 It is now actually possible to heat and re-mix quantities of bituminous materials on site with all the associated benefits of not having to transport materials long distances to be recycled.
Mobile plants are now available that are capable of remixing amounts of up to 4.0 tonnes in a single batch.
The reclaimed bituminous materials are remixed / heated in the mobile heater/mixers and the resulting "fresh" recycled material is used for appropriate small scale patching or footway refurbishment.
The (re)mixers which perform this task are becoming more widely available as "environmental concerns" become a greater factor in all road maintenance issues.
However more significantly with the increase in the cost of bitumen and bitumen products the mobile plants are being increasingly seen as a more cost effective option for some "small" tonnage work, i.e. 20/30 tonnes per normal working day, and this is driving development work to produce more sophisticated and still larger mobile plant.
At the other end of the scale quite small remixer models are available specifically for producing small batches (50 /100kgs) of hot bituminous materials for emergency and planned patching work, anywhere at anytime, and are able to be towed behind a conventional maintenance "works" lorry.
Freshly excavated bituminous material being placed in the remixer for heating and mixing, with the addition of a small amount of new binder, in this instance approximately 10% of estimated existing binder.
E.g. Existing binder estimated to be 4.5% of 3000kgs., so this gives 135kgs. of existing binder, to rejuvenate this particular reclaimed material it was decided an addition of 10% of new 200pen. bitumen would be appropriate, so 13.5 kgs. of new binder was added prior to mixing.
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It may be necessary to add a small amount of "rejuvenator" to the planings to produce the workability you require in your recycled material.Bitumen hardens during heating in mix production, and further stiffens by oxidation during the life of the road, this needs to be rectified when recycling to provide the grade of binder and workability for the nature of work intended.
The "rejuvenator" can be a proprietary liquid, (they are now produced specifically for this market) or it can be something as simple as a cut-back oil, e.g. a creosote type liquid, or a flux oil, e.g. a diesel type liquid, according to what properties you require in the recycled material.
But in most cases it will be as simple as adding an appropriate amount of bitumen of the required viscosity, e.g. 300pen or 200pen.., it is unlikely anything stiffer would be required for most recycling work.
The cut-back and flux options may be needed to modify stiff reclaimed bituminous materials e.g. hot rolled asphalt wearing course planings, into more workable materials for general "hand lay" patching and basecourse work
A cut-back oil is a volatile oil which when mixed with a stiff bitumen grade, e.g.100 pen., will make it less stiff / more workable at lower temperatures.
In time the volatile oil will evaporate and the bitumen will revert to its'' original 100pen. viscosity.
Until the volatiles evaporate there can be problems with cut-back material being "sticky" / soft.
A flux oil is a none volatile oil which when mixed with a stiff bitumen, e.g.100pen. will make it a less viscous grade.
A 100pen. bitumen plus the correct amount of flux oil will become a 300pen. grade, and it will remain at that lesser viscosity.
N.B. It is most important to know what the "Flash Point" is of any rejuvenator you may be thinking of using so you do not remix at a temperature above this point, or a "flashover" fire will occur, and even below the flash point you will be generating unacceptable amounts of fumes. It is important to know what you are working with and adopt suitable heating regimes to produce the material you require.
Although this form of hot recycling may have higher production costs the bituminous mixtures produced will replace the more expensive range of hot mix virgin materials and therefore achieve overall greater savings. The materials produced will be of a high stiffness as soon as they reach ambient temperature, similar to the original reclaimed surfacing materials, and most importantly they can be used as the wearing course material when correctly formulated.Other environmental benefits, and cost savings are made because there are no lorry journeys to tip/recycling depot, no lorry journeys delivering/collecting fresh bituminous material, and no reprocessing/crushing of transported reclaimed material to produce granular or "foamed" recycled products. |
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Although this form of hot recycling may have higher production costs the bituminous mixtures produced will replace the more expensive range of hot mix virgin materials and therefore achieve overall greater savings. The materials produced will be of a high stiffness as soon as they reach ambient temperature, similar to the original reclaimed surfacing materials, and most importantly they can be used as the wearing course material when correctly formulated.Other environmental benefits, and cost savings are made because there are no lorry journeys to tip/recycling depot, no lorry journeys delivering/collecting fresh bituminous material, and no reprocessing/crushing of transported reclaimed material to produce granular or "foamed" recycled products.
COSTS AND PERFORMANCE
It is my belief that the cost of recycled material MUST be no greater than the cost of conventional material, and the performance of the recycled product MUST be equal to that of conventional / new materials or it is very difficult for an engineer with a limited budget to make out a case for specifying recycled material to the customer or authority employing him.
With the recent introduction of Land Fill Tax there is now quite a large cost incentive to recycle a greater amount of suitable material, rather than pay for it to be taken to tip.
There is however the considerable cost of transport, stockpiling, crushing and blending, to facilitate the processing of reclaimed material to make it suitable for inclusion in highway works.
The considerable amount of paperwork involved in gaining planning position for recycling sites , and the health and safety regulations which are associated with this type of work adds even further to the cost.
The supplier of recycled material should also have a suitable level of laboratory backup to ensure the quality of his product.
SITE SPECIFIC MATERIAL SPECIFICATIONS
Many organisations have specifications for recycled material which allows the use of suitably processed reclaimed material (which may or may not meet existing D.O.T. or British Standards) into low stressed situations, e.g. lightly trafficked rural roads, residential estate roads and footways.
This initiative is to be encouraged with the proviso that materials approved for sites experiencing lesser traffic loadings do not find there way on to sites with more demanding traffic conditions with claims that it is "an approved material".
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