SUPERPAVE Digest 253

Topics covered in this issue include:

1) Transversal cracks

by "Luiz Alberto Schmidt" <>

  • To: <
  • Subject: Transversal cracks
  • From: "Luiz Alberto Schmidt" <
  • Date: Thu, 14 Oct 1999 22:07:50 -0300

To everybody:

What could be the possible causes of a kind of transversal cracks on the surface of an asphaltic overlay?

These cracks are very frequent (at every 10 centimeters, about 4") and appeared inmediately after construction, in severaladjacent jobsfrom different contractors (at the same road).

They cannot be atributed to reflection, since they have only about 4 cm (about 1 1/2") from the surface and the total overlay thickness is 13 cm deep (a little bit more then 5").

They don't have the resilient moduli yet, as determinedby laboratory, but the analysis of deflection basins indicates 15,000 kgf/cm2 (about 220,000 psi) at 35 degrees centigrade (95 Fahrenheit).

The MMAT varies from 15 C to 30 C.

Could it be a problem related tothermal gradient?

Thanks,

Luiz A. Schmidt

They are not induced from the old bituminous layers.

SUPERPAVE Digest 255

Topics covered in this issue include:

1) Re: Transversal cracks

by "Bruce W. Peebles" <>

  • To: Luiz Alberto Schmidt <
  • Subject: Re: Transversal cracks
  • From: "Bruce W. Peebles" <
  • Date: Fri, 08 Oct 1999 01:35:53 -0500
  • CC:

Several items need to be looked at. It could be a laydown compaction

problem and/or an asphalt film thickness problem.

If the mat is over-rolled as it cools it will become tender and start

shoving on the interface with the lower layer. This can happen when

overlaying bituminous or concrete pavement. Pay attention to you

temperatures and the "tender zone".

If it is a mixture problem I suggest looking at the asphalt content and

the dust to ac ratio. A mix that is too dry (thin film thickness) will

behave in the manner you described.

SUPERPAVE Digest 256

Topics covered in this issue include:

2) Re: Transversal cracks

by

  • To:
  • Subject: Re: Transversal cracks
  • From:
  • Date: Sun, 17 Oct 1999 17:48:35 EDT

I agree with the idea that it could be compaction temperature/compactor

operation related ... especially if it is a mixture with which you have had

other good experiences. It almost sounds like roller checking ... is that

what it is? I tried to get TxDOT to look at a Canadian device that addresses

this problem some time ago because I thought it might help to counteract some

of the compaction problems that were being anticipated with crumb rubber

mixtures, but they were not interested so I have never seen the device in

action. However, I think the rights to the compactor were bought by Pioneer

Road Services, Ltd. in Australia and they have had extremely good luck with

it for finishing. It's relatively low contact pressure, but applied over a

longer period, so it has both creep and temperature implications and seems to

stop anything that resembles roller checking.

SUPERPAVE Digest 257

Topics covered in this issue include:

1) RE: Transversal cracks

by Steve Goodman <>

8) Re: Transversal cracks

by "Kenneth Hobson" <>

  • To: "''" <
  • Subject: RE: Transversal cracks
  • From: Steve Goodman <
  • Date: Mon, 18 Oct 1999 09:30:24 -0400
  • Cc: "A. O. Abd El Halim (E-mail)" <>, "Ian Rickards (E-mail)" <>, "Yasser Hassan (E-mail)" <

The Canadian device that the Shedworks representative discussed is

called the AMIR compactor, which has been subsequently improved by

Pioneer Road Services and is now called HIPAC. As mentioned, the AMIR

and HIPAC eliminate roller checking by compacting the mixture with a

"rolling flat plate" through the use of a rubber belt surrounding the

drums. The belt applies a constant pressure over a long period of time

that allows the hot asphalt to flow and therefore compact. Roller

checking is eliminated because there is no pushing or pulling of the

asphalt by the round steel drums of conventional compactors. Repeated

trials in Canada and Australia have shown that 96% of Marshall can be

achieved with a single pass. Also, tenderness of the mix does not

occur with this device due to its low contact pressure through the large

compaction area. At this time, Pioneer is developing a strategy to

bring the HIPAC to Canada and the US.

You may find out more about the AMIR and HIPAC at the Centre for

Advanced Asphalt Research and Technology (CAART) at Carleton University

in Ottawa at Look under the current

research section of the website.

Sincerely,

Stephen Goodman, B.A.Sc.

Technology Transfer Manager

Canadian Strategic Highway Research Program (C-SHRP)

Transportation Association of Canada (TAC)

2323 St. Laurent Blvd., Ottawa, Ontario K1G 4J8 Canada

Tel: (613) 736-1350

Fax: (613) 736-1395

Email:

Internet:

  • To: <
  • Subject: Re: Transversal cracks
  • From: "Kenneth Hobson" <
  • Date: Mon, 18 Oct 1999 19:24:21 -0600

I assume you used a superpave mix and a PG binder? What type of PG binder

and in what part of the country? Did the quality assurance testing verify

that you got what you paid for?

What were the results of PG fields tests? In particular the G*/sin(delta).

In conventinal asphalt cements the penetration test might show the problem

more clearly. You might try running an abson recovery and test for

penetration and G*/sin(delta).