Most people would probably agree with the adage that necessity is the mother of invention.

These words are as relevant today as they were when first written in Plato's Republic more than 2,300 years ago.

So if necessity drives invention, what then, leads inventors to try, sometimes fail, and then try again until an invention is delivered successfully?

It is simply that voice inside that says, "I can build it better." We think that voice is what leads engineers to engineering; roadbuilders to placing concrete pavements; and others to meet the changing needs of people all around us. It is what leads inventors to invent.

That spirit exists in the concrete pavement industry, and indeed, in the broad transportation- construction community. And so it is that we devote this issue of CONCRETE PAVEMENT PROGRESS to the pioneering spirit of those who came before us as well as those current and future inventors whose attitudes about building it better are putting this industry on the cutting edge of progress.

This is not a be-all, end-all story, but simply a current snapshot of those emerging technologies that hold tremendous promise for enhancing the safety, efficiency, and overall performance of concrete pavements. As these technologies continue to emerge, the road-users benefit from wiser investments in better highways, roadways, and airfields. The agencies benefit in much the same way, but also benefit because their jobs will be easier, too. The industry, of course, benefits from the efficiencies and process improvements.

We think this is an exciting and interesting time to be a part of the transportation community, particularly as the story continues to unfurl and emerging technologies—those things just showing up on the proverbial radar screen today—become the best practices of tomorrow.

What is or will be your role in this sea-change of emerging technologies that will impact the transportation-construction community. Whether you're a pioneer or a relative newcomer, we'd like to hear from you.

Drop us a line at acpa@pavement.com to let us know your views about the leading edge of progress!

As the demand increases for better performing, longer-lasting, and maintenance-free highway infrastructures, it becomes increasingly important that concrete pavements are readily constructible, and capable of meeting structural and ride requirements. Moreover, they have to do so for the specified amounts of traffic loadings and expected design life. 

Although much has been published about how to design and proportion general-use concrete mixtures properly, very little has been focused solely on concrete paving mixtures.  This is important because there are unique demands placed on a concrete pavement mixture, including its placement requirements; high temperature and moisture variations; high surface-area-to-volume ratio; wide range of loadings; and varying degrees of underlying support.

Why This?  Why Now?
A number of factors underscore the critical need for a uniform concrete pavement mix design.

Shift of Responsibility … The roadbuilding community is trending away from strictly prescriptive specifications toward more advanced acceptance tools, such as end-result and performance specifications. This will make contractors more responsible for concrete pavement mixture design and proportioning. 

ACPA recently participated with the National Concrete Pavement Technology Center on a comprehensive state-of-the-practice manual that discusses both materials and construction practices for concrete pavement. Even though this manual provides a vast amount of immensely valuable information pertaining to pavement design, concrete materials, cement hydration, pavement construction, quality control, testing and troubleshooting, it does not elaborate on practical concrete paving mixture proportioning strategies to provide the reader with easy-to-implement guidance – the mixture proportioning guidance is essentially identical to that presented in ACI 211.1. 

Recognizing the lack of guidance related specifically for concrete pavement mixtures, the Federal Highway Administration (FHWA) and the concrete pavement industry have dedicated the first track of the comprehensive and collaborative Concrete Pavement Road Map (CP Road Map) to this purpose.

Significant Advances
A preliminary implementation plan for this “Performance-Based Concrete Pavement Mix Design System” has taken shape recently.  The first task in this plan is to develop an easy-to-use and reliable method—in the form of a guide-book—to design and proportion robust concrete paving mixtures. Industry has taken on the challenge of leading the development of this guide, and anticipates completion within three years.  Although the effort is industry-led, the guide will be developed through a true collaborative effort with involvement from FHWA,

State agencies, the consulting community as well as academia. 

The guide, whose working title is “Design and Proportioning of Concrete

Paving Mixtures” will complement PCA’s perennially popular publication, “Design and Control of Concrete Mixtures” (PCA EB001). 

Other Important Steps
As identified in the Implementation Plan for Performance-Based Mixture Design and Analysis Track (NCPTC 2007), there are several other tasks included in the MDA track, including:

• Mixture Testing and Analysis Manual—This project consists of developing a manual with two discrete elements.  The first part of the manual will identify and describe all relevant concrete design properties/characteristics than an owner may require as part of a concrete pavement specification, as well as the accompanying test procedures to measure those properties.  The second part of the manual will focus on procedures for analyzing concrete pavement mixtures in specific applications and predicting their performance under anticipated placement conditions.  Several tools are already available that can aid in this effort, including the Mechanistic-Empirical Design Guide (NCHRP 1-37a), HIPERPAV, and COMPASS.  State agencies will take the lead in this effort.
• Evaluation of Emerging Laboratory Testing and Equipment—This task focuses on evaluating two important tests currently under development: the calorimetry heat signature test and coefficient of thermal expansion test.  It is anticipated that both of these tests will be included among the tests considered in the Mixture Testing and Analysis Manual above, and that the test protocols ultimately be considered for adoption by American Association of State Highway and Transportation Officials (AASHTO).  State agencies will lead efforts under this task.
• Modeling and Software Assessment—State of Practice and Future Advancement.  This project calls for an assessment of available software tools and models, with recommendations for improvements and options for integration.  The ultimate goal is to establish the framework for a fully integrated software package that is reliable, flexible, easy to use, and minimizes the required inputs.  FHWA will lead this effort.
• Field Evaluation, Coordination, Training and Outreach—This task provides for field evaluations of the mixture tools developed in previous tasks, and will generate specifications and practices.  A series of technology transfer activities will also be included in this task.  At this writing, no specific task leader has yet been identified for this project.

In November, ACPA will present a paper at the International Conference on Optimizing Paving Concrete Mixtures and Accelerated Concrete Pavement Construction & Rehabilitation. For more information on ACPA's paper, contact Leif Wathne at 202-638-2272. For more information on the conference, click here or contact Shiraz Tayabji at 410-997-0400.

For more information about this article, contact Leif Wathne at 202-638-2272.

Transportation-construction stakeholders are currently investigating two-lift construction for use in certain applications.

This technology, which may help address issues with aggregate quality, was identified as a top priority for review during the recent international scan tour of long-life concrete pavements.

Based on the interest in two-lift construction, ACPA members and staff identified the technology as one that needed further investigation.

the upcoming ACPA Annual Meeting in November.

In its report, "Reassessing Two-Lift Construction," the National Concrete Pavement Technology Center (CP Tech Center) notes that cost, mix design, and construction concerns inhibited its use.

Since the report was published in 2004, though, there's been a resurgence of interest in the technology, owing in some part to the International Scanning Tour for Long Life Pavements, in which ACPA, CP Tech Center, the Federal Highway Administration, other stakeholders had the opportunity to see first-hand how the technology is used in Europe.
                                                                                                                          

What is two-lift paving?
Two-lift construction involves the placement of two wet-on-wet layers or bonding wet to dry layers of concrete, instead of the homogenous single layer commonly placed in concrete paving, according to the CP Tech Center.

The bottom layer is thick and consists of lower quality (lower durability or strength), locally avail­able aggregate or recycled aggregate (such as recycled asphalt, concrete rubble, or local aggregate). The top layer is thin and consists of high-quality aggregate designed to provide better resistance to freeze-thaw damage, reduced noise, or improved friction. The high-quality surface also increases friction and reduces noise, according to the tech transfer summary.

As quality aggregate becomes scarce in some regions, two-lift paving may become a more viable economic option. It may help some agencies around the country consume growing recycled asphalt stockpiles, which could reduce overall costs while benefiting the environment, according to the CP Tech Center.

Existing composite pavements (concrete pavements with asphalt overlays) can be successfully recycled by first separating the asphalt overlay and then using 15% to 40% asphalt in the final lower lift of concrete, according to the CP Tech Center's report.

For its part, ACPA has not adopted a formal position on two-lift construction, but is currently evaluating this emerging technology. Look for more information in future issues of CONCRETE PAVEMENT PROGRESS.

Click here to download the report from the long-life concrete pavement scan tour, which includes an assessment of two-lift construction.

Click here for the complete tech transfer summary on two-lift construction from the CP Tech Center.

Nano Defined

To understand how nanotechnology can play a role in cement and concrete industries, it’s

important to have a macro view of this microtechnology, according to Birgisson.