ACPA Concrete Pavement Progress - Quarter 2, 2022

www.acpa.org T E C H N O L O G Y , P A R T I said Taylor. Using a device bolted on the back of the slipformpaver, the contractor can view information in real-time to identify adjustments that need to be made. Three to four demonstration projects each year have been supported by SHRP, and lessons learned from the projects include: • The contractor and agency can “see” things in real-time which used to take 24–48 hours. • RTS is well suited for identifying operational changes on smoothness, tuning the paver, quality control, and troubleshooting and correcting problems early. • RTS improves the paving process overall through better quality and improved efficiency. While contractors see an immediate financial benefit when smoothness bonuses are included in a contract, acceptance by the on-site crew can be a challenge at first, said Taylor. “In one demonstration project, the crew was very skeptical of the device as we bolted it to the paver, but on the second day, the foreman saw the benefits of seeing the information on a screen in real-time as he adjusted the paver,” Taylor said. RTS systems enable the contractor to evaluate the effect of adjustments—negative or positive—almost immediately rather than 18–36 hours later when hardened profile data is available. “On the third day, the remaining crew members agreed that RTS was a valuable tool.” » continued from page 11 There is a growing use of RTS systems, said Taylor. “In Iowa, all but one contractor uses RTS,” he said. “It is important to remember that the information provided by RTS is a guide to help the contractor produce a smooth pavement while paving, the data is not used by agencies for project acceptance.” RTS aids agencies, owners, and contractors with quality control, improved paving efficiencies, and a better pavement, according to Taylor. “It is a tool that helps contractors sleep better at night,” he said. Nanotube concrete: increased strength and durability The use of carbon fibers to improve concrete pavement’s flexural strength and resistance to cracking is not a new concept, but the use of carbon nanotubes in concrete pavements is pushing the cutting edge of the approach. After his company developed its proprietary method of producing carbon nanotubes (CNTs), the next step was to identify where the technology adds the most value, saidRobert Cavaliero,MCE, Vice President of EdenCrete® Admixtures at Eden Innovations. “Conventional fibers provide crack-resistance, but CNTs are much stronger and more durable than conventional fibers, even stronger than carbon nanofibers,” said Cavaliero. One of the early tests of CNTs in a pavement maintenance project was conducted by the Georgia Department of Transportation. Two 35-footlong test sections were placed on I-20 near the border between South Carolina and Georgia. The “control” was poured with the standard 24-hour accelerated concrete mix formula used by the Georgia Department of Transportation. “The CNT admixture significantly increased abrasion resistance and compressive strength of the concrete,” said Cavaliero. “Following the test, GDOT specified the product to be used for full-depth slab replacements using 24-hour accelerated concrete.” The minuscule size of the carbon nanotubes—up to 50,000 times smaller than a hair—means they are respirable in a dry form. To overcome this challenge, the admixture was designed as a liquid suspension of CNTs able to be transported and added to concrete safely and easily, just like any standard concrete admixture. “This alleviates the risk toworkers,” saidCavaliero. Adding nanotubes to a concretemix causes lower permeability, resulting in pavements that are easier to place and finish and achieve higher ultimate tensile and compressive strengths in some cases. Pavements with nanotubes also have improved durability with greater resistance to wear and shrinkage-related cracking and curling, resistance to scaling from deicer chemicals, and a lower tendency of steel corrosion. The future of concrete with CNTs is bright, with projects inColorado, Georgia, Kansas, North and SouthCarolina, Texas, andUtah, at port authority Driven by a pursuit of excellence and helped along by various federally funded research projects and private-sector research and development initiatives, the industry has developed a growing number of options to reduce the environmental impact of concrete pavements. continues on page 14 » Concrete Pavement Progress 12

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