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What is Full-Depth
Reclamation?
Between mill-and-fill and total reconstruction,
there’s an economical,
long-life alternative that’s gaining
popularity in North America
Everyone from highway engineers to
frustrated motorists has fantasized about a machine that would move
steadily down a road, gobbling up bad pavement in front and leaving
a trail of perfect pavement in the rear. No more construction
backups. No more breathlessly expensive rebuilds. No more
pockmarked, rutted roads waiting to break axles and bend wheels.
Although pavement recycling technology has not yet evolved to
fulfill that fantasy, the industry is getting closer.
Cold planing, cold-in-place recycling, and hot-in-place recycling
are accepted, widely used techniques for rehabilitating flexible
pavements with surface course imperfections. Each delivers a piece
of the road-renewal dream, leaving in the wake of its recycling
train a smooth, flat surface that is accomplished relatively quickly
and inexpensively.
In recent years, another recycling technology has gained
popularity in North America — full-depth reclamation. It comes even
closer to the road-renewal dream because it gives pavement managers
a fast, inexpensive, long-wearing alternative to rebuilding roads
that require major repairs or total reconstruction.
While the other recycling technologies grind off a portion of the
surface course of asphalt and replace it, full-depth reclamation
penetrates the entire flexible pavement section and a predetermined
portion of the base material, uniformly pulverizing and blending
them together to produce a stabilized base course. Thus, FDR can
correct deficiencies in the base as well as the bound asphalt
layers.
Full-depth reclamation technology can be utilized to depths of 12
inches or more; the most typical applications involve depths of 6 to
9 inches. As it pulverizes and mixes, the road reclaimer can also
meter in precise amounts of additives to further enhance the
structural characteristics of the stabilized base course. Its
benefits start with the fact that FDR completely erases deep
pavement cracks, eliminating the potential for reflective cracking.
It also allows for cross-slope and profile grade adjustments, and
road widening is easily accomplished.
The Evolution
 At the heart of full-depth
reclamation is a small fleet of road reclaimers, machines that use
milling drums similar to those found on milling machines, but which
are designed to cut and mix at much greater depths. Road reclaimers
evolved from machines designed to handle mass production soil
stabilization work. Indeed, the only difference between many of
today’s reclaimers and soil stabilizers is the milling drum.
These machines have been in use in Europe and in North America
for many years, but their suitability for FDR, North American style,
has evolved with the advent of high-horsepower diesel engines.
Powered by engines as big as 800 horsepower, today’s reclaimers cut
harder and deeper, mix faster, and cover more ground than ever
before. And with these improvements, popular FDR applications have
broadened from low volume country roads to include city streets and
medium volume roadways.
The classic application for FDR is a secondary or tertiary road
with a 2- to 4-inch asphalt overlay on a compacted base. When the
overlay is too deeply cracked or rutted for a mill-and-fill remedy,
full-depth reclamation is the next cheapest alternative — and it can
produce a much longer-lasting solution.
The full-depth reclamation process is fast and straightforward. A
reclaimer pulverizes and mixes the asphalt and base material,
creating a strong new base. The reclaimer is typically followed by a
grader, a water truck, and various compactors. Minutes after the
last compactor completes its pass, the road can usually be opened to
traffic until the contractor is ready to apply the final surface
treatment.
For some low-traffic roads, the surface treatment can be as
simple as a double chip seal. For higher traffic roadways, the FDR
operation is typically followed by an asphalt overlay, creating a
new road that should have much better wear and load-bearing
properties than the old road. More to the point, say FDR advocates,
the new road is the equivalent of a traditionally rebuilt road in
terms of life expectancy, wear, and load-bearing characteristics,
but it costs a fraction as much and can be completed with far less
interruption of traffic.
Full-depth reclamation can be used to rehabilitate and improve
gravel roads, and it has also been used on major highways, including
interstates. There have even been cases where a road was first
milled, to reduce the bound asphalt depth to an appropriate
thickness, so that FDR techniques could be applied. This milling is
also sometimes done to allow for proper curb reveal on curb and
gutter streets or to control grade prior to the subsequent asphalt
overlay.
The full potential of full-depth reclamation is still being
defined, but it has emerged as an important and valuable option for
road managers to consider as they search for budget-stretching
solutions to the thousands of miles of roads in Canada and the U.S.
that can no longer be cost-effectively repaired.
Reprinted from Better Roads
Magazine
July
2001 | 
