"Clean", (i.e. no contamination with soil, organic matter, wood or other general rubbish) is stockpiled until sufficient is available to make it cost effective to bring a mobile cusher to the stockpile.
The material that is best suited to recycling is concrete, bituminous road materials and loose granular material from the lower road pavement layers.
It cannot be stressed strongly enough that you must have strong control over what is initially stockpiled.
Permitting the inclusion of "clay" subgrade, top soil and vegetation produced during excavations will have detrimental performance on the recycled materials during their use in new construction.
That is if the recycled product meets the appropriate specification.
Perhaps the most difficult aspect of recycling reclaimed road making material is not the actual various recycling processes but the obtaining of Planning Permissions and Environment Agency "approvals" to actually provide yourself with a site/s where recycling can actually take place.
This is an area of knowledge outside of my "comfort zone". All I will say is that if you put forward a site that is well designed to provide prevention of contamination by dust, drainage and noise of surrounding areas you should be able to put together a successful application with a little help from the "legal boys and girls".
This is because there are common sense and inexpensive methods of dealing with all these issues, such as water spraying "mists" to prevent dust, soil bunds for absorption of noise, and settling tanks and reed bed water filtration to purify water before introduction into a water course.
But of course the water can be re-used in "washing" processes, which is a cost saving by more recycling.
I recommend the TRL Report,
TRL (un-numbered report) : Recycling in Transport Infrastructure, to provide understandable advice and guidance
This is an excellent report covering many aspects of various recycling processes in road maintenance and construction.
It includes advice, guidance and reference on many of the necessary rules and regulations that must be complied with in any recycling process, as well as practical examples of recycling initiatives already undertaken.
But bear in mind regulations are continually altering regarding recycling, and this report is now a few years old, so changes in the procedures in obtaining "permissions" may have resulted.
The good news is that more knowledge is continually being gained on the many recycling processes undertaken in highway maintenance and construction.
This increase in knowledge has resulted in a more enlightened approach to the "legislation" associated with the various recycling processes, the "legislation" being related to the perceived problems of a particular recycling process, rather than the strict blanket approach to the awarding of all "permissions" in the early days of recycling.
The
quality of recycled material will be directly related to the quality of
the reclaimed material that you are recycling, and good quality reclaimed
material can be made poor by contamination with "unsuitable"
materials, because some "misguided" individuals feel it is a
cheap way of disposing of materials that should really be going to tip.This "saving" will cause an increase in cost somewhere down the line that somebody will have to pay for, make sure it is not you !
The worst scenario is that you can have a road pavement failure (it has happened) some years after the recycled material has been used, and this will be very, very, expensive to rectify.
This type of bad practice gets recycling a bad name, that is not deserved.
Also, once produced and meeting the appropriate specification the recycled material shall be treated in the same manner as any "virgin" product supplied to the same specification.
( All "new" materials are not necessarily good materials, just because they are "new". )
A correctly produced recycled material is not a "second class" product that can for some unexplainable reason be treated in a lesser "engineering" manner during construction.
I mention this because I have seen it happen, please do not let poor engineering practice with regard to recycled materials occur on sites for which you have responsibility.
A mobile crusher is brought to site, as it is more environmentally friendly than making many trips with stockpiled material to the crusher.
Adjustment of the opening between the crusher jaws controls the size of the aggregate produced.
Good judgment by the operator feeding the crusher will produce a well blended recycled material suitable for many road making purposes.
Excellent material suitable for use as "capping" or "Type 2 Sub-base".
However with different screens on the screening process a variety of materials can be produced for a number of construction processes.
E.g's Type 1 and drainage media.
If you choose to produce particular materials you must have a use for the remainder of the crushed material or the operation is unlikely to be cost effective.
You may produce significant amounts of a higher value product, but it can result in large stockpiles of remaining reclaimed/recycled materials that do not have an immediate use.
Unless you have an unlimited amount of stockpiling space and permission to stockpile, this material could become "embarrassing".
It may be wise to produce granular materials that supply your biggest need rather than to produce a limited amount of a "premium" product.
ACCESSING APPROPRIATE, AND HELPFUL, SPECIFICATIONS
Information and specifications on particular unbound granular materials that can be, or can contain, recycled materials can be found in the,
Manual of Contract Documents for Highways Works - Volume 1 : Specification for Highway Works
Series 800 - Road Pavements - Unbound, specifies the unbound granular materials that can contain recycled aggregate, e.g.'s Type 1 Unbound Mixture and Type 2 Unbound Mixture,
(NOTE : This is the new terminology for Type 1 and Type 2 Sub-base, you may want to read the current edition of the Series 800 - Road Pavements just to update yourself, if you were not aware of these description changes.)
Also,
Series 600 - Earthworks, makes considerable reference to a range of unbound materials, many of which contain recycled aggregates, in, Tables 6/1 and 6/2 of this section of the Specification for Highway Works.
e.g.'s various capping materials.
And, in, Series 700 - Road Pavements - General, you will find,
Clause 710 - Testing for Constituent Materials in Recycled Aggregate and Recycled Concrete Aggregate
which describes the procedure for testing amounts and types of recycled material in particular unbound mixtures.
And one more useful document from the, Design Manual for Roads and Bridges - Section 7.1.2, is
HD 35/95 - Technical Information, the title not really telling you that its content relates to the,
"Conservation and use of reclaimed materials".
I do not believe in "reinventing the wheel", read these documents to gain information, a lot more than I have provided here, on how recycled aggregate can be used in many granular materials, how they can be specified and how they can be sampled and tested.
Copies of these documents can be downloaded from www.standardsforhighways.co.uk.
Also, a,
"Quality Protocol for the Production of Aggregates"
is published by the
"Waste and Resources Action Programme (WRAP)"
and contractors producing recycled aggregate shall comply with the procedures of the protocol, and be able to provide relevant documents indicating compliance should they be requested.
A copy of " Quality Protocol for the Production of Aggregates" can be downloaded from, www.wrap.org.uk.
There are also many "case studies" that can be referred to on the above website.
The excess of chippings always initially laid with any surface dressing operation are swept and returned to the recycling stock ground to be washed and re-screened.
The recycling of chippings in this manner is not only environmentally friendly (less holes in the ground), it is very cost effective with the increasing cost in "new" materials.
The recycled chippings must meet the appropriate nominal size and grading requirements of the particular chipping specification.