In July 2019, National Road Research Alliance (NRRA) had a link to a special provision for the Automated Machine Guidance (AMG)—Milling Method written by Rebecca Embacher, Advanced Materials Technology Engineer-Minnesota DOT (MnDOT):
Automated Machine Guidance—Milling Method: This work consists of using automated machine guidance when removing the existing pavement by cold milling. The steering functions of the milling machine are operated by a contractor personnel, however, the milling operation is controlled by an onboard data acquisition system which automatically follow a Milling Surface Model to control variable depth milling based on inputs from robotic total stations.
- (2232) Mill Pavement Surface – Automated Machine Guidance – Milling Method Using Robotic Total Stations
- (2011) Construction Surveying – Automated Machine Guidance – Milling Method
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MnDOT currently recommends the use of AMG milling when milling an existing asphalt surface for whitetopping and when using the existing asphalt pavement as a bond-breaker for an unbonded concrete overlay. The AMG milling method allows for variable depth milling that helps address the varying in-place profiles, super elevations and crowns that are present in many of our roadways. Prior to use of this technology, corrections for these factors were achieved when paving the concrete and not during the milling operation. Consequently, this generated quantity overruns and negatively impacted pavement smoothness. All pavers perform best when operating at a consistent speed and placing a consistent depth of material. The AMG milling method creates the best opportunity to place a predictable amount of material in a uniformly smooth operation.
The AMG—Milling Method special provision says: “The steering functions of the milling machine are operated by a contractor personnel, however, the milling operation is controlled by an onboard data acquisition system which automatically follows a Milling Surface Model to control variable depth milling based on inputs from robotic total stations.”
The “Model” was the topic of an all-day discussion of Building Information Modeling (BIM) at MnROAD‘s recent Pavement Workshop. In short, the model is an agreed-upon computer generated 3D representation of the project. With this model, you can do a simple pave-to-depth after the AMG milling operation, said Embacher.
Dale Harrington, Snyder and Associates-Iowa, concurs and advocates a number of 3D modeling tools to save time, improve accuracy and save money on materials. He worked on a report titled “Implementation Manual 3D Engineered Models for Highway Construction.: The Iowa Experience” from NRRA Member, National Concrete Pavement Technology Center (CP Tech Center)-Iowa State University. In this report, “It describes how the state of Iowa uses 3D engineered models for construction of highway projects, from planning and surveying through design and construction.” Iowa has been using variable 3D milling since 2003.
Harrington said most of the major contractors in Iowa have adopted 3D modeling (and milling) because it saves them so much time and money. The smaller contractors who haven’t accepted these new construction technologies are going to be at a competitive disadvantage now and in the future. He added that accurate milling is important because it determines the profile of the road and, in turn, the quality of the paving. When the profile is good, the road surface doesn’t get too thin-risking failure, and is consistently smooth-which affects both the ride and overall performance of the road. Controlling thickness also helps control costs and overruns.
The future of 3D milling is now. With this special provision, it’s clear MnDOT is going in that direction. Embacher will be working with contractors to establish a roadmap for moving forward, as well as date to have this technology in place throughout Minnesota.
To read the MnDOT article about the AMG, please go to: http://www.dot.state.mn.us/mnroad/nrra/newsletter/currentissue.html?utm_content=&utm_medium=email&utm_name=&utm_source=govdelivery&utm_term=#3d