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NEWSLETTER
December 2002
TOPICS

High Modulus Base Materials

In-situ Recycling of Bituminous Surfacing

 "Sustainable Construction in Practice - SCiP"

 Motto of the Month
 Introduction
Instead of the usual introduction, this month I am going to tell you a story, it is a true story of long ago when I was a young materials technician newly appointed by the organisation that I am still working for.
 It was 30 years ago when I started  work in the Soils and Materials Laboratory of my current employer. (Yes, I am that old, do not let these youthful good looks fool you.)
The County Surveyor at that time was a Mr. Grigson, a County Surveyor of the "old school", who actually used to spend time visiting work sites around the county.
The organisation possessed two of its own Blaw Knox paving machines and practically all bituminous paving work was undertaken by our own machines and gangs. Even to the extent that it was only our own gangs that were allowed to lay the wearing (surface) courses on any new road schemes that were constructed.
At this time most of the local quarries were still independent, usually family owned, and bituminous materials could be bought competitively to supply our machines on an annual tender basis.
At that time there were two councilors, a Mr. Hill and a Mr. Sparrow, both I believe former chairman of the Highways Committee, it is unlikely they are still with us, but if they are I hope they do not mind me telling this story.
These gentleman took pride and a sense of responsibility for the role that they had been elected to represent. 
They decided that to encourage quality in the laying of bituminous materials that they would each award a trophy, a silver cup, one for the best length of Hot Rolled Asphalt (HRA) wearing course laid in the county and another for the best length of Dense Bitumen Macadam (DBM) wearing course. 
The authority was divided into four divisions at this time and the Divisional Surveyors of each  would submit what they thought were their best lengths of surfacing for consideration. 
These sites would be judge  according to certain criteria laid down by the Materials Engineer. These included testing the ride quality of the site with the Bump Integrator, a piece of kit little used now, and visual inspection of such items as the quality of joints, setting of ironwork, etc..
The winning sites would be chosen and the cups would be awarded to the appropriate Division. There was much pride taken in the winning of these cups both by the winning Divisional Surveyor and the particular paving gang that had laid the material. 
It usually culminated in a good night out (faggots, mushy peas and chips, and a few "Vimtos" at a local hostelry) with the bill being met by the supplier whose material had been used on site, ( the better the quality of the bituminous material, the easier it is to lay satisfactorily), without any hint of "influence" being suggested. 
And it is a fact I am still able to take you to areas of surfacing laid up to 25 years ago that are still performing, some surfaces have not even received a preventive maintenance surface dressing. 
It is true these long lived surfaces are HRA wearing course and precoats and they would have been more expensive to lay than coated macadam wearing (surface) courses, but they have more than made up for the original extra cost.
I think I told this story to show there is more than one way to achieve quality and perhaps we ought to pause to consider them from time to time, rather than rushing head long into "paper" schemes proposed by bureaucrats that do not really know a great deal about highway
maintenance, and the nature of the people employed in it,  at all.
And one most important point, never underestimate the pride your work force take in the work they do, it is not just the money. But "surfacing gangs" are under pressure just like everybody else these days so good supervision is essential, often to protect the conscientious gang from their own supervisors.
In the industry we are employed we are continually riding around on the roads we have created, and you get a good feeling traveling on good road surfaces, and you hope the less good areas are few and far between.
However in this day and age, I for one am not prepared to take responsibility for other peoples mistakes, if engineers and technicians cannot specify the materials they wish to include in their road pavement designs they cannot be held responsible for their failure. 
We are not, and never will be in the situation, where one type of road pavement material fits all engineering requirements and cost considerations. 
If you not going to enable engineers and engineering technicians to do some "engineering", and pay them for the responsibility, it is not surprising they do not want to join the profession.

High Modulus Base Materials
I thought it worth referring engineers and technicians in the UK to an article in the journal New Civil Engineer of the 28/11/2002. 
This article states that the current ban on the "ultra stiff" high modulus base asphalts has been confirmed, by the Highways Agency, as  remaining in place for the next eighteen months.
I suggest you gain access to a copy of NCE and read the brief article in full.
But, it does make reference to the fact that "French HMB's have smaller maximum aggregate size and higher binder contents than the first generation UK mixes".
I believe this acknowledges a fundamental difference in the French mixtures and those used in the UK. 
The UK bituminous mixtures employed in documented trials had, more or less, conventional BS 4987 mix proportions for coated macadam binder courses (basecourse) and base (roadbase), with associated relatively low bitumen contents.
And, if you take the "design" approach to create your high modulus base, i.e. Clause 929 of the Specification for Highway Works this could well result in an even "drier" mix design.
For those of you who have an interest in this subject may I suggest you look at the mix designs/proportions of 28mm. and 20mm. hot rolled asphalt basecourse and roadbase found in BS 594. 
I believe you will find these materials much similar to the French HMB's, both in aggregate proportions and binder content.
It is a fact that the recent practice of calling all bituminous mixtures "asphalt" is still causing confusion in the UK where we have two distinct types of bituminous mixture used for road pavement construction and surfacing.
These two types of surfacing being Hot Rolled Asphalt, as specified in BS 594, and Coated Macadam, as specified in BS 4987.
It is my belief that many purchasing organisations, whether local authorities or large PFI consortia do not have knowledgeable and experienced people in place who fully understand the total engineering implications of the materials that are being offered to them.
A desire for the lowest cost initial design is not necessarily going to give the best return over a thirty year period.

If you wish to a little more more background knowledge on "stiff roadbases and basecourses", you may wish to access the page on this website that will provide some information and further reference sources.

In-situ Recycling of Bituminous Surfacing
For those of you in the UK who wish to know more about the recycling / repairing of bituminous surfaces using infrared / hot in-situ recycling methods can I urge you to read the excellent report in the journal "Surveyor" of the 5th. of December.
This article, "Turning up the heat", describes the process in some detail and is well worth reading.
You are able to see pictures demonstrating the nature of the process by visiting the page on this website, ON SITE RECYCLING BY HOT PATCH TREATMENT .

"Sustainable Construction in Practice - SCiP"
The above title is the name of a website that has been set up as a subsidiary to the TRL website with the purpose of focusing attention on recycling matters particularly related to construction and road building.
The SCiP website is an excellent site and I definitely recommend a visit.
At present it is promoting a number of "Road Shows" around the UK so that interested parties can attend to learn of recycling initiatives currently being undertaken and to suggest/pursue new areas of possibility.
It is necessary to click on "Registration Details" to find the dates of the "Road Shows", there are still five remaining in the new year, which may still have booking vacancies.
The site has many links to other websites that are keen to play an active part in recycling, also sites where you can obtain information on recycling "schemes" and "initiatives", including access to government research funding if you have a particularly good idea.
Any organisation such as this deserves to be supported, and we must all keep ourselves aware of new possibilities in highways maintenance.
However, and there is nearly always a however with the information I provide, there does seem to be far more coverage to research and development undertaken by the larger companies than the smaller more immediately workable initiatives such as the one I refer to in the above news item.
Big is not always beautiful, some good things do arrive in small packages. 
I do understand that some of the recycling processes envisaged, e.g. the use of crushed glass, do need large scale processing to make it viable. But small scale processes, especially on site recycling of bituminous materials have an immediate environmental benefit of reducing vehicle trips to and from site, as well as the saving in virgin materials. 

Motto of the Month

"You don't need a weatherman to know which way the wind blows"

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