Development of Balanced Mix Design for Thin Asphalt Overlays for Collector and Local Roads
Description
Thin overlays are favored by local agencies due to their ability to extend the pavement'slifespan and enhance ride quality. However, the low thickness of thin overlays presents
some inherent challenges. The use of conventional mixes for constructing thin overlays has
led to numerous premature failures, primarily due to the relationship between compaction,
the Nominal Maximum Aggregate Size (NMAS), and lift thickness.
The current study's objective was to utilize a balanced mix design to enhance the quality
of mixes used by local agencies by developing two new dense-graded mixes and one Stone
Matrix Asphalt (SMA) mix. Local mixes were collected and studied, working closely with
industry experts. This research work aimed to identify the performance characteristics of
commonly used mixes, optimize these mixes, and design new mixes that better suit their
intended application, thereby prolonging the life of overlays.
The findings indicated that while the current mix designs are fundamentally wellstructured, they are not appropriate for the given application due to the unsuitability of a
12.5 mm NMAS for mix designs below 38 mm, especially considering that most overlays
are less than that. The results also showed that the current mixes are already optimized in
terms of cracking and rutting resistance.
Three new mixes with 9.5 mm NMAS aggregates and SBS modified binder were
designed. These include two dense-graded mixes using PG 76-22 SBS and PG 70-28 SBS
modified binders, and one SMA mix utilizing the PG 76-22 SBS modified binder. All theseii
mixes demonstrated better cracking properties compared to commonly used mixtures.
While their rutting properties were either comparable or occasionally inferior but meeting
the rutting criteria.
Based on these findings, it can be proposed that the use of a 9.5 mm NMAS mix
improves compaction and compatibility with lift thickness. Additionally, these mixes
reduce susceptibility to cracking and extend service life of the overlay. To get a superior
overlay mix, SMA can be employed as it had 2.5 times better CT Index compared to the
conventional 12.5 mm mix.
Date Created
The date the item was original created (prior to any relationship with the ASU Digital Repositories.)
2023
Agent
- Author (aut): Hasan, Morshed Washif
- Thesis advisor (ths): Kaloush, Kamil E
- Thesis advisor (ths): Noorvand, Hossein
- Committee member: Ozer, Hasan
- Publisher (pbl): Arizona State University