Environmental Engineering Reference
In-Depth Information
GHG emissions and 85% of these are generated by road transport, the contributions
from design and construction activities cannot be ignored. Road agencies, road
designers and contractors need to be aware of and consider these issues in policy
and decision-making. Energy consumption and GHG emissions also depend on the
type of pavement structure. Both were lower for the long lasting high modulus
pavements than for the conventional asphalt pavements
[2]
. This study also showed
that energy consumption for pavement construction and maintenance was about 9%
lower for high modulus pavement (i.e. those made with high strength asphalt layers)
than for conventional asphalt pavement over a 30 years analysis period. A similar
difference can be anticipated for perpetual pavement and it is likely that this differ-
ence would be even higher for an analysis period of 50 years.
Perpetual Pavement Design Strategy
The traditional pavement designs developed originally were compared with the
initial perpetual pavement design. As part of the feasibility study, life-cycle costs,
environmental benefits of the perpetual pavement design, pavement sustainability
aspects and public satisfaction were analyzed. Traditionally designed pavements
tend to fail in either one of two modes, fatigue cracking or permanent deformation,
also referred to as rutting. To significantly extend the life of a traditional pavement,
it needs to have two main attributes as follows
[4, 5]
:
1. Total asphalt thickness of more than 200 mm. It has been shown that lexible
pavements with more than 200 mm of hot mix can resist fatigue cracking (bottom-
up cracking) regardless of the number of axle load repetitions. The resistance to
fatigue cracking is further enhanced by increasing the asphalt cement content of
the bottom lift of hot mix asphalt and the air voids in the mix are reduced to
about 2-3%. This specially designed layer is described as a 'rich-bottom lift'.
2. The increased hot mix asphalt thickness above the rich-bottom lift comprises
high quality, rut-resistant mixes that protect the rich-bottom mix from distress
and resist asphalt rutting.
Damage to the pavement is now limited to surface tyre abrasion and loss of friction.
This surficial damage can be corrected by surface milling and thin overlay.
Case Study
The Red Hill Valley Parkway (RHVP) is a modern urban Expressway in the City of
Hamilton, Ontario, Canada. It is the final leg of a longer Freeway project considered
to be the largest municipal road project in Canada with an estimated final total cost
of Can$430 Million. An initial traffic volume of about 40,000 vehicles per day and
full capacity volumes in excess of 90,000 vehicles per day are expected for this
