California Department of Transportation

Random Crack Sealing

Random Crack Sealing Machine
Random Crack Sealing Machine

Technical Description

The unique technologies developed in this project are the long-reach robotic arm, operator control system, and automated sealant application system.

The telescopic robotic arm has a 12 ft by 13 ft workspace. A telescopic arm was used, because it does not require a supporting frame that extends beyond the standard eight foot wide highway width restriction, either for transport or during operation. The telescopic design also fits neatly under the truck bed, leaving the entire truck bed available for supplies and support equipment.

The arm is driven by two electronic servo motors, one for extension and the other for rotation. The arm can position the sealant head anywhere in the workspace within a couple of millimeters. The arm pivots up for transport.

The controller was designed for simplicity of use and reliability of operation. Because an operator chooses cracks from a screen, the system is less complex than a fully-automated, vision-recognition system. As a result, the system is robust, can operate under a wide variety of lighting conditions, and can better respond to operator preferences.

The controller system makes full use of current computer networking technologies and uses multi-threaded program code. The computing power has been distributed among several independently functioning sub-systems, which allows for execution of many automated tasks simultaneously and reduces the cost of computer hardware. As a result, the system can be operated from a standard laptop computer in the cab of the truck, or over a wireless network from a remote location.

The automated sealing head is similar to a head developed for previous AHMCT projects, except that it has been redesigned to operate at the end of a telescoping arm, require less maintenance, incorporate additional remote control features, be cheaper to build, and be easier to clean.

Since the head is designed to seal cracks at speeds up to three feet a second, the sealant delivery system is a key component. The sealant is delivered to the head through an electrically heated flexible hose that uses a revolutionary new low power, flexible internal heating element. The hose runs from the melter pump through the hose tray below the truck bed deck and out through a passage inside the telescoping arm to the sealing head mounted at the end of the arm.

Development Goals

The goal of this project was to build a fully functioning self-contained truck mounted automated sealing system that could a seal full lane-width of in-lane cracks. The machine is intended to be a showcase of technology and the use of new technology to increase the safety of highway maintenance operations. The demonstration of this machine is intended to set in motion a discussion of how this technology could be packaged into a crack sealing machine that could be commercialized. We welcome any suggestions and inquiries to this end. You can email comments to


The OCCSM has used to successfully seal several random pavement cracks on campus roads with sealant. In an effort to obtain the best possible tooled seal appearance, several types of sealant ring materials have been experimented with. A thin silicone rubber ring seems to produce the best appearance. Unfortunately, before highway testing could begin, an electrical short in the sealant hose assembly developed, which halted testing. The hose assembly is in the process being replaced so testing can be continued. Progress on the OCCSM has been put on hold until after the TTLS is completed.