It's an old old problem, and it still is around - stripping and damage due to moisture. The issue is that pavement surfacings have failed because an underlying asphalt layer has stripped and turned to mush. Technically it is called the separation and removal of asphalt binder from aggregate surface due primarily to the action of moisture and/or moisture vapour.
In the identification of the cause of stripping, practitioners have, sometimes, tended to focus their attention on the sensitivity of the aggregate and asphalt system in the presence of moisture. Other practitioners (Dolf) try to blame the bitumen or the contractor or anyone but them. Well, now there is more science to throw at it. There is a good paper PREMATURE FAILURE OF ASPHALT OVERLAYS FROM STRIPPING: CASE HISTORIES by Kandhal (NCAT expert) and Ian Rickards (recently with PRS, now a consultant, and of HiPAVE and APSDS4 fame). The paper was presented at Association of Asphalt Paving Technologists, Florida in 2001. Go read it to learn more about the topic.
My quick checklist to detect the possibility of stripping
occurs within 6-18 months of construction, and
either a moisture surplus area (i.e. wet, humid), or
sufficient diurnal temperature range to start the heat pump and get moisture movement within the road
Sometimes called hydrogenesis (from my first PhD, I found that you need a mean pavement temperature of 20 degC and a diurnal (day/night) temperature range of at least 10 deg C and solute suction less than 100kPa [i.e. not salty] to get the heat pump going and get this so-called "hydrogenesis".
Credit to Frank Netterberg who suspected that there was a diurnal variation of pavement response and sent us to find it. Thanks for Nandus, Dave and Simon for the day and night testing, and the memorable winter night when the Benkelman Beam Truck battery died and we had to push start it every three hours through the night as we tested the road. Thanks to Hertz as well, because when Frank showed up on site the next morning, his hire car donated its battery to the worthy cause of scientific research.
and finally, although you probably didn't want to hear this, if you get this problem, then the whole road is probably going to give trouble. It may have shown itself in only a couple of spots so far. Tomorrow, it will be worse. Extensive milling-out may be needed.
Symptomatically, if top layer = seal
you'll find bleeding or pickup on tyres
and you probably have a rubber-bitumen or polymer seal
or if top layer = asphalt
potholes, shallow failures
underlying asphalt has turned to mush beneath the top layer
you can see WHITE grains of sand in the mush with the naked eye
any signs of moisture within the asphalt at all (re-read Kandhal & Rickards - a moisture content of just over 1% can be enough to get saturation of asphalt)
The case histories in the K&R paper document the effect of pavement saturation. The authors suggest that under saturated conditions all asphalt mixes may fail as a consequence of cyclical hydraulic stress physically scouring the asphalt binder from the aggregate. The authors classify this stripping as a mechanical failure of the asphalt pavement system, and the classical moisture sensitivity tests are irrelevant. While under saturated conditions a less moisture sensitive asphalt system may survive longer, it is probable that failure is deferred and not avoided.
In one investigation I did [urban road, busy with much truck traffic, adjacent lawn watering so water was going onto the road surface even in the dry season, construction was asphalt on crushed rock base on sand subgrade], we found the presence of large voids in the pavement between the base and the asphalt due to a poor primer seal in-between. This focussed our attention to the capillary suction mechanism, diffusion of moisture through the asphalt and opened up another way of assessing this sort of failure (or is it another manifestation of the problem?). It needs (a) water, (b) permeability, AND (c) voids large enough to defeat the suction within the asphalt due to the moisture differential (wet bottom and dry top), and of course (d) traffic.
of bituminous seals (chip seals) on airport pavements
A newly constructed bituminous seal or reseal needs to be rolled to embed the stone into the bitumen, and to ‘work’ the bitumen around the stone. On the highway, 20% of the necessary rolling is done at the time of construction (or less if you listen to the contractor's foreman), and the remaining 80% is provided by traffic. On runways and taxiways, the traffic is much less than on highways, and much more rolling should be done at construction (although often it is not). The remainder of the rolling should be provided by maintenance rolling during the first few years of life of the seal, because sure-as-eggs the aircraft traffic isn't going do it. Click here for the Word file which discusses this.
Seal design: comparison of Australian, New Zealand, South African and UK methods
Certain countries lead the world in the use of sprayed seals (chip and spray). At the ARRB First International 2008 Sprayed Sealing Conference in Adelaide, there was a session on national practice with highly respected presenters from each of four countries. For research purposes only, their papers and presentations are here:
Mr Walter Holtrop, AAPA, Australia paper presentation
Mr Barry Gundersen, Gundersen Consulting Ltd, New Zealand paper presentation
Dr Cliff Nicholls, TRL, UK paper presentation
Mr Trevor Distin, Sabita, South Africa paper presentation
The 2nd ARRB Sprayed Sealing conference was held in 2010, and hopefully there will be a 3rd.
Reseal and resurfacing selection chart
This is a comprehensive chart that myself, Tom van Rijckevorsel [technical and practical aspects of asphalts and slurries], Gerrie van Zyl aka Crokodil Dundee [seals, choice of surfacings, low volume roads design] and Christo Olwagen [development and production] put together for Colas Southern Africa. The idea of such a chart came from those charts in the old Corps of Engineers publications. We've got all the newer surfacing types (such as Novachip from Jean-Claude Roffe at Screg/Colas), and then, for the first time ever in the world, we were able to combine seals, asphalts and slurries in one chart. Click here for that chart.
INVESTIGATION OF A SURFACING PROBLEM
Messed up the seal? Read how to start your investigation here:
Start by getting the background quality control details (NB this is written in terms of Australian standards, and other authorities use other tests - the same concept applies irrespective of test method).
Aggregate Source and test results that relate specifically to your works.
Old results are no good unless the traceability can be confirmed back to stockpiles of material that were actually used on the works.
Test results should include:
Particle Size Distribution
Los Angeles Abrasion Value
Wet / Dry Strength Variation
All testing should have been performed in accordance with AS1141 under the guidelines of AS 2758 Part 5 Asphalt Aggregates.
Bitumen Source and test results that relate specifically to your works.
These results should include:
Viscosity @ 60C
Viscosity @ 135C
Penetration @ 25C
Matter Insoluble in Toluene
Short Term effect of heat and air
Viscosity of residue as % of original after heat and air effects
Long Term effect of Heat and Air
Density @ 15C
and I'd give some thought to doing extra tests. Wax content if it looks like the bitumen has been flowing in hot weather. If you smell diesel or tar, or you suspect contamination, then maybe GC and HPLC testing is needed. I've got a paper on reverse engineering a bleeding seal in my list of papers and another paper on tracking bitumen quality.
All testing should have been performed in accordance with AS 2341 under the requirements of Table 2 of AS2008 Residual Bitumen.
If it is asphalt and not a seal: it should have been in accordance with AS 2150 Hotmix Asphalt and asphalt laying should have been in accordance with AS 2734 Guide to Good Paving Practice - Asphalt.
Hidden secrets of top investigators
The hidden secrets are to go and look for:
Delivery dockets (of stone, lime or what-have-you)
Test results from manufacturing on the day
Access to any retained samples of aggregate, bitumen or asphalt held by the asphalt company or others (of course since all bitumen looks alike, so if you ask for a sample from some suppliers of the bitumen for NEXT year, they already have the sample waiting for you plus the test certificate.
Paving notes or plans detailed what was laid, with what equipment where.
For checking rolling, get the number of hours from the hire dockets.
For bitumen and asphalt, check delivery dockets for: Date (PMB) Grade, Origin, Sampling point, Manufacturing certificate number or batch number, Customer Customer order number, etc. Delivery details (delivery point, time and temperature).
Check the actual weather from Met Bureau vs stated weather on dockets/spray sheets to catch them lying
Check asphalt VMA calculation from fundamental calculation in case they have fiddled to drop the b.c.
Find the haul distance - cause it cools the mix and it won't compact
Thanks to Lyndon White who wrote most of this.
These are a series of troubleshooting charts which were developed when I was at Colas Southern Africa for all types of bitumen and bituminous surfacings.