Surface Rehabilitation Treatments Module 3-5 Surface Rehabilitation Treatments

Learning Objectives Describe the function of surface treatments Compare usage of various surface treatments Describe conditions best suited for each treatment Describe the design and construction considerations and techniques

Introduction Surface rehabilitation techniques Low-volume roads – most historical use High-volume roads - improved materials and processes Pavement preservation application Increased emphasis on pavement preservation has created a demand for more surface rehabilitation techniques. Does your state have a pavement preservation policy? What surface treatments are used as a part of that that policy?

Definitions Fog seal Sand seal Scrub seal Asphalt chip seal Slurry seal Microsurfacing Cape seal Sandwich seal Nova Chip® Open graded friction course (OGFC) Surface application of asphaltic material with or without aggregate. Which of these treatments do you use? Do you use others not listed here?

Fog Seal Fog seals are very light applications of an emulsion to the pavement surface with no aggregate. These applications seal the surface and provide a small amount of rejuvenation, depending on the type of emulsion used and the condition of the existing pavement surface. Many users are now applying this treatment to shoulders to counter the oxidation and weathering that takes place there.

Fog Seal Seal pavement surface Rejuvenate oxidized HMA Provide delineation Fog seals are a light application of a diluted asphalt emulsion (typically 8:1 or 9:1 mixture) placed primarily to seal the pavement and prevent raveling. The pavement must be in relatively good condition, without cracking or major raveling. Slow-setting emulsions are most commonly used for fog seals, and these take time to break, so the pavement must be closed to traffic for about 2 hours after placement. Because fog seals have the potential for reduced surface friction if excess asphalt is inadvertently applied to the pavement, they are not recommended on high-speed roadways. Again, fog seals are most effective on pavements in good condition. The performance life of a fog seal is about 1 to 2 years, and repeated applications are expected to provide improved effectiveness. However, no formal studies have been conducted to evaluate the effect of fog seals on prolonging pavement life.

Sand Seal Seal pavement surface Rejuvenate oxidized HMA Provide delineation Improve friction A sand seal usually consists of a spray application of a rapid-set emulsion with a light covering of sand or screenings. This application serves the same function as a fog seal, but provides better surface friction. However, the surface appearance of a sand seal does not provide the delineation that a fog seal does. A sand seal is typically 2- to 5-mm (0.08- to 0.2-in) thick.

Scrub Seal Photo from demonstration by Missouri Department of Transportation at the Iowa Summer Maintenance Expo, April 1999. Scrub seals are applications similar to sand seals but with broom used to force the asphalt cement and aggregate into cracks.

Scrub Seal Surface restoration that rejuvenates asphalt and fills voids and cracks Application process Apply polymer-modified asphalt agent Broom asphalt into voids and cracks Apply sand or small aggregate Broom aggregate and asphalt mixture Roll with pneumatic tire roller Scrub seals have become the new kid on the block in the past year or two. Actually if you check the 1979 edition of the Asphalt Institute Manual Series No. 19 they discuss scrub seals and that they are going out of fashion.

Asphalt Chip Seal An asphalt chip seal, also referred to as a seal coat or a bituminous surface treatment, consists of sequential applications of asphalt and stone chips, applied either singly or in layers, to build up a structure that can approach 25 mm (1 in) thick. This application is the traditional seal coating done by local agency maintenance crews and contractors. It serves as the surfacing for many miles of low-volume unpaved roads or as the wearing surface for many miles of paved roads. Many agencies apply multiple surface treatments to produce a thickness on the order of 10 to 25 mm (0.4 to 1 in).   A rubberized asphalt chip seal is a special type of chip seal in which rubber (ground-rubber tires) is blended with the asphalt cement. This application has been used both as a SAM (stress-absorbing membrane) and a SAMI (stress-absorbing membrane interlayer) to help reduce reflection cracking, but it has also been used without overlays. The ground rubber adds stiffness and resiliency to the asphalt, and also improves bonding with the aggregate. The added stiffness and resiliency may also enable the seal to “bridge” existing cracks better.

Asphalt Chip Seal Photo of chip spreader in operation.

Asphalt Chip Seal Provide wearing course Improve surface friction Rubberized Bridge and seal cracks Delay reflective cracking

Slurry Seal A slurry seal consists of a diluted emulsion mixed with fine aggregate in a special mixer on the job site, and then squeegeed onto the pavement surface. It is effective in sealing surface cracks, waterproofing the pavement surface, and improving skid resistance at speeds below about 64 km/h (40 mph). Different types of slurry seal are used that differ by the size of aggregate used. The thickness of the slurry seal is generally less than 9.5 mm (0.38 in).

Slurry Seal Seal pavement surface Retard surface raveling Improved surface friction

Microsurfacing Developed in Europe, microsurfacing is a term used to describe the application of a polymer-modified slurry seal, with latex rubber being the most commonly used polymer. Microsurfacing materials consist of asphalt and latex mixed with aggregate, fillers, and other additives and is a modification of the slurry and sand seal (Pederson 1986). It has been used as a wearing surface and for rut-filling. Ralumac is probably the most widely known example of this process in the United States (Asphalt Institute 1986).  

Microsurfacing Level pavement surface Fill ruts Restore surface friction Note dark brown color of microsurfacing, before emulsion breaks.

Cape Seal This application is a combination of both a chip seal and a slurry seal. For paved roads, the chip seal is applied first and, between four and 10 days later, the slurry seal is applied. For unsurfaced roads, an application of penetration oil (MC-70 or SC-70) is applied first as a prime coat. Then, about two days later, the chip seal is applied, and about two weeks after that, the slurry seal is applied after most of the cutter stock has cured out of the cutback. The advantage of the cape seal is that a thicker and longer-lasting surface is obtained, and it can be used on higher volume roads (Raza 1991). The cape seal also has a smoother, more pleasing appearance, and it is more resistant to damage from snowplowing.  

Cape Seal Seal pavement surface Improve surface friction

Sandwich Seal Seal pavement surface Improve surface friction A sandwich seal consists of an application of a one-layer course of aggregate particles, followed by an application of emulsion (although asphalt cement can also be used), followed by a second course of smaller aggregate to fill the voids. The term “sandwich” is derived from the fact that the asphalt application is placed between the two layers of aggregate. Typical sandwich seals are between five and 20 mm thick.

Nova Chip® A Nova Chip® friction course consists of a layer of HMA placed over a heavy tack coat. The HMA thickness ranges from 10 to 20 mm (0.375 to 0.75 inch) depending upon the maximum size of the stone used in the mix. Layer thickness is generally 1.5 time the maximum stone size used.

Nova Chip® Gap graded HMA Heavy tack coat applied first (0.7-1.0 l/m2) Proprietary machine and process Paver applies both tack coat and HMA Functional, not a structural overlay Tack coat 0.15-0.22 gals/sy. Nova Chip® advantages: Can be placed in one pass, without milling. Quick construction and return to traffic mean shorter user delays and lower user delay costs. Coarse aggregate matrix results in reduced backspray for greater visibility in wet weather as well as good skid resistance. Special NovaBondTM polymer modified asphalt membrane for superior bonding to and protection of existing surface. Ultra-thin lift means maintaining overhead clearances, curbs and drainage profiles as well as lower costs. Construction by specially trained, reliable, quality contractors. Long lasting performance.

Open-Graded Friction Course                                       Open-graded friction courses (OGFC), also called plant mix seals or popcorn mixes, are porous surface mixes produced with large amounts of voids (minimum 15 percent) that allow water to drain rapidly through the mix and flow to the side of the road. These mixes are used to improve the friction properties of the surface and also reduce the tire spray and hydroplaning potential, thereby reducing wet weather accidents. The OGFC also tends to provide a quieter riding surface, as it produces lower tire noise. Typical thicknesses of OGFC are 25 to 50 mm (Raza 1991). An excellent summary of the performance of OGFC is found in references by TRB (1990) and Smith (1992).  

Open-Graded Friction Course Provide surface drainage Reduce hydroplaning Reduce tire spray Improve surface friction Noise reduction

Purpose and Application Provide a new wearing surface Seal cracks in the surface Waterproof the surface Improve pavement surface friction and surface drainage What will surface treatments not do? They will not provide structural value to the pavement. Why apply a surface treatment?

Purpose and Application Slow pavement weathering and aging Improve the surface appearance Provide visual delineation between the mainline pavement and the shoulder Why do you use surface treatments?

Matching Condition to Treatment Performance of surface treatments highly dependent upon existing surface condition Key is to match the treatment to the pavement, traffic, and climatic conditions.

Pavement Surveys Type of distress Surface treatment type More severe cracking “Heavier” surface treatment Distorted pavement surface “Leveling” treatment Need to determine if the pavement is structurally adequate.

Applicable Pavement Conditions Oxidation Fog seal Scrub seal Sand seal Slurry seal Bleeding Sandwich seals Friction Slurry seal Asphalt chip seal Microsurfacing Nova Chip® Treatments which are applicable to remedy the identified distress. The listing on this slide and the next are not all inclusive but are meant to generate discussion.

Applicable Pavement Conditions Cracking Scrub seal Slurry seal Asphalt chip seal Microsurfacing Cape seal Nova Chip® Rutting Microsurfacing Nova Chip®

Cost Considerations Typical surface treatment costs Chip seal $1.02 /m² Db. chip seal $1.35 /m² Slurry seal $1.08 /m² Microsurfacing $1.50 /m² Fog seal $0.54 /m² Sand seal $0.70 /m² Cape seal $1.70 to $2.40 /m² How do these costs compare with what you are paying? Reference: Hicks, Seeds, and Peshkin 2000. Chip Seal $1.02/m2 ($0.85/sy) Double Chip Seal $1.35/m2 ($1.13/sy) OGFC $2.45/m2 ($2.05/sy) Rubberized Chip Seal $1.80/m2 ($1.50/sy) Slurry Seal $1.08/m2 ($0.90/sy) Microsurfacing $1.50/m2 ($1.25/sy) Fog Seal $0.54/m2 ($0.45/sy) Sand Seal $0.70/m2 ($0.59/sy) Cape Seal $1.70 to $2.40/m2 ($1.42 to $2.00/sy) Sandwich Seal $1.20 to $1.30/m2 ($1.00 to $1.10/sy) Nova Chip $3.00/m2 ($2.50/sy)

Design and Construction Considerations

Design Considerations Asphalt Chip Seals Existing pavement condition Asphalt type Aggregate Quantity selections Local conditions and experience General environment Traffic volume and handling Contractor experience and availability Existing pavement condition – Do we want to apply a treatment such as this to a pavement that does not have an adequate structure? How long of a fix are we looking for with a chip seal? Asphalt type – You have basically three options; asphalt cement, emulsified asphalt, or cutbacks. Asphalt cements are felt to be the most effective but require ideal weather conditions for construction. The use of cutbacks has been severely restricted due to the release of hydrocarbons during the curing period. Emulsions are the most popular choice for chip seals and are used very successfully when designed correctly. The choice of the emulsion must be balanced with the type of aggregate selected. The charge on the aggregate must be compatible with the charge of the emulsion. Aggregate – Type, gradation, quality must all be considered when designing your chip seal. The angularity and shape of the aggregate are also important consideration. Ideally, a one-size, cubic aggregate particle will be chosen for chip seals. Unfortunately, availability of this aggregate is usually limited. Flat and elongated particles and aggregates containing large amount of fines require more asphalt to adequately coat the particles You can also consider the use of precoated aggregate in chip seal construction. Quantity selections – Based on the type of chip seal selected and the aggregate chosen you must then develop quantity calculation. What is different if you are dealing with a cutback or emulsion? If you are using a cutback or an emulsion you must allow for the evaporation solvent/water when developing the application rate. Aggregate application is affected by the traffic level. The heavier the traffic the more the aggregate will be embedded in the asphalt. A 50 to 70 percent embedment is desirable to hold the aggregate in place (Linden, Mahoney, and Jackson 1989). Local conditions and experience – What is the typical emulsion used here? Why? What aggregate size do you normally use? Why? Is windshield breakage a problem? Do you use chip seals only on lower volume roads because of problems in the past? General environment – Weather conditions before and after placement need to be considered. Will it be warm enough to allow use of an asphalt cement? Will the weather conditions allow the curing necessary for an emulsion? Will the weather conditions cause our normal emulsion to break to soon and not permit the proper coating of the aggregate and embedment? Traffic volume and handling – What traffic level do you apply chip seals on? How soon after the chip application do you allow traffic on the finished roadway? Do you control the speed of the cars? If so, how? Do you use pilot cars? South Africa recently revised their surface treatment recommendation to take into account such things as traffic level, turning movement, and grade.

Construction Procedures Chip seal construction issues: Equipment calibration Pavement surface preparation Application of asphalt Application of aggregate Rolling of aggregate Curing of binder Brooming of loose aggregate

Fog Seals Light coating of asphalt cement applied usually as an emulsion Traffic allowed on in 2-4 hours after water has evaporated Surface may be slick if traffic allowed too soon

Open Graded Friction Course Similar to HMA Butt joints only Limited time for compaction due to thin lift (≤25 mm) Usually seasonal restrictions on placement Air/pavement temperature critical No vibratory compaction equipment The construction procedures for an OGFC are different than those for dense-graded asphalt concrete. Butt joints should be used in lieu of slope or lap joints because of the mixes’ resistance to lateral movement. The rolling should consist of one pass or two passes of a medium weight [7.3 metric ton to 9.1 metric ton (8 T to 10 T)] static steel-wheeled roller. Compaction should follow immediately behind the paving operation.   The OGFC should be placed only on a structurally sound surface, free of ruts and a large amount of cracking. Construction should only take place during good weather, when the temperature of the underlying pavement will be at least 15 ºC (60 ºF). Nighttime paving operations and seasonal restrictions have resulted in many agencies limiting their use of OGFC. A tack coat is needed prior to the placement of the OGFC, regardless of the surface on which the OGFC is placed. Strict gradation control is required to ensure that adequate air voids are obtained. The most critical element is the temperature control in the mixture. The viscosity of the asphalt cement binder must not be allowed to drop below the point where the binder runs off the aggregate and reduces the coating thickness. This necessitates lower mix temperatures than those typically used with other hot mixes in the range of 110 ºC (230 ºF) to 120 ºC (250 ºF)which produce an asphalt viscosity of 800 centistokes. The laydown of the OGFC uses conventional asphalt paving equipment. The paving operation can proceed at a faster pace than conventional paving operations, although excessive speeds should be avoided to prevent tearing of the mix (TRB 1978). The rolling of the OGFC is generally limited to one or two passes of a 7.3 metric ton (8 T) to 9.1 metric ton (10 T) static, steel wheel roller. Pneumatic rollers should not be used because they tend to track the asphalt and they close the voids excessively (Roberts et al. 1991). It is important that the rolling operations begin as soon as possible after placement because the OGFC loses heat quickly. The OGFC may be opened to traffic as soon as it has cooled. Because of the high cost of OGFC, the thickness of the OGFC layer is usually kept to a minimum (Raza 1991). A 20 to 25 mm (0.75 to 1 in) thick layer is typically placed in the United States (Huber 2000). Thinner layers may produce raveling and wearing away of the mix, leaving bare spots in the surface. In Europe and South Africa porous asphalt is typically placed in layers of 40 to 50 mm (1.5 to 2.0 in).

Review Why would you apply surface treatments? Which treatments could be applied to correct a rutted pavement? Which treatments could be applied successfully to a pavement with cracking? What are key considerations in the construction of a chip seal? Why would you apply surface treatments? Slow pavement weathering. Improve surface appearance. Provide visual delineation between driving surface and shoulder. Provide a new wearing surface. Seal cracks in the surface. Waterproof the surface. Improve pavement surface friction and surface drainage. Which treatments could be applied to correct a rutted pavement? Microsurfacing and NovaChip. Which treatments could be applied successfully to a pavement with cracking? Chip seals, scrub seals, slurry seal, Cape seal, sandwich seal, microsurfacing, and NovaChip. What are key considerations in the construction of a chip seal? Chip seal construction issues: Equipment calibration. Pavement surface preparation. Application of asphalt. Application of aggregate. Rolling of aggregate. Curing of binder. Brooming of loose aggregate.

Key References Van Zyl, G. D., J. P. Nothnagel, and C. J. Semmelink. 1999. “Rationalisation of Seal Selection and Single Seal Design Methods in South Africa.” Seventh Conference on Asphalt Pavements for Southern Africa. RSA/USA Pavement Technology Workshop CD-Rom, Pretoria, South Africa.

Key References (continued) Eltahan, A. A., J. F. Dalieden, and A. Simpson. 1999. “Effectiveness of Maintenance Treatments of Flexible Pavements.” Transportation Research Record 1680. Transportation Research Board, Washington, DC.

Key References (continued) Huber, G. 2000. Performance Survey on Open-Graded Friction Course Mixes. NCHRP Synthesis of Highway Practice 284. Transportation Research Board, Washington, DC. Janisch, D. W., and F. S. Galilard. 1999. Minnesota Seal Coat Handbook. Report Number MN/RC-1999-07. Minnesota Local Road Research Board, Minnesota Department of Transportation, St. Paul, MN.

Key References (continued) Hicks, R. G., S. B. Seeds, and D. G. Peshkin. 2000. Selecting a Preventive Maintenance Treatment for Flexible Pavements. FHWA-IF-00-027. Federal Highway Administration, Washington, DC. Raza, H. 1992. An Overview of Surface Rehabilitation Techniques for Asphalt Pavements. FHWA-PD-92-008. Federal Highway Administration, Washington, DC.