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New building codes and rising insurance costs are triggering a drive to develop new materials and structures that
are more resistant to hurricanes, as well as other natural calamities such as earthquakes.
One of the more exciting developments is new bendable concrete in which aggregate is replaced with a network of finely engineered
and coated polymer fibers. The new engineered concrete under development at the University of Michigan
is 500 times more resistant to cracking and 40% lighter than regular concrete. The new concrete will
redistribute loads in a manner very similar to metal. The synergistic working of the materials provides
the key to success of the engineered structure. When an initial defect grows into a crack due to a large
amount of load, the crack will grow in a very controlled manner. The crack will be very much less than the
dimension of a human hair or less than 100 microns. The load is carried across that crack through the bridging
fibers. These fibers, in turn, carry the load back into other parts of the composite.
Specialty polymer fibers that comprise about 2% of the mixture's volume are critical in providing the enhanced performance.
The micro scale fibers in effect replace stone aggregate and act as ligaments that allow the concrete to flex.
The research team is focused primarily on three types of polymers for use as fibers: polyvinyl alcohol (PVA),
high-modulus polyethylene and high-strength polypropylene. The key to the ductility of the new concrete composite
is a coating on the plastic fibers that allows movement under stress. The fibers are mixed with sand and concrete
using conventional equipment, making them isotropic or exhibiting equal strength in all directions, as is the case
with metal. The fibers can be aligned if the design requires it to. The composite material can be cast, sprayed
like foam or even extruded like a pipe. As a result, the emphasis of the University of Michigan material is
protection against natural calamities.
Another flexible concrete - Ductal, under development in France, has been recently commercialized.
The material was developed by researchers at Lafarge and its partners, Bouygues and Rhodia. It aims at
reducing materials required, speed construction and reduce labor and maintenance. Ductal has approximately
twice the strength of ECC, while ECC has approximately 20 times the tensile ductility of Ductal. Relatively
speaking, Ductal is stronger than ECC but more brittle. Because of the high ductility of ECC, it has a much
higher energy-absorption capability for impact resistance.
Structural engineers are using the Engineered Cement Composites as cores of buildings in Japan as protection
against earthquakes. ECC also saves costs because less material is used in the design.
The University of Alabama has developed new material combinations that could provide protection in hurricane-force winds.
Improved building materials have the potential to reduce life and property losses.
National Science Foundation has a project to create fiber-reinforced polymer composites that form a structural
insulated panel (SIP). The new panels would replace plywood or similar face-sheet materials that use moulded
expanded polystyrene as the core material, which have poor resistance against wind-borne debris. The panels
survived a test without harm in which the equivalent of a 15-ft piece of wood traveling at 20000 Km/hr hit the
less-than-12 mm thick SIP. These panels have better penetration resistance against wind-borne missiles during
weather events like hurricanes and tornadoes. However, they are also heavy and foster mould growth.
Scientists envision use of natural fiber-reinforced composites of jute, sisal and kenaf in the reinforced
panels. Meanwhile, major plastics' producers have several solutions on the market that could ease wind and
water damage right now.
The Home Depot in USA & Sabic IP are jointly marketing a hurricane protection system in southern Florida.
The installed system, which includes track mounting, is said to be more than four times stronger than 12 mm
plywood sheets often used to protect windows from wind-borne projectiles. Plywood can split and crack and
open up little holes. The UV-coated, corrugated sheets are more than 250 times more impact resistance than glass.
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