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Overcoming Expansive Soils -
San Antonio finds
Cement a Useful Tool
By Jeff Hawk
 The
City of San Antonio is wielding a new tool to rebuild failing city
streets. Officials selected a 1/2-mile stretch of Saltillo Street
near downtown San Antonio as one of its first recycling projects.
"Full-depth reclamation using cement just poses a whole new
tool in our toolbox to be able to combat problems with our soils,"
says Rocky Aranda, operations manager for the city's streets and
drainage department. "Many of the city streets sit atop expansive,
clayey soils", he adds, which can wreak havoc on untreated
roadways.
The
city hired local firm Drash Consulting Engineers to design and monitor
the rehabilitation of the old street. "We drilled borings to
determine the existing materials, took samples of the subgrade and
characterized its strength, and then designed the new road according
to traffic counts given to us be the city," says Chuck Gregory,
a principal at the firm. Gregory says using cement offers two major
benefits: "It improves the strength of the base material so
you need a thinner section to carry the same number of wheel loads.
The second thing is that it helps to make the base material a lot
less susceptible to damage from water, which makes the pavement
last longer."
 With
no new materials to haul in and no disposal costs for old material,
the process offers environmental and cost savings over removing
and replacing a street, says Aranda. "Removing and replacing
is very time consuming, very inefficient, and very expensive. It
also has a negative impact on the environment when we have to properly
dispose of old material," says Aranda. "Full depth recycling
actually minimizes the need to buy virgin material," Gregory
agrees. "Instead of filling up a landfill somewhere, which
is not environmentally friendly, we're re-using materials in-place
and in the process, saving money for the city and the taxpayers."
City
crews assisted by local contractor Olmos Construction worked together
to build the project. The process entailed pulverizing the existing
granular materials and asphalt surface, mixing in a cement slurry,
and then grading and compacting the new base. A new hotmix surface
topped the street. "The construction process is very simple
and straightforward," says Gregory. And it allows the city
to quickly return the street to its residents. Says Aranda: "With
this option, we actually recycle and replace all in one day. It's
really revolutionary for the process of reconstructing streets."
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