In-Place Pavement Recycling
Roadbed Modification (RBM) is an in-place recycling method for pavements. Pavements showing distresses such as base failure, stripping, rutting, transverse cracking, flushing and bleeding are candidates for reconstruction using roadbed modification instead of simply overlaying with additional asphalt concrete. Poor or wet subgrade is often the most critical contributing factor for many pavement distress situations. RBM increases the load-carrying capacity of the base course, thereby allowing the asphalt section to be constructed more thinly. RBM can increase the Traffic Index of an existing roadway by increasing the recycling depth. The recycling of the existing base and old asphalt section into the new base course means that the only material brought to the job is the new asphalt wearing course. In addition, since the road can be opened for traffic at the end of each day, it requires less traffic control, resulting in less inconvenience to the driving public.
In terms of construction, RBM is quite versatile. The project engineer does not normally have to deal with issues relating to poor subgrade. RBM “bridges” over most problem areas, thus avoiding cost overruns and project delays. Options available to the engineer include increasing the reagent content or increasing the depth of the section to accommodate any problem areas.
Description of the Process
The existing surface is pulverized full depth, usually 8 to 12 inches. The pulverized material is then graded to allow for the new asphalt section. Following the grader is the spreader truck, laying down 3 to 5 percent Cement or Quicklime Plus to the pulverized base and old surfacing material. Processing of the RBM includes mixing all materials to a specified depth, compaction of the mixture, and finishing of the completed base. The roadmixing machine is a cross shaft type and is capable of providing a uniform homogeneous mixture. It is also equipped to introduce water at the time of mixing. Computers control the input of water and reagent. A metering device is used to control the correct quantity of water to produce a homogeneous mix with uniform moisture content. After the materials have been mixed, bladed and compacted to the engineers specifications, a curing seal is placed and the road opened up to limited travel. This can all be achieved on the same day.
- Pavement distress caused by subgrade or base failure, cracking, oxidation, or flushing
- Under-designed pavement section
- Pavement that has reached its life span
- Recycling of existing pavement section eliminates the need to off-haul old pavement materials
- Eliminates the need to import new baserock and reduces the amount of asphalt required
- Eliminates having to expose soft, saturated subgrade soils
- Roadbed Modification provides a long-term solution to base failure, which is a contributing factor to many pavement distress situations.
- The benefits of using this method to stabilize and improve the performance of the base include increasing the load-carrying capacity of the pavement structure, which increases the pavement life.
- RBM utilizes the existing pavement, eliminating the need and cost of transport and disposal of the material. It is a cost effective, versatile construction method that utilizes existing material and equipment.