Road Surface Texture

Winter Maintenance - De-icing

Comment

New TRL 
Road Notes
(added 6/11/08)

Road Pavements
Containing Tar
(added 8/11/08)

Motto of the Month

Reduced Use of High PSV aggregate in Thin Surfacing
I acknowledge the copyright of the following extract from the Highways Agency - Research Compendium, this was downloaded from the Highways Agency website and is presented in full without any change. 

Project » Reduced use of high psv aggregate in thin surfacing
Request more information
Section: Asset Use All projects in this section
Start-End Date: 12/2005 - 03/2008
Project status: Current
Publication Status: Not Published
Project value: £100,000
Project Contractor: Jacobs UK
HAContact: Sinhal, R
Reference: Y204271

Introduction:
The introduction of thin surfacing into the UK from Europe in 1992 has almost completely ousted Hot Rolled Asphalt. The current national design guidance published in the Design Manual for Road and Bridges for pavement performance was primarily based on this material.
Research on the performance of Thin surfacing has shown that the combination of wear and polishing that takes place on the road surface under the action of traffic is not the same as with Hot Rolled Asphalt. It has shown that smaller aggregate size, the texture shape and the subcutaneous drainage properties of thin surfacing has altered tyre/ wet surface interaction. Wear is increased exposing new surfaces, water drainage is easier. The SCRIM values (skid resistance measurement) of the surface over time do not decrease as with HRA but actually increase.
Research has also shown that with the current planned resources, i.e. high Polished Stone Value (psv) aggregates will be in short supply in 14 years. It has also show that Thin Surfacings use considerably more high psv aggregate than hot rolled asphalt.
This research will investigate whether the current design guidance can be amended to reduce the psv of the aggregate used in Thin Surfacings without compromising safety.
Project Objectives:

1. Initial Skid Resistance Data will also be obtained on the rolling road between the skid resistance of an aggregate in a 20mm chipped asphalt and the same aggregate in a 10mm thin surfacing and a 6mm thin surfacing demonstrating that the initial skid resistance ( once the aggregate is exposed) is higher.
2. Durability of Skid Resistance The objective is to confirm that for a wide range of sites, SCRIM and/or Griptester values on Thin Surfacings, using 14mm, 10mm and 6mm aggregate, are not deteriorating as fast as one would expect from the published information, i.e durability of skid resistance is enhanced.

Summary:
Deliverables Additional or amended guidance will be produced for publication in DMRB, to supplement current HA Advice The results will be disseminated using papers, journals and conferences.
Executive Summary:

Those of you who regularly read my website will know immediately there are elements of the précise of this project with which I disagree, but that is irrelevant to my intention at this point. 
But how can generic Hot Rolled Asphalt or Stone Mastic Asphalt compete in tonnage terms when "government" only permit proprietary Thin Surfacing on motorways and trunk roads in England, and approval for these materials is only allowed in Scotland and Wales after referring to the overseeing body. See Part 1 HD 36/99 TABLE 2.2 E, and subsequent tables.
Also proprietary Negative Textured Surfacing is actively being encouraged by "government" on Local Authority highway networks.
So has the "ousting" been performed on a fair engineering basis, I think not.
My intention being to make you aware of this project so that you may become involved in the discussion that it should provoke, even at this late stage.
I do not wish input into this project to remain with people who have declared themselves "Excellent" and are often remote from the real world of highways maintenance and engineering.

Look what happened to "High Modulus Base and Binder Course", and any "Excellent" person who continues to say that the failure of this material was due to poor workmanship perhaps they would like to go on site and explain to the laying gangs how it should have been laid for a successful outcome.
My comments on the page,
NOTES ON HIGH MODULUS ( STIFF ) DENSE BITUMEN MACADAM BASE (ROADBASE),
& ENROBÉ À MODULE ÉLEVÉ (EME),  were not placed there with hindsight, but from experience of actually being involved in laying bituminous materials..   

But I digress from the topic in hand, if you wish to read an excellent in depth report on the topic of the use of the scarce resource that is high specification aggregate may I recommend,
"The Sustainable Use of High Specification Aggregates for Skid-Resistant Road Surfacing in England"
published a few years ago and is/was available on a CD-ROM, at that time it was available from the following address, 

Capita Symonds,  
Tel.   01342 327161,
Fax.  01342 315927,
or, email : claire.huxley@capita.co.uk,
asking for the Project Manager, Claire Huxley, a CD-ROM copy will be sent to you without charge.

This 162 page A4 report represents part of the output from research carried out by Capita Symonds Limited (CSL - formerly Symonds Group Ltd., and before that, Travers Morgan Ltd.), for the Office of the Deputy Prime Minister (ODPM) under research contract SAMP/1/039.
I understood at the time that this report would become obtainable from the MIRO (Mineral Industry Research Organisation) website, after some refurbishment of the site. 
I do not know if this ever came about, I have not been able to find it.
This is a comprehensive report on the subject of High Specification Aggregates, and aggregate properties, containing a wealth of information on the subject of highway surfacing, aggregate procurement and its efficient use.
This report raises serious issues on the use of scarce resources of premium quality aggregate in England, and in my opinion needs to be obtained and studied.
This document contains a number of tables that give an indication of the properties of aggregates from various sources in the UK, however the properties of aggregate within quarries can change as blasting moves into different seams of stone within the quarry and verification of current aggregate properties is always a good idea.

I am sure that the consultants undertaking this current project for the Highways Agency fully understand that there is not just "one" hot rolled asphalt and precoats, as there is not just "one" thin surfacing, the variables that need taking into account are going to be considerable.
I draw your attention to the comments that I made in the March/April 2005 Newsletter.

Perhaps when this project is concluded, and its completion date was March 2008, it will be a published report that the Highways Agency allows to be downloaded from their website for all to study.

Road Surface Texture - Interim Advice Note (IAN) 101/07
NOTE - I intend leaving this item as it was originally written for the Summer 2008 Newsletter.
Except for pointing out here, that both IAN 101/07 and IAN 102/07 have been superseded by the actual, 
Series 900 - Road Pavements - Bituminous Bound Materials of the Specification for Highway Works, Volume 1. 
This was released in August 2008, and can be download from the HA website, www.standardsforhighways.co.uk.
It is necessary to again draw to your attention to,
Clause 921-Surface Macrotexture of Bituminous Surface Courses, as in the revised Table 9/3, you will see that the initial texture depth on lower speed roads, including roundabouts on these roads has been decreased further to that stated in IAN 101/07.
Unless I am mistaken this means a 0.5mm. decrease in texture depth on roundabouts on low speed roads, from the previous Series 900 published in November 2004, a 33% decrease in required initial texture depth for this particular site category.
It further reinforces the question who is receiving the benefit of these reductions in required initial texture depth. 
Are we "designing" the specifications to meet the bituminous mixtures, when we should be designing the bituminous mixtures to meet the specifications.
I will leave it for each of you to draw your own conclusion, not every motorist drives around a roundabout at the speed they are meant to, perhaps a "safety" camera on every entrance.

Road Surface Texture - Interim Advice Note (IAN) 101/07 (continued)
This is a complete revised 900 Series of the Specification, MCHW1 for Road Pavements -Bituminous Bound Materials.
It has been introduced to coincide with the publication of the new European Standards for bituminous mixtures BS EN 13108 family of standards for Bituminous Mixtures. from the 1st.of January 2008. 
The specification has also introduced a number of important changes other than those related to the specifying of bituminous mixtures to BS EN 13108

One of the most important of these changes, which in my opinion is not a "minor revision", is the reduction in initial texture depth of "thin surface course systems" (TSCS) on high speed roads, to not less than 1.3mm., and to not less than 1.2mm. on low speed roads and all roundabouts.
I urge you to obtain a copy of this IAN, it can be download from the HA website mentioned above, and study Clause 921-Surface Macrotexture of Bituminous Surface Courses.
In previous editions of the "900 Series" , e.g. November 2004, the figure quoted was the single figure of 1.5mm. for "high speed roads" but with no clear indication of what a high speed road was so the default was 1.5mm.
In the current IAN 101/07 there is a table containing the minimum texture depth requirements for defined surfacing materials and locations.
In my opinion this reduction in surface texture relating to thin surface course systems raises many questions as to how and why this reduction has been introduced.
Do not forget one of the basic reasons for having significant road surface texture is to promote removal of excess surface water from the road surface by the presence of "passageways" between the tyre and the road surface, not everybody is driving around on new tyres with deep texture depths.
The tyre cannot make contact with the actual road surface until the excess water is removed.
Do not forget that the assessment of skid resistance of road surfaces is in relation to wet roads, and testing of road surfaces is performed after wetting the road surface.
If specifications and design criteria in relation to aggregate properties and texture have been adhered to in road surfacing all dry "clean" roads will provide sufficient skid resistance at "normal" driving speeds.
(The original, low void content stone mastic asphalt developed in Germany over 30 years ago, which had a relatively low texture depth was off set by a requirement for a high tyre tread depth on German vehicle tyres. The policy in the UK, certainly during my period in the industry, is to have relatively high texture depths on high speed roads and permit reduced tyre tread depth requirements.
Both principles successfully allowing removal of excess water on road surfaces to achieve contact between the actual road surface and the tyre, with other engineering factors then coming in to action to provide wet skid resistance.
It is also stated in a number of reports that the roughness from deep texture dissipates energy contained in the forward movement of a skidding vehicle by the rapid manipulation (hysteresis) of the tyre tread and wall, producing heat, and hence reducing stopping distance.)

The questions and possible answers to this change in initial texture depth are so sensitive that even I will not enter into detailed discussion here, as anything I may say could be regarded as safety related and may put any organisation in a difficult situation if claims are made on a highway network manager as a result of an accident.
The fact that the HA have reduced the initial texture depth for TSCS has to be taken to mean that they regard these bituminous mixtures as safe at these initial texture depths. 
However in view of the continuing debate relating to safety issues of thin surface course systems this may not seem a very "politic" change in the specification. 
This specification change is likely to cause a number of Highways Engineers to ponder where this "advice" came from, and what its inclusion is meant to achieve, is it increased durability.   
It is not likely to increase safety even if it does not cause a decrease in road surface skid resistance.
Although the "900 Series" is specifically for motorways and trunk roads, the Specification for Highway Works is usually taken as the default document for local highway networks. 
It follows that Clause 921 is likely to be the default specification for initial texture depth for proprietary "Negative Textured Surfacing", that has been mentioned earlier on this page.
Highway engineers working for local authorities may like to take note of this situation and discuss it with their "management", because as I understand it a local authority is not bound to use the SHW as its default specification on all things, but usually does so because it is such an excellent document. On this occasion local engineers may like to give it some thought, remember this is an "Interim" Advice Note.
I am also puzzled that the initial texture depth requirements for hot rolled asphalt (HRA) and precoats, that you cannot use on motorways and trunk roads anyway, remains at 1.5mm.
In my opinion it would have been more logical to have reduced the initial texture depth requirement of a "positive" textured surfacing material than a "negative" textured bituminous mixture.
It follows that, in the future, you will not be able to make any like for like tyre noise generation comparisons between thin surface course systems and chipped hot rolled asphalt laid to the requirements of IAN 101/07, as it is generally recognised that texture depth plays an important role in tyre noise generation.

A few further points on this subject, 
(1) We are referring to initial texture depths, i.e. newly laid surfacing.
Surfacing materials supplied under the description of Thin Surfacing Systems are not all of the same nature/characteristics. 
The texture depth of low void content stone mastic asphalt type thin surfacing will increase with time as the "mastic" coating is worn off the larger aggregate particles, presented to the surface.
The texture depth of open textured, high void content surfacings, of a  porous asphalt type, will tend to lose texture as the voids fill up with detritus. 
And there are thin surfacing bituminous mixtures that can be regarded as a hybrid of both material types.

(2) Do not forget that we are talking texture depth measurement using "sand patch" measuring techniques, these figures must not be confused with the sensor measured texture depth (SMTD), they are different.
SMTD's are obtained from laser devices, e.g. SCANNER.
Talk to your Materials Engineer, to obtain clarification on this point, as I am beginning to cover too many related topics in this item, and will not try to explain the difference here. 

(3) We are talking initial texture depth, just one important aspect of the skid resistance of a bituminous mixture laid as a road surface, yes it will play a significant contribution in the early stages of newly laid road surface, and throughout its life, but you must also consider,

• Polished Stone Value (PSV) of the coarse aggregate
• In my opinion, PSV of the fine aggregate, e.g the fines in HRA has/had a requirement of a minimum of 45 PSV.
• Aggregate Abrasion Value (AAV)
• The actual design of the mixture, as there are a number of ways to design a bituminous mixture that will provide an initial texture depth of 1.2mm, or even 1.5mm. depth.
  The differing designs with similar initial texture depths may well have differing initial levels of skid resistance.
• The above can be dependent upon the grade/type of bitumen binder in the mixture, particularly the rate at which it will be abraded, by traffic, from the surface presenting coarse aggregate.

Texture depth of a road surface when it has reached its "natural" state can be quite different from the initial texture depth, often the critical factor being how long it takes to reach this "natural" optimum skid resistance condition.

My apologies, I have developed this item far further than I intended, but without being too specific.
I really do think that you need to discuss this matter with your Materials Engineer / Road Pavement Engineer / Consultant, as the topic is complex and, in my opinion, does need to be examined. 
I am beginning to form the opinion that major changes are taking place relating to highways maintenance, without full consultation of those actively engaged in the industry, which in my opinion is resulting in higher costs and poorer performance/condition of the highway network.

Winter Maintenance - De-icing
Whilst browsing through the HA Research Compendium I could not help but notice the considerable number of Projects that were listed that concerned de-icing, most of the Projects having a greater or lesser connection with "modern surfaces" / "thin surfacing".
I thought I would provide a short list, for those of you who have an interest in Winter Maintenance, as a lot of money has been spent on the various studies, and they would appear relevant, if you could only get to read them.

I list some of the more relevant in order of completion

I am not going to discuss this topic further at this point and leave it to you as to whether you wish to view the introductory information that is available on the above projects.

Comment
It has to be said that the bulk of this newsletter, even de-icing,  is related to the introduction of proprietary Thin Surfacing, some ten years ago, and its continued promotion to the point where commonly held highway engineering views (and specifications) are being changed, or are being proposed to be changed, to continue to support/promote the use of these materials.
This is a very serious topic for our customers, the road users, those responsible for maintaining highway networks, and those who wish to continue to improve the safety record of our highways.
In my opinion it follows that we need large amounts of solid engineering evidence before we make these critical changes to our highway specifications, supported by input from actual highway maintenance Engineers and Technicians, perhaps even input from Police Accident Investigation teams, but not lobbying from "suits".
I hold the belief that "people" are blowing more and more hot air into a bubble that is dangerously close to bursting, and if those seriously involved in this situation wish to retain any integrity they had better start sorting it out.
I know from the number of emails that I get to this website that British highways engineering is held in great respect around the world, with much of this reputation being built on the quality of the "Design Manuals", "Specifications" and "Standards" developed by British Engineers.
I would not like to see this hard earned reputation damaged.

I offer my usual advice when I have referred to downloading information from the "web", perhaps best to do it quickly, as downloads I have mentioned in the past sometimes "disappear", I do not jest.
I believe that somebody of an engineering background has placed this information on the internet so that you may read it and be aware, at least pay them the respect of studying it before other influences may have it removed, or worse still have a public relations company manage the release of HA Project information.

New TRL "Road Notes" are Published
"Old Timers" like myself can remember a time when there were a considerable number of TRL Road Notes on many aspects of highways maintenance, a few I readily recall being, Skid Resistance (RN 27), Road Pavement Design (RN 29), Rubberised Bitumen (RN 36), and of course the one we still know and use,
ROAD NOTE 39 : Design guide for road surface dressing - (6th. Edition now current)
Recently two new Road Notes have appeared, these being,
TRL Road Note RN41-Best practice guide for overlaying concrete
and,
TRL Road Note RN42 - Best Practice Guide for the Durability of Asphalt Pavements, 
I have had access to both of these documents and found them to contain a large amount of excellent engineering advice and guidance. 
I strongly recommend that you read both of these documents from front cover to back cover to obtain the total amount of information that you can derive from such documents, it is not just engineering information that you can ascertain.
I personally regard RN41 as providing the greater amount of engineering information and guidance compared to RN42, which I feel contains mainly information on good practice rather than specific guidance.
In my opinion neither document gives truly specific advice and I believe that you will need knowledgeable Engineers and Engineering Technicians to put this guidance in to practice by the use of appropriate road pavement designs, the correct selection of particular bituminous mixtures and good supervision of the works.
I also feel that it does not sufficiently embrace the recently encountered problems with the "new" proprietary bituminous mixtures employed in the construction and maintenance of road pavements, an opportunity missed. 
Perhaps it was not the remit of the public relations company that controlled the "focus group" approach to the production of these documents.
Road Notes 41 & 42 are available to be downloaded free from the TRL website, providing you supply them with fairly comprehensive personal details. 
I did not take this route to obtain copies, but I leave it to you to decide your means of access to the documents.
Perhaps access to these Road Notes will be placed on the Highways Agency website as HA personnel were amongst those steering the "Best Practice Focus Group", that supplied advice, which helped in the preparation of the Road Notes.
The submission of personnel details is not required to download the majority of the excellent free specification/guidance documents on the Highways Agency website, www.standardsforhighways.co.uk.
These are my own views on the publication of these documents, and any of you who read much of my website will know I do not appreciate the growing control that public relations companies have over the views of qualified and and experienced Highways Engineers and Highway Engineering Technicians.
However, in as far as they go, both these Road Notes are excellent documents and I strongly recommend that you obtain copies of them both and read them thoroughly, because for those of you who are not familiar with these subjects you will gain a tremendous amount of broadly based knowledge on the stated aspects of highways maintenance.
But you will need to "fine tune" this guidance to match bituminous mixtures and practices to particular sites, and you, the Engineers and Engineering Technicians, need to be taking these decisions yourselves not the "salesman", the "public relations" people, or the "lobbyists".
If you feel that you are not able to make these decisions (you know what is coming), then you need to consult a qualified and experienced Highways Materials Engineer, or Road Pavement Engineer, if you can find one.

Road Materials (Pavements) Containing Tar
I suppose that I must first apologise for the fact that this newsletter is becoming a saga, but important issues are coming to light, and being addressed. 
If I can be of help in making this information more widely available I will continue to do so, and in this manner will hopefully promote discussion and debate, maybe even criticism, but the various subjects will be being openly discussed.
Before you read further perhaps you will take the time to read the Autumn 2006 Newsletter, specifically the item on on tar in road planings and the implications with regard to recycling older road pavements, in relation to the new "waste" regulations introduced in 2005.
But just to recap, as I understand/understood it, bituminous road planings and arisings are not a "waste" material, they are a reclaimed product awaiting recycling in a safe and cost effective process.
So much in the procedures for the recycling of reclaimed bituminous material, as I have experienced it, is in the use of words and not highway engineering at all. It is also in the lack of knowledge of the "regulators" who do not understand that bituminous materials, and I use this term to specifically refer to materials containing bitumen, are practically inert.

The menu page Recycling in Highways Maintenance on this website will provide web pages of useful information in relation to this subject.
However I will take the opportunity to recommend an excellent document produced/published by TRL, this is, the un-numbered report,
TRL : Recycling in Transport Infrastructure
This report covers practically all aspects of undertaking recycling processes in road maintenance and construction. It includes advice and guidance on all the necessary rules and regulations that were current at its time of publication and need to be complied with in any recycling process, as well as describing many example of types of recycling, that are already being undertaken. 

Obviously when there is the possibility that the planings/arisings may contain tar there are increased considerations in the safe reuse of these materials.
Matters in relation to this possibility have now progressed and there is now published a Guidance Document from the the CSS, although the County Surveyors' Society "Logo" is still on the top of the document.
(It would appear that this organisation still cannot decide what it wants to be called, but I have written on this topic previously so I will not continue here, but I personally would like it to revert to a strong "engineering" base and let the "strategic" element go and talk strategy some where else.)
However elements of the CSS have produced an excellent Guidance Note,
"Road Materials Containing Tar",
which can be obtained from the CSS through a member, and I understand that there is no charge for the document.
I would suggest that you obtain a .pdf copy of this Guidance Note if you can, as the document contains many references to "official" sources of information that have extremely long web addresses, and to use the links on the digital document is by far the easiest way of successfully accessing these sites.
This is an excellent document and all Engineers and Engineering Technicians involved in the maintenance of existing highways, especially older "evolved" road pavements will benefit from having this document to hand.
I certainly wish it had been around towards the end of my career, to point us in the right direction, when the presence of tar bearing materials in a large deep planing road pavement refurbishment was the last big "materials" issue that I was involved in.
It was a very steep learning curve and without the competent, knowledgeable and experienced engineering team that we had in house, coupled with support from management who had an engineering background, it could have turned out very expensive, and with an incomplete scheme.
The scheme was completed on time with a much reduced increase in cost compared to that originally promoted by the contractor.
You do need to take the possibility of the presence of tar in road planings very seriously and you will only be able to cost effectively deal with this situation from the basis of knowledge. 
The CSS Guidance Note will provide a very effective start to you knowledge base.
Finally I will draw your attention to a couple of items in the document, the first being item (23), where it states the value of 25 ppm shall not be exceeded for the PAH 17 value where the material is to be included in hot (bituminous) mixes. 
As the paragraph states this is QPA advice and is not based on technical or legal requirements. 
Also take the advice of paragraph (c) in item (35), only take a "reaction" to the marker spray as an indication of a PAH presence, you must then have the material tested by a UKAS accredited laboratory before taking any action.

I hope that this will be the final addition to this newsletter, but who knows, there may be more if I think an item I become aware of will be of interest to Highways Maintenance Engineers and Engineering Technicians.

Motto of the Month
"He uses statistics as a drunken man uses lampposts - for support rather than for illumination."