You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
[0001]    This application claims priority from provisional application no. 61/184,034, filed on Jun. 4, 2009, and from provisional application no. 61/249,068, filed on Oct. 6, 2009. These two applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND INFORMATION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a porous paver. More particularly, the invention relates to a porous paver and a method of providing a porous pavement. 
         [0004]    2. Description of the Prior Art 
         [0005]    It is known to use porous pavement to provide pavement that allows stormwater to infiltrate back into the ground naturally, rather than to run off. The porous pavement made with pavers typically includes a method of laying out non-porous pavers to provide a load-bearing pavement surface, with regularly dispersed void areas between the pavers. The non-porous pavers are typically concrete blocks, bricks, or reinforced plastic mats. The void areas are then filled with gravel, sand, or grass turf, which allow the stormwater to infiltrate into the ground. 
         [0006]    Porous pavers or pavement serve their function only if the water can actually pass through the paver or pavement at a minimum specified rate. Porous pavement is known. With time, however, the porosity is substantially diminished, because the porous material becomes clogged with sediment, debris, or other materials that prevent the stormwater from flowing through the pavement. The construction of porous pavement also requires attention to certain temperature parameters. For example, if the porous pavement is laid down and then subjected to freeze-thaw cycles before it is cured, the pavement will crack and crumble. The remedy for dogged or cracked porous pavement is to dig it up and replace it, a costly undertaking. 
         [0007]    What is needed, therefore, is a porous paving system that is readily cleanable, maintainable, or replaceable. What is further needed is such a system, the components of which can be manufactured under controlled conditions. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The invention is a porous pavement stem that is based on a paver made of porous material, whereby a retrieval means is provided in the porous paver, so as to allow individual porous pavers to be removed from the pavement for cleaning, replenishing, or replacement, as needed. The invention also encompasses a paved surface that is made up of a combination of porous and non-porous pavers, and/or one that uses a hybrid paver. 
         [0009]    The hybrid paver is a bi-material paver block that provides the desired load-bearing properties of conventional non-porous pavers and the desired filtration properties of porous pavement for allowing passage of stormwater through the pavement into the ground. The hybrid paver according to the invention comprises an outer portion that is non-porous and an inner portion that is porous. In other words, the hybrid paver has a donut-like non-porous outer portion and a donut-hole-like porous inner portion. The outer portion includes the entire perimeter of the hybrid paver, is a structural wall around the porous inner portion, the structural wall having the necessary strength characteristics to provide the desired load-bearing strength of the pavement. 
         [0010]    The inner portion is constructed of a porous concrete that provides a specified filtration rate of water, typically stormwater. Additives may be mixed with the porous concrete to filter out specific pollutants. it may be desirable to be able to remove the inner portion from the outer portion for cleaning or replacement. For this reason, the hybrid paver may be constructed as a modular unit from which the inner portion may be readily removed or inserted, In this case, the inner portion is constructed as a cartridge or a modular piece that fits into a cavity in the outer portion. A means for inserting and retrieving the cartridge may be incorporated into the cartridge. 
         [0011]    The inner portion and outer portion are made according to conventional industry standards, such as, for example, ASTM standards, if the paver is made of concrete. Each portion of the paver provides the desired load-bearing capability, The inner portion may also be used as a stand-alone porous paver, that is, does not have to be inserted into an outer portion, but may instead be inserted into a cavity that is created by a particular layout configuration of other porous and non-porous pavers. 
         [0012]    The pavers used in the porous pavement system according to the invention may be any suitable shape and size. Thus, for example, pavers may be constructed as large slabs, as small regularly shaped blocks, or as decoratively shaped elements. Depending on the size and shape of the payers, the retrieval means may also be adapted to be coupled to a lifting means that is incorporated into a vehicle that is equipped with some type of hoisting or lifting mechanism, to assist in lifting the paver from the pavement surface or, in the case of large slab-like pavers, also to install the paver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements, The drawings are not drawn to scale. 
           [0014]      FIG. 1  is a top plane view of the hybrid paver according to the invention. 
           [0015]      FIG. 2  is a side elevational view of the hybrid paver of  FIG. 1 , showing a grid-like cradle for a single paver. 
           [0016]      FIG. 3  is a cross-sectional view through the center vertical plane of the porous cartridge. 
           [0017]      FIG. 4  is an illustration of the retrieval means. 
           [0018]      FIG. 5  is a bottom plane view of the porous cartridge. 
           [0019]      FIG. 6  is an exploded view, illustrating the assembly of the retrieval insert and the use of a tool to remove the porous cartridge from the hybrid paver according to the invention. 
           [0020]      FIG. 7  is a multi-paver cradle, showing keys for locating pavers. 
           [0021]      FIG. 8  illustrates a hybrid paved surface formed by an alternating layout of non-porous pavers and porous pavers. 
           [0022]      FIG. 9  illustrates a porous paved surface. 
           [0023]      FIG. 10  illustrates a retrieval means for large-slab porous pavers. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. 
         [0025]      FIGS. 1-5  illustrate the elements of a hybrid paver  100  according to the invention, which comprises a non-porous paver  10 , a porous paver  20 . The non-porous paver  10  is constructed of a conventional non-porous concrete, which has the desired strength and compression properties for the intended use. As seen in  FIG. 1 , the non-porous paver  10  has an open center portion that receives the porous cartridge  20 . The porous paver  20  is constructed of a porous or pervious concrete or other porous material, according to established industry standards, and allows water, for example, stormwater, to pass through the paver at a given rate. For example, concrete made according to ASTM C941C94M is a pervious concrete made with aggregates coarse enough to allow water to pass through the concrete to the substrate below and strong enough to be traffic bearing. It is also possible to provide a hybrid paver  100  wherein the non-porous paver  10  has a higher compression strength than that of the porous paver  20 , in which case the height dimension of the porous paver  20  may be slightly less than that of the non-porous paver  10 . Conventional porous paving material has a height dimension that is greater than that of a non-porous material that provides a corresponding compression strength. Using the hybrid paver  100  according to the invention enables the implementation of a porous paving system in which the height dimension is determined by the strength characteristics of the non-porous paver  10 , and thus, the use of a paver that is lower in height than would be expected with conventional porous paving material. 
         [0026]    In the embodiment shown in the figures, the porous paver  20  is shown as a porous cartridge that is selectively insertable into and removable from the non-porous paver  10 . The porous paver  20 , being constructed according to industry standards, may also serve as a paver without the non-porous paver  10 . 
         [0027]      FIGS. 3-6  illustrate details of a retrieval means  30  that may be used to facilitate insertion and removal of the porous paver  20  into the non-porous paver  10 . Porous concrete may become plugged with debris that reduces or blocks the rate of filtration of water through it. The porous cartridge is provided with the retrieval means  30 , to facilitate removing the porous cartridge  20  from the non-porous paver  10 , for purposes of replacement, replenishing, or cleaning.  FIG. 3  is a cross-sectional view along the vertical plane shown in  FIG. 1 . A through-bore  32  with a cross-groove  34  is provided through the porous paver  20  that is constructed to receive the retrieval means  30 , which, in the embodiment shown, includes a bar  38  assembled in a sheath  36 . The retrieval means  30  is inserted into the porous paver  20  through the cross-groove  34  in the bottom of the porous paver. A tool T shown in  FIG. 6  may be inserted into the porous paver  20  from the top face, such that the hook portion of the tool T engages the bar  38 . The porous paver  20  may then be lifted out of the non-porous paver  10 . 
         [0028]    In the embodiment shown, the retrieval means  30  is illustrated together with the porous paver  20  and the non-porous paver  10 . It is understood that the porous paver  20  does not have to be used as a cartridge, but can be used as a stand-alone paver. 
         [0029]    In this embodiment, a cradle  40  is provided to hold the non-porous paver  10  and the porous paver  20  together as a single unit. The cradle  40  facilitates handling and placement of the pavers. The cradle  40  may also serve to ensure proper spacing between pavers  100  when they are laid out. In the embodiment shown in  FIGS. 1 and 2 , the cradle is a shallow rectangular container which is dimensioned to hold the non-porous paver  10  and the porous paver  20 . Ideally, the cradle  40  has an open structure, to allow water to pass through it. The cradle  40  may have another construction, for ornamental or functional reasons. For example. the cradle may have a half-high wall that separates the non-porous paver  10  from the porous paver  20  so as to create a space between the two elements, or may be constructed as a bottom flange that extends into the through-bore  32  and connects to or is integrally formed with the retrieval means  30 . The cradle  40  thus supports the non-porous paver  10  around the porous paver  20 . The material used to construct the cradle  40  is not considered within the scope of the invention. Any suitable material, with the required strength and rigidity properties to support the non-porous paver  10  and the porous paver  20  may be used. 
         [0030]      FIG. 7  illustrates another embodiment of the cradle  40 , a multi-paver cradle. The cradle  40  has a bottom support and is large enough to receive and support a plurality of pavers. The bottom may be constructed as a grid, as described above, or in some other manner, so as to allow water to pass through it relatively unhindered, and the perimeter may be provided with a lip that hinders a translational motion of the pavers. In the embodiment shown, the cradle  40  is dimensioned to accommodate four hybrid pavers  100 , the dashed lines indicating the locations of four hybrid pavers  100 A- 100 D. This is by way of illustration only. It is understood, however, that, depending on the size and shape of the pavers, and the type of equipment used to handle the multi-paver cradle  40 , a number of pavers  100  other than  4  may be assembled on the cradle. A guide  42  may be provided on the cradle  40  to aid in holding the hybrid pavers  100  in place. The guide  42  may be a key or ridge; the bottom surfaces of the inner pavers  20  and the outer pavers  10  would then have a corresponding groove or slot. An advantage of the multi-paver cradle  40  is that it greatly enhances the structural stability of a paving system and facilitates handling and installation. The cradle  40  may be handled as a single unit, in which case, four pavers  100  can be moved, handled, or installed as a single unit. The cradle  40  with the pavers  100 A- 100 D provides much greater stability when installed as a paving system, because the weight of a multi-paver unit provides much greater resistance to tipping. For example, a load applied to a corner of a paver that is individually placed in the paving system may result in the paver tipping. A load applied to a corner of a paver that is assembled on a multi-paver cradle will be much less likely to result in tipping, because of the total weight and the distribution of weight across a much greater area. Also, a shifting of a paver within a paving layout is much less likely, because of the constraint of the cradle, For example, a force applied laterally to one paver is less likely to shift the paver, because it is constrained within the cradle and keyed in position. 
         [0031]    In the embodiments described herein, the non-porous paver  10  and the porous paver  20  are constructed of concrete. It is understood, however, that other suitable materials may be used, for the non-porous paver, for the porous paver, for both. Also, the non-porous paver and the porous paver may be made of different materials. Thus, it is possible to make the non-porous paver of brick or a manufactured stone, and the porous paver of pervious or porous concrete, or any suitable porous material, such as recycled glass, tires, asphalt, and combinations of material. 
         [0032]    The hybrid paver  100  has been illustrated as a two-component paver. It is considered within the scope of this invention to also provide the paver  100  as a unitary paving block having an outer non-porous paver portion  10  and an inner porous paver portion  20 . 
         [0033]    The shape of the pavers  100  is irrelevant. A rectangular hybrid paver  100  is shown in the drawings herein, but it is understood that any suitable shape, whether the shape be chosen for ornamental or functional reasons, may be used. 
         [0034]      FIG. 8  illustrates a hybrid paved surface  200  according to the invention comprising the non-porous paver  10  and the porous paver  20 . The hybrid paved surface  200  is created by laying the pavers  10  and  20  in an alternating pattern. The particular shape of the pavers  10  and  20  shown here is for illustration purposes only. In the embodiment shown, a conventional paver has four recesses formed about its perimeter. Four adjacent pavers together form an approximately circular opening  210 . The porous paver  20  is placed in this opening  210 . The porous paver  20  includes the retrieval means  30  described above. The particular shape of the pavers  10  is not relevant to the invention. For example, rectangular or square pavers  10  may be laid out in a configuration that creates an space  210  into which the porous paver  20  is inserted. 
         [0035]      FIG. 9  illustrates a porous pavement surface hat is not necessarily a hybrid surface, as described above, but instead. may be made up primarily of porous pavers  20 . The embodiment shown uses large-slab porous pavers  20 , Such large-slab pavers are heavy and difficult to handle. Being porous, it is also possible or desirable, that such porous pavers  20  be cleaned or replaced. Depending on the size of the paver, one paver may be too heavy to handle manually.  FIG. 10  illustrates a further embodiment of the retrieval means  30 , one that is well suited for manipulating, i.e., retrieving, lilting or lowering large, heavy pavers  20 . Reference is made in the following description to porous pavers  20 , but it is understood, that is possible to provide non-porous pavers  10  with the same retrieval means  30 , and any description of the retrieval means  30  with reference to porous pavers  20  shall also apply to non-porous pavers  10 . One or more lifting receptacles or lifting lugs  31  are embedded into the paver  20 . The number and the location of the lugs  31  depends on the size and shape of the pavers  20 . Four lifting lugs may be provided in a large rectangular paver; three or two or only one lug may be provided in smaller pavers. The lifting lugs  31  are constructed so as to be able to support the weight of the paver and withstand downward forces and are devices that are ideally countersunk into the pavers. The area around the countersink is capped with some suitable closure means  39 , so as to provide a closed upper surface on the paver. There are many possible and acceptable constructions for the lifting lugs  31 . For example, the receptacle  31  may be a threaded insert that is embedded in the paver, or may be a keyed opening that will receive and constrain some tool or device that is inserted into the opening. A lifting mechanism  33  for lifting the pavers is couplable with the one or more lifting receptacles or lugs  31 . One embodiment of the lifting mechanism  33  is shown only schematically in  FIG. 9 . It is understood that various types and configurations of lifting devices maybe used. One such suitable lifting mechanism is a hook suspended from a cable that is couplable with an attachment means  37  and that is operated by means of some conventional equipment that is typically used to lift heavy items in the construction industry, such as a tractor, or front-end loader, or a vehicle with a hoisting capability. The attachment means  37  may be specially constructed for a particular type of paver with a particular configuration of lifting lugs, such as the spider-like device shown in  FIG. 9 . The spider  37  has at least the number of legs  37 ′ that corresponds to the number of lugs  31 . Each leg  37 ′ is attached to a corresponding one of the lifting lugs  31 . Alternatively, the attachment means  37  may be a set of cables, each cable connectible at one end to a lifting lug and at the other end to the lifting mechanism. 
         [0036]    It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the hybrid paver and/or the porous paved surface may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.

Summary:
A porous pavement system and a method of maintaining the porous pavement system are disclosed. A combination of porous and non-porous pavers are laid out to create a porous pavement. A receptacle or retainer for receiving a tool is in incorporated into the porous pavers, to facilitate lifting the pavers by means of the tool. A cradle may be used to hold multiple pavers.