Questions for CAPA’s “Asphalt Man”
QUESTION: One of the members of our HOA was complaining about the contractors doing the crack sealing in our neighborhood. He told us he “Googled” the way to do it and they are doing it all wrong. Is there a way to determine if the contractor is doing this correctly?
ANSWER: One of our work groups has created a document titled “Best Practices for Crack Seal Materials & Construction”.. This document was developed with industry and owners in mind. This is a good reference for property owners to use when contracting out their pavement maintenance.
QUESTION: What really is segregation in Asphalt Paving Materials (APM)
ANSWER: Segregation in Asphalt Paving Materials (APM) can be defined as the separation of the coarse aggregate particles in the mix from the rest of the mass. The segregation can take one of three forms-random, side-to-side or longitudinal, and truckload to truckload.
Each type of segregation is caused by a different problem or problems. But each type of segregation affects the long-term durability of the asphalt pavement concrete structure.
This article deals with truckload segregation, and more specifically, with best practices for using end-dump trucks.
The Contractor and producer need to follow best practices for loading and unloading the haul trucks. This includes multiply drops when loading and charging the tailgates prior to unloading.
Loading the Haul Truck
Truckload segregation appears typically as two very rough textured areas in a transverse direction, one on each side of the centerline of the asphalt paver. The primary cause of truckload segregation is how the HMA mix is delivered from the silo into the haul truck. In order to completely eliminate truckload segregation, it is necessary to load the truck correctly. This means that a normal tandem or triaxle truck needs to be loaded with three drops of mix instead of one large drop. The first drop is immediately next to the front bulkhead of the truck bed—as far forward as reasonably possible. This process reduces the distance that the coarse aggregate particles can roll to the front of the truck bed, and thus significantly reduces the amount of segregation that will occur during the loading operation.
Unloading the Haul Truck
If the haul truck is properly loaded—using multiple drops of mix into the length of the truck bed with mix against both the front bulkhead and against the rear tailgate—unloading the truck should not create segregation problems. If the haul truck is loaded improperly and the large aggregate particles in the mix have rolled both to the tailgate and the front bulkhead of the truck, the segregation problem has already occurred. The problem can be minimized, but probably not completely eliminated, by using a different procedure to unload the haul truck. In this latter case, the tailgate on the truck bed should remain closed and the truck bed should be raised.
Raising the Bed
The bed should be raised high enough for the mix to shift in the bed and move toward the tailgate. This process will add more mix on top of the segregated material at the tailgate. After the mix has shifted, the tailgate can be opened.
With the bed up in the air and with the additional mix moved against the tailgate, the combined mix will be moved in a mass into the paver hopper. Some or all of the segregated material will be blended into the rest of the mix and the amount of segregation which will occur behind the paver screed will be significantly reduced. While it is important to unload the haul truck correctly, it is more important to load the truck bed properly so that the segregation of the mix does not occur in the first place.
To discuss this further, contact Tom Clayton.For more information you can contact Tom Clayton
QUESTION: Is it acceptable to rake a longitudinal joint to create a smooth transition?
ANSWER: In today’s world of Asphalt Placement the best joint are those which do not get worked. By this we mean the materials are placed using the paver and slightly overlap the previous pass by about one to one and a half inches. The laborer (Lute person) should only bump the materials back to the natural joint. They should in no way “Break” the materials across the mat. By “Breaking” the materials they have created a segregation issue which cannot be over come through the compaction process. By “Bumping” the materials to the natural joint they have created a method to achieve the required, specified density at the joint by placing more materials than would otherwise be there. It is like cramming 3 pounds of candy in a 2 pound bag at that point.
Some contractors only overlap three quarters of an inch to inch and do not “bump” the materials back. This is an acceptable method, however in many case it causes a visual difference in the appearance of the finished mat(s). By not adding the additional materials at the joint, they may also not show the same or increased density at the joint as those who do “bump” the joints.
To discuss this further, contact Tom Clayton.
QUESTION: Is there an easy way to identify a “traveler (Gypsie)” paving company?
members offer a six warning signs:
1. Claims that it’s “leftover” asphalt. Asphalt is never left over from a project. Leftover hot-mix asphalt would be too cold to place properly, while cold mix is used exclusively for small patches, not general paving. Asphalt is a perishable product and if it cools too much it is useless as a hot mix paving product.
2. Deals that seem “too good to be true.” If the quoted price seems very low, chances are the quality of the work will be low as well.
3. Cash-only terms. Most reputable contractors take checks, and don’t require cash only terms.
4. “One-time offer” price quotes. Reputable contractors will provide a quote before doing any work so that the homeowner has a chance to shop around.
5. Door-to-door sales. It’s worth repeating: reputable asphalt contractors do not sell their products door-to-door. Consumers should be very suspicious of anyone appearing at their front doors offering low-cost asphalt.
6. Vehicles with out of State license plates. This type of scam many times will be run by persons traveling through our area from other states. The big equipment may be licensed in Colorado, but many times the smaller equipment (pickups, and trailers) will be licensed in other states.
7. In this time of rebuilding, work with others in your area to seek out a reputable contractor and partner in the rebuilding. Contractors can and will make deals to those who work together to get the work done. There will be less cost to the contractor to move in and do several projects at one time rather than one at a time. The potential savings can be absorbed by all who work together.
For additional information contact Tom Clayton.
QUESTION: Should we use the State Highway specification when designing local roadways?
ANSWER: The short answer is NO. When designing local agency roadways the challenges are inherantly different. The traffic volumes (ESAL’s) don’t match up, even on a highly traveled local agency roadway. The majority of the local agency roadways have light car and trucks where State highways carry heavy truck traffic.CDOT’s traffic data baseshows, In the Denver area there are only 3 roadways that would be classified as high volume (greater than 3 million ESAL’s) and they are all Interstate highways. Even on the State system for surface streets in the metro area, there are no high volume roads. When high numbers are assumed for design and roadways built using inflated numbers, it can cause premature aging of the APM. To discuss this further, contact Mike Skinner or Tom Clayton.
Question: Is the proper application of a tack coat really an important pert of a good asphalt overlay?
ANSWER:A key component of an asphalt pavement is the bond strength between asphalt pavement layers. Tack coat is a sprayed application of an asphalt binder upon an existing asphalt or Portland cement concrete pavement prior to an overlay, or between layers of new asphalt concrete. This thin membrane of asphalt binder provides the glue between the layers, creating a monolithic structure which performs as a unit as opposed to unbound, independent, layers. Poor bonding of a pavement surface layer is a direct result of inadequate tack coat practices resulting in slippage and shoving of the pavement. Materials used for tack coats are emulsified asphalt (most common) and performance grade asphalt. While cutbacks are still used, their usage is much less than other options, and will not be addressed in this answer because of the limited availability of this material. Moreover, research has shown that cutbacks achieve lower bond strengths than other options. Failure to bond pavement layers is known to result in delamination and then sliding and shoving of surface layers of pavement. However, a reduction in fatigue life is also a very probable consequence of poor bonding. When pavement layers are not properly bonded, the layers exhibit independence, resulting in an alteration to the stress distribution profile. A variety of researchers have reported on this situation over the years. Some select examples are presented below. A more complete listing is found in NCHRP Report 712 (I). It has been reported that if a pavement displayed no bonding within its layers, a 60% loss of life could be expected. Similarly, reported that no bonding would cause a 75% reduction in pavement life, and at 70% bond strength, a 70% reduction in pavement life could occur. Moreover, King and May (4) reported that with only a 10% loss of bond, a 50% reduction in fatigue life would be expected. Perhaps the most definitive research effort on optimization of tack coats for HMA was the National Cooperative Highway Research Project (NCHRP) 9-40 (1). As reported in NCHRP Report 712, bond strengths were tested for a variety of tack coat materials including emulsions and paving grade binders; various residual application rates from no tack coat to 0.155 gallons per square yard (gsy); various surface types including old HMA, new HMA, milled HMA, and grooved Portland cement concrete (PCC); and in shear, tension, and torsional configurations at 4 a range of test temperatures. Test specimens were obtained from both field and laboratory produced materials.
The Source for this answer is in FHWA Technical Brief FHWA-HIF-16-017 Dated April 2016. The entire FHWA Technical Brief can be downloaded here!
For additional information contact Tom Clayton
Question: I am an HOA manager in Colorado. One of the HOAs I manage has two large asphalt driving “lanes” running through the property. I understand from two local asphalt companies that these driveways/roads should be seal coated every 3-5 years. It has been 6 years since they were last seal coated.
The HOA Board questions the need to seal coat the asphalt this year because they roads “look good” and look like they only need a crack fill?
ANSWER: Seal coating is a process to seal the surface to slow deterioration of the asphalt.
The need to seal coat an asphalt surface is not a clock or calendar driven process. It is simply driven by the weather conditions and weathering which occurs to a pavement.
Every year is different and every lot is different. The recommendation to seal every 3 to 5 years is just that a recommendation.
As unprotected pavement ages the asphalt binder hardens, losing flexibility and becoming increasingly brittle. Ultraviolet rays from the sun break down the carbon bonds in asphalt, further weakening the pavement. Also, daily and seasonal cycles of heating and cooling cause the pavement to expand and contract. These stresses eventually exceed the pavement’s ability to flex, and cracks form. If water seeps into the cracks and freezes, the cracks expand, allowing more water to penetrate, making the cracks wider and deeper. This cycle leads to accelerated deterioration of the parking lot surface. Early sealcoating can prevent all these preliminary dangers to the life of the asphalt.
Pavement maintenance begins by filling cracks, patching deteriorated areas, and cleaning (and possibly priming) oil-saturated spots on the pavement surface. The asphalt also must be cleaned of dirt and debris before sealer can be applied.
With all of this said, looks can be deceiving. Is most important to look at the pavement and determine if the surface has opened up which will allow water to penetrate and cause damage in the winter months. The infiltration of water is the biggest cause of damage in any pavement. A good test.
How do you determine if the surface is opened up? This is a rule of thumb. If 75% or more of the asphalt surface is coated (black) you are most likely in a good place. If you can see the color of the rock that means the surface oils have dissipated and should be sealed up.
You mentioned crack sealing. This is something we would recommend at least one time per year. It may be considered 2 times per year, spring and fall.
We mentioned at least once per year and if this is chosen I would do this in late summer or early fall before the temperatures start falling, but earlier enough to seal things up before the summer rains saturate the subsurface materials. It would be impossible for me to give you an educated opinion without physically looking at the asphalt pavement, but I hope my descriptions will help.
For additional information contact Tom Clayton
Question: What elements should be considered when specifying construction of Residential streets vs. Collectors or arterials?
ANSWER: There are two different methodologies that will be used. You can pick either Gradation Control where you are specifying the structure you want to have in place or Volumetrics Control during the production of the APM. In many cases in low volume roadways the choice is to use Gradation Control which will allow for the contractors to produce a high quality APM and provide the owner with assurance the materials will provide long term performance. Volumetric Control provides for a method to control the void space being constructed into a APM. This is generally used in high traffic roadways where rutting is a potential problem. It is not possible to commingle the two different methods, Gradation Control or Volumetric Control as the producer will need to make adjustments based on the method prescribed to achieve acceptable end result. If one would specify Volumtric Control are specified and the producer makes an adjustment which forces the gradation to scew slightly it would appear the gradation is out of spec. In reality, the mixture is still as good as it was in the beginning. For additional information contact Tom Clayton
Question: What smoothness specifications should be used for county roads or city streets?
ANSWER: Generally NO smoothness requirements should be assigned to Local Agency roadways. Local agency roads have inherent complications already built in to them such as cross pans, utilities handicap ramps, curb and gutter. Instead of assigning a smoothness specification the agency should make sure the contractors are following “Best Paving Practices”. CAPA and our industry partners have created a document which describes these best practices. For additional information contact Tom Clayton
Question: We are being required to use a Pneumatic Tire Roller on a Polymer Modified Asphalt, Is this appropriate?
ANSWER: The issues when specifying polymer modified asphalts begin with affinity of the binder to adhere to the rubber compounds for the tires of the PTR. Release agents can be effective when the placement of APM do not include polymer binders but are typically not used with Polymer Modified Binders. This pickup can and will be more detrimental to the long-term life of the asphalt pavement than not using the PTR for compaction. The density requirements for any APM do not change because the binders change. The density requirements must be met in APM’s with or without Modified binders. It is up to the placing contractor to meet eh local requirements for density. The issue becomes a time effort for the placement contractor. They may need to alter the type and number of steel wheel rollers, the spacing of the rollers and the initial and final compaction timing for the roller operations. All of the decisions about the number and type of rollers on a project will be determined by the contractor and based on the in-place density being achieved and the amount of effort which is being applied to the APM (Read More)
Question: We just installed a new asphalt parking lot. What is the best way to deal with snow and ice in the winter? Sand only? If chemicals, what to use/avoid? We want to protect our investment and avoid degrading the new asphalt surface
Thank you for your inquiry.
Here are a few tips, which you can do, to insure that your property is prepared:
What to use for ice control, you can use salt or chemical deicers such as Mag-Chloride. Keep in mind mag-chloride is a chemical which can have adverse effects on landscaping if it is constantly coming in contact with the vegetation. No matter what is used it should be used in moderation, using only what is needed and not to over treat the pavements.
If mag-chloride is going to be used it can be applied before a snow event to deter the formation of ice. This is the procedure most agencies use before a snow event. It is typically not as effective in parking lots.
Water is the primary culprit to any damaged asphalt during the colder months. So, whenever possible, as cracks develop they should be sealed to prevent water infiltration.
• Seal all cracks on your paved surfaces. This should be looked at 2 times per year to help protect your investment. You should look at the lot in the fall to seal the cracks prior to winter moisture and in the spring to see if the freeze thaw cycles of winter have created any thermal cracking. Crack sealing is one of the most inexpensive preventative maintenance procedures you can perform.
• Seal all open joints on your paved surface. This refers to any joints which were created during the construction of your asphalt pavement.
• Seal joints between concrete and paved surfaces especially on the north side of buildings where daily sunshine is at a minimum. This refers to those areas adjacent to any curb and gutter, drainage cross pans, etcetera. The purpose of this is to keep surface water from penetrating the surface and deteriorating the structural support for the asphalt materials.
• Make sure that your property has appropriate drainage. Proper drainage prevents potential pavement damage by quickly escorting unwanted water from the paved surface. Water is the biggest enemy of an asphalt pavement. Have a designated area where the snow will be piled when plowed. It should be on the lowest part of the pavement or off of the pavement if at all possible. If you pile the snow at a high point you will get water running across the pavement as it melts. During nighttime when that water freezes it will begin to deteriorate your asphalt from the constant freeze- thaw cycles. If the snow will be piled off of the asphalt it is best to not pile it on a high side where the melting snow and subsequent runoff will be directed under the asphalt. If at all possible all snow should be piled in a low point.
• Clean any debris from existing swales on your property that are used to contain and direct storm water from the pavement.
• Clean out any debris that has accumulated inside any drainage inlets. If the drainage is not moving as designed it can cause damage which will be unseen for some time. Once it appears the cost of repairs could be costly.
• Insure that the pipes used to transport the storm water to and from these inlets are not clogged and free from debris. (See above)
• Snow plows can cause heavy damage to adjacent structures, yards, landscaping, curb and sidewalks. To prevent collateral damage you will need mark these areas for those who clear the snow from your pavements. Another thing to consider about snow plows, is to watch for them causing damage simply from the plow being driven into the asphalt surface. One consideration is to require rubber edged blades on snow plows. This is not common so it may be difficult to find a vender who has rubber edged plow blades.
• Place reflective markers along the edge of existing pavements. Your plow company will not be as familiar with the lot as you are. Having monuments for them to see and not damage the curb, gutter, etcetera will help to keep the pavement intact.
• Place reflective markers along the edge of existing curb. (See above)
• Clearly mark sidewalks. This will help to keep you landscape intact. Many snow removal contractors use mechanical method for removing the snow on sidewalks. If the landscaping is left in place moisture can and will be absorbed back into the soils.
Follow these simple tips and you will be ready for the snow to fall.
Question: What is this NEW acyronym PC/OA?
ANSWER: “ PC/OA (PC = Process Control, OA =- Owners Acceptance) Testing” are the new terms to describe what for years we have refereed to QC/QA. The FHWA moved to change the description in 2015 and CDOT has adopted the change to the terms at of July 1, 2016. The RMAEC offers an introductory course designed to teach current CDOT/AASHTO test procedures used in the process control and owners acceptance of asphalt materials, and in the placement of asphalt pavement. This training is useful for both entry level technicians who are preparing for asphalt technician certification, as well as for more seasoned technicians who may be re-entering the testing arena. Inspectors and Engineers who desire more knowledge about testing procedures, how they are to be carried out during a paving project, and basic information on how the test results may affect the quality of the pavement, will also benefit from this course.
QUESTION: What specifications are available regarding release agents?
ANSWER: Your question is about Trucks and Paving equipment. It is in section 400 of the CDOT Specifications. 401.09 Hauling Equipment. Trucks used for hauling bituminous mixtures shall have tight, clean, smooth metal beds thinly coated with a minimum amount of paraffin oil, lime solution, or other approved release agent. Petroleum distillates such as kerosene or fuel oil will not be permitted. Each truck shall have a cover of canvas or other suitable material to protect the mixture from the weather. In 401.10 Bituminous Pavers it is not specifically spelled out. With that said it is stated in the CDOT specifications all release agents used on CDOT asphalt pavement projects must be on the Approved Products list (APL). To See all “Asphalt Man” Questions, click here
QUESTION: What is Roadway Smoothness? Understanding the importance of roadway smoothness.
ANSWER: Why should we care about pavement smoothness? Here are five basic reasons why: 1. Pavement smoothness is important to the user (taxpayer)., 2. Smoother roads last longer., 3. Smoother roads stay smoother longer., 4. Smoother roads are safer., 5. Smoother roads save money.
There are two basic types of smoothness specifications: those that consider measured smoothness, and those that consider actual ride quality. See the entire article from SmoothPavements.com
QUESTION: What is Intelligent Compaction for Asphalt?
ANSWER: Intelligent compaction (IC) is a construction method relatively new to the USA that uses modern vibratory rollers equipped IC components and technologies.
Though used for decades in the rest of the world, the IC technology is less mature for its application in the asphalt compaction than its counter part for the soils and subbase compaction. Under the on-going FHWA/TPF IC studies, tremendous amount of knowledge has been gained on HMA IC.
Components of asphalt IC include: double-drum IC rollers, roller measurement system, global position system (GPS) radio/receiver/base station, infrared temperature sensors, and integrated reporting system…. See the entire FHWA Brief
QUESTION: What is the proper thickness to place an Asphalt Mixtures based on Nominal Maximum Aggregate Size (NMAS)?
ANSWER: Lift thickness governs aggregate size. Minimum lift thickness should be at least 3 times the nominal max. aggregate size to ensure aggregate can align themselves during compaction to achieve required density and also to ensure mix is impermeable. The maximum lift thickness is dependent also upon the type of compaction equipment that is being used. When static steel-wheeled rollers are used, the maximum lift thickness that can be properly compacted is three (3) inches. When pneumatic or vibratory rollers are used, the maximum thickness of lift that can be compacted is almost unlimited. Generally, lift thicknesses are limited to 6 or 8 inches. Proper placement becomes a problem in lifts thicker than 8 or 8 inches. For open-graded mixes, compaction is not an issue since it is intended that these types of mixes remain very open. Therefore, the maximum size aggregate can be as much as 80 percent of the lift thickness.
QUESTION: What is the proper role of an inspector on an asphalt paving project?
ANSWER: Great question and very timely! As we start the paving season it is important to emphasis the important and yet proper role of the inspector. CAPA’s Tom Clayton provided a perspective that will be included in the June, 2016 issue of the Colorado Public Works Journal. Inspection for Quality Asphalt Pavements – Proper Inspection is a Key Component
QUESTION: Why is it important to manage my pavement condition index?
ANSWER: Pavement condition data is a critical component of any pavement management system. Establishing a quality management (QM) plan for pavement condition data collection will aid in achieving reliable, accurate, and complete condition data and will address steps to take when dealing with data quality issues. Without a documented plan, agencies are less likely to apply QM activities consistently from year to year and assess the effectiveness of the techniques used. See the entire FHWA Report
QUESTION: What goes into constructing an award winning project?
ANSWER: A quality project is based on: Overall Appearance, Segregation. Joint Construction, Ride Quality, Complexity/ Difficulty.
Overall Appearance This refers to the uniformity of the materials placed, consistency of appearance, construction quality, texture, workmanship, and the contractor’s attention to detail
Segregation Projects showing segregated areas due to paving operations, raking or broadcasting mix, etc. will be taken into consideration.
Joint Construction Longitudinal Joints will be evaluated as to how straight they are on tangents and how even and smooth their line is on curves. They will also be evaluated on how tight they appear and how even and smooth they are across the joint and how noticeable they appear.
Transverse joints will be evaluated as to how tight they appear and how even and smooth they are across the joint and how noticeable they appear and will be considered as part of both Ride Quality and Joint Construction.
Ride Quality Ride Quality addresses the smoothness of the ridge between lanes. Bumps, wheel chatter, areas of localized roughness, and transverse joints effect overall Ride Quality.
Complexity/Difficulty Project Complexity/Difficulty will be used when the complexity of issue to construct the project would and will weigh on the construction process. Examples of this are, but not limited to, winding mountain roadways, steep grades, dam face paving, etc.
The over all approach should be to concentrate on the small items and the big things will take care of themselves.
Question: What is the lift thickness to aggregate size ratio when using a Superpave mix?
ANSWER: Superpave guidelines require the minimum lift thickness be no less that 3:1 based on Nominal Maximum Particle Size (NMPS).Minimum lift thickness should be at least 3 times the nominal max. aggregate size to ensure aggregate can align themselves during compaction to achieve required density and also to ensure mix is impermeable. The maximum lift thickness is dependent also upon the type of compaction equipment that is being used. When static steel-wheeled rollers are used, the maximum lift thickness that can be properly compacted is three (3) inches. When pneumatic or vibratory rollers are used, the maximum thickness of lift that can be compacted is almost unlimited. Generally, lift thicknesses are limited to 6 or 8 inches. Proper placement becomes a problem in lifts thicker than 8 or 8 inches. For open-graded mixes, compaction is not an issue since it is intended that these types of mixes remain very open. Therefore, the maximum size aggregate can be as much as 80 percent of the lift thickness.
Question: Are there products on the market to make traditional asphalt in colors?
ANSWER: YES There are products in themarket toady where colorant can be added to the mixture as it is being produced and it will color the asphalt completely through not only a surface coating. One of the products is Asphacolor. The Asphacolor Corporation was created in 1992 to provide an alternative to plain black asphalt. In the not so distant past, asphalt could only be used for its utilitarian type qualities due to its plain black color. With the advent of the Asphacolor product line, asphalt takes on a whole new beautiful look while maintaining its unparalleled asphaltic qualities. There is no other colored paving anywhere that is more cost effective than the Asphacolor product line. The Asphacolor product line consists of two innovative products, Asphacolor Integral Color for Hot Mix and Asphacolor Integral Color Dry Sealant Mix.
Asphacolor Integral Color for Hot Mix is a cost effective; integral colored additive for conventional asphalt. The Asphacolor Integral Color for Hot Mix is added to the hot asphalt at the asphalt batch plant and delivered to the project site fully colored.
Conventional asphalt paving procedures are utilized in laying the integral colored asphalt.
Asphacolor Integral Color Dry Sealant Mix is our polymer fortified color additive for asphalt emulsion sealers. It is utilized to color asphalt that is already paved and for long-term maintenance of Asphacolor Integral Color for Hot Mix applications. Read more about the Asphacolor product
Question: Is there a big risk of placing Asphalt when the air temperatures drop below 30 F?
Answer: There is potential for problems to arise if Asphalt Paving Materials are placed in low temperatures! It is incumbent upon the contractor to adjust their operation to account for the difference in air temperatures. This is something that should be discussed early in a project if it is suspected paving will continue into the cold weather months by the contractor and owner or owner’s representatives. It is a no different in what happens when a project starts in the spring months and then is continuing into the hot and very hot Summer months. The paving operation needs to adjust to the conditions.
While the surface temperatures should be strongly considered in almost every case, the ambient temperature should be used as a guideline for the contractor and owner to use when making the decision to place materials. If the surface temperature is within the specified range in the specification for the lift to be placed based on location and thickness, the ambient temperature should be discussed even if it is not within the range described in the specification. If the ambient temperature is below those shown in the specification, the contractor should present a plan on how they will proceed with the placement. Low surface temperatures may decrease the temperature of the asphalt materials rapidly thus not allowing the contractor time to achieve the required compaction depending on the lift thickness and layer.
With the increased use of Warm Mix Asphalt (WMA) the temperature chart in many specifications will once again need to be discussed. Based on information readily available, the placement of WMA can and has occurred in temperatures much lower than the current temperature charts would allow.
In any case, there should be dialog from the contractor to owner to discuss all options available. If placement is delayed due to low AMBIENT temperature may have a much bigger consequence and cost than moving forward with caution. Ultimately the owner will make the decision as to what rick they are willing to accept! If they are determined to pave and the contractor feels the risk is too great, there will be discussion about a voided warranty and a warranty waiver which the contractor will ask the owner to sign with will limit or eliminate any warranty for the materials placed which are not following industry “Best Practices”.
Should we be concerned about rutting using thin overlays and smaller sized aggregates?
Answer:The best information on rutting of thin overlays or mixes with smaller aggregate size comes from the NCAT test track. The following are excerpts from NCAT Report 13-05, THIN HMA OVERLAYS FOR PAVEMENT PRESERVATION AND LOW VOLUME ASPHALT ROADS. ( Click here to see the entire answer)
What is “Pave Xpress” and how is it used to help design asphalt pavements?
Answer:Designing the right pavement for the job got easier thanks to PaveXpress, a free Web-based pavement design scoping tool for roadway and parking lot pavements. PaveXpress —www.pavexpressdesign.com — creates technically sound pavement structural designs for flexible and rigid pavements.
The American Association of State Highway Transportation Officials (AASHTO) has been developing the Mechanistic-Empirical Design Guide (MEPDG) over the last 15 years for State Highway Agencies. While the MEPDG has improved designs for high truck volumes and interstate highways, it has created a gap for local agencies and designers when the 1993 AASHTO Guide for the Design of Pavement Structures and associated DARWin software was discontinued.
To address this gap, NAPA and the SAPAs developed the PaveXpress web based software. It is an unbiased design tool based on nationally accepted methodologies including the 1993 AASHTO and 1998 AASHTO Supplement to the Guide for the Design of Pavement Structures.
Version 1.0 provided a tool to develop flexible and rigid designs and was released in October 2014. Version 2.0 provides an additional tool for Overlay Design (currently being deployed). Version 3.0 will provide a simplified mechanistic design for both new construction and overlays.
NAPA is currently providing free webinars to State and Local Agency Engineers, Consultants, Students, Pavement Design Instructors, and Contractors on the use of the PaveXpress design tool. CAPA will be presenting a webinar on November 17, 2015 on PaveXpress<< click to register >>
What is “Modified Rubblization”?
Answer:On some rubblization and asphalt overlay projects it is determined beforehand or during construction that the existing base and subgrade support is not adequate for complete rubblization. An effective solution is to reduce the fracture energy to produce a somewhat stiffer rubblized concrete layer that will provide adequate long-term support for the asphalt overlay while still eliminating “reflective cracking”. << click to read more information >>
Should a correction be applied to a nuclear gauge to achieve an accurate in place density number?
Answer: A nuclear gauge is only as accurate as the operator who is operating it and following “Best Practices” makes it. By this we mean, the surface which is being tested must be free of any loose materials and as tight as possible. In the case of an asphalt surface the the grading of the materials being placed and the ability of the crew placing the materials make a big difference. The more hand work being done, the more open the surface which causes air gap and loss of apparent density. This is why the testing technician needs to be looking at the surface and working with the paving crew to provide the best possible scenario for the testing to be accurate.
The testing technician needs to verify they have the most current laboratory information available on the materials being placed (IE Rice value) and not guess. Being off one pound can be detrimental to the long term results.
If the nuclear gauge has not been verified by obtaining cores recently, this should be done periodically as it is done on each State DOT project.
Question:What materials should be used when filling cracks 1.5 inches or wider?
<< click to read more information >>
Question: What are the important temperatures to be monitored for cold weather paving?
Answer: Temperature specifications are most often bundled for both ambient and surface temperatures, when in the asphalt paving world today ambient temperature should be considered and surface temperature used as a guideline.
Specifications often refer to the CDOT temperature specification (401-3) when deciding if Asphalt Placement should or can occur in a cold weather situation. The CDOT specification provides ranges of allowable temperatures depending on the situation. The situations are defined as top layer or layers below the top layer. Further the layer thicknesses are defined from less than 1.5 inches, from 1.5 to less than 3 inches and 3 inches or more. There is guidance and restrictions depending on the combination of the elements described above; however most specifications typically do not differentiate between ambient and surface temperatures.
In the Asphalt paving world today, these numbers should be considered when the placement of Asphalt is to occur but there should be a clearer definition as to what is trying to be accomplished by limiting placement at lower temperatures. While the surface temperatures should be strongly considered in almost every case, the ambient temperature should be used as a guideline for the contractor and owner to use when making the decision to place materials. If the surface temperature is within the specified range in the specification for the lift to be placed based on location and thickness, the ambient temperature should be discussed even if it is not within the range described in the specification. If the ambient temperature is below those shown in the specification, the contractor should present a plan on how they will proceed with the placement. Low surface temperatures may decrease the temperature of the asphalt materials rapidly thus not allowing the contractor time to achieve the required compaction depending on the lift thickness and layer.
With the increased use of Warm Mix Asphalt (WMA) the temperature chart in many specifications will once again need to be discussed. Based on information readily available, the placement of WMA can and has occurred in temperatures much lower than the current temperature charts would allow.
In any case, there should be dialog from the contractor to owner to discuss all options available. Not allowing the placement to occur due to low ambient temperature may have a much bigger consequence and cost than moving forward with caution.
Question: Where are we at on Intelligent Compaction?
Answer: FHWA recently did a demonstration here and our University research center took a bunch of cores to try to correlate and will be issuing a report soon. The technology is interesting and easy for the operators to understand. However, I have concerns about the accelerometer measuring stiffness of asphalt… a cold mat will measure stiffer and might suggest to the operator that he/she has achieved the desired density. It’s just not as easy as a red light and green light since asphalt stiffness is temperature dependent. It’s good technology but it seems like we’ve got a long way to go before it could be used as a true QC or QA tool.
One day it may be good for QC, but not for acceptance. Too many things are being measured with the accelerometer besides the asphalt. Just like testing with a FWD (not four wheel drive Jim Warren), you need more than one measurement. Mapping passes is great as long as everything is homogeneous, but with spatial variability you have to adjust. If the accelerometer reading tells the operator something has changed, then a new RP can be established. I see a big learning curve for operators once all the moving parts are put in place.
Question: What should you do if it begins to rain or rain is eminent?
Answer: In the CDOT required, LabCAT executed, RMAEC managed Asphalt Inspector Certification the subject of rain is discussed in some detail. In the training/certification this is what is instructed. In the Specification section of the certification program it states:
What are Contract Documents and Specifications? Specifications define the responsibilities of the Owner and the obligations of the contractor.
– Provide for the proper exercise of competent professional engineering judgment in obtaining satisfactory completed work encouraging the use of new equipment, materials, processes and
– Specifications are used to convey information concerning desired products from a buyer to a seller or potential seller.
Later in the section it states:
In the following slides, some of the items noted are required by project specification, while some are construction “Best Practices”. In the end all items will apply to the project and end result.
The information used is directly as it comes off of one of the slides in module. This information is based on what you have referenced from the Hot Mix Asphalt Paving Asphalt Paving Hand book (The Black Book).
– NEW! CDOT has removed the minimum compaction temperatures. The Specification now reads “The contractor may continue to apply compactive effort as long as they can demonstrate to the owner damage is not occurring”.
– HMA should be discouraged when temperatures are too low. WHY? Cold temperatures remove the heat from the mat too quickly.
– The mat may not stick to the intended surface.
– Be aware of any calendar day restrictions.
– Do not start paving when rains is about to start.
– Do not start paving too soon after a rain when there is free wather on the surface to be paved.
– Sprinkles will not harm the mat.
– Can cause problems with tac coat application.
– Can cool the mat rapidly so compaction can not be obtained.
– Check individual project specification, agency requirements may diffrer.
Question: Are you strugglling to achieve density?
Answer: A few possible issues causing your headache! What is causing the density to vary? This is a question which has been asked for years. The answer is long and complex but we will try to give you some highlights of possible issues:
– Mixture Porperties. What is your mixture made of? Is it a course graded mix or a fine graded mix? Fully crushed or only required to have two fractured faces? These can effect the way the materials move wityhin the structure. The more fractured the aggregate the more effort it will take to compact.
– What binder is in your mixture? “Neat Grade” binders will have a totally different effect that will a modifed binder. Not only the type of binder but the temperature of the binder will have a big effect on the way the materials move within the structure. Following the binder producers recommended mixing temperatures is important. The temperature should not be taken lightly, but special attention should be observed.
– Compaction equipment is another issue which should be considered when the density is not being achieved. Do you have the proper equipment from size and capibility? Are the operatiors utilizing all of the availble capacity of the equipment? The capcity of the equipment should be maximized when ever possible.
– Is segregation present? Not only material segregation, but more importantely thermal segregation should be looked at and attention should be apid to it. Varying temperatures in them aterials placed can cause major problems in achieving compaction. If the operator who is applying compactive effort has to determine what to do withthe equipment. When the temperatures are consistent across the mat, compaction is much easier to achieve because the roller patterens can be detrmined and followed.
For additional information, contact Tom Clayton.
Question: Tips on Minimizing Test Result Variability
Answer: Reducing the problems associated with test result differences is a continual challenge and one that we are regularly asked for information. The key is to minimize variability. Variability in test results is a combination of the variability caused by sampling, the test procedure and the material and construction process used. Sampling variability is caused by the random variation in the sampling methods and procedures. Even when everything is done right there will be some variation caused by the sampling process. Testing variability is caused by the random variation in the testing methods and procedures. Even when everything is done right there will be some variation caused by the testing process. Sampling and testing variability can cause up to 50% of the overall variation in the test results. Therefore, it is very important that the sampling and testing personnel be properly trained and that it is emphasized to them that they must follow the established procedures. There is some natural variation in the variability in materials and construction, but, it can also be controlled by using consistent construction practices and procedures.
Resources:<< Effects of Test Variability – 2000 AAPT TTI – Presentation >>
Question: Use of a Transfer Device:
Answer: In nearly all cases contractors are using a transfer device for placing SMA. Either a Roadtec or Weiler transfer vehicle shuttle buggy or a CoalCal or a remixer paver (ie. a paver with augers versus transfer chains being fed by flow boy trucks. Remixing reduces temperature variations and reduces the potential of fat spots. One contractor stated that it helps with both mat and temperature uniformity. Dumping the SMA mix directly from the truck into the paver is not advised (drain down, fat spots, inconsistencies in the mat, etc.). Make sure your fibers are consistent and consistently fed is a way to mitigate fat spots.
Question: Longitudinal Joints:
Answer: No single bullet for joint density. Two keys: 1. Getting enough material to the joint and 2. Developing a good roller pattern. One contractor triple tacks the joints, paves square and then uses a Wacker side plate to pre-compact a 2:1 slope. They used a heavy breakdown roller used in vibratory mode, first pass one foot off of the joint, second pass 2″ overlap, intermediate heavy roller in static mode. They also drove the water truck up and down on the joint. Another contractor uses a Wacker side plate to pre-compact material. Another contractor installed a tapered joint shoe on the paver, added a separate roller between breakdown and intermediate to focus exclusively on the joint. The best joint is one that is isn’t there through echelon paving. Another contractor stated that they pave an 1/8th of an inch high to ensure adequate material at the joint location. They tack the joint once, often use a small roller (DD34) to just work the joint. They also use two breakdown rollers in tandem to reduce roller marks. Best practice indicates the hot pass should overlap the cold pass by 1 to 1-1/2″. The material should be bumped back to the natural joint and not be broadcast across the mat. The first pass of the breakdown roller is 6″ to 1’ off of the joint, then back to confine the material at the joint over lapping the joint 4″ to 6″. It is imperative the joint be worked equally as the rest of the mat.
Question: Is CDOT approval needed to lower our design air voids from 4% to 3.5% and get more asphalt binder in our mixes?
Answer: No. State (CDOT) approval is not needed for a city to change the design air voids for mix requirements. The Pikes Peak Region Asphalt Spec. air voids requirement was changed in 2013 to 3.5%, see Section 1.003 on page #8. CDOT has established an approval process for warm mix asphalt technologies that local agencies can reference
Question: Is It Too Cold To Pave?
Answer: This question comes up every fall. We all know what the specifications say: “Hot mix asphalt shall be placed only on properly prepared unfrozen surfaces which are free of water, snow, and ice. The hot mix asphalt shall be placed only when both the air and surface temperatures equal or exceed the temperatures specified in CDOT Table 401-3 and the Engineer determines that the weather conditions permit the pavement to be properly placed and compacted.”
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Question: “A project that has situation where melt water is flash-freezing on the surface of a concrete parking lot. Grade of the parking lot is good. They want to explore if coating the surface with a black product could take advantage of thermal heat gain.”
Answer:<< click to read more>>
Cold Weather Paving
Question: Are there benefits of paving thicker in cold weather?
Answer: Often times specifications will require thinner lifts to be placed (1.5”) as the owner/specifier feels the compaction may be better achieved with thinner lifts. In cold weather conditions this may actually work against the contractor, and end result user.
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Minimum Layer Thickness
Question: Does CAPA have best practices for paving lift thicknesses?
Answer: There are industry standards on minimum paving thicknesses based on nominal maximum aggregate size. These standards are incorporated into the CDOT Lift Thickness Standards (shown below). The CDOT Pavement Design Manual (Section 3.6.2) includes guidance on both minimum and maximum lift thickness as it pertains to long term pavement performance.
2014 CDOT Pavement Design Manual (Section 3.6.2, page 3-11) Required Minimum Thickness of Pavement Layer
Compaction of a hot mix asphalt pavement during its construction is the single most important factor that affects the ultimate performance of the pavement. Achieving adequate compaction increases pavement performance by decreasing rutting, reducing damage due to moisture and oxidation, and increasing the stability of the mix. Factors affecting the cooling rate of the mat include the layer thickness, the temperature of the mix when placed, ambient temperature, temperature of the base, and wind conditions. Layer thickness is the single most important variable in the cooling rate of an asphalt mat, especially for thin lifts. This is especially true in cool weather because thin layers of asphalt mat have less capacity to retain heat than thicker lifts of pavement. The thicker layers of asphalt mat help to maintain the temperature at a workable level thus increasing the time available for compaction. Because of the increased difficulty in achieving density and the importance of achieving compaction, a minimum layer thickness for construction is two inches.
Coal Tar Sealants
Question: Does CAPA recommend the use of coal tar sealants?
Answer:The National Asphalt Pavement Association has never recommended the use of coal-tar sealants. The University of Wisconsin’s Solid & Hazardous Waste Education Center has a good fact sheet on alternatives to coal-tar sealants: In addition, a good person to ask about sealants in general would be Mike Kristoff at the International Slurry Surfacing Association: email@example.com or telephone: 410-267-0023.
Volumetrics in Asphalt Mixtures
Question: What about controlling asphalt mixtures during the mixture design process and during production?
Answer: Click the .PDF document to find the answer.
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Question: What are average prices for surface treatments in the Denver Metro Area (2013)?
Answer: Type II Micro — $4.00 – $4.75 a square yard.
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Question: How long have Perpetual Asphalt Pavements been around?
Answer: The Perpetual Pavement concept was first articulated in 2000 and the concept has rapidly gained acceptance.
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Question: Which Costs More, Concrete or Asphalt?
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Question: What Are The Types of Asphalt Pavement?
Answer:Mix Type Selection, Perpetual Pavement, Porous Asphalt, Quiet Pavement, Warm-Mix Asphalt.
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Question: Why Is Asphalt The Choice For The Colorado High Country?
Answer: Asphalt is the preferred pavement of choice in the Colorado high country because it:
– reduces the cost of construction
– the flexible nature of asphalt is better suited for the freeze/thaw cycles
– reduces the time of construction
– reduces the motorist impact during construction
– is easily maintained – at a lower cost and less motorist impact
– reduces snow and ice build up, thereby reducing road snow plowing costs.
Question: What Determines Minimum Lift Thickness?
Answer: Lift Thickness. Each lift of uncompacted Hot Mix Asphalt pavement shall be of uniform thickness. The minimum compacted lift thickness shall be three times the nominal maximum aggregate size of the mixture. The maximum lift thickness shall be 3 inches unless the Contractor can demonstrate his ability to achieve required compaction of thicker lifts. The final lift, when placed adjacent to guttering, shall extend 1 to 1 inch above the lip of the gutter when compacted for a catch curb and gutter and shall be even with a spill curb and gutter at the time of construction.” The standard thickness ratio is a minimum of 3:1. If your placing a S mix minimum thickness is 2.25” SX materials will have a minimum lift thickness of 1.5″.
This is from the document Guide Contract Documents for Asphalt Construction on Colorado Pavements.
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There is another document in the library which may help you as well, “Guideline for the Design and Use of Asphalt Pavements for Colorado Roadways”.
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Question: Can an asphalt overlay be placed over a roadway with an existing chip seal?
Answer: Placing an overlay on a road with an existing chip seal surface is not unusual and for some standard practice. The tack coat is the most important issue. Get it even, apply it at the correct rate, use the proper materials, make sure it is set and make sure the surface is clean and dry before you start. No problem. For more information, contact Scott Shuler, CSU Construction Management, Associate Professor, 720-289-2153, firstname.lastname@example.org.