University of Florida Research Foundation, Inc. (Gainsville, FL) earned U.S. Patent 7,786,192 a concrete additive for a reinforced concrete composite is provided. The nanomodified concrete additive results in high performance cement paste and concrete,
Inventors Bjorn Birgisson and Charles L. Beatty say the additive is an exfoliated clay having an exfoliated layered silicate plate comprising structure, and at least one of an oligomer or polymer linking at least a portion of said silicate plate comprising structure. The additive can have a dispersant between the silicate plates. The clay can include sodium or calcium montmorillonite or a phosphatic clay. The oligomer or polymer can include polyvinyl alcohol.
The primary chemistry of M-clay can be very similar to conventionally used pozzolanic materials. M-clay can exhibit a layered silicate platelet structure. The advantage of this configuration over other small particles is that the multi-layer silicate structure can be penetrated between layers by small molecules forcing the silicate platelets apart (as shown below). This process is called intercalation. If the penetrating polymer molecules are reactive species, subsequent polymerization can result in complete separation of the silicate layers (i.e. exfoliation).
As a result of exfoliation, a small mass of M-clay can result in numerous small, thin (e.g. 20-nm) platelets, with a very large surface area, that are fully separated. The resulting polymer chains tends to bond to all of these surfaces, creating a linkage effect among the silicate platelets. This bonding can also be considered as a flocculated material since one polymer chain can link several clay particles together.
Normally, the exfoliation process requires that the polymer must wet the clay for it to be able to diffuse into the gallery (i.e., the spacing between silicate sheet layers). This process can be slow, and can require mechanical mixing.
As a result of exfoliation, a small mass of M-clay can result in numerous small, thin (e.g. 20-nm) platelets, with a very large surface area, that are fully separated. The resulting polymer chains tends to bond to all of these surfaces, creating a linkage effect among the silicate platelets. This bonding can also be considered as a flocculated material since one polymer chain can link several clay particles together.
Normally, the exfoliation process requires that the polymer must wet the clay for it to be able to diffuse into the gallery (i.e., the spacing between silicate sheet layers). This process can be slow, and can require mechanical mixing.
Conventional concrete, as a construction material, suffers from a number of inherent deficiencies. The primary drawbacks relate to its lack of ductility, low tensile strength, and a tendency to undergo significant shrinkage during curing. The brittle nature of concrete has had a direct effect on the specifications and guidelines used in the design of concrete structures. Since the ultimate goal in the design of any structure is generally safety, there are a number of precautions that needed to be taken when formulating the design approaches used today. Chief among these is the avoidance of brittle failure modes.
If a structure were to fail in service, people inside that structure would be at great risk if they had insufficient warning to vacate the premises before collapse. If such a failure occurred instantaneously, as in brittle behavior, there would be no warning. Alternatively, if there was a large amount of deformation, movement and noise produced by the structure before failure (ductile), people would have time to get out. Current design codes recognize this dilemma and base their criteria around ductile failures. The question becomes how to force a brittle material (concrete) to fail in a ductile manner.
The behavior of typical concrete beam to which a uniform load is added is well known. When the load is applied, the beam deflects. This causes a shortening of the upper surface of the beam, resulting in compressive stresses in this region of the member as the material of the beam (i.e. concrete) tries to resist the change in shape. The bottom surface, on the other hand, is lengthened or stretched, resulting in an induced tensile stress as the concrete tries to resist elongation.
Concrete is relatively strong in compression but very weak in tension. If the beam were to be made entirely from concrete, it would fail at the bottom surface under a very low load, possibly even its own weight, and that failure would be very brittle in nature. Thus, something must be done to the lower portion of the beam to prevent the tensile stresses from failing the concrete.
If a structure were to fail in service, people inside that structure would be at great risk if they had insufficient warning to vacate the premises before collapse. If such a failure occurred instantaneously, as in brittle behavior, there would be no warning. Alternatively, if there was a large amount of deformation, movement and noise produced by the structure before failure (ductile), people would have time to get out. Current design codes recognize this dilemma and base their criteria around ductile failures. The question becomes how to force a brittle material (concrete) to fail in a ductile manner.
The behavior of typical concrete beam to which a uniform load is added is well known. When the load is applied, the beam deflects. This causes a shortening of the upper surface of the beam, resulting in compressive stresses in this region of the member as the material of the beam (i.e. concrete) tries to resist the change in shape. The bottom surface, on the other hand, is lengthened or stretched, resulting in an induced tensile stress as the concrete tries to resist elongation.
Concrete is relatively strong in compression but very weak in tension. If the beam were to be made entirely from concrete, it would fail at the bottom surface under a very low load, possibly even its own weight, and that failure would be very brittle in nature. Thus, something must be done to the lower portion of the beam to prevent the tensile stresses from failing the concrete.
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