Strange But True

Does White Cement Glow in the Dark?
Technically, no. White Cement does not "glow" in the dark. But what it does do is MAKE CONCRETE MUCH MORE REFLECTIVE . This means that light bounces off of it and makes it highly visible. Why is this important? There are many reasons. SAFETY, for example! Pavement and highway dividers made with white cement highly reflect the headlights of automobiles. This improves visibility for drivers in all types of conditions and situations. Another benefit of white cement reflectivity is energy conservation. Darker colors absorb light and heat from the sun. Lighter colors reflect it. Simply put, that means that if a building has reflective white cement for roofing, the cost of keeping that building cooler would decrease. On a larger scale, imagine the difference this makes in an entire town! Dark asphalt pavement absorbs 95% of the sunlight that hits it and retains that heat energy long after dark. Using lighter color pavements like white cement can reduce that asphalt furnace effect.

For in-depth information of the reflectivity of white cement and report/presentation materials, download the following documents:

1. Albedo: A Measure of Pavement Surface Reflectance
2. Solar Albedo of Concrete and Select Other Materials
3. Solar Reflectance of Cool Paving Materials: Effects of Composition and Exposure on the Solar Reflectance of Portland Cement Concrete
4. Reflective White Roofing Saves Energy, Money (graph)
5. Solar & Luminous Reflectivity (collection of graphs/images)
6. The Asphalt Furnace

The Concrete in the Hoover Dam Isn't Fully Cured!
While concrete usually gains most of the total strength within the first month or two of curing, the Hoover Dam continues to gain. The reason is that the Hoover Dam has significant moisture present to continue the cement hydration process. It is true that all concrete will continue to gain strength if some moisture is present, but the rate of gain is not significant.

Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.*

Design requirements for strength of conrete differ and thus the concrete mixes used for projects will differ. There is an old rule called the 28-day strength rule. It indicates that a project should typically reach total expected design strength by 28 days.

For more information on The Hoover Dam (including history, teachers guide's and library videos):

PBS: The American Experience | Hoover Dam
http://www.pbs.org/wgbh/amex/hoover/

US Department of the Interior: Reclamation - Lower Colorado River
http://www.usbr.gov/lc/hooverdam/

For more information on the cement hydration process:
*The Portland Cement Association (PCA)
http://www.cement.org

The Concrete Rose: A Blossoming Legacy
This concrete rose was first given to the Lehigh Cement Company by Dr. Peter Schuhmacher, the then Chairman of the Board of HeidelbergCement AG. The "trademark" gift of the long-stemmed red rose created with red concrete was to mark the occasion of our first Lehigh Cement Company Board of Directors meeting in our new headquarters building in Allentown on October 21, 1992. He presented us with another concrete rose to mark the occasion of the 100th anniversary of the Lehigh Cement Company on November 26, 1997. This second rose is one of the keepsakes preserved in a time capsule secure at the corporate headquarters. The rose represents the promise of kinship with HeidelbergCement AG and their best wishes for the future of the company. Most people are familiar with the strength of concrete, but this artistic form serves also as an ambassador for the design versatility of the medium.

PICTURE CAPTION: The concrete rose pictured above is displayed in a thick Lucite(R) case in the Board Room at the corporate headquarters in Allentown, PA.