Abstract:
A dry polymer cement overlay for trafficked pavement substrates (both asphalt and concrete). The dry polymer cement overlay is a thin overlay that can handle the load of traffic in a relatively short time and has a relatively long life cycle. Moreover, the dry polymer cement overlay can hold aggregate that is applied on the surface of dry polymer cement overlay before it cures in order to provide a friction surface. A stencil is used during application of a dry polymer cement layer to provide a patterned overlay that includes patterns separated by gullies. The patterned dry polymer cement overlay exhibits improved performance including short and long term substrate adhesion, reduced risk of delamination, safety through improved surface runoff and enhanced visibility, improved macro and micro friction, reflective crack management, and withstands higher deflections under heavy loads. The patterned dry polymer cement overlay may also reduce noise and improve aesthetics.

Description:
BACKGROUND 
       [0001]    Pavement surfaces, such as asphalt and concrete, are used to carry traffic, including vehicles (e.g., automobiles, bikes, construction equipment) and humans. Pavement surfaces may need to be marked for various reasons (e.g., divide lanes, identify different areas, provide directions, aesthetics). Pavement surfaces may be marked with paints, or different color polymer coatings (e.g., epoxy), but these markings often do not last a long time because they fade and/or wear off from the traffic riding thereon and/or exposure to ultraviolet (UV) light. 
         [0002]    In addition to marking the pavement surface, pavement surfaces may need additional friction on portions thereof (e.g., sections with cornering, sections where braking is required) to increase the safety of the traffic traveling thereon. The additional friction may be provided by placing an overlay on the underlying pavement surface (substrate). The overlay may be provided by applying (overlaying) a wet polymer layer (e.g., epoxy) on the substrate and then applying aggregate onto the wet polymer layer prior to the polymer layer curing. The polymer layer may break down over time due to, for example, continued exposure to UV light. Furthermore, the polymer layer may be thermally incompatible with the pavement surface which may result in delamination of the epoxy from the pavement surface or damage to the pavement surface. 
         [0003]    Polymer cements have also been used as the overlay material that provides friction on trafficked pavement surfaces. Polymer cements can also be produced in different colors for delineation and demarcation, and are able to receive traffic and are durable on their own. However, the polymers utilized in these materials are typically acrylic latex polymers (wet polymers) which result in high air voids within the polymer cement. The air voids lead to the polymer cement being porous which enables water to reach the underlying pavement surface without a means of escape. Furthermore, the air voids result in the polymer cement layer being more susceptible to freeze thaw, wear, abrasion and friction loss. Moreover, the use of wet polymers may result in a thin polymer layer forming on the surface and depending on the temperature and humidity during installation may have accelerated curing compared to the rest of the polymer cement layer which commonly results in surface tension cracks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The features and advantages of the various embodiments will become apparent from the following detailed description in which: 
           [0005]      FIG. 1  illustrates an example flow chart for providing a stenciled overlay for use as a pavement surface, according to one embodiment; 
           [0006]      FIG. 2  illustrates an example overlay with rectangle patterns formed therein creating an extended gulley, according to one embodiment; 
           [0007]      FIG. 3A  illustrates a top view of an example stencil that may be placed over a substrate to create an overlay with non-directional gullies, according to one embodiment; 
           [0008]      FIG. 3B  illustrates a cross sectional view of the example stencil placed on the substrate, according to one embodiment; 
           [0009]      FIG. 4A  illustrates a top view of the example stencil after application of a dry polymer concrete layer, according to one embodiment; 
           [0010]      FIG. 4B  illustrates a cross sectional view of the example substrate showing the dry polymer patterns between the lines of the stencil, according to one embodiment; 
           [0011]      FIG. 5A  illustrates a top view of the substrate after the example stencil has been removed, according to one embodiment; and 
           [0012]      FIG. 5B  illustrates a cross sectional view of the example substrate showing the dry polymer patterns separated by the gullies, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The air void and thin polymer layer issues associated with wet polymer cements described above may be resolved by using polymer powders (dry polymers). Dry polymers do not rewet which reduces air voids that are created within the dry polymer cement layer. Dry polymers may also improve adhesion to the underlying pavement surface (substrate), as well as improve the mix workability and flexibility of the cured dry polymer cement layer. Furthermore, the dry polymer cements may cure and be available for traffic in a relatively short amount of time. 
         [0014]    According to one embodiment, the dry polymers may be redispersible binders. According to one embodiment, the redispersible binders may be based on a copolymer of vinyl acetate and ethylene. The use of a dry redispersible polymer improves the quality control during the mixing of the product on site. The dry polymer will allow the blended mixture to be delivered to the site and simply require the addition of water which simplifies the mixing and placing operation on site. The redispersible polymer may also include defoaming and self-leveling properties to assist with the reduction of air during the mixing process that is common with the use of wet polymer cements as noted above. The reduction of air improves the impermeability of the surface mix and increases the abrasion resistance of the cured material. 
         [0015]    According to one embodiment, the dry polymer cement may also include aggregate to provide layer thickness, to improve mixing, limit segregation and increase skid resistance. Larger aggregates (e.g., single sizes of 4.75 mm, 6.3 mm) including, but not limited to, granite, bauxite, porcelain or other low absorption—hard aggregates may be added to the dry polymer cements, to provide a naturally forming textured surface for the purpose of providing additional skid resistance. 
         [0016]    According to one embodiment, the dry polymer cement may also include microfibers to limit segregation, limit shrinkage, improve workability and limit exothermal generation. The microfibers may be between approximately 1/16 th  of an inch to 1 and ½ inch long. 
         [0017]    According to one embodiment, the dry polymer cement may also include a plasticizer to increase workability and accommodate less water to reduce water to cement ratio. According to one embodiment, the dry polymer cement may include an accelerator to increase curing process that may be needed for night time applications and time sensitive applications. According to one embodiment, the dry polymer cement may also include a retarder along with the accelerator to delay the change in workability that comes from adding the accelerator. 
         [0018]    According to one embodiment, the dry polymer cement may also include a filler, such as a pozzolanic filler. The filler increases workability, limits segregation and shrinkage and increases long term compressive strength. The filler may be fly ash, such as class C or class F fly ash. 
         [0019]    According to one embodiment, the dry polymer cement may be the same or similar to the dry polymer cement overlay described in U.S. Pat. No. 8,784,557 which is herein incorporated by reference. According to one embodiment, the dry polymer cement may use different versions for at least some of the various ingredients described therein (e.g., may use different dry polymers than the Elotex® polymers noted therein), may use different ratios for at least some of the ingredients, may replace certain ingredients, may add ingredients thereto, may delete ingredients therefrom, may use a single ingredient in place of a combination of different ingredients and/or may use a combination of different ingredients instead of a single ingredient. The ingredients and the ratios may depend on the specific application of the dry polymer cement overlay. 
         [0020]    According to one embodiment, the dry polymer cement may be Endurablend™ provided by Pavement Surface Coatings, LLC, a New Jersey Corporation. 
         [0021]    The dry polymer cement overlay may be applied over both asphaltic and concrete surfaces, including sealcoats; single chip, double chip or cape seals; all asphalt slurry types; all asphalt microsurfacings, thin hot mix flexible asphalt pavement surfaces with high surface deflections (0.8 mm deflection); thick hot mix flexible asphalt pavement surfaces with low surface deflections (0.8 mm deflection); all Portland cement concrete pavements; roller compacted concrete; and whitetopping. 
         [0022]    The overlay may be used for pavement surfaces that are trafficked with, for example, pedestrians, bicycles, passenger vehicles, trucks, aircraft and heavy duty equipment. The overlay may be used to mark the pavements and/or to provide a friction surface. 
         [0023]    Dry polymer cements have advantages over the use of wet polymers (e.g., epoxy) or wet polymer cements to produce an overlay. For example, the dry polymer cement layer can be applied as a thin overlay (e.g., between approximately ⅛ and 3/16 inch thick) that can handle the load of traffic in a relatively short time and has a relatively long life cycle. Furthermore, the dry polymer cement layer can provide additional friction and if colored, the color may have a relatively long life cycle. Moreover, the dry polymer cement layer can hold aggregate that is applied on the surface of dry polymer cement layer before it cures in order to provide a friction surface. 
         [0024]    However, the dry polymer cement (overlay) still may be thermally incompatible with the underlying pavement surface (both asphalt and concrete). The thermal incompatibility may lead to the layers flexing, expanding and the like at different times and to different degrees. This may cause delamination of the overlay from the underlying pavement surface and/or damage to the overlay and/or underlying pavement surface. 
         [0025]    In order to reduce the effect of the thermal incompatibility, the continuous amount of surface area where the two layers overlap may be limited. The limited overlap limits the strain caused from the thermal incompatibility from building up between the two surfaces. Limiting the amount of continuous surface area may be accomplished by patterning the surface layer so that uniform gullies (e.g., grout lines) are located between the patterns. The use of patterns and gullies limits the amount of continuous contact between the two layers to the patterns formed in the overlay. The thermally developed strain that may build up between an overlay pattern and the underlying surface may be relieved at the location of the gullies. Limiting the accumulation of strain may prevent delamination and stress to the underlying surface that can cause cracking and eventually failure of the underlying surface. 
         [0026]    A shrinkage crack that develops in the underlying surface, will likely form in the gulley (may be limited to forming in the gulley). Limiting the damage (e.g., cracks) to the underlying surface to within the gullies may prevent future more severe damage to the overlay and thereby failure of the underlying surface. Additionally a crack formed within a gully will not be felt by traffic traversing the riding surface or be visually seen. 
         [0027]    The overlay patterns may be formed by using stencils. The stencils may be pre-manufactured to produce the desired pattern shape, size and thickness. The stencils may be made from, for example, paper, metallic materials, plastic, synthetic materials or some combination thereof. The shapes, size and thickness of the patterns (shapes formed within the overlay) may be dictated based on, for example, the look desired and the primary use of the overlay. 
         [0028]    For example, a walkway for foot traffic may be made of rectangle size patterns that look like bricks (an aesthetic look). The thickness of the overlay and the patterns formed therein may be based on, for example, the weight of the traffic that will be using the pathway. For example, the thickness of the overlay may increase as the anticipated weight of the traffic increases (thicker overlays may be used to support heavier vehicles, such as construction equipment, while thinner overlays may be used to support lighter vehicles, such as bicycles). Furthermore, the size of the gullies between patterns may be based on the traffic using the overlay. For example, the gullies for bicycle or walking paths may be smaller than the gullies for heavy equipment. Bike tires or feet could get caught in the gullies if the gullies are too large while a large tire would not get caught in a large gulley and a larger gulley may provide more stress relief for heavy traffic conditions. 
         [0029]    The use of patterns and gullies provides additional benefits other than stress relief. For example, the gullies provide a means for water run-off and thus reduces the amount of standing water on the riding surface. That is, the water enters the gullies rather than pooling on the riding surface. If the gullies extend to the edge of the overlay, the water may follow the gullies to the end of the overlay and escape therefrom. The reduction of water on the riding surface reduces the amount of water that may spray up as a vehicle traverses the riding surface and also increases the effective friction of the riding surface. This increases the safety of the pathway at times when the overlay may be inundated with water (e.g., during inclement weather such as when it&#39;s raining) 
         [0030]    Moreover, the patterned overlay may provide noise reduction for traffic tire noise. The gullies may also provide sound reduction by, for example, capturing some of the sound of the traffic (e.g., sound of tires traversing the riding surface) therein and/or reducing the amount of contact between, for example, the tires and the overlay and thus reduce the amount of noise generated. 
         [0031]      FIG. 1  illustrates an example flow chart of steps to be taken for providing a thin stenciled overlay (dry polymer cement layer) for use on a pavement surface. As with the application of any overlay, the underlying surface must be prepared  100 . The pavement surface should be clean and dry to ensure proper adhesion of the polymer cement materials. All pavement marking materials should be removed, or masked, using an appropriate technique (e.g., shot blasting, high pressure water blasting, grinding). Any loose dust or dirt should be removed. Typically, the loose dust or dirt can be removed with blowers (e.g., industrial blowers). However, if the pavement surface is soil contaminated, then the surface may require pressure washing. Any wet spots, oil spots, dirt, curing compounds and any films should be removed as part of the surface preparation. 
         [0032]    During the preparation of the surface, the polymer cement materials may be mixed or prepared in accordance with the manufacturer&#39;s recommendations and instructions  110 . 
         [0033]    The area to be surfaced should be clearly marked out in accordance with the plan (e.g., drawings, engineering instructions)  120 . The boundary of the area (e.g., curbs, utility boxes) to be surfaced should be taped using, for example, 6″ wide duct tape. The stencils are then placed to produce the desired pattern. The individual stencils may require being attached to each other or the pavement to ensure that they do not move while they are trafficked by the work crews and or due to wind. 
         [0034]    Once the stencils cover sufficient area, the polymer cement materials are applied onto the surface covered by the stencils  130 . Preferably, the polymer cement materials are sprayed onto the stencils using a spray gun to achieve the same uniform thickness. Alternatively, they can be poured on the surface and squeegeed to form a uniform thickness. 
         [0035]    If topically applied aggregate is specified to deliver a high friction surface, then the aggregate is broadcast by hand or by mechanical means onto the uncured surface  140 . It should be noted that the application of aggregate to provide additional friction may not be required/desired for every application and is therefore an optional step that is illustrated as a dashed box. Topically applied aggregates (e.g., single size of 2.65 mm, 4.75 mm, 6.3 mm) including, but not limited to, bauxite, crushed granite and slag may be used to provide the high friction surface. Depending on the size of the aggregate specified, a light roller might be required to seat the aggregate in the polymer cement material. The type of topical aggregate utilized may be based on the use of the pavement surface. Different aggregates may be utilized in different portions of the patterned polymer cement layer if different degrees of friction are required. 
         [0036]    The stencils are removed once the dry polymer cement has cured to a point when the stenciled pattern can maintain its shape integrity to allow defined gullies to promote water runoff and substrate strain relief paths  150 . The stencil can be re-used to continue the operation depending on the staging requirements. Any masking or edging tape should be removed immediately after the stencils to ensure sharp edges. 
         [0037]    After the material is cured, any loose aggregate is then removed by, for example, using hand held brooms, or by a mechanical broom, or by using a vacuum truck  160 . As the application of aggregate may not be utilized for every application the removal of excess aggregate may not be required/desired and is therefore an optional step that is illustrated as dashed box. 
         [0038]    Where appropriate, or where specified, a curing agent or sealant should be applied after the material has cured  170 . The curing agent or sealant should be spray applied, and then to ensure uniform coverage, a roller should be used to spread the sealant uniformly. It should be noted that the application of a curing agent/sealant may not be required/desired for every application and is therefore an optional step that is illustrated as dashed box. 
         [0039]    Once the curing agent or sealant has fully cured, then the edging can be removed and traffic can then be allowed onto the surface  180 . 
         [0040]    It should be noted that the example flow chart is not intended to limit the steps required to form a patterned polymer cement overlay for traffic to those defined or to the order defined. Rather, steps may be added, deleted, combined, separated and/or the order of the steps may be modified without departing from the scope of the current invention. The invention is intended to cover the various manners in which a patterned dry polymer concrete layer may be formed on a traffic surface where the overlaying layer will be used to handle traffic. 
         [0041]    Using certain patterns (e.g., squares, rectangles) may result in either the tops and bottoms or the sides of successive patterns being aligned. This results in an extended gulley formed in the overlaying surface.  FIG. 2  illustrates an example overlay  200  with rectangle patterns  210  formed therein (only a subset of the patterns are illustrated with reference numbers for ease of illustration). As illustrated, the rectangle patterns are aligned in columns but not in rows (the placement of the rectangles from column to column are staggered). Accordingly, the gullies formed horizontally  220  (only a subset of the horizontal gullies are illustrated with reference numbers for ease of illustration) only extend the width of one pattern (rectangle) while the gullies that extend vertically  230  extend the length of the overlay  200 . As the vertical gullies  230  extend over a large area, cracks formed in the underlying surface may extend between patterns and may extend over a large area. 
         [0042]    In addition to the formation of extended gullies, the use of rectangles  210  as the pattern presents an overlay  200  in which the spacing of the gullies is different based on direction. For example, the distance between gullies from side to side is much smaller than the distance between gullies from top to bottom. Such a configuration may result in a different feel and/or different sound based on the direction in which the riding surface is traversed. 
         [0043]    According to one embodiment, the shapes utilized for the patterns may prevent the gullies from aligning together to form a long gulley that may create an extended stress line and/or result in different spacing of gullies based on direction the riding surface is being traversed. That is, the patterns utilized may form non-directional gullies. Effective patterns may have multiple sides that will result in gullies not traversing the same path when placed side by side. For example, hexagons and/or octagons may result in non-directional gullies that do not extend further than a side of one pattern. 
         [0044]    It should be noted that patterns utilized for forming non-directional gullies result in additional gullies being formed. For example, a hexagon pattern results in formation of six gullies while a square or rectangle pattern results in only four gullies. These extra gullies may provide additional area for water run-off which may result in a better friction surface. Furthermore, the additional gulley area (reduced overlay surface area) may also result in increased sound reduction or may reduce the sound created as the riding surface is traversed. 
         [0045]      FIG. 3A  illustrates a top view of an example stencil  300  that may be placed over a substrate (underlying pavement surface) to create an overlay with non-directional gullies. As illustrated, the stencil  300  includes lines  310  surrounding hexagon patterns  320 . Only a subset of the lines  310  and patterns  320  are illustrated with reference numbers for ease of illustration. The lines  310  (which is where the gullies will be formed between the patterns as the polymer concrete will not be located there) do not traverse is the same direction for more than one pattern (hexagon)  320 . At the end of each pattern  320  the lines  310  switch direction at a  120  degree angle associated with hexagons. 
         [0046]      FIG. 3B  illustrates a cross sectional view of the example stencil  300  placed on the substrate  330 . The lines  310  of the stencils are located on top of the substrate  330  and the patterns  320  are formed between a plurality of lines  310 . It should be noted that while the pattern  320  is labeled between the two lines  310  for ease of illustration, the actual pattern would not be visible from this view. 
         [0047]      FIG. 4A  illustrates a top view of the example stencil  300  after application of a dry polymer concrete overlay so that the patterns are now dry polymer patterns  400 .  FIG. 4B  illustrates a cross sectional view of the example substrate  330  showing the dry polymer patterns  400  between the lines  310 . 
         [0048]      FIG. 5A  illustrates a top view of the substrate  330  after the stencil  300  has been removed leaving a patterned overlay  500 . The patterned overlay  500  includes a plurality of dry polymer patterns  400  separated by a plurality of gullies  510 .  FIG. 5B  illustrates a cross sectional view of the example substrate  330  showing the dry polymer patterns  400  separated by the gullies  510 . 
         [0049]    The dry polymer cement layer may be colored different colors depending on the use of the overlaying layer. For example, cross walks may be colored red, bike paths green, and dividing lines yellow. If the pathway requires multiple colors a first color will be applied and then the first color will be masked when the second color is applied. For example, the yellow stripes in a roadway may be applied first and then they may be masked when the rest of the roadway is applied. 
         [0050]    While the invention has been described with respect to dry polymer concrete layers it may also be applicable to other types of layers that may be applied as a thin overlay that cures in a relatively short amount of time and can support the necessary traffic. These layers may also be capable of receiving a surface aggregate and being formed into patterns separated by gullies by utilizing a stencil during application. 
         [0051]    Although the invention has been illustrated by reference to specific embodiments, it will be apparent that the invention is not limited thereto as various changes and modifications may be made thereto without departing from the scope. Reference to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described therein is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” appearing in various places throughout the specification are not necessarily all referring to the same embodiment. 
         [0052]    The various embodiments are intended to be protected broadly within the spirit and scope of the appended claims.