In 1974, Phoenix built Deer Valley Airport's parallel runways with a tire-rubber membrane beside a full-depth asphalt control; 11 years later, upkeep fell by 90%

Phoenix built two parallel runways at Deer Valley Airport in 1974 and used different pavement designs to deal with a problem of soil expansion and contraction because of changes in moisture content, with an 11-year assessment finding that maintenance had fallen by 90% after the new designs were introduced, while the runway that incorporated an asphalt-rubber membrane also recorded lower construction costs for materials. The project was documented by Russell Howard Schnormeier, who was an engineer with the City of Phoenix, in a 1986 paper published in Transportation Research Record, and described how the airport's subgrade contained swelling material that was capable of going through volume changes of 8% as moisture levels varied. The city tested two designs to control those changes by keeping moisture conditions in the soil beneath relatively stable. The comparison gave engineers an opportunity to examine how different pavement structures performed under similar conditions, and rather than relying only on surface appearance, the study recorded moisture conditions in the subgrade and compared the designs' construction costs and maintenance requirements.One runway used conventional asphalt; the other added a rubber membraneThe first runway design made use of full-depth asphaltic concrete that was laid directly on native soil, while the second placed an asphalt-rubber membrane between the aggregate base and the subgrade, with asphaltic concrete being laid over the aggregate base. Asphalt-rubber combines asphalt cement with ground tire rubber, and in pavement applications, the material can form a sealing layer that limits how moisture moves and helps protect the underlying structure.The Federal Highway Administration describes asphalt-rubber as a binder that is made by blending crumb rubber with asphalt cement, and the material can be used in chip seals and other pavement treatments, including stress-absorbing membranes, with its properties depending on the rubber content, mixing temperature, and processing method. Phoenix had begun experimenting with asphalt-rubber in the 1960s, and the airport project was part of the city's wider effort that assessed whether the material could reduce pavement deterioration and the expense of maintaining roads and other paved surfaces.The 11-year assessment recorded a 90% maintenance reductionPeriodic checks found that subgrade moisture remained 3% to 4% below the optimum moisture content under both runway designs over 11 years, as per Schnormeier's report, and the design that incorporated asphalt-rubber also saved approximately 10% on construction material costs. The report recorded that maintenance was reduced by 90% after the designs were introduced, and linked the earlier maintenance burden to volume changes in the subgrade, which had created problems before the new pavement designs were applied.The report discusses the maintenance reduction after the application of the two methods, but it does not establish that the rubber membrane alone accounted for the entire 90% decline, as both designs were part of the airport's approach to managing the underlying soil. A later Phoenix pavement study that was published in 1991 reviewed pavement applications that dated back to the 1960s and described the use of rubberized seals to limit cracking and extend pavement service life. The authors also noted that performance varied according to pavement condition, construction details and traffic. The Deer Valley project provided an extended field comparison of two runway designs that were built on swelling soil, and its reported results included stable subgrade moisture readings, lower material costs for the asphalt-rubber design, and a substantial reduction in maintenance after the new methods were introduced.You use AI every day. Now get your AI Quotient. Take the AIQ test.