Landscape Architect Articles

LASN PMBR News June 200806-02-08 | News

What Does It Weigh, or, Just How Dense Is It?

What weighs more, a cubic foot of concrete or a cubic foot of sand? Those and other weighty subjects herein.

The weight of various materials may surprise you. A cubic meter of water, for instance, weighs one metric ton (1,000 kg), or 2,205 lbs. Perhaps that’s a little too big to picture in your mind’s eye. Let’s imagine instead one cubic foot. A cubic foot of “pure” water weighs in at 62.43 lbs. A cubic foot of salt water, as you would expect, is heavier at 64.30 lbs. A cubic foot of ice weighs only 56.19 lbs., in case you’re still wondered why ice floats in your Coke.

A cubic foot of gold, now there’s a mental picture, would require a forklift to load into your truck bed as you make your get-away. It weighs 1,204.86 lbs. (Editor’s aside: One Troy Landwehr has carved a statue of liberty from a 1,200 pound block of cheddar cheese! We’ll go with the gold, instead. We didn’t bother, but you can see said sculpture on YouTube.)

You probably think of concrete as heavy. A cubic foot of concrete weighs 143.58 lbs, but a cubic foot of chalk or china weighs the same, and a cubic foot of sand weighs more (156.07 lbs.). A cubic foot of solid porphyry is 159 pounds. A cubic foot of fired clay brick? It weighs 150 lbs., but common red brick only 120 lbs. A cubic foot of Portland cement is only 94 pounds.

How about aluminum? Fairly light, huh? A cubic foot of solid aluminum weighs 168.56 lbs, about 25 pounds more than the cf of concrete. However, if you pulverized the aluminum, a cubic foot would weigh only 47 lbs.

Second aside: With our thoughts often today on gasoline prices, do you think a cubic foot of gas weighs more or less than a cf of water? Gas is heavy on the pocketbook, but lighter than water—weighing 45.57 lbs. FYI a cubic foot of gas equals 7.48 gallons. Next time a Prius owner asks what kind of mileage you get, say, “Oh, about 164 miles … per cubic foot.” (Translation: 22 miles to the gallon, highway miles.)

Sources: Firefly’s World of Facts and www.reade.com

Going Green with Pervious Concrete

ABOVE and BELOW: Pervious concrete recharges groundwater, resulting in zero discharge of polluted runoff into waterways, lessening of urban flooding, improved health of adjacent trees, on-site bioremediation of pollutants, and a reduction or elimination of the need for storm drain infrastructure.

Manhattan Beach, Calif. has taken a significant step toward protecting the earth’s resources by installing pervious concrete in nine city parking lots. Pervious concrete pavement is a permeable, porous material that is often said to resemble a rice cake. Pervious pavements help improve ocean water quality by allowing storm and nuisance water to infiltrate into the ground, decreasing the amount of runoff carrying pollutants.

The Manhattan Beach pervious parking lot project was made possible by a $900,000 competitive grant awarded to the city from the Calif. Water Resources Control Board. Pervious concrete is not a new material. It was originally used 100 years ago in Europe as structural insulation in buildings. It has been successfully used as a paving material in Europe for the past 80 years and in the American Southeast for the past 20 plus years.

“Unlike conventional concrete, you can’t do slump or compact tests with pervious, so it’s a little harder to predict,” explains Ish Medrano, engineering technician for Manhattan Beach. “Although pervious concrete has been used in many other cities, it’s our first time using the material, so there is a bit of a learning curve.”

One of the challenges faced by the Manhattan Beach team over the course of construction was the tighter tolerances required by pervious concrete as compared to traditional concrete. “Pervious concrete needs to be placed, covered and cured more quickly,” says Medrano, “We worked with the police and fire departments to close off the road so the trucks would be able to get here on time. We timed the trucks so they came just when we needed them. And we used a conveyer belt to pour the concrete so it was in constant motion.”

Medrano adds, “Another example of something we hadn’t figured on is that after the pervious concrete has dried, it takes two coats of paint to draw the street markings, where usually it takes one. This is because of the irregular texture of the cured pervious concrete. Little things like this that we’re learning will help us know how to approach the next pervious project, and sharing our experiences with other contractors, owners, and municipalities who embark on pervious concrete projects can be helpful to them.”

PCA Sees Double Digit Decrease in Cement Use

The Portland Cement Association predicts an 11 percent decrease in cement consumption for 2008, followed by an additional 5.5 percent in 2009. PCA predicts total cement consumption this year at 101.7 million metric tons. (A metric ton=2,205 lbs.)

The Portland Cement Association (PCA), as opposed to other veritable PCAs—Porsche Club of America, Professional Cricketers’ Association, Philippine Coconut Authority (humor never hurts), expects an 11 percent decrease in cement consumption for 2008.

The Florida market is instructional. The sunshine state’s cement consumption during 2003-2005 was exaggerated by the past housing boom and mortgage lending excesses and the cement numbers are now correcting. PCA expects housing construction in Florida to continue to decline through 2008 and 2009. PCA believes Florida’s economy has already entered a recession or soon will and that the housing and general economic slowdown will spread to nonresidential and public construction this year and next and adversely affect cement consumption.

PCA expects cement capacity in Florida to increase by 3.9 million metric tons by 2010.