Dowel bar insertion or “DBI” is the process for mechanically inserting reinforcing dowel bars into concrete during the paving process. It is intended to eliminate tied rebar cages or mats placed in front of the paver. The traditional method of dowel bar insertion is the automatic dowel bar inserter which is a highly automated and dedicated machine.
The dowel bar inserter offers contractors advantages of convenience, flexibility and labor cost savings. With no tied cages or baskets in front of the paver, it allows the concrete to be delivered and placed directly in front of the paver rather that requiring a placer, pump or conveyor to deliver concrete from the side. A dowel bar inserter also eliminates the need to purchase the pre-tied rebar cages or baskets and the labor required to place them.
There are several challenges with the traditional automatic dowel bar inserter system.
- There is inconsistency of bar placement. Bars are often missing and misplaced. Because of the automated nature of the process, there is no way to verify the correct placement until the testing equipment (sonar, etc.) test the placement and then it is too late as tear out is then required. Because of this, some states in the USA have banned automatic DBI systems.
- Current Automatic DBI systems are extremely complicated. There are many moving parts that require extreme precision. This creates constant mechanical issues.
- Unwieldy size of the equipment requires disassembly/reassembly for movement to and from the job site. A crane is required and the machine is down for days.
- An automatic DBI system is overwhelmingly expensive, costing upwards of $2 million USD.
- The machine has limited use, it is restricted to DBI projects without significant modification.
The HEM Manual Dowel Bar Inserter (MDBI) Alternative
HEM has developed as alternative to the automatic DBI system which achieves the advantages discussed above and addresses the challenges. The Manual Dowel Bar Inserter (MDBI) system utilizes standard paving equipment with an attachment which allows for controlled dowel bar insertion.
The MDBI attachment connects to the rear of a standard slip form paver and uses the existing hydraulics. The dowel bars are placed into the delivery chutes by operators on the work platform and pressed into the concrete by a series of hydraulically driven rams.
The Six Step HEM MDBI Process
FIRST. The concrete is delivered via dump truck or transit mixer. The concrete can be placed directly in front of the first paver as no dowel bar cages or baskets are obstructing. No additional placing equipment is needed.
SECOND. The first slip form paver paves as normal. Vibrators, tamper bars and pans consolidate as a normal or non-DBI project.
THIRD. As the first machine approached the designated dowel bar insertion point, the operator stops the machine momentarily. Insertion points are visually marked on the ground or overlapping pour with a stake or paint. The MDBI operator station has a switch which allows the machine travel to be paused (the vibrators, augers, tampers, etc., continue to run). This pause allows for correct placement of the bars without dragging the bars through the newly poured concrete.
FOURTH. Once the machine is stopped, the operator cycles the MDBI to insert the dowel bars into the concrete. The operator opens the gates on the chutes to release the dowel bars onto the top of the newly consolidated concrete. Then he and workers inspect the drop to ensure that all the dowel bars are in the correct position and orientation.
The operator now lowers the carriage of the MDBI, which starts the vibrators and lowering rams to drive the dowel bars into the concrete to the appropriate depth. The operator then raises the carriage of the MDBI, pulling the rams from the concrete and shutting off the vibration. While the carriage is cycling, the workers are reloading the chutes with the dowel bars for the next cycle. The operator now releases the paver and it continues paving forward until the next dowel bar insertion point.
FIFTH: As the first paver moves forward workers inspect the freshly inserted dowel bars for proper placement and orientation. Any adjustments can be made at this time.
SIXTH. A second paver closely follows behind the first paver to reconsolidate the concrete and provides the smooth finished surface. If a transverse center dowel bar is required, it is inserted with this machine. The auger is NOT run on the second machine so as not to disturb the consolidation.
The tamper bar and vibrators run on the grade level to liquify just the concrete surface for the pans to provide the final consolidation and finish. Burlap is drug behind the second machine or on a trailing texture cure machine if required.
Advantages of the HEM MDBI System
With the HEM MDBI system you receive all the advantages of a DBI system (no dowel bar cages, labor and equipment saving) PLUS:
- Cost. Two machines with the HEM MDBI attachment cost less that a traditional Automatic DBI.
- Dual Purposed. When the MDBI is not needed, the two pavers can be easily converted to traditional slipform paving.
- Ease of Maintenance. Significantly fewer moving parts.
- Reliable. Visually verified placement of dowel bars.
- Transportable. Each machine can be self-loaded onto a trailer for movement to/from work site.
- Resale Value. As standard slip form pavers, each machine can be resold for everyday use.
Click on video to watch the HEM MDBI system in operation.
Your contacts at HEM are:
- Darren Huinker for USA domestic at
+1.319.240.9068 or Darren@hempaving.com.
- For international contacts, Rick Eisiminger at
+1.540.729.0619 or firstname.lastname@example.org.
The HEM website is www.hempaving.com.