Doing your homework pays off. TxDOT engineers in Hebbronville proved that adage recently by saving taxpayers nearly a half million dollars through research. The opportunity came when TxDOT Hebbronville area office engineers explored non-conventional options for rehabilitating Farm-to-Market Road 1017 in Jim Hogg County.

TxDOT let two $6-million dollar contracts for the road, which sees increasingly heavy traffic as an unofficial truck route from Laredo to the Rio Grande Valley, according to Albert Quintanilla, TxDOT Hebbronville area engineer. Quintanilla and his staff began considering ways to build a road that could handle the load.

The conventional practice of using lime to stabilize the subgrade "would not provide long-term cohesive strength," says Albert Quintanilla. So TxDOT looked to cement. Lab testing performed on sub-grade samples determined that a two percent cement mixture provided the desired compressive strength that is usually obtained in 3 percent lime. "The simple change from lime to cement allowed us to decrease the amount of stabilization additive needed on this project, which provided a savings of $470,300," says Quintanilla.

With a total project cost of $12.2 million, a cost savings of four percent may not appear as much, says Quintanilla, but it's "a significant amount of money." And the office was able to "obtain higher subgrade and flex base strengths to hopefully extend the life of the pavement," he added.

Choosing to recycle the existing roadbed materials also helped stretch highway funds and added about 15 additional miles to the total project. The decision to recycle the road allowed engineers to rehabilitate 38 miles of roadway with the available highway funds as opposed to 23 miles using conventional remove/replace construction, figures Quintanilla. "That process would have involved hauling out tons of sandy soil subgrades and existing roadbed material, and hauling in lime-stabilized clay materials," says Quintanilla. "The use of cement lets us stabilize the materials we have in there right now. We don't have to haul in asphalt stabilized base and don't have to haul out existing materials," he says. Additionally, cement binds the sandy soils and provides additional strength.

The existing road, consisting of 2 inches of asphalt and 8 inches of base, provided an ideal candidate for recycling. But engineers questioned how much cement to specify. "The initial assumption was to go with higher concentrations of cement around the 5 percent range," says Quintanilla. But laboratory tests found that lower factors would work. In the field, engineers required 2-percent cement by weight of dry material for subgrade and flexible base stabilization. The new roadway calls for a 1.5-inch thick asphalt concrete surface placed on an 8-inch cement stabilized flexible base and a 12-inch cement stabilized subgrade. Quintanilla says he sees a growing trend to use cement, adding that "every material has its use. It comes down to what's the most effective material." In this case, cement came out miles ahead.