The Sustainable Benefits of Concrete Pavement

The Sustainable Benefits of Concrete Pavement
Tim Smith, P.Eng., Cement Association of Canada
Ottawa
Pierre-Louis Maillard, ing., Association Canadienne du Ciment
Montréal
Paper prepared for presentation
at the
42e Congrès annuel de l'AQTR
Defi: Transport Durable
2 Au 4 Avril 2007, Montréal
Abstract
Portland cement concrete pavement (PCCP) has long been known as a long lasting, durable
pavement surface with low maintenance costs. Although DOT's sometimes consider these
advantages by including Life Cycle Cost Analysis (LCCA) in the tender process, currently, they do not
consider the many sustainable benefits of using PCCP. Including sustainable performance of
different pavement types provides government agencies with a better understanding of the true cost
of the roadway structure. This paper looks at the sustainable performance characteristics of concrete
pavement by examining and documenting some of its many social, economic and environmental
advantages.
Some of the social benefits of concrete pavement that are identified in this paper include: reduced
potential for hydroplaning and good night time visibility. Several environmental benefits of PCCP are
examined and presented including: findings of the Athena Institute study on the life cycle embodied
primary energy use for PCCP and hot mixed asphalt (HMA) roadways; findings of several studies on
truck fuel savings from traveling on PCCP compared to HMA pavements and the resulting reduction
in greenhouse gas (GHG) and smug emissions; and the recyclable nature of PCCP. Use of
supplementary cementing materials (SCM) is also be discussed to show how industry by-products
such as fly ash, blast furnace slag and silica fume can be used in PCCP to improve performance
characteristics and divert their disposal to landfill sites. Economic benefits such and life cycle cost,
advantage of two-pavement system and potential for reduced lighting requirements for PCCP are
also provided.
La deuxième partie illustrera à partir des résultats de l'étude Athena quels sont 1:l'énergie nécessaire
et 2: les gaz à effet de serre générés lors de la construction, de l'entretien sur 50 ans et de la
considération de l'économie de carburant appliqués aux 16 tronçons types définis par le MTQ dans le
cadre du renouvellement de l'orientation sur le choix des types de chaussées.
1.0 Introduction
Portland cement concrete pavement (PCCP) has long enjoyed the reputation as a longer lasting,
durable pavement surface with low maintenance costs. Cities such as Montreal, Winnipeg, Windsor,
and Toronto have extensive networks of PCCP and have been using exposed PCCP or composite
pavements for some time. Many other cities are also using PCCP at high traffic and high wear areas
such as intersections and bus stops where turning movements and static loading are rutting and
showing asphalt pavements.
Traditionally many Provincial and Municipal Government agencies in Canada have chosen pavement
type based solely on an initial cost bases. With the need to stretch ever decreasing public funds
government agencies are looking for ways to provided the general public with economical and longer
lasting pavement structures. This has lead DOT’s and municipalities to consider different types of
flexible and rigid pavements structures for their roadway networks. To compare the cost of one
pavement structure to another some DOT’s have started using life cycle cost analysis (LCCA) as part
of the pavement tender process. Calling alternate bid tenders with both equivalent asphalt and
concrete pavement structure options and predetermined maintenance and rehabilitation schedule
costs provides the government agency with a clearer understanding of the actual cost of a roadway.
Since 2002 a total of nine alternate bid tenders with a LCCA component have been called across
Canada. Eight of these projects went PCCP.
Although alternate bid tenders with a LCCA component are a step in the right direction in helping
government agencies to determine the best pavement option for a particular job they do not provide
the true cost of a roadway project. To have a complete understanding of the cost of one pavement
type compared to another, one must consider the sustainability of each product. Although everyone
2
has their own definition of what sustainable development is, the key is to ensure we leave our
children and their children with sufficient resources to have the same standard of living we enjoy
today. This can be accomplished by ensuring that every government and corporate decision
considers the impact of the triple bottom line as depicted in Figure 1 below. Provincial and municipal
governments which consider the Social, Environmental and Economic (SEE) impacts when
evaluating different pavement structures to build will have a better understanding of the their true
cost.
Figure 1: The Triple Bottom Line of Sustainable Development
2.0 Social Benefits
There are many social benefits from utilizing PCCP ranging from roadway safety issues to passenger
ride and comfort. The following subsections explain how PCCP provides enhanced pavement
qualities through the following attributes: decreased potential for hydroplaning, better night time
visibility, smooth ride for long period, and quite ride.
2.1 Decreased Potential for Hydroplaning
Vehicles hydroplane when there is tire separation from the pavement surface by a layer of water,
which causes loss of vehicle steering and braking control. Several factors may contribute to
hydroplaning potential such as tire wear, driver speed / experience and pavement surface
characteristics. Since Government agencies have little control over the condition of tires and driver
experience the following discussion focuses on the one area Government agencies do have control of
- pavement surface characteristics.
All types of pavement whether gravel, asphalt or concrete have the potential for hydroplaning when it
is raining or water is present on the surface. However, since concrete pavement is a mouldable
material when it is first placed it can be textured to provide good friction and wet weather
characteristics and performance. Figure 2 below shows a close-up of a concrete pavements surface
after it has been texture. The texture is classified into two categories:
1) microtexture – which is the fine-scale roughness on the surface of the pavement contributed by the
fine aggregate (i.e. sand) in the concrete matrix. The texture is created in the concrete surface by
dragging burlap or astro-turf over the surface of the plastic concrete prior to applying the curing
compound. This created texture provides the pavement with superior dry weather friction.
3
2) macrotexture – which is the measurable striations or grooves formed in the plastic concrete by
hand operated tining brooms or automated machines provides the wet weather friction. Macrotexture
may also be formed by cutting or sawing grooves into the hardened concrete surface [ACPA 2000].
Macrotexture - formed into surface
Microtexture - from aggregate particles
near the surface
Source: Special Report Concrete Pavement Surface Textures by ACPA
Figure 2: Close-up of Microtexture and Macrotexture on PCCP
The pavement’s macrotexture is the main contributor to providing a pavement’s superior performance
in wet weather conditions. The grooves (i.e. tining) in the concrete pavement surface provide water
with a channel to escape from underneath the vehicle’s tires thereby increasing the tire pavement
interface and greatly reducing the potential for hydroplaning. Another contributor to PCCP’s superior
performance in wet weather conditions is its rigid structure. This quality prevents heavy vehicles from
causing deformations such as ruts and washboarding in the pavement surface where water can
accumulate and create increased potential for hydroplaning. If studded tires are permitted to be used
on provincial roadways higher strength concrete pavement can be used to virtually eliminate potential
wear ruts in the vehicle wheel paths.
2.2 Superior Night Time Visibility
Darkness on a roadway decreases driver visibility, thereby increasing the potential threat of possible
hazards on the roadway. In fact, an industry report identifies night time fatality rates are
approximately three times greater than during daylight hours [Gajda 97]. The report notes that
concrete pavement reflects light in a diffuse manner while asphalt reflects light in a slightly spectral
manner. Asphalt’s spectral light reflection can be compared to a ball bouncing off a floor. When the
ball strikes the floor at an angle it bounces of the floor at approximately the same angle. On the other
hand, concrete’s diffusely reflected light is like a ball bouncing off water -regardless of the angle the
ball strikes the water the water will splash at all angles. Similarly light hitting concrete pavement is
reflected at all angles, therefore, illuminating a greater area of the roadway compared to asphalt
pavements [Gajda 97]. Figure 3 illustrates the difference in the illumination between the concrete (a)
and asphalt (b) pavement surfaces. Even with the asphalt example having more overhead lighting
the concrete pavement option still has superior illumination, thereby, providing better night time
visibility.
4
a) Concrete pavement night picture
b) Asphalt pavement night picture
Figure 3: Night Time Pictures of PCCP and ACP on City Street
2.3 Quiet Ride
Roadside noise levels are a public concern especially when the pavement is in an urban
environment. Producers of the various pavement types are investing time and money to develop
quieter pavements structures. In fact, the Cement Association of Canada in conjunction with the
American Concrete Pavement Association (ACPA) is conducting research to develop quieter
concrete pavements to better serve the transportation community. This effort involves
standardization of tire/pavement noise assessment; establishment of acoustic performance curves for
existing surfaces; development of new surface textures through a laboratory test program; a field
validation program; and an implementation phase.
The development of new surface textures requires the ability to easily modify surface characteristics
and to readily evaluate their impact on acoustic performance. To accomplish this, the ACPA has
contracted with Purdue University to conduct laboratory testing using the Purdue Tire Pavement Test
Apparatus (TPTA). The TPTA provides efficient evaluation of any surface that can be cast or formed.
Efforts to date have focused on development of quieter diamond ground surfaces through alteration
of the blade size, spacer arrangements, and by controlling fin profile.
When looking at the acoustic performance of different pavement types one needs to consider the
pavement characteristics throughout the pavements service life and not just the as-constructed or
nearly new pavement condition. Most research to date shows longitudinally tined, astro-turf drag
textures, and diamond grinding textures provide the quietest new construction techniques for
concrete pavement, while diamond grinding provides the quietest rehabilitation strategy. Most loud
concrete pavements, however, have been constructed using random transverse tining. The Cement
Association of Canada has had testing completed on a number of concrete pavements across
Canada to determine Sound Intensity (SI) noise measurements. Figure 4 below shows the results of
the first year of testing on roadways in Montreal. The random transversely tined concrete pavement
had aggressive tining (deep) which is known to cause increased vehicle noise. Note, the different
test sections of varied concrete surface textures show equal to or lower SI noise values than the
asphalt section that was tested.
5
OBSI Noise Levels By Surface Type
109
OBSI Level (dBA)
108
107
106
Random
Transverse
5-20mm
5-14mm
105
Longitudinal
104
Exposed
Aggregate
103
Skid Abrader
102
Surface Type
Dense Graded
Asphalt
Figure 4: OBSI Noise Level by Surface Type in Montreal
Further evidence that concrete pavements can be constructed quiet is noted in a report by the U.S.
Department of Transportation in 1996 concluded that, “Properly constructed PCCP, with transversely
tined surface, matches the performance of dense-graded asphalt considering both safety and noise
factors” [FHWA 1996]. In addition, a report by the Wisconsin Department of Transportation
concludes, “That it is possible (very simply and at no extra expense) to build a PCC pavement that
does not “whine” and has the desired frictional properties. Such a pavement is a “good neighbour”, is
safe, provides user comfort and is durable” [WIDOT 1997]. Based on the comments from these two
reports, the research currently on going by ACPA and the findings noted in Figure 4 it evident that it is
possible to build quiet PCCP similar to that of an ACP surface. Initial pavement smoothness can also
affect the quietness of a highway as rougher pavements are noisier pavements. New paving
equipment and construction techniques have allowed paving contractors to construct smoother
concrete pavements.
2.4 Smooth Ride for Long Period
Advances in concrete paving construction equipment and techniques along with Government
agencies’ tenders having bonuses and penalties clauses have helped lead to PCCP being built
smoother than previously accomplished. This initial smoothness decreases the dynamic loading on
the pavement structure and helps the pavement stay smoother for a longer period of time. In fact, the
new Mechanistic – Empirical Design Guide (MEPDG) recognizes this fact requiring an initial
international roughness index (IRI) value inputted into to model when evaluating pavement thickness
designs. Concrete’s natural rigid structure also helps the structure to stay smoother for a long period
of time.
The Nova Scotia Department of Transportation and Public Works (NSTPW) completed a five-year
study on an adjoining section of asphalt and concrete pavement built in 1994 on Highway 104
TransCanada Highway [NSTPW 1999]. Results of the study, which concluded in 1999, showed both
pavements performed well over the evaluation period. However, the concrete pavement section
outperformed the adjoining asphalt pavement in both riding comfort and road smoothness.
6
Data from the comparative study noted above indicated that although the new asphalt pavement had
a higher initial riding comfort index (RCI), over time it deteriorated to a lower level than the adjoining
concrete pavement. Figure 5 provides an illustration of how the RCI values changed over the 5-year
evaluation period. Note, the higher the RCI value the more comfortable the ride. The RCI reading at
year five was good for both pavements but the PCCP value was superior to the ACP number - 7.4
compared to 6.9 [NSTPW 1999].
Source: Asphalt Concrete Pavement and Portland Cement Concrete Pavement,
Test Results of Riding Comf ort Index
9
Improved Comfort
Concrete
Asphalt
8
7
6
5
1
2
3
Year
4
5
Highway 104, Cumberland County, Year 5 of 5 Year Study, October 1999.
Figure 5: Comparison of Test Results of Riding Comfort Index
Profile ride index (PRI) which is a measure of the pavement smoothness was also collected during
the NSTPW study. Unlike the RCI measurement, an increase in the PRI value represents increased
roughness in the pavement. Figure 6 illustrates how the two pavement structures performed over the
5-year evaluation period. As can be seen in the diagram both pavements were constructed quite
smooth with the ACP having a slightly better IRI reading than the PCCP – 4.0 compared to 4.1.
However, over the next four years, the concrete pavement maintained close to its original
smoothness, while the asphalt section showed increased roughness. In fact, the roughness of the
ACP more than doubled that of the PCCP after five years of service (i.e., 6.8 mm/100 metres on
concrete versus 16.2 mm/100 metres on asphalt) [NSTPW 1999].
Test Results of Profile Index (Smoothness)
Increased Roughness
18
16
Concrete
14
Asphalt
12
10
8
6
4
2
0
1
2
3
4
5
Year
Source: Asphalt Concrete Pavement and Portland Cement Concrete Pavement,
Highway 104, Cumberland County, Year 5 of 5 Year Study, October 1999.
Figure 6: Comparison of Test Results of Profile Ride Index
7
3.0 Environmental Benefits
Concrete pavement also provides many environmental advantages compared to other
pavement structures. This section of the report looks at some of the many environmental
benefits including: reduced energy consumption when using PCCP, reduced carbon dioxide
emissions from operating on PCCP, reusable and recyclable paving material, and use of
industrial by-products.
3.1 PCCP Reduced Energy Consumption
The Athena Institute was commissioned by the Cement and Concrete Industry to undertake a review
and update the research it completed in 1999 on the Life Cycle Embodied Primary Energy and Global
Warming Emissions for PCCP and ACP Roadways. A key component of the new study was to
update the life cycle inventory data for various road construction materials such as cement, concrete,
steel and asphalt. This change, as well as, the decision to evaluate different roadway sections in the
second study means the results of the two different reports can not be compared.
In the new study, concrete and asphalt roadway structures were analyzed for four different roadway
examples including the following:
1) Canadian (average) arterial roadway
3) Ontario freeway (401) section
2) Canadian (average) high volume highway
4) Quebec urban freeway section
The first two designs are equivalent concrete and asphalt pavement designs prepared by ERES
consultants, now known as Applied Research Associates, Inc. ERES Consultants Division [ERES 03].
These designs were prepare for subgrade strengths of California bearing ratio (CBR) 3 and 8. The
other two designs were actual ministry of transportation designs used on the 401 highways in Ontario
and freeway system in Montreal. Note, the Quebec PCCP option has substantially more aggregate
than is required in an equivalent concrete pavement design but is what is required by the Ministry as
they design their pavement structures for frost not expected vehicle load.
The report shows the PCCP pavement has lower total primary energy results for all roadway examples
analyzed. The asphalt designs analyzed consumed from two to four more times the primary energy
than the PCCP counterparts. Figures 7 shows the comparative embodied primary energy results for the
Quebec urban freeway example noted above at 0% RAP (recycled asphalt pavement). The figure
shows the embodied primary energy broken into its feedstock portion and primary energy use portion.
If feedstock energy (i.e. bitumen in the asphalt pavement) is not considered in the analysis the savings
for the four examples decrease to a range of as low as 31 % for the MTO design to a high of 81 % for
the MTQ design. If 20 % RAP is added in the binder course mix for the Canadian arterial and high
volume highway examples the embodied primary energy estimates are reduced by 3.5 to 5 % for the
PCCP option and 5 to 7.5 % for the ACP option [Athena 06]. The reason for the reduction of embodied
primary energy for the PCCP option is the use of asphalt shoulders and an asphalt overlay as part of
the maintenance activities during the later stages of the pavement’s maintenance and rehabilitation
schedule.
It should be noted the scope of the Athena study did not include operational considerations such as
truck fuel savings from operating on different pavement types and energy savings due to the different
light reflectance properties of the pavement types. These types of issues should, however, be taken
into account in any decisions predicated on life cycle environmental effects. The report notes areas
where Athena was conservative with PCCP data including ignoring the subgrade benefits of narrower
PCCP structure and treating RAP as free of environmental burdens [Athena 06].
8
Feedstock energy portion
Primary energy
50000
46,359
45000
40000
35000
32,559
30000
GJ 25000
20000
15000
10000
8,823
5000
1,205
0
Asphalt
Concrete
Portland
Concrete
Pavement Structure
AC – Asphalt Concrete PC – Portland Cement Concrete
Source: A Life Cycle Perspective on Concrete and Asphalt Roadways: Embodied Primary Energy and
Global Warming Potential, Athena Institute
Figure 7: Comparative Embodied Primary Energy Quebec Urban Freeway Designs
3.2 Reduced Carbon Dioxide (CO2) Emissions from Operating on PCCP
Differences in fuel consumption as a function of pavement structure are an important consideration
for users and government agencies. Heavy vehicles cause greater deflection on flexible pavements
than on rigid pavements. This increased deflection of the pavement absorbs part of the vehicles
rolling energy that would otherwise be available to propel the vehicle. Thus, the hypothesis can be
made that more energy and therefore more fuel is required to drive on flexible pavements [Zaniewski
1989].
Several studies have been completed that support these findings. The first study was part of a larger
1989 study to update vehicle operating costing tables by the Federal Highway Administration
(FHWA) for the World Bank. In this study, the FHWA found that the savings in fuel consumption for
heavy vehicles traveling on concrete versus asphalt pavements was up to 20% [Zaniewski 1989].
Considering the results of the FHWA work, the Cement Association of Canada (CAC) initiated its own
series of studies to investigate the potential truck fuel savings when operating on concrete pavement
compared to asphalt pavement. In the fall of 1998 a small test study was undertaken to verify the
findings of the FHWA work. Based on the findings of the Phase I study CAC contracted NRC to
perform a second and much more detailed study during 1999 and 2000 comparing several PCCP,
9
ACP and composite pavements roadways in Quebec and Ontario. This Phase II study also included
several other variables in the analysis including:
- Pavement roughness (IRI<1.5, IRI>2)
- Vehicle type (Semi-trailer, Straight, B-train)
- Load (Empty, Half, Full)
- Speed (100, 75, 60 km/h)
- Seasons (Spring, Summer, Fall and Winter)
- Temperature (<-5,-5 to 10, 10 to 25, >25 ° C)
- Grade < 0.5%
- Ambient wind (< 10km/h average)
Onboard state-of-the-art real time computerized data collection equipment along with Cummins
supplied in-site software was used in the tractor trailer unit to collect and calculate instantaneous fuel
flow while traveling over the desired pavement locations. The tanker semi-trailer data was analyzed
using a multivariate linear regression analysis tool to determine the potential savings and the
statistical significance of the results. The results of the Phase II MVA Study entitled, “Additional
Analysis of the Effect of Pavement Structure on Truck Fuel Consumption” showed statistically
significant fuel savings for heavy vehicles operating on PCCP versus ACP as follows:
- 4.1 to 4.9 % compared to ACP at 100 km/hr
- 5.4 to 6.9 % compared to ACP at 60 km/hr [Taylor et al 2002]
Based on the request of several Government agencies a third fuel study was undertaken by NRC to
verify the Phase II study findings. This study, however, was funded under the Government of Canada
Action Plan 2000 on Climate Change with some dollars from the Cement and Concrete Industry.
Terms of reference for the study were set by a government committee that included people form
various organizations including Natural Resources Canada, the Ministry of Transportation of Ontario
(MTO), Ministère des Transport du Quebec (MTQ) and others. Like the Phase II study this was a
year long study comparing fuel consumption data for ACP, PCCP and composite pavements. The
main difference with this Phase III study and the Phase II study was the test vehicle was a van semitrailer and the DOTs chose the sections to test in Ontario and Québec.
The results of the Phase III Fuel Study show statistically significant fuel savings for heavy vehicles
traveling on PCCP compared ACP ranging as follows:
- 0.8 to 1.8 % savings compared to ACP pavement at 100 km/h.*
- 1.3 to 3.9 % savings compared to ACP pavement at 60 km/h.*
* This excludes summer night data which was not statistically significant [Taylor 06].
Based on the findings identified above Table 1 shows the yearly potential savings in dollars, CO2
Equivalent, NOX, SO2 if a tractor trailer operated a total of 160,000 km/year. It is assumed the tractor
trailer has an engine fuel consumption of 0.430 litres / km and Cost of diesel fuel $0.8964 / litres
(Average for Jan to June 2006).
Table 1 Yearly Potential Savings in $, CO2 Equivalent, NOX, SO2 Per Tractor Trailer*
% Fuel
Savings
Fuel Saved
(litres)
Fuel
Savings ($)
CO2 Eq
(tonnes)
NOX
(kg)
SO2
(kg)
0.8 min.
3.85 avg.
6.9 max.
550.4
2,648.8
4,747.2
$493
$2,374
$4,255
1.51
7.31
13.09
17.18
82.68
148.18
2.17
10.45
18.73
Note: CO2 Equivalent calculations include carbon dioxide, methane and nitrous oxide.
CO2 = carbon dioxide, NOX = nitrogen oxides, SO2 = sulphur dioxide
Section 5.0 of the report gives a detailed analysis of 16 different Quebec roadway designs identifying
the global warming potential and potential fuel savings on a per kilometre basis.
10
3.3 Reusable and Recyclable Paving Material
Concrete pavement can be placed over deteriorated asphalt pavement to provide a new pavement
structure. This type of paving process is known as “whitetopping” and utilizes the existing asphalt
pavement structure as a strong base for the new concrete overlay. In fact, the known performance of
the asphalt pavement will minimize the potential for pumping, faulting and loss of support in the new
concrete pavement. No repairs are required to the existing ACP unless there are large areas of soft
spots or the pavement ruts are over 50 mm. The key point is that the asphalt pavement is reused
and becomes part of the new PCCP structure.
Concrete pavement is also a versatile product which can be reused by performing concrete pavement
restoration (CPR) techniques on the damaged areas. Repair techniques such as full depth / partial
depth repairs and load transfer restoration combined with diamond grinding will restore the pavement
to an almost new state. Pavements in an advanced state of deterioration may be able to be left in
tack and used as a base for a new PCCP. In these cases a thin layer of asphalt of 25 to 50 mm is
placed over the old PCCP and then over laid by a new PCCP.
Another possible reuse option for PCCP is a bonded overlay. When traffic patterns change and a
roadway is receiving substantially more traffic than originally designed for a bonded overlay can be
used to increase the PCCP thickness. As long as the underlying pavement is in good condition a
new layer of concrete pavement can be placed over the existing PCCP by bonding the new layer to
the old surface and matching joints locations. This effectively increasing the amount of traffic the
pavement structure can handle and increases the pavements expected life.
Concrete pavement is also a 100 percent recyclable material and provides government agencies an
attractive option at reconstruction time. If subgrade or pavement condition does not allow the older
PCCP to be reused in its existing state it can be rubblized and used as granular fill, base course for
new pavement and / or as an aggregate for new concrete pavement. In addition, the steel in the
PCCP such as dowels and tie bars can be recycled [ACPA 1993]. In fact, a company in the United
States is developing a prototype machine called Paradigm which is an in-place recycling system for
concrete pavements. This machine breaks and crushes the concrete into the desired aggregate
sizes and collects the reinforcing steel. The system is still in the experimental stage of development.
Reusing the concrete pavement minimizes the amount of non-renewable resources required for a
new pavement structure and eliminates potential material going to landfill sites. In addition, the short
hauling distance for the aggregate reduces the cost of providing aggregates to the job.
3.4 Use of Industrial by-products
Concrete pavement is a mixture of fine and coarse aggregate, cement, water and admixtures.
However, it is possible to replace a portion of cement with a variety of industry by-products often
referred to as supplementary cementing materials or SCMs. These materials if used in the proper
proportions will enhance the properties of the concrete mix, as well as, stabilize the by-product
material in the pavement structure rather than dumping them at local landfill sites. The three most
commonly used SCMs are fly ash (by-product of coal burning), blast furnace slag (by-product of steel
manufacturing) and silica fume (by-product of manufacture of silicon or ferrosilicon alloy). Some of
the enhanced properties of using SCMs include improved concrete pavement durability, permeability
and strength. Fly ash and blast furnace slag also increase workability of the concrete mixtures. Fly
ash, blast furnace slag and silica fume can also control alkali - silica reactivity also known as ASR (a
chemical reaction that occurs when free alkalis in the concrete combine with certain siliceous
aggregates to form an alkali-silica gel. As the gel forms, it absorbs water and expands, which cracks
the surrounding concrete) [Kosmatka et al 2002].
Another added benefit of utilizing SCMs in concrete pavement is the reduction of CO2 emissions
associated with the PCCP. The SCMs replace a portion of the cement in the concrete mixture and
thereby decreases the total amount of CO2 associated with the construction of PCCP structure. The
amount of CO2 reduction is related to the percentage of the SCM used in the mix design. Details on
what is done on the use of SCMs across Canada and in the Northern States can be found in a report
11
completed in March 2005 by Norman MacLeod entitled, “A Synthesis of Data on the Use of
Supplementary Cementing Materials (SCMs) In Concrete Pavement Applications Exposed too Freeze
/ Thaw and Deicing Chemicals” [MacLeod 05].
4.0 Economic Benefits
Concrete pavement provides many economic advantages compared to other types of pavement
structure. Some of the advantages are of follows: life cycle cost analysis, two-pavement system,
eliminates spring weight restrictions and reduced lighting requirements.
4.1 Life Cycle Cost Analysis Advantage
The concept of Life Cycle Cost Analysis (LCCA) is to combine the incurred cost and accrued benefits
over different periods of service lifetime in a consistent manner. Whether the basis is the present
value, annualized cost, future cost, salvage value or some rate of return measure, the heart of the
reduction is the use of an appropriate discount rate. The decision to use LCCA as part of the alternate
bid process provides government agencies with better knowledge of the true cost of a roadway rather
than just consider the initial cost of the pavement. The greater the level of detail provided in the
LCCA the better the agency is equipped to make an informed decision on which pavement type is the
best for that particular job. The key points to consider in a LCC analysis are as follows:
1) Use of equivalent ACP and PCCP design sections
2) Selection of accurate maintenance and rehabilitation (M&R)activities schedules
3) Selection of appropriate discount rate
4) Inclusion of user costs such as user delay and accident costs
5) Inclusion of sustainability of pavement type
The ACPA has prepared an in depth Engineering Bulletin entitled “Life Cycle Cost Analysis: A Guide
for Comparing Alternate Pavement Designs” which gives a detailed review of the basic factors in the
analysis such as Agency costs, user costs, and discount rate [ACPA 2002].
There have been nine alternate bid tenders called across Canada since 2000. Six of these projects
were tendered in Ontario, two in Alberta and one in Nova Scotia. Table 2 below gives a summary of
the projects with the year tendered, project length, concrete LCCA advantage, discount rate used in
the analysis and pavement type selected.
Table 2: Summary of Alternate Bid Tender Projects in Canada
Location
2003
Project
Length
(Lane km)
21.8
Highway 417 E, ON
2000-01
78.2
Concrete LCCA
Advantage
($)
$1.5 M or 20%
more than ACP
433,321
Highway 417 W,
ON
Highway 401,
Chatham, ON
Highway 401,
Chatham Ph2, ON
Highway 401,
Chatham Ph3, ON
Highway 410, ON
Deerfoot Trail, AB
2004-05
73.8
860,719
5.3
PCCP
2004
63.6
620,219
5.3
PCCP
2005
75.6
588,969
5.3
PCCP
2006
93.6
548,551
5.3
PCCP
2006
2002
21.6
44 + PCCP
shoulders
58 + PCCP
shoulders
378,780
3,522,000
5.3
4
PCCP
ACP
2,372,800
4
PCCP
Highway 101, NS
Tender
Year
Anthony Henday,
2004
AB
Source: tender documents
12
Discount
Rate
Pavement Tpye
Selected
(ACP / PCCP)
7
PCCP
PCCP
NA
4.2 Advantage of Two-Pavement System
A study by ACPA of data from the Oman System, State data system, for 14 states confirmed that
states who utilize a two-pavement system get a much larger “bang for the buck” than states that
utilize only one pavement type. The research shows competition between the two paving industries
lowers the average unit cost for both the PCCP and ACP, thereby, allowing the government agencies
to place more pavement for the same dollars spent. Figure 8 below illustrates that as the market
share becomes more balanced between the amount of ACP and PCCP being placed, the average
unit cost of the asphalt and concrete pavements goes down. This translates into government agency
being able to pave more roadways with the same amount of funding levels compared to a single
pavement system [ACPA 2005].
120.00
Pavement Cost ($/SY or $/ton)
PCC Unit Price
100.00
AC Unit Price
80.00
60.00
40.00
20.00
0.00
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
PCC Pavement Market Share (%)
States: 5-year average for data for GA, IL,IN,KS,KY,MD,MO,NC,OH,PA,TN,VA,WI,WV
Figure 8: Benefit of a Two-Pavement System on Pavement Costs
4.3 Eliminates Spring Weight Restrictions
Concrete’s durability is most evident during Canada’s spring thaw season. Simply put, concrete is
not affected by seasonal weakening of the subgrade during spring thaw, as are many asphalt
pavements. A Study by the AASHO Road Test showed that 61% of asphalt roads fail during spring
conditions compared to 5.5% for concrete as shown in Figure 9 [ACPA 98].
Source: American Concrete Pavement Association Engineering Bulletin
- Whitetopping – State of the Practice, ACPA 1998
Figure 9: Example of the Weakening of Asphalt Roads During Spring Months in the Data from
AASHO Road Test
13
Although asphalt pavement design has changed since the original AASHO tests there is still concern
with the strength of asphalt structures during spring thaw periods. This is evident in the fact that
many provincial Departments of Transportation (DOTs) still put spring weight restrictions on truck
traffic to minimize road damage during this period. In fact, the Ministère des Transports du Quebec
(MTQ) employs spring weight restrictions on all their highway systems including the Trans Canada
Highway (TCH). In addition, although the New Brunswick Department of Transportation does not
reduce allowable weight on the TCH during the spring thaw period, it does not allow the extra axle
tolerances that it does at other times of the year.
4.4 Reduced Lighting Requirements
As stated in the environmental and social benefits section PCCP’s light reflective surface provides a
pavement surface that minimizes heat island effect in urban areas as well as provides better night
time visibility for the driving public. These advantages can also translate into an economic savings.
A report entitled “A Comparison of Six Environmental Impacts of Portland Cement Concrete and
Asphalt Cement Concrete Pavements” notes that concrete pavement’s mode of reflectance is mostly
diffuse (R1 class) compared to asphalt pavement’s mode of reflectance typically falling in slightly
specular (R3 class). Therefore, ACP requires more lights per unit length of ACP pavement to
achieve the same illumination as PCCP. The report goes on to identify the potential cost savings
when utilizing concrete pavement compared to asphalt pavement based on a 1985 Chicago example.
The results show the cost savings represent up to 31 % decrease in initial, energy and maintenance
costs for lighting PCCP versus ACP pavement. [Gajda 97]
5.0 Développement durable appliqué aux conditions du Québec
En 2006, l’Association Canadienne du Ciment a produit deux rapports d’études, le premier réalisé par
le Conseil National de Recherche du Canada porte sur les économies de carburant des poids lourds
lorsqu’ils circulent sur les chaussées rigides et le second, réalisé par l’institut Athéna est une analyse
comparative de l’énergie nécessaire à la construction d’une chaussée en béton par rapport à une
chaussée en asphalte et les émissions de gaz à effet de serre générés pour la construction de ces
deux types de chaussées.
Parallèlement à la parution de ces rapports, le ministère des transports du Québec a commencé les
rencontres avec l’industrie dans le but de renouveler l’orientation ministérielle sur le choix du type de
chaussée.
Pour ce faire, 16 cas types d’autoroutes sont définis avec des DJMA variant de 20 000 à 90 000 et le
pourcentage de véhicules lourds de 5, 10 et 25 % (Tableau 3). Le tableau 4 résume les épaisseurs
de matériaux devant être mis en œuvre et le tableau 5 les différentes interventions sur 50 ans.
Tableau 3: Cas analysés
Type de trafic
% camions
C.A.M.
Nombre
de
DJMA
voies
(000)
2
20
2
40
3
50
3
90
Urbain
Rural
5
1,0
10
1,0
10
2,0
25
3,2
1
5
9
13
2
6
10
14
3
7
11
15
4
8
12
16
Bien que le MTQ ait mandaté le CIRAIG pour procéder à une ACV (analyse du cycle de vie)
comparative des deux types de chaussées et étant donné que celle-ci n’est pas encore terminée
l’Association Canadienne du Ciment a utilisé les résultats de l’étude qu’elle a fait faire par l’Athena
14
Institute afin de voir comment se comparent les pavages souples et les pavages rigides au niveau de
l’énergie et des gaz à effet de serre.
Ce qui suit est donc la présentation de l’énergie requise et des gaz à effet de serre produits pour
la réalisation de 1000 mètres de chaussée, à partir des résultats de l’étude Athena et le tout appliqué
aux 16 cas types définis par le MTQ :
1- pour la construction initiale
2- pour la construction initiale + 50 années de maintenance selon les interventions définies par
le MTQ (tableau 5)
3- pour la construction initiale + 50 années de maintenance + 1% de réduction de
consommation de carburant des poids lourds
4- pour la construction initiale + 50 années de maintenance + 4% de réduction de
consommation de carburant des poids lourds
L’étude du Athena Institute a déterminé, spécifiquement pour le Québec, l’énergie intrinsèque des
matériaux granulaires de la fondation, du revêtement d’asphalte, du revêtement de béton et de l’acier
des goujons et tirants ainsi que les émissions de gaz a effet de serre (en kg de CO2 équivalent)
associées à ces mêmes matériaux. Le tableau 6 résume ces valeurs.
- Dans le cas du béton, l’usage d’un ciment ternaire a été considéré
- Dans le cas de l’asphalte, il a été tenu compte de l’énergie du bitume qui est stockée dans
la chaussée
Quant au rapport du CNRC sur l’économie de carburant, celui-ci concluait à une réduction de
carburant sur chaussées de béton de 0,8 à 6,9 %. Nous avons donc considéré, pour cet exercice,
l’effet d’une réduction de 1% et 4%. Les calculs ont été faits à partir d’une consommation moyenne
de 43 L /100 km et sans tenir compte de l’accroissement du trafic de 2 % par année. Les gaz à effet
de serre produits par 1 litre de carburant considérés pour l’exercice sont de 2,76 kg / L.
Tableau 4. Épaisseur requise des matériaux (en mm) pour les 16 cas types
Urbain
25%
Asphalte Béton
2 voies
DJMA
20 000
10%
Asphalte Béton
Revêtement
162
162
189
190
213
217
269
275
MG-20
258
150
264
150
283
150
299
150
MG-112
659
767
626
739
583
712
511
654
2 voies
DJMA
40 000
10%
Asphalte Béton
Revêtement
185
186
210
214
238
242
294
304
MG-20
270
150
283
150
286
150
310
150
MG-112
624
743
586
715
555
687
475
625
3 voies
DJMA
50 000
5%
Asphalte Béton
Rural
Revêtement
186
187
211
214
239
242
294
305
MG-20
267
150
279
150
283
150
315
150
MG-112
626
742
589
715
557
687
470
624
3 voies
DJMA
90 000
Type de trafic
% Camions
Revêtement
200
198
227
225
257
254
311
318
MG-20
279
150
285
150
283
150
321
150
MG-112
600
731
567
704
539
675
447
Largeur des voies de roulement: 3,7m
Largeur des accotements: 2 voies (1,3 m à gauche, 3 m à droite), 3 voies (3 m chaque coté)
Pour les cas 1à 9, l'épaisseur des accotements est calculée pour 2% du trafic
Pour les cas 10 à 16, les accotements ont la même épaisseur que la chaussée
611
15
Tableau 5. Interventions sur 50 ans
cas
1-2-3-5-6-9-10-13-14
4-7-11-15
8-12
16
cas
1-2-3-5-6-9-10-13-14
4-7-11-15
8-12
16
Interventions asphalte
planage 40 mm à 14 ans, planage 50 mm à 25 ans et reconstruction à 36 ans
planage 40 mm à 12 et 44 ans et reconstruction totale à 32 ans
planage 40 mm à 10 et 36 ans, planage 50 mm à 18 et 44 ans et reconstruction
à 26 ans
planage 40 mm à 9 et 32 ans, planage 50 mm à 16 et 39 ans et reconstruction à
23 et 46 ans
Interventions béton
réparation béton 0.5 % à 19 ans, réparation béton 4.0 % + asphalte 75mm à 29
ans, planage et resurfaçage asphalte 50 mm à 40 ans
réparation béton 0.5 % à 19 ans, réparation béton 4.0 % + asphalte 75mm à 29
ans, planage et resurfaçage asphalte 50 mm à 39 ans, reconstruction complète
à 49 ans
réparation béton 0.5 % à 19 ans, réparation béton 4.0 % + asphalte 75mm à 29
ans, planage et resurfaçage asphalte 50 mm à 37 ans, reconstruction complète
à 45 ans
réparation béton 0.5 % à 19 ans, réparation béton 4.0 % + asphalte 75mm à 29
ans, planage et resurfaçage asphalte 50 mm à 36 ans, reconstruction à 43 ans
Tableau 6. Résultats de l’étude Athena
Matériaux
Énergie
GES
MG112
MG20
Béton
Asphalte
Acier
0.151 GJ/m³
0.152 GJ/m³
1.7269 GJ/m³
7.516 GJ/m³
9.08 GJ/t
12.6 kg/m³
12.7 kg/m³
261 kg/m³
135 kg/m³
428.62 kg/t
16
Graphiques synthèse des résultats pour l’énergie nécessaire asphalte versus béton
(Fig. 10 à Fig. 13)
Énergie: asphalte vs béton
(construction + entretien 50 ans)
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
120000
Énergie(GJ / km)
Énergie (GJ / km)
Énergie :asphalte vs béton
(construction)
1
2
3
4
5
6
7
8
9
100000
80000
60000
40000
20000
0
10 11 12 13 14 15 16
1
2
3
4
5
6
7
CAS
Énergie asphalte
Énergie asphalte
Énergie béton
Figure 10. Énergie à la construction
9 10 11 12 13 14 15 16
Figure 11. Énergie à la construction + entretien 50 ans.
Énergie: asphalte vs béton (construction + entretien 50 ans
+ économie carburant 1% sur 50 ans)
Énergie: asphalte vs béton ( construction + entretien 50 ans +
économie de carburant 4% sur 50 ans )
120000
120000
100000
É n erg ie (G J / km )
Énergie (GJ / km )
8
CAS
Énergie béton
80000
60000
40000
20000
0
100000
80000
60000
40000
20000
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
CAS
Énergie asphalte
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CAS
Énergie béton (-1%)
Énergie asphalte
Figure 12. Énergie à la construction + entretien 50 ans +
réduction 1% consommation carburant
17
Énergie béton (-4%)
Figure 13. Énergie à la construction + entretien 50 ans +
réduction 4% consommation carburant
Graphiques synthèse des résultats pour les Gaz à Effet de Serre produits asphalte versus béton
(Fig. 14 à Fig. 17)
GES: asphalte vs béton
(construction + entretien 50 ans)
2000
2500
1500
2000
GES (t / km)
1000
500
1500
1000
500
0
8
0
9 10 11 12 13 14 15 16
CAS
15
7
13
6
11
5
9
4
7
3
5
2
1
1
3
GES ( t / km)
GES: asphalte vs béton
(construction)
CAS
GES asphalte
GES béton
GES asphalte
GES béton
Figure 15. GES à la construction + entretien 50 ans
Figure 14. GES à la construction .
GES: asphalte vs béton ( construction + entretien 50 ans + effet
de l'économie de carburant de 1% durant 50 ans )
GES: asphalte vs béton (construction + entretien 50 ans + effet de
l'économie de carburant de 4% durant 50 ans )
2000
5000
1000
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
-1000
-2000
16
GES (t / km )
GES (t / km)
3000
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
-5000
-10000
-15000
-3000
CAS
GES asphalte
-20000
GES béton (-1%)
CAS
Figure 16. GES à la construction + entretien 50 ans +
réduction 1% consommation carburant.
GES asphalte
GES béton (4%)
Figure 17. GES à la construction + entretien 50 ans
+ réduction 4% consommation carburant
À la lueur de ces graphiques, force est de constater que l’énergie utilisée pour les chaussées de
béton est de loin inférieure à celle utilisée pour les chaussées d’asphalte et cela dès la construction
initiale. La différence s’atténue lorsque l’on considère l’entretien sur 50 ans principalement à cause
du fait qu’après 29 ans le programme impose un recouvrement d’asphalte. Il y aurait donc lieu de
reconsidérer cette pratique pour la remplacer par une réhabilitation faisant intervenir entre autre la
technique du meulage au diamant. Quant à l’énergie du carburant économisée, cela a un impact
relativement faible face à l’énergie totale associée à la construction et à l’entretien sur 50 ans.
Dans le cas des émissions de gaz à effet de serre, bien qu’elles soient supérieures au niveau de la
construction initiale pour les chaussées de béton, elles sont pratiquement identiques à celles de
l’asphalte au terme de 50 années d’entretien. C’est toutefois lorsque l’on considère l’effet de
seulement 1% de réduction de consommation de carburant que l’on constate l’annulation des gaz à
effet de serre associés aux chaussées de béton. On pourrait même attribuer des crédits ‘carbone’
aux chaussées de béton dans un proche avenir.
18
16
6.0 Conclusion
For the general public to get the most cost effective pavement structure Government agencies must look at more
than just the initial cost of the pavement in the pavement selection process. It is clear from the preceding
sections of this paper that concrete pavement has many sustainable benefits which should be considered by
roadway decision makers when trying to compare the overall cost of one type of pavement alternative to
another. Environmental benefits of PCCP include important issues such as reduced energy consumption,
reduced CO2 emissions, reusable construction material, and use of industrial by-products in the concrete mix
design. Social benefits of PCCP centre on roadway safety issues and passenger ride and comfort, while
economic advantages include life cycle cost advantage, two- pavement system, truck fuel savings, elimination
of spring weight restrictions, and reduced lighting requirements.
7.0 References
[ACPA 1993] American Concrete Pavement Association, “Recycling Concrete Pavement “, TB-014P,
Skokie, Illinois, 1993.
[ACPA 98] American Concrete Pavement Association, “Whitetopping – State of Practice“, EB210P,
1998.
[ACPA 2000] American Concrete Pavement Association, “Concrete Pavement Surface Textures”,
Special Report, Concrete Pavement Technology & Research, SR902P, 2000.
[ACPA 2002] American Concrete Pavement Association, “Life Cycle Cost Analysis: A Guide for
Comparing Alternate Pavement Designs”, Engineering Bulletin, EB22P, 2002.
[ACPA 2005] Southeast Chapter American Concrete Pavement, “Who Says…”Concrete Pavement
Cost too Much”?”, Count on Concrete Pavement, 2005.
[Athena 06] The Athena Institute, A Life Cycle Perspective on Concrete and Asphalt Pavement
Roadways: Embodied Primary Energy and Global Warming Potential, Submitted to Cement
Association of Canada (CAC), Ottawa, September 2006.
[ERES 03] Applied Research Associates, Inc. ERES Consultants Division, “Pavement Engineering
Technical Services Equivalent Pavement Designs Flexible and Rigid Alternatives”, Toronto, Ontario,
December 2003.
[FHWA 96] Federal Highway Administration, “Tire-Pavement Noise and Safety Performance”,
Publication No. FHWA-SA-96-068. 1996.
[Gajda 97] Gajda, J. W., Van Geem, M.G., “A Comparison of Six Environmental Impacts of Portland
Cement Concrete and Asphalt Cement Concrete Pavement”, PCA R&D Serial No. 2068, Portland
Cement Association, 1997.
[Kosmatka 2002] Kosmatka S., Kerkhoff B., Panarese W., MacLeod N., McGrath R., “Design and
Control of Concrete Mixtures”, EB101.07T, Portland Cement Association, Skokie, Illinois, 2002.
[MacLeod 05] MacLeod N., “A Synthesis of Data on the Use of Supplementary Cementing Materials
(SCMs) In Concrete Pavement Applications Exposed too Freeze / Thaw and Deicing Chemicals”,
March 2005.
[NSTPW 1999] Nova Scotia Transportation and Public Works, “Asphalt Concrete Pavement and
Portland Cement Concrete Pavement, Highway 104, Cumberland County, Year 5 of 5 Year Study,
October 1999.
19
[Taylor 02] Taylor G.W., Dr. Farrell, P. and Woodside A., “Additional Analysis of the Effect of
Pavement Structure on Truck Fuel Consumption”, prepared for Government of Canada Action Plan
2000 on Climate Change Concrete Roads Advisory Committee, August 2002.
[Taylor 06] Taylor G.W., Patten, J.D., “Effects of Pavement Structure on Vehicle Fuel Consumption –
Phase III”, prepared for Natural Resources Canada Action Plan 2000 on Climate Change and
Cement Association of Canada, January 2006.
[WIDOT 97] Wisconsin Department of Transportation, “Impacts Related to Pavement Texture
Selection”, Serial No. WI/SPR-06-96, Final Document 1997.
[Zaniewski 89] Zaniewski, J.P., “Effect of Pavement Surface Type on Fuel Consumption”,
SR289.01P, Portland Cement Association, Skokie, Illinois, 1989.
20