Expanded ShaleClay & SlateInstitute

Information Sheet 5650.1

aggregate has minimal dust, unlike normal weight aggregatethat is often coated with dust that prevents uniform bonding

and creates public complaints during application.

Lightweight aggregates consistently pass Los Angelesabrasion requirements as well as other quality tests. Light-weight aggregate also shows superior freeze/thaw resistanceand durability to de-icing salt corrosion. When snowplowdamage occurs, lightweight aggregate is far more resistant tobeing stripped out than normal weight aggregate.

Damage tO windshields, headlights and paint caused byflying stones is practically eliminated with lightweight aggre-gate thus avoiding time consuming motorist complaints andcostly insurance claims. The lightness of this aggregate, plusthe higher wind resistance of the rough surface texture, lowersthe speed at impact. The resulting striking force is too smallto do damage. The clean rough surface texture also bonds tothe asphalt better so there are fewer flying particles in the first

place.

INTRODUCTION Lightweight aggregate asphaltsurface treatment (chip seal, seal coat) is an advanced roadsurface made with expanded shale, clay or slate lightweightcover aggregate. Selectively mined shale, clay or slate is firedin excess of 20000 F in a rotary kiln. The result is a highquality ceramic lightweight aggregate that is inert, durable, and

tough -ready to meet stringent specifications.

Highway safety is increased due to the superior skidresistance (wet or dry) of road surfaces made with lightweightaggregates. This high skid resistance is maintained throughoutthe road's service life because under wear, fresh interior cellswith rough ceramic-like edges are continuously exposed.Lightweight aggregate does not polish as it wears.

The roadway service life is extended because of lightweightaggregate's unique and superior bonding capabilities with

asphalt. When bonded to the asphalt lightweight aggregatepresents a tough, durablepavement that holds up well under traffic and outlasts most

pavements made with normal weight aggregate. Lightweight

TES TIM O NIALS

The following testimonials verify that lightweight aggregateasphalt surface treatment offer the engineer an economical,long lasting road surface that is safer to drive on and free of

motorists complaints.

Cit): of Phoenix. Street Transportation Department:"In May 1992 we checked the two miles of lightweightaggregate chip seal we put down in 1988. Peoria Avenue from35th Avenue to 43rd Avenue was chipped with expanded shalelightweight aggregate and conventional asphalt. Cactus Roadbetween 43rd Avenue and 51st Avenue used rubberized asphaltas the binder with the lightweight aggregate. Peoria Avenuecarries approximately 42,000 cars a day and Cactus Roadcarries about 29,000 cars a day.

Oklahoma: Tulsa County chose lightweight aggregatebased on the 1990 cost data of 102 miles of road paved withlightweight aggregate chip seal. Ray Jordan, Tulsa CountyEngineer, decided the County could no longer afford to uselimestone chips. "In 1989 and 1990 lightweight aggregate wasused instead of limestone to eliminate windshield and paintdamage and to increase skid resistance. The county was veryimpressed with the lightweight aggregate performance andespecially pleased with the overall cost as summarized below.

"Neither street is showing any indication that the chip sealis wearing. There is the usual reflective cracking starting tocome through but no stripping, raveling or polishing of theaggregate is evident. There are no signs of loose rock in thegutter and the chips appear to be embedded in the asphaltbinder to about two-thirds of their length.

"We are quite happy with the results from these twoexperimental sections and would definitely consider specifyingexpanded shale lightweight aggregate in any future chip seal

program."James Matteson, P .E., Street Transportation Directorand Jeffrey Van Skike, P.E. Engineering Supervisor

Colorado: Frank F. Holman, Senior Highway

Maintenance Supervisor, State of CO, Dept. of Highways,Dist. 3, Section 6, has used lightweight expanded shale aggre-gate for cover coat on chip seal projects in NorthwesternColorado for the past four years. "The lightweight chips wehave in place are performing very well.

(1) The lightweight aggregate meets Oklahoma

Grade 3 and Texas Grade 4 specifications.

(2) These prices include labor, equipment and

materials."We've found the cost of the lightweight chips to be compa-

rable to rock chips with a number of advantages. The ad-vantages are: we can haul more cubic yards per truck allowingus to reduce the equipment and man-power required to do thejob. With the lighter weights the chipper has less strain on thebelts and drive-train. The porous aggregate adheres to theliquid asphalt very well and provides a driving surface withexcellent skid resistance. Brooming is much simpler because ofthe lighter weight and traffic blows much of the loose materialoff before we sweep. On some projects we haven't had tosweep at all. Last, and perhaps one of the most important ad-vantages, damage to motorists' windshields has been elimi-

nated."

"Tulsa County computer analysis clearly shows lightweightis more effective to handle than limestone. The labor andequipment costs have dropped remarkably with lightweight.Also, the consumption of CRS-2 has dropped from 0.42gallons per square yard to 0.34-0.36 gallons per square yard.These cost savings have more than off-set the higher unit costfor the lightweight aggregate which was approximately

$.08/sq. yd.

"The crew benefits by using lightweight as they are provideddamp and dust-free chips. The emulsion bonds best to a dust-free, very irregular surface. Crew members say driving a fulltruck of lightweight is much easier than a load of limestone."

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prevent loss of control skidding when wet can also make itrollout of the asphalt under constant turning or braking. Thissituation occurs at busy intersections and on a hot summer day-no asphalt membrane is strong enough to overcome this forceand hold it. To eliminate these isolated trouble spots the light-weight aggregate chip seal application is stopped slightly shortof busy intersections. The intersections are then treated differ-ently: hot mix, concrete, crack sealing or just do nothing. Inother words--you can't have your cake and eat it too."

A Limitation To Consider: Quoting R. P. Haun, Jr.,p .E., a highway consulting engineer from Eastland, Texas,with over 25 years of L W A asphalt experience.

"Synthetic expanded shale, clay or slate lightweight aggre-gates (L W A) has a micro surface texture that is highly resistantto skidding even when wet. This quickly creates a very highfrictional force build up between the tire and the road surface.This reaches a maximum during a turning or braking action.The same thing that makes lightweight aggregate excellent to

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C:\ESCSI\Asphalt\5650.1.2/93- Reprinted 11/99