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 subject areas listed in the contents dropdown box below.
We tried to keep both the questions and answers concise. Additional information is referenced where applicable for those seeking more in-depth information on a given subject.
We also recommend that you attend our Asphalt Academy courses at sites throughout the country to obtain expert instruction on asphalt topics.
Thickness & Mix Design FAQs Contents
|Q.||What is the proper mix temperature?|
|A.||Mix temperature is dependent on the grade of asphalt used in the mix. Less viscous the asphalt requires lower the temperatures, while more viscous asphalt requires higher temperatures.At the start of a mix design project, target temperatures are specified for proper mixing and compaction. These temperatures should be adjusted for project conditions (weather, haul distances, etc.). Whenever possible, variances of more than 25 degrees from the mix temperature should be avoided.Note: When working with modified binder, the binder supplier should provide mix temperature recommendations.|
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)?
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.
|Q.||How do you determine the thermal conductivity of asphalt cement?|
|A.||The equation we have used for thermal conductivity is:K = (0.813/d)*(1-(0.0003*(t-32)))where:
d is the specific gravity at 60F/60F
t is the temperature in F
K is the thermal conductivity (BTU-in)/(hour-ft2-F)This information comes from page 870 of Asphalts and Allied Substances, 4th Edition , by Herbert Abraham (published in 1938).
|Q.||What is the vapor pressure of asphalt at typical storage temperatures?|
|A.||It is estimated that at a typical inventory temperature of 325°F, the vapor pressure of petroleum asphalt is less than 0.01 psia (1.5e-3 kPa).|
|Q.||What is the typical thermal BTU value for a pound of asphalt?|
|A.||BTU varies by temperature and per cent mineral matter in the asphalt. A range is usually quoted, but we have used approximately 158,500 BTU/gal. This value is an average for an AC-10 grade. Most refineries will have a calorimeter somewhere in the lab that is used to run this test. Each company should run its own test on the specific product that is being used.|
|Q.||What is a typical value for the specific heat of asphalt cement?|
|A.||The conventional method for determining specific heat for asphalt is listed as follows:c = (0.388 + 0.00045*T)/(d 0.5 )Where c = specific heat in BTU per pound per °F or calories per gram per °C
d = specific gravity of the asphalt at 60/60°F
T = temperature, F A typical value for specific heat for a paving grade asphalt binder at 300°F is 0.515. This assumes a specific gravity of 1.030.This information comes from page 870 of Asphalts and Allied Substances, 4th Edition , by Herbert Abraham (published in 1938).
|Q.||How can I learn more about polyphosphoric acid modification of asphalt?|
|A.||Two excellent resources:1) Our publication IS-220, Polyphosphoric Acid Modification of Asphalt. You can order off our website. 2) A workshop on Polyphosphoric Acid Modification of Asphalt Binders was conducted in Minneapolis , MN on April 7-8, 2009. This workshop was jointly sponsored by the Transportation Research Board (TRB), Federal Highway Administration, Minnesota Department of Transportation, TERRA, Association of Modified Asphalt Producers, Innophos, ICL Performance Products, and the Asphalt Institute. All the speaker presentations (both slides and videos) are now available for public viewing at the following link. https://engineering.purdue.edu/NCSC/PPA%20Workshop/2009/index.html|
|Does AI have any information about asphalt and its use in railroad beds?|
|Railroad information can be found in the Construction, Thickness and Design, Maintenance and Rehabilitation, and Pavement Performance Documents pages.
You can also visit a web page on the University of Kentucky website where you can download papers, PowerPoints and also the computer program called KENTRACK, which is computer program for hot mix asphalt and conventional ballast railway trackbeds.
Additional AI Resources:
- Mix Design Technology Certification
- Optimizing Volumetrics and HMA Compactability
- An Introduction to the Bailey Method (Optimizing Volumetrics and HMA Compactability)
- Asphalt Mix Design Basics
- Asphalt Mix Design Using RAP & RAS
- Interpreting Asphalt Test Results
- Laboratory Performance Testing of Asphalt Mixtures
- MS-1 Thickness Design-Highways & Streets
- MS-2 Mix Design Methods for Asphalt Concrete and Other Hot-Mix Types
- MS-4 The Asphalt Handbook
- MS-17 Asphalt Overlays for Highway and Street Rehabilitation
- MS-22 Construction of Hot Mix Asphalt Pavements
- MS-22S Principios de Construccion de Pavimentos de Mezcla Asfaltica en Caliente
- MS-23 Thickness Design – Asphalt Pavements for Heavy Wheel Loads