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OCR for page 70
71 GLOSSARY The following pages represent an attempt at developing a Crumb rubber--A modifier that can be blended into bitumen comprehensive glossary of chip seal terminology. One of the to enhance the elasticity and adhesion characteristics of great challenges in this study was to determine the precise the binder. Rubberized asphalt chip seals are successful at definition of much of the technical vocabulary that was mitigating reflective cracking, improving aggregate reten- found both in the literature review and the survey responses. tion, and reducing noise. It is strongly advised that readers use this glossary for defin- Cutback--Asphalt cement that has been diluted with a sol- itions of terms used in this report, to ensure that the best prac- vent such as kerosene or naphtha. The use of cutbacks is tices that are cited are not unintentionally misunderstood. becoming less common because of environmental and safety concerns. Adhesion agents--Substances that improve the degree of Distributor--An insulated tank with a circulating and heating wetting of the aggregate by the binder, thus enhancing the system that is mounted on a truck and distributes binder adhesion between the binder and aggregate. through a spray bar at the rear. It is critical for the distrib- Aggregate--A granular material usually crushed and utor to apply the binder at a constant rate and to the correct screened to appropriate gradations, which is used as the width. Distributors with computerized rate controls are cover stone in a surface treatment. desirable. Asphalt binder--Commonly referred to as asphalt cement, Double seal--A seal characterized by two separate applica- pure asphalt binders are graded based on viscosity and tions of both binder and aggregate. The design of a penetration. double-course seal requires the application rates for both Average least dimension (ALD)--A metric that represents layers of binder and aggregate to be determined as an the expected chip seal thickness when the aggregate is integrated treatment. Multiple seals provide a quieter oriented to lie on its flattest side. treatment. Binder--A bituminous material that provides a waterproof Embedment--A measured percentage of the portion of the seal and also bonds the cover stone to the pavement. aggregate enveloped by the binder. Embedment checks are a visual inspection of the chip seal construction, with typ- Bleeding--Upward movement of asphalt through the chip ical recommendations of at least 70% embedment. seal. Bleeding, also commonly referred to as flushing, can Emulsified binder--A liquid mixture of asphalt binder, be identified by dark patches of asphalt forming on the water, and an emulsifying agent. Emulsions are either surface, most commonly in wheelpaths or intersections. anionic (negatively charged) or cationic (positively Blotter material--See Chat. charged). Emulsions are not as sensitive to moisture, Cape seal--A chip seal followed by a slurry seal that fill the inherently contain antistripping agents, and require much voids in the surface of the cover aggregate. The slurry seal lower application temperatures than do asphalt cements. increases aggregate retention and reduces tire noise. Emulsion break--The point in time, shortly after the appli- Chat--Fine aggregate used to spread on flushed/bleeding cation of the emulsified binder, when the emulsifying chip seals as an emergency repair measure to restore skid agent and water evaporate from the asphalt cement, leav- resistance. ing behind the asphalt cement that bonds the aggregate Chip seal--A bituminous surface treatment that can be a particles to the binder. A "breaking" emulsion can be single, double, or triple application of bituminous binder observed when the binder changes color from brown to and cover aggregate on an existing paved surface. black. Chip spreader--Also referred to as a spreader box or aggre- Flakiness--A general description of the shape of aggregate. gate spreader, the machine that evenly applies the aggre- A flakiness index can be used to determine how cubical the gate to the binder. Self-propelled spreaders with comput- aggregate used in a chip seal is. A lower flakiness index erized rate controls are preferred. indicates a more cubical aggregate and better aggregate Choke--A layer of sand applied to the chip seal after the shape for a chip seal. cover stone has been rolled but before opening to traffic. Flushing--See Bleeding. Choke produces a tighter chip seal because it fills surface Fog seal--An application of asphalt applied on top of a pave- voids. ment surface. Fog seals are commonly used on oxidized Choke stone--A layer of smaller size aggregate applied to pavements to provide resistance to water intrusion and the chip seal after the cover stone has been rolled but raveling. Fog seals are also used on newly constructed before opening to traffic. Choke stone fills the voids on the chip seals to promote adhesion and enhance aggregate surface and "locks in" the cover stone against dislodge- retention. ment that is the result of rolling in areas with traffic turn- High float emulsions--Emulsions that result in a thicker ing movements. Also called "sacrificial stone" or "scatter asphalt film and are believed to show less susceptibility to coat." the defects associated with unclean and dusty aggregate.

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72 The thicker asphalt film characteristics result in high float Precoated aggregate--Aggregate precoated with asphalt emulsions preventing drain-off of the binder. cement to improve the adhesion of the aggregate to the Hunger factor--Kearby chip seal design terminology to binder on dusty or dirty aggregate. describe the existing surface's potential to absorb binder Prespraying--Australian terminology for shooting a prepa- and thereby require an adjustment in the design binder ration coat of binder outside and between the wheelpaths application rate to ensure that either sufficient binder is to adjust the surface texture of the previous chip seal to a applied to achieve desired embedment when the surface is uniform transverse depth. oxidized or that too much binder is not applied if the sur- Preventive maintenance (PM)--A planned strategy of cost- face is flushed. effective treatments that preserves and maintains or Geotextile seal--Geotextile-reinforced seals are used over improves a roadway system without substantially increas- cracked and weak surfaces. They provide a waterproofing ing structural capacity. membrane that not only seals the underlying moisture- Racked-in seal--A surface treatment where the first course, sensitive base material from water infiltration, but also which has a larger nominal size aggregate, is locked in aids in retarding reflective cracking. with a light application of smaller aggregate. This is par- Glass fiber chip seal--A chip seal that entails blowing glass ticularly useful for increasing aggregate retention during fibers onto an application of a binder, with the aggregate the curing process. being spread quickly after this application. Characteristics Raveling--Commonly referred to as shelling, it is the loss of of this seal are similar to a geotextile-reinforced seal. aggregate from the surface treatment. Low binder applica- Inverted seal--An Australian term for a seal that is used to tion rates, inadequate rolling, cool weather construction, correct flushing or bleeding pavement surfaces. and incompatible binder and aggregate types are common Ionic compatibility--Different types of aggregate are better factors that lead to raveling. suited to certain binders as a result of electrostatic charges. Reseal--A term used in New Zealand to describe a process For sufficient adhesion, the binder and aggregate must for recycling chip seals, in which construction methods are have opposite charges. designed to minimize the bleeding and flushing character- Lightweight aggregate--A synthetic granular material that istic of sealing over an existing seal. Sandwich seals and can be used to replace natural aggregates as the cover water blasting are two construction methods used by a stone for a surface treatment. These materials have a low reseal. specific gravity and do not have the same potential for Rock land--The length over which one truck's load of windshield and vehicle damage. aggregate is spread when spread at the design aggregate Lump-sum contract--A contract whereby the contractor is application rate. required to furnish a single sum for the cost of completing Sacrificial stone--See Choke stone. the scope of work described in the plans and specifica- Sand patch--A test for determining texture depth of a pave- tions. The contractor assumes the risk that in the event ment surface (refer to ASTM E 965). Also known as the actual quantities exceed the contractor-estimated quanti- sand circle test. ties the contractor is not paid extra. Modified binder--Binder modifiers that include polymers, Sand seal--An application of a binder followed by a sand latex, rubber crumb, and antistripping agents. Modifiers cover aggregate. have proven successful at enhancing flexibility, minimiz- Sandwich seal--A two-course surface treatment where ing bleeding, increasing aggregate retention, and extend- aggregate is spread on an existing binder rich surface, ing the service life of chip seals. before the application of a single-course surface treatment. Otta seal--A Norwegian term, adopted in many places Scatter coat--See Choke stone. including parts of Africa and the United States, that Seal coat--A bituminous surface treatment that is a single describes a low traffic volumegraded aggregate surface application of bituminous binder and cover aggregate on treatment. an existing paved surface. A seal coat is essentially a single- Pavement preservation--The sum of all activities undertaken course chip seal. to provide and maintain serviceable roadways. This Shelling--See Raveling. includes corrective maintenance and preventive mainte- Shot--The distance that a distributor sprays binder from start nance, as well as minor rehabilitation projects. to finish. Pneumatic roller--Pneumatic rollers have inflated tires that Slurry seal--A mixture of graded aggregate and binder provide the required forces to properly orient the cover applied with a squeegee or broom device. Slurry seals are aggregate. Also referred to as a rubber-tired roller. commonly used for mass crack filling or on pavements Pocked--A condition in which the surface of the chip seal with highly oxidized surfaces that are raveling. has lost aggregate in numerous localized areas. Spray bar--A series of spray nozzles at the rear of the dis- Polymer-modified binders (PMBs)--Polymer modification tributor that serve to spray a fan-shaped pattern of binder of binders reduces the binder's temperature susceptibility, directly on the road surface. Typically, a double- or provides increased adhesion characteristics, and increases triple-lap spray pattern is desirable. It is critical for the the overall flexibility of the chip seal. Common polymers spray bar to be properly adjusted and at the correct used are latex and crumb rubber. height.

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73 Sprayed seal--Australian term, essentially synonymous with treatment. It is an application of asphalt binder and cover a chip seal, that refers to the application of a bituminous aggregate on a prepared gravel or crushed stone base. binder and cover aggregate on various surfaces. Texturizing--An Australian/New Zealand practice whereby Steel roller--Steel rollers provide a rolling energy necessary excess binder is removed before chip sealing to allow a for some surface treatments such as those with rubber constant rate of binder to be shot during binder application crumb modifiers. Care must be taken to ensure that aggre- operations. gate is not being crushed or degraded by the steel roller. Unit-price contract--A construction contact whereby the Also referred to as a flat-wheeled roller. contractor furnishes unit prices (i.e., dollars per pay unit) Streaking--An aesthetic and construction defect caused by for each pay item in the contract, and the contract is nonuniform application of binder across the lane width. awarded to the lowest bidder computed by multiplying the Streaking leads to a considerable shortening of the life contractor-furnished unit price with the engineer's esti- expectancy of a chip seal. mated quantity for each pay item and extending that to a Stripping--Separation of the binder from the aggregate. See total bid price. The contractor is then paid its unit price for Raveling. the actual quantities even if exceeding the engineer's esti- Surface dressing--Term used in the United Kingdom, essen- mated quantities. tially synonymous with a chip seal, to describe the appli- Variable spray bar--A spray bar whose purpose is to put cation of binder and aggregate as a means of maintenance more binder outside the wheelpaths to combat raveling on flexible pavements. outside the wheelpaths and bleeding within the wheel- Surface enrichment--A light application of a bituminous paths. material, without the use of a cover aggregate, to an exist- Void--The space between the aggregate particles after they ing chip sealed surface to increase the binder content of the have been spread on the road's surface that is filled with seal. Essentially the same as a fog seal, surface enrichment binder. can assist with aggregate retention on seals with insuffi- Wheelpaths--The longitudinal areas of a pavement's surface cient binder. where the greatest proportion of vehicle tires track. Wheel- Surface texture--The macroscopic and microscopic charac- paths are particularly sensitive owing to bleeding and teristics of the pavement surface. Surface texture depth is flushing when application rates are not strictly adhered to, a metric that influences material application rates, design or when flaky or elongated aggregate has been used. life, skid resistance, and road noise. Whip-off--McLeod's definition for aggregate loss owing to Surface treatment--A surface treatment, commonly referred traffic dislodging the aggregate during and shortly after to as a bituminous surface treatment or asphalt surface construction.