Attend the education session "Performance Engineered Concrete Mixtures for Paving" on Thursday, March 12, 2020 from 1:00 p.m. - 2:30 p.m. at CONEXPO-CON/AGG.
“Concrete pavement done well lasts 40 years; done badly it can fail quickly.” That’s how Peter Taylor sums up the motivation for improving concrete paving. Taylor is the director of the National Concrete Pavement (CP) Technology Center and a research associate professor at Iowa State University. “We did a study a few years ago and determined that by merely eliminating errors we could move the average life of concrete from 25 years to that 40 year benchmark.”
Gordon Smith is also at Iowa State. He works with Taylor as an assistant director of the CP Technology Center. Smith notes that concrete pavement held status quo for a long time but changes eventually arrived. Some were external to the industry, such as the chemicals and procedures used for de-icing pavement. Some were internal, such as the addition of supplementary cementitious materials (SCMs), of which fly ash is one example. “Around 2005 the National Concrete Consortium started looking seriously at issues affecting the performance of concrete pavement,” says Smith. There are now 18 states in the consortium, many from the snow belt but California and Georgia are also member states.
Concrete Testing Procedures
One thing that grew out of this increased effort was a battery of tests. Some were new while others were improvements to existing tests. The goal of testing is twofold. One, tracking and confirmation of quality control throughout the paving process, from the batch plant to the trowel. And two, early detection and correction of problems. The first indication of trouble should not be the premature failure of the pavement and thorough testing guards against this.
One of the most comprehensive changes was the development of Performance Engineered Mixtures (PEMs). Taylor wrote a Tech Brief for CP Technology Center in November 2018 with extensive information on both PEMs and the associated testing procedures. “At the heart of the PEM program are three fundamental philosophies,” writes Taylor. The first is that the tests should be relevant to the actual service and environmental conditions the specific pavement must endure. The second is that the emphasis on testing is at the pre-qualification stage. “Testing at the point of delivery is simply to assure the agency that the material delivered is close to the prequalified mixture.” And the third is cost reduction by checking the early-age properties of the mixture to prevent problems from emerging later.
Concrete Cost and Quality Control
Cost control is one immediate way these new practices can improve contractor profitability. The long-term goal is to entrench practices that routinely provide outstanding pavement service over the years, making way for performance-based bonuses. Another objective is to allocate responsibility and liability concerns equitably among the many players in a concrete paving project. As it is, contractors often find themselves liable for the consequences of procedures over which they have little or no control.
Here are Smith and Taylor’s top five tips for operating successfully under this new paradigm.
- Understand the shift in responsibility. “At one time agencies formed the corps of expertise,” says Taylor, “but retirements and shifts in philosophy changed all that.” He says consultants have great knowledge but are grossly overworked and not all agencies will pay for them. “So like it or not, contractors are now expected to be the repositories of knowledge.”
- Understand and follow proper test procedures. Know what defines good concrete and how to test for that.
- Be able to spot problems and know how to react. Recognizing problems is not the objective; fixing them is or, ideally, avoiding them in the first place. Pay attention and respond quickly and appropriately.
- Process management and quality control will become ever more important. Fostering an attitude of excellence among crews will go a long way in meeting these challenges.
- Acceptance and involvement. Technology is thrusting concrete paving forward. Whether you, as a contractor, see that as an opportunity or a setback won’t alter the curve of change. Accept that things are changing. Better yet, become involved. Be pro-active in implementing higher standards in your market. “Know that things are changing, embrace the change, and get involved for the sake of your business and the sake of the industry,” says Smith.
Smith and Taylor will be co-presenting “Performance Engineered Concrete Mixtures for Paving” on Thursday, March 12, from 1:00 to 2:30 p.m. at CONEXPO-CON/AGG 2020.