Embedding photocatalytic titanium dioxide in asphalt surfaces to reduce pollutants via photocatalytic reactions

Abstract

Methods for embedding photocatalytic titanium dioxide in asphalt surfaces to reduce pollutants via photocatalytic reactions include applying an amount of an asphalt surface treatment compound to an upper surface of the asphalt surface, the asphalt surface treatment compound including a mixture of a liquid carrier compound with a titanium dioxide (TiO₂) photocatalyst.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

an

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

Other reactive 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 an asphalt roadway, it removes a significant quantity of NO_x and VOCs from the environment nearest their source. If TiO₂ is uniformly impregnated into the asphalt to a given depth the pollution-reducing capability of the asphalt will automatically and continuously self-regenerate as the surface layers are subjected to the normal wear of traffic and other environmental factors.

The present technology impregnates the asphalt surface with TiO₂ by applying specialized penetrating carrier liquid(s) to the surface of an asphalt surface. These carriers are designed and proven to carry chemicals into asphalt. The TiO₂ is blended into the carrier liquids at a proportion that will result in a uniform distribution of TiO₂ nanoparticles throughout the upper three-eights (0.375) inches of the asphalt surface (or alternatively at least a quarter to half an inch in depth).

Examples of carrier liquids that may be used for this purpose are Most of these carrier liquids have the added benefit of restoring the plasticity and durability of the asphalt binder and protecting the asphalt surface from water damage, chloride ion penetration, deicing salts, and freeze/thaw damage.

For example, warm mix asphalt typically contains an additive that allows the warm mix asphalt to be produced and applied at lower temperatures than traditional asphalt. The lower temperature offers lower consumption of fossil fuels and greater flexibility when transporting and laying the mix. Applying the present technology to provide a method of embedding photocatalytic titanium dioxide into existing warm mix asphalt provides the added benefit of improving resistance to premature fracturing.

The present technology utilizes an anatase powder form of TiO₂ nanoparticles at a specific concentration that will result in TiO₂ being delivered at the designed rate of application for the impregnated region. It will be understood that other penetrating liquid carriers and/or forms of TiO₂, other semiconductors that are photocatalytic and alternate concentration levels, can be employed as deemed suitable by one of ordinary skill in the art.

In one embodiment, an asphalt surface treatment compound is created by mixing together any of the carrier liquids described above with a set amount of TiO₂ nanoparticles.

The asphalt surface treatment compound is sprayed onto horizontal road surfaces by a distributor truck with a spray bar of variable length, two to three inches in diameter, utilizing industry standard No. 1 to No. 3 nozzles. The application rate is controlled by a computerized flow manager, which allows the asphalt surface treatment compound to be precisely applied to the road surface, ensuring that the amount of asphalt surface treatment compound applied to the asphalt is sufficient to penetrate to a desired depth.

Once the flow rate computer has been set to the desired application rate, the application of the asphalt surface treatment compound is very accurate due to the computer control of the flow, regardless of travel speed variations of the sprayer. On other surfaces inaccessible to a distributor truck with spray bar, the asphalt surface treatment compound can be applied by hand spraying with a wand, or any other suitable means of application that maintains the required accuracy.

If conditions for a given application dictate that an asphalt pavement be textured for safety or other reasons, abrasive media application methods can be employed prior to spray application of the asphalt surface treatment compound. Exemplary methods are the Skidabrader process and conventional shot blasting, and the like.

In some embodiments, the amount of asphalt surface treatment compound (e.g., carrier compound plus photocatalytic material) that is applied to an asphalt surface should be enough to penetrate asphalt surface down to between a depth range of approximately a quarter of an inch to approximately a half of an inch, inclusive. Further, a concentration of photocatalytic material within the asphalt surface treatment compound should be sufficient to achieve a desired concentration of the photocatalytic material within the asphalt surface. This process of delivering photocatalytic material using a penetrating carrier compound is referred to as distributive embedding.

The depth to which the photocatalytic material should be distributively embedded may depend upon a variety of factors such as aggregate composition of the asphalt surface. By example, the photocatalytic material may only need to penetrate up to one quarter of an inch for asphalt surface that includes an aggregate that resists wear off, whereas an asphalt surface that is known to wear off quickly may require photocatalytic material to be embedded further into the asphalt surface 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 asphalt surface treatment compound of the present technology, which will be required to penetrate the asphalt surface down to a sufficient depth relative to an upper surface of the asphalt 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 asphalt surface composition and traffic pattern that an average wear off of 0.005 inches per years is expected, and the lifespan of the road is forty years, the asphalt surface 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 inches over the forty years.

FIG. 1 is a flowchart of an exemplary method of treating an asphalt surface to reduce the production of nitrogen oxides (NO_x), volatile organic compounds (VOC), and other pollutants by in proximity to the asphalt surface.

The method optionally includes preparing 105 the asphalt surface, if necessary, to remove surface contaminates to ensure that the compounds of the present technology can adhere to and penetrate the asphalt surface.

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

The method also comprises applying 115 an amount of an asphalt surface treatment compound to an upper surface of the asphalt surface (e.g., asphalt roadway or highway for example). As mentioned above, the asphalt surface 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 method includes allowing 120 the treated asphalt surface to dry for a period of time.

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

The method also includes selecting 210 a photocatalytic material for the asphalt surface treatment compound that is capable of reducing an amount of nitrogen oxides (NO_x) and volatile organic compounds (VOC) produced by in proximity to the asphalt surface.

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

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

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 present technology 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 warm mix asphalt surface, the method comprising:

impregnating an upper surface of the warm mix asphalt surface with a mixture of a liquid asphalt carrier compound with a titanium dioxide (TiO₂) photocatalyst, the liquid asphalt carrier compound carrying titanium dioxide (TiO₂) nanoparticles into the upper surface of the warm mix asphalt surface, forming a photocatalytic layer within the warm mix asphalt surface that oxidizes nitrogen oxides (NOx) and other pollutants when the warm mix asphalt surface is exposed to ultraviolet sunlight and airborne water molecules, the liquid asphalt carrier compound penetrating the warm mix asphalt surface to a depth range of between approximately a quarter of an inch to approximately a half of an inch, as measured from the upper surface of the warm mix asphalt surface, so as to embed the titanium dioxide (TiO₂) photocatalyst in the asphalt surface and to ensure that as the upper surface of the warm mix asphalt surface wears off, the photocatalytic layer appears on the warm mix asphalt surface.

2. The method according to claim 1, further comprising texturing the upper surface of the warm mix asphalt surface.

3. The method according to claim 1, wherein the TiO₂ photocatalyst comprises an anatase powder form of TiO₂ nanoparticles that is mixed into the liquid asphalt carrier compound.

4. A method, comprising:

impregnating an upper surface of a warm mix asphalt surface with a photocatalytic compound, the photocatalytic compound including a liquid asphalt carrier compound and a titanium dioxide (TiO2) photocatalyst, the titanium dioxide TiO2) photocatalyst including titanium dioxide (TiO2) nanoparticles, the liquid asphalt carrier compound carrying the titanium dioxide (TiO₂) nanoparticles into the upper surface of the warm mix asphalt surface, forming a photocatalytic layer within the warm mix asphalt surface that oxidizes nitrogen oxides (NOx) and other pollutants when the warm mix asphalt surface is exposed to ultraviolet sunlight and airborne water molecules, in which the impregnation allows the photocatalytic compound to penetrate the warm mix asphalt surface down to a depth of at least a quarter of an inch relative to the upper surface of the warm mix asphalt surface, the liquid asphalt carrier compound being combined with a the titanium dioxide (TiO₂) photocatalyst so as to embed the titanium dioxide (TiO₂) photocatalyst in the warm mix asphalt surface and to ensure that as the upper surface of the warm mix asphalt surface wears off, a submerged layer of the titanium dioxide (TiO₂) photocatalyst appears on the warm mix asphalt surface.

5. The method according to claim 4, further comprising selecting an asphaltic carrier liquid for the photocatalytic compound that reduces an amount of nitrogen oxides (NOx) and volatile organic compounds (VOC).

6. The method according to claim 4, wherein the TiO₂ photocatalyst comprises an anatase powder form of TiO₂ nanoparticles.

7. The method according to claim 4, wherein the liquid asphalt carrier compound improves resistance to premature fracturing of the warm mix asphalt surface.

8. The method according to claim 4, further comprising calculating an amount of warm mix asphalt surface treatment the liquid asphalt carrier compound that is necessary to ensure that the warm mix asphalt surface is penetrated and embedded with the photocatalytic material compound to a sufficient predetermined depth.

9. A warm mix asphalt surface treatment compound, comprising: an amount of an asphaltic liquid carrier compound mixed with an amount of a titanium dioxide (TiO₂) photocatalyst, wherein the asphaltic liquid carrier compound penetrates a warm mix asphalt surface down to a depth of at least a quarter of an inch relative to an upper surface of the warm mix asphalt surface, the liquid carrier compound impregnating the warm mix asphalt surface.

10. The warm mix asphalt surface treatment compound according to claim 9, wherein the TiO₂ photocatalyst comprises an anatase powder form of TiO₂ nanoparticles.

11. The warm mix asphalt surface treatment compound according to claim 10, wherein the asphaltic liquid carrier compound restores plasticity and durability of an asphalt binder of the warm mix asphalt surface.

12. The warm mix asphalt surface treatment compound according to claim 10, wherein the asphaltic liquid carrier compound improves resistance to premature fracturing of the warm mix asphalt surface.