California Department of Transportation

History of Automated Crack Sealing Development

Fully Automated Sealing Effort

Crack filling and sealing is necessary to ensure roadway structural integrity and extend the time between major rehabilitation. Conventional crack sealing operations exposes workers to traffic and can be tedious. A typical sealing operation involves a large crew sealing 1.5 to 3 km per day, while the crew is exposed to moving traffic in adjacent lanes.

Early Version of the Automaed Crack Sealing Machine
Early Version of the Automated Crack Sealing Machine

AHMCT began the development of automated pavement crack sealing systems in 1991 when we were contracted by Caltrans and the Strategic Highway Research Program (SHRP) to design and build a fully automated, self-contained crack sealing machine.

The SHRP H107A Automated Crack Sealing Machine (ACSM) was fully operational in 1993 and could rout, hot blow and seal longitudinal and random cracks automatically. The ACSM completion had to coincide with the previously scheduled SHRP sunset and was then to be passed over to the Federal Highway Administration (FHWA) for implementation.

FHWA was interested in continuing the support and operation of the ACSM as a nationwide demonstration of this technology and requested that we submit a proposal for continued funding. Meanwhile Caltrans, the other funding partner, felt that our resources would be better focused on the development of less sophisticated near term deployable pavement sealing systems. To determine the best direction, an independent product marketing study and cost benefit analysis was conducted on the ACSM.The marketing study favored the development of smaller scale machines that distributed ACSM sub-systems onto specialized independent vehicles. Reacting to the study results, AHMCT moved away from the all-in-one full automation system approach and focused development of specialized sealing systems.

The Automated Crack Sealing Machine (ACSM) was developed to identify and seal all types of highway pavement cracks. It was a self-contained vehicle that could both seal cracks entirely within a highway lane and seal longitudinal cracks alongside the vehicle.

The ACSM's integrated system was completely modular, and allowed various combinations of sub-assemblies for sealing procedures that may differ from state to state. It was a three-axle truck with line scan vision (video) systems mounted on the front and side, and a robot positioning system mounted at the rear of the vehicle. Computer systems were housed on the truck bed, as were peripheral support systems.

The ACSM was demonstrated a few times over the next year, but without continued support, systems were becoming inoperable. The fast pace of computer technology and the then lack of industry standardization, made the job of maintaining the ACSM in working order very complicated and demonstrations ceased. The ACSM was later used as a platform for a related automated router project and in 1998 it was disassembled.

The ACSM project was a success in that it was intended as a demonstration of technology and has been the only fully automated pavement sealing machine ever put in operation.

Development has continued on many of the systems initially developed in the SHRP H-107A project, but on separate smaller scale platforms that someday may be used in conjunction to constitute a fully automated crack sealing system.

Specialized Sealing Systems Effort

AHMCT continued the development of specialized sealing systems after the SHRP contract ended without interruption. The development of separate SHRP subsystem machines not only had marketing advantages, but also had technical advantages as well.

The move away from a fully automated system drastically reduced system complexity. The machine no longer required a program that in all practicality could never account for every possible "what if" scenario and of course the hardware to run it in real-time. Instead the objective would be to develop human operator supervised automation where an operator's assets could be combined with the machine's abilities to increase system capabilities while reducing its complexity. Operator interaction is intended to be supervisory in nature leaving the mundane tasks to be automated.

Another technical benefit was gained by adopting the specialized function approach. The separate machines would be developed to function together if necessary to complete a multi-operation task. Our experience revealed that the disadvantages of all on one platform systems out number their advantages and the shear volumes of waste created with the crack preparation and consumables required for sealing effectively overburdens any single truck's capacity. The ACSM truck chassis was the largest legally available and it still lacked the material capacity to ever be used in the field.

Longitudinal and Random Sealing

During the ACSM development, it quickly became evident that automated crack sealing needed to be divided into two categories, longitudinal and random.

Longitudinal and random crack types have altogether different accessibility and technology requirements. Both crack types could in principle be addressed by one system in one pass, but the overall production rate would be considerably slower and cumbersome.

The ACSM actually consisted of these two separate sealing systems, the Longitudinal and Random that were mounted together on one platform utilizing common resources. Therefore, developing separate machines was fairly straightforward, especially because different groups initially developed the various ACSM sub-systems separately and later integrated them together on the ACSM platform.

The longitudinal sealing system was spun-off as the Longitudinal Crack Sealing Machine (LCSM) and the random crack sealing system was spun-off as the Operator Controlled Crack Sealing Machine (OCCSM). AHMCT has continued our evolution of automated sealing systems through the development of these two machines.

Crack Preparation

Quality crack sealing is a synthesis of many factors, and depending on climate zone, crack preparation is one of the most important.

The SHRP project dictated that the ACSM be capable of performing the most common methods of crack preparation. Our analysis showed that if the machine was developed with the ability to rout and blow with hot air cover, it could be utilized in all of the nation's climate zones.

The two crack preparation systems were only operational on the longitudinal part of the ACSM at the end of the SHRP project. The system to blow the crack out with hot air consisted of a high CFM propane fired blower capable of traveling at seven feet per second.

The pavement router was similar to the standard impact wheel with carbide star cutters, but was hydraulically driven. The router device could rout asphalt pavement at three feet per second. After the SHRP project ended, AHMCT continued the development of the routing system to deal with random cracks. The project was called the Tethered Mobile Robot Router (TMRR).