California Finding Cost-Effective New Ways to Make
California is taking a new look at the pavement on its aging highways. Employing a combination of radar, automated pavement scanning machines, and an advanced computer modeling program, the California Department of Transportation (Caltrans) is working to reshape the State Highway System (SHS) with smoother, longer-lasting paving surfaces — coupled with a lower “carbon footprint” than previous California roadways.
The challenge is substantial. At an estimated value of $1.2 trillion, the 50,000 lane-mile SHS carries 35 million vehicles that log approximately 264 billion miles a year. In addition, California’s climate ranges from mountain snow and rain forests in the north to vast deserts of rocky soil and yucca trees in the south. The state is home to salty air and foggy coastlines and the high summer heat of the Central Valley. And, of course, highways must stand up to those highly varied conditions.
It’s little wonder that California’s urban freeways and rural roadways take such a merciless beating. Nonetheless, Caltrans engineers are unwilling to make excuses for poor roads. There must be a better way to construct and maintain those highway miles.
Scanning for Highway Faults
Caltrans has chosen to attack the highway system’s cracks, potholes and obsolete sections through PaveM, a pavement management system that combines automated highway surveys and radar soundings with an advanced computer program that sorts multiple variables and recommends the best strategies to improve not only a specific roadway but the entire SHS. For example, PaveM might consider such factors in a project as the anticipated lifetime of a roadway, how easily it can be constructed, the type and life expectancy of materials used, smoothness of ride, costs of its entire life cycle, safety characteristics, and the sum of greenhouse gases (GHG) the project would generate.
The new system is likely to take several years to be put completely into place. But when
A Caltrans History of Pavement Management
In 1979, California was among the first states to adopt a pavement management system, based upon information from biennial pavement condition surveys, which were then stored on a mainframe computer. Maintenance supervisors used the information to confirm their suspicions about pavement deterioration, and then to make recommended repairs. The process, based on a method developed by former Caltrans employee Francis N. Hveen, was derived from road test sections from the 1940s.
However, Hveen’s system to manage pavement failed to account for a number of variables, including local climates, and structural properties of certain materials and designs. By 2007, Caltrans had moved to a new means of analysis, known as the Mechanistic-Empirical (M-E) pavement design method. The M-E method helped to create more efficient and cost-effective pavement designs that could predict specific pavement failures, make better use of available materials, and account for the effect of California’s climatic zones.
A New Way of Understanding Pavement
Today, Caltrans engineers are pushing for even better ways of designing, building, and rehabilitating highways. “There are more choices in pavement than concrete or asphalt,” said Hector Vergara, an engineer with the Caltrans Office of System Development and Performance (System Development). Using PaveM, “We want to plan strategies for pavement that could potentially save California billions of dollars in highway design for both building and maintenance.”
To do this, System Development is executing the first phase of a three-part strategy. Part one is to collect “structural section” snapshots of the entire highway network by using ground penetrating radar (GPR), that is, to look into the layer cake profile beneath a highway’s pavement. These structural sections will be collected on every lane mile on the SHS. The GPR vehicle, containing both high-resolution and lower frequency antennae, can move at the speed of adjacent traffic while mapping for voids and moisture within or below the pavement, said Michael Hughes, a branch manager with Fugro West, Inc., Caltrans’ GPR contractor.
That might mean, for example, that GPR can peer into a roadbed through four inches of asphalt concrete paving, a foot of aggregate base, and another two feet of subbase. By looking at the radar profile, engineers can see the details beneath the pavement. This subsurface picture will allow Caltrans to understand repairs to the highway that have been forgotten over the years, unrecorded maintenance, or faulty engineering and construction. “All states have pavement management systems,” said Pyle, “but only California uses ground penetrating radar at the network level for pavement management. We’re moving from eyeballs to electronic scanning equipment — but double-checked by eyeballs.”
The second part of the strategy is the Automated Pavement Condition Survey (APCS), which automatically evaluates the surface condition. The APCS consists of radar equipment packed into a van to measure the profile of the pavement surface to within a few millimeters. It sees cracks, faults, and potholes on the pavement surface, and keeps
In the third part of the strategy, the GPR and APCS information can be loaded into a computer program called PaveM. Based on that program, Caltrans can develop models that determine life-cycle cost analysis (LCCA) of different pavement preservation strategies. The strategies in turn, allow engineers to select the most cost-effective strategies to keep good pavement in acceptable condition, replace bad pavement, and predict the extended life of pavement.
The computer program could be compared to a hypothetical time machine. Assume that Caltrans wants to design a new highway. Engineers would feed a number of variables into the computer, such as climate, highway traffic load, the number of truck axles that will pass over the pavement, and how long the highway needs to last. Then they press a button, and within minutes PaveM can predict how long the pavement will last and what kind of failures it might experience. How rough will it be? Will it crack in winter or melt in hot weather? Will it begin to show rutting patterns too early?
And perhaps the best part, PaveM will provide realistic data to feed another computer program called RealCost developed to calculate LCCA, which the Federal Highway Administration (FHWA) describes as “an engineering economic analysis tool” for a
“The LCCA is used to evaluate long-term investment options,” said Mario N. Velado, P.E., Senior Transportation Engineer with the Division of Maintenance (DM). “It is an economic analysis that compares sound engineering solutions for a given project and is used to evaluate competing pavement alternatives to determine which one is the best investment option for a given project over an extended period of time.” The LCCA analyzes not only a transportation agency’s direct expenditures, but user costs resulting from work zone operations, according to the FHWA.
The Caltrans DM is also working with the University of California, Davis, and UC Berkeley to develop an updated version of RealCost. Velado said that the new version will be able to compare more than two alternatives at a time, predict future costs, and select a rehabilitation schedule to follow after a pavement type is selected.
Global Warming Concerns
In addition to understanding the condition of California highways, Caltrans is also concerned about the threat of global climate change and the carbon footprint that constructing highways may leave.
In fact, the U.S. Environmental Protection Agency awarded Caltrans first place for Innovation in the Coal Combustion Products Partnership Awards. The award recognizes that California has always been a leader in protecting the environment, and we are leading the nation in our commitment to reduce greenhouse gas emissions.
Caltrans and the rest of state government have taken tangible steps to reach this goal, and the reformulated cement concrete will help make the San Francisco-Oakland Bay Bridge (SFOBB) stronger.
For example, Pyle who formerly managed the Concrete Office at the Caltrans Transportation Lab for 10 years, recently worked on a special assignment with the California Air Resources Board, and led the statewide efforts to reduce carbon dioxide (CO2) emissions from cement production and concrete use per AB 32 requirements.
He pointed out that Caltrans often uses concrete for long-lasting highways throughout the state. Yet, the 11 cement plants in California, alone, produce between 1.5 and 2 percent of all CO2 emissions in the Golden State. For example, producing a ton of cement also renders about a ton of CO2. Or, think of it this way: just one delivery truck full of cement concrete represents 5,150 pounds of CO2 generated into the air. Compare that to a passenger car that spews approximately 11,450 pounds of CO2 through its tailpipe in a year’s time. In other words, just two trucks full of cement concrete, each making a delivery, equals about the same amount of the greenhouse gas CO2 as one passenger car releases in a year.
The question then becomes: can Caltrans continue building high-strength, long-lasting concrete highways, given the “carbon cost” to our air? Well, yes, it is possible, said Pyle. One solution may be “fly ash,” a product of coal-powered electric plants. The United States produces more fly ash than any other country in the world, except for the People’s Republic of China.
The good news is that Caltrans has a mandate to replace about 25 percent of its cement with fly ash. On such projects, fly ash released during its manufacture has already been “spent” — at the electrical plant — so Caltrans is adding only minimally to the problem of climate change. Instead, Caltrans and others that use fly ash are reducing the amount of coal-burning waste going into landfills, and reducing by 25 percent the amount of cement needed on a given project.
The fly ash solution makes so much sense that Caltrans engineers have used it to construct the new SFOBB. And because concrete with a 50-50 mix of Portland cement and fly ash is highly resistant to salt and marine fog, in addition to generating less heat, Caltrans used it to build the under-the-bay water footings on the SFOBB, which is designed to carry some 350,000 vehicles a day and last 150 years.
In summary, Caltrans is on the cutting edge of concrete technology with newly released concrete specifications that call for maximum use of supplementary materials. For the first time, Caltrans allows ternary blends, a concrete mix with three different cement materials. This results in concrete mixes that set earlier and stronger, are more permeable, and shrink less than other mixes. These concrete mixes result from an engineering prospective but also lead to more environmentally friendly concrete.
Caltrans is committed to pursuing new techniques, materials, and ideas to overcome the challenges of increased traffic on its transportation system and is working hard to reinvent itself to design, build, and maintain the highway system of the 21st century.