S22 / CONCRETE PROGRESS www.ROADSBRIDGES.com

Leif Wathne, P.E.

GG reen highways are no longer just a concept, but

are increasingly becoming a reality as agencies

turn to concrete pavements to meet the three-

pronged requirements of sustainable develop-

ment.

The World Commission on Environment and Development

defi ned sustainable development as “meet[ing] the needs of

the present without compromising the ability of future genera-

tions to meet their own needs,” according to a report to the

United Nations General Assembly in August 1987.

More precisely, in terms of highway and roadway construc-

tion, sustainable development involves being good stewards of

the environment, balancing the needs of business and provid-

ing societal benefi ts. Within the broad framework of sustainable

development, green highways are environmentally responsible

and sustainable in all aspects, including design, construction

and maintenance. The green highways initiative was begun in

2005 as a pilot program by the U.S. Environmental Protection

Agency (EPA). The program has stayed true to its original mis-

sion of coordinating transportation needs and environmental

requirements.

A friend of energyConcrete pavements offer some inherent features and ben-

efi ts that are well-suited for sustainability goals and objectives.

The following sections describe those attributes in greater de-

tail.

Longevity: The durability and longevity of concrete pave-

ments are both well-known and well-documented. There are

many examples of concrete pavements that have far exceeded

their original design lives.

Among those are the very fi rst concrete pavement placed in

Bellefontaine, Ohio, in 1891. The pavement sections on Court

Street there are still carrying traffic more than 117 years later.

Belknap Place in San Antonio, Texas, was paved with concrete

in 1914 and is still carrying traffic today.

I-10 in California’s San Bernardino valley was originally con-

structed as part of historic Rte. 66. Portions of this concrete

pavement highway are still carrying traffic today, and with more

than 200,000 vehicles per day, the traffic volume is substantial-

ly higher than originally intended. The pavement has been re-

stored by diamond grinding three times since originally placed,

but otherwise has required few repairs and little maintenance

after more than six decades of service.

Heading due north to Minnesota, more than half of the

concrete pavements older than 50 years still have a present

serviceability rating of 3.1 (considered good to very good) or

greater. Other examples abound, each of which underscores

the durability and long-term value of concrete pavements.

Further contributing to pavement longevity is concrete pave-

ment restoration, including full- or partial-depth repairs, dowel-

bar retrofi tting and diamond grinding. A concrete pavement

Concrete pavement paints a pretty picture for the environment

surface can be renewed by diamond grinding, which improves

ride quality, noise and surface texture. Studies by the Califor-

nia Department of Transportation suggest the average time be-

tween additional rehabilitation needed for a diamond-ground

pavement is approximately 17 years.

The longevity of concrete pavements not only provides sig-

nifi cant economic advantages in terms of life-cycle costs, but

also contributes directly to the system’s sustainability in several

important ways. A long-lasting concrete pavement does not

require rehabilitation or reconstruction as often and therefore

consumes less raw materials in the long run. This longevity

benefi ts our environment in other ways as well. Energy sav-

ings are realized, since rehabilitation and reconstruction efforts

consume energy. Also, congestion is reduced (with accompa-

nying energy savings and reduction in vehicle pollutants) by

employing long-lasting concrete pavements because of fewer

construction zones impeding traffic fl ow.

Because of this longevity, concrete pavements have the po-

tential to help society address the challenges of sustainable

development in numerous ways. Ultimately, all these environ-

mental and social benefi ts add up to greater long-term eco-

nomic benefi ts to the public. In a sense, longevity is a crucial

element of sustainability.

Reduced vehicle fuel consumption and emissions: One key

to reduced fuel consumption and emissions is the profi le stabil-

ity of a pavement, the ability of the surface to resist deforma-

tion and defl ection caused by repeated or sustained loadings,

such as heavy truck traffic.

Concrete pavements, being rigid substrates, do not deform

under heavy vehicle loadings and, therefore, defl ect less. In

sharp contrast, asphalt pavement is viscoelastic and more

sensitive to both temperature variations and applied wheel

loads. This not only makes asphalt susceptible to rutting and

shoving, as well as increased hydroplaning potential, but it also

increases fuel consumption.

The reason is that fuel consumption is partly a function of

the degree of pavement defl ection in response to the load ap-

plied as the wheels move along the surface. Several studies

suggest the resistance (amount of defl ection) encountered by

heavy-vehicle wheels on asphalt pavements is measurably

greater than the resistance on concrete pavements. Therefore,

it takes more energy and fuel to move heavy vehicles on fl ex-

ible pavements.

The most in-depth studies on this phenomenon were con-

ducted by the National Research Council of Canada (NRC).

The fi nal study included collaboration between National Re-

sources Canada (NRCan) and the Cement Association of Can-

ada, with input from various departments of transportation.

The studies concluded tractor-trailers traveling on concrete

pavements have statistically signifi cant lower fuel consump-

tion than those traveling on asphalt pavements throughout the

summer to wider temperature range for fully loaded trucks op-

erating on smooth pavements.

The fi ndings from studies by Taylor Consulting (2002) and

Taylor and Patten (2006) show that fuel consumption for truck

types (a tanker and a van, both tractor trucks with semitrail-

ers) can be reduced by 1% to 6% when traveling on concrete

versus asphalt. Table 1 shows the yearly potential savings in

dollars, carbon dioxide (CO2), nitrogen oxides (NOx) and sulfur

dioxides (SOx), all of which are signifi cant. In this model, the

assumptions include a tractor-trailer traveling 100,000 miles

per year; an average engine fuel consumption of 5.5 miles per

gallon; and a diesel-fuel cost of $3.99 per gallon.

Lower construction fuel demand: Constructing highway

pavements requires a large amount of energy, most of which

comes from fossil fuels, which of course we are dependent on

oil imports to produce. Of that fuel, most of it is diesel, which

has experienced sharp price increases recently.

The Federal Highway Administration (FHWA) reports on fuel

usage for various aspects of construction, including highway

paving, in its “Technical Advisory T 5080.3 on Price Adjustment

Contract Provisions” (FHWA 1980).

The document shows the fuel usage factor for asphalt pave-

ments is 2.90 gal per ton and 0.98 gal per cu yd for concrete

pavements. Converting construction fuel usage factors to fuel

required per mile of roadway constructed, the fi gures are as

follows: 10,718 gal of fuel for a 10-in. asphalt pavement, com-

pared with 1,916 gal of fuel for a 10-in. concrete pavement.

This means if concrete pavements were constructed in place

of half of the roughly 500 million tons of asphalt pavements

constructed each year, the savings in diesel fuel from con-

struction alone would be over 0.5 billion gal.

Use of industrial by-products: In most concrete used for

highways in North America, some of the portland cement is

replaced or supplemented with one or more industrial by-prod-

ucts. Known as supplementary cementitious materials (SCMs),

the two most common include fl y ash (from coal burning) and

slag cement (from iron production).

Using SCMs in concrete pavement has several environmen-

tal benefi ts. First, recovering industrial by-products reduces the

use of virgin materials needed in cement manufacturing. It also

reduces or, more precisely, diverts materials away from landfi lls.

Fuel Savings Fuel Saved Fuel Cost

Saved

CO2

NOx SOx

(%) gal (liter) ($ US) tons (metric tons)

lb (kg) lb (kg)

Minimum: 0.80 145 (549) $580 1.66 (1.50) 37.2 (16.9) 4.80 (2.18)

Average: 3.85 700 (2,650) $2,800 8.06 (7.31) 182 (82.6) 23.00 (10.40)

Maximum: 6.90 1,250 (4,730) $4,990 14.4 (13.00) 327 (184) 41.30 (18.70)

Table 1. Yearly potential savings in cost, CO2, NOx and SOx, per tractor-trailer

CONCRETE PROGRESS / S23

Equally important, using SCMs also saves energy and re-

duces emissions associated with cement production. Many

state highway agencies allow up to 25% of portland cement

to be replaced with fl y ash and 50% to be replaced with slag

cement. Some states allow even higher SCM replacement lev-

els.

Besides these environmental benefi ts, SCMs generally en-

hance concrete properties when used in appropriate quantities.

For example, they improve workability of the mixture, decrease

concrete permeability, improve durability, increase strength

and, most important, enhance longevity. Cost savings also may

result in markets where SCMs are less expensive than port-

land cement, or where mixture optimization can provide en-

gineering properties (for example strength,

durability and longevity) that would be more

expensive to achieve without SCMs.

Recyclability and reusability: Concrete is

the most recycled material in North Amer-

ica, according to the Construction Materi-

als Recycling Association (CMRA). In fact,

CMRA reports that in 2004 somewhere in

the range of 130 million to 140 million tons

of concrete were crushed and recycled. At

the ultimate end of its service life, concrete

pavement can be crushed and reused in

many ways, including as granular fi ll, sub-

base material or base course for new pave-

ment.

Recycled concrete pavement also can be used as an ag-

gregate for new concrete pavement. Some state departments

of transportation allow up to 100% of coarse aggregate in con-

crete mixtures to be recycled concrete aggregate. This leads to

reduced demand for nonrenewable natural resources.

Using recycled concrete aggregates from pavement, particu-

larly in applications that expose it to the atmosphere (such as

embankment fi ll, gravel roads, roof ballast and railroad ballast)

has additional benefi ts toward mitigating global warming, no-

tably from a process called carbon sequestration. The Recy-

cling Materials Resource Center reported in 2005 that such

exposure might allow for the recapture of all the CO2 originally

evolved from the cement raw materials associated with calci-

nation during cement manufacture. Carbon sequestration, ac-

cording to the U.S. Department of Energy, is “the provision of

long-term storage of carbon in the terrestrial biosphere, under-

ground or the oceans so that the buildup of carbon dioxide (the

principal greenhouse gas) concentration in the atmosphere will

reduce or slow.”

Refl ectivity and coolness: Concrete surfaces readily refl ect

light. This characteristic of concrete, generally referred to as

albedo, is advantageous for several reasons. First, it can sig-

nifi cantly improve both pedestrian and vehicular safety by en-

hancing nighttime visibility on and along concrete roadways.

Concrete pavements also reduce the amount of energy need-

ed for artifi cial roadway illumination during the night. There are

also other factors related to the refl ectivity of concrete pave-

ments, as well as their relative coolness compared to asphalt

pavements, including mitigation of the urban heat island effect

and smog reduction.

During daytime hours, concrete’s high refl ectivity means

that more of the sun’s incoming radiation is refl ected back into

the atmosphere, lowering the amount of heat absorbed by the

pavement and its surroundings (this heat retention is often re-

ferred to as urban heat island). This in turn reduces the cool-

ing requirement during the summer heat and can substantially

lower the associated energy demand. This in turn not only has

cost implications, but it also leads to higher emissions from

power plants. According to recent work by Lawrence Berkeley

National Laboratory, paving urban roadways with concrete is

one useful strategy to help mitigate urban heat island effects.

Lower energy footprint: Embodied pri-

mary energy is a measure of all energy use

associated with the production, delivery and

maintenance of a facility over a predeter-

mined time. It includes both feedstock ener-

gy (the gross combustion heat value of any

fossil hydrocarbon that is part of the pave-

ment, but is not used as an energy source;

for example bitumen) as well as primary

energy (fossil fuel required by system pro-

cesses including upstream energy use).

An embodied primary energy analysis in

this context accounts for the energy needed

to extract materials from the ground (such

as aggregates, raw materials for cement

production and oil for asphalt), process these materials, pro-

duce the paving mixtures, construct the roadway, maintain it

and rehabilitate it over a predetermined time. This approach

is an effective means to evaluate the energy footprint a facility

makes during its lifetime.

A recent study conducted by the Athena Institute presents

embodied primary energy and global warming estimates for

the construction and maintenance of equivalent concrete and

asphalt pavement structures for several different road types in

various geographic regions in Canada.

The study period was 50 years, which takes into account

original road construction and all maintenance and rehabili-

tation activities for both pavement alternatives. In the study,

concrete pavement alternatives clearly require signifi cantly

less energy than their asphalt pavement counterparts do from

a life-cycle perspective. Results show that asphalt pavements

require two to fi ve times more energy than equivalent concrete

pavement alternatives.

Improved water quality: Storm-water quality can be improved

through the innovative use of pervious concrete pavements.

Pervious concrete pavements comprise specially graded

coarse aggregates, cementitious materials, admixtures, water

and little or no fi nes.

Pervious concrete pavements reduce storm-water runoff

and help recharge groundwater aquifers. They also reduce the

amount of pollutants, such as car oil, antifreeze and other au-

tomobile fl uids, contained in nonrunoff storm water. By allowing

some rainfall to percolate into the ground, pervious concrete

S24 / CONCRETE PROGRESS www.ROADSBRIDGES.com

Concrete’s high refl ec-

tivity means that more

of the sun’s radiation

is refl ected back into

the atmosphere, reduc-

ing the heat absorbed

by the pavement.

promotes natural fi ltration and “treatment” of rainwater via soil

chemistry and microbial activity.

Quiet surface textures: Noise pollution is a growing con-

cern in North America. The surface texture of a highway pave-

ment controls many important factors, including tire-pavement

noise.

One of the advantages of concrete pavements is that vir-

tually any texture can be created during or after fi nishing op-

erations, including textures that minimize tire-pavement noise

while maintaining wet- and dry-weather friction for the life of

the pavement.

Research by the concrete paving industry is in the process

of identifying optimal textures for low noise generation at the

tire-pavement interface in a variety of circumstances. In North

America, a signifi cant amount of noise issues are related to

existing transversely tined concrete pavements. Consequently,

some of the ongoing research is focused on identifying dia-

mond grinding techniques for retexturing and renewing pave-

ment to produce the quietest surface textures. The FHWA, in its

recent “Technical Advisory on Surface Texture for Asphalt and

Concrete Pavements,” includes longitudinal tining, grooving

and grinding as recommended practices to provide the desired

texture over the performance life of the pavement and minimize

objectionable levels of tire-pavement noise (FHWA 2005).

Results from research recently conducted at both Purdue

University’s Institute for Safe, Quiet, and Durable Highways and

the National Concrete Pavement Technology Center indicate

that for ordinary concrete pavements, longitudinal textures—

including tining, grooving and grinding—are particularly favor-

able in terms of low noise generation. Some of the quietest

concrete pavements measured in North America are longitudi-

nally ground pavements, often called “whisper ground.”

Whisper grinding refers to the practice of grinding concrete

pavement specifi cally for improving its noise profi le instead of

simply grinding for smoothness and ride quality. Blade width,

blade spacing and grinding depth are selected with noise miti-

gation in mind.

Furthermore, the concrete pavement industry is currently

conducting fi eld trials of its Next Generation Concrete Surface

(NGCS), which is showing great promise, both in terms of its

relative tire-pavement noise features and its durability.

While these examples underscore the sustainability benefi ts

of concrete pavements, there also is more to the story. The in-

dustry continues to pursue initiatives that make concrete pave-

ments an even better value to agencies and road users. With

sustainability and cost considerations in mind, concrete pave-

ments are increasingly becoming the right choice for a growing

number of agencies.

Wathne is director of highways for the American Concrete Pavement Association, Washington, D.C.

LearnMore! For more information related to this article, go to:

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CONCRETE PROGRESS / S25

“It was the fi rst pour on the job and we had a lot of people

watching us, from Corps of Engineers personnel to civilians,”

Cloyd said. “It went very well. The roundabout had a 100-ft ra-

dius, and we started and stopped paving in the exact same

spot. They’re big enough around that by the end of the day

we just had to put burlap out and wash the paver. We left the

paver there for three or four days until we got our needed cure

time on the concrete. Once we got cure time, we made a ramp,

tracked the paver out of there and moved it to the site of the

next pour.”

With the roundabout complete, paving on the rest of the

roadway started. All of the concrete pavement on the project

was 24 ft wide and 9 in. thick. Production averaged between

110 and 120 cu yd per hour. A portable batch plant was set up

onsite to supply the concrete. The mix was a Corps of Engi-

neers-approved design with slump averaging 2.5 to 2.75 in.

Another interesting aspect of the project, and something not

found on an ordinary road project, was the tank crossing.

“There’s a tank crossing through the roadway, an intersection

for the tanks to travel across while moving from their battalion

headquarters on the base out onto the fi ring range,” Cloyd said.

“The Corps wanted the intersection to have a little bit thicker

concrete, 0.5 in., and it has a little bit different steel in it for extra

reinforcing.”

The paver is equipped with a frame-mounted bar inserter on

the front. It placed a transverse bar every 24 in. for the longi-

tudinal joint. A timing wheel on one of the paver’s tracks mea-

sured out the spacing of the bars automatically.

A second wheel on the track is part of Smoky Hill’s vibrator

monitoring system. They are using a Minnich Auto Vibe II sys-

tem, which helps them control vibrator vpm, as well as moni-

tors and stores their vibrator data.

“It wasn’t a specifi cation on this Corps of Engineers project,

but the Kansas Department of Transportation started requiring

it a few years ago,” Cloyd explained. “They wanted to be able to

have a readout of our vibrator frequencies and other measure-

ments. With this Auto Vibe II, we just take the card out, take it

into the office and we can print them out a chart showing all of

our information.”

The concrete paving portion of Smoky Hill’s fi rst project with

their new paver is now completed and they have moved on to

other work within the state of Kansas.

Krueger is editor of GOMACO World, Ida Grove, Iowa.

LearnMore! For more information related to this article, go to:

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Continued from p 17

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