For those of us who never get tired of seeing quality concrete pavements, smelling wet "mud," or observing all the attention to detail that goes into a typical project, there's no doubt that there's a real art to paving.

Naturally, there's an equal amount of science to it, as well. It's our view that this combination of art and science yields some of the best quality concrete pavements in the world.

Just one area where ACPA and others are focusing increased attention is on materialsscience, essentially evaluating, controlling, and providing information

"Developing solid, durable concrete pavement mixtures is a significant key to achieving long-lasting pavements," he said, adding, "the current paving environment has shifted responsibility for developing these mixtures onto the contractor, and current technical resources don’t take that transition into account.

To bridge this information gap, the concrete pavement and cement industries, in collaboration with the Federal Highway Administration and the National Concrete Pavement Technology Center (CP Tech Center), are authoring a step-by-step manual to guide concrete paving contractors through every step of the mixture design and proportioning processes.

ACPA and Portland Cement Association, working with the CP Tech Center, are writing the guide. The collaborative effort is one significant step closer to completion: the contents have been outlined; authors have been named; and a panel of reviewers has been established. The publication, "Design and Proportioning of Concrete Paving Mixtures," will include:

..• In-depth coverage of all ingredients used in concrete paving mixtures. This information will focus on key characteristics and the effects of the interactions among cementitious materials, aggregates, mixing water, and chemical admixtures• Important factors to consider during the design process, including environmental aspects, economy, and sustainability• Step-by-step guidance on the actual design process• Detailed instruction on the methodologies and procedures used for proportioning• A thorough description of how to evaluate concrete paving mixtures.

Following the completion of this content at different stages, the manual will undergo a peer review by FHWA officials, state DOT's, the CP Tech Center, contractors, and material suppliers. The manual is slated for production and release in spring or summer 2009 and will be available for purchase through ACPA and PCA's websites.

To help contractors and others adapt the new guide’s procedures into best practices, ACPA plans to incorporate it into its Education & Training program, including webinars, Concrete Pavements 101 and 201 training seminars, and the Professors’ Seminar.

The goal for this collaborative effort is to thoroughly prepare contractors for developing concrete paving mixtures that, when placed, meet owners’ performance expectations, Wathne said.

"Achieving 'desirable' optimized concrete means producing one or more cost-effective mixtures that the contractor can consistently batch, deliver and place to meet all of the owner's requirements, from acceptance through years of performance," said Samuel S. Tyson, P.E., Federal Highway Administration’s Office of Pavement Technology.

"These mixtures lend themselves well to accelerated construction practices that are planned and executed in a manner that increases construction efficiencies and which minimize overall disruptions to traffic," he said.

ACPA’s CONCRETE PAVEMENT PROGRESS will announce more details about the guide as they are finalized. For more information on concrete paving mixture design and proportioning, contact Leif Wathne at 202-638-2272.

One of the most common mistakes made in concrete paving mixture design is focusing on material strength alone, according to ACPA's technical staff. This singular focus can occasionally lead to cracking and pavement failures, an unnecessary and costly risk for state officials already facing increasingly tight budgets.

There are several easy—yet often overlooked—preventive steps when considering concrete pavement materials to maximize performance potential, said Robert Rodden, E.I.T., ACPA’s Director of Technical Services.

First, focus on materials compatibility when the mixture is still in its plastic state. It is during the plastic state that primary components of the mix, as well as added ingredients will interact. These interactions can often be very dependent on ambient conditions, as well as materials chemistry, Rodden said.

Second, pay attention to the stability of the concrete materials.

”If the mixture can be placed, consolidated, and finished successfully, it must then be capable of being stable, both chemically and volumetrically, in the long-term,” Rodden said.

In simpler terms, this means there must be no secondary long-term reactions among materials after placement, and all materials must have coefficients of thermal expansion that work well with each other.

Also, crews should pay attention to elements that affect durability. These include the pavement’s air void system, air content, and more.

These may be difficult to account for using traditional concrete pavement design methodologies, but by using new tools, such as the Mechanistic-Empirical Pavement Design Guide (M-E PDG), designers can now use many of these factors as inputs. By focusing on materials compatibility, stability, and durability during the different phases of construction, engineers can assure within reasonable doubt that they have produced a long-life concrete pavement.

For more detailed information on the reactions that occur during these steps, see ACPA’s EB237P: Concrete Pavement Field Reference—Pre-Paving or the Integrated Materials and Construction Practices for Concrete Pavement: A State of the Practice Manual. Visit ACPA’s online bookstore at www.pavement.com/bookstore to order these products.

For more information, contact Robert Rodden at 847-966-2272.

ACPA's Next Generation Concrete Surface (NGCS) continues to show promising results, based on recent testing conducted more than six months after the projects were originally constructed.  NGCS is one of the key deliverables from a three-year research initiative focused on concrete pavement surface characteristics and tire/pavement noise.

The new surface validates proof-testing research conducted at Purdue University and confirms that blade width and spacing are not the controlling factors in noise generation. The determining factor is the resulting profile or smoothness of the fins.  Equally important, NGCS test results represent the concrete paving industry’s progress in achieving quieter concrete pavement surfaces.

To date, two sites have been tested: In Minnesota, two, 500-ft. lanes on Interstate 94, part of  MnROAD’s test area; and, in Chicago, a single, 1,200-ft. travel lane on suburban Interstate 355. 

Initial test results last fall revealed the NGCS tested at 100.1 dBA in Minnesota and 100.5 dBA in Chicago.  The tests earlier this month show the NGCS in Minnesota is lower, at 99.0 dBA, while the section in Chicago remains about the same, at 100.9 dBA.

On the conventional diamond-ground (CDG) surfaces, initial measurements last fall were 104.3 in Minnesota and 100.7 in Chicago.

Testing earlier this month showed an adjusted noise level of 100.7 dBA on the sections in Minnesota, a decrease of almost four decibels, which likely is associated with the fin breakage (a desired and expected effect).

Chicago readings showed readings were in about the same range—100.7 dBA in the fall and 100.9 earlier this month.

The 100 dBA reading is competitive with most quiet pavements of all surface types available today, said Larry Scofield, P.E., ACPA's Director of Environmental Technology.

To collect these readings, ACPA uses the On Board Sound Intensity (OBSI) method, which allows the assessment of acoustic performance of pavements over time. Since no traffic control is necessary, testing can be conducted in normal traffic flow for efficient and cost effective testing. The method was recently developed by the Federal Highway Administration and approved by the American Association of State Highway and Transportation Officials as a provisional specification.

ACPA will continue to report periodically on the progress of testing as this technology continues to evolve. For more information, contact Larry Scofield at 480-220-7144.

ACPA has countered misleading information about equivalent pavement designs of asphalt and concrete in its latest publication.

The latest ACPA R&T UPDATE (9.01) takes aim at a plaintive memo from the Asphalt Institute, titled, "Debunking StreetPave's Claim of an 'Equivalent' Asphalt Design." In the memo, the Asphalt Institute takes issue with ACPA's software, claiming that the software does not fairly compare asphalt and concrete pavements.

In direct response, the four-page R&T UPDATE explains and demonstrates how StreetPave incorporates reliability into asphalt designs by adjusting the user-inputted resilient modulus to yield a design resilient modulus in a manner that is equivalent to that suggested by the Asphalt Institute.

The document also describes reliability in StreetPave and design resilient modulus formulation. It also includes a thorough explanation of the equations used, as

equations. ACPA encourages readers to download this issue of R&T UPDATE to better understand the facts about StreetPave and equivalent pavement designs.

Click here to download this R&T UPDATE or here to see all other R&T UPDATES.