This process uses the thermoplastic principle, used in many highways maintenance and construction materials.
That principle being that thermoplastic materials are plastic, workable, able to be moulded when hot, and for all practical purposes solid when cold.
The thermoplastic component of the material used for imprinting is a resin, not a bitumen.
The resin can be a natural resin obtained from natural sources such as old tree roots and waste timber from commercial forests, or it can be a synthetic resin obtained from the oil industry.
An appropriate amount of resin is mixed with suitable proportions of fine aggregate, sand and fillers, and pre-packed in a mixed condition in polythene sacks ready to be placed in a boiler and heated and mixed.
As with nearly all thermoplastic material there are temperature guidelines that must not be exceeded and recommended times for storage at particular temperatures.
Overheating or keeping material hot for long periods of time will cause the degradation and embrittlement of the resin component and hence a reduced life of the laid material.
Performed correctly by a skilled gang, with well designed thermoplastic material, this process does produce long lived patterned road surfaces.
The main cause of failure that I have encountered with this process has been caused by weakness in the underlying road pavement, causing cracking and detachment of the resin bound layer.
There are several patterns available to choose from according to the effect desired.
CREATING A VISUAL AND TEXTURED DEMARCATION BETWEEN A SIDE ROAD AND A MAIN ROAD
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This
is one of a number of junctions where low trafficked roads are accessing a
busy main road. To add emphasis to this situation and, hopefully, to make vehicles more aware of a potential hazard situation, it has been decided to apply a raised, textured and coloured surface to the junction, as shown. Because the junction was in both good surface condition and good structural condition it was decided to employ an imprinted hot thermoplastic process as described in this sequence of pictures. Although expensive this process was the least cost option because no work was involved in reconstruction of the road pavement. Should a reconstruction, or new construction, be necessary other options are available with competitive overall costing. |
| EQUIPMENT All the equipment necessary for the process is bought to site on a large lorry. This includes two "boilers" for heating the thermoplastic material, and a compressor. The compressor is used to provide compressed air for the "jack hammer" in preparing the joints, and for the hot air lance. All the thermoplastic material also comes to site on the lorry but only a couple of bags remain to be seen (next to the blue "oil drum") as the work is almost complete and stocks have been used. |
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HEATING
THE THERMOPLASTIC MATERIAL The thermoplastic comes pre-blended in 25kg. polythene bags. It comes in a "neutral" condition/colour and pigment is added at the time of heating to produce the required colour for the particular site. There are two "boilers" on this lorry so that material can be used from one boiler while the other boiler is heating material to the required temperature. This eliminates time waiting for materials to heat up, increasing the production of a steady stream of hot material You will see this is a labour intensive operation, if a steady flow of the operation is to take place, and a continuous surface with no "breaks" in the appearance is to be achieved. |
| PREPARATION
OF THE ROAD SURFACE Here you can see the "tie in" between the existing surface and the hot applied thermoplastic material. A vertical joint of approximately 20mm. depth has cut into the existing road surface, in this case hot rolled asphalt and precoats. This vertical joint is feathered to the existing road surface over a distance of approximately 25cms.. As the thermoplastic is laid approximately 15/20cms. thick this creates a level "tie in" at the existing road surface and then forms a slight hump that can be felt by traffic as they pass over it. You can also see the road surface being prepared by blasting with hot compressed air, this removes any dust, dampness and mild contamination. |
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APPLYING HOT THERMOPLASTIC
MATERIAL TO THE ROAD SURFACE The hot thermoplastic material, fresh from the boiler, being poured on to the road surface for the operators with the "paddles" to form a level, uniform thickness layer that can be imprinted. For most sites the thickness of layer is usually between 15cms. and 20cms.. |
| PREPARING THE SURFACE OF THE
MATERIAL PRIOR TO IMPRINTING Sufficient area of prepared thickness of thermoplastic needs to be achieved before imprinting can take place, and it has to be achieved quickly so that the materials is still hot enough to be "molded" by the pressure from the pattern "former". In the background you can see an operator preparing absolutely dry sand. This is achieved using a conventional cement mixer with a gas "torch" (not the hot compressed air lance) being angled into the cement mixer mouth. The dry sand is applied to the laid surface prior to imprinting to prevent the hot materials sticking to the pattern former. |
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POSITIONING THE IMPRINT PATTERN The pattern former has to be carefully positioned adjacent to already created imprinting to ensure a successful total appearance. |
| APPLYING PATTERNED IMPRINT TO THE HOT SURFACE Once the pattern former has been correctly aligned pressure is applied to the tool to mould the pattern. Individual experience and skill, as well as strength, is need to achieve uniform depth of patterning to ensure a uniform appearance of the work. Thickness of layer and the temperature of the thermoplastic will affect the amount of pressure and time of applying that pressure, and it is the skill of the operator that will achieve uniformity. However if the whole process is conducted in a structured and uniform manner this will make the job of the pattern/imprint creator a lot easier. |
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FINISHED BLOCK PAVING EFFECT Here we can see that the bulk of the work has been completed, with the last joint area remaining to be performed. A lot of the applied surface sand remains to be swept away before the full colour of the surface can be observed. This has already occurred on the right hand side of the picture, where the exiting lane was completed first. |
