The five-year initiative, dubbed Task 65, will reach public and private sector end users with new research in whitetopping, weekend reconstruction of intersections, the efficacy of sealing transverse joints (see below), and improvements in smoothness criteria.

But Task 65 is only part of the new dynamic changes in portland cement concrete (PCC) construction that are unfolding in 2004.

o New designs for thin PCC overlays are being field-proven which involve use of a virgin hot mix asphalt (HMA) interlayer that will reduce both first and long-term costs, making them price-competitive with full HMA overlays.

o Durable high-performance concrete (HPC) mix designs -- optimized for compressive strength and resistance to chloride penetration -- continue to move from structural (bridge) applications to pavement designs, with great success.

o Once again the industry is reconsidering the wisdom and cost of sealing concrete joints under all circumstances, with substantial savings if there is no functional reason for doing so; success there will further narrow the initial-cost price advantage of HMA over PCC.

o By incorporating wireless electronics in pavements, concrete is further narrowing the time difference in getting newly constructed pavements open to traffic, compared to hot mix asphalt.

o Mirroring research underway with reclaimed asphalt pavement (RAP), new study is ongoing that may make crushed, reclaimed concrete aggregate (RCA) acceptable for use as aggregate in concrete mixes. The FHWA last year surveyed state use of RCP in pavements and now has handle on what is done and a base line from which to work.
 

New FHWA Outreach

As 2004 begins, the FHWA is launching a multifront effort to speed up  transfer of PCC technology. The contract for Task 65 was awarded in September 2003, and is underway now by Construction Technology Laboratories, Inc. (CTL) in Skokie, Ill., and includes a PR subcontractor.

"We have the technical engineering expertise combined with the communications expertise in a single contract," said Sam Tyson, P.E., concrete pavement engineer, FHWA Office of Pavement Technology. "We have more than 30 concrete research projects, each of which is generating one or more 'products', each of interest for potential implementation in the field by either state DOTs or paving contractors. Task 65 will get this technology out to the field."

While not deviating from previous practice, the volume of finished and incoming products in PCC research over the next five years is such that FHWA wanted a mechanism in place for orderly technology transfer. "This research was earmarked under TEA-21 and focuses exclusively on improved quality in concrete pavements that was addressed in that legislation," Tyson said.

In addition to joint sealing, PCC overlays and smoothness, projects to be publicized include efficacy of elliptical dowel shapes vs. circular dowels, different dowel materials, HPC technology demonstrations in at least 12 different states, and precast HPC pavements in different states. "Task 65 will take the technology from all of those efforts and deliver it for potential use by the state DOTs and contractors," Tyson said.

Another vector for outreach will be the long-standing FHWA Mobile Concrete Laboratory. Since the late 1980s, the Mobile Concrete Lab -- a state-of-the-art concrete testing facility on wheels -- has brought innovative concrete technologies to end users in the field.

This 48-foot trailer, pulled by a semi-tractor, is equipped with both new and conventional testing equipment. Its skilled engineers and technicians provide state and local road agencies and contractors with equipment evaluations and field demonstrations of specific concrete technologies. The trailer is displayed each year at the Transportation Research Board meeting in January in Washington, D.C., and has been displayed at recent Conexpo/ConAgg shows.
 

HPC Penetrating Pavements

Much of this technology transfer will involve high-performance concrete (HPC) mixes, Tyson said. Since the mid-1990s, the building of highway infrastructure using durable HPC has dominated PCC research and application for civil engineering.

HPC is often called "durable" concrete because its strength and impermeability to chloride penetration makes it last much longer than conventional PCC. It's an engineered concrete made up of the classic elements of water, portland cement and fine and coarse aggregates, but with added components.

In HPC, materials and admixtures are carefully selected and proportioned ("optimized") to form high early strengths, high ultimate strengths and high durability beyond conventional concrete.

HPC provides enhanced mechanical properties in precast concrete structural elements, including higher tensile and compressive strengths, and heightened modulus of elasticity (stiffness). In frost-prone regions the benefits of HPC are great. The enhanced durability of HPC helps it resist penetration of chloride-laden snow and ice melt water. This results in longer life for the reinforcing steel within, and a reduction in spalling, cracking and associated repairs.

The Strategic Highway Research Program (SHRP) studied the efficacy of HPC in bridge structures as a way to quell corrosion of rebar from meltwater from deicing salt. The first HPC structural designs were constructed in the mid-1990s. HPC began migrating to pavements in the late 1990s and now in 2004 it has fully penetrated PCC pavement construction.

These durability criteria include air void structure, low permeability, proper water content of fresh concrete, and low susceptibility to cracking. Also important are fast and accurate ways to evaluate in situ properties of curing concrete. One way getting attention in 2004 is the wireless maturity meter.

Some industrial "waste" materials of a few decades ago now are integral elements of this new engineered concrete. These admixtures, such as coal fly ash, silica fume and ground granulated blast furnace (GGBF) slag, add both strength and durability to the concrete, and enhance its marketability as an environmentally friendly product.
 

HPC PCC Over HMA

Such industrial byproducts figured into a breakthrough PCC overlay project which used a hot mix asphalt interlayer between the existing PCC pavement and the PCC overlay, conducted in summer 2003 by the Michigan DOT in conjunction with the Michigan Concrete Paving Association (MCPA).

This overlay was a four-mile stretch of northbound I-75 in Ogemaw County in the north-central Lower Peninsula. Constructed by John Carlo, Inc., the project overlaid the existing 30-year old PCC pavement with a 6-inch concrete overlay, with a 1-inch lift of HMA as a separation layer intended to eliminate reflective cracking. HPC was attained by using conventional Type I cement with 25 percent of cement replaced with GGBF to provide durability.

"The goal of this demonstration is to explore options that could lower costs to the department for concrete overlays," said Bob Risser, P.E., MCPA executive director. "Reflective cracking is the Achilles Heel of overlays, but the separator layer stops it."

The MCPA determined that the total cost of the concrete overlay was only 6 percent more per square yard than the rubblize-and-asphalt project on the southbound side, but with the potential of delivering twice the life.

On another thin PCC overlay project, Outer Drive in Wayne County, Mich., a 1 inch HMA separator layer was placed atop a 1920s-era concrete pavement, then topped with a 4-inch PCC overlay.

"We jointed it in 6-by-6-ft. squares, and it's been performing beautifully," Risser said. "They built two more overlays [in 2003] using the same design, and what's really remarkable about all three projects is that Wayne County reported they cost only 15 percent more in initial cost than a 3.5-inch mill-and-fill with HMA, but they're expecting at least twice the life."

Thus these thin PCC overlays have real potential to cut into HMA market share. "To reconstruct Outer Drive in concrete would have cost over $2 million," Risser said. "We did the PCC overlay for $750,000. On this and the other projects, Wayne County is reporting a 10 to 15 percent cost premium over HMA to obtain twice the life. Now we have a solution that fits into the budget constraints that so many agencies have."
 

Wireless Maturity Meters

Also in Michigan last year, wireless portland cement concrete maturity meters were placed in fresh concrete of a road in Oakland County, Mich., by Tony Angelo Cement Construction Co. of Novi, Mich., in conjunction with the city of Novi, consultant JCK, and the Michigan DOT.

These wireless maturity meters, only a few inches long, were attached to rebar and concrete was placed around them. Then, a handheld computer permits data to be compiled and analyzed to provide a real-time concrete strength value. Because the wireless meter provides instantaneous data, such as strength gained in the slabs, Michigan DOT was able to monitor and open the pavement without delays due to lab specimen curing and testing.

"You literally walk up to the concrete, tap in the serial number of that maturity meter, and it transmits what the concrete is doing to the palm-held device," MCPA's Risser said. "The data are downloadable into a spreadsheet. You can track the progress of the concrete without having to cure and break test cylinders. This also eliminates the hazard of thermocouple wires used to track concrete maturity."

And since the long cure time and testing has been a selling point of asphalt against concrete, the advent of wireless maturity meters may give the "white stuff" a new weapon to use against the "black stuff".

"There were so many businesses along this route, that the county wanted to get the pavement open as quickly as possible," Risser said. "The wireless maturity meters helped this. And because the data are from the slab itself, not the lab specimen, the meters provide a more accurate portrayal of the slab condition."
 

New software for cost-benefit figuring

The higher initial material and labor costs of PCC construction always work against it when matched against HMA, when long-term costs are not considered. But new software to be available early in 2004 may help PCC narrow that gap.

Performance-related features of PCC pavements that are taken for granted -- such as load-transfer devices like dowel bars between slabs, or shoulders "tied" to driving lanes with dowel bars -- add cost to the pavement design, and have the potential of discouraging PCC use because of the added cost differential vs. hot mix asphalt.

Other such features include drainable bases and joints sealed in PCC pavements to keep out water and incompressibles. Water is the enemy of pavements, the old saying goes, and keeping water out of the base will prolong pavement life.

At the 1986 Transportation Research Board (TRB) meeting, Wisconsin DOT's Steve Shober, P.E., upset the apple cart when he articulated in a technical paper the case against sealing PCC joints, even in a freeze/thaw climate.

"The need to seal PCC pavement joints/cracks is so ingrained in the United States pavement culture and is so seemingly sound from a theoretic perspective that it has been considered an unchallengeable truth," Shober said in a late-1990s follow-up paper, The Great Unsealing: A Perspective on PCC Joint Sealing. "The 'truth' of keeping water and incompressibles out of joints may have had a basis when PCC pavements were built directly on the subgrade, but since the use of base courses the need to seal joints has not been proven."

Shober also linked joint sealing's utility to whether it directly serves the taxpaying customers who use Wisconsin's roads. "Sealing has to somehow enhance pavement performance (ride or longevity) and/or convenience and/or safety," he said. "In addition, joint sealing has to be cost-effective, i.e., the measured benefits have to exceed the costs (which include user delays and safety problems related to closing lanes to reseal joints)."

Shober's paper may be downloaded here. 

Now, the FHWA has revisited the issue of the cost-benefit ratios of various PCC pavement features, especially sealed joints, and new software that would assist designers and contractors determine the benefits was to be released in January 2004.

In August 2003 an FHWA expert panel reviewed the new software, which assesses the costs and benefits of PCC design features. When complete, the program will provide planners, project managers and highway engineers with insights into which features provide the biggest return on investment.

The FHWA states that the cost-benefit ratio of sealing transverse joints -- which can increase the initial costs of placing a PCC pavement by up to 5 percent -- is a major feature that the software will analyze.

Both the report and the software was to be available from FHWA by January 2004. For more information, contact Peter Kopac, 202.493.3151, e-mail peter.kopac@fhwa.dot.gov.
 

Evaluating Reclaimed Concrete

Reclaimed asphalt pavement (RAP) is being used increasingly in asphalt base courses, pavement foundations, and driving courses. But until now, crushed, reclaimed concrete aggregate (RCA) from demolition materials has been used only for road foundations.

This began changing in 2003, when the the FHWA concluded and released a survey of a National Review of Recycled Concrete Aggregate use. This survey determined how state highway agencies are using RCA, established a base line for future RCA adoption, and profiles the more advanced uses of RCA in five states: Minnesota, Utah, Virginia, Texas and Michigan.

RCA is being used throughout the U.S. as base material, but rarely is used as actual aggregate in PCC. Quite often RCA has large amounts of dirt mixed in and must be further processed, which adds cost. The RCA must be tested to determine its main components.

And certain types of RCA may contribute to a malady of concrete, alkali-silica reactivity (ASR). A four-year study of ways to detect and mitigate susceptible RCA should conclude in 2004 at the Recycled Materials Research Center at the University of New Hampshire.