[ Top ] Hot rolled asphalt and precoated chippings

The Idiots' Guide to Highways Maintenance
Copyright © 2000/08, C.J.Summers

''Aspho-Chip' & 'Aspho-Chipless'

The two proven bituminous surfacing materials of the 70's, 80's and 90's (and in some authorities the 21st. century).

'Aspho-Chip'

Comprising of a layer of durable and impervious bituminous material with a surface applied layer of high PSV aggregate chippings, of 14mm or 10mm size, coated with a layer of 50pen bitumen.

The bituminous material having 30/35% aggregate content of a 10mm. or 14mm. nominal size aggregate.

"Aspho-Chipless"

Comprising of a layer of durable and impervious bituminous material incorporating 55% aggregate of 10mm. or 14mm. nominal size with an appropriate PSV for the site conditions.

PERSONAL NOTE
If you have not guessed already there are no such materials as "Aspho-Chip" and Aspho-Chipless", well not just yet, but give the marketing boys time, especially with the increased complication of specifying the materials that you require to the
BS EN 13108 family of standards for specifying bituminous mixtures.
The above are the excellent reasons for, and the drawbacks against using hot rolled asphalt wearing course and precoats, as formerly specified in,
BS 594 : 2005 : Hot rolled asphalt for roads and other paved areas : 
Part 1 : Specification for constituent materials and asphalt mixes

I am a great believer in this material for more reasons than I care to bore you with, and I am not going to stop supporting it because for some very strange reason it is no longer "fashionable".
Although it is still far more used than the "engineering journals" and public relation "boys and girls" would have you believe.

However you will now (from 1st. January 2008) need to refer to, 
BS EN 13108 : Bituminous mixttures - Material specifications - Part 4 : Hot Rolled Asphalt,
and,
BS EN 13108 : Bituminous mixtures - Material specifications - Part 20 : Type testing
BS EN 13108 : Bituminous mixtures - Material specifications - Part 21 : Factory Production Control

so that you may define the target specification of the bituminous mixture (hot rolled asphalt) that you wish to be supplied with.
This specification (recipe) will take the form of a "CE" conformity marking, an example of which can be found in,
BS EN 13108 : Bituminous mixttures - Material specifications - Part 4 : Hot Rolled Asphalt, Appendix ZA.3 CE marking and labelling.
It is entirely possible to specify, for practical purposes, the same materials that it has always been possible to purchase, you just need to put in a little more effort, initially, until you have defined a number of specifications/recipes to cover the range of HRA's that you wish to employ on your highway network.

I will bore you with just one justification for my support of HRA materials equivalent to BS 594 specifications/recipes, that is BS 594 : Col. 6/4 : 30%/14mm. hot rolled asphalt wearing course, has a binder content target of 7.8%.

Most modern proprietary "Thin Surfacings" have binder targets of between 5.0% and 5.5%, all these figures have binder tolerances of at least plus or minus 0.5%.
It is important to note these figures are by mass not by volume , aggregate is approximately 2.7 times more dense than bitumen.
So a material with a binder content of 7.8% by mass has about a 20% binder content by volume, and in my experience durability of bituminous material is dependent on an adequate bitumen content of the appropriate grade and properties.
( Your friendly Materials Engineer will explain it to you in more depth.)

The evidence for my support of this material is on roads all around me, with many, many miles of this type of road surface over twenty years old with no subsequent treatment, and some just receiving a surface dressing.
If this surfacing process is good enough, and quiet enough, to surface The Mall outside Buckingham Palace I am not too proud to keep recommending it for general use, but without the red chipping, (except in traffic calming areas).

At my last  "London Marathon - 2007" inspection of the Mall as I watched the event on television, the surface still looked excellent to me, as you do get a good view of the surface when the camera angle follows the feet of the "elite" runners.
Those of you that may be interested in looking at this excellent HRA surface, the 2008 "camera survey" will be taking place very soon and transmitted to your home.
Although I cannot exactly remember when it was laid, I think it is likely be at least 15 years old, probably nearer to 20 years, and looks good for another 15 to 20 marathons, if it does not experience too much "utility" work.
Even with utility work, providing you have a supply of the original chippings a "match" with the original surface should not be difficult to achieve.

[ Top of Page ]