Expanded Shale Clay & Slate Institute
INTRODUCTION Lightweight aggregate asphalt surface treatment (chip seal, seal coat) is an advanced road surface made with expanded shale, clay or slate lightweight cover aggregate. Selectively mined shale, clay or slate is fired in excess of 20000 F in a rotary kiln. The result is a high quality ceramic lightweight aggregatethat is inert, durable, and tough -ready to meet stringent specifications. Highway safety is increased due to the superior skid resistance(wet or dry) of road surfaces made with lightweight aggregates. This high skid resistanceis maintained throughout the road's service life because under wear, fresh interior cells with rough ceramic-like edges are continuously exposed. Lightweight aggregate does not polish as it wears. The roadway service life is extended becauseof lightweight aggregate's unique and superior bonding capabilities with asphalt. When bonded to the asphalt lightweight aggregate presents a tough, durable pavement that holds up well under traffic and outlasts most pavements made with normal weight aggregate. Lightweight
Information
Sheet 5650.1
aggregate has minimal dust, unlike normal weight aggregate that is often coated with dust that prevents uniform bonding and creates public complaints during application. Lightweight aggregates consistently pass Los Angeles abrasion requirements as well as other quality tests. Lightweight aggregate also shows superior freeze/thaw resistance and durability to de-icing salt corrosion. When snowplow damage occurs, lightweight aggregate is far more resistant to being stripped out than normal weight aggregate. Damage tO windshields, headlights and paint caused by flying stones is practically eliminated with lightweight aggregate thus avoiding time consuming motorist complaints and costly insurance claims. The lightness of this aggregate,plus the higher wind resistanceof the rough surface texture, lowers the speed at impact. The resulting striking force is too small to do damage. The clean rough surface texture also bonds to the asphalt better so there are fewer flying particles in the first place.
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The following testimonials verify that lightweight aggregate asphalt surface treatment offer the engineer an economical, long lasting road surface that is safer to drive on and free of motorists complaints. Oklahoma: Tulsa County chose lightweight aggregate based on the 1990 cost data of 102 miles of road paved with lightweight aggregate chip seal. Ray Jordan, Tulsa County Engineer, decided the County could no longer afford to use limestone chips. "In 1989 and 1990 lightweight aggregatewas used instead of limestone to eliminate windshield and paint damage and to increase skid resistance. The county was very impressed with the lightweight aggregate performance and especially pleased with the overall cost as summarized below.
Cit): of Phoenix. Street Transportation Department: "In May 1992 we checked the two miles of lightweight aggregatechip sealwe put down in 1988. Peoria Avenue from 35th Avenue to 43rd Avenue was chipped with expanded shale lightweight aggregateand conventional asphalt. Cactus Road between 43rd Avenue and 51st Avenue used rubberized asphalt as the binder with the lightweight aggregate. Peoria Avenue carries approximately 42,000 cars a day and Cactus Road carries about 29,000 cars a day. "Neither street is showing any indication that the chip seal is wearing. There is the usual reflective cracking starting to come through but no stripping, raveling or polishing of the aggregate is evident. There are no signs of loose rock in the gutter and the chips appear to be embedded in the asphalt binder to about two-thirds of their length. "We are quite happy with the results from these two experimental sections and would definitely consider specifying expanded shale lightweight aggregate in any future chip seal program." James Matteson, P .E., Street Transportation Director and Jeffrey Van Skike, P.E. Engineering Supervisor
Colorado:
(1) The lightweight aggregate meets Oklahoma Grade 3 and Texas Grade 4 specifications.
(2) These prices include labor, equipment and materials.
"Tulsa County computer analysis clearly shows lightweight is more effective to handle than limestone. The labor and equipment costs have dropped remarkably with lightweight. Also, the consumption of CRS-2 has dropped from 0.42 gallons per square yard to 0.34-0.36 gallons per square yard. These cost savings have more than off-set the higher unit cost for the lightweight aggregate which was approximately $.08/sq. yd. "The crew benefits by using lightweight as they are provided damp and dust-free chips. The emulsion bonds best to a dustfree, very irregular surface. Crew members say driving a full truck of lightweight is much easier than a load of limestone."
Frank F. Holman,
Senior Highway
Maintenance Supervisor, State of CO, Dept. of Highways, Dist. 3, Section 6, has used lightweight expanded shale aggregate for cover coat on chip seal projects in Northwestern Colorado for the past four years. "The lightweight chips we have in place are performing very well. "We've found the cost of the lightweight chips to be comparable to rock chips with a number of advantages. The advantagesare: we can haul more cubic yards per truck allowing us to reduce the equipment and man-power required to do the job. With the lighter weights the chipper has lessstrain on the belts and drive-train. The porous aggregate adheres to the liquid asphalt very well and provides a driving surface with excellent skid resistance. Brooming is much simpler becauseof the lighter weight and traffic blows much of the loose material off before we sweep. On some projects we haven't had to sweep at all. Last, and perhaps one of the most important advantages, damage to motorists' windshields has been eliminated."
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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 aggregates(LW A) has a micro surface texture that is highly resistant to skidding even when wet. This quickly creates a very high frictional 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 aggregateexcellent to
prevent loss of control skidding when wet can also make it rollout of the asphalt under constant turning or braking. This situation occurs at busy intersections and on a hot summer day -no asphalt membrane is strong enough to overcome this force and hold it. To eliminate these isolated trouble spots the lightweight aggregatechip seal application is stopped slightly short of busy intersections. The intersections are then treated differently: hot mix, concrete, crack sealing or just do nothing. In other words--you can't have your cake and eat it too."
C:\ESCSI\Asphalt\5650.1.2/93-Reprinted 11/99