Concrete materials and pavement structures are designed to meet performance requirements and also the demands of the California traveling public to limit construction windows and the resulting traffic delays, Harvey said. California pioneered the use of concrete that can be placed at night and opened to truck traffic by the next morning, gaining strength within two to four hours. Center researchers are working with Caltrans on ways to place thinner concrete slabs on existing pavement, engineering the interface between the new and old pavement to reduce cost and construction time.
Cement production for roads and construction makes a significant contribution to greenhouse gas emissions worldwide, consuming energy and fresh water. Sabbie Miller, assistant professor in the Department of Civil and Environmental Engineering, is researching ways to reduce cement’s carbon footprint by making it more efficiently, using it more effectively or replacing it all together.
Once pavement is laid down, it has to withstand years of car and truck traffic as well as the effects of heat, cold, rain and depending on location, snow and ice. Asphalt surfaces become brittle over time and more prone to damage. By better understanding the properties of road materials, engineers could better predict how fast roads will wear and schedule repairs before damage becomes advanced and costly.
Another area of research is to develop new, rapid methods to resurface roads. Replacing worn-out road once involved breaking up the pavement, hauling it away and laying completely new material. New techniques rely instead on grinding up the old road on site and turning it into at least part of the aggregate for the new road, stabilized with a dash of cement sometimes mixed with foamed asphalt (asphalt bubbles). This recycling of asphalt pavement is faster and generates less waste material than older methods of road repair.
A California state law calls for the Department of Transportation to use asphalt containing recycled tire rubber in a large percentage of its asphalt materials . The Pavement Research Center is working with Caltrans and industry to evaluate the properties of new kinds of mixes using tire rubber crumbs and how best to use them in different applications. Based on this research, they will develop draft specifications for Caltrans to use.
So how do these new mixes and additives perform in practice? The rubber hits the experimental road outside the center’s lab on the experimental test track.
The center has two Heavy Vehicle Simulators, machines that roll wheels back and forth over pavement, simulating 20 years of truck traffic in a few months. Researchers can lay down a stretch of experimental pavement, embedded with instruments, and observe the results as simulated years of wear rack up.