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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the field of concrete building products, and in particular, provides an improved concrete building block that can be used in dry stack, i.e., mortarless building environments. 
         [0003]    2. Description of the Related Art 
         [0004]    There are numerous building blocks available on the market, and one of particular relevance to the present invention is described in relation to FIGS. 44 to 50 of applicant&#39;s published U.S. Patent Application Pub. No. US2006/0059839. The block shown in those figures is of a rectangular design, with substantially parallel front and rear walls that are provided with deep grooves or projecting tongues at their ends, so as to permit consecutive blocks in a course of blocks be interlocked, to form a straight and level course of blocks. The front and rear walls are spaced apart by transversely extending webs. The walls increase gradually in thickness from the web to the ends thereof. 
       SUMMARY OF THE INVENTION 
       [0005]    The block of the present invention is, essentially, a modified and improved version of the aforesaid block shown in applicant&#39; s pending U.S. application. The specific improvements made in the design of the block of the present invention include thickening the front and rear walls of the block, from the transverse webs to the ends of the block, and utilizing vertical beads that project outwardly from the ends of the wall panels for block to block alignment, instead of tongue and groove, or overlapping joints for end to end connection. 
         [0006]    The upper and lower surfaces of the block of the present invention may be substantially flat or may be profiled. 
         [0007]    In a broad aspect, then, the present invention relates to a concrete block for construction, said block having a front wall and a rear wall, said front and rear walls being spaced apart by a pair of transverse webs, each of said front and rear walls comprising a middle portion and a pair of end portions, wherein said end portions have a uniform thickness that is greater than the thickness of said middle portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    In the drawings that illustrate the present invention by way of example: 
           [0009]      FIG. 1  is a top view of a stretcher block of the present invention. 
           [0010]      FIG. 2  is a cross sectional view through line A-A in  FIG. 1 . 
           [0011]      FIG. 3  is a cross sectional view through line B-B in  FIG. 1  or  FIG. 6 . 
           [0012]      FIG. 4  is a cross-sectional view, including a detail view of a corner, though line C-C in  FIG. 1 . 
           [0013]      FIG. 5  is a perspective view of the block of  FIG. 1 . 
           [0014]      FIG. 6  is a top view of a corner block of the present invention. 
           [0015]      FIG. 7  is a cross sectional view through line D-D. 
           [0016]      FIG. 8  is a perspective view of the block of  FIG. 6 . 
           [0017]      FIG. 9  is a top view of a half size block according to the present invention. 
           [0018]      FIG. 10  is a cross sectional view through line E-E in  FIG. 9 . 
           [0019]      FIG. 11  is a cross sectional view through line F-F in  FIG. 9 , with a detail. 
           [0020]      FIG. 12  is a perspective view of the half size block of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring now to the drawings, the present invention provides a building system that uses three specially designed blocks: 
         [0022]    1. a stretcher block  1   
         [0023]    2. a corner block  2   
         [0024]    3. a half length block  3 . 
         [0025]    Each stretcher block  1  and corner block  2  is twice as long from end to end as it is wide, from front surface to rear surface. This permits blocks to be placed in staggered courses and to form corners. Detailed dimensional views of a preferred embodiment of a stretcher block according to the present invention are shown in  FIGS. 2-5 . 
         [0026]    Each stretcher block  1  has a front wall  11 , a rear wall  12  parallel thereto, and webs  13  transversely extending between the front and rear walls  11 ,  12 . The front and rear walls  11 ,  12  end in vertically extending front and rear end wall surfaces  14 ,  15 . At each end of the block, end wall surfaces  14 ,  15  are coplanar with each other. 
         [0027]    Each corner of the block, where a front  11  or rear  12  wall ends is beveled with a small angled surface  16 , which may be convex, concave or planar. For aesthetic purposes, it is usually concave. At the inside edge of end wall surfaces, a vertical bead  17  or groove  18  is formed. One bead  17  and one groove  18  is formed at each end of the block, so that each end is provided with a groove  18  and a bead  17 . The front  11  and rear  12  walls each have one groove and one bead formed therein (at opposite ends) whereby blocks laid end to end in a course will have the bead of one wall fitting into the groove of the next, with the end walls  14 ,  15  on adjacent blocks firmly abutting each other. Similar beads  17  and grooves  18  are provided on cover blocks  2  and half length blocks  3 . 
         [0028]    The ends  19  of the front and rear walls are considerably thicker than the portions of the walls between the webs  13 , which adds needed strength to the ends to protect them against cracking during transport. The middle portions of the walls  11 ,  12  are not as susceptible to breakage, since they form a rigid box channel with the transverse webs  13 . Moreover, as can be seen most clearly in  FIGS. 1 and 5 , the beads  17  and grooves  18  may be formed in the thickened portions of the walls. The bead or groove will not in that case extend the full height of the front and rear walls, as thickened portion of the front and rear walls terminates before the bottom edge of the front and rear walls, as can be seen in  FIG. 3 , to provide a lower profile  41  to inter-fit with the upper profile ridge  42  of the block, as will be discussed below. 
         [0029]    Referring now to  FIGS. 2 ,  6 ,  7  and  8 , the present invention provides a corner block  2  that is provided with front  21 , rear  22  walls connected together by inner and outer transverse webs  231 ,  232 . Inner transverse web  231  may be eliminated entirely, if desired, to improve the water resistance of walls constructed with the blocks of the present invention. That is, eliminating web  231  will permit concrete or grout poured into a wall constructed with the blocks of the present invention to flow more freely, so that a continuous concrete core is formed around the corners of such a wall. 
         [0030]    The front and rear walls  21 ,  22  are also connected together, at one end, by a planar end wall  24 . The other ends  29  of the front and rear walls  21 ,  22  of corner block  2  are thickened similar to the ends of front and rear walls  11 ,  12  of the stretcher block, and also have coplanar end surfaces  25 ,  26 . The corners  16  of the corner block are beveled in a manner similar to the stretcher block  1 . Accordingly, corner  2  and stretcher  1  blocks can be aligned end to end in a straight line. Moreover, the end surfaces  25 ,  26  of walls  21 ,  22  of the corner blocks  2  are provided with beads  17  and grooves  18  in a manner similar to stretcher block  1 . 
         [0031]    The front and rear walls  21 ,  22  of corner block  2  are provided with grooves  28  on their surfaces alignable with beads  17  of a stretcher or corner block. The grooves  28  are also provided on the outer surface of end wall  24 . Grooves  28  are positioned on the walls  21 ,  22  such that a stretcher  1  can be butted against a corner block  2  firmly and snugly, to construct a right angle corner. Grooves  28  are provided on each wall  21 ,  22  to permit right or left corners being made without special right and left corner blocks. Grooves  28  are provided on end wall to permit stretcher blocks to be aligned with the closed end wall  24  of a corner block  2 . This novel feature permits the easy construction of four way corner, or cross-shaped wall structures using the present invention. 
         [0032]    The present invention also provides a half-width block  3 , as shown in  FIGS. 9-12 . Use of this block permits walls to be constructed with vertical non-corner edges, such as in connection with doors and windows. 
         [0033]    Half-width blocks are provided with four equal length sides three of which are provided with vertical grooves  32  spaced from the beveled corners  33 . Grooves  32  are alignable with the beads  17  on the ends of the stretcher  1  or corner blocks. The fourth side is an open end, shaped like the end of a stretcher block, with a bead on one side and a groove at the other. Accordingly, a half width block can be used to abut the open end of a stretcher or a corner block, using the open end of the block, or one of the three other sides. The so-called open-end can also be used to abut the closed end of a corner block, depending on the overall layout desired. 
         [0034]    It will be observed that because the ends  14 ,  15  of the front and rear walls of the stretcher  1  are coplanar (as are the ends  25 ,  26  of the front and rear panels of a corner block  2 ), then aligning a course of stretchers is simplified, as is making a corner square. 
         [0035]    The top and bottom surfaces of the blocks are also profiled to interfit with each other, as can be seen most clearly from  FIGS. 3 ,  4  and  11 . On the stretcher, ridges  42  extend upwardly from the adjacent top edges of the inner face of the front and rear walls  11  and  12 . The ridges  42  are beveled inwardly slightly, to fit within the beveled inner face at the lower edge of the front and rear walls  11  and  12 . The ridges  42  are not present in the area between the transverse webs of the block, nor are they present around the hollow vertical core at the closed end of the corner block, except at the edge thereof. The reason for the ridges is to facilitate accurate vertical alignment of blocks in a wall. 
         [0036]    It will also be understood that after a wall or other structure is built using the blocks of the present invention, the wall should the be filled with concrete or grout, so as to create a continuous concrete wall, with no cracks or seams extending therethrough. It if becomes necessary to lay the blocks in such a way that a seam extending through a wall is created, then durable caulk, or mortar should be applied to the entire inner surface of such a crack or seam, to ensure the wall is water resistant to the maximum extent. It will also be noted in this regard that shallow channels are formed in the top and bottom of transverse webs, to permit the flow of concrete from one hollow core to the next. Moreover, it will be noted that the transverse webs are provided with downwardly depending legs  44 . These legs do not have a structural function, but rather are an artifact of the molding process, and are provided to present the web from collapsing before curing.

Summary:
A concrete block for construction, the block having a front wall and a rear wall. The front and rear walls are spaced apart by a pair of transverse webs. Each of the front and rear walls comprises a middle portion and a pair of end portions, wherein the end portions have a uniform thickness that is greater than the thickness of the middle portion.