On the northeast edge of San Diego International Airport, years of heavy truck and air cargo deliveries had taken their toll on the West Washington Street roadway. So as part of the Green Build project, the San Diego County Regional Airport Authority hired a soils engineering consultant to analyze the weakened roadbed. That firm, Kleinfelder Inc., performed a pavement evaluation to determine a pavement rehabilitation strategy that would meet the long-term performance requirements of the roadway, while considering the project budget and logistics.
"The pavement investigation found the soils at the site were generally clays with a poor capacity to carry traffic loads," said Marco Estrada, Business Development Manager for Pavement Recycling Systems Inc., an employee-owned company. "The concern is that when you have soils with such a low capacity, you have to construct a thicker pavement section, which is associated with higher costs and construction time. So in an effort to reduce both, the pavement recommendation called for lime stabilization of the on-site soil materials."
The lime-stabilization process, Estrada said, involves incorporating high-calcium quicklime into the soil. (Quicklime is produced by heating limestone in specially designed kilns. It has been used for centuries as a form of mortar.) The quicklime reacts with the soil to form a cementitious product that increases the strength of the soil and allows for the soil to be used as a part of the pavement section instead of being hauled away. The specific recommendation for the airport project was 4 percent quicklime to a depth of 18 inches.
"The process itself involves the delivery of the quicklime, pneumatic transfer into a specialty distributor truck that spreads the lime onto the grade at the prescribed rate of application, and subsequent initial mixing and hydrating of the lime with a road-reclamation machine" Estrada said.
Utilizing this process led to significant savings in materials, time and manpower, Estrada said. By the time of the project completion, traditional methods would have required an estimated 750 trucks for excavating and exporting the unsuitable soil, and then 650 truckloads importing over 16,000 additional tons of aggregate base to be deposited below the roadbed and paved over. Instead, only 23 truckloads (580 tons) of high-calcium quicklime will be required. Significantly reducing the construction truck traffic resulted in a reduced impact on the site management and the environment.
"Additionally, the lime-stabilization process was the optimal way of minimizing impact to airport operations because we didn't need to remove the original soils material," Estrada said. "Overall, the greatest benefit is to the San Diego general community because of reduced costs, construction time and environmental impact."
704 Rock Springs Road | Escondido, CA 92025 | (760) 489-6888 | www.pavementrecycling.com
~ By Glenn Grant, The Daily Transcript