloride

Great Western Chemical Co.

Seattle, WA

(206) 763-2350

Hills Brothers Chemical Co.

Portland, OR

(800) 257-1920

Oxford Inc.

Moyie Springs, ID

(208) 267-2297

The Dow Chemical Company Customer Information Group at 1-800-447-4369 or visit www.dowcalciumchloride.com

3. For this project, the Pay Item 30801 A Roadway Aggregate, Design Quantity 17,994 cubic yards, is that a loose yardage or compacted yardage?

Answer: Pay Item 30801 is a compacted in-place yardage. See FP-03 section 109 Measurement and Payment, 109.02(b)(1)Terms and definitions "cubic yard in place".

See SPS 109 Measurement and Payment, 109.10 "Designed Quantities (DQ)" and SPS 204 Excavation and Embankment 204.11 Compaction "Method A - Roller Compaction".

These specifications explain that the volume of roadway aggregate is measured in place on the road after compaction efforts are performed. For example the first 5.12 miles of road 913, are designed to receive aggregate spread 24 foot wide, by 4 inches deep, 5.12 miles long; totaling 8,345 cubic yards of Roadway Aggregate. The aggregate to be used on this part of the road is premixed with bentonite by Gov. The number of yards measured in a hauling vehicle i.e. loose yards or VQ - Vehicle Quantities would swell & measure more yards.

Copies of the FP-03 are also available electronically on the U.S. DEPT of TRANSPORTATION Federal Highways Administration website at http://www.wfl.fhwa.dot.gov/design/specs/fp03.htm.

4. The 351, 351B Bootjack Lake roads appear to be much narrower than the 913 Tally Lake road. Can a contractor use a blade to mix the additives into the aggregates on these roads?

Answer: Blade mixing of Calcium Chloride and Bentonite additives will not be allowed on this project. An amendment has been made to update this information in Specification 311, “Road Surface Stabilization”. The contractor will be required to supply a tractor-tiller, traveling pug, rototiller or rotary milling machine to perform the mixing of the Aggregate Additives.

5. As a road construction contractor I have never performed Aggregate Surfacing Stabilization with Chloride. Are there any supporting manuals or studies on the subject?

Answer: The Dept. of Transportation Maintenance and Design Manual, South Dakota LTAP, Journal of the Transportation Research Board, and US Dept. of Agriculture Forest Service all have published documentation on the Internet addressing this subject. These manuals have been posted below as supporting documentation.

6. Is all the crushed aggregate at the pit premixed with government supplied bentonite or just part?

Answer: In our pit we have approximately 30,000 cubic yards of grade F-SR material. 10,000 yards (F-SR w/ bentonite) has bentonite and 20,000 yards (F-SR) without bentonite.

7. The Scope of work indicates mixing of bentonite and CACL2 by the contractor but the drawings show bentonite is mixed by the Government. What additives are required to be mixed by the contractor? Does the contractor have to supply and mix Bentonite?

Answer: For FSRD 913. The government has supplied 17,900 cubic yards of Crushed Aggregate. The government has mixed bentonite with 8,345 cubic yards. This mixture of bentonite/aggregate yardage should cover 5.12 miles of 24 wide road with 4 inches of aggregate.

The contractor will be required to:

1) Haul and spread government supplied premixed bentonite and crushed aggregate (DQ 8,345 Cubic Yards) and

2) Haul and spread government supplied crushed aggregate without any additives (DQ 9,555 Cubic Yards) and

3) On 2.7 miles of FSRD 913 the contractor shall road mix using a tractor tiller, traveling pug, or rotary milling machine 121 tons of contractor supplied Calcium Chloride @ 94% salt with the government supplied aggregate/bentonite mixture. and

4) Supply and mix both bentonite (32 tons) and CACL2 (34 tons) for FSRD 351. Aggregate exists in place on 1.2 miles of road. and

5) Supply and mix both bentonite (5 tons) and CACL2 (5 tons). For FSRD 351B. Aggregate exists in place on 0.15 miles of road.

Please Review the Road Logs and Project Construction Plans for these full work descriptions.

8. Is it possible to look at the roads/project, or is there too much snow to access the site?

Answer: The first 3 miles of this road is plowed by Flathead County Road Crews and is open to the general public but the rest of the road is under a lot of snow. It is unknown what is visible or what is still buried under snow.

Due to the winter weather conditions, icy roads and snow levels at the project locations, safety is a concern hence the reason no formal site visit will be conducted. If you choose to visit the site on your own, you are cautioned to be aware of the dangers and to be careful.

Law enforcement personnel has informed me that the full length of this road has been accessed via pickup truck by people taking more than a reasonable risk to drive it.

9. Is a bid guarantee and payment & performance bonds needed on this project?

Answer: Yes, please see clause 52.228-1 and clause 52.228-15 located in the solicitation body on page 28. That information will be required with your bid.

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Stabilization.pdf

Section IV:

Dust Control and Stabilization

Section IV: Dust Control and Stabilization/Types of Stabilizers 51

All gravel roads will give off dust under traffic.After all, they are unpaved roads that typically serve a low volume of traffic, and dust is usually an inherent problem. The amount of dust that a gravel road produces varies greatly. In areas of the country that receive a high amount of moisture, the problem is greatly reduced.Arid or semi-arid regions such as the desert southwest and much of the great plains region in the USA are prone to long periods of dry weather. Similar regions around the globe can have similar weather patterns. Dust can really bring complaints in these areas if there are residences located near the road and traffic is high.

The quality and type of gravel also has some effect on the amount of dust. Some limestone gravels can dust severely while some glacial deposits of gravel with a portion of highly plastic clay can take on a strong binding characteristic that will resist dusting remarkably well. Still, in prolonged dry weather, there will be dust! Whether to provide some type of dust control or not can be a hard decision to make.

Virtually all methods of dust control require annual treatment.

The cost can be prohibitive if traffic volume is low. On the other hand, if traffic is high, the cost of dust control can more than pay for itself with the benefits of reduced material loss and reduced need for blade maintenance.

(28) At this point, many agencies will face pressure to pave the road. It may actually be a good economic decision in the long run, especially if there is good indication that traffic will continue to increase in the future. However, never pave a road before it is ready! There is good information on making this decision in Appendix D.

Types of Stabilizers Chlorides These are the most commonly used products across the country. They fall into three categories: Calcium Chloride in flake or liquid form, Magnesium Chloride generally in liquid form, and Sodium Chloride (road salt). Sodium is seldom used and is the least effective.

Calcium and Magnesium Chloride can be very effective if used properly. They are hygroscopic products which, in simplest terms, means they draw moisture from the air and keep the road surface constantly damp. They are reasonably simple to use.

Resins These are products available under vari-ous commercial names. The basic com-position is lignin sulfonate which is a by-product of the pulp milling industry.

The product is sometimes called “tree sap” in the field. These products work best when incorporated into the surface gravel. They then provide cohesion to bind the soil particles together.

Natural Clays Some regions of the country have excellent deposits of natural clay that are highly plastic and provide strong cohesion when added in the right quantity to gravel.However, in pro-longed dry weather, these roads will seldom be completely dust free. It can be difficult as well to haul the clay onto the road and mix it into the gravel.

Because it is highly plastic,it tends to stick to the truck boxes and requires quite an effort to mix with the gravel.

Asphalts The use of cut-back liquid asphalts to surface-treat gravel roads was once popular for dust control. However, because of the great amount of fuel oil

52 Benefits of Stabilization or kerosene in these products, they have been banned in many places. Some emulsified asphalts may work for this purpose, but their use is very limited.

The product must be applied with special asphalt application equipment.

Soybean Oil This product is known technically as Acidulated Soybean Oil Soapstock.

It is a by-product of the caustic refining process of soybean oil. It is a biode-gradable material that has many of the characteristics of a light petroleum-based oil. It will penetrate a gravel surface and provide a light bonding of the gravel that effectively reduces dust when it is used properly.

Other Commercial Binders There are too many of these to mention individually. They are marketed under various trade names across the country.

It is always wise to try a test section of no more than 1000 feet in length to see how any of these products work with your gravel. One caution: do not use waste products such as crankcase drain oil from engines. This is harmful to the environment and is in violation of EPA rules.

Benefits of Stabilization

Once a road is stabilized there are several benefits. On high volume roads, these benefits can make stab-ilization very cost effective.

Reduced Dusting It may be hard to justify the use of any of these products for dust control alone.

However, when the products are work-ing well, the added benefit of a stabi-lized surface that controls the loss of fines through dusting is a great eco-nomic benefit.When the fines are lost from a gravel surface, the stone and sand-sized particles that remain will tend to remain loose on the surface, leading to some distresses like wash-boarding and reduced skid resistance.

It will become very hard to maintain.

Fresh gravel with a higher percentage of fines needs to be hauled in. This becomes very expensive.

Reduced “Whip Off” of Aggregate This is another economic bonus to dust control when it is working well.

As mentioned earlier, when dust control products are working well, the fine material in the gravel cannot loosen and dust away. This also means that the stone portion of the gravel will tend to remain embedded in the surface and will not be lost to the edge of the road or even whipped off onto the inslope from heavy traffic. Studies have shown that as much as one ton of aggregate per mile is lost each year for each vehicle that passes over a road daily. This means that a road carrying 200 vehicles per day will experience the loss of 200 tons of aggregate per mile each year. (7) Obviously this will vary with the amount of rainfall received, the quality of the gravel and other factors. Retaining aggregate is a good added benefit to dust control.

Reduced Blade Maintenance A road surface that remains tightly bound and stable will require much less blade maintenance. The manufacturers of some dust control products highly recommend that the surface should not be bladed at all after their products are applied.While extra blading, shap-ing and mixing is needed to prepare a road for dust control, the overall need for blade maintenance should be greatly reduced. This can be a great savings in equipment expense and labor. A county highway official once commented:“I don’t react to dust complaints. All gravel roads have dust.

But I do react to high maintenance costs. When we have to regravel a road frequently and do blade maintenance frequently, then it’s time to look at stabilizing the surface with Magnesium Chloride. Reduced maintenance is what we’re after. Dust control is just a bonus!”

Application Tips

Application Tips 53

There is not enough space to cover application tips for all products. Since the Chlorides are the most commonly used products, we will address the use of those. However, some or all of these tips would apply to the use of most other products as well.

Need for Good Surface Gra v e l Keep in mind the Chlorides are not binders. They simply draw moisture from the air. The gravel itself must have a good gradation — particularly a good percentage of fine material with some plasticity. This will give the gravel a natural binding char-acteristic. The Chlorides then will take over and keep the surface damp and it will remain tightly bound. It will not give up its fines in the form of dust. This point cannot be emphasized enough.If good gravel is not present on the road,it will be wise to haul in good fresh gravel prior to treatment. The cost of the Chloride treatment has been virtually wasted on some roads when the gravel was poor and very short-lived dust control resulted.

Road Preparation This is another critical point in prepar-ing for dust control treatment.Make sure the road has a good crown in the driving surface. Also, make sure there is good shoulder drainage. Standing water anywhere in the roadway will cause the surface to soften and fail.

It will leave a pothole in an otherwise good, stabilized roadway. These can be hard to correct afterwards with-out disturbing the stabilized surface around it.Another key to preparation is to loosen a minimum of one to two inches of the existing surface and leave it loose at a uniform depth across the roadway. This allows the Chloride to penetrate evenly and quickly into the gravel.

Do not compact the surface at all prior to applying chlorides.

The carbide-tipped bits on a cutting edge can be a valuable tool in preparing a road for Chloride treatment.They penetrate the road and give a shallow scarifying effect to loosen and mix the existing gravel.This leaves a nice uniform loose layer of material on the surface.

This road has been prepared well for a liquid Magnesium Chloride treatment.Notice the uniform, loose and nicely crowned surface looking over the hilltop. There is also good shoulder drainage as well.This is an excel-lent example of road preparation.

Applying the Product The most important need here is for equipment that can be calibrated accu-rately and that will apply either the liq-uid or flakes evenly across the surface.

Then a good application rate needs to be selected. This will vary with the type of gravel being treated and the length of time dust control is needed.Check with vendors and experts in your area to see what recommended rates are.

Next, watch the weather! If rain is forecast or appears to be likely, don’t take a chance. Rain on a freshly treated surface will leach out and dilute the Chloride and cause it to run off the road. It can temporarily harm grass on adjacent areas. But the bigger problem will be very poor performance after-wards. Also, it is ideal to keep traffic off of the road for up to two hours after application. This is not always possible, but it is very helpful. It is recommended that one side of the road be treated at a time. Rolling can be helpful, but is not essential. If rollers are used, pneu-matic ones are best, and watch to see that the gravel does not start picking up from the surface. If that happens, wait until the surface cures a bit before finishing rolling.

54 Application

Example of a good piece of application equipment.This truck has a pressurized spray bar with a computerized application system that meters the liquid Chloride with extreme accuracy.

This photo shows part of the spray bar with spraying nozzles.

A very effective, yet simple method of applying flake Chloride accurately with an old farm fertilizer spreader.

These machines can be cali-brated with great accuracy.

Quick cleanup afterward is important since Chloride is corrosive to equipment.Once it is bound in the gravel, corrosive effect on vehicles is very low.

Optimum Moisture It is important to have the gravel close to optimum moisture just before apply-ing Chlorides. This will cause the prod-uct to be absorbed much more quickly and evenly into the gravel.Never apply the Chloride to dry gravel. It will not be evenly absorbed and may show failure in spots.

Test Sections It is always wise to try a test section of dust control/stabilization treatment if this type of work has not been done before. If there is uncertainty about the suitability of the gravel being used or if there is doubt about the equipment, and/or other products being applied, the process can be tried on a 500-1000 foot road test section. If the process fails at the test section level, then only a small investment and time are lost.

Also you have less public complaint.

The outcome from the failed test section will present an opportunity to analyze what may have gone wrong.

Another test section can then be tried with a modified process and/or mate-rials. If field performance proves satisfactory, the process can then be applied to larger jobs.

Application 55

A water truck being used to prewet some very dry gravel just prior to treatment.This dramati-cally improves the success of the treatment.

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Stabilizer_9 pgs.pdf deliquescent and hygroscopic. They promote an increase in density and capillary tension of fines in aggregate surfacing that helps bond the materials together. Application rates used for stabilization are three to five times the normal application rate used for dust abatement.

The goal in road selection was to obtain a broad cross section of roads that were in relatively dry climates in three U.S. Department of Agriculture (USDA) Forest Service Western Regions. Twelve roads were selected in four states. Each road had three types of test sec-tions. Some were maintained according to usual practices, others were mixed with chloride materials, and some were untreated con-trol sections. Test sections were constructed with different forms of chloride materials and monitored for 2 years.

Performance monitoring, measurements, and testing were a signif-icant part of this project. Road surface defects were measured three or four times each season to develop deterioration curves and to determine the effective life of each test section. Deterioration curves using a condition index were the basis for performance measurement and life prediction. The primary inputs for a life-cycle cost analysis were treatment life and costs for aggregate loss, construction, main-tenance, and the road user. Environmental effects were measured before and after construction by testing chloride concentration in roadside soils, trees, and adjacent streams. Continuous on-site traf-fic and weather monitoring was conducted on all projects for the 2-year period. Extensive testing was done to define aggregate characteristics on all projects.

The following intangible benefits were identified: (a) increased stan-dard of road surface, (b) reduced stream sediment, (c) reduced resource damage from aggregate sources, (d ) increased road-user safety,

(e) reduced health hazard from inhalation of airborne particulate, and ( f ) improved public relations.

Thirty-eight appendices (1) provide cost and performance analy-sis, testing protocols and results, an implementation guide, and con-struction and maintenance specifications. This work is based on field performance and not on engineering analysis of stabilized materi-als. This paper provides a summary of the findings from that report, which contains extensive information; it can be obtained from the USDA Forest Service (1).

PROJECT SCOPE AND OBJECTIVES

Between 1995 and 2000, the USDA Forest Service completed three projects using in-place stabilization (2). This project replicates these practices on a larger scale by including other types and forms of magnesium chloride and calcium chloride, additional construction practices, different aggregates, and different climates. Monitoring efforts were intensified and more detailed analysis was done. The primary objective was to provide guidelines and tools for effective implementation of the technology.

Chloride Stabilization of Unpaved Road Aggregate Surfacing

Stephen Monlux and Michael Mitchell

There are few alternatives for improving long-term performance of aggregate surfacing materials in dry climates other than annual dust abatement treatments. In-place stabilization of properly graded aggre-gate with chloride additives is cost-effective and provides performance and intangible benefits. Similar results are achieved by mixing additives with aggregate during crushing. This 2-year study identifies conditions in which chloride-stabilized roads have a projected life of 10 years or more if properly maintained. The greatest benefits are realized in proj-ects with high aggregate surfacing replacement costs and average daily traffic volumes that exceed 100. Stabilization provides a higher stan-dard of road surface performance by improving ride quality and reduc-ing dust, corrugations (washboarding), and raveling (loose aggregate).

Other intangible benefits include reduced sedimentation in streams, reduced aggregate resource depletion, reduced health hazards from dust, and increased road-user safety. This project developed guidelines for chloride stabilization of various aggregate surfacing materials in semiarid to arid environments. Performance and cost-effectiveness of chloride stabilization were measured on 12 projects and monitored for two seasons in four western states; monitoring included construction and maintenance costs, road surface deterioration, traffic, weather con-ditions, environmental effects, and materials testing. Treated surfaces needed blading after 25,500 vehicles, whereas untreated surfaces needed blading after only 3,200 vehicles. Environmental effects on trees, streams, and roadside soils were insignificant. Many tools were developed to assist in the proper implementation of chloride stabilization of road surface aggregates.

Each year, most low-volume road agencies maintain thousands of miles of unpaved aggregate-surfaced roads by surface blading.

Blading is a costly activity that is done frequently and lasts a short time on heavily traveled roads. Road surface conditions can deteri-orate so rapidly that blading is often recognized as an ineffective but politically necessary activity. Blading also contributes to the increase of stream sediments and contamination and to loss and breakdown of expensive aggregate surfacing.

When used correctly, road surface stabilization with magnesium chloride and calcium chloride materials reduces blading significantly, increases road quality, and saves money (1). These two chlorides absorb moisture from the air and retain the moisture because they are

S. Monlux, U.S. Department of Agriculture Forest Service, 3738 Central Avenue West, Missoula, MT 59804. M. Mitchell, U.S. Department of Agriculture Forest Service, San Dimas Technology and Development Center, 444 East Bonita Avenue, San Dimas, CA 91773. Corresponding author: S. Monlux, monlux@montana.com.

Transportation Research Record: Journal of the Transportation Research Board, No. 1989, Vol. 2, Transportation Research Board of the National Academies, Washington, D.C., 2007, pp. 50–58.

DOI: 10.3141/1989-48

Monlux and Mitchell 51

TEST SECTION DESIGN

Within each road, test area location was based on similar aggre-gate, exposure, canopy, aspect, grade, and curvature. Three types of test sections were constructed on each project. At least one un-treated control section was mixed with the blade or tractor-tiller to see if the construction process provided significant benefits by itself. At least one section was built to model the normal mainte-nance blading. All other sections were treated with chloride materials in various forms and application rates. Project details are presented in Table 1.

TEST ROAD CONSTRUCTION

A service contract for construction was awarded to Moline Grading, Standpoint, Idaho, in September 2002. Oxford Inc., Moyie Springs, Idaho, provided, applied, and mixed all chloride materials. The Trout Creek Road project was built as a pilot project in October 2002. The remaining 11 projects were built between mid-May and early July 2003. The general construction process was as follows:

• All sections were watered to assist the initial blading to remove ruts, washboards, potholes, and mix in loose aggregate. The road surface was shaped to a 4% crown.

• Where solid (dry) products were used, the road surface was watered to ensure that the aggregate would be at optimum moisture during mixing. Water was not applied to the road surface before mixing liquid products for fear of exceeding optimum moisture.

• For tractor-tiller mixed sections, chloride was applied and tilled into the top 2 in. (50 mm) of aggregate (Figure 1). The surface was lightly shaped to ensure a 4% crown and then compacted. A light application of chloride was spread on the finished surface.

• For blade-mixed sections, a windrow was built, sized, and flat-tened. The size of the windrow is based on a 2-in. (50-mm) com-pacted depth times a swell factor of 1.25. Chloride materials were spread on the flattened windrow and then mixed by moving mater-ial from one side of the road to the other, two times. The mixed sur-facing was spread from the windrow and then shaped to a 4% crown and compacted. A light application of chloride was spread on the finished surface.

Chloride application rates are presented in Table 2.

PROJECT MONITORING

Weather

Relative humidity and temperature were measured with on-site gauges for all 12 projects. Rainfall was measured on site for six projects, and remote automated weather station data were used for the other six projects during 2003. In 2004, all projects had on-site rainfall gauges.

Dry summer season monitoring began and ended when the aver-age air temperature for three consecutive days reached 32°F (0°C).

Deterioration of the road surface essentially stopped when temper-atures were below freezing unless snowplowing took place. Snow-plowing on Trout Creek Road removed substantial amounts of loose aggregate on the road surface and flattened the crown so much that pothole failure occurred the following season.

Relative humidity and temperature data were reduced to average daily average seasonal minimum and maximum values. Average daily

TABLE 1 Project Details

Test Number of Test Sections (Length from 750 to 900 ft)

Mixing Method Sections CaCl2 CaCl2 CaCl2 MgCl2

Project per Untreated Normal @ 94% @ 77% @ 36% @ 28% Tractor- Number Road Name Project Location Project Controla Bladingb Salt Salt Salt Salt Tiller Blade

Total number of sections aAn untreated control section is bladed, mixed, and compacted the same as treated sections except no chloride is added.

bNormal blading assimilates the traditional practice of blading to the bottom of all surface defects in the road surface and then shaping to the desired crown.

Trout Creek

Tucannon River

Miller Lake

Williamson River

Wickiup Rd.

Conklin

Payette River

East Fork

South Side

South Side II

Deer Creek

Snow Creek

Western Montana

Southeastern Washington

South central Oregon

South central Oregon

Central Oregon

Central Oregon

Southwestern Idaho

Central Montana

Northwestern

Northwestern

Northern Idaho

Northern Idaho

52 Transportation Research Record 1989

Soil, Water, and Trees

Environmental influences were measured by testing chloride con-centration in roadside soils, trees, and adjacent streams before and after construction. Forty-eight samples of soil from both treated and untreated sections on the road shoulder were taken before construc-tion on each project. After two seasons, 48 additional samples were taken at the same locations to see if there was a significant change in chloride concentration. Data showed a rise in soil chloride levels but they were still below the thresholds for concern.

Chloride levels in the Tucannon River were measured before and after treatment of the Tucannon River Road. The river varied 15–20 ft (4.6–6.1 m) from the road shoulder. Results indicate no change in calcium or chloride ion levels in the water after treatment.

On four projects, before construction, 101 samples of conifers were taken close to the road and adjacent to a treated and an untreated test section. Locations of trees ranged from 5 to 50 ft (from 1 to 15 m) from the road shoulder. Duplicate samples were taken from the same trees after two growing seasons to see if there was a signifi-cant increase in chloride concentration. Data from tree samples indi-cate that the level of chloride increased but that it is not a significant long-term threat to survival.

Construction

Construction equipment time was monitored and a cost guide was developed for the stabilization process. Construction costs also are used in each project’s cost analysis.

Several quality assurance methods were used during construc-tion to ensure that the specified chloride application rate was ob-tained and that liquid chloride materials met the minimum specified concentration.

Road Surface Performance

Road surface defects were measured three or four times each season to develop performance curves and to determine the effective life of each test section. Treatment life along with costs for aggregate loss, (a)

(b)

FIGURE 1 (a) Spreading calcium chloride flake and (b) mixing with tractor-tiller.

TABLE 2 Calcium Chloride and Magnesium Chloride Application Rates (2-in. Compacted Thickness of Aggregate Surfacing)

Chloride for Stabilization Percentage by Weight of

Chloride Product Type Dry Aggregate

Surface and Concentration 1.5% 2% Application

Calcium chloride 3.23a 4.31a 1.06a solid @ 94%

Calcium chloride 3.94a 5.26a 1.30a solid @ 77%

Calcium chloride 0.74b 0.99b 0.24b liquid @ 36%

Magnesium chloride 1.01b 1.35b 0.33b liquid @ 28% aPounds per square yard.

bGallons per square yard.

relative humidity ranged from 15% to 98% and temperature ranged from 35°F to 98°F (2°C to 37°C). Average seasonal relative humidity and temperature ranged from 47% to 83% and from 50°F to 61°F (10°C to 16°C), respectively.

Precipitation during spring, summer, and early fall was light in 2003 (0.5–5.5 in.; 13–141 mm) and heavy in 2004 (5.3–13.9 in.;

136–356 mm). About two-thirds of this precipitation occurred dur-ing the hot summer months as isolated thunderstorms dropped 0.3–0.5 in. (8–13 mm) of rain over a 1-h period.

Traffic

Seasonal average daily traffic counts ranged from 25 to 157. Four roads had peak daily traffic counts of >400 vehicles, with the great-est count being 922. The primary operating season is from April to November and is controlled by freezing road conditions or snowfall.

Traffic classification fit into the following three categories:

• 79% light vehicles, including pickup trucks;

• 16% two-axle trucks and light-duty trucks with trailers; and

• 5% trucks with more than two axles.

construction, maintenance, and the road user are the primary inputs for a life-cycle cost analysis.

The unsurfaced road condition index (URCI) (3) was used to monitor road surface performance. The URCI is a road management tool for scheduling maintenance and avoiding costly repairs. Simi-lar but less measurement-intensive methods are used by many low-volume road agencies. The defects rated for these projects are corrugations (washboards), dust, potholes, ruts, and loose aggregate (raveling).

Each defect measured is categorized into three severity levels (low, medium, and high) and the extent of each level is measured in square feet. Each measured distress level is converted into a value and subtracted from 100 to obtain the condition index. A road with no defects has a condition index of 100. Values below 60 usu-ally indicate that blading is needed. Performance curves for each project were developed. Examples of the Tucannon River Road project performance curve are presented in Figures 2 and 3.

Before construction, aggregate loss measurements were done by a vertical survey grid on two sections of each project, one treated and one untreated. It is assumed that all loss is from the road surface and not from intermixing with the subgrade because all roads have been arterials for many years and the subgrades are stable.

Road surface conditions were observed to determine whether blading was needed and to determine reasonable vehicle speed on each section. Vehicle speed influences user costs and provides another indication of road serviceability. Reasonable vehicle speeds and corresponding thresholds for “blading needed” and “blading critical” are on performance curves to provide a better description of the extent of deterioration that was taking place during each season. A 25% reduction in vehicle speed correlates with blading needed and a 40% reduction in vehicle speed correlates with blading critical.

Road Blading Maintenance

Controlled blading and monitoring were done the third season and illustrated the significant benefits of correct maintenance techniques.

These blading techniques are essential if long-term performance is expected.

LABORATORY TESTING OF AGGREGATE

AND CHLORIDE MATERIALS

Road-surfacing aggregate on 11 of the 12 projects is good quality, well-graded crushed aggregate. Gradation tests show from 48% to 72% passing the No. 4 sieve (0.425 mm) and 11.1% to 17.2% per-cent passing the No. 200 sieve (0.075 mm). These types of grada-tions have been found to perform well in relatively dry climates because they capture the chloride ions in a relatively impervious gradation (4). Impervious gradations prevent rains from flushing chloride ions in the aggregate down into the subgrade. A smaller amount of minus No. 200 (0.075 mm) would be necessary if the mi-nus No. 40 (0.425 mm) were plastic. Aggregates on all projects are nonplastic, including the Payette River Road aggregate that was treated with 2.5% bentonite clay in 1999. Aggregate quality test results are described by Monlux and Mitchell (1).

The percentage of chloride used for stabilization was based on past experience (2). The 1.5% and 2% chloride salt concentrations by weight of aggregate surfacing are similar to concentrations obtained

-20

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

Cumulative Traffic

C o n d it io

In ex

Untreated

2% CaCl2 Solid, T iller 1.5% CaCl2 Solid, T iller

1.6% CaCl2 Solid, Blade 1.9% CaCl2 Solid, Blade

Blading Needed

Blading Critical

2003 ADT = 78 2004 ADT = 83

A ve rage Maxi mum Reasonable Speeds:

Treated = 37 mph Untreated = 31 mp h

FIGURE 2 Tucannon River Road surfacing performance for 2003 and 2004 (all sections, by type of treatment).

(ADT � average daily traffic.)

Monlux and Mitchell 53

54 Transportation Research Record 1989 by annual dust abatement treatments over a 4- to 6-year period.

An indication of the optimum chloride content for a particular aggre-gate can be determined by running moisture density tests with vari-ous percentages of chloride, similar to an asphalt mix design. Higher amounts last longer in arid areas because higher concentrations evaporate more slowly (4).

Two samples of each chloride were tested to verify concentration percentage, impurities (sulfates and nitrates), and hazardous waste (arsenic and lead). All chloride materials were acceptable and within specification limits.

COST AND PERFORMANCE ANALYSIS

Performance of treated sections for each project is most easily seen by viewing the graphs of cumulative traffic versus condition index in Fig-ures 2 and 3. These graphs show significant road surface performance benefits during 2003 and 2004. Several trends are as follows:

• Untreated sections show an initial rapid deterioration due to high-speed traffic. After a significant number of defects develop, vehicle speed decreases and the rate of deterioration decreases.

• Thresholds for blading needed and blading critical are based on reductions in vehicle speed, road manager comments, and visual observations of monitoring personnel. A 25% reduction in vehi-cle speed correlates with blading needed and a 40% reduction in vehicle speed correlates with blading critical.

One method for predicting performance is to use the life ratios in Table 3. Life ratio is defined as the amount of traffic on treated sec-tions divided by the amount of traffic on untreated sections before blading is needed. Essentially, the ratio is a number that represents how much longer the initial performance life of the treated sections is versus the untreated sections before maintenance blading. The ratios vary from a low of 4 to a high of 57. Taking the average of all projects, treated sections needed blading after 25,500 vehicles and untreated sections needed blading after 3,200 vehicles. Thus, the average life ratio for all projects was 8.

Construction costs were developed for the four chloride products mixed by blade and tractor-tiller. The construction times for each equip-ment operation came from detailed monitoring during test-project construction. Chloride costs came from regional suppliers.

Blade-maintenance costs are based on the blading cost per mile and number of bladings required over the 2003 and 2004 performance

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 it

In ex

Treated Untreated

Treated Sections, Avg of 4

Sect ions, Avg of 5

Bladed Untreated Sections

Blading Needed

Blading Critical

Year 2003 ADT = 78 Year 2004 ADT = 83

All sect ions bladed in

November

Average Maximum Reasonable Speeds:

Treated = 37 mph Untreated = 31 mph

FIGURE 3 Tucannon River Road surfacing performance averages for 2003 and 2004.

TABLE 3 Life Ratios for Each Project

Traffic Volume Prior to Blading Needed

Project Treated Untreated Life Ratio

Trout Creek 21,000 2,000 11

Tucannon 50,000 10,000 5

Miller Lake 10,200 2,800 4

Williamson 9,000 1,200 8

Wickiup 32,000 3,000 11

Conklin 17,000 3,000 6

Payette 52,500 5,000 11

East Fork 50,000 6,700 7

South Side 12,000 700 17

South Side II 20,000 350 57

Deer Creek 22,000 2,700 8

Snow Creek 11,000 1,000 11

Average 25,558 3,204 8 period. The number of bladings required is based on staying above the blading needed line on performance curves for each project. As expected, blading frequency is strongly influenced by traffic volume and speed as well as by the quality of aggregate surfacing.

The average condition indexes for normally bladed sections ver-sus untreated control sections were very similar, which indicates there are few long-term performance benefits from compaction while doing routine blading on untreated aggregate surfacing. Results were inconsistent, but an overall average showed a slight increase in condition index and vehicle speeds for the compacted segments over those not compacted. These increases in performance probably do not justify the added expense of compaction. Greater increases in performance can probably be obtained by watering while blading.

Road-user costs were determined by the World Bank Roads economic decision model (5). Variables in this model include road roughness, vehicle speeds and types, terrain, and road surface. The analysis was based on only one vehicle, which was described as a goods vehicle driven in mountainous terrain on an aggregate sur-face. This vehicle has a 4,000-lb (1,800-kg) gross weight, a new cost of $14,000, and is driven 20,000 mi (32,200 km) per year.

Fuel costs are $4.32 per gal ($1.14 per liter). Increasing vehicle and fuel costs to current values and selecting the desired mix of vehicles would show even greater savings in user costs.

An estimated aggregate loss is based on loss of dust from the aggregate and assumes that aggregate loss is proportional to dust loss (6, pp. 4–5).

The cost–benefit summary and analysis compares all costs for untreated and treated sections. Results indicate that the treatment cost is recovered during the second season for some projects. Fig-ure 4 compares the life-cycle cost benefits of untreated and treated sections of all projects. This graph is based on 2 years of actual per-formance and long-term projections that depend on correct mainte-nance. Figure 5 presents the cumulative cost by year for treated and untreated sections on one project.

INTANGIBLE BENEFITS

Stream sediments are reduced when road surface blading is decreased (7 ). This project shows that blading is reduced when road surfaces are stabilized. When stream sediments are reduced, costs are reduced or eliminated for design, construction, and maintenance of sediment control structures.

Resource damages from aggregate sources are decreased if the demand for aggregate surfacing is lowered. Road surface stabiliza-tion clearly reduces the need for aggregate replacement. Less aggre-gate usage would conserve aggregate resources, which are scarce in many areas, and save funds currently spent for locating, drilling, and surveying new sources; preparing pit development plans; securing necessary permits; and developing and restoring sites.

Road-user safety is increased when dust from the road surface is decreased. Chloride materials are an effective dust abatement prod-uct as well as a stabilization agent. Less dust reduces vehicle acci-dents, which lowers costs associated with vehicle repair, medical expenses, and loss of life.

Public health costs are less when a known health hazard, such as dust, is reduced. The extent of the benefit is based on the amount, type, and speed of vehicular traffic; the number of vehicle occupants;

and the number of individuals exposed for long periods in roadside residences and campgrounds.

Negative public opinion is generated from roads in poor condi-tion. Public complaints use employee resources and reduce the road agency workforce’s productivity.

PROJECT SELECTION AND DESIGN GUIDE

The information provided by Monlux and Mitchell (1) is useful for deciding whether chloride stabilization is a good option for improv-ing road surface performance on specific projects. The following steps are recommended.

R2 = 0.952

R2 = 0.9628

$0

$50,000

$100,000

$150,000

$200,000

$250,000

$300,000

$350,000

0 50,000 100,000 150,000 200,000 250,000 300,000 350,000 400,000

L if e-yc le st s Untreated Sections

(Average of 40 Sections)

Treated Sections (Average of 39 Sections)

FIGURE 4 Life-cycle costs for all projects.

Monlux and Mitchell 55

56 Transportation Research Record 1989

Project Selection

The average daily minimum humidity should be 20%. Recommended aggregate characteristics are presented in Table 4. Acceptable char-acteristics are typical of most sections treated in the 12 projects. Bet-ter performance will be achieved by aggregate with the preferred characteristics.

Performance Estimate

Eight performance-related road characteristics are provided, allow-ing road managers to determine whether roads they want to stabilize are similar. The characteristics are traffic volume, ambient temper-ature, relative humidity, rainfall, road geometrics, aspect, canopy, and aggregate surface. Compare characteristics of the proposed project with those listed by Monlux and Mitchell (1). Select the proj-ects with the closest project characteristics, and then look at the performance curves of the selected projects listed by Monlux and Mitchell (1) to see whether results are desirable.

Cost Analysis

• Perform a preliminary construction cost estimate.

• Tabulate the savings in annual blading maintenance, road-user cost, and aggregate loss.

• Evaluate the significance of intangible benefits related to sedi-mentation, resource damage, road-user safety, dust health hazard, and public opinion.

• Obtain price quotes for chloride materials.

• Complete the cost–benefit analysis.

Contract Preparation

Visit the project, dig holes to confirm depths of aggregate surfacing, and measure road crowns. Take representative samples for testing of gradation, Atterberg limits, and moisture density. Using project data, check the original performance estimate and cost analysis.

Finally, review and edit the construction specification.

OBSERVATIONS AND CONCLUSIONS

The following conclusions are from field observations and data monitoring.

General

The greatest economic benefits of stabilization are on projects well suited for stabilization, with higher traffic volumes and greater costs

$0

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

0 1 2 3 4 5 6

Time, Years u m u la ti ve

Treated

FIGURE 5 Tucannon River Road life-cycle costs.

TABLE 4 Recommended Aggregate Characteristics

Characteristic Preferred Acceptable

Maximum size (in.) 3⁄4 1

Grading description Well graded—not uniform or skip graded

Percent pass Νο. 4 55 to 70 50 to 75 (AASHTO T11 and 27)

Percent pass Νο. 200 14 to 17 12 to 17 (nonplastic)

Percent pass Νο. 200 (plastic) 12 to 15 8 to 15

Plasticity index 2 to 9 Nonplastic

(AASHTO T89-90)

Los Angeles abrasion Less than 30 Less than 40

(AASHTO T96)

Percent fracture, one Greater than Greater than face (1) 85 75 for aggregate replacement. Life-cycle cost analysis shows that the investment in stabilization pays off in less than 3 years for roads with average daily traffic greater than 50. A 10-year or longer life is realistic for projects with good aggregate, adequate humidity, light annual blading maintenance to rebuild crowns, and additional surface treatments of high-wear areas at 3- to 5-year intervals.

Many intangible benefits exist that may be more important than tangible benefits.

The rate of deterioration decreases as more defects develop in the road surface and traffic speed decreases. Road condition index improves after precipitation because dust is eliminated and traffic reduces washboards and loose aggregate while the road surface is wet.

Treated Sections Versus Untreated Sections

Blading was needed on treated sections after 25,500 vehicles and on untreated sections after 3,200 vehicles; thus, the average initial per-formance period for the treated sections lasted eight times longer than for the untreated sections. This number is even greater when typical blading techniques are used. Performance curves show that typical blading done by contract by the mile lasts a shorter time than blading done on the test sections.

The average speed on treated sections was 37 mph (60 km/h) and the average speed on untreated sections was 26 mph (42 km/h) for the 2-year period. During the 2003 season, 4 of the 39 treated sec-tions needed blading one time and all 40 untreated sections needed blading 95% of the time. Blading became critical on several untreated sections in the first year.

Visual observations indicate that treated sections reduced dust by about 90%. The condition of all test sections improved after periods of wet weather and over the winter season. Treated sections improved more than untreated sections.

Treated Sections

During the first 2 years of monitoring, 13 of 39 treated sections needed blading. Six of the 13 sections had construction problems or the crown was removed by snowplowing. Relatively minor defects in the other seven sections were potholing, washboarding, and rut-ting. All the pothole problems existed where the crown was less than 2% because of snowplowing or at the centerline where the crown was flattened.

No distinct difference in performance existed between the four chlo-ride products. No distinct difference in performance was noticed on 2% versus 1.5% chloride content. A greater difference in performance may be evident after 3 or more years of service.

Aggregate materials on 11 of 12 projects performed well when stabilized. Miller Lake Road was the exception, because larger top-size aggregate caused raveling. All other projects were essen-tially 3⁄4-in. (19-mm) minus and well graded with a minus No. 200 (0.075 mm) range of 11.2% to 17.1% and no plasticity. Well-graded aggregates with this amount of minus No. 200 (0.075 mm) work well because chloride ions are held within a relatively impervious medium (4). Minus No. 200 (0.075 mm) contents between 8% and 12% may also work well if the minus No. 40 (0.425 mm) portion were plastic.

No correlation existed between project performance and gradations plotted on the 0.45 power curve.

In dryer climates, treated road surfaces may dust in early spring before spring rains. These surfaces regain their treated appearance (wet look) and harden up when rains come or when the surface is watered.

All project characteristics influence the performance of chloride-treated aggregate surfaces. The most significant ones appear to be aggregate characteristics (Table 4), relative humidity, maintenance blading practices, traffic speed, and traffic volume.

Humidity influences performance. However, projects with an aver-age daily minimum humidity as low as 15% in central Oregon per-formed as well as some projects with higher humidity. Periodic rains improve performance but do not have as significant an influence as daily humidity. Projects located next to streams or that had roadside vegetation to provide shade performed better.

Blading when moisture is below optimum or allowing the bladed surface to remain loose and dry out reduces long-term performance.

The wet blading process works very well for relatively impervious gradations shown in Table 4. Wet blading is done by saturating the road surface after blading and wheel tracking to flush fines and residual chloride to the surface.