|June 2017 Newsletter|
Perpetual Pavement Award Section on I-35 Continues Long Life
Brandon Brever, P.E. (MAPA) – In 2002 a section of I-35 was awarded a national Perpetual Pavement Award. This summer the same section of Interstate 35 from Willow River to Scanlon is undergoing full depth reclamation for nine miles on the north and southbound lanes to continue as a long life pavement. The section has been in service for 50 years from initial base construction followed by mill & overlays. Various innovative technology and construction techniques were used on this project to provide a long-lasting asphalt pavement for the traveling public.
Software Update Helps Ensure Long Life of Pavements
The 4.3 version of PerRoad Perpetual Pavement design software has been released. Developed at Auburn University, PerRoad uses the mechanistic-empirical design philosophy to estimate stresses and strains that would prove detrimental for fatigue cracking or structural rutting.
PerRoad Version 4.3 incorporates recent research conducted on the Pavement Test Track at the National Center for Asphalt Technology at Auburn University and then validated with live traffic on Perpetual Pavement sections. The new features allow PerRoad to perform a conventional mechanistic-empirical (M-E) design to directly compare against Perpetual Pavement designs. It can also use strain distribution or a single endurance limit strain value to design a Perpetual Pavement.
“Perpetual Pavement designs allow us to limit distresses to the easily repaired surface,” stated David Timm, Ph.D., P.E., developer of PerRoad. “By coupling layered elastic analysis with a statistical analysis procedure, PerRoad helps a designer understand the layer thicknesses and other values that will ensure a long-life asphalt pavement.”
PerRoad is available for free at www.asphaltroads.org/perroad
Cold In-Place Recycling Presentation & Project Visit
On June 23rd Midstate Reclamation and Trucking hosted a presentation in Taylors Falls followed by a project visit to a nearby Cold-in-place Recycle (CIR) operation. CIR uses a train of equipment to mill, crush, inject additives, pave, and compact the mix. Once the existing old pavement is milled and crushed, additives are injected into the cold mix. Emulsion and foamed PG graded binder are commonly used additives in the process. Other modifiers are: portland cement, Quicklime/hydrated lime, lime slurry, and add rock.
CIR is a tool to be used at the right place and at the right time. Project selection is important in this process. The base needs to be structurally sound with adequate drainage. Coring, GPR, construction records and mix design should all be used in the selection process to determine if CIR is the correct choice. The depth of CIR is typically 3 to 4 inches but can also be done at 4 to 5 inches.
Balanced Mix Design for Asphalt Mixtures
Reprinted with permission from National Center for Asphalt Technology (NCAT) – In September 2015, the FHWA Expert Task Group on Mixtures and Construction formed a Balanced Mix Design Task Force. This group defined balanced mix design (BMD) as “asphalt mix design using performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate and location within the pavement structure.” In short, BMD incorporates two or more mechanical tests such a rutting test and a cracking test to assess how well the mixture resists common forms of distress. The Task Force identified three potential approaches to the use of BMD: volumetric design with performance verification, performance-modified volumetric mix design, and performance design.
Thinlay Projects On The Ground – Pavement preservation projects in Ohio
Thinlay asphalt mixtures made their debut this construction season beginning with the placement of Thinlay preservation treatments in Dark, Vinton, Clemont, and Preble counties in Ohio. The trials demonstrated Ohio’s Thinlay could be placed in a 0.75 inch thin course and with a consistently uniform texture – a factor important to pavement preservation and overall pavement durability.
2018 Specification Updates