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, :: f 'l...l u l \\ '. , I:!! I.Waste M,)niJ:JcmenlWit5hington DC 20460

Development

SWl81eOctober 1919

of GovernmentalProcur,ement Guidelinesfor Construction ProductsContaining RecoveredMaterials

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Section 11USE OF WASTE RUBBER IN HIQ1II'AY CONSTRUCTION

INTRODUCTIONIn recent years, there has been a growing in teres t in the use ofrubber from discarded t i res in various highway construction and main-tenance operations. Applications of asphalt-rubber materials currentlybeing examined include:

Seal coatsJoint and crack f i l lersStrain relieving interlayers

In particular , th e use of an asphalt-rubber paving c o m p o s ~ t ~ o n as thebinder in a seal coat and/or inter layer application has been the subject of extensive f ield t r ia ls in recent years. The Federal HighwayAdministration has funded studies in several states on the use of t i rechips in asphalt under Demonstration Project No. 37. The results ofthis demonstration program are s t i l l being evaluated. In a statusreport published in July 1978, the comments of investigators from 18states were generally favorable although some observers noted nodifferences in the performance of control sections which were instal ledusing conventional materials and test sections instal led using asphalt-rubber mixtures. .ASPHALT-RUBBER PAVING METHODS

There are two major methods ' in use for incorporating waste rubberinto asphalt paving operations. Both methods use discarded t i res asthe major source of rubber, but they differ in the way th e rubber i sprepared and then mixed with the asphalt .In the f i rs t method, a typical specification requires that" . . . the rubber shall be a dry free flowing blend of 40% powdered devulcanized rubber and 60\ ground vulcanized rubber scrap speciallyselected to have a high natural rubber content. I t shall be free fromfabric, wire, or other contaminating materials except that a smallquantity of mineral powder may be included to prevent caking of theparticles., ,20 For this method, the sieve analysis is specified asfollows:

20. Personal communication.to William H. Clark I I I .IS December 1978.Robert C. Ziegler, Calspan Corporation,N.Y.S. Thruway Authority, Albany, N.Y.

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Screen % Retained10 030 20-40SO 40-60

100 5-15pan 10-25

The second method requires that n the rubber shall be a goodquality ground t i re rubber, dry and free flowing. The specific gravityof the rubber shall be 1.15 !.02 and shall be free from fabric, wire,or other contaminating materials except that up to 4 percent of calciumcarbonate shall be included to prevent the particles from stickingtogether." The corresponding sieve analysis is specified as:Screen

1625

% Passing95% Min.10% Max.

Because the f i rs t method requires that part of the rubber be devulcanized, the cost of the prepared ruober is somewhat higher than thatrequired for th e second method. Recent inquiries indicated that rubberof type 1 was $0.30/ lb . compared to $0.20/ lb . for type .2 rubber.In 'the preparation of the binder for the f i rs t method, an asphaltoil blend is heated to at least 400 0 F and thoroughly mixed before therubber is added. The rubber is added in amounts up to 22 to 24 p'ercent.

Adequate agitation of the liquid blend must be maintained to insureproper dispersion and mixing. The asphalt-rubber mix is applied at atemperature of 375F to 425F at a minimum rate of 0.6 gallon persquare yard.For the second method, the binder is prepared by combining therubber, in amounts of 23 to 27 percent by weight. with asphalt at atemperature between 350F and 450F. Following mixing. the blend isdiluted with a kerosene-type diluent. The asphalt-rubber mix isapplied at a temperature of 300F to 350F a t the rate of 0.4 to. 1.0gallon per square yard.Perhaps the most common use of the asphalt-rubber mixtures is as astress absorbing membrane interlayer (SAMI). In this application, themixture-is applied over old deteriorated pavement or base. Later afriction course of asphaltic concrete is generally applied. The SAMIhas shown to be effect ive in preventing reflective cracking of thefinal surface layer due to the cracks in the old underlaying pavemene.

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,Since some special equipment is required for blending and applying the 'asphalt-rubber mixture, a capital investment is required on the part ofthe paving contractor. The cost of the asphalt-rubber mix is 2 to 3times that of asphalt alone.ASPHALT SALES IN THE U.S.

Sales of petroleum asphalt for consumption in the U.S. by typeand principal use are shown in, Table 11-1 for the years 1972-1976.Total sales of petroleum asphalt as well as the use of asphalt forpaving have declined during the past 2 years, i . e . , 1975 and 1976, froma high in 1973. The proportionate amount of asphalt used for paving,as a percentage of tota l sales, remained constant throughout the S-yearperiod at 78-79 percent.RUBBER RECYCLING

Recycled rubber stat is t ics for the years 1973-1977 are shown inTable 11-2. Listed under Consumption, item i , RubQer Surfacing,includes recycled t i res used in paving products. The stat ist ics do notinclude the approximately SO million or more t i res which are retreadedeach yea'r.

However, the amount of rubber recycled or the recycling capacity,even when considered jointly with t ires destined for retreading, s t i l lrepresents only a small percentage of the 200 to 300 million t i resdiscarded each year. The remainder is added to the already existingpiles of tires strewn everywhere. I t has been estimated that thereare over 2 bill ion scrap t ires presently in storage or l i t ter ing thelandscape. 21POTENTIAL BENEFITS

Although the use of discarded tires in asphalt is s t i l l underinvestigation and evaluation, i t is possible to bound potential benef i ts by means of a simple parametric analysis. Benefits in this contextare defined as the removal of discarded t i res from the nation's wastestream.The independent variable in the analysis is the amount of asphaltreplaced by 'ground-up t i res in the paving mixture. The dependentvariable is the amount of waste rubber uti l ized. i . e . , thenumber oft i res consumed.

21. ''Ways to Use Waste Products in Highway Construction." Prepared byTask Force 16 Subcommittee on New Highway Materials of the JointCooperative Committee of American Association of State Highway andT r a ~ p o r t a t i o n Officials, American Road and Transportation BuildersAssociation.

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TABLE 1'1. SALES OF PETROLEUM ASPHALT FOR CONSUMPTION IN THE UNITED STATES,BY TYPE AND PRINCIPAL USE' (SHORT TONS)

1912 1973 1974 1975=' 1976Uniled Slol.s. Tolal 31.120.928 34.333.031 . 31,035,026 27,495,156 27,300,148

By Type:Asphalt Cemonts and Fluxes 24,728,001 27,370.153 25,129,258 22,113,178 21,882,700Emulsified Asphalts 2,532,833 2,742,732 2,626,991 2,309,812 2,379,556Cutback Asphalts 3,860.094 4,220,146 3,358,777 3,072,166 3,037,892

BV Principal U .P.v!ng Products 24,305,490 27,040,551 24,641,766 21,592,860 21,474,850Roofing Products 6,346,860 6,677,335 4 , 8 1 4 , ~ 5 1 4,803,164 4,791,987All Othor Products 1,468,678 1,615,145 1,678,409 1,099,132 1,033,311

1. Exclud . domestic biluminou,lim one and sand lIono, gil.onilo and road oil.2. R led.'Source: S.les of Asphalt in 1976, Minerallndusuy Surv.ys, U.s. Deparlmenl 01 the Inlorior, Bureau 01 Mines, 27 Juno 1977.

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TABLE 112. RECYCLED RUBBER STATISTICS, 1977-

1917 1976 1975 1974 1973MILLIONCONSUMPTION POUNDS

" ." " " "-,a) Tires Repair Material 129.9 53.1 56.0 58.8 58.8 58.8b) Inner Tube Reclaim 21.0 .8.6 8.8 10.3 6.3 8.4c) Ground Crumb 35.2 14.4 10.2 9.6 6.7 N.A.d) Auto Mau. Mtchanicals 20.2 8.3 12.8 8.3 13.5 15.4.) Heels. Soles, Footwear 0.2 -- 0.1 0.2 0.3 0.1t) Cemenu. Dispersions 5.6 2.3 2.1 4.1 4.6 4.2g) Hose, Belting Packing 2.4 1.0' 0.9 0.5 0.7 1.7h) Mechanicals (not auto) 16.1 6.6 7.0 _5.7 7.4 7.7il Rubber Surfacing 6.5 2.7 '0.8 1.2 1.2 2.5j) All Other 7.4 3.0 1.3 1.3 0.5 0.7TOTAL Million Pounds 244.5 100.0 217.9 223.1 259.8 285.6SCRAP RUBBER 259.0 221.0 188.6 263.3 287.7PROCESSEDOPERATING CAPACITY 289.6 263.9 247.0 325.3 299.4(300 day operation)N.A. Not Availabl.Source: Tochnicol Commin Survey RuIU, Tabla 1, Rubber Recycling Division, A Division of National

Association of Recycling Industri Inc.For the purpose of the analysis, i t is assumed that 23,800,000short tons of asphalt paving mixture are used annually. This represents the average quantity for the 1972-1976 time period. I t is furtherassumed that a t ire will yield 10 pounds of ground rubber after removalof the bead and the major part of the fabric. The quantity of g,oundrubber substituted in the asphalt paving mixture is varied from 0.01percent to 25 percent.The results of this analysis are shown in Table 11-3. Accordingto Table 11-2, 3,250 short tons of rubber are presently used for rubber

surfacing. This is equivalent to substituting, on the average. 0.014percent of ground rubber in the total quantity of asphalt paving mixtures used in the U.S. and represents approximately 650,000 t i res .

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TABLE 113. POTENTIAL USES OF DISCARDED TIRES INASPHALT PAVING MIXTURES

GROUND RUBBER RUBBER REOUIREDSUBSTITUTE (%) (Short Tons) NO. OF TIRES

0.01 2,380 476,0000.02 4,760 952,0000.05 11,900 2,380,000-0.10 23,800 4,760,0000.25 59,500 11,900,0000.50 119,000 .23,800,0001.00 238,000 47,600,0005.00 1,190,000 238,000,000

10.00 2,380,000 476,000,00015.00 3,570,000 714,000,00020.00 4,760,000 952,000,000.25,00 5,950,000 1,190,000,000

It is estimated that the substitution of ground rubber in pavingasphalt in amounts of 2 to 3 percent would consume all the t i res discarded annually. While this would provide a means for disposing of thet ires, i t would have no noticeable beneficial effects on the pavement.The amount of rubber which must be added to the asphalt mixturesto obtain improved performance varies between 6\ and 25\, depending onapplication (e.g" as a stress-absorbing membrane, or as a wearingcourse) .The percentage of all asphalt paving where the addition of rubbercould provide enhanced performance is not known. I f we assume that thisis the case in 10 percent of a l l asphalt paving and that, on theaverage, the average rubber addition is 2S percent, the ,total number of

t ires consumed would be 120 million. This quantity is 183 timesgreater than current t ire use for this application. I t is readilyapparent that any significant application of rubber-asphalt pavingmixtures would eliminate large numbers of t ires from the waste stream.

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The use of rubber in asphalt paving mixtures does not come free.Plants for grinding rubber require substantial investments. Extraequipment is also required by c o n t r a c t o ~ s applying the rubber-asphaltmixture. 20The purpose behind capital investment decisions is to protect andincrease the profit-making abil i ty of a corporation. The privatesector will not make investments necessary to implement the rubberasphalt paving concept until the profit potential exists. Basic hereis th e existence of a market place for the materials and services beingoffered.The use of rubber-asphalt pavement mixtures is almost certain toresul t in higher prices than regular asphalt, particularly during thein i t ia l years of implementation. Therefore, the government would haveto not only guarantee ( i . e . , require) the use of asphalt-rubberpavement mixtures but also indicate that i t would absorb the incremental costs associated with ' t h ~ use of the mixture.

GUIDELINESExperimental uses of rubber-asphalt paving mixtures have shownencouraging resul ts . Widespread application of such paving mixtureshas the potential to remove a significant n u r r ~ e r of discarded t iresfrom the nation's waste stream.Increased use of this paving mixture will require capital investments in two areas in the private sector of the economy: (1) theestablishment of plants to prepare th e ground rubber, and (2) themodification of equipment used to-spread the paving mixture.Guidelines promulgated for the use of this paving mixture mustguarantee the private sector a market for materials and services. Amajor obstacle is that most highway construction and repair contractsare le t by the sta tes . The states may hesitate to uti l ize the newpaving mixture because of incomplete or inconclusive test results andhigher costs which may be incurred as a resul t of i ts use. A largescale promotion and education program appears necessary to se l l thisconcept to the sta tes .Implementation of a specific guideline(s) must await the comple-tion and evaluation of demonstration projects currently being conductedby the Federal Highway Adminstration.

20. Personal communication.to William H. Clark III ,15 December 1978.Robert C. Ziegler, Calspan Corporation,N.Y S. Thruway Authori ty , Albany. N.Y.

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. -

The present production capacity for ground rubber is inadequatesat isfy significantly increased demand. Any guideline must, therefore, provide .for a gradual increase in the use of rubber in pavement.Further, i t must-provide sufficient guarantees for the employment ofsuch material (including the absorption of higher costs) to stimulatethe private sector to enlarge i ts production capacity .

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