Hot recycling in site
Hot recycling in site – complex environment-friendly repair of bituminous roadways in one working process.
Reasons to use it
Symptoms of the beginning disintegration of bituminous roadway wearing course of roads, motorways, local roads and other areas are various. Damage or wear can be characterized according to following visible marks:
- Various kinds of surface cracks
- Surface corrosion (crumbling and falling-out or grains)
- Insufficient surface roughness
- Insufficient coherence of layers, separations of the wearing course and the base course
- Permanent surface deformations, such as road grooves etc.
The above mentioned damages can be repaired either by traditional methods of bituminous roadway surface repairs, like various large area maintenance modifications (maintenance coats, micro-carpets, slurry seal), or by means of total replacement of decomposing roadway wearing courses, milling them and laying new courses including the prescribed connecting sprays. Hot recycling in site offers new, progressive technologies of bituminous roadway repairs. The reason why these repair methods are more and more used is the regeneration of existing roadway surface in site. The original surface structure and surface flexibility are renovated and according to the used technology the original profile grade is either kept or strengthened in one or two layers. In comparison with the traditional repair works, this method is cheaper, faster (only one working process) and it is environment friendly.
Technology and fields of application
Hot recycling set consists of some preheaters (Baltom uses three of them), which slowly warms the repaired bituminous layer up to the needed temperature with a propane-butane infra heater. Then, the key building machine, the remixer, comes, and disintegrates the heated layer and mixes thoroughly the bituminous mixture obtained this way, according to the requested finish with or without additional components (bitumen, aggregates, bituminous mixture). The final part of the remixer is in fact a finisher, spreading the mixture again, re-profiling and precompacting it. Finally, the compaction of the recycled mixture by means of rollers is carried out. This equipment in fact allows four basic variants of hot bituminous layers recycling.
In this kind of recycling, only the bituminous wearing course re-profiling (reshaping) is done (mostly only the wearing course) in the case, when the composition of bituminous mixture of this layer has the required mechanical and physical properties. By means of infrared heat the bituminous layers are warmed up to depth between 60 and 70 mm. Then the remixer disintegrates and profiles (reshapes) the heated material up to depth between 30 and 50 mm.
This technology also includes re-profiling (repaving) the original bituminous wearing course of the roadway, but it requests strengthening of the roadway with another wearing course. The recycled and re-profiled original wearing course now becomes the base course, on which the wearing bituminous layer of new bituminous mixture is laid at the same time without connecting spraying. Between 30 and 100 kg of new mixture can be laid per 1 m2, which represents strengthening of the roadway by 10 to 40 mm.
The principal difference of this technology against the first two variants (Reshape, Repave) is that the original bituminous layer is conditioned (remixed) to get the requested physical and mechanical properties by adding necessary components. The remixer construction enables to add a bituminous bonding agent and bituminous mixture according to the specified mixing formula. To stabilize and soften the original bituminous mixture, 5 to 30 % of new materials are usually added.
This method of roadway bituminous layer repairs is the most modern one, and it is connected with the permanent improvement of remixers. As well as in the 'repave' variant, it includes two bituminous layers being created at the same time. The difference is that the original bituminous wearing course is conditioned by means of the 'remix' technology, adding necessary components on the basic recycled layer corresponding to base course properties. On this course, the new wearing course is laid. The institution responsible for management of roads must have information about the state of roadway construction (including bearing power and transport load) and about wearing course mixture properties in order to decide for one of the ways of bituminous roadway repair. The most convenient way to determine properties is a laboratory analysis of the mixture from sample bores. To get the most convenient proposal of hot recycling, it proves good if the institution responsible for management of roads cooperates with an independent road laboratory. According to our present experience, the repair works are mostly carried out by technologies remix and remix plus.
Influence on the environment
Hot recycling in site has a positive influence on the environment for the following reasons:
- All original materials are 100% recycled.
- Hot recycling in site saves raw material resources and costs, and eliminates the problem of milled material storage.
- On the top of this, the surrounding of the site is not disturbed by dust, as the bituminous mixture is disintegrated and processed without the need of crushing. This way no dust is created, like it happens for example when using the traditional method of road cold milling and following surface cleaning.
- The only waste product arising from the repair process is water vapour.
Other advantages of hot recycling in site
Compared with the other methods to repair bituminous roadway wearing course, the hot recycling in site has the following technical, technological and economic advantages:
- Hot recycling (especially the technologies remix a remix plus) is a method of complex roadway repair during one working process.
- This technology is used without the need to exclude the traffic (road transport is guided to one traffic lane and directed by mobile light signalling).
- Remix and remix plus are jointless technologies, because the transversal and longitudinal joints are heat treated directly during the laying, which makes the degree of compacting the same as in the centre of the traffic lane.
- During hot recycling, the material of the original bituminous layer is 100% reused.
- During hot recycling, the profile grade of the repaired roadway wearing course is minimally increased, which in many cases excludes secondary costs, as it is not necessary to adjust the height of kerbs.
- The remixer is designed for re-profiling (reshaping) of recycled layer based on the removal of longitudinal unevenness and on the adjustment of transversal grade.
Types of equipment used
The optimal solution of hot recycling in site is also connected with a possibility to use various types of remixers, because it is possible to carry out some repair works with a machine of a different working width.
It is possible to choose from five different types of remixer. The most frequently used remixer RM 4500 of working width up to 4500 mm used for repair of the whole traffic lane can be replaced by the remixer of working width between 1000 and 1250 mm, or between 1600 and 2500 mm. These remixers are suitable for smaller and local repair works.
Joint remixers represent a special group of machines, being used for longitudinal working joints. Opening of working joints in traffic lanes is a frequent defect of bituminous wearing courses. For these repair works we use remixers of working width 300 and 600 mm. It is a jointless technology as thanks to warming up an area wider than the remixed traffic lane during compaction, the mixture of the original roadway and the recycled mixture of the repaired joint connect perfectly.