01474975

Component

Open graded friction course (OGFC) is widely used in Florida and many southern states as a final friction surface in high speed roads. FDOT friction policy requires the use of OGFC on multilane highway facilities with design speeds greater than 50 miles per hour. OGFC reduces the possibility of hydroplaning and water splash during rain, thereby reducing crashes. About half the Florida State Highway System is surfaced with OGFC, amounting to about 22,000 lane miles of roads. The use of FC-5, the current OGFC mix type in Florida, started in 2000. Some roads with FC-5 have reached the end of their useful life and have been milled and resurfaced. Given the high cost of FC-5 mix, it made economic sense to try to reuse the prime aggregate and high quality material incorporated in OGFC using the hot in-place recycling (HIR) process. The HIR process heats, hot-mills the surface pavement layer, applies a rejuvenating agent, mixes and then places the material in one pass. The process uses 100% of the existing road material and can produce significant cost and environmental savings. This paper reports on three attempts to hot in-place recycle OGFC in Florida. One was to hot in-place recycle an FC-5 mix as part of a hot in-place recycling project in Pasco County, Florida (SR-54) in 2012. The second is laboratory study of recycling FC-5 mix based on samples taken at SR-60 in Polk County, Florida in 2011. The third references SR-471 case study conducted by FDOT in 2002 in which an OGFC (type FC-2) was hot in-place recycled, lasted 10 years to date and still remains in service. The three referenced projects have shown that HIR of OGFC can be done successfully and should be considered as a cost effective rehabilitation option in the future. FC-5 is 0.75 inch thick. The recycling thickness for successful HIR is 1.0 to 2.5 inches. Thus, recycling FC-5 requires blending it with the dense-graded mix beneath it. The blending ratio of the two mixes depends on the thickness of each layer. The gradation of the recycled mix was dense graded. The blending ratio can be varied by changing the recycling depth and can produce either coarse or fine mix. While the recycled mix is not open- graded and does not meet FDOT’s requirement, it provides an economical option to milling and resurfacing OGFC. That option is to recycle the old OGFC into the structural layer and resurface with a new OGFC. Current resurfacing practice entails milling the FC-5 and a portion of the structural layer underneath it, replacing the structural layer then replacing the FC-5 course. FC-5 cannot be overlaid and must be removed before overlay. The OGFC can be in-place recycled and mixed with the structural layer underneath, and then a new friction course can be placed over the recycled mix. This can save money as it eliminates the need to mill and replace the top structural layer under the FC-5. Raising the road grade by 0.75 inch, the thickness of the new FC-5 layer, while increasing the section’s structural number, remains an issue in this approach. This may be acceptable if there are no limitations on raising the road elevation in the selected project. Among the interesting findings is the increased amount of fines in the mix compared to construction gradation. Over time, the voids in the mix get filled with dirt and dust. Water flow brings fines into the mix and as the water evaporates, it leaves the fines in the voids, reducing the drainage capacity and resulting in a finer mix.

This paper was sponsored by TRB committee AFD70 Pavement Rehabilitation.

01470560

13-0924
13-0924

English

14p

2013

Transportation Research Board 92nd Annual Meeting

Digital/other

Figures; Photos; References; Tables

Friction course; Hot in-place recycling; Open graded aggregates

Florida

Highways; Pavements; I22: Design of Pavements, Railways and Guideways

Transportation Research Board Annual Meeting 2013 Paper #13-0924

TRIS, TRB, ATRI

Feb 5 2013 12:17PM