Archive for March, 2005

Concrete Trucks

March 16th, 2005 by dstmartin

Listen to the episode

We see these noisy trucks everywhere – ready mix concrete. Today, on Engineering Works!

Concrete is one of the handiest construction materials there is. It’s been around since the Romans. Engineers design and build streets, highways and bridges out of concrete; high-rise office buildings; dams. You can even build your house out of concrete. Take that, big bad wolf.

About three-quarters of all the concrete we use is ready mix concrete. That means it’s mixed one place but used somewhere else. It’s hard to find room for a concrete plant and its mountains of sand and gravel just anywhere. This is where the ready mix truck comes in. Ready-mix trucks haul about 340 million cubic yards of concrete – every year. That’s enough to build 78 Hoover Dams – every year.

The earliest version of a ready mix concrete truck was pulled by a horse. In 1909. Paddles connected to the cart’s wheels kept the concrete stirred up. In 1916, a contractor in Ohio came up with the first motorized concrete mover. By the 1940s, heavier trucks and stronger engines brought ready mix trucks to about what we see on the road today.

And just in case you were wondering why the big drum on the back of ready mix trucks turns around while the truck is going down the street – It keeps the cement, gravel and water inside from separating before the truck delivers the load.

Our load is just about mixed. We’re outta here.



March 2nd, 2005 by dstmartin

Listen to the episode

It’s getting easier for people who have lost legs to get around. We’ll see how, today on Engineering Works!

If you read the same stories we did when we were children, you remember what happened to pirates that lost a leg. They walked around on wooden peg legs — sometimes with a funny-looking crutch.

People who lose legs to accidents or disease these days don’t have to depend on wooden legs. Replacement legs, or prostheses, are getting better all the time. Some are hard to tell from natural legs. Some use hydraulic or pneumatic cylinders to control the way they move. In fact, biomedical engineers are designing prostheses that let the people who wear them run or do other sports.

Let’s look at knees. There are more than a hundred different knee designs in use today. Think about it. An older person who doesn’t get around much needs a knee that’s different from a 25-year-old who runs marathons. Yes, people do run marathons with replacement legs.

Engineers are working on knees that are controlled by microprocessors. They’ll allow the person wearing them to react more quickly – like catching yourself when you stumble. Designers are even looking to the animal kingdom for design ideas. The lower part of a replacement leg used by a young woman who competes in triathlons is flexible and modeled after the rear leg of a cheetah.

It’s time to catch the winners at the finish line. See you later.

Photo: Athlete Marlon Shirley wearing the Ossur Flex-Foot.



March 2nd, 2005 by dstmartin

Listen to the episode

Venice has a problem. We’ll look into what engineers are doing to help, today on Engineering Works!

The beautiful piazzas and famous canals of Venice are in trouble. They’ve got more water than they know what to do with. The thousand-year-old city is sinking into its famous lagoon, a few inches at a time. The water level is nine inches higher than it was a hundred years ago, 40 inches higher than 250 years ago.

The high water damages brick walls never intended to be in the water. There’s a lot of salt from the Adriatic Sea, too. Between the water and the salt, a lot of the city’s beautiful historic buildings are rotting.

A team of Italian engineers is working on a gigantic government-funded construction project they say will save Venice from the rising water. At its heart is a high-tech system of 300-ton concrete barriers that will be raised and lowered to protect the city from damaging tidal surges, plus thousands of steel poles and other barriers on the floor of the lagoon to slow down the water.

They also plan to re-establish vanished wetlands and reinforce damaged foundations in the city itself. Altogether, the project will cost more than four billion dollars and take seven years to complete.

Not everyone thinks it’s a good idea, or that it will help. But the engineers think it will. And it’s better than letting the city sink, they say.
We say, that’s it for this time. See you next week.