Better Roads

August 2014

Better Roads Digital Magazine

Issue link:

Contents of this Issue


Page 9 of 35

RoadScience 8 August 2014 Better Roads In response, new-design asphalt mixes have come to the fore as stakeholders seek better-performing mixes at lower cost, say Son and Al-Qadi. These new asphalt mixes offer significant cost savings while improving structure and func- tion characteristics, including durability, friction, quietness, rutting, cracking and moisture susceptibility resistance. To evaluate field performance of these new mixes under actual traffic loading and environmental conditions, includ- ing the control mixes, pavement sections with six asphalt mixtures and various wearing surface thicknesses were con- structed. Two typical Illinois surface mixtures were selected as control mixes: a 9.5-mm NMAS coarse dense-graded mixture (F-mix) and a 12.5-mm SMA. The SMA mixture generally re- quires more durable aggregates, modified asphalt binder, and cellulose fibers, which makes it more expensive than typical dense-graded mixtures. Three fine dense-graded asphalt mixes with a 9.5-mm NMAS and one SMA with a 4.75-mm NMAS were developed for a relatively thinner wearing course. Locally available ag- gregates were employed, among them being a steel slag/fiber mix designed to provide good friction and high resistance to stripping and permanent deformation due to the use of steel slag. A blend of polypropylene and aramid fibers was added into the slag mix to improve its tensile strength, allowing placement at a relatively thinner layer thickness. A PG 70-22, SBS-modified asphalt cement was utilized, and the aggregate mix was 62.2 percent dolomite, 17.5 percent natural sand, and 20.3 percent slag. In-place field testing was performed immediately after construction and every four months up to two years. Testing at these intervals provided results for initial field performance and short-term performance for each section. The in-place field testing included onboard sound intensity measurement, laser longitudinal texture profiling, locked-wheel friction, and walking foot inclinometer (dipstick) rut measurement. Then the pavements were evaluated and scored, and using a formula, the authors converted the ranks to numbers to calcu- late the overall performance numerically from 0 to 10 (worst to best). The steel slag/fiber mix scored second highest in their performance rankings. LANDOLL DETACHABLES LANDOLL CORPORATION tXXXMBOEPMMDPN 22' to 32' Usable Deck /HQJWKVò´'HFN+HLJKW 35/55 TON DETACH 835 DETACH Call for a FREE Demo! 7H[W,1)2WRRUYLVLWZZZEHWWHUURDGVFRPLQIR

Articles in this issue

Links on this page

Archives of this issue

view archives of Better Roads - August 2014