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For as long as there have been paved roads, there have been questions about the longitudinal joint between lanes. How do you make the joint last longer? How do you prevent raveling, cracking and erosion? How do you prevent water infiltration? What are the critical factors? It’s always been assumed that what was most critical for good road performance was density.

Over the years great attention was given to analyzing the effect of density, both on the main part of the mat and at the joint region. Mix designs have concentrated on maximizing the achievable density.

Screed designs aimed at increasing the initial density that could be achieved as the asphalt left the paving machine. The hope was if density could be achieved in spreading the asphalt initially, then it would alleviate the necessity of increased rolling.

With regard to the rolling of asphalt, roller weight was maximized. Roller vibration was introduced in hopes of moving aggregate and nesting it in a more close packed geometry, hence increasing density. Vibration was also added to the paving machine in an attempt to increase initial density.

With all this attention given to density, the performance of the longitudinal joint did not appreciably improve. Looking at the actual joint geometry seemed a logical step.