Before writing a specification for your chip seal project, review A165 Recommended Performance Guideline for Chip Seal provided by The International Slurry Surfacing Association (ISSA) . This resource will help in design, testing, quality control, measurement and payment procedures for your project.
provided by The International Slurry Surfacing Association (ISSA). This resource will help in design, testing, quality control, measurement and payment procedures for your project. It is important to understand the traffic level of the road to determine if a slurry seal or a micro murfacing application is best.
Note: It is important to keep in mind that ISSA includes recommended guidelines, not specifications. There are many important factors to consider after reviewing the A105, A143 and A165 and your project may demand different processes and measurements from the included guidelines.
For the chip seal section, here are the major components needed for a good specification:
Letting chip seal contracts in time to permit early season construction
Timing the letting of the contract to allow sufficient time for the curing requirements of preconstruction pavement preparation activities
Packaging chip seal contracts in jobs large enough to attract the most qualified contractors
Conduct electrostatic testing of chip seal aggregate source before chip design to ensure that the binder selected for the project is compatible with the potential sources of aggregate.
Specify a uniformly graded, high-quality aggregate.
Consider using lightweight synthetic aggregate in areas where post-construction vehicle damage is a major concern.
Use life-cycle cost analysis to determine the benefit of importing either synthetic aggregate or high-quality natural aggregates to areas where availability of highquality aggregate is limited.
Use polymer-modified binders to enhance chip seal performance.
Use computerized distributors.
Preproject analysis of the ability of the chip seal equipment fleet to keep up with the production rate of the distributor is important.
The use of variable nozzles reduces the amount of binder that is sprayed in the wheelpaths.
All types of chip seals are best applied in the warmest, driest weather possible.
Ambient air temperature at the time of application should be a minimum of 50°F (10°C) when using emulsions, and 70°F (21°C) when using asphalt cements with a maximum ambient air temperature of 110°F (43°C).
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.
Complete patches at least 6 months in advance and apply crack seals at least 3 months before the application of chip seals.
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.
Either hand-raking or drag-brooming can correct minor aggregate spread deficiencies such as corrugation, uneven spread, or missed areas.
Aggregate should be applied as quickly as possible with both emulsified and asphalt cement binders. Waiting for the emulsion to break reduces the effectiveness of the rollers in achieving the desired embedment depth of the aggregate.
Have the most experienced inspector predrive each shot and paint binder rate adjustment on the pavement to facilitate field rate adjustments.
In areas where extensive stopping and turning movements take place, the application of a small amount of excess aggregate may reduce scuffing and rolling. The use of a racked-in seal may be a viable engineered solution for determining the precise amount of aggregate for these problematic areas.
Rolling guidelines and specifications for roller coverage, rolling patterns, and minimum rolling time or passes achieve full lane coverage and a similar number of passes for all areas of the lane. Minimum rolling times are generally in the range of 3,000 to 5,000 square yards per hour.
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.
Have rolling follow as closely as practical behind the aggregate spreader.
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 aggregate and underlying road surface. Accordingly, it is important to control the sweeping and not dislodge the embedded aggregate particles from the binder.
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.
Assign experienced personnel who understand the dynamics of chip seal construction as field QC and QA persons.
Regularly calibrate both the distributor and the chip spreader.
Evaluate aggregate–binder compatibility tests for local appropriateness and before and during construction.
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.
Measurement and Payment
Aggregate by the ton and emulsion by the gallon is a typical method of payment.
Chip seal placement can be paid by the square yard.
For warranty contracts, a lump sum payment could be made.
For term bid contracts, multiple prices could be bid dependent on square yardage.
For the slurry seal/micro surfacing application:
Use the A105/A143and the following statements to inform decisions and provide support when writing a final specification for your slurry seal/micro surfacing treatment:
Determine if any changes to the specifications as stated are required for the asphalt emulsion and aggregate per AASHTO/ASTM specifications.
State the storage limitations for the asphalt emulsion.
Determine if screening of the aggregate will be required.
Screen the material immediately prior to loading the nurse truck/mobile support unit. This way, there is no possibility of contamination when re-handling the material.
State the Type of slurry seal/micro surfacing to be applied: Type I (slurry seal only), Type II or Type III.
Type I is for low traffic areas.
Type II provides skid resistance, while being quieter and smoother than Type III.
Type III is typically used when a high skid resistance is required.
Note: many state specifications call out their own specific slurry seal/micro surfacing aggregate types that are not exactly the same as ISSA’s.
Determine the application rate to be applied.
Note: A specific application rate must be defined based on the traffic level and expectations of the treatment.
General guidelines for application rate:
Specify at the higher end of the range for high traffic roads to provide more of a wearing surface.
Specify at the higher end of the range for very rough pavements, as the voids will require more material.
Specify at the lower end of the range for pavements with a consistent profile, or a smooth surface.
Specify at the lower end of the range to save money (which will lower the lifetime of the treatment).
Note: The roughness of the pavement being surfaced is a factor in the proper application rate (rougher surface requires more material to fill the voids).
Determine specific requirements for the spreader box, such as a fixed width spreader box or a variable width spreader box. Determine if a secondary strikeoff or drag will be used, or if it is up to the contractor.
State if the project requires a calibration in the presence of an inspector, or will a previous calibration suffice. If a previous calibration is used, state the time limitation (for example, calibration must have been performed with the same materials in the last three months).
Require a recalibration when material changes, conveyor seals and/or, emulsion pumps have been replaced.
Require the contractor to perform a calibration with the inspector on site, with the specific materials for the job. This step has a high potential for increasing the quality of the job.
State the specific instructions related to notification.
The agency can provide early notification by website, newspapers, signs and/or door hangers. The contractor can notify by signs and/or door hangers the day before and the day of the application.
Determine if a test strip is required.
Determine if rolling will be required on the project. (generally required on airports).
To increase the longevity of the cape seal, roll parking lots, cul-de-sacs, and other pavements that will not receive regular traffic.
State specifically how the project will be measured for payment.
Determine if a pre-bid meeting be held to discuss the specifications.