National Academies Press: OpenBook

Chip Seal Best Practices (2005)

Chapter: Chapter Seven - Construction Practices

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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
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Suggested Citation:"Chapter Seven - Construction Practices." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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INTRODUCTION To a great extent, the construction phase drives the quality and performance of chip seals during their service life. There- fore, it is critical that the construction system be well defined, controlling the construction means and methods critical to the performance of the chip seal. Construction practices and pro- cedures vary from region to region and are generally associ- ated with local equipment availability and empirical knowl- edge of its use. This chapter draws information from both the survey responses and the standard chip seal specifications from several highway agencies to identify those construction practices that are associated with successful chip seal proj- ects. Special attention has been paid to method specifications that prescribe specific construction equipment or that serve to enhance equipment operation. WEATHER It is widely recognized that weather-related factors are often responsible for the failure of a newly constructed chip seal (Asphalt Surface Treatments—Construction Techniques 1988; Asphalt Seal Coats 2003). Because the performance of emul- sions depends on evaporation for developing their adhesion characteristics, ambient and pavement temperatures, relative humidity, wind velocity, and precipitation all have an impact on the constructability of emulsion chip seals. Ideal chip seal weather conditions are those with low humidity, without wind, and with sustained high temperatures (Maintenance Chip Seal Manual 2000). Chip seals constructed with hot asphalt cements have been shown to experience serious adhesion problems when there is high humidity or moisture present during construction (Wegman 1991). High humidity is a detri- ment to any chip seal operation mainly because of the result- ing poor adhesion between the binder and the aggregate. The MDT recommends that binder be shot only if the humidity is 50% or lower (Maintenance Chip Seal Manual 2000). The Minnesota DOT (Mn/DOT) allows chip seal placement with a relative humidity of up to 75% (Minnesota Seal Coat Hand- book 1998). Additionally, when using emulsions, break times are significantly increased with high humidity (Asphalt Surface Treatments—Construction Techniques 1988). Ambient Temperature It is accepted that ambient temperatures at the time of con- struction closely affect the quality of chip seals (Asphalt Sur- CHAPTER SEVEN CONSTRUCTION PRACTICES 40 face Treatments—Construction Techniques). Because the adhesion process is closely related to the viscosity of the binder, warmer ambient air temperatures result in better adhesion obtained between not only the aggregate and binder, but also between the chip seal and pavement surface. It is also accepted that roadway surface temperature at the time of con- struction closely affects the quality of chip seals. General consensus among the majority of respondents is that ambient air temperature should be a minimum of 50°F (10°C) when using emulsions, and 70°F (21°C) when using asphalt cements. Responses from Caltrans and a number of counties in Cali- fornia specify a maximum ambient air temperature of 110°F (43°C) for their chip seal construction projects. The Indiana DOT allows placement in air temperatures from 40°F to 60°F only if the aggregate has been heated to a temperature of 120°F to 150°F (Seal Coat Placement 2004). Roadway Surface Temperature The surface temperature of the existing roadway is also a crit- ical factor, because energy transfer between the binder and the pavement surface greatly affects the resultant viscosity of the binder and the speed at which it will break. In regard to sur- face temperature, the survey responses showed that signifi- cant variation in requirements between agencies and trends on a regional basis were difficult to develop. This is a concern, because low surface temperatures can lead to poor adhesion of the chip seal to the existing pavement surface (Asphalt Sur- face Treatments—Specifications undated). The Asphalt Insti- tute recommends that the temperature of the surface be a min- imum of 70°F (21°C) when constructing a chip seal (Asphalt Surface Treatments—Specifications undated). If the surface temperature were low as, for example, during the morning, asphalt would be more viscous than desired to attain appro- priate adhesion between aggregate and binder. On the other hand, excessive pavement temperatures can also be a prob- lem, particularly with the emulsions. In such a case, viscosity would be so low that binder could not secure the aggregate in place. The survey results indicate that Michigan limits con- struction to a pavement surface temperature of less than 130°F (54°C), whereas Ohio specifies a maximum surface temperature of 140°F (60°C). Rain Chip seals should never be constructed when rain is likely. A rainfall, during or shortly after the construction of a chip seal,

41 can cause a chip seal project to fail. If an unexpected rainstorm ensues, sufficient aggregate should be spread to cover all of the applied binder. If possible, the road should be closed to traffic and, if not, traffic must be kept to a minimum speed during this period, because adhesion between the binder and aggregate is at risk (Asphalt Seal Coats 2003). The amount of rolling should be reduced, if not completely ceased, while the aggre- gate is wet, because the binder may emerge from the voids and be picked up on the wheels of the roller (Bituminous Sprayed Surfacing Manual 2003). Wind Chip sealing during windy conditions raises a number of issues. Wind can be either beneficial or detrimental to a chip seal during construction. The benefits of wind are directed toward the curing process for emulsions, because wind may speed up this process and thus allow for earlier sweeping and opening to traffic (Gransberg et al. 1998). The destructive nature of wind is noted during the application of the binder. Wind can distort spray patterns, which may lead to a non- uniform application (Asphalt Seal Coats 2003). A shield may be installed on the distributor to prevent any disturbance to the spray pattern from wind (Seal Coat . . . 2003). ROAD PREPARATION Preparation activities before the chip seal work are essential to produce a uniform surface, because most chip seal activ- ities are applied on pavements that show various distresses. A pavement that is well prepared for chip sealing should have a uniformly textured surface and a smooth ride, and it should contain only those minor defects that can be corrected by the chip seal. Figure 42 shows the results of the survey responses for this area. The following are requirements for preparation of a pavement surface for chip sealing (Asphalt Surface Treatments—Specifications undated): • Repair all holes and depressions and replace with a tight surface conforming patch; • Fill and seal all cracks; • Level all bumps, waves, and corrugations that will impair riding qualities; • Remove all excess asphalt on patches and joints; and • Clean full width of the surface to be treated. Repairs Significant deficiencies in the pavement surface must be repaired before applying a chip seal to the roadway. Potholes must be filled, and ruts of significant depths must be leveled. The survey analysis revealed that the most common repair activities to be completed before a chip seal are hot-mix and cold-mix patching and crack sealing. In addition to prevent- ing water from entering the base, crack seals prevent loss of chip seal binder through existing cracks, and patches are intended primarily to level up the pavement surface as well as address isolated pavement distresses. The type of material used for the various repairs is important and can affect the quality and overall longevity of the finished chip seal surface. Patching materials and crack sealant need time to cure before placing a chip seal. This work, when possible, needs to be pro- grammed and scheduled to take place several months in advance of the chip seal construction to allow for crack sealant and paving materials to cure (Sprayed Sealing Guide 2004). As a rule of thumb, patching should be completed at least 6 months before construction and crack sealing should be applied at least 3 months before the application of chip seals (Gransberg et al. 1998). Road Note 39, the United Kingdom’s chip seal design and construction policy manual, 0% 20% 40% 60% 80% 100% Fresh Pavement Crack Sealing Fog Coat Patch and Level Texturizing North America AU, NZ, UK, SA FIGURE 42 Typical road preparation methods.

indicates that surface preparation activities such as patching and crack sealing be completed “the previous autumn” before the year the chip seal will be applied (Design Guide . . . 1996). In contrast, the Indiana DOT states that patches must be com- pleted not less than 10 days before a chip seal (Seal Coat Placement 2003). Preconstruction Sweeping Preconstruction sweeping with rotary broom sweepers often creates considerable dust. If dust poses a danger to the trav- eling public, a flush truck may be employed to keep dust to a safe level. Preconstruction sweeping is performed to remove any dirt, dust, or debris from the existing pavement surface. Adequate sweeping will provide the necessary clean surface that permits good adhesion with the bituminous binder. It is important that the full width of the existing surface be swept to remove all foreign material to ensure a clean surface before application of a chip seal (Asphalt Surface Treatments— Specifications undated). If the surface is swept too far in advance, it may need to be swept again on the day of con- struction. Figure 43 shows a typical rotary broom sweeper engaged in this task. Water Retexturizing The restoration of texture to a road surface that is slick with excess binder can be performed by the use of the water- retexturizing machine as shown in Figure 40. Its results are shown in Figure 44a and b. In addition to restoring road sur- face texture before chip sealing is done, water retexturizing could be used as a repair technique for a bleeding surface with poor skid resistance. Logically, care needs to be taken when water retexturizing to prevent nonexcess binder from being removed or stripped from the aggregate, because such a situa- tion could invariably create a greater problem (Sprayed Seal- 42 ing Guide 2004). An AASHTO scan tour report recommended that this and other Australian chip seal techniques be investi- gated for use in the United States (Beatty et al. 2002). Transit New Zealand’s belief in the value of water retex- turing to prepare existing bleeding surfaces is exemplified by the following statement from the agency’s chip seal manual: Texturing seal coats . . . can be expected to provide a service life of up to 75% of the normal reseal [chip seal] life, ensur- ing a satisfactory surface for resealing [chip sealing] at the end of that period (Notes . . . 2002). Prespraying Australia and New Zealand have identified prespraying as a method for adjusting the transverse surface texture of a pave- ment surface before construction of a chip seal. Surfaces that have significant disparity in binder content between wheel- paths and non-wheelpaths can be corrected with this technique. The areas outside of the wheelpaths are sprayed with an appli- cation of binder sufficient to increase binder content so that it is consistent with the texture of the wheelpaths. The spray run must be carefully planned to circumvent spraying the already binder-rich wheelpaths with additional binder (Sprayed Seal- ing Guide 2004). As is shown in Figure 45, the Australians prespray two lanes of traffic in one pass. Binder-deficient areas such as the centerline joint, the area between wheelpaths, and shoulders are typically sprayed. This technique and water retexturing are done to allow a constant rate of binder to be shot when applying the chip seal, thus eliminating the need to adjust binder and aggregate rates in the field. SPRAYING OPERATIONS Before spraying the binder, a number of procedures should be followed to ensure an accurate application:FIGURE 43 Rotary broom sweeper preparing surface for sealing. (a) (b) FIGURE 44 (a) Before and (b) after image of water retexturizing.

43 spraying correctly. Scrutinizing the binder distribution will ensure that any spraying problems, such as a clogged nozzle, nonparallel nozzles, or improper application temperature are mitigated immediately. Distributor Production Characteristics The chip seal system production rate is constrained by the asphalt distributor’s ability to apply the binder. Therefore, every other component in the chip seal equipment train must at least be able to equal the distributor’s sustained production to maximize the system’s sustained production (Peurifoy et al. 2001). Observations in the field confirm that the distributor sets the production rate for the rest of the equipment fleet (Gransberg et al. 1998). As a result, the types and numbers of each category of equipment must be carefully determined to ensure maximum production, minimum disruption to the traveling public, and desired quality in the finished product. If there are not enough dump trucks, the aggregate spreader will lag behind the distributor, allowing the binder to cool before application of aggregate. This can create the potential for raveling owing to lack of sufficient adhesion between the aggregate and the binder. If a project uses two distributors at the same time, the dis- tributors’ production rate may be greater than that of the aggregate spreader. It is essential that this not become a prob- lem, and in concurrence with the practice illustrated in Fig- ure 47, that the distributor not advance far in front of the aggregate spreader. The Asphalt Institute recommends not applying more binder than can be covered with aggregate within 1 min (Asphalt Surface Treatments—Construction Techniques 1988). The operator should always strive to keep a minimal distance between the distributor and chip spreader (Maintenance Chip Seal Manual 2000). FIGURE 45 Prespraying of areas outside wheelpaths. FIGURE 46 Spray bar applying bituminous binder. • Determine distributor velocity and pump speed; • Delineate the distributor shot (limits); • Construct paper joints; • Blow out nozzles to make sure that none are plugged; • Ensure proper transverse alignment of distributor; and • Ensure that binder temperature is within specification limits. The distributor cannot begin spraying the binder until all other required equipment has been prepared. The aggre- gate spreader, dump trucks, and rollers must be in position to begin their functions. A paper joint needs to be placed at the beginning of the shot so that the distributor not only attains the proper application speed on crossing the paper joint, but also to provide a neat line and avoid a double application of binder at the construction joint. At confir- mation that the distributor’s transverse alignment is per- pendicular to the centerline, the binder application can commence (Figure 46). The binder application should appear as a uniform sheet of binder across the entire width of the shot. One of the most important factors in any spraying operation is to visually inspect each shot to ensure that all nozzles are FIGURE 47 Aggregate spreader within proximity of distributor.

Variable Application Spraying Variable binder application rates are particularly useful for maintaining a consistent texture across the entire lane width. Because aggregate in the wheelpaths will be embedded more deeply, the amount of binder required will be less than in the other areas of the lane. The use of variable nozzles permits the application of a reduced rate of binder in the wheelpaths, while still achieving the design binder rate outside of the wheelpaths. The justification for using variable nozzles is to combat bleeding in the wheelpaths. The modified Kearby design method recommends that the binder application rate outside the wheelpaths be 20% greater than the design rate calculated for the wheelpaths. (See Appendix C for a detailed case study on a New Zealand contractor’s method for design- ing variable transverse application rates.) Construction Joints An area of both aesthetic and service life concern is found with transverse construction joints. Special attention must be paid to the transverse construction joints at the start and end of each shot. Seamless transverse joints can be obtained through placing starting and finishing tar paper at the joint. This should ensure that the correct rate of application is achieved for the full length of the shot and avoid double appli- cations of binder. The binder application shall commence with a running start on a strip of tar paper. The spray bar needs to be stopped on the tar paper at the end of each shot to ensure a straight transverse construction joint (Figure 48). Longitudinal joints should not be in the center of the lane width, as this leaves an undesirable appearance and can lead to raveling. The number of longitudinal joints should be kept to a minimum and be located so that they will coincide with painted lines between traffic lanes to the greatest degree pos- sible (Seal Coat . . . 2003). Careful attention should be given 44 to the skill and workmanship of the distributor operator in regard to the longitudinal joints between adjacent sprays. When the outside nozzle is parallel with the other nozzles, overlapping is essential to ensure that binder application rates are achieved. The distributor operator should make a longitu- dinal overlap of 2 to 4 in. (50 to 100 mm) to ensure that the texture of the finished surface is uniform (Supplemental Spec- ification 882 . . . 2002). AGGREGATE SPREADING As with the binder distributor, the aggregate spreader needs to have correct transverse alignment before commencing the spread. To allow for timely aggregate coverage of the sprayed binder, it is essential to have two or three loaded trucks in queue behind the aggregate spreader and before the rollers. It is criti- cal that the trucks stagger their wheelpaths, to assist the rolling operations when backing into the spreader (Maintenance Chip Seal Manual 2000). A self-propelled spreader pulls the dump trucks through the aggregate spread area, known as a “rock land.” As each dump truck is emptied, the aggregate spreader operator releases that truck, and the next truck in queue is attached to the aggregate spreader (Figure 49). Achievement of design application rates will generally mean that the aggregate uniformly covers the binder without excess aggregate. Overspreading can increase the risk of wind- shield damage as a result of dislodged aggregate, is not cost- effective, and requires additional post-construction sweeping efforts. Underspreading, as evidenced by visible areas of uncovered binder, will result in aggregate loss, because the excess voids in the aggregate will result in the binder not ris- ing high enough to securely hold the aggregate particles in place. The material needs to be applied thick enough so that the tires of the dump trucks, aggregate spreader, and rollers are not picking up the binder. If the aggregate is being applied at the calculated rate and tires are still picking up FIGURE 48 Paper used to ensure seamless transverse joint. FIGURE 49 Aggregate applied with self-propelled spreader.

45 binder, then the binder application rate is either too high and the aggregate is rolling over on contact with the binder or the aggregate is too wet. When the aggregate spreader is pro- ceeding too fast or alternatively when the binder is too vis- cous, the aggregate may roll over. Minor aggregate spread deficiencies such as corrugation or missed areas can be corrected with the use of a drag broom or hand rake. Drag brooms are typically fitted on the roller doing the initial roller pass and will assist in redistributing minor spread inequalities. If the aggregate is uneven, nonuniform, or irregular for any reason, it should be drag-broomed or hand- raked immediately after spreading and before initial rolling. Excess Aggregate Loose aggregate, the application of excess chips, is a serious concern for all chip seal projects. There is also a tendency to apply more aggregate than is required when it is paid for by the ton, which ultimately just gets swept off the road and wasted (Asphalt Surface Treatments—Specifications undated). Application of chip quantities in excess of 10% of the designed rate makes sweeping challenging, and as the likelihood of unswept excess aggregate increases, so does the likelihood of vehicle damage from flying stones. Excess aggregate can also dislodge embedded chips under traffic, leading to the failure of the chip seal (Shuler 1990). A leading cause of excess aggregate is an improperly calibrated aggregate spreader. In an attempt to curtail excess aggregate spread, Montana performs a sweeping test in the field (Maintenance Chip Seal Manual 2000). Excess aggregate spread will be dif- ficult for the sweeping equipment to remove and therefore weighing the quantity of unswept chips is an indication of whether or not the design rate was exceeded. Montana requires that the amount of excess chips be less than 10% of the design rate. The only possible exception to regulations about minimizing excess aggregate are when dealing with areas where extensive stopping and turning movements take place (Janisch and Gaillard 1998). In these locations, appli- cation of a controlled amount of excess aggregate may reduce the dislodging of the aggregate in the same fashion as with the racked-in seal method. ROLLING OPERATIONS The roller is the tool used to seat the aggregate and create embedment in the hot asphalt or emulsion binder. Rolling operations need to be preplanned and carefully spelled out for field personnel to follow. Verification of the rolling pat- tern should be done with a visual analysis of lane coverage, aggregate orientation, and embedment (Minnesota Seal Coat Handbook 1998; Seal Coat . . . 2003). Careful roller operation will ensure that the roller itself does not cause damage to the freshly constructed chip seal, especially by displacing aggregate. The number of rollers should be determined by the width of the area to be covered, as well as the nominal aggregate size and traffic volume. As nominal aggregate size in- creases, the area that can be effectively covered by each roller decreases (Sprayed Sealing Guide 2004). Develop- ment of rolling guidelines such as patterns and minimum rolling time should be directed toward achieving full lane coverage and a similar number of passes for all areas of the lane. The survey responses indicated that most highway agencies use an average of only two rollers, with some agencies “requiring” only one. Such a phenomenon is in agreement with a Texas study, which found that rolling requirements are often ignored in the field because QC test- ing associated with chip seal rolling operations is not com- mon (Gransberg et al. 1998). Achievement of the service life of a chip seal is not pos- sible without the bonding that results from proper embed- ment and orientation of the chips. A recent paper offered a straightforward mathematical equation to compute the required number of rollers based on maximizing distributor production rate (Gransberg et al. 2004). Distributor speed for the desired asphalt rate can be calculated from Eq. 1 (Epps et al. 1981). Spray bar output is dependent on the type of the binder sprayer used. where Sf = distributor speed (ft/min), Gt = spray bar output (gal/min), W = sprayed width (ft), R = rate of binder application (gal/yd2), and 9 = conversion factor (from yd2 to ft2). Distributor speed, Sf, can be modeled as the distribu- tor production rate (P) by converting speed from feet per minute to lineal miles per hour. Next, assuming that the production rate of the rollers must be greater than or equal to the planned production of the distributor to ensure that the maximum system production is achieved (Peurifoy et al. 2001), the required number of rollers can be calculated by using Eq. 2 if a specified rolling time (also called linger time) is known. where N = required number of rollers, P = distributor production (lineal mph) obtained by con- verting distributor speed (from ft/min to lineal mph), X = shot width (yd), A = roller linger time (yd2/h), and 1760 = conversion factor (from yd to mi). N PX A = 1760 2( ) S G WRf t = 9 1 ( )

Similar computations can be made for each of the different shot widths that will be encountered during a chip seal project. The inspector can then be given a list of how many rollers are required with which to enforce the rolling time provisions in the contract. Figure 50 is taken from the aforementioned paper (Peurifoy et al. 2001) and illustrates the need to plan rolling patterns and roller coverage. It can be seen that the use of three rollers in this example results in an uneven roller coverage— and the least amount of rolling in the areas outside of the wheelpaths where possible loss of aggregate is the greatest potential. It should be noted that this roller has an effective rolling width of only 69.3 in. (176 cm), although it is widely accepted as being a 72-in. (183-cm) roller. Additional rollers will be required when the viscosity of the binder is increased, “such as with the use of polymer-modified binders or during cool weather construction” (Notes . . . 2002). It may seem counterintuitive, but the Minnesota study found that the greatest rolling attention needs to be paid to roads that have light traffic volumes. The reason being that traffic assists in the orientation and embedment of aggregate, actually pro- viding a level of rolling not obtainable with pneumatic rollers (Janisch and Gaillard 1998). The Mn/DOT constructability study (Janisch and Gaillard 1998) also found that aggregate loss typically occurs outside and between the wheelpaths where the roller coverage is min- imum with use of three rollers on a 12-ft (3.7-m) shot width (see number of passes in roller coverage graphs in Figure 50). The use of four rollers provides a uniform coverage and twice as much rolling between the wheelpaths as three rollers for the case study discussed earlier. Prompt rolling is critical to achieve adequate aggregate embedment. It is important that the aggregate is rolled before the binder becomes cold or too viscous to achieve proper embedment. The justification behind prompt rolling is that as the binder cools, its viscosity may increase, which in turn increases the amount of rolling energy required to achieve the same embedment. Therefore, rolling must follow as closely as practical behind the spreader. Allowing emulsions to break before applying aggregate contributes to aggregate loss (Jackson et al. 1990). This emulsion-specific issue indicates that by waiting too long, the ability of the rollers to properly seat the aggregate is greatly reduced. The binder will be brown in color at applica- tion and will turn black as it breaks. On a hot, low-humidity day, the binder will break in 3 to 5 min (Janisch and Gaillard 1998). A rule of thumb is that the first pass should roll the aggregate just before the binder breaking (Asphalt Surface Treatments—Specifications undated). Rolling Requirements Effective rolling specifications should detail the roller types permitted, number of rollers required, time between aggre- gate spread and initial rolling, maximum speed limit, and 46 minimum rolling time or number of passes. Figure 51 shows the typical rolling requirements used by survey respondents. It is interesting to note that none of the North American respondents specify a rolling time. This does not mean that there are none followed in North America. Some agencies have specified roller linger times in the range of 1,000 to 5,000 yd2/h (Gransberg et al. 1998). Times in Australia range from 3,000 to 7,000 yd2/h depending on traffic volume, as shown in Table 9 (Bituminous . . . 2003). New Zealand uses the following equation (Eq. 3) to cal- culate the required rolling time (T ) based on volume of binder to be shot (Vt), the rolling speed (S ), and the number of rollers (N ) (Notes . . . 2002): where T = rolling time (h), Vt = volume of binder (L), S = roller speed (km/h), N = number of rollers, and 450 = conversion factor. A consensus from the survey responses is that a maximum speed of approximately 5 mph (8 km/h) for pneumatic rollers should be mandated, to prevent the roller’s tires from dis- placing the aggregate. Special attention should be given to ensure that the tire pressures of the rollers are set to obtain optimum embedment of the material without undue crushing of the aggregate. Pneumatic-tired rollers should have a total coverage width of not less than 60 in. (1.82 m), while also pro- viding a minimum contact pressure of 40 lb/in.2 (2.81 kg/cm2) to the surface (Asphalt Surface Treatments—Specifications undated). Texas specifications require that all tires on pneu- matic rollers be inflated so that there is no more than 5 lb/in.2 variation within all tires (Seal Coat . . . 2003). Typically, additional rolling is beneficial to the success of the chip seal, unless aggregate degradation is occurring. Aus- tralian agencies have recognized that the failure to achieve design embedment depth is primarily a function of achieving QC requirements for rolling time. Thus, minimum rolling times are specified, and the importance of adequate rolling has led to practices in Australia whereby extra equipment operators relieve the roller operators during breaks and even extend rolling operations into the evening after the construc- tion has ceased (Bituminous . . . 2003). Table 9 highlights the necessity to pay particular attention to monitoring rolling times on roads with low traffic volume. Steel-Wheeled Rollers Steel-wheeled rollers are primarily used on multiple-course chip seals to rapidly achieve levels of embedment not possible T V S N t = ( )( )450 3( )

47 FIGURE 50 Roller patterns and coverage (Source: Peurifoy et al. 2001).

48 excess chips that can dislodge and strike windshields causing damage. Sweeping operations need to be properly executed because the sweeping process itself can dislodge embedded chips (Shuler 1990). However, sweeping the loose aggregate from the roadway immediately following rolling is a critical mistake, for the residual binder has not yet cured enough to bond to the aggregate and underlying road surface. The time frame for sweeping depends on how long it takes the binder to cure to a point sufficient to retain the aggregate. As the temperature declines into the evening, aggregate retention will be higher if sweeping is done at this time. The WSDOT recommends that final brooming occur “during the cool period of the day (early morning)” and that “if rock is dislodged (by the broom), that brooming be delayed until the asphalt has cured further or the weather is cooler” (Asphalt Seal Coats 2003). Typically three passes are required to adequately sweep each driving lane (Seal Coats . . . 2003). Figure 52 illustrates the typical number of sweeping passes as identified by the survey respondents. Of note is that in spite of the number of sweeping passes required, the objective should be to remove all excess aggre- gate from the surface of the chip seal. Logically, the sweep- ing operation should direct dust away from the traveling public. In areas where loose aggregate cannot be swept off the side of the road, a pickup sweeper should be used. Sweeping should be started in the center of the pave- ment and progress to the edges (Seal Coat . . . 2003). Post- construction sweeping may occur for several days after the 0% 20% 40% 60% 80% 100% No. of Passes Rolling Patterns Speed Limits Roller Weight Rolling Time North America AU, NZ, UK, SA FIGURE 51 Typical rolling requirements. Traffic Volume (vehicles/lane/day) Aggregate Size <300 300–1,200 >1,200 [yd2/h (m2/h)] 1/4 in. (5–7 mm) 4,780 (4,000) 5,975 (5,000) 7,170 (6,000) 3/8 in. (10 mm) 3,585 (3,000) 4,180 (3,500) 5,380 (4,500) 9/16 in. (14 mm) 2,990 (2,500) 3,585 (3,000) 4,180 (3,500) Source: Bituminous . . . 2003. TABLE 9 MINIMUM ROLLING TIME with pneumatic rollers (McLeod 1969). A survey respondent from the United Kingdom indicated that steel-wheeled rollers had been used primarily to assist with the rideability of the chip seal, that this had been discontinued in favor of using rubber- clad steel rollers. When steel-wheeled rollers are being used, they should be lightweight models of 6 to 8 tons, as heavier rollers will likely break down the aggregate (Asphalt Surface Treatments—Specifications undated). Because degradation of aggregate is a serious concern with steel-wheeled rollers, those rollers should be operated only in static mode. If any fracturing or crushing of the aggregate becomes evident, the operation should immediately stop the use of such rollers. As mentioned earlier, steel-wheeled rollers will have difficulties when the underlying pavement is rutted, for they will bridge over the ruts and fail to properly seal the aggregate in the ruts. Steel-wheeled rollers should never be used alone (1) because they will not orient the particles into their least dimension and (2) because of contour bridging (riding on the high spots while spanning over the low spots), they will not contact the entire width. When achieving embedment becomes a con- cern, and the aggregate is not hard enough to sustain rolling with a steel-wheeled roller, larger pneumatics such as 10-ton, 11-wheeled pneumatic rollers may be an option to consider (Wegman 1991). SWEEPING AND BROOMING Sweeping is performed to remove the excess chips from the roadway. With adhesion of the aggregate to the binder, sweep- ing commences. Adequate sweeping is crucial to remove the

49 placement of the chip seal. Australian agencies follow the sweeping operations with a roller to ensure that any disturbed aggregate is rolled back into place (Sprayed Sealing Guide 2004). If embedment is visibly low after sweeping, a fog seal, which is a second application of binder sprayed on top of the aggregate to enhance adhesion, should be applied to the chip seal. The MDOT recommends that if the embedment is more than 80%, no fog seal be applied even if one is required by contract (Maintenance Chip Seal Manual 2000). TRAFFIC CONTROL Traffic control designed in accordance with the Manual on Uniform Traffic Control Devices is not only vital to the safety of the traveling public and construction workers, it is also an indispensable tool for achieving levels of orientation and embedment beyond conventional rolling. Vehicle damage can also be prevented through adequate traffic control. Ample traffic control should be in full force for every chip seal proj- ect. Generally, loose gravel signs complement signage that indicates the reduced speed limits. Traffic control is generally accomplished using signage, pilot vehicles, and flaggers during construction operations. The consensus among survey respondents was that the maxi- mum speed limit should be 25 mph (40 km/h). A pilot vehi- cle is recommended to not only provide safe passage to the traveling public at reduced speeds, but also to assist in reduc- ing windshield damage and increasing aggregate embedment. Besides restricting the speed of traffic through the work zone, a pilot vehicle can stagger traffic movement on the new chip seal to prevent vehicles from traveling in the same wheelpaths and helping to embed stone retention outside of them (Asphalt Seal Coats 2003). It is good practice to delay the opening to normal traffic speeds until the midday road surface temperature drops, such as in the evening (McLeod 1969). The construction operation should avoid opening the chip seal to uncontrolled traffic in hot conditions when the ability of the binder to hold the aggregate is reduced (McLeod 1969). Opening a freshly con- structed chip seal to traffic during midday is not recom- mended, because the binder is less viscous and there is an increased chance of the loss of aggregate. Asphalt cements are advantageous during hot weather because the roadway can be quickly reopened to traffic. CONSTRUCTION PRACTICES FOR HIGH-VOLUME TRAFFIC Survey results indicated that chip seals may be highly effec- tive on high-volume traffic roads. California, Colorado, and Montana regularly construct chip seals on roads with greater than 20,000 ADT and reported that the performance of their chip seals was either good or excellent. The belief that chip seals are not suitable for high-volume traffic roads is rooted in perceptions that chip seal projects on those roadways are predestined to failure because of the liability and claims associated with damage to vehicles from loose aggregate (Shuler 1990). Several factors should be considered to prevent vehicle damage for high-volume traffic applications. Common causes of vehicle damage from chip seals include the application of excess aggregate, inadequate low-speed traffic control, and poor sweeping (Shuler 1990). Shuler’s recommendations for construction practices when constructing high-volume chip seals are shown in Table 10. Sweeping is essential to high- volume traffic chip seal applications. Vehicle damage can be avoided if the excess chips placed to minimize chip pickup on 0 10 20 30 One Pass Two Passes Three Passes N o. o f R es po nd en ts FIGURE 52 Typical brooming requirements. Practice Reason Reduce excess aggregate Sweeping proficiency increased Reduce aggregate size Larger aggregate causes more damage Use of double chip seals Smaller aggregate in contact with tires Use of lightweight aggregate Lower specific gravity causes less damage Use of choke stone Locks in larger aggregate Fog coat Improved embedment Precoat aggregate Improved adhesion Use of polymer modifiers Improved adhesion Allow traffic on chip seal Vehicles provide additional embedment Control traffic speed on chip seal Reduced whip-off TABLE 10 BEST PRACTICES FOR CONSTRUCTING HIGH-VOLUME CHIP SEALS

equipment tires are swept from the pavement surface before opening to traffic. In cases where chip seals fail after a period of months owing either to loss of aggregate or flushing, the problems may be caused by materials, design, or construction (Shuler 1991). Figures 53 and 54 summarize chip seal construction prac- tices. Their intent is to present this information in a compara- tive manner where it can be easily understood and applied. QUALITY ASSURANCE AND QUALITY CONTROL The success of a chip seal is highly associated with the con- trol implemented over the quality of materials and con- struction. Constructability reviews during planning, design, and construction phases improve the quality of only the final product. The QC measures widely implemented intended for chip seal projects are provided by material testing and inspection forces. 50 This synthesis subscribes to the definitions of QC and quality assurance (QA) recommended by TRB (1999). As such, QA is the “planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service.” Additionally, QC is defined as the “quality assurance actions and considerations necessary to assess production and construction processes so as to control the level of quality being produced in the end product.” Both terms are inherent in all of the best practices identified in this synthesis. Special attention was directed toward identifying labora- tory and field tests that can be correlated with successful chip sealing practice. The QC section of the survey empha- sized the requirements that respondents use for ensuring conformance of the materials and the construction operation to the contract specifications. Table 11 is an indication of some specific chip seal testing methodologies that were ver- ified in the literature review. FIGURE 53 Preventive maintenance chip seal construction practices (adapted from Peshkin et al. 1999).

51 LABORATORY DESIGN AND MATERIALS TESTING Chip seal material testing should be performed both in the lab- oratory and in the field. In regard to quality, it is essential that an aggregate sample be provided to the materials laboratory performing the design of the chip seal. The critical reason for providing binder and aggregate samples during the design phase is to ensure that the binder is compatible with the aggre- gate selected for use on the project. Failure to design the chip seal based on the binder and aggregate that the contractor will use could lead to failure if the specifications require the use of a binder that is incompatible with the aggregate. The compat- ibility of aggregate–binder combinations should be tested in the laboratory (Yazgan and Senadheera 2003). Table 12 illus- trates the aggregate–binder compatibility tests identified in the literature review. FIELD TESTING There is a significant material testing QA and QC concern in regard to aggregate testing in the field. With chip seal material FIGURE 54 Chip seal construction practices for distressed pavements (adapted from Peshkin et al. 1999).

testing, most aggregate properties are considered only in the design process. In general, survey responses indicated that field sampling is very limited for aggregates. If the aggregate is to be stockpiled on site or at a local plant, it is important to test samples from the pile to ensure that the material has not been susceptible to segregation or degradation during the period following its manufacture. Aggregate transport and stockpiling can significantly alter the gradation of aggregate and generally increase the amount of fine material in the aggregate (Gransberg et al. 2000). In such conditions, the original gradation of the stockpile can adversely change. However, it is intuitive to carry out field sampling, especially in regard to gradation, at the stockpile site. In addition, the only logical way to confirm that the same materials tested in the laboratory are being used for the project is to perform ran- dom samples at either the stockpiles or from the aggregate spreader applying the material. In addition, binders can become contaminated by foreign substances inside the tanks of transports. Survey responses indicated that field testing of binders is more prevalent than is field testing of aggregate. Figure 55 shows that 44% of 52 North American respondents and 75% of overseas respon- dents perform field tests on their binders. Qualified Field Personnel Engineers or other qualified personnel generally administer the quality management program during the construction phase of a chip seal project. Generally known as field inspectors, these personnel ensure that specifications are being adhered to and specified quality standards are met. A noteworthy feature of chip seal construction is the requirement for knowledge and judgment in forming decisions that are the result of those same site-specific conditions that have caused many authori- ties to perceive chip sealing as an art (Wegman 1991). In terms of field inspection personnel, an important distinction between North American and international practices results because U.S. and Canadian agencies do not adjust surface texture before the construction phase of the project. Some road surface conditions may require that adjustments be made during binder application. These adjustments are sometimes quite subjective, with the magnitude of the adjustment based on an Name of Test Property Measured Standard Test Number Manufacturing Control Sieve analysis Gradation AASHTO T26, ASTM C136 Cleanness value Fine materials Caltrans Test 227 No. 200 washed sieve Fine materials AASHTO T11, ASTM C117 Foreign materials Clay and friable particles AASHTO T19, ASTM C29 Decantation Dust Tex-217-F, Part 1 Plasticity index Deleterious material AASHTO T90, ASTM D4318 Aggregate Soundness Los Angeles abrasion Abrasion resistance AASHTO T96, ASTM C131 British pendulum test Skid resistance AASHTO T278, ASTM E303 British wheel Polishing AASHTO T279, ASTM D3319 Sodium sulfate loss Freeze–thaw degradation AASHTO T104, ASTM C88 Magnesium sulfate loss Freeze–thaw degradation AASHTO T104, ASTM C88 Aggregate Shape Percent fracture Roundness ASTM D5821 Flakiness index Flatness/elongation ASTM D4791 Asphalt Binder Emulsion penetration Penetration ASTM 244 Emulsion viscosity Saybolt viscosity ASTM 244 Emulsion sieve test Gradation ASTM 244 Asphalt cements Penetration AASHTO M226, ASTM D3381 Float test Drain-off, high float AASHTO T50, ASTM D139 TABLE 11 QUALITY CONTROL TESTS FOR CHIP SEALS Name of Test Agency Characteristic Aggregate Retention TxDOT, Tex-216-F Light sweep test Vialet French Public Works Inverted tray, ball impact Pennsylvania Retention Pennsylvania DOT Inverted tray, sieve shaker BST Sweep ASTM WK139 Replicates sweeping Film Stripping Caltrans and San Diego County, CT 302 Aggregate-emulsion compatibility Macrosurfacing Sweep Koch Materials TM101 Replicates sweeping TABLE 12 AGGREGATE–BINDER COMPATIBILITY TESTS

53 individual’s experience. Therefore, a considerable portion of the field inspector’s responsibilities are to adjust the applica- tion rates as the texture of the pavement’s surface changes (Janisch and Gaillard 1998). As a result, North American field personnel have an expanded role in comparison with their international counterparts. In general, qualified personnel need to be responsible for the following: • Ensuring that all equipment is calibrated, • Sampling and testing of materials, • Verifying material application rates, and • Monitoring construction methods. Calibrating the Distributor To maintain accuracy, several calibration procedures and checks should be regularly performed on the binder distrib- utor. Calibrating the binder distributor ensures that the dis- tributor spray bar is applying the appropriate designed appli- cation rate from each nozzle, and that the spray bar height is correct so that that the appropriate fanned spray pattern results. A standardized method for calibrating the transverse application rate of a distributor can be found in ASTM 2995, Standard Recommended Practice for Determining Applica- tion Rates of Bituminous Distributors. Given the significant quality issues that derive from accurate binder application, Figure 56 shows that 25% of North American agencies do not require the distributors on their projects to be calibrated. Calibrating the Aggregate Spreader The calibration of the aggregate spreader is crucial to the sat- isfactory performance of chip seals (Janisch and Gaillard 1998). Calibrating the aggregate spreader ensures that all gates are applying the same rate of aggregate across the entire spread width and therefore that the aggregate spreader is applying the desired amount of aggregate per square yard. The recommended procedure for calibrating an aggregate spreader is ASTM D5624, Standard Test Method for Deter- mining the Transverse-Aggregate Spread Rate for Surface Treatment Applications. Figure 57 shows a significant dis- parity in philosophies concerning aggregate spreader cali- bration; the overseas respondents show little concern with their aggregate application, with only 29% of these agencies requiring spreader calibration. When the survey results for both the binder distributor and aggregate spreader calibration are taken together, they show a fairly widespread disregard for basic QC practices in the chip seal project. Perhaps this finding accounts for the per- ception that chip seal is more art than science and for that rea- son it cannot be reliably designed and applied. A number of the states reporting that they no longer use chip seals cited uncontrollable variability as their reason for discontinuing its use. Perhaps adopting the best practices identified in this report could reduce this variability. Verifying and Adjusting Material Application Rates The methods used to verify actual application rates have been identified. Respondents also provided details of their policies toward accepted tolerances allowed for binder and aggregate 44% 56% 75% 25% 0% 20% 40% 60% 80% 100% North America AU, NZ, UK, SA Yes No FIGURE 55 Proportion of agencies performing field tests on binders. 75% 25% 100% 0% 20% 40% 60% 80% 100% North America AU, NZ, UK, SA Yes No FIGURE 56 Proportion of agencies requiring distributor calibration. 62% 38% 29% 71% 0% 20% 40% 60% 80% North America AU, NZ, UK, SA Yes No FIGURE 57 Proportion of agencies requiring spreader calibration.

rates. The most important reason for scrutinizing field appli- cation is to ensure that application rates are within the toler- ances of the project’s design standards. The field inspector scrutinizes the binder application during construction. Imme- diately preceding and following each shot, a procedure known as “strapping the distributor” occurs, which involves measur- ing the amount of binder remaining in the distributor’s tank and allows the inspector to calculate the actual rate of binder being applied (A Basic Emulsion Manual 1997). This field test means that the amount of binder remaining in the tank is measured to determine precisely how much binder was used on every shot. The North American philosophy toward chip seal appli- cation rates is that the chip seal design process can be used only as a guideline; the actual binder application rate must be verified in the field. The main responsibility of the project’s inspection personnel is to verify if the binder and aggregate rates are being properly applied. In addition, these personnel generally need to be knowledgeable about how to adjust material application rates to account for localized variations in road surface characteristics. Survey respondents were requested to provide the application rate tolerances they typ- ically allow for in their contracts. A common response is to allow a tolerance rate of ±10% for aggregate spreading and ±5% for binder application. Monitoring Construction Operations Field inspection responsibilities include ensuring that con- struction operations are conducive to high-quality workman- ship specified in the contract. Perhaps most important, every distributor shot needs to be carefully observed to monitor a number of spray characteristics. The operation of the distribu- tor is judged by visual observation. A uniform application both in the transverse and longitudinal directions is particularly important in chip seal work. Streaking is the most observable characteristic and is usually caused by one of the following four conditions: applying the binder at an inappropriate tem- perature, high binder viscosity, improper spray bar height, or incorrect pump pressure. Fan patterns and the appearance of a “uniform sheet of binder” need to be observed (Gransberg et al. 2000). Desired fan width is usually obtained with a dou- ble lap and needs to be equal for all nozzles (Asphalt Surface Treatments—Construction Techniques 1988). The actual rate of aggregate spread needs to be regularly compared with the design rate, to ensure that overapplication is not occurring. Experienced field personnel can generally observe any variation. It is essential that a uniform “curtain” of aggregate be applied across the entire binder shot width (Gransberg et al. 2000). The depth at which the aggregate is embedded into the binder should be continuously monitored during rolling. For the chip seal to be successful, the inspector must be able to 54 determine if the proper embedment is being obtained. Many agencies perform embedment checks in the field. In practice, aggregate is removed from the freshly constructed seal, and the percentage of embedment of the average chip is subjec- tively estimated (Janisch and Gaillard 1998). A 50% embed- ment after initial rolling and a 70% embedment after 2 or more weeks of traffic application are typically recommended (Jackson et al. 1990). If adequate embedment is not achieved owing to inadequate rolling, the chip seal will be susceptible to raveling between wheelpaths and along edges of the lane where the lowest levels of embedment are present as a result of less traffic action (Jackson et al. 1990; Gransberg et al. 1998). CONSTRUCTION CONCLUSIONS AND BEST PRACTICES Construction was the one area in which best practices are plentiful. This underscores the idea that there is only one chance to properly construct chip seal projects. As a result, both the literature review and the survey responses offered many examples of practices that can be observed to achieve successful chip seal projects. Thus, there is one overarching conclusion for this chapter. Both the agency and the contractor must understand the chip seal construction process and be pre- pared to execute the project in strict observance to the required procedures. This conclusion is underscored by the responses from agencies that use chip seals on high-volume traffic roads. Those responses were from agencies that not only rated their chip seal performance as good or excellent, but they were also from agencies that applied a more detailed set of specifications to the construction process. In other words, those agencies see chip seal as a science that can be repli- cated through adherence to strict technical guidelines during construction, rather than as an art that must follow a recipe to work properly. Another conclusion deals with the importance of the roller to chip seal success. The idea that the rolling can be ignored because the rollers are not trying to achieve a specified level of compaction is without merit. The major mode of early chip seal failure is loss of aggregate. The rolling operation is the tool in the chip seal paving train that ensures that proper ini- tial embedment is achieved. Therefore, greater attention must be given to both the specifications for rolling and inspections in the field to ensure that those specifications are being met. Because the roller is the slowest member of the chip seal train, it is critical to ensure that a sufficient number of rollers are both furnished and maintained, so that the aggregate is embed- ded when the binder is as soft as possible and, in the case of emulsions, before the emulsion has broken, as indicated with a color change from brown to black. Recognition that chip seal construction QC is very visual should not be contested. However, many performance con- cerns do not appear during construction. Therefore, a QA/QC program for chip seals needs to consist of more than just qual- ified personnel; it must also be a well-planned system of sci-

55 entific tests and engineering principles to ensure that quality materials conform to performance expectations. Additionally, it is very difficult to correct an error that was made during chip seal construction. The contractor must literally get it right the first time. A number of best practices were observed in this area: 1. All types of chip seals are best applied in the warmest, driest weather possible. 2. Ambient air temperature at the time of application should be a minimum of 50°F (10°C) when using emul- sions, and 70°F (21°C) when using asphalt cements with a maximum ambient air temperature of 110°F (43°C). 3. The temperature of the surface should be a minimum of 70°F (21°C) and no more than 140°F (54°C) when using emulsions. 4. Complete patches at least 6 months in advance and apply crack seals at least 3 months before the applica- tion of chip seals. 5. Variable nozzles permit the application of a reduced rate of binder in the wheelpaths and combat flooding in the wheelpaths, a defect that makes chip seals prone to bleeding. Conversely, the Australian use of pre- spraying is another method for adjusting the trans- verse surface texture of a pavement surface before construction of a chip seal. 6. Either hand-raking or drag-brooming can correct minor aggregate spread deficiencies such as corrugation, uneven spread, or missed areas. 7. Aggregate should be applied as quickly as possible with both emulsified and asphalt cement binders. Wait- ing for the emulsion to break reduces the effectiveness of the rollers in achieving the desired embedment depth of the aggregate. 8. The Montana field-sweeping test (Maintenance Chip Seal Manual 2000) curtails the bias to spread excess aggregate created by paying for it by the ton. Montana requires that the amount of excess chips be less than 10% of the design rate and adjusts the pay quantities based on the sweeping test results. This may also reduce the potential for windshield damage claims. 9. Have the most experienced inspector predrive each shot and paint binder rate adjustment on the pavement to facilitate field rate adjustments. 10. In areas where extensive stopping and turning move- ments take place, the application of a small amount of excess aggregate may reduce scuffing and rolling (Janisch and Gaillard 1998). The use of a racked-in seal (see Figure 13) as used in Australia and South Africa may be a viable engineered solution for determining the precise amount of aggregate for these problematic areas. 11. Rolling guidelines and specifications for roller cover- age, rolling patterns, and minimum rolling time or passes achieve full lane coverage and a similar num- ber of passes for all areas of the lane (see Table 9). Minimum rolling times are generally in the range of 3,000 to 5,000 yd2/h. 12. The required number of rollers is a function of desired binder distributor production and required rolling time or passes for each shot width on the project. 13. Have rolling follow as closely as practical behind the aggregate spreader. 14. Do not sweep the loose aggregate from the roadway immediately following rolling, because the residual binder has not yet cured enough to bond to the aggre- gate and underlying road surface. Accordingly, it is important to control the sweeping and not dislodge the embedded aggregate particles from the binder. 15. Maintain traffic control for as long as possible to give the fresh chip seal the maximum amount of curing time before opening it to traffic. 16. Assign experienced personnel who understand the dynamics of chip seal construction as field QC and QA persons. 17. Regularly calibrate both the distributor and the chip spreader. 18. Evaluate aggregate–binder compatibility tests, as shown in Table 12, for local appropriateness and before and during construction. 19. Field test binder at both the distributor and aggregate stockpiles daily to ensure that material has not degraded as a result of handling during transportation.

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 342: Chip Seal Best Practices examines ways to assist in the development and implementation of pavement preservation programs by identifying the benefits of using chip seal as part of a preventive maintenance program and by highlighting advanced chip seal programs in use around the world. The report includes approximately 40 best practices in the areas of chip seal design methods, contract administration, equipment practices, construction practices, and performance measures. According to the report, the increased use of chip seals for maintenance can be a successful, cost-effective way of using preventive maintenance to preserve both low-volume and higher-volume pavements.

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