ROAD USDepartment of Ft.'deral HighwayAdministration BUSINESS · Soil stabilization and dust control ... mixingprocesses are usually the best choice for lowvolume roads where both

USDepartme nt of l ronspor tonon

Ft.'deral Highway Administration

ROADBUSINESS

Address:Technol og y Transfer CenterUniversity of New HampshireDepartment of Civil Eng ine e ringTra nsportati on Research a ndComputation GroupDurham, New Hampshire 03824 -3591

Phon e :603- 86 2-4348(aut of sta te )

- Edito ria l Staff -o r 1-800-423-0060

(in N ew Ha mpsh ire) John A. And erson Proj ect Direct or

Yvo nne E. Allen Ad min. Assista nt

Charles H. G oodsp e ed Univer sity Lia iso n

Vol. :1 No.2 Spring 1988

Above: Section of same road recycledwithout using calcium chloride.

Above: Section of road recycled in 1979using calcium chloride.

• Preventing Sexual HarrassmentSuits 11

Asphalt Recycling:Know Your Options

• Technical Innovations(New approach to crack sealing) _ 10

• Did You Know?(Grading gravel roads) 10

- ALSO IN THIS ISSUE -

• Has Your Computer Or YourTown's Computer Been InfectedWith A Virus? 3

• Strive For A Pothole-FreeEnvironment 9

With the cost of roadway materialsincreasing and road budgets decreasing, as­phalt recycling is becoming more and morepopular. However, if you or your town areinterested in looking into asphalt recyclingyou should be forewarned: asphalt recyclingcan mean two different things to twodifferent people. It is important whentalking to a contractor or consultant thatboth of you are speaking the same languageand that you know your options. One typeof asphalt recycling procedure may cost 40%

continued on p. 4

• A Marked Increase In TrafficAccidents Can Be Reduced ByIncreasing Markings 2

• Quick And Easy Patching 10

You ma y be able to save up to 40­60% per job

Calcium Chloride(CaCI

2)

Soil stabilization and dust control

Stabilization is a technique for up­grading the engineering properties of soilsused in pavement construction. It involvesthe modification of soils or aggregates by in­corporating materials that will increase loadbearing capacity, firmness, and resistance toweathering or displacemen t. Soil stabiliza­tion is a tool that may be able to reduceyour road building costs and conserve mate­rials. Calcium chloride (CaCI2) is one ofmany products now being used for soil stabi­lization. Other products include such thingsas asphalt, lime, fly ash, magnesium chlo­ride, and kiln dust.

In order to illustrate the cost effec­tiveness of soil stabilization, FHWA hascompleted cost benefit studies on 24 sepa­rate cases. Generally speaking, soil stabili­zation leads to cost savings; however, themagnitude of these savings can vary signifi­cantly depending on the many factors thataffect construction costs.

The rest of this article will dealstrictly with CaCI2 as a soil stabilization anddust control product.

Calcium Chloride in NewConstruction --During new construction, using CaCI2

will help in the compaction process. It doesthis by properly maintaining moisture levels.The maintenance of optimum moisture dur­ing construction is the most important factorin obtaining maximum density and uniform­ity, both of which are necessary for goodperformance. Moisture limits for maximum

continued on p. 2

REPoRT

sPECIA'L

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Asphaltrecycling...continuedfrom p. 1

less than another type; or, depending on thecharacteristics of the job, one proceduremay not give you results as good as anotherprocedure will .

For explanatory purposes, the AsphaltRecycling and Reclaiming Association(ARRA) has divided asphalt recycling intofour types: hot-mix recycling, hot surface re­cycling, cold planing, and cold in-placerecycling. Although some types of recyclingare more common in our area than others,each of the ARRA categories will bedefined below for information purposes.However, more time will be spent on coldin-place recycling since it is the category ofmost interest to the majority of NewHampshire towns.

Hot-Mix Recycling - This type ofrecycling involves a central plant blendingand mixing operation to produce hot-mixpaving mixtures. The mix may include anycombination and amount, as necessary, ofreclaimed asphalt pavement (RAP),reclaimed aggregate materials (RAM), newasphalt, new aggregate, or recycling agents.The recycling agents are used to restoreaged asphalt to current standards.

There are two main types of hot-mixrecyclingprocesses: batch plant hotrecycling and drum-mix hot recycling. Themost common batch plant method acceptedby the industry involves introducing thereclaimed asphalt pavement (RAP) from aseparate cold feed bin into the pugmill, orweigh hopper, by a chute and belt conveyer.A batch plant can recycle RAP with newaggregate up to a 40:60 blend, although thepractical limit is approximately 20:80. Theindustry-preferred drum-mix method is thecenter-entry method which introduces RAPinto a drum downstream of a burner flameto mix it with superheated new aggregates.In this method, the maximum ratio of RAPto new aggregate is approximately 50:50; thepractical ratio, however, is 30:70.

The performance of recycled asphaltconcrete has been proven to equal that ofconventional mixes. When quality controlmeasures have been strictly adhered to, theuses and benefits of hot-mix recyclinginclude the following:

1. Surface and base structural problemscan be corrected;

2. Significant structural improvementscan be obtained with little or nochange in thickness (ex: untreatedgranular bases can be recycled intohot-mix asphalt concrete and thenplaced back in the same thickness);

3. Existing mix deficiencies, such as

aggregate gradation problems, can becorrected;

4. Frost susceptibility may be reduced;and

5. It can be done repeatedly, using thesame materials.

Hot Surface Recycling - The mostcommon hot surface recycling method is theheater-scarifying method which involves theheating and scarification of an asphaltsurface to a depth limited to 3/4 to one­inch. This type of recycling is least familiarto New Hampshire town road agents andpublic works directors primarily because ofthe cost. In order to provide a reasonablecost per square yard, the job would have tobe large enough so that the contractor couldcover the necessary move-in costs.

The main advantages of hot surfacerecycling is that it can reduce reflectioncracking and application of the final ridingsurface (seal or overlay) may be separatedfrom the recycling process for a long enoughperiod allowing for thorough inspection ofthe heating, scarification, leveling, andcompaction processes .

Cold Planing - This type of recycling(also known as cold milling) involves theautomatically controlled removal ofpavement to a desired depth with speciallydesigned equipment, and restoration of thesurface to a specified grade and slope, freeof bumps, ruts and other imperfections.The resulting textured pavement can beused immediately as a driving surface, or itcan be overlayed with a minimum ofmaterial. Cold planing has been done bytown governments using motor graders withhardened steel blades for maintenancepurposes. In recent years, cold millingmachines have become more popular. Theyare more versatile, faster, and provide betterresults than would the motor graderapproach.

Cold milling is an accepted recyclingmethod for correcting ruts and washboard­ing, poor skid resistance, poor bonding po­tential, poor pavement profile, and dimin­ished capacity of curbs and gutters. Themain advantages of cold planning are asfollows:

1. It can be done quicklywith minimuminterruption to the traffic flow;

2. When the process is complete, therestored pavement can be immedi­ately opened to traffic;

3. A wide range of planing machinesmakes the process available to smallercities and towns;

4. The process consumes substantiallyless energy than other methods ofroad rehabilitation; and

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5. The reclaimed material can be savedfor future use, as is, or taken to a hot­mix recycling plant.

On the other hand , the main disad­vantage of cold planing is that the only typeof distress that it will correct is a surfacedistress . It is sometimes very difficult, if notimpossible, to determine if the distress iscaused by surface, structural, or subgradedeficiencies.

Cold In-Place Recycling - This typeof recycling is a road constructiontechniquethat re-uses existing pavement structure in­cluding, in some cases, the underlyinguntreated base material. All work takesplace on the existing roadway and usuallyrequires no transportation of material. Coldin-place recycling results in a stable road ata total expenditure of 40 to 50 percent lessthan that required by conventional construc­tion methods.

Previously referred to as stabilization,cold in-place recycling is not a new ap­proach to road rehabilitation; it has beenaround for close to 50 years . Equipment forthis type of recycling has included rippers,scarifiers, pulvimixers, and stabilizers .Emulsions, cutbacks, and other additiveshave been used in conjunction with theseapproaches.

In New Hampshire, the two mostcommon cold in-place recycling methods usehammermill or a recycler (Bomag typerecycling machine) . These pulverizing­mixing processes are usually the best choicefor low volume roads where both asphaltand base rehabilitation are needed. Thebasic approach is to pulverize the pavementwith the base and mix the two together.The mix is then graded and compacted.

Both the hammermill and the recycler(Bomag type) processes have been shown tobe effective methods for cold in-place recy­cling. The two processes are distinctly dif­ferent and their applicability is primarily de­termined by the existing subbase conditions.As a result, some construction companiesare capable of using either method depend­ing upon conditions; however, othersspecialize in one method only. Theproponents of these recycling methods havebeen able to point to specific advantages ofone method compared to the other ashighlighted below:

hammermill• This method has successfully re­

cycled to a depth of 18 inches whenrequired;

• This method will break up largecobbles found in the existingroadway into approximately 2-inchdiameter stones vs. the recycler

\j

Calcium Chloride ...continued from p. 2

duce the frost heave of that soil appreciably.In general, however, protection from frostheave in silt is afforded by two percentCaCI2, in clay by one percent CaCI2, and in.graded mixes by one-half percent CaCI2.

The above information was extractedfor this article from the following sources :

• Soil Stabilization and Cold In-PlaceRecycling. This publication is available bywriting to: BOMAG (USA), P.O. Box 959,Springfield, OH 45501-0959.

• Bomaging A Road... A Guide to SoilStabilization and Cold Mix Asphalt RecyclingThis publication is available by writing to:BOMAG (USA), P.O. Box 959, Springfield,OH 45501-0959.

• Stabilization and Pavement Recy­cling. Prepared and approved by the Stabili­zation, Rehabilitation and Recycling Com­mittee, American Road and TransportationBuilders Association. A copy of this educa­tion and information guide is availablethrough the Technology Transfer Center bycalling 800-423-0060 or sending in the mailerattached to this newsletter.

.A Reporton Long-Term PerformanceofRoute 108, West Peru, Maine on Soil Ce­ment Base, Asphalt Stabilized Base, andCrushed Gravel with Calcium Chloride Base.Presented to the U.S. Corps of Engin eersGeotechnical Engineering Branch on Octo­ber 22, 1987, Waltham, MA. James B.Picket. A copy of this education report isavailable through the Technology TransferCenter by calling 800-423-0060 or by sendingin the mailer included in this newsletter. •

Migration and Leaching of CaCI 2 - One ofthe most commonly asked questions iswhether the CaCl 2 will eventually leach itsway out of the subbase. All indications atthis time suggest that the migration ofCaCI2 from the road is minimal and lateralmigration in silty clay soils under pavementis very slow. The fastest migration occursup and down through the soil by rainfall orevaporation.

Cores taken from Route 108 in WestPeru, ME (a road constructed in 1963) weretested by the Maine Department of Trans­portation. After 24 years there was stillfour -tenths of a pound of CaCl 2 per squareyard remaining in the base. Furthermore,tests showed that there was a need for a oneand one-half inch overlay on the road sec­tion with the asphalt stabilized base and noneed for an overlay on the road section withthe gravel and CaCl 2 mix.

O.5XCaCl2

30 1-- +--++---+---+-+---1

% of Calcium Chloride in the RoadBase and Frost Heave Action

percent

o 3.0rCaC1222 16 10 4 0 -2 -8

Temperature, Degrees Fahrenheit

Heay 101--,li.......",I+---+-r-+--+-+--;e

The above information was extractedfrom the following sources:

• Proven Guidelines for Hot-mixRecycling. Guideline Specifications for HotSurface Recycling. Guideline Specificationsfor Cold Planing. Guidelines for Cold In­place Recycling. Information on pricing andordering copies of these pamphlets may beacquired by writing to: ARRA, #3 ChurchCircle, Suite 250, Annapolis, MD 21401.

• Pavement Recycling Guidelines forLocal Governments. FHWA report numberFHWA-TS-87-230. This publication isavailable for FREE by calling the Technol­ogy Transfer Center at 1-800-423-0060 or bysending in the attached mailer.

• Soil Stabilization and Cold In-PlaceRecycling. This publication is available bywriting to: BOMAG (USA), P.O. Box 959,Springfield, OH 45501-0959.

• Recycling ofAsphaltic Pavements:Past, Present, and Future. Unpublishedreport submitted in 1987 by Thomas N.True, UNH student. A copy of this report isavailable from the Technology TransferCenter by calling 1-800-423-0060or sendingin the attached mailer. •

7. It minimizes traffic disruption sinceconstruction is confmed to one laneand usually only needs a single passwith the equipment; and

8. It can be used in conjunction withvarious soil stabilizing additives.

In general, the asphalt recyclingcategory referred to as cold in-placerecycling can result in a stabilized road forabout a 40-60% lower cost than conven­tional methods. Its advantages can besummarized as follows:

1. Restores old pavement to the desiredprofile;

2. Eliminates all types of pavementdistresses (i.e., existing crack patterns,potholes, wheel ruts, and other ir­regularities);

3. Improves resistance to frost penetra­tion;

4. Requires low production andengineering costs compared toconventional methods;

5. A thin overlay or chip seal is generallyall that is required for a surfacecourse;

6. It can add considerable strength tothe road;

recycler• This method has successfully

recycled to a depth of 12 incheswith one pass and can go deeperwith additional passes if required;

• The recycler method usually costsover 40% less than the hammermillmethod;

• This method is a pulverizingprocess, whereas the hammermill isa crushing process. With the righttype of subbase (no cobbles), therecycler will result in a uniformedcold-mix type subbase blend for alesser cost than the hammennill;and

• When thin pavements exist (1/2 to3/4 inches) this method is notusually recommended; however, therecycler is designed for addingemulsified asphalt (or other appro­priate soil stabilizers) directlythrough a spray bar during therecycling operation.

method which can not adequatelyhandle cobbles;

• The pavement/subbase mixappears to be a more uniform, ho­mogenized blend than the salt andpepper mix produced by the recy­cler; and

• On thin asphalt pavements thehammennill will produce its usualmaximum 2 inch diameter stonesize while a recycler may have atendency to break the asphaltsurface into 4 inch slabs that arethen driven below the surfaceproducing a less uniform base.

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