Pavimentos

INCORPORATION OF SULFUR EXTENDED ASPHALT MIX
IN PERPETUAL PAVEMENT DESIGN

Submitted to the International Conference on Perpetual Pavement 2009

July 23, 2009



Dr. David H. Timm, PhD, P.E. (Corresponding Author)
Gottlieb Associate Professor of Civil Engineering
238 Harbert Engineering Center
Auburn University
Auburn, AL 36849
Phone: 334-844-6282Fax: 334-844-6290
email: timmdav@eng.auburn.edu

Mary M. Robbins
Graduate Research Assistant
238 Harbert Engineering Center
Auburn University, AL 36849
Tel: 334-844-4320
email: mmr0001@auburn.edu

Richard W. May
Senior Research Engineer
Shell Sulfur Solutions
6505 E. Central Street, #294
Wichita, KS 67206
email: rmayconsult@gmail.comAbstract
It has been well documented that controlling the tensile strain at the bottom of an asphalt pavement can prevent the development and propagation of bottom-up fatigue cracking. Preventing this distress, through rational mechanistic-empirical (M-E) pavement design, is one step toward perpetual pavements. Though controlling this strain can beachieved by increasing asphalt concrete (AC) thickness, some engineers and researchers have proposed using higher-modulus asphalt materials in the lower pavement lifts without increasing, or perhaps even decreasing, the asphalt thickness. A recently-developed material called Shell Thiopave®, which is a warm mix asphalt (WMA) sulfur-based additive, has been proposed as a means of increasing theAC modulus and reducing the thickness in perpetual pavements. To fully test this material, a perpetual pavement section was constructed at the National Center for Asphalt Technology (NCAT) Test Track in 2009 and subjected to accelerated traffic loadings over an initial two-year research cycle. Prior to construction, however, there was a need to conduct M-E analysis to investigate this material ina theoretical framework. This paper details the laboratory testing results and M-E design process undertaken to evaluate the Thiopave-modified warm mix asphalt (WMA). Dynamic modulus testing was conducted on mixtures with 0%, 30% and 40% Thiopave. These data, along with previously-developed data sets from the NCAT Test Track, were entered into the computer program, PerRoad, to execute a seriesof perpetual pavement designs. Eight Thiopave cross-sections were evaluated that utilized different combinations of sulfur-modified lifts. Additionally, one control section was developed that did not contain Thiopave in any of the lifts. The designs were first evaluated in PerRoad such that 90% of the strain values were kept below 100 . The 100  value was chosen as a conservativethreshold based on historical laboratory testing. A second set of designs was developed where 90% of the strains were kept below 295 . This value was based on in situ strain measurements made at the Test Track over previous research cycles in sections that did not develop bottom-up fatigue cracking. The 100  limit control section resulted in 16 inches of AC to control fatigue cracking while it wasfound that the Thiopave sections could be 2-4 inches thinner, depending on the amount of sulfur-based modifier used in the cross-section. The control section for the 295  limit was 7.5 inches of required AC to alleviate fatigue, with the Thiopave sections requiring 0.5 to 1.5 inches less, again depending on the amount of sulfur based modifier in the cross section. Based upon thisinvestigation, it appears that Thiopave has the potential to reduce the overall required pavement depth while still controlling strain at the bottom of the pavement. A vertical stress investigation was also conducted to evaluate rutting potential. Based on the findings of this study, it was recommended that 7 and 9 inch cross sections be constructed. The full-scale experiment will serve to validate many...