The Delaware Department of Transportation in Sussex County experimented using CIR equipment to FDR Portland cement stabilize a roadway.
Full-Depth Reclamations using Cold In-Place Recycling can correct delinquent cross sections, increase the load-bearing strength of the base material, and utilize 100% of the existing materials at the required depth.
One of the advantages of CIR during FDR is the material is laid by a paver and not a motor grader.
E.J. Breneman believes in pavement preservation. One new process the company is trying is Full-Depth Reclamations using Cold In-Place asphalt equipment and technologies.
This process, says the company, can address an entire pavement section - correcting delinquent cross sections, increasing the load-bearing strength of the base material, and utilizing 100% of the existing materials at the required depth.
Following are four municipalities which have successfully used this method for limited depth Full Depth Reclamation (FDR) projects.
Limerick Township used the process in an industrial park that had been scheduled for Cold In-Place Asphalt Recycling. The park was relatively new; it was curbed with a few sanitary sewer manholes and catch basins.
The industrial park was growing in size, and the increased construction activity was coursing premature failure. The industrial park had an asphalt depth of four inches on top of a thin aggregate base. There where signs of some isolated soft areas and the municipality new some other areas may become evident after the CIR process had concluded.
Unfortunately shortly after starting the CIR process the pavement under compaction became wavy and distorted. It was determined that CIR could not correct the pavement problems and that FDR Portland cement was the alternative. To move all the CIR equipment out and haul the FDR equipment in was going to be a huge mobilization cost.
It was decided by both the municipality and the contractor that they would try to Portland cement stabilize the base using the CIR equipment.
The weight of the mill did not seem to disrupt the pavement during the earlier process (CIR); it seemed to happen only when under compaction with vibratory compactors and large pneumatic rollers.
The CIR equipment train had no difficulty in cutting the eight inches or mixing the Portland cement into the milled material. The mixed Portland cement was totally hydrated, one reason for this, the material stays in the cutting head for a long period of time and is continuously rotated and mixed around the drum unlike a reclaimer that mixes the material once and expels it into the cut.
A truck-mounted cement spreader laid the Portland cement at 35 pounds per square yard. A mix design was not completed on this project because of the late time of year and the necessity to complete the project so as an asphalt overlay could be applied while temperatures stayed reasonable. We recommend a mix design is formulated before any type of CIR or FDR project commences.
The project in Limerick was successful no failures have occurred and the park has grown over the past four years. The equivalent to 19mm Super Pave hot mix asphalt was applied on top of the FDR at a depth of 2.5 inches.
In 2008, the Delaware Department of Transportation in Sussex County had been Cold In-Place Asphalt Recycling several roadways under contract to George & Lynch Inc. of Dover, DE.
During the construction of SR 20 near Dagsboro, DE the department had an adjacent roadway that was scheduled to be Full Depth Reclaimed under contract to E.J. Breneman.
Since this FDR project was so far south and also because the CIR equipment was basically on-site and no mobilization would be required, the department under took their own experiment using the CIR equipment to FDR Portland cement stabilize the roadway.
The depth once again was eight inches using around 40 pounds of Portland cement. Wilguse Cemetery Road runs between SR 20 and 54A.
Wilgus Cemetery is a two-lane rural roadway with residential and agricultural traffic and is used as a short cut between the two state roadways. The roadway has several layers of oil and chip on top of a small layer of hot mix asphalt. The sub-base was primary sand and gravel material.
A tractor pulled a Stolfus spreader that laid the Portland cement in front of the CIR train that comprised of a water tanker that is pushed by the down-cutting milling machine in this case a CAT 750C. A down-cut machine was used to control the size of the particles that were being milled.
The cutting mandrel down-cuts on top of the asphalt, the milling machine chips at the surface with pressure being applied from above, the forward speed of the mill along with the down-cutting action produces a modified sizing of the materials.
If an up-cut mill would be used the up-cutting action would course over sizing of the material and a secondary crusher would be needed to control sizing.
Because all the milled material including the Portland cement is mixed in an enclosed chamber the mixing resembles that of a cement mixer. Hydration is complete with no dry cement being left behind. The water is metered into the head and the continuous auger built into the cutting mandrill makes sure the mix is thoroughly mixed and hydrated.
The material is then placed onto the first stage conveyor, transferred onto the second stage conveyor and placed directly into the Caterpillar 1050B bituminous paver.
Once the material is in the hopper of the paver it is placed back onto the roadway through the paver screed. The paver screed can adjust the full depth reclaimed material to whatever the depth and scope of the new material profile will be.
Wilgus Cemetery was overlaid using a 12.5mm Super Pave Asphalt at a depth of two inches.
In Plymouth Township, PA during the 2010 construction season, two roadways have been re-constructed using FDR Train method.
Brook Road had severe distress. This two-lane industrial roadway serviced several steel recycling centers as well as a major "Trash to Stream Plant."
During the FDR process the roadway also took traffic from an adjacent roadway that had been closed to traffic while a new bridge was being built. Brook Road had an estimated traffic count during construction of about 12,000 vehicles. About 60% of which was truck traffic, steel carrying and tractor-trailers and tri-axel refuge trucks.
Brook Road also has a large shopping mall and connects the very heavy used Ridge Pike and Philadelphia by-pass I-495 to the area around Plymouth and Conshohocken.
Brook Road needed to be constructed quickly, cured as fast as possible, prime coated and opened to traffic that same day. With the in-line train part of the issue was resolved, traffic could at least be kept moving although only one lane at a time.
While traffic was stopped in the traffic pattern it very quickly became a half mile back-up. The other major problem was turning tractor-trailers who needed to enter and exit from the recycling plants along the roadway. This meant turning onto the newly placed FDR base.
Breneman crews in most cases kept the trucks from turning until at least the first compaction effort had been accomplished. The trucks need to use both lanes when exiting these plants, driveways into and out of the plants are also very narrow.
The only other issue was a concrete culvert that had been built and was now discontinued. This obstacle was at the north end of the project and was at grade so it had to be milled down to the correct profile to allow for the new hot mix asphalt overlay.
West Norriton Township
West Norriton Township, Montgomery County, PA had two major industrial parks that had little maintenance over the past 25 years.
The pavement was composed of two to three inches of very oxidized and very heavily cracked, alligator and potholed hot mix asphalt on top of a failed pozzolan base course. Pozzolan base course was an engineered mixture of aggregate, fly ash and lime and if constructed with the proper moisture content, became a very stabile sub-base material.
The industrial parks required in-line operations due to the amount of truck traffic, employees reporting for work shifts, and a very large child care facility.
If windrowed material had been allowed, there would have been major traffic issues due to personal vehicles not being able to traverse the windrowed material. The CIR equipment was ideal in this situation.
In recent years, a new shopping mall and a series of strip-malls and hotels had sprung up around the industrial mall. A major retirement community had also been constructed in a neighboring township and within a few thousand feet of the industrial mall. The intersection, which was also part of the project, included one entrance into the new mall, the intersection also comprised of 14 lanes of traffic that had to be controlled through four different directions.
The industrial mall was curbed with no catch-basins. Water was controlled by running its natural course and wherever the undulating pavement allowed it to run.
Stormwater eventually ran to the lower end of the four major roadways that made up the industrial mall Boulevard of the Generals, and exited through curb cuts into natural swales.
Breneman used a Wirtgen WR 2500S to excavate along all curb lines at a distance of four feet out from the curb face to gain valuable curb reveal. Sanitary sewer manholes where removed and steel plates placed over the holes before the in-place FDR could take place.
The problem with an 8-inch cut around utilities is the bituminous paver that is returning the mixed material to perfect lines and grades cannot pass over the high monuments.
All utilities in West Norriton Township are required to be raised or lowered using brick and mortar or concrete risers; no steel riser rings are aloud in the municipality due to snow plows hitting the rims and damaging the plow or steel covers. The entire road system has a width of 32 feet; the crown is a central crown with no super-elevations on the curves.
One of the companies located within the industrial mall - an over the road carrier that used the mall 24 hours a day - could not change their scheduled arrival and departure times to co-inside with construction time.
The Boulevard of the Generals has only one entrance and one exit both being the same roadway, keeping traffic moving became a problem. It was determined that the Boulevard of the Generals should be constructed at night while Foundry and Industrial Road had two exits and could be constructed during day light hours.
The CIR Train using Portland cement to FDR the roadways allows for only one lane to be disrupted during the operation. The dry Portland is placed in front of the operation and followed by the train shortly behind.
Once milled and sized the Portland cement and pavement are mixed with a predetermined amount of water that is controlled by an on-board computer. Once laid in-place a Geo-technical engineer checks for moisture and after compaction checks density. Samples are taken of the un-disturbed material before FDR and after the process more samples of the mixed material are taken.
The mixed samples are used to make plugs in the laboratory to verify that the mix and strengths of the materials is in-line with the project specifications.
The greatest advantage of using this method is the material is laid by a paver. There is no motor grader moving materials from side to side and coursing segregation of the mat in some cases. There are no low areas or high areas that are normally coursed by operator error.
There are draw backs to using this operation; the depth of cut due to the type of equipment is limited. Eight inches compacted is normally the thickness that the paver can accomplish.
Greater depths and the paver has a significant trouble handling the material both in the hopper and through the screed. In metropolitan areas to many utilities are a disadvantage with the CIR equipment that normally only recycles three to four inches, once it goes to eight inches the paver once again has great difficulty traversing water and gas valves as well as sanitary and storm sewers.
Once the FDR is constructed, a prime coat is placed over the entire surface to slow the cure down and also to protect against airborne dust that is a product common with the drying of cement treated bases in the FDR process.
In West Norriton Township a three inch 19mm Super Pave wearing course was applied by Glasgow Inc.
E.J. Breneman offers these words of advice when using the Full-Depth Reclamations with Cold In-Place asphalt equipment:
- Critical to the success of this process is the preliminary testing to establish design criteria for gradation, residual asphalt content and the use of additives.
- A certified geo-technical engineering company that is independent from the construction company should complete the mix design, do all on site testing and establish a final report for the municipality.
- This reconstruction process requires a wearing surface that is a thickness determined by an analysis of traffic volumes and loading.
- Some Departments of Transportation have experimented using the Cold In-Place asphalt recycling train to recycle up to depths of 8 inches of asphalt and sub-base materials using Portland cement.