Asphalt Concrete Paving Interview Questions & Answers

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Asphalt Concrete Paving Interview Questions & Answers

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Asphalt Concrete Paving Interview Questions

Asphalt Concrete Paving Interview Questions
    1. Question 1. What Is A Prime Coat?

      Answer :

      An application of a low viscosity asphalt to a granular base in preparation for an asphalt surface course.

    2. Question 2. What Is The Purpose Of A Prime Coat?

      Answer :

      To coat and bond loose material particles on the surface of the base. To harden or toughen the base surface to provide a work platform for construction equipment. To plug capillary voids in the base course surface to prevent migration of moisture. To provide adhesion between the base course and the succeeding course.

    3. Question 3. What Asphalt Materials Should Be Used For Prime Coats?

      Answer :

      For a prime coat 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-30 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:

      Most emulsion manufacturers make proprietary products, one of which is an emulsion specifically designed for use in prime coats.

      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 1 part emulsion. By applying several (4 or 5) light applications (0.10 gal/sy), a waterproof surface can be obtained on the base course.

      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).

      Complete placement of the base course material, then scarify up about 3/4 inch. 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.

    4. Question 4. Is A Prime Coat Necessary?

      Answer :

      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 20 years, few, if any, pavement failures can be attributed to the lack of prime coat.

    5. Question 5. Why Is A Tack Coat Needed?

      Answer :

      To ensure a bond between the succeeding layers of a pavement.

    6. Question 6. What Material Should Be Used For A Tack Coat?

      Answer :

      A slow-setting emulsion, either SS-1, CSS-1, SS-I h, or CSS-1 h, works well when diluted 50/50 with water.

    7. Question 7. What Application Rate Should Be Used?

      Answer :

      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 tackled (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.

    8. Question 8. When Is A Tack Coat Necessary?

      Answer :

      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 in rapid succession, a tack coat may not be necessary. However, a good cheap insurance policy is to always use tack coats.

    9. Question 9. What Will The Asphalt Look Like When You Are Finished?

      Answer :

      Your edges should have pleasing lines, or contours. Smooth transitions, with no scalloping or depressions.

      The surface tension of the product is indicative of the density achieved in compaction.

      The black look of new asphalt begins changing almost immediately, until in a few years the aggregate appears in it’s true colour at the surface.

    10. Question 10. Why Does Asphalt Appear To Have Different Textures In Different Areas?

      Answer :

      here can appear to be some desegregation of course materials from fine at the surface. This is normal. Finishers will minimize this, but it does not reflect on the products integrity. The product’s appearance will change over time, and minor textural variations will fade.

    11. Question 11. Can The Same Paving Equipment Be Used For Superpave Mixes That Was Used For Conventional Mixes?

      Answer :

      Yes. However, since Superpave mixes tend to be coarser and contain modified binders than conventional mixes, good construction practices are more important than ever. Segregation is more likely to occur with coarser mixes if proper equipment and techniques are not used. Density can also be more difficult to achieve with Superpave mixes. Proper rolling techniques and adequate equipment are essential to achieve sufficient compaction. Breakdown rolling for Superpave mixes is normally done right behind the paver when the mix is hottest. Some contractors have found that additional and/or heavier rollers are sometimes needed. Pneumatic rubber-tired rollers work well, but tend to stick to the mat when polymer modified asphalt is used. Hand-working should be minimized. Sufficient well-graded (not segregated) material should be supplied by the paver augers to the joint to facilitate a low-void, low-permeability seam.

    12. Question 12. Is There A Problem With Milling Up And Recycling Asphalt Mixes That Used Polymer Modified Binders?

      Answer :

      Generally speaking, there are no unique problems with using polymer modified mixes as RAP. Some individuals express environmental concerns about running millings containing ground tire rubber (GTR) through a drum plant. Florida uses a small percentage of GTR on most of their highway surface mixes. California and Arizona also use GTR frequently.

    13. Question 13. What Is The Proper Mix Temperature?

      Answer :

      Mix temperature is dependent on the grade of asphalt used in the mix: Less viscous asphalt requires lower temperatures, while more viscous asphalt requires higher temperatures. At the start of a mix design, target temperatures are specified for proper mixing and compaction. These temperatures should be adjusted for 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.

    14. Question 14. What Is A Minimum Temperature For Asphalt Mixes?

      Answer :

      Mixes must be placed and compacted before they cool to 185° F, so the minimum temperature will depend on the temperature of the layer upon which it is being placed as well as ambient conditions. Generally, agency specifications will spell out a minimum acceptable temperature for the mix. Some specifications will use 225° F, and others may use 250° F.

    15. Question 15. What Is Asphalt?

      Answer :

      Asphalt is an engineered mixture of aggregate (stones and sand) with liquid asphalt cement (a petroleum product). Various sizes of aggregates are heated and then mixed in exact proportions with asphalt cement that has been liquefied at about 300°F.

    16. Question 16. What Are The Main Benefits Of Asphalt?

      Answer :

      Asphalt offers installation speed, usability and durability. It is also easy to maintain and the cost is not as expensive as using a paver or concrete.

    17. Question 17. How Long Does An Asphalt Driveway Last?

      Answer :

      If paved and maintained properly, it can last 20 years or more.

    18. Question 18. How Extensive Do My Repairs Need To Be? Will I Need To Replace The Entire Deteriorated Pavement?

      Answer :

      Have a Burnaby Blacktop estimator determine if a topical fix can work for you. For example, a parking lot with longitudinal cracking and some areas of fatigue (alligator cracking) can be fixed topically. None of the repairs are full depth. But areas of upheaval, rutting, large ponding are usually indicative of problems involving the base, or sub base.

      One of our friendly estimators will investigate the situation and provide consultation.

    19. Question 19. What Is A "thin Overlay"?

      Answer :

      Asphalt pavements can be prepared and overlaid with hot mix asphalt, resulting in a pristine product at a significant savings to a re/re. (Removal & Replacement).

      Your Burnaby Blacktop estimator will determine if a 1.5″ (40mm) overlay is a suitable application.

    20. Question 20. How Do You Ensure Hma Is Impervious To Water?

      Answer :

      Conventional mixes should be impervious to water as long as the total in-place air void content is below 7 to 8%. Mixes with higher void contents can be pervious to air and water leading to premature aging and raveling.

    21. Question 21. What Is The Proper Nominal Aggregate Size To Use?

      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.

    22. Question 22. What Should Be Used As A Mix Release Agent For Truck Beds And Rollers?

      Answer :

      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 approved release agents.

    23. Question 23. What Is The Proper Paver Speed?

      Answer :

      Paver speed should be geared to mix production and delivery. 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.

    24. Question 24. Why Does The Paver Pass Has A Rich Shiny Strip Down The Middle With Dull, Torn-looking Edge Strips?

      Answer :

      The paver screed has too much lead crown in it.

    25. Question 25. What Causes The Paver Pass Have Rich Shiny Strips On Each Side And A Dull, Torn Look In The Middle?

      Answer :

      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.

    26. Question 26. How Many Rollers Are Required?

      Answer :

      Contrary to popular belief, 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, one roller may be adequate. On very large projects, six or eight rollers may be needed. A lot of projects are impacted with three rollers: a breakdown roller, a compaction roller, and a finish roller. On most average projects, two rollers are used – a vibratory steel-wheel 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.

    27. Question 27. What Is The Recommended Air Void Content For Compaction Of Asphalt Pavements?

      Answer :

      Efforts should be made to control compacted air voids between 7% and 3%. At 8% or higher, interconnected voids which allow air and moisture to permeate the pavement, reducing its durability. On the other hand, if air voids fall below 3%, there will be inadequate room for expansion of the asphalt binder in hot weather. When the void content drops to 2% or less, the mix becomes plastic and unstable.

    28. Question 28. How Is Air Void Content Controlled?

      Answer :

      Air voids are 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.

    29. Question 29. What Is The Best Way To Check Density?

      Answer :

      Nuclear gauges are generally 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.

    30. Question 30. How Do The Lab-compacted Air Voids Of “reheated” Asphalt Mixture Samples Compare To The Air Voids Of “original” Mixture Samples (as-produced, Not Reheated)?

      Answer :

      There is not a predictable value or “rule-of-thumb number” for the difference in air void content of original and reheated samples. The general trend would be for the reheated samples to have higher air voids than the original, compacted specimens. Absorption and hardening or stiffening of the asphalt binder in the reheated samples likely causes this difference. Reheated samples can be utilized to give an overall check of the original sample results. Before any significant precision is attributed to reheated sample results, a correlation should be developed for reheated sample air voids and original sample air voids by performing a series of comparative tests.

    31. Question 31. Can Asphalt Be Applied In The Rain (light Drizzle)?

      Answer :

      It is not advisable to start paving if it is raining. If rain starts after paving has begun, the work can continue as long as there is no standing water and the rain is not too hard. The 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 to achieving adequate density.

    32. Question 32. Can You Pave In The Rain?

      Answer :

      New construction paving can often be completed in rain, but in some cases rain will cause delays in scheduling. Asphalt overlays are not done in the rain because the new asphalt will not properly adhere to the old asphalt.

    33. Question 33. What Should We Consider When Hiring Contractors?

      Answer :

      It is important that you look into the materials that will be used, and the reputation (and credentials) of the contractor. You will want a contractor who understands your needs. Some clients have economic constraints. Burnaby Blacktop will work with you; though we may not always “say what you want to hear.”

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