PAVEMENT LIFE CYCLE

I RECENTLY RECEIVED A PAVEMENT DESIGN COMMENT FROM THE NEW JERSEY DEPARTMENT OF TRANSPORTATION WITH REGARDS TO THE DESIGN LIFE OF PAVEMENT STRUCTURES.

QUOTE:  IT IS RECOMMENDED THE NEW PAVEMENT FOR 30 TO 50 YEAR RANGE DESIGN LIFE TO ACCOMODATE THE 75 YEAR LIFE OF THE BRIDGE STRUCTURE. THE DESIGNER SHOULD CHOOSE THE DESIGN WHICH PROVIDES THE MAXIMUM DESIGN LIFE WITHIN THE BUDGET CONSTRAINTS.


MY QUESTION IS : I HAVE BEEN LOOKING FOR THE 75 YEAR REQUIREMENTS OF A BRIDGE STRUCTURE IN "ANY" DESIGN MANUAL AND HAVE NOT YET SEEN IT. CAN ANYONE POINT ME IN THE DIRECTION TO A REFERENCE THAT STATES SOMETHING SIMILAR??????

In the UK and now under the latest European Standards, Bridges should be designed for a 'design life of 100 years'.
For example the concrete used for a reinforced concrete bridge should be designed to last for a 100 years under the conditions it is likely to encounter. So the strength of the concrete, depth of cover, durability, fire resistance, chemical contamination resistance, cement type and content etc... need to be designed to last for 100 years,(as opposed to temporary structures which only have a design life of 10 years).
For pavement design, in the UK the design life could be as little as 10 years, with increasing requiements for stiffness to prolong life. As stiffness goes up, so should the 'potential' life of the pavmement.
Sorry, but I don't think that looking for references within the design manual for bridges in order provide specific data on a 30 to 50 year pavement design will be there. I could be wrong, its just not one I have come accross before.
You are more likely to get the info by increasing the predicted MSA upto what you can expect for 50 years (if you can predict what we will be driving in 50 years that is!)