The new World Trade Center in New York City looks like a gleaming tower of mirrored glass or shiny metal, depending on the light. In spite of that, a “green” kind of concrete was used to conform to Port Authority codes in New York. Many recycled materials were used, reducing the use of Portland cement by 71%. Portland cement is still holding up the Hoover Dam and the Panama Canal among many other structures, so there is no question about its worth.
Since the World Trade tower is 1776 feet tall, it took 38,000 cubic yards of this cement to shore up the first 40 floors. BASF was part of the project, and this company estimated that more than 25 million kilowatt hours would be saved throughout the construction process. BASF also predicted a reduction in greenhouse gases and the use of fossil fuels. Less water usage was needed, and less solid waste was produced as well.
This kind of monster-sized construction project happens every few years on a global basis, but concrete is essential for success to this day. Something the Egyptians used 5,000 years ago is still the go-to material for all sizes of homes and commercial buildings. As we know, Greek ruins, at a mere 2500 years of age, still stand because of their concrete bases.
Concrete continues to change with new ideas, but its strength and durability remain as highly valued building components. Fiber is used to reinforce concrete by reducing cracking and shrinking if liquid seeps in. Fibers also reduce how permeable the concrete is. Resistance to shattering and abrasion is better when fibers are mixed into the concrete.
Ancient civilizations used horsehair and straw in mixing concrete. Later on, in the early 1900s, asbestos was used as fiber until outlawed for its toxicity. Steel, glass and polypropylene fibers are used now to increase tensile strength with their elasticity.
Spalling occurs when a big enough impact hits a structure and the concrete flakes off or small pieces come off the surface. Fibers help prevent this as well.
Fibers help reduce problems from the freeze-thaw cycle that takes a toll on concrete. They also increase structural strength, reducing the amount of steel that is needed in most concrete constructs. Fiber is used in concrete for small frames like countertops and decorative dishes, too. Countertops might take a beating in some homes, so increasing elasticity and structural strength is a good idea.
Some buildings have no steel rebar in their concrete walls. A composite concrete and steel structuring is used with foam insulation, water and a vapor barrier to erect horizontal walls. Panels are involved, too, and door and window casings can be let into the wall. Different types of insulation and new ways to use them improve the performance of concrete without steel frames.
One kind of concrete roof tiles literally eats smog. The chemical reaction residue that occurs from the materials gets washed away with the rain. This has existed for just a very few years, so there are no long term observations on durability. It is something to watch as time goes by.
These new products and procedures are not used widely, and many have not seen a decade of history yet. Only time will show the quality and strength of such potential improvements. Let your contractor advise you on tried and true materials and construction on your next project.
If buildings made from old concrete have been standing for 2500 years, there is nothing to worry about with the concrete of today. It lasts through storms, earthquakes, heat and cold. Concrete dams hold back millions of gallons of water after a century of use. Keep calm and concrete on.