The figure is a scanning electron micrograph (SEM) showing the failure mechanisms in cementitious nano admixture reinforced concrete containing carbon nanotubes. The nanomaterials give the material a smart structure with inherent sensor capabilities whereby its structural health can be monitored.
In U.S. Patent 7,666,327, Oceanit Laboratories, Inc. (Honolulu, HI) reveals a high performance multifunctional cementitious nanocomposite material. The material is made by adding a nano admixture to the water used in a conventional cementitious material manufacturing process. The cement concrete-carbon nanotube structure displays high tensile and flexural strengths and fracture toughness, low electrical resistivity, and high thermal conductivity and electromagnetic interference shielding effectiveness.
According to inventor Vinod P. Veedu, a “revolutionary but simple method” is used for the effective and uniform dispersion of nanomaterials in water, up to single tube level. The nanomaterial suspension (nano admixture) remains stable for more than 3 months and does not experience significant degradation of physical or chemical characteristics. This approach is of paramount importance in the use of nanomaterials in a variety of areas, including structural materials, paints, coatings, adhesives, electronics and optics.
The nano admixture is made by dispersing nanomaterials in a solvent and sonicating the mixture, adding a hydrophilic emulsifier, thickener, additive or cellulose derived compound to hot water, where it separates and expands, cooling the water, causing the compound to dissolve, and then adding the solvent and nanomaterial mixture to the water and mechanically mixing. The contact between the nanomaterials and the surrounding matrix changes with applied stress, affecting the volume electrical response of the finished nanocomposite material. By measuring the electrical resistance of the material, its structural health, as well as the stress applied to it, can be monitored. A bridge made with the material is monitored for structural integrity and for the weight, speed, and location of traffic over the bridge.
Concrete is an essential material for building all types of infrastructure including buildings, roads, dams, etc. As for brittle materials in general, concrete is strong under compression and weak under tension or flexure and has the tendency to crack and has poor thermal conductivity. The exothermic reaction in the formation of concrete and the poor thermal conductivity of the materials in concrete pose a problem for large pours such as dams, where coolant systems must be built into the slabs for proper curing.
The nanoconcrete manufacturing method uses a process to create nano admixtures that transform traditional cementitious composite material, such as concrete, into multifunctional smart structural material (nanoconcrete) without adding any additional weight and without altering the manufacturing process. The process and materials are easy to scale up. Also, the nano admixture introduces ductility, durability and other multifunctionalities without sacrificing existing concrete properties.
The Nanoconcrete uses a nanomaterials based admixture for use in reinforcements and multifunctional performance of cementitious composites. The nanomaterials in the admixture may be graphitic or non-graphitic carbon materials or nanoparticles such as silicon carbide, dispersed and stabilized in water. The carbon material that is preferably used in the nanoconcrete is carbon nanotube. The carbon nanotubes used may be single walled, multiple walled, as prepared or functionalized.
The nano admixture-reinforced structural materials, such as cementitious composites, have smart materials characteristics and multifunctionalities. In contrast to other approaches, the nanoconcrete admixture does not alter the manufacturing process, is easy to incorporate in traditional concrete materials and to scale-up, and is cost effective. The newly developed nano admixture transforms traditional concrete material into multifunctional smart nanoconcrete without adding any additional weight.
This novel approach reforms traditional concrete into crack-resistant self monitoring multifunctional smart material. The addition of nanomaterials based admixture in concrete enhances mechanical properties, vibration damping capacity, air void content, permeability, steel rebar corrosion resistance, coefficient of thermal expansion, and workability. Also the nanomaterials admixture reinforced composite has improved alkali silica reaction inhibition properties.
The presence of nano-admixture in concrete will also result in significant improvements in crack resistance, thermal conductivity, and fiber dispersion.
The many advantages of Nanoconcrete include: lower environmental impact–advanced concrete will result in higher-strength, less-volume, lighter-weight structures with lower CO2 emissions; simplicity of use–builders/workers and other users will require no special training to manufacture NanoConcrete and safety–nanotubes and nanoparticles will be suspended and stabilized in a solution, mitigating safety risks for users
In the new method of making a multifunctional cementitious nanocomposite material, a prepared nano admixture comprising nanomaterials and water is provided, the prepared nano admixture is added to a measured amount of water to form nano admixture modified water, and the nano admixture modified water is used in place of ordinary water in a cementitious material manufacturing process.
As part of providing the prepared nano admixture, nanomaterials are dispersed in a solvent and the solvent with dispersed nanomaterials is sonicated. A hydrophilic emulsifier, thickener, additive or cellulose derived compound is added to hot water, separated and expanded in the water, and dissolved in the water. The solvent with dispersed nanomaterials is added to the water with dispersed hydrophilic emulsifier, thickener, additive or cellulose derived compound, and the combination of solvent with dispersed nanomaterials and water with dispersed hydrophilic emulsifier, thickener, additive or cellulose derived compound is mechanically stirred.
The hydrophilic emulsifier, thickener, additive or cellulose derived compound may be methylcellulose. The nano materials remain suspended and stabilized in the nano admixture for over three months, posing no significant safety risk to workers handling the admixture.
Cement and aggregates are provided and mixed together. The nano admixture modified water is mixed with the mixture of cement and aggregates to form a concrete. The concrete is placed in a mold, compacted, and cured. Chemical additives or fibers may be provided, and may be mixed with and at the same time as the cement and aggregates. Silica fume may be used as a dispersing or densifying agent.
The cementitious nanocomposite exhibits improved mechanical and chemical properties without significant additional weight compared to a corresponding conventional or carbon fiber reinforced cementitious material without nanomaterials.
The material displays high tensile and flexural strengths, fracture toughness, thermal conductivity, and electromagnetic interference shielding effectiveness and low electrical resistivity compared to corresponding conventional or carbon fiber reinforced cementitious material without nanomaterials. The material exhibits significantly improved crack resistance, vibration damping capacity, permeability, air void content, steel rebar corrosion resistance, coefficient of thermal expansion, thermal conductivity, fiber dispersion, and workability compared to corresponding conventional or carbon fiber reinforced cementitious material without nanomaterials.
The material has improved alkali silica reaction inhibition properties compared to corresponding conventional or carbon fiber reinforced cementitious material without nanomaterials. The nanomaterials reduce the permeability of the material, preventing the ingress of water. The nanomaterials strengthen the interfacial transition zones in the material, acting as tiny mechanical rebar to suppress the effects of alkali silica reaction.
The sensor capabilities of the material include a change in volume electrical response depending on applied stress, whereby strain on the material can be detected by measuring its electrical resistance. Roads are paved with such a material, the material’s electrical resistance at different points is measured, and the measurements are used to determine the location, weight, and speed of traffic.
The nanomaterials may comprise carbon nanotubes and reduce pores and prevent micro-cracking by fiber-bridging across micro crack regions. The carbon nanotubes form a stitching on fracture surfaces, diverting crack energy into a matrix and inhibiting crack propagation. The negative coefficient of thermal expansion of the carbon nanotubes results in a higher thermal stability for the material.