City of Stephenville, Tex., officials have at least a dozen reasons to endorse using cement to rehabilitate their streets. None of Stephenville’s cement-recycled streets have had problems or failed in the past 12 years.
“They’ve not done any re-work on any of the bases that we’ve (cement) stabilized,” said Sanford LaHue Jr., consulting engineer, Schrickel, Rollins and Associates, Arlington. Stephenville used a process called full-depth reclamation with cement, or FDR, to recycle the streets. FDR recycles the materials from deteriorated asphalt pavements and, with the addition of cement, creates a new stabilized base.
LaHue designed the city’s first recycled streets in 1992. The street reconstruction program initially included visual evaluations to determine which streets would require FDR. LaHue recommended recycling and a new asphalt surface course when the street had experienced base failure. If there was only minor cracking, workers placed a standard asphalt overlay on the street. This evaluation and selection procedure allowed the city to rehabilitate as many streets as possible. But over the years, LaHue observed serious deterioration in the streets with overlays, while the recycled streets held firm. He began to specify FDR with cement for all of the streets.
“From 2000 on, we stopped straight overlays and just did cement recycling,” said LaHue.
“Recycling with cement is our preferred option,” said Drew Wells, Stephenville’s director of community services. Surface treatments have proven “very unpredictable and unreliable. We’ve had some differing results,” he added.
But all the cement-recycled streets have produced a “very favorable outcome,” said Wells. “It has been the best process for us.”
The city begins FDR by taking material samples from streets targeted for rehabilitation to determine the right amount of cement to use. Streets with good base and surface materials require less cement than those with marginal materials. City specifications require contractors to pulverize the existing asphalt surface and base 6 in. deep and then incorporate, through additional mixing, 25 lb of cement per sq yd or 5% cement by volume of dry weight of the material.
After adding the proper amount of water to hydrate the blended cement material, the streets are reshaped, compacted and bladed to final elevation. The newly bonded base layer is cured with moisture before applying a prime coat. A 1.5-in. asphalt surface finishes the street.
Because the city is using existing roadway materials, there is no need to import new aggregate base. This eliminates the need to haul the existing roadbed material off to landfills or to bring in new base materials.
“The process of adding cement naturally yields some additional resultant material. On most of the streets this material is used to restore the crown on the streets. However, if excessive crown is a problem, the excess material will have to be hauled off,” said LaHue. The profile of the street remains basically the same. “You’re not overlaying the gutters and you’re not changing the drainage,” he added. Most street departments welcome this excess material for their stockpiles.
Unlike other road construction processes, the cost of FDR with cement has not risen dramatically over the years. City of Stephenville bid tabulations from 1992 show that contractors charged $2.60 per sq yd. In 2003, the price rose only 80 cents to $3.40 per sq yd, according to records provided by LaHue.
