Asphaltic Plug Joint Overlay

Asphaltic Plug Joint Overlay
The overlaying of existing Asphaltic Plug Joints (APJ’s) with suitable high modulus materials
is a cost effective and quick means of maintaining and increasing the life of the installed
Asphaltic Plug Joint.
It is common knowledge that conventional APJ’s are prone to rutting, deformation under
loading and loss of skid resistance. The Permatrack H system incorporates a high modulus
running surface, which demonstrates excellent resistance to both rutting and deformation and
retains skid resistance properties akin to the existing carriageway surface.
Existing Carriageway
Existing Asphaltic Plug Joint
Permatrack High Modulus
Permatrack PSB Movement Interface
The main concern with overlaying the Permatrack system over an existing asphaltic plug joint
is the restriction of movement that a high modulus system would impart onto the APJ.
The reason for this conclusion is that the movement principals for the two systems are
Asphaltic Plug Joints
The asphaltic plug joint being a mixture of graded aggregate and an elastic bituminous
compound means that the movement accommodation for the system is provided by the full
cross section of the material over the joint.
Permatrack System
The system provides the running surface from the high modulus inner material with the
movement accommodation being provided by the elastic bituminous material surround.
The concern is that the interface between the two systems restricts the movement of the
asphaltic plug joint underneath.
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System Behaviour
The behaviour for the compatibility of the two systems can be determined through a
theoretical approach using suitable engineering principals and the historical information
available on the in-situ performance of the system.
Theoretical Approach
The first aspect for determining the movement performance of the system is the restriction
that is placed on the APJ.
If we look at the behaviour of a volume of elastic material then we can determine how much
of an effect an applied ‘static’ system would have.
If the depth of the material is equal to the width of the joint then the movement
accommodation will be reduced by 50%. The non-elastic interface applies a restrictive force
upon the elastic material (APJ in this case) and reduces the movement accommodation. The
depth of the material dictates how much of an effect this will have until the depth is greater
than width.
Cross Section of Joint
Area affected by non-elastic
Depth of Joint
Area not affected and under
Typical movement
To put this in relative terms an asphaltic plug joint with a specified movement of +/-20mm
overlaid with a non-elastic material would have potential unrestricted movement of +/-10mm.
This is assuming that the width and depth are equal. So therefore a joint of 500mm wide by
50mm deep would have 5% of the material un-affected by an overlaid non-elastic material.
Cross Section of Joint
Area affected by non-elastic
Depth of joint
Area not affected and under
Typical movement
The material under restriction will still maintain elastic behaviour. However, there will be a
graduated increase in the inherent force upwards through the affected volume to the
interface. This may cause problems with shear failure at the interface between the asphaltic
plug joint and a non-elastic overlay.
However, in order to prevent this mode of failure the Permtrack system for APJ overlays
incorporates an elastic compound (Permatrack PSB) with a movement accommodation of
300% @ 0ºC which will allow the underlying system to perform upto design movements of +/10mm (The current Permatrack system movement limit).
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Historical Information
Permatrack asphaltic plug joint overlays have been laid over the past six years in locations
such as; Coventry Ring Road, Birmingham Expressway and the M6 (Midlands) with great
success with regard to prolonging the life of overstressed APJ’s without the need to
undertake a complete replacement.
The Permatrack asphaltic plug joint overlay has a registered movement capability of +/10mm. The underlying asphaltic plug joint has a typical movement capability of +/- 20mm.
With this in mind the underlying APJ is when first installed functioning well within its
movement capabilities.
The interface between the two systems, as previously stated is a highly elastic compound
providing the overlay system (Permatrack) its base movement capabilities and allowing the
underlying system to function.
Alistair Puddick
Technical Development Manager
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