Method of embedding photocatalytic titanium dioxide in concrete structures to reduce pollutants via photocatalytic reactions

Abstract

Methods for embedding photocatalytic titanium dioxide in concrete surfaces to reduce pollutants via photocatalytic reactions are provided herein. One method includes applying an amount of concrete treatment compound to an upper surface of the concrete, the concrete treatment compound comprising a mixture of a liquid carrier compound with a titanium dioxide (TiO₂) photocatalyst.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

by

The hydroxyl radicals in turn oxidize nitrogen oxides as follows:
NO+*OH→NO₂+H⁺
NO₂+*OH→NO₃⁻+H^+.

Other reduction effects occur with volatile organic compounds (VOC) and some other pollutants. Since TiO₂ functions as a catalyst and is not consumed in the reaction, the photocatalytic effect continues. If the TiO₂ is in place at the surface of concrete, it removes a significant quantity of NO_x and VOCs from the environment nearest their source. If TiO₂ is uniformly impregnated into the concrete to a given depth the pollution-reducing capability of the concrete will automatically and continuously self-regenerate as the surface layers are subjected to the normal wear of traffic and other environmental factors.

Other reduction effect occurs with volatile organic compounds (VOC) and some other pollutants. Since the TiO₂ functions as a catalyst and is not consumed in the reaction, the photocatalytic effect can continue. If the TiO₂ is in place at the surface of a concrete roadway or other concrete structure in close proximity to the roadway, it removes a significant quantity of NO_x and VOCs from the environment near their source. If TiO₂ is uniformly impregnated into the concrete at depth using a liquid carrier compound, the pollution-reducing capability of the concrete will automatically and continuously self-regenerate as the surface layers are subjected to the normal wear of traffic and other environmental factors.

Traditional methods of NO_x reduction (e.g., catalytic converter reduction of motor vehicle emissions) have reached a point of diminishing returns in terms of cost effectiveness, resulting in the need for new and innovative methods of pollutant reduction. A method of reducing these pollutants may be the use of photocatalytic titanium dioxide blended into concrete paving mixtures at the time of construction. This method has not seen widespread acceptance or practical implementation yet for a number of reasons.

One key disadvantage of the method described above is its limitation to usage in freshly placed concrete surfaces, reducing its economic viability for existing roadbeds that are structurally sound, which comprise a large percentage of the roadbeds and structures that would be most subject to violating the forthcoming Environmental Protection Agency (EPA) guidelines. The tremendous cost that would be created by replacing these roadbeds and structures with new concrete would be prohibitive, both in terms of dollar cost and user delays.

The present technology impregnates the concrete with TiO₂ by applying specialized proprietary penetrating liquid carriers to the surface of a concrete structure. These carriers are designed and proven to carry chemicals into concrete. The TiO₂ is blended into the liquid carriers at a proportion that will result in a uniform distribution of TiO₂ nanoparticles throughout the upper one-half (0.5) inch layer of the concrete structure, or to other depths according to road or structure design requirements. As mentioned above, the combination of liquid carrier compound and TiO₂ is referred to as a concrete treatment compound.

Examples of liquid carrier compounds that may be used for this purpose are Litho1000Ti (for existing, cured concrete) manufactured by Pavement Technology, Inc. and Lithium Cure Ti (for new concrete that is in the curing process) manufactured by Sinak Corporation.

These carrier compounds have the added benefit of sealing and hardening the concrete and filling voids in its structure to increase resistance to water damage, chloride ion penetration, de-icing salts, and freeze/thaw damage. In some embodiments, an anatase powder form of TiO₂ nanoparticles at a specific concentration is combined with the liquid carrier that will result in TiO₂ being delivered at the designed rate of application for the impregnated region. To be sure, other penetrating liquid carriers and/or forms of TiO₂, other semiconductors or inorganic pigments that are photocatalytic and alternate concentration levels, can be employed as deemed suitable.

In some embodiments the concrete treatment compound comprising the TiO₂ additive (or other photocatalytic compound) is sprayed or otherwise applied to horizontal road surfaces by a sprayer applicator with a spray bar of variable length utilizing industry standard nozzles. The application rate is controlled by a computerized flow manager, which allows the carrier compound to be precisely applied to the road surface. Once the flow rate computer has been set to the desired application rate, the application of the carrier compound is very accurate due to the computer control of the flow, regardless of travel speed variations of the sprayer. On vertical surfaces, or other surfaces inaccessible to a sprayer applicator with spray bar, the compound can be applied by hand spraying with a wand, or any other suitable means of application that maintains the required accuracy.

If conditions in a given application dictate that a horizontal concrete surface requires texturing for safety, adhesion or other reasons, abrasive media application methods will be employed prior to spray application of the liquid carrier compounds. Exemplary methods are the Skidabrader process, conventional shot blasting, diamond grinding, water blasting, and the like.

In some embodiments, if the concrete surface is damaged or the surface has an unacceptable slip coefficient (e.g., a surface texture that is likely to cause an individual to slip and fall on the surface) the surface to be treated may be textured using the aforementioned abrasive process, or repaired if necessary.

Additionally, the concrete treatment compounds of the present technology can be applied to a concrete surface without first priming the surface, which is often required for concrete treatment processes such as painting or sealing.

As mentioned above, the amount concrete treatment compound (e.g., carrier compound plus photocatalytic material) that is applied to a concrete surface should be enough to penetrate the concrete down to between a depth range of approximately an eighth of an inch to approximately a half of an inch, inclusive. Further, a concentration of photocatalytic material within the liquid carrier compound should be sufficient to achieve a desired concentration of the photocatalytic material within the concrete surface. This process of delivering concrete treatment compounds is referred to as distributive embedding.

The depth to which the concrete treatment compound should be distributively embedded may depend upon a variety of factors such as the composition and size of the aggregate used to create the concrete or the binder used to hold the aggregate together. By example, the photocatalytic material of the concrete treatment compounds may only need to penetrate up to one quarter of an inch for asphalt cement that includes an aggregate that is small and tightly packed such that it resists wear off, whereas a cement that is known to wear off quickly may require photocatalytic material to be embedded further into the concrete to account for additional wear. Other factors may include expected or average traffic or use patterns that may predict wear off rates, as well as weather information. Other factors that would be apparent to one of ordinary skill in the art are also likewise contemplated for use.

Thus, in some instances, it is required to calculate an amount of concrete treatment compound of the present technology, which will be required to penetrate the concrete surface down to a sufficient depth relative to an upper surface of the concrete surface. The examples of factors that affect wear off may be used as a part of this calculation. For example, if it is determined that based upon concrete composition and traffic pattern that an average wear off of 0.005 inches per year is expected, and the lifespan of the concrete surface is forty years, the concrete treatment compound should be applied so as to penetrate to a depth of at least one quarter of an inch, as the expected wear off would be 0.2 (two tenths) inches over the forty years.

FIG. 1 is a flowchart of an exemplary method of treating concrete to reduce nitrogen oxides (NO_x), volatile organic compounds (VOC), and other pollutants.

The method optionally includes preparing 105 the concrete, if necessary, to remove surface contaminates to ensure that the concrete treatment compound can adhere to and penetrate the concrete to the depth required.

In some embodiments, the method optionally includes texturing 110 the upper surface of the concrete. Again, this includes, for example, using an abrasive technique to prepare the surface of the concrete.

The method also comprises applying 115 an amount of concrete treatment compound to an upper surface of the concrete. As mentioned above, the concrete treatment compound comprises a mixture of a liquid carrier compound with a titanium dioxide (TiO₂) photocatalyst. In some instances, the TiO₂ photocatalyst is an anatase powder form of TiO₂ nanoparticles that is mixed into a liquid carrier compound. The liquid carrier compound may include any liquid that can seal and harden concrete and fills voids therein to increase resistance of the concrete to water damage, chloride ion penetration, de-icing salts, freeze/thaw damage, and other deleterious effects.

The method includes allowing 120 the treated concrete to dry for a period of time.

FIG. 2 is a method for preparing the concrete treatment compound that includes calculating 205 an amount of concrete treatment compound that is necessary to ensure that the concrete is penetrated and embedded with photocatalytic material to a sufficient depth.

The method also includes selecting 210 a photocatalytic material for the concrete treatment compound that is capable of reducing an amount of nitrogen oxides (NO_x) and volatile organic compounds (VOC).

The method also includes selecting 215 a carrier liquid for the concrete treatment compound that is capable of penetrating and delivering the photocatalytic material to a sufficient depth of the concrete. In some embodiments, the method includes mixing 220 the concrete treatment compound by combining a liquid carrier compound with an amount of the selected photocatalytic material.

FIG. 3 illustrates an asphalt concrete section 305 that has been treated with concrete treatment compound 310. The concrete section 305 is shown as having an upper surface 315. The amount of concrete treatment compound 310 has penetrated down from the upper surface 315 to a depth D. This depth D can range anywhere between at least an eighth of an inch, down to a quarter of an inch. Other depths may also be utilized and can vary according to design requirements and usage.

Other examples of compounds that may be used as carrier liquids include SurfCrete Ti manufactured by Pavement Technology, Inc., and RELAY Ti manufactured by Sinak Corporation. One embodiment of the present technology utilizes an anatase powder form of TiO₂ at concentrations of 3% to 5% by weight. Other resurfacing compounds and/or forms of TiO₂, and alternate concentration levels, can be employed as deemed suitable.

In some embodiments the compound is applied with squeegees to a concrete surface that has previously been roughened with abrasive media, such as the Skidabrader process, conventional shot blasting, diamond grinding, water blasting, and the like. For thicker applications, the compound is applied in layers, typically nine (9) mils thick, with each layer being allowed to dry before the next layer is applied.

While the present technology has been described in connection with a series of steps, these descriptions are not intended to limit the scope of the technology to the particular forms set forth herein. It will be further understood that the methods of the invention are not necessarily limited to the discrete steps or the order of the steps described. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art.

Claims

1. A method for treating a concrete structure, the method comprising: applying an amount of concrete treatment compound to an upper surface of the concrete, the concrete treatment compound comprising a mixture of a liquid carrier compound with a titanium dioxide (TiO₂) photocatalyst, the liquid carrier compound carrying the TiO₂ photocatalyst into the concrete structure, wherein the liquid carrier compound penetrates the concrete to a depth range of approximately an eighth of an inch to approximately a quarter of an inch, as measured from the upper surface of the concrete, so as to embed the TiO₂ photocatalyst therein, and simultaneously seals and hardens the concrete, and fills voids in the concrete so as to increase resistance of the concrete to deleterious effects, the application of the concrete treatment compound to the upper surface of the concrete causing a reduction of pollutants proximate to the concrete, the pollutants including nitrogen oxides and volatile organic compounds, the concrete treatment compound uniformly impregnating the concrete such that normal wear of the upper surface of the concrete exposes an underlying photocatalytic reactive layer of the concrete, so that a pollution-reducing capability of the concrete treatment compound is self-regenerated.

2. The method according to claim 1, wherein the deleterious effects include at least one of water damage, chloride ion penetration, de-icing salts, and freeze/thaw damage.

3. The method according to claim 1, further comprising texturing the upper surface of the concrete.

4. The method according to claim 1, wherein the TiO₂ photocatalyst comprises TiO₂ nanoparticles that are mixed into the liquid carrier compound.

5. The method according to claim 4, wherein the TiO₂ nanoparticles are in an anatase powder form.

6. A method, comprising applying a photocatalytic compound and a liquid carrier compound to concrete, wherein the photocatalytic compound is capable of uniformly penetrating the concrete down to a depth of at least an eighth of an inch relative to an upper surface of the concrete, the application of the photocatalytic compound to the upper surface of the concrete causing a reduction of pollutants proximate to the concrete, the pollutants including nitrogen oxides and volatile organic compounds, the photocatalytic compound uniformly penetrating the concrete such that normal wear of the upper surface of the concrete exposes an underlying photocatalytic reactive layer of the concrete, so that a pollution-reducing capability of the photocatalytic compound is self-regenerated; and the liquid carrier compound is selected such that it simultaneously seals and hardens the concrete and fills voids in the concrete so as to increase resistance of the concrete to deleterious effects.

7. The method according to claim 6, wherein selecting the liquid carrier compound further comprises selecting a first type of carrier liquid if the concrete is fully cured and selecting a second type of carrier liquid if the concrete is not fully cured.

8. The method according to claim 7, further comprising calculating an amount of TiO₂ nanoparticles that is necessary to ensure that the concrete is penetrated and embedded with photocatalytic material to a sufficient depth.

9. A method, comprising applying a photocatalytic compound and a liquid carrier compound to concrete, wherein the photocatalytic compound uniformly penetrates the concrete to a depth of at least an eighth of an inch relative to an upper surface of the concrete, the liquid carrier compound including a resurfacing compound that is applied to the concrete using a squeegee, the application of the photocatalytic compound to the upper surface of the concrete causing a reduction of pollutants proximate to the concrete, the pollutants including nitrogen oxides and volatile organic compounds, the photocatalytic compound uniformly penetrating the concrete such that normal wear of the upper surface of the concrete exposes an underlying photocatalytic reactive layer of the concrete, so that a pollution-reducing capability of the photocatalytic compound is self-regenerated.

10. The method according to claim 9, further comprising selecting the liquid carrier compound such that it is configured to simultaneously seal and harden the concrete and fills voids in the concrete so as to increase resistance of the concrete to deleterious effects.

11. The method according to claim 10, wherein selecting the liquid carrier compound further comprises selecting a first type of carrier liquid if the concrete is fully cured and selecting a second type of carrier liquid if the concrete is not fully cured.

12. The method according to claim 11, further comprising calculating an amount of TiO₂ nanoparticles that is necessary to ensure that the concrete is penetrated and embedded with photocatalytic material to a sufficient depth.