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| Small Paving Projects and Residential FAQs |
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While there are an infinite number of questions that can be asked, we compiled a list of those questions that have been directed to us the most. These FAQs are categorized into the 12 subject areas shown below. We tried to keep both the questions and answers concise. Additional information related to the question and answer can be found in the references provided at the end of the answer.
You can also refer to our TECHNICAL PUBLICATIONS and WORLDWIDE HOT LINKS sections to find the information you need. We also recommend attending our technical seminars at sites throughout the country to obtain expert instruction on asphalt topics. You can obtain more information about these seminars, including schedules and registration, in our EVENTS section. Note: Some questions are repeated. Whenever a question is appropriate for more than 1 subject area they have been put each applicable area. |
A link provided at the end of each question which takes you to a list of Asphalt Institute Publications and Audio-Visual Programs that have more in depth information on this subject area.
See a list of Asphalt Institute Construction Leaflets (CLs). Items pertinent to the Asphalt Pavement Construction subject area.
Q. |
What is a prime coat? |
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A. |
An application of a low viscosity asphalt to a granular base in preparation for an asphalt surface course. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What is the purpose of a prime coat? |
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A. |
More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What asphalt materials should be used for prime coats? |
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A. |
For a prime to be effective it must be able to penetrate into the base course. Usually a light grade of medium curing cutback such as an MC-70 will work well. However, in a lot of areas air quality is of concern and the EPA has restricted or eliminated the use of cutbacks. In such areas the use of an emulsified asphalt is necessary. There are several ways to accomplish a prime when using an emulsion: First , most emulsion manufacturers make proprietary products, one of which is an emulsion specifically designed for use in prime coats. Second : If the granular base material has a gradation that is somewhat porous, placing a prime coat can often be affected by placing a slow-setting emulsion (SS-1, SS-1 h, CSS-1, CSS-1 h) diluted 5 parts water to I part emulsion. By applying several (4 or 5) light applications (0.10 gal/sy), a waterproof surface can be obtained on the base course. Third : Incorporate an emulsion into the compaction water while placing the last 2 to 3 inches of the base course. Use a dilution and application rate which will provide 0.1 to 0.3 gallon per square yard (3:1 dilution; 4 applications; 0.15 gal/sy rate). Fourth : Complete placement of the base course material, then scarify up about three quarters inch (3/4"). Apply about 0.20 gal/sy 2 of straight emulsion (undiluted) and blade mix it with the scarified material. Then relay the mixed material and compact. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
Is a prime coat necessary? |
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A. |
At one time it was thought that a prime coat was an essential element of good pavement construction. However, in recent years some engineers have eliminated the use of a prime, especially when asphalt layer(s) (surface and/or base) is 4 inches or more in thickness. In many instances, prime coats have not been used even when surface thickness have been as thin as 2 inches. Over the past twenty years, few, if any, pavement failures can be attributed to the lack of prime coat. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What is the proper mix temperature? |
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A. |
Mix temperature will be dependent on the grade of asphalt used in the mix. The less viscous the asphalt, the lower the temperatures should be. The more viscous the asphalt, the higher the temperature can be. During mix design temperatures are specified for proper mixing and for compaction. These are good targets with which to start a project. However, they will have to be adjusted for the project conditions (weather, haul distances, etc.). If at all possible, avoid discrepancies from the mix design temperature of more than 25 degrees. Note: When working with modified binder, the binder supplier should provide mix temperature recommendations. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What is a minimum temperature for asphalt mixes? |
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A. |
Mixes must be placed and compacted before they cool to 185 o F, so the minimum temperature will depend on the temperature of the layer upon which it is being placed as well as ambient conditions. Temperature session charts are shown on Page 6-6, Fig 6.03 of the new MS-22 and Page 234 of the old MS-22. Generally, agency specifications will spell out a minimum acceptable temperature for the mix. Some specifications will use 225 o F, and others may use 250 o F. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
How do I ensure HMA is impervious to water? |
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A. |
Conventional mixes should be impervious to water as long as the total in-place air void content is below 7 to 8%. Mixes with void contents higher than this can be pervious to air and water leading to premature aging and raveling. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
Why is a tack coat needed? |
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A. |
To assure a bond between the succeeding layers of a pavement. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What material should be used for a tack coat? |
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A. |
A slow-setting emulsion, either SS-1, CSS-1, SS-I h, or CSS-1 h, works well when diluted 50/50 with water. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What application rate should be used? |
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A. |
You want to accomplish a very uniform application of about 0.03 to 0.05 gal/sy of residual asphalt on the layer to be tacked (a paint job, so to speak). Slow-setting emulsions generally have a residual asphalt content of about 2/3. Therefore, an application rate of 0.10 to 0.15 gals/sy of the diluted material will give you the 0.03 to 0.05 gals/sy. Caution #1 : Once the tack coat is applied, time must be allowed for emulsion to break (turn from brown to black) prior to placing hot mix on it. The length of time required for this to happen will depend on the weather. In good paving weather, it will take only a few minutes. In marginal weather it may take several minutes. Caution #2 : Never apply an emulsion tack coat to a cold pavement (below the freezing point). The emulsion will break, but the water and emulsifying agents will freeze and remain in the layer that has been tack coated. If either of these cautions is violated, there is a good chance that upper layer will not bond to the under layer and a slip plane will develop. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
When is a tack coat necessary? |
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A. |
Almost always! On rare occasions when a pavement is being constructed which is not being used by traveling public and each succeeding lift is placed only a short time later, a tack coat may not be necessary. However, a good cheap insurance policy is to always use tack coats. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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PLANT OPERATIONS |
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Q. |
How can you tell that a mix is properly mixed? |
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A. |
When all the aggregate particles are coated with asphalt. The large aggregate particles are always the last to be coated. If the large aggregate particles are completely coated, the mix is properly mixed. Generally we see mixing problems only with batch plants. The producer is trying to mix each batch as quickly as possible (probably in about 30 seconds) which may or may not be adequate mixing time. Typical specifications set minimum coated particle percentages at 90 to 95 percent. The Ross Count procedure for determining these percentages (ASTM-D2489 or AASHTO T195) is outlined on pages 4-41 to 4-44 of the new MS-22 and 162 and 163 of the old MS-22. Minimum mixing times to meet the specified requirement should carefully adhered to in order to avoid excess oxidation of the asphalt films on the aggregate particles as it is exposed to air (oxygen) during the mixing process. As a general rule we do not see this problem with drum mixes. The mix remains in the mixing portion of the drum for much longer periods of time (maybe 2 to 3 minutes) than in the pugmill of a batch plant, so the aggregate particles get very well coated. Keep in mind that we are not as concerned about oxidation in drum mixes as the mixing portion of the drum mixer is essentially an oxygen-free atmosphere. Another way to look at it is this: In a 6000 lb. batch of mix, there are about 5600 lbs. of aggregate and about 400 lbs. of asphalt. Dense-graded aggregate has about 35 sq. ft. of surface area per pound, or 196,000 sq. ft/6000 lb. batch; 400 pounds of asphalt is about 48 gallons. The mixing process has to take 48 gallons of asphalt and paint about 3.8 football fields. When the aggregate particles are coated, it's mixed. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What should be used as a mix release agent for truck beds and rollers? |
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A. |
Far too often we still see diesel fuel used as a mix release agent. Diesel fuel is a solvent. Any excess amount will dissolve the asphalt films on the aggregate particles, thus contaminating the mix. Commercial mix release agents are readily available and should be used. They generally are soap or emulsified wax or other stick-resistant materials that do not contaminate the mix. A couple of suggestions are a bag of hydrated lime mixed with 1000 gallons of water or a bottle of dish soap (Joy) mixed with water. The portions depend on the water with which it is mixed. Soft water won't need nearly as much as hard water. It has been our experience that a special release agent is required for modified asphalts. Contact your local State Department of Transportation for a list of approaved release agents. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
How do I determine how much asphalt is required for a project? |
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A. |
Here's the process: 1. Calculate the number of cubic feet to be paved. (Remember to convert the thickness to feet - by dividing by 12 inches per 1 foot). 10' x 25' x (4/12)' = 83.3 cubic feet of HMA 2. Asphalt Mixture typically weighes from 142 to 148 pounds per cubic foot (PCF) in-place. Use 148 PCF. 3. Calculate the tonnage needed. (remember to convert from pounds to tons; 2000 pounds per ton). 83.3 cubic feet x 148 PCF = 12328 pounds of mix = 12328 / 2000 tons = 6.1 tons More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What is the proper paver speed? |
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A. |
Paver speed should be geared to mix production, delivery and compaction; with emphasis being placed on compaction. Every effort should be made to maintain a constant paver speed. Several factors effect that constant speed. With a consistent production and delivery flow, the speed of the paver will vary with lift thickness and width of paver pass. Thicker lift -- slower speed; thinner lift -- faster speed. Wider pass -- slower speed; narrower pass -- faster speed. Most equipment manufacturers will give a suggested maximum speed for their paver. A lot of agency specifications will specify a maximum speed, such as 30 or 40 feet per minute. Most compaction manufacturers recommend a maximum roller speed of 3 mph and most often more than one roller pass is needed to get compaction. Therefore, the number and type of rollers being used is very important. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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| Q. | Is it ok to cool down the laid mat immediately using water for early traffic? | ||
| A. | We do not recommend spraying water on freshly laid hot mix asphalt (HMA) in order to cool the mat faster and open to traffic sooner. First, spraying water on the hot mat is not very effective since the water should drain properly on a new surface and only cools the crust temporarily, with the internal HMA temperature not being affected much. In addition, there is a concern that the water could cause a foaming effect with the hot asphalt binder, making the HMA less stable under traffic. We believe it is best to let the hot mat cool naturally. | ||
| Q. | What is acceptable in terms of standing water or “ponding” on parking lots and other asphalt pavements? |
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| A. | The Asphalt Institute recommends a transverse slope of between 1.5 to 3.0% on all pavement surfaces, and an even steeper slope of 3 to 6% on shoulders. Maintaining a slope of at least 1.5% on parking lots will ensure proper surface drainage (no ponding or birdbaths) and minimize infiltration, hydroplaning and the detrimental effects of water. | ||
Q. |
How many rollers are required? |
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A. |
Contrary to most people's thinking, the number of rollers required for proper compaction is based on the square yardage placed rather than the production or delivery tonnage. Roller speed should be limited to 3 mph. With this speed and the width of the roller, the coverage rate can be calculated. The width of paver pass and speed can give you the square yardage placed. The number of required coverages will then tell you the total area in square yards the roller must be able to cover. On very small jobs, 1 roller may be adequate. On very large projects, six or eight rollers may be needed. A lot of projects are compacted with three rollers: a breakdown roller, a compaction roller, and a finish roller. On most average projects, two rollers are used - a vibratory steel-wheeled roller for breakdown and compaction, and a heavy static steel wheel for finish rolling. Occasionally, agency specifications will require a light (65 to 75 psi contact pressure) pneumatic roller to be used to knead or seal the surface prior to the finish rolling. |
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Q. |
What is the recommended air void content for compaction of asphalt pavements? |
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A. |
Efforts should be made to control compacted air voids between 7% and 3%. Once voids reach 8% or higher, you get interconnected voids which allow air and moisture to permeate the pavement which reduces the durability of the pavement. On the other hand, if air voids fall below 3%, there will be inadequate room for expansion of the asphalt binder in hot weather and when the void content drops to 2% or less, the mix becomes plastic and unstable. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
How is air void content controlled? |
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A. |
Air voids is a reverse proportion of the density of the compacted mix. By specifying a density requirement, the voids are inversely controlled. Keep in mind that density is a relative term, compared to a target density of either lab compacted mix, a maximum theoretical density, or a control strip density. Procedures for using the three methods are spelled out on 7-17 to 7-21 of the new MS-22 and Page 241 of the old MS-22. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What should compaction requirements be? |
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A. |
Testing should be done on a random sampling basis with a minimum of five tests per lot ("lot" as spelled out in agency requirements, usually a 'A day's or full day's production). The average of the five density determinations should be equal to or greater than: 1) 96% of lab density with no test less than 94% 2) 92% of maximum theoretical with no test less than 90%. 3) 99% of the control strip density More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What is the best way to check density? |
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A. |
Generally we see nuclear gauges used for density testing because of the ease and speed with which the testing can be done. This allows for many more tests - more than the five minimum for a better statistical result. Caution : The nuclear density gauge needs to be correlated to core densities that are taken from the same location as was nuclear gauge tested. This should be done for each different mix that might be used. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What causes tire scuffing and what should be done about it? | ||
A. |
See the following pdf document: Position Paper - Tire Scuffing & Indentations by the Ontario Hot Mix Producers Association | ||
Q. |
Why does paver pass has a rich shiny strip down the middle with dull, torn-looking edge strips? |
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A. |
The paver screed has too much lead crown in it. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What causes the paver pass has rich shiny strips on each side and a dull, torn look in the middle? |
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A. |
The paver screed does not have enough lead crown in it. Note : Paver screeds should have slightly more crown in the leading edge than in the trailing edge - usually about 1/8 inch. This may very with equipment manufacturer and/or width of paver pass. Even if the trailing edge of the screed is to place a flat or straight grade, the leading edge must still have the increased crown. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What might cause surface cracking on newly placed asphalt concrete? The cracking occurred during the breakdown rolling and finish rolling. |
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A. |
Without knowing what the surface cracking looks like, it is hard for us to identify the problem. Could the "surface cracking" be checking cracking from the rolling operation? It is shallow hairline surface cracks spaced an inch or two apart from each other and running transverse to the direction of rolling. The cause is rolling on the mat too hot and/or too tender of a mix. You can reference page 6-9 of the new MS-22 and page 219-220 of the old MS-22 manual if you are not sure what checking is. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
What structural value does a chip seal add to a pavement? |
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A. |
None More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
Should a newly paved driveway or parking lot be sealed (or seal-coated)? |
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A. |
No. A well designed and constructed low traffic volume pavement, such as a driveway or parking lot, should not require sealing for approximately 2 to 5 years – depending on severity of climate and quality of original work. If a new pavement is porous, meaning it allows water into the pavement rather than shedding, or draining off, the rain, this pavement might benefit from a light application of a low viscosity asphalt emulsion. See Application Instructions below. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
When should a driveway or parking lot be sealed? |
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A. |
Sealing is effective to renew old asphalt surfaces that have become dry and brittle with age, to seal small surface cracks and surface voids, and to inhibit raveling (loss of surface aggregate). So, sealing should be done as soon as any of these distresses are noted. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
How should driveways and parking lots be sealed? |
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A. |
A light application of a slow-setting asphalt emulsion diluted with water should be applied. In most cases, a dilution of one part emulsion to one part water is used. SS-1, SS-1h, CSS-1, or CSS-1h asphalt emulsions are typically used. Commercial sealers are also available. Those containing coal-tar compounds are not recommended. The diluted material is sprayed or squeegeed onto the surface in a thin, uniform coating. The total quantity of diluted sealant normally applied is 0.1 to 0.15 gallons per square yard. Exact quantities should be based on the surface texture, dryness, and degree of cracking or raveling. Excess application must be avoided since this may result in pick-up on shoes or tires. Vehicles must be kept off the seal until it is absorbed into the existing surface. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
Why do potholes occur and what is the best way to fix them? |
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A. |
A very good reference on causes of potholes and the best way to fix them is our MS-16 manual, Pavement Maintenance. This manual discusses all the various asphalt pavement distress types and the proper repair methods. See also Pavement Distress and Repair Chart. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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Q. |
Do de-icing salts or calcium magnesium acetate (CMA) have a detrimental affect on asphalt? |
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A. |
Research has proven that well-designed and well-constructed asphalt pavements are not damaged by sodium and calcium chloride salts used for ice and snow control. The same is true for calcium magnesium acetate (CMA), which is often used as an alternative to road salt. References include: Performance of Asphalt Pavements Subjected to De-Icing Salts , B.F. Kallas, Highway Research Record #24, 1963. Effects of Calcium Magnesium Acetate on Pavemetns and Motor Vehicles , D.S. Slick, Transportation Research Record #1157, 1988. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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| WEATHER | |||
Q. |
Can asphalt be applied in the rain (light drizzle)? |
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A. |
Definitely not good to start paving if it is raining. If it starts raining while paving, the work can continue as long as there is no standing water and the rain is not too hard. Primary concern is achieving adequate compaction, as the mix will cool much faster due to evaporative cooling if laid on a wet surface or rain falls on an uncompacted mat. Additional compactive effort will be needed and monitoring temperatures is key. Not a good situation, but can work. Getting adequate density is key. More detailed information can be found in the list of Asphalt Institute Publications, and Audio-Visual Programs dealing with this topic area. |
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| Driveway Construction | |||
Q. |
What do I need to know about building my asphalt driveway? |
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A. |
The following document, developed by the Ontario Hot Mix Producers Association (OHMPA) in Toronto , CA , is an excellent introduction to the key elements in constructing a quality asphalt driveway. Thickness is a crucial element that cannot be compromised. 2” of compacted Hot Mix Asphalt should perform well when placed on a stable, well-compacted granular base of 6" or more . 3” or more of Hot Mix Asphalt should be used if the driveway is placed in areas of unstable soils and/or when marginal granular base is provided. |
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| SPECIAL APPLICATIONS | |||
Q. |
Is there a way to color an asphalt pavement other than shades of black and grey? |
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A. |
While not widely used, there are ways to color an asphalt pavement other than the different shades of black and grey we are used to. The first is to use a natural colored aggregate. As the asphalt binder wears way from the surface with traffic, the colored aggregate is exposed and that natural color will be exposed. A second way to color asphalt is to use an additive in the asphalt binder such as an iron oxide (rust) to give it a reddish tint. Green, yellow and orange are also possible with different iron compounds. Other colors require different metal compounds. A special “synthetic” binder that contains no asphaltenes has been used because it colors more readily. By tinting the asphalt binder, the hot mix asphalt pavement is colored full depth for that material, so there are no surface wear-off concerns. A third way to color asphalt is to coat the surface with a material that penetrates the voids and bonds well to an asphalt pavement, such as an epoxy-fortified acrylic emulsion. Many colors are available with these types of surface coatings. Care should be taken that these surface coatings do not negatively affect surface friction if the pavement is used for vehicular traffic. One possible disadvantage of these systems is that they may wear off with time and need to be renewed. The second and third options are considered specialty products and more information can be obtained by contacting individual manufacturers. |
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