A familiar road rehabilitation process can be made urban-friendly thanks to a new way to spread cement slurry.
UDOT has used full-depth reclamation for about five years. The process recycles installed concrete or asphalt and base material into new road base by pulverizing, grading, stabilizing and compacting the old material.
Dr. Spencer Guthrie, Associate Professor at BYU and Research Assistant Charles Hope presented a case study to illustrate the advantages of cement stabilized FDR at the 2011 Annual Utah ACPA Concrete Workshop last week.
A smart strategy
FDR can be part of an overall smart pavement strategy. “If a project is suitable, you get a lot of benefits,” said Guthrie, including reduced project costs, less impact on stakeholders and better conservation of natural resources.
- The process reuses materials “your mom and dad paid for,” so project costs are reduced.
- FDR reduces mining of virgin materials.
- Materials do not need to be hauled off, so there is less impact on surrounding roads and roadusers.
- Only brief access closures are necessary since traffic can drive over the FDR surface during most of the process, so resident and business inconvenience is minimal.
Stabilization is the key
FDR can sometimes be mechanically stabilized, but usually stabilization agents, including cement or emulsion are used.
Cement powder has been used with FDR in rural areas for decades. But, powder use results in fugitive dust which is unacceptable in an urban setting.
Guthrie and Hope’s presentation showed how a cylindrical spreader with spouts, attached to a ready-mix truck, can be used to distribute cement slurry evenly without producing fugitive dust. The newly developed spreader should be available for use soon.
Cement vs. emulsion
When emulsion is used to stabilize FDR, full strength is achieved after evaporation occurs. This factor makes using emulsion risky during cold or rainy weather — not so with cement.
“Cement loves water,” said Guthrie. “If it rains, no problem.”
Using cement stabilized FDR has other advantages over emulsion:
- Increased rigidity
- Elimination of rutting below the surface
- Reduced susceptibility to moisture, frost and fatigue cracking
- Thinner pavement sections
Because of the elimination of fugitive dust, the new spreader has potential for making cement stabilized FDR available for use in urban areas.