A very difficult surface maintenance job is restoring utility cuts because the soil has been excavated and then replaced in a loosened condition. Until the replaced soil has been adequately compacted - progressively in layers with vibratory rollers, or by the pounding of traffic - settlement and resulting depressions are inevitable and most unsatisfactory. It is extremely frustrating to public officials and especially to the road superintendent to see a newly placed pavement torn up soon thereafter by a utility agency. When road repaving projects are being contemplated, enlist the cooperation of utility companies early so any needed subsurface work can be completed before new pavement is placed.
Most failures in asphalt surfaces begin with a minor crack or series of cracks. These cracks can progress to secondary cracking and depressions or bumps that increase impact loading, and then progress further to potholes and total failure. Proper crack maintenance can minimize or prevent many of these failures.
The first signs of weathering or fatigue cracks may be a mere shadow of moisture when the pavement surface dries following a rain. Unless these cracks are treated immediately, they will progress by raveling (due to frost and repeated wheel loads) until spalls develop. These will deepen and lead to water ponding that will penetrate the pavement, soak up the base, and eventually cause pavement failure.
Thermal cracks develop as temperatures cause the pavement to expand and contract. These cracks generally penetrate full thickness of the pavement. Thermal cracks less than 1/4 in. wide may not be visible at legal highway speeds but they will allow large quantities of moisture to enter the surface and penetrate the base. Moisture entering the small cracks will freeze and expand, fracturing the asphalt pavement structure. Repeated axle loads over this saturated and fractured area will cause the free moisture to flush the asphalt cement and fines from the mix and carry it away leaving voids. These voids will cause secondary cracking on the surface.
Excess moisture that flows through the pavement, saturating the base and sub-grade, causes frost heaves in the winter and instability following rains. The moisture works like a cancer, destroying the structure needed to support the loads. This moisture must be kept out.
Asphalt patching can be done using paint patching techniques to seal small surface cracks or ravels, penetration patching for deeper and larger failures, or premixed hot- or cold-applied patching compound.
Reconstructing and resurfacing old bituminous wearing surfaces is a very important phase of modern highway construction, since many existing surfaces that have become rough or otherwise inadequate may continue to function satisfactorily when properly resurfaced.
Surface treatment mats are thin and therefore breaks in them should be repaired promptly. The patrol system is best suited to this type of maintenance. Equipment should include a heating kettle with spray nozzles, a light truck equipped to carry aggregates, small tools, material for the patches, and traffic safety equipment.
Retreatment must be made at intervals. For this work, bituminous distributors, spreaders, and rollers are needed, and usually a grader or maintainer. Premixed material or limestone asphalt in a thin coat, 16 to 40 lb per sq yd, is commonly used in routine retreatment operations of this type.
With the macadam aggregate type of road mix, it is usually better to use pre-mixed material for patching and repairing small holes. On larger areas, a mix about the same as that employed in the original surface is used. If there is much raveling, a thin surface may be applied.
To permanently patch potholes or depressions in the surface, the pavement may be heated by infrared units until it is soft and rakable, then add the required amount of new hot plant mix, rake to grade, and compact the area. This technique may also be used to correct alligatored pavement.
With the dense graded aggregate, raveling may be caused by insufficient binder. In each case scarify the surface, add a small additional amount of bituminous material, and mix and replace the aggregate. Shoving under traffic may be due to excess moisture in the mixture when it was placed or to improper curing. In the first case, scarify and add and work in enough aggregate to make a properly proportioned mix; if there is excess moisture in the mix (more than 1 1/2 percent will usually cause trouble), scarify and allow to dry out, then respread and compact.
The supervisor should document the pothole repair work. Proper record keeping of what type of materials were used, how much material was used, what the work site conditions were, how long the repair lasted, etc., will enable management to decide what if any changes are needed in that area in the future. Accurate record keeping will help the agency to make the best use of its money while ensuring a longer lasting repair.
Contraction or other movement of the base and sometimes drying out of the surface may cause cracks. When caused by base contraction or movement these usually run across the pavement; when caused by drying out or shrinkage of the surface, the cracks are irregular and may run in any direction. In case the base is at fault, remove the surface and rebuild the base. A mat or reinforcement placed in the base will help prevent repetition of cracking.
Small surface cracks should be brushed full with a lean mix of sand and two to four percent by weight of cutback asphalt. When poured, these small cracks are unsightly and usually the crack is not filled. Wider cracks can be filled with the sand-asphalt mixture after careful cleaning, preferably with an air jet, and poured. A hot smoothing iron may be run over the crack after pouring. Where cracking is very extensive a surface treatment may be applied, but first determine the cause. Geotextiles or engineering fabrics have successfully controlled reflective cracking and chronic pothole areas on many occasions. Geotextiles are discussed in section B-1.
Asphalt patching mixtures are prepared by Akzo Nobel - Asphalt Applications, Inc.; Canadian Protective Products; Chevron U.S.A. Products Co., Asphalt Div.; Garon Products, Inc.; Grappler Specialty Products; PERCOL Polymetrics Inc.; Pioneer Products Inc.; ReClaim, Inc.; Transpo Industries, Inc.; U.S. Pro-Tec, Inc.; Unique Paving Materials Corp.; Witco Corp.
Membranes for inhibiting reflective cracking are supplied by Bayex, a div. of Bay Mills Ltd.; Erosion Control Systems, Inc.; Owens-Corning Fiberglas Corp., Tank Div.; Phillips Fibers Corp.; Royston Laboratories, Div. A cold-applied, self-adhering pavement repair material for asphalt and concrete surfaces is offered by Tapecoat Co.
A base mastic material combined with a fiber reinforcement system to handle reflective cracking is supplied by Contech Construction Products Inc.
Asphalt reconditioners, binders, sealers, recycling agents, crack fillers, and asphalt overlay materials are supplied by Witco Corp. Asphalt surface restoration treatments and crack sealants are available from W. R. Meadows, Inc. A cold-applied asphalt crack sealant is available from Owens-Corning Fiberglas Corp., Tank Div.
"Boni-Fibers" from Kapejo Inc., are heat-stable polyester fibers that can be mixed into asphalt concrete to inhibit reflective cracking.
Infrared heaters are valuable aids in patching operations. They are used to soften and recondition the existing pavement near the patch to facilitate its blending and bonding with the newly added patch material. The technique is said to eliminate the need for future maintenance and present a reduced traffic hazard to the public. A close-graded asphaltic concrete binder six or more inches deep can be substituted for the traditional concrete slab to bridge a backfilled excavation. After it is compacted, the binder patch is inspected regularly to check on settlement.
Once adequate compaction, as revealed by lack of settlement, has been achieved, a maintenance crew moves in with an appropriate propane-fired heater and applies in-frared heat to the pavement for three or four minutes. Immediately thereafter, the softened material is raked and capped with a dense plant mix of hot asphaltic concrete, which has been transported and stored in a heated trailer. The new mix and the softened older material are rake-blended and then compacted with a portable vibratory compactor. In this fashion, a permanent patch is provided without the need to remove temporary patching and in less time than was formerly required.
Another patching aid is the use of foamed asphalt. The addition of cold water into hot asphalt causes the mixture to foam. Reportedly the foamed mix has superior mixing and coating abilities and requires less asphalt. Also, aggregate selection is apparently not as critical as the material has been used with wet or dry aggregates of varying quality, without washing or screening. The foam mix can be stockpiled for future use.
Manufacturers of tar and asphalt kettles and miscellaneous asphalt tools are Aeroil Products Co., Inc.; Asphalt Equipment Co.; Inc.; Huber Essick; Marathon Road Maintenance, A Div. of Marathon Equpt. Ltd.; RGS Consolidated Industries, Inc.; Roofing and Contractors Equpt. Co.; Rosco Mfg. Co.; Stepp Mfg. Co., Inc.; Tarrant Mfg. Co., Inc.
Joint/crack sealing equipment for asphalt pavements is supplied by Aeroil Products Co., Inc.; Cimline Inc.
Road maintenance vehicles that provide hot patching mix at the job site are furnished by Aeroil Products Co., Inc.; Marathon Road Maintenance, A Div. of Marathon Equpt. Ltd.; Midland Machinery Co., Inc.; Roofing and Contractors Equpt. Co.; Spaulding Mfg., Inc.
Asphalt pothole patching machines are supplied by Akzo Nobel - Asphalt Applications, Inc.; BPI-LAB Inc.; Crafco, Inc.; Cutler Engineering, Inc.; Duraco Ind., Inc.; Ejecto Corp.; E.D. Etnyre Co.; E.L. Hilts & Co.; H.D. Industries Inc.; B.R. Lee Ind. Inc. d/b/a/, Lee-Boy Mfg. Co.; Linear Dynamics Inc.; PB Loader Corp.; Process Heating Co.; RGS Consolidated Industries, Inc.; Ridley Asphalite Corp.; Roadpatcher Wildcat; Rosco Mfg. Co.; Sweeprite Mfg. Inc.; VIBCO, Inc.; Wildcat Mfg. Co., Inc.; Zimmerman Equpt.
Manufacturers of infrared patchers include Aeroil Products Co., Inc.; Poweray Infrared Corp.; Roofing and Contractors Equpt. Co. Trailer-mounted infrared heaters, reclaimers, and storage boxes are available from Ray-Tech Infrared Corp.
Asphalt cutters are supplied by Allied Construction Products Inc.; Arrow-Master, Inc.; Attachments Int'l.; Barrett Diamond Products, Inc.; Construction Technology, Inc. (CTI); General Equpt. Co.; Guest Industries, Inc.
Smooth wheel rollers in the 1- to 3-ton category are offered by BOMAG (products of Compaction America, Inc.) A United Dominion Co.; Beuthling Mfg. Co.; Caterpillar Paving Products Inc.; Champion Road Machinery Ltd.; Dynapac Mfg.; Eager Beaver; Gehl Co.; HYPAC (products of Compaction America, Inc.) A United Dominion Co.; Huber Essick; Ingersoll-Rand Co., Road Machinery Div.; M-B-W, Inc.; Mauldin Brothers Equpt., Inc.; Multiquip Inc.; Rosco Mfg. Co.; Stone Construction Equpt. Inc.; Vi-bromax 2000 (USA) Inc.
Vibrating tampers for use on asphalt patches are offered by J I Case Co.; Dynapac Mfg.; E.L, Hilts & Co.; Ingersoll-Rand Co., Road Machinery Div.; M-B-W, Inc.; Stone Construction Equpt., Inc.; Wacker Corp.
Patching mixers are offered by Aeroil Products Co., Inc.; Akzo Nobel - Asphalt Applications, Inc.; Asphalt Equpt. Co., Inc.; Dispensing Technology Corp.; Muller Machinery Co., Inc.; Roofing and Contractors Equpt. Co.; Stone Construction Equpt., Inc.
Manufacturers of road widening equipment include Barber-Greene, Div. of Caterpillar Paving Products Inc.; Blaw-Knox Construction Equpt. Corp.; Midland Machinery Co., Inc.
Surface treatment is an economical type of roadway surfacing and under favorable conditions may have a reasonably good life expectancy. One fundamental principle is the fact that a surface treatment has little structural value and hence is useful only when the underlying base coarse is strong enough to carry the traffic load. Two very essential functions of a surfacing can be accomplished with the surface treatment: 1) create a waterproof layer; and 2) establish of a non-skid surface with adequate resistance to traffic abrasion. In addition, the surface treatment can be used to "liven up" an existing bituminous surface.
Any reasonably sound aggregate such as gravel, crushed gravel, crushed stone, or crushed slag can be used successfully for surface treatments. In general, the aggregate should be reasonably resistant to abrasion and a maximum Los Angeles abrasion loss of 35 is often specified. However, aggregates with losses up to 40 have been used successfully. Grading aggregate for surface treatment is important. The nature of the construction procedure is such that only one layer of aggregate will adhere. The average surfacing thickness will then be dependent upon the size of the aggregate. If the aggregate has an appreciable variation between the largest size particles and the smallest size of bitumen film sufficiently thick to hold, the largest size may completely submerge the smallest size. For this reason the aggregate should be uniformly graded throughout.
Particle shape is important in aggregates. Probably the ideal shape would be uniform cubical or pyramidal. Predominantly flat and elongated particles are undesirable. However, successful surface treatments have been produced with aggregates having various shapes and surface areas.
A very important characteristic of the aggregate is good adhesion between the aggregate and asphalt and the ability to retain this adhesion in the presence of water. The bitumen-aggregate contact is directly exposed to the action of surface waters, and stripping or loss of adhesion between stone and bitumen can be disastrous.
Experience is the best test of this aggregate quality. The immersion-compression test (ASTM D 1075-54, Effect of Water on Cohesion of Compacted Bituminous Mixtures) is valuable in predicting stripping characteristics, which are important to know.
Cleanliness is extremely important in surface treatment aggregates. If the aggregate at the time of placement is dusty or coated with silt and clay, adhesion problems will occur.
Wet aggregates should be avoided and the ideal situation is to place a hot, dry aggregate. Field conditions are generally such that cover aggregates will contain some moisture and their use in this condition therefore is often necessary. The presence of moisture in the aggregate is detrimental to adhesion but presents no serious field problem when the work is accomplished in warm dry weather, which promotes rapid drying. There is some evidence that dusty aggregates give better results when placed damp than when placed dry. The dust is bound to the stone surfaces and thus does not tend to form a film over the surface of the bitumen. For this reason, many field personnel when faced with the necessity of using dusty aggregates wet them down before application.
The construction procedure is simple. It consists of the following:
1. Base preparation.
2. Application of bituminous material.
3. Aggregate spreading.
Like many other forms of bituminous construction, surface treatments are best done in hot, dry weather. Both the surface to be treated and the aggregate should be essentially dry, except that when asphalt emulsions are used they may be damp.
Thoroughly compact new surfaces before applying a surface treatment. The base course must be able to carry the traffic loads and structural adequacy should be assumed before surfacing. It is good practice to place a prime coat on a new surface to promote good adhesion of the surface to the base and eliminate absorption of bitumen into the base. If the surface treatment does not follow closely after the prime, the surface should be cleaned.
Patch existing bituminous surfaces and clean by brooming before applying a seal coat. A seal coat cannot be used to level existing surfaces since it has no structural quality.
Asphalt sealants are supplied by Akzo Nobel - Asphalt Applications, Inc.; PM Supply; U.S. Pro-Tec, Inc.; Witco Corp.
Modern distributors, properly operated, will do a good spreading job. Distributor speed should be measured by a fifth-wheel tachometer. The tachometer should be checked by operating the distributor over a measured course of at least 1,000 ft at the speeds of application.
Application of bitumen should begin and end on paper to obtain straight joints without overlapping applications. During actual shooting operations, each fan should be a solid sheet of asphalt from the nozzle to the roadway surface. This can be obtained with proper nozzle size, proper pump pressure, and proper distributor speed. Adjust the total length of the shot to that which can be covered promptly with cover aggregate. A string line placed along the side of the road is used to guide the distributor operator: the engineer should establish a nail line about 2 ft outside the area as a guide in setting the string line.
One other important factor, often overlooked in applying bitumen, is the necessity of having proper viscosity at the time of application. Proper viscosity for application is the subject of some difference of opinion with values of 40 to 60 and a 30 to 100 seconds Saybolt Furol at the nozzle being quoted.
If a value of 50 to 60 seconds is chosen, the temperature at which a given material should be applied is fixed. There are appreciable variations in the temperatures at which different materials meeting the same specifications reach this viscosity. As an example, the temperature required for a viscosity of 50 seconds Saybolt Furol varies from 268 [degrees] to 325 [degrees] for the 210 to 250 penetration asphalt cements commonly used for surface treatments. Field engineers placing surface treatments should obtain viscosity-temperature curves for the materials being used.
Manufacturers of bituminous distributors include: E. D. Etnyre Co.; W. E. Grace Mfg. Co.; E.L. Hilts & Co.; Marathon Road Maintenance, A Div. of Marathon Equpt. Ltd.; PB Loader Corp.; Rosco Mfg. Co.
Bituminous Spray Systems
Spray systems for use with asphalt products are manufactured by Aeroil Products Co., Inc.; Cimline Inc.; E. D. Etnyre Co.; Bob Fisher Enterprises Inc.; E.L. Hilts & Co.; Huber Essick; Marathon Road Maintenance, A Div. of Marathon Equpt. Ltd.; Midland Machinery Co., Inc.; PB Loader Corp.; Rosco Mfg. Co.
Sealcoat application machines are available from Akzo Nobel - Asphalt Applications, Inc.; GRACO Inc.; Rosco Mfg. Co.; Sealmaster Inc.
Three basic types of spreaders are available. One type is the vane spreader, which is a steel plate fitted with vertical vanes and attached to the rear of a truck. Another type consists of a steel plate mounted on small wheels; the aggregate is dumped from the truck onto the steel plate, which revolves as the truck moves. Still another type is the hopper spreader, which consists of a hopper mounted over a steel roll with a small brush set along one side so as to regulate the flow of aggregate as the truck moves along. Other commercial types of spreaders are available. In any case, trucks should be backed over aggregate previously spread, so that there is no traffic over the fresh bituminous material. Be careful to see that a uniform spread of aggregate at the prescribed rate is achieved.
Manufacturers of aggregate spreaders for use in surface treatment operations are listed in Section B-1 of this manual.
Rolling seats the aggregate in the bitumen and thus develops the bond between aggregate and bitumen that is necessary to resist the traffic stresses. Both flat wheel and pneumatic rollers have been used successfully. Some engineers recommend initial rolling with a flat-wheel roller while others follow the reverse procedure. The important requirement is early and adequate rolling.
Broom dragging to spread the aggregate should not be allowed before initial rolling, as it tends to shift the small particles to the bottom and prevent adhesion of the larger particles. After initial rolling the broom drag may be used to distribute loose aggregate and promote maximum retention. The broom drag must be operated quite slowly, 4 miles per hour or less, to prevent bouncing which leads to an undesirable rhythmic surface roughness. During warm weather, broom dragging and rolling may be continued for several days.
Excess aggregate may be removed after all rolling is completed by lightly brooming with a rotary broom during the cool of the early morning. This operation must be performed with care so that the bond of the properly cemented aggregate is not broken.
When a greater thickness of mat is desired on new construction, without the tire noise due to the use of a single larger aggregate, double and triple surface treatments may be used. This type of construction will produce surfaces with thicknesses up to about 1 1/2 in., which, if placed on a good base, can carry rather large traffic volumes for up to 10 to 15 years.
When multiple applications are used, it is essential that each succeeding aggregate nest with the layer previously placed so that the completed construction will form a nearly compact mass with a dense, tight surface. The success of this type of construction depends upon this nesting of the particles and the redistribution of the bituminous material through the mass. The largest size aggregate is placed in the lower course with succeeding courses using smaller aggregate. A good general rule is that the second course aggregate should be about half the size of the first course aggregate, and the third course aggregate half the size of the second.
Slurry seals consist of a finely graded stone aggregate, mixed with an emulsified asphalt or similar binder, applied without heat to the pavement surface. The small size of the aggregate and the nature of the highly fluid binder causes the slurry to penetrate into cracks and seal them, while bonding enough of the mixture on the surface to give a new surface to the street.
Engineers have recognized the potential of slurry sealing for years, but results were often greatly varied until the introduction, in 1960, of a machine expressly designed to mix and lay slurry on a continuous basis. It was found that best results are obtained when the mix-lay cycle is about 2 1/2 to 3 minutes. Longer mixing times tended to cause a "break" in the asphalt emulsion before the mixture was applied to the street. This led to an uneven application, either too rich or too lean in residual asphalt, inadequate bonding, or unequal distribution of aggregate.
The International Slurry Seal Association has published specifications for three basic types of slurry seal. Type I, a fine seal, with approximate application rate of 4 to 8 lb per sq yd based on dry aggregate weight, gives maximum crack penetration and filing properties with a very light surface course. Type II, a general seal, is most frequently used and is recommended to fill and seal surface voids, correct severe surface conditions and provide minimum wearing surface. Application rate should result in from 8 to 12 lb per sq yd. Type III slurry seal is suggested for highly textured surfaces that require heavier aggregate to fill large voids and give a moderate wearing course. Application rate should be 12 lb on the aggregate.
Mineral fillers of fines such as portland cement, lime dust, or fly ash are often added to slurry mixes. In figuring final mix design, all such fines should be considered part of the blended aggregate and should not constitute more than two to three percent by weight of dry aggregate.
Mixing grade emulsified asphalts, as specified by the Asphalt Institute are available throughout the country. Usual slurry seal applications specify types SS-1 or SS-1h, and all emulsion should be tested in accordance with AASHTO T-59-60, with an accepted viscosity range of 20-50. The amount of emulsion in the final mix should result in a residual asphalt content of as little as 6.5 to as much as 16 percent by weight of dry aggregate, depending on the characteristics of the aggregate used and the type of application.
Water is added to the mixture to bring it to a correct slurry consistency. In a continuous-flow machine, the water is introduced to the aggregate in the mixing chamber only seconds before the emulsion enters. This ensures complete prewetting of the aggregate and lets the asphalt of the emulsion to bond faster and more securely to the aggregate. Excessive water in the mix should be avoided to prevent settling of fine aggregates and to assure proper "break," or separation of water from the slurry seal mix.
Emulsified asphalts and manufacturers of the same are discussed in section B-3 of this manual.
Equipment for slurry sealing is manufactured by Akzo Nobel - Asphalt Applications, Inc.; Bergkamp Inc.; California Pavement Maintenance Co., Inc.
A versatile tool pioneered in Germany, micro-surfacing is a cold-mix paving system used to remedy a wide variety of problems on streets, highways, and airport runways. Like its parent product, slurry seal, micro-surfacing begins as a mixture of dense-graded aggregate, asphalt emulsion, water, and filler. Although conventional slurry seal is used as an economical treatment for sealing and extending the service life of both urban and rural roads, micro-surfacing has additional capabilities thanks to the use of advanced polymers and other modern additives.
Applications include increasing skid resistance, color contrast, and service life to high-speed, heavy-traffic roadways; filling wheel ruts up to 2 in. deep; and creating a new, stable surface that better resists rutting and shoving in summer and cracking in winter.
A specialized, self-contained machine is used to mix and apply polymer-modified micro-surfacing to existing pavements. Manufacturers include Akzo Nobel - Asphalt Applications, Inc.; Bergkamp Inc.
Cold Mix Paving
Cold mix paving finds its place, both functionally and economically, somewhere between surface treating or seal coating and hot bituminous concrete. Cold mixed pavements can and do fill important roles in highway maintenance applications, performing well in subgrade, binder, and wearing surface applications. Cold mixing is probably among the oldest paving methods, but is still a very desirable and workable solution to many paving problems. The work, however, must be done carefully.
The most desirable aspects of the cold mix paving process are attractive to municipal highway maintenance organizations and to contractors who support these activities. The process is particularly advantageous to the municipality in that the personnel in the normal maintenance work force and the equipment normally on hand can support the cold mix operation.
Equipment required to support a cold mix operation include dump trucks, a grader, a roller, a front end loader, and some sort of chip spreader. Some or all of these items will be required depending on the mixing method used. The mixing device can be a grader, for blade mixes; a rotary type tiller, mix-in place; stationary pug mill, for stock pile cold patch and lay down surface mixes; or traveling mix plant, for mixing and placing materials in one continuous operation. Where methods other than blade mixing are desired, equipment can be rented.
The advantages of the cold mix process are again evident when the remaining logistical requirements (aggregate and bituminous materials) are considered. Few aggregates are unsuitable for cold mixing of one sort or another. Bank run or graded natural aggregates as well as coarse and fine graded crushed mixtures, are common. Each coupled with an appropriate bituminous material, has a wide range of applications. Aggregate sizes can range from 2 in. to 200 mesh and can be used in single gradation or in combination depending on the desired mix design. The aggregate can also be prelocated at or near the paving site allowing optimum use of man-hours during inclement weather.
The bituminous material can be one of several types and grades depending on the chemical and physical properties of the aggregate and the mix design. If necessary, a bituminous product can be tailored to suit a specific aggregate or conditions. Liquid asphalt and road tars have been used extensively in cold mix operations. More recently asphalt emulsions are gaining favor as they tend to be more reliable over a wider range of aggregate and weather conditions, more economical to produce, and they can be handled at lower temperatures.
The cold mix operation lends itself well to unexpected interruption. If unexpected or poor weather conditions develop, the user needs only to mix the amount of material necessary to close down the job. The bituminous material can be returned to storage or held over; aggregate trucks can remain loaded or dumped, as convenient, and the operation can be suspended.
The application for cold mix designs are as varied as the materials in each different mix. Cold mixes are suitable and in many cases desirable for patching, truing and leveling operations, upgrading or reconstruction. Cold mix operations are totally flexible and can be supplied to any normal paving situation.
It has become increasingly difficult to close a road for reconstruction or maintenance. But with new, modern equipment and construction methods most roads can remain open to traffic and can be completed without sacrificing quality. A travel plant made by Midland Machinery Co., Inc. can mix and lay cold mix material in one continuous operation for fast completion of road work.
Hot Mix Overlays
Asphalt overlays provide are among the most cost-effective methods of improving existing pavements. Asphalt overlays can be used to strengthen existing pavements, to reduce maintenance costs and increase pavement life, to provide a smooth ride, to improve service to the user, and to reduce safety hazards by improving pavement surface skid resistance. In addition, asphalt overlays in conjunction with widening and other geometric improvements, can be used to increase roadway capacity and further improve safety.
Asphalt overlays can provide major economic advantages to both users and owners of roadway pavements. For users, both automobiles and commercial vehicles are more fuel-efficient and require less maintenance when operated on safe, smooth pavements. For owners, more miles of modern roads can be provided. In addition, roads can remain in use while being modernized with asphalt, and old roads frequently can be improved and put back into service in a shorter time for less cost than new roads can be built, providing economic advantages to both owner and taxpayer.
The major reasons for overlaying otherwise adequate pavements are excessive permeability, surface raveling, surface roughness, and surfaces with low skid resistance.
Evaluating the condition of the road, both geometrically and structurally, is the essential first step in planning the improvement. The term "pavement condition," for the purpose of overlay design, is considered to include measures of skid resistance, ride quality, structural capacity, and surface distress. "Surface distress" includes raveling, cracking, and channeling (rutting) or other forms of asphalt pavement distortion; in portland cement concrete pavements it includes cracking and spalling, pumping and faulting at joints. Evaluating pavement condition involves assessing the current state of these distress conditions and estimating their future state, or the time when the distress will reach a critical or terminal level; at this time an overlay usually will be required.
Not all measures of pavement condition will reach a terminal level at the same time. For example, a structurally sound asphalt pavement may have a low resistance to skidding, which may be corrected with a thin overlay. A pavement having considerable distress caused by an inadequate structural thickness will require a thicker overlay. In a broader sense, the condition evaluation will help in setting priorities for overlays or other rehabilitation measures.
These evaluations should extend to all roads in the system. Road evaluation includes consideration of geometric adequacy and surface condition of the road, as well as its structural adequacy and current and future use. Geometric adequacy may be evaluated by studying the construction plans, by field inspection, by photographic inventory techniques, or by all these methods. Many older roads were designed for lesser traffic volumes and slower speeds than those of today. If a geometric evaluation shows that a pavement has become inadequate for modern traffic because the lanes are too narrow, the curves are too sharp, the sight distance too short, or if the surface is distorted, the deficiencies should be corrected. In all such cases, asphalt pavement construction can be used to widen, improve alignment, re-establish cross-section and improve shoulders for any type of existing pavement structure. Surface condition usually must be evaluated by field inspection; however, the photographic inventory method can also be used to record surface condition. Structural adequacy may be evaluated by studying both surface condition and pavement components or by measuring pavement deflection. To determine if a road is presently serviceable or will serve adequately for a projected period, all the evaluations - surface condition, structural adequacy, and geometric adequacy - may need to be performed. When an informed judgment is made as to what is needed, the most economical improvements can be planned and carried out.
The preceding information was taken from publications available from The Asphalt Institute, Research Park Drive, P.O. Box 14052, Lexington, KY 40512-4052.
Multi-Purpose Asphalt Equipment
Because maintenance systems are increasingly important, new equipment is constantly being developed for such operations. Specialized units are available from B.R. Lee Ind. Inc. d/b/a/, Lee-Boy Mfg. Co.; RGS Consolidated Industries, Inc.