Difference between revisions of "Category:470 Bituminous Asphalt Maintenance"

Bituminous asphalt maintenance consists of the restoration and repair of the pavement roadway surface and base within the traveled portion of the roadbed or within the portion that lies between the inside edges of the shoulders. Bituminous asphalt maintenance may be preventive or corrective, and must be given first priority. Lack of proper and timely maintenance contributes to increased failures, presents a hazard for traffic, and contributes to adverse public opinion. Asphalt surfaces shall be maintained smooth and safe and as true to type, cross-section, alignment, and grade as originally constructed or within limitations.

470.1 Bituminous Surface Types

The asphalt surface of the roadway consists of the wearing course placed over the sub-grade or on a prepared base. The basic asphalt surface type classifications are bituminous surfaces including surface treatments, bituminous mats, and asphaltic concrete decks or pavements.

Bituminous surfaces are classified according to the type and makeup of the wearing surface. All wearing surfaces are placed on some type of prepared base, and the thickness and stability of this base usually has a direct influence on the life of the surface. There are three main types of surfaces.

LOW-TYPE BITUMINOUS SURFACES - Low-type bituminous surfaces are those produced by surface treatment with light road oils or liquid bituminous materials such as oil earth, oil aggregate, seal coats, and leveling courses. Each surface treatment being less than 1 in. in thickness.

INTERMEDIATE-TYPE BITUMINOUS SURFACES - Intermediate-type bituminous surfaces consists of a plant-mixed machine laid surface. The thickness of the surface course is usually greater than in the low-type classes, and may consist of one or more bituminous courses. The base course may be of the same material as described for the low-type bituminous surface.

HIGH-TYPE BITUMINOUS SURFACES - High-type bituminous surfaces consist of asphaltic concrete (dense and open graded) mixes, machine laid. This type of surface, because of traffic loads, usually require a more substantial base than low and intermediate types. The base may be of either rigid or non-rigid design. The surface wearing course is usually 1 1/4 in. or more in thickness.

470.2 Asphalt Surface and Roadbed Widths

Asphalt surface and roadbed widths shall be maintained according to their constructed widths. Uniformity in width is especially important at district and maintenance area boundaries. Efforts must be made to prevent abrupt changes in widths at these and other locations.

Low type bituminous surfaces are normally built and resurfaced by maintenance forces, and it is important that uniform surface width be established.

Surface width of high type bituminous surfaces is fairly well established when constructed. At some locations spot widening may be desirable to improve safety.

Roadbed width, which includes the width of the roadbed and shoulders, should not exceed current design standards without approval from the District Engineer. In some cases, it may be desirable and economical to widen roadbed widths during heavy ditching operations, and the widening of roadbeds less than 24 ft. in width is encouraged. Spot construction of bridges and culverts to new design standards may also make widening of the remaining portion of the roadbed desirable. The possible effect on traffic safety must be taken into consideration prior to widening any surface or roadbeds that have numerous bridges or culverts that limit the overall width.

In no case shall surface or roadbed widths be decreased from the widths constructed or reconstructed. For more information regarding lane and shoulder widths, see Typical Section Elements for Roadways.

470.3 Types of Bituminous Materials

A working knowledge of the characteristics of all bituminous products employed in maintenance operations should be understood for satisfactory and efficient maintenance of bituminous surfaces. Quite as important as the type of bitumen to be used in surface maintenance is the selection of an aggregate having desirable qualities such as proper size and gradation, wearing qualities, adhesive quality, cleanliness, etc.

All bituminous surfaces should be repaired with materials best suited for the job. All materials used shall meet standard specifications unless otherwise approved by the State Maintenance Engineer.

AGGREGATE - Aggregate for bituminous surfaces shall meet standard specifications unless otherwise approved. Modification should be held to a minimum, but may be approved if justified and necessary. For specific jobs, a specific aggregate, limestone or gravel, may be approved, otherwise consideration must be given to both limestone or gravel as available. In addition, slag, trap rock and lightweight aggregates (haydite) may be used in special applications.

ASPHALT - Asphalt is a natural constituent of most petroleums in which it exists in solution. The crude petroleum is refined to separate the various fractions and recover the asphalt. Natural deposits of asphalts are also found in various parts of the world, some practically free from extraneous matter. Natural deposits in which asphalt occurs within a porous rock structure are known as rock asphalts.

All asphalt used for maintenance operations is refined from petroleum and must meet standard specifications. It is produced in a variety of types and grades with the three major types being asphalt cements or penetration asphalts, liquid asphalt, and asphalt emulsions. Liquid asphaltic products are prepared by cutting back or blending asphalt cements with petroleum distillates, and asphalt emulsions are prepared by blending (homogenizing) asphalt cement with water.

1. PENETRATION ASPHALTS - These are asphalt cements with varying degrees of hardness or consistency. Penetration is determined by a penetration test which measures the distance a standard needle will penetrate vertically into a sample of asphalt under known conditions of temperature, loading, and time. It is evident that the softer the asphalt cement, the higher the penetration will be. Penetration asphalts are listed in Standard Specifications as 40-50, 60-70, 85-100, 120-150 and 200-300 penetration.

2. LIQUID ASPHALT MATERIALS - Liquid asphaltic materials are produced by cutting back or blending asphalt cement with petroleum distallates or by emulsifying with water. The liquid asphalt materials used are:

a. RC Cut-Back Asphalts, Rapid Curing Type - This material is produced by cutting back asphalt cement with naptha or gasoline-type distillate. This distillate evaporates more rapidly than kerosene, and this type of cut-back is known as rapid curing.

RC cut-backs are often used for seal coat work. Lighter grades are also used for tack, fly, and prime coats. AASHTO designations are RC 70, 250, 800 and 3,000.

b. MC Cut-Back Asphalts Medium Curing Type - This material is produced by cutting back asphalt cement with kerosene type material. The presence of kerosene makes the asphalt workable in a relatively low temperature. The kerosene evaporates slowly when exposed to air and to heat leaving the asphalt cement intact. Medium curing cut-backs are commonly used for maintenance repair work, maintenance leveling course (road mix or pre-mix) and cold patch mix. AASHTO designations are MC 30, 70, 250, 800 and 3,000.

c. SC Cut-Back Asphalt Slow Curing Type or Road Oils - This material may be asphaltic residual oil which contains little or no volatile portions, or it may be a blend of asphalt cement and residual oil. The slow curing liquid asphalts are used mostly for dust alleviation work. The lighter grades have relatively poor binding characteristics and do not form a hard mat when used for dust alleviation work. AASHTO designations are SC-70, 250, 800 and 3,000.

The rapid curing and slow curing asphalts all come in four grades while the medium asphalts come in five grades. The higher the indicating number, the greater the percent of asphaltic cement and more viscous the material.

3. ASPHALTIC EMULSIONS - Emulsified asphalt may be either anionic (negative) charged asphalt globules or cationic (positive) charged clobules, types depending on emulsified agents. The major types are RS, MS, and SS indicating rapid, medium, or slow setting.

COMMERCIAL PLANT MIX - Plant mix asphaltic concrete mixes or other commercial plant mixes shall meet standard specifications or be approved after consultation with or tests made by the Field Material Engineering Section. The use of small quantities on a trial basis is recommended for untried commercial mixes. If approved for use, the production of commercial plant mixes should be inspected and controlled closely.

BLADE MIX - Blade mix material is normally used for all patching on low-type bituminous surface due to the economy. It shall be mixed on "mixing boards" off the roadway surface if large quantities are desired for future use as patch material. Blade mix materials for blade seals, leveling courses, or spot decks are normally mixed on the roadway at the time needed.

PRE-COATED AGGREGATE - Pre-coated aggregate or "half-mix" for use during adverse weather or ground conditions has proved successful. It is produced by blade mixing the aggregate with just a sufficient quantity of asphalt to precoat the aggregate and exclude moisture until such time as it is needed for sealing or patching. It is used as is for sealing or with additional asphalt added, just prior to use, for patch material.

SAND-ASPHALT MIX - A sand-asphalt mix called "Black Annie" or "Hannibal Rock Asphalt" has proved very useful for certain types of patching on asphaltic concrete and concrete surfaces. It can also be used for filling spalled or open joints and cracks but not for expansion joints. It is not recommended for deep patches, unless larger aggregate is substituted for a portion of the sand, or for use on low type surfaces due to the cost. This mix is prepared as follows:

Materials:

1000 lbs. - Sand

250 lbs. - Agricultural lime

1/2 sack - Portland cement

10-12 gallons - MC-250 asphalt

The sand, lime, and cement must be dry and mixed thoroughly in a pugmill or by hand. MC-250 is added at pouring temperature and the exact quantity will depend on working temperature. Mixing is continued until complete. The material may be used immediately or place in a stockpile for future use. Stockpiling for future use will require reheating.

470.4 Changing Grades of Asphalt

It is necessary at times to change the grade of asphalt in the field for emergency use. While this practice is not recommended for extensive use, the percentage or quantities of kerosene to add to the available grade may be determined from the following formula or table.

${\displaystyle X={\frac {100\times (a-b)}{100-b}}}$

Where:

X = Percent of kerosene to be added

100 - X = Percent of available grade to be added

a = Percent kerosene in desired grade

b = Percent kerosene in available grade.

Note: a and b are determined from residue percentages given in Standard Specifications.

The quantities to mix as obtained by use of this formula for reducing MC-3000, MC-800 and MC-250 to lower grades are as follows:

470.5 Types of Bituminous Failures

All bituminous surface failures with the exception of raveling and oxidation can be attributed to a base or subgrade failure, either because of improper materials, poor construction, under-design, or the influence of moisture.

Breaks, potholes, and settlements in the surface may be due to inadequate base or to continued lack of support due to moisture in the base and subgrade. Edge failures often result from a reduced thickness of the base and deterioration of the base along the shoulder due to porous shoulders, inadequate drainage, and lack of lateral support. High shoulders or the presence of a traffic rut at the edge of the surface may be contributing causes.

Slippery, bleeding and fat surfaces are caused by an excess of bituminous material and a dense surface texture. The excess may result from excessive bituminous material applied during construction, the loss of aggregate due to dampness and cold temperatures during application, the bleeding of fat patches, or stripping of aggregate material.

Ruts, corrugations, and other distortions of the surface may be due to an unstable or fat surface, inadequate base, or a base permeated by moisture.

Cracking may be due to brittleness of the surface, expansion and contraction as temperatures change or the presence of moisture in a base or subgrade that destroys stability.

Raveling usually results from poor aggregate which degrades badly, from lack of sufficient asphalt binder, wrong class of bituminous material, or from a dry oxidated surface.

Oxidized surfaces usually result from years of use and exposure to the elements.

470.6 Bituminous Surface Maintenance

Bituminous surfaces require continuous inspection so that preventive or corrective maintenance may be initiated without delay. This is of primary importance during the winter and early spring when low type bituminous surfaces with negligible bases are subjected to freeze-thaw cycles and after periods of wet weather. Every advantage should be taken of favorable weather during such periods to carry out repairs or preventive maintenance. Methods of maintenance will vary with the type of surface and base and type of failure but in all cases the quality and timing of maintenance will have a direct bearing on the life of the surface. Priorities for maintenance should be based on traffic volumes and degree of failure.

470.6.1 Traffic Controls for Bituminous Repairs

Traffic controls for bituminous repairs shall be according to the Traffic Control for Field Operations Manual. All standard signing shall be in place before operations start and shall remain in place as long as any hazards or inconvenience for traffic exists.

All windrows of premix left on the roadway edge or adjacent to the roadway shall be marked at intervals with required signing if left overnight. The windrows should be vented to avoid ponding of water on the roadway surface.

Extreme care must be exercised by all crew members, particularly by equipment operators, while working near at-grade railroad crossings. Working near at-grade railroad crossings shall be in accordance with department requirements. Coordination with the specific railroad company responsible for track maintenance is required to insure that the tracks are checked for damage and the flangeways cleaned of debris if necessary.

Operations shall be coordinated between areas and districts in order to complete blade seal and leveling course operations on specific routes to minimize the disruption to the traveling public. Every effort shall be made to complete work on major through routes or on heavy traffic sections as soon as possible. Consideration should be given to local activities such as fairs and carnivals and seasonal tourist attractions when scheduling major bituminous repair work.

470.6.2 Mintenance Limitations

The definitions and limitations for various types of bituminous surface repairs have been established.

Spot sealing and spot patching consists of spot sealing or patching small areas, and is to be done by Maintenance Forces.

Maintenance leveling course consists of mixing and laying from 3.0 cubic yards and not to exceed 5.0 cubic yards of aggregate per station. Work is to be done by maintenance forces.

Seal coats consist of applying asphalt to the roadway surface at a specified rate and covering the asphalt with aggregate. All continuous seal coats will be contracted and financed from the District Maintenance Budget.

Contract leveling course is based on 650 tons per mile, regardless of the width. For a route to qualify, it must meet the following:

1. A bituminous surface route without a constructed base.

2. Have a minimum of 225 ADT.

3. Have sufficient thickness to support this type surface and be relatively free of base failures.

4. Bituminous decks generally financed from Construction funds should be considered for improvement of bituminous surfaced routes on a constructed base.

The maintenance of bituminous surfaces includes maintenance of distorted surface and fat or slippery areas, sealing or pouring of cracks, priming and tacking to provide a bond for added surfacing, spot seal coating to correct dry oxidized gravel, cracked, or slick surfaces, and fly or fog coating.

470.6.3 Maintenance of Distorted Surfaces

Fat spots and areas often push and shove out of shape under traffic, forming ruts, troughs, ridges and corrugations. Distorted areas may also be caused by blowups and base failures in the concrete under asphaltic concrete upper decks. Distortion is usually more serious where vehicles are required to apply braking action. Procedures for repairs are as follows, and a regular program should be scheduled each year to correct distortions.

On low-type bituminous surfaces the distortions may be corrected by milling, cutting with blades, or in extremely bad cases by scarifying and relaying. In most cases, a new wearing course will have to be placed over the area to prevent reoccurrence. Milling, and blade cutting should be done in hot weather to obtain best results.

Corrugations or raised distortions on asphaltic concrete surfaces and high-type mats may be milled if the areas are small. For larger areas of raised distortion and corrugations, milling and replacement of the material with hot mix asphalt has proven very effective. If surface distortions are extensive consideration should be given to resurfacing by contract. If base failures are involved, the base condition should be corrected.

Raised or buckled joints occur on asphaltic concrete upper decks and are usually caused by the expansion of the concrete underneath. High joints should be removed or cut off at once by milling. The milled area should be sealed with asphalt mix to prevent deterioration of the milled surface. Joints which have buckled or deteriorated to such an extent that the condition cannot be corrected by millingwill have to be repaired.

470.6.4 Maintenance of Fat or Slippery Surfaces

Fat spots or slippery areas develop occasionally in all types of bituminous surfaces and result from a variety of causes. They may result from the application of too much bituminous material, from improper gradation of the aggregate, or the degradation of the aggregate. Heavy traffic has a tendency to flush bituminous material to the surface, or under certain conditions will tear aggregate from the surface leaving an excess of bituminous material. Also there are cases where aggregate is soft and wears down and polishes under traffic leaving a slick surface. Regardless of cause, fat spots and slippery areas are a serious traffic hazard. In extremely hot weather, they bleed and in wet weather they become slick. In heavy traffic, urban areas light oil films deposited by vehicles also add to the problem especially at approaches to signalized intersections.

On low-type bituminous surfaces, blade seals, leveling courses, or spot sealing, will usually correct fat and slippery conditions if done properly. If the areas are extremely fat and also soft and distorted, it may be more advantageous to scarify, re-mix and re-lay.

Fat spots on higher type surfaces may be helped to some degree by sanding with repeated applications usually necessary. A seal coat may be applied if approved by the ???????. However, if the fat area contains an excessive amount of asphalt, the fat spots soon flush to the surface again, unless the excess bituminous material is burned from the surface before sealing. Portable burners may be used for this purpose.

On areas where a seal coat is not practical, a thin overlay may be used. The mix used may vary from a standard road mix on low-type bituminous surfaces. In heavily traveled urban areas, an asphaltic concrete mix prepared with Iron Mountain chat or lightweight aggregate (haydite) is justified and has proved very effective.

470.6.5 Bituminous Surface Crack Maintenance

Refer to Section 413.1.2.5 Bituminous Pavement Crack Sealing regarding proper procedures for crack sealing bituminous surfaces.

470.6.6 Priming and Tacking

See procedures for and.

470.6.7 Spot Seal Coating

Spot seal coating consists of sealing lean, oxidized, or map cracked areas small in size. If spot sealing cannot be controlled to a maximum of 10 percent per mile of the roadway surface on each mile at any one time, other means of repair should be considered.

Spot sealing is considered preventive maintenance and should be done before the oxidized or cracked areas deteriorate further. Refer to Surface Treatment and Preventive Maintenance for additional information.

470.6.8 Fly Coating/Fog Sealing

Refer to Section 413.1.2.4 Bituminous Fog Sealing regarding procedures for Fly coating/Fog Sealing Asphaltic surfaces.

470.7 Patching Bituminous Surfaces

470.7.1 Patching Methods

Patching may be pothole patching or blade patching. Pothole patching is used to patch holes in the surface and possibly the base. Blade patching may be used to correct map check areas, large surface failures, distortions, fat and slippery areas, and settlements.

The patching of potholes should receive immediate attention. Holes are dangerous to traffic, increase rapidly in size, and feed water into the base and subgrade. Good techniques should be used in placing patches. This is particularly important in placing winter patches on high type pavement in order to avoid failures which are expensive to both MoDOT and to the traveling public. The edges of the hole should be trimmed to sound material and cut vertically and the hole should be cleaned thoroughly by brooming. If the base material is found to be soft, loose, or mushy, it should be removed and replaced. If the bottom of the hole is wet, the wet material should be removed or it can be dried by the addition of a small amount of dry portland cement, hydrated lime, or by the use of a portable burner.

The bottom and the sides of the hole should be given a light tack coat. If a hand spray is used for tacking holes, do not apply an excess of bituminous material, as it will penetrate into the patching material causing a fat spot. A stiff brush may be used for even distribution. Allow a short period of time to elapse after tacking for the water from the emulsion or the volatiles from the cutback to evaporate before starting to fill the hole.

The pre-mix material should be placed in thin layers. Each layer should not exceed 2 in. after being compacted. Level the patch with the back of a rake or shovel to prevent segregation. Use a straight edge or string line as a guide so the patch will conform to the cross section and drain of the roadway surface. All patches should be thoroughly compacted before they are opened to traffic. Patches are normally compacted with rollers, compactors, or tampers. When the compacting is finished, the surface of the patch must be the same height as the surrounding surface. A universal tendancy is to overfill holes and cause bumps or humps in the pavement.

If an upper deck on concrete pavement is involved, and the concrete has also deteriorated, the concrete will have to be replaced. Instead of replacing the concrete deck and then waiting for the concrete to cure before replacing the asphaltic wearing surface, the concrete mix may be placed full depth to allow for the roadway to be opened as soon as the concrete has cured to the required strength.

The areas to be repaired with blade patches, spot decks or overlays should be bladed, leveled, and rolled as necessary. Corrugation and distorted areas should be leveled. All areas should be either primed or tacked, depending upon the condition of the area being patched. The patching material may be layed by hand, motorgraders, spreader boxes, or asphalt pavers. In all work the patch should be smooth riding and feathered out at the ends. Patches for edge failures should not extend past the outside limits of the normal roadway surface. All patches should be rolled thoroughly and deep patches to correct settlement or edge failure should be compacted in lifts.

In addition to the procedures set out on Page 6.11 of the Maintenance Manual, we are establishing the following guidelines to be followed when flycoating.

1. Only one direction of the roadway is to be flycoated within any 24 hour period. Flycoating is to be limited to sections no longer than 1 mile in length. If a route requires continuous treatment, it should be done by alternating one mile treated sections with one mile untreated sections. The second half of the roadway or skipped sections should not be treated until the previously treated sections have completely cured.

2. Flagmen are to be stationed at both ends of the project, at all intersecting State Routes and at all major County Road Intersections until the fresh asphalt is safe to drive on.

3. "One Lane Road" and "Fresh Oil" signs shall be placed at both ends of the job and at all State and County road intersections. Signs should also be placed in advance of each section of treated roadway. Signs should be placed for both directions of travel.

4. No flycoating operations should be done if rain is predicted for the area within 4 hours of the estimated completion time or if the sky indicates that rain is a possibility within the 4 hour period. Flycoating shall be stopped immediately if a rain shower develops during the operation.

5. On hilly and curvy roads, the rate of application should be reduced to avoid runoff. It may be necessary to apply the material in several light applications, rather than one heavy application. The maximum application rate is 0.15 gallons per square yard. However, this should be reduced accordingly on hills anc curves.

470.7.2 Patching Material

Bituminous material used for patching should be comparable to or better than the existing surface material. Cold mix patching material is normally used for low type surfaces and asphaltic concrete is used on high type surfaces whenever possible.

Since asphaltic concrete is not always available, every advantage should be taken to patch high type surfaces when a plant is in the area. If asphaltic concrete cannot be obtained, hot commercial plant mixes or a Department mix produced in our patch mixers may be used.

The commercial hot mix is preferable to the Department mix when it is available and can be obtained reasonably. However, it should not be used when the waiting period is excessive, particularly if it cannot be obtained in time to use a full load that day. Travel distance also enters into consideration. Every effort should be made to keep the material hot, particularly if it cannot all be used immediately. Tarpaulins should be used over the load and the use of plywood in the bed of the truck for additional insulation can be considered.

Much of the winter patching material for high type pavement is prepared in the asphalt patch mixers. These mixers can be used either at the maintenance lot or at the site on the roadway where the mixed material is needed. Normally more efficient mixing can be obtained at the maintenance lot as endloaders can be used to change the mixer instead of shovels. This reduces the size of the crew needed for mixing and avoids the poor public relations we receive when a fairly large crew is standing around the mixer on the road waiting for material to be heated.

A mixture of one part sand to two parts of Sec 1004 material will provide a good mix. The use of an anti-stripping agent will also improve the mix. The addition of 1% hydrated lime to the aggregate will provide the same benefit as an anti-stripping agent.

470.8 Continuous Bituminous Maintenance Operations

470.8.1 Seal Coating

Refer to procedures in 409 Seal Coat.

470.8.2 Seal Coat Design

See design procedures in 409 Seal Coat.

470.8.3 Contract Leveling Course

Refer to Bituminous Surface Leveling for information on the Contract Level Course Program.

470.8.4 Maintenance Leveling Course Program and Procedure

A Maintenance Leveling Course Program is established annually by each District. Funds should be allocated in the maintenance budget for the Bituminous Repair Program and should be used for repairing bituminous pavements.

To achieve an efficient and productive operation, proper supervision must be given to assure the use of proven methods and techniques in leveling course operations. On road mixing of aggregate and asphalt is no longer practiced due to traffic control concerns, labor requirements to mix the materials on the road and safety concerns for department personnel and the traveling public.

Off Road Mixing - Maintenance leveling course material is mixed off road by either stockpile site blade mix, pug mill mix, or by contract pre-mix.

Tacking - After mixing has been completed, the roadway surface must be cleared or free of all dust and fines before a tack coat is applied. The application rate per square yard of the tack coat will vary with the condition of the old surface.

Laying - Laying or spreading is done with motorgraders and this operation should be coordinated with the tacking operation to avoid unnecessary passes of the motorgrader in moving the windrow so that the balance of the road can be tacked. Generally six to eight passes of the motorgrader are adequate to lay a leaveling course. Motorgrader operators must exercise care in laying operations so that the material is not laid or spread past the desired limits of roadway widths. A straight and even edgeline should be maintained for appearance and also to provide stability at the roadway edge. The use of an edge mounted on the end of the moldboard has proven to be an effective tool in laying a straight edgeline. The surface should be completed with an acceptable crown, usually a 3 in. crown measured from the centerline is sufficient.

Rolling - Rolling should be done with traffic and should begin immediately and continue until all loose material is embedded in the surface. If necessary, it should be continued the following day. This is especially important where the aggregate used is gravel. Any section or spots excessively oily should be blotted sparingly with blotting material and rerolled. If the material has been mixed properly, the need for blotting will be minor. Finished sections should be checked afterwards for several days to correct bleeding, "picking up", or needed repairs to bad spots.

The roller truck used should be equipped with a water tank hooked to a sprinkling bar on the roller. This will eliminate the need for a man to ride in the bed wetting down the roller during rolling operations.