Patent Publication Number: US-9410316-B2

Title: Post-tension concrete leave out splicing system and method

Description:
FIELD 
     This description relates generally to floor construction using post-tensioned concrete slabs. 
     BACKGROUND 
     Generally, a process for new floor construction using post-tensioned concrete slabs requires a gap (also known as a leave out, a pour strip out, etc.) that separates adjacent concrete slabs (also known as pours or castings). Generally, the gap is four feet and more in length. That is, several feet in distance separates the two ends of the post-tensioned concrete slabs. Sometimes the gap distance (the distance which separates the two ends of the post-tensioned concrete slabs) may be called a “width,” but for clarity and consistency, the term “width” is used herein to describe the distance along the direction labeled “W,” and the term “length” is used herein to describe the distance along the direction labeled “L” (e.g., see  FIGS. 1-3 ). Accordingly, ΔL is used herein to describe a change in distance along the “L” axis direction. Generally, the gap is filled in (i.e., lap spliced) with a pour strip at a later time, connecting the slabs together to form the entire floor. 
     Prestressed concrete is a type of reinforced concrete which has been subjected to external compressive forces prior to the application of load. Prestressed concrete is categorized as either pre-tensioned or post-tensioned. 
     Pre-tensioned concrete is formed by a process including initial stressing of a wire strand system and then casting concrete around the stressed wire strand system. The stress from the wire strand system transfers to the concrete after the concrete has reached a specified strength (e.g., cured to a set specification). 
     Post-tensioned concrete is formed by a process of casting wet concrete around an unstressed wire strand system and then stressing the wire strand system after the concrete has reached specified strength (e.g., cured to a set specification). For example, post-tensioned concrete can have a wire strand system which has a wire enclosed in a duct (e.g., pipe, conduit, etc.). Concrete is formed around the duct and the concrete sets and cures. Then, the wire is stressed and grout material (e.g., a mixture of cement, sand, aggregate, and water) is pumped into the cavity surrounding the wire. The grout material bonds the wire to the duct, and the duct is bonded to the cured concrete. Thus, the stress applied to the wire can be transferred to the concrete. The applied stress (e.g., forces applied to the wire strand system) in the post-tensioning process causes a volume change (and/or a length change) to the concrete material. The volume change of the concrete material causes a change in the length of the concrete slab. The length change is a shortening in the direction parallel to applied stress (e.g., the post-tensioning force). 
       FIGS. 1-2  show schematic diagrams of a floor construction  10  according to a generally known process using post-tensioned concrete.  FIG. 1  shows a top-down plan view of the floor construction  10 . The floor construction  10  includes post tensioned slabs  12 ,  14  separated by a gap  16 .  FIG. 1  shows the “width” direction indicated by “W” and the “length” direction indicated by “L” ( FIGS. 2 and 3  also show the length direction indicated by “L”).  FIG. 2  shows a side view of the floor construction  10 , also showing the slabs  12 ,  14 , and the gap  16 . The floor construction  10  is made by a process wherein the post tensioned slabs  12 ,  14  are each poured separately, tensioned independent of each other after they have sufficiently cured. Thus, the rebars in the post-tensioned slab  12  do not necessarily lineup (e.g., axially) with the rebars in the post-tensioned slab  14 . 
     Each of the slabs  12 ,  14  changes volume due to their tensioning processes. The typical tensioning process for a typical floor construction uses the gap  16 , which is typically four to eight feet in length, for accommodating appropriate tooling and equipment (and also for access by workers) to tension the slabs  12 ,  14 . Further, the gap  16  (i.e., the separation between the two slabs  12 ,  14 ) becomes longer (e.g., along direction L shown in  FIG. 1 ) during and after the tensioning of one or both of the slabs  12 ,  14 . That is, the volume changes in the slabs  12 ,  14  and the slabs  12 ,  14  become shorter. And because the slabs  12 ,  14  become shorter, the separation between them, which is the gap  16 , becomes longer. 
     For example, in a typical hotel floor construction, the gap  16  can be about sixty to seventy feet in width and four to eight feet in length. Generally, the gap  16  is left open for twenty to thirty days to allow most of the volume changes (i.e., slab shortening) to occur to the post-tensioned concrete slabs  12 ,  14 . After the twenty to thirty days, the gap  16  is filled in (i.e., lap spliced) with a pour strip  18  to provide a structural continuity of the floor construction  10  required by the final design to resist all required loads. 
       FIG. 3  shows a close-up schematic view of a portion  20  of the floor construction  10  shown in  FIG. 2 . The portion  20  shows the first slab  12  having a post-tensioning wire strand system  22  for stressing the concrete  23 . The slab  12  includes a steel reinforcing bar  24  (also known as rebar) which reinforces the concrete  23  in the slab  12 . Generally, the rebar  24  and other rebar in the slab  12  are somewhat regularly positioned in the slab  12 , and extend out from the end of the slab  12  towards the gap  16 . The second slab  14 , which is also shown in the portion  20 , has its own post-tensioning wire strand system  26  for stressing the concrete  27 . The slab  14  includes a rebar  28  which reinforces the concrete  27  in the slab  14 . Generally, the rebar  28  and other rebar in the slab  14  are somewhat regularly positioned in the slab  14 , and extend out from the end of the slab  14  towards the gap  16 . In the prior art process of forming the floor construction  10 , the positioning of the rebar  28  is not based on or with respect to the position of the rebar  24 . Further, prior to the filling in of the gap  16  with the pour strip  18 , the rebar  24  extending out from the slab  12  is not connected to the rebar  28  extending out from the slab  14 . That is, prior to the filling in of the gap  16  with the pour strip  18 , the rebar  24  extending out from the slab  12  is not directly connected to the rebar  28  extending out from the slab  14 . That is, prior to the filling in of the gap  16  with the pour strip  18 , the rebar  24  extending out from the slab  12  is not indirectly connected to the rebar  28  extending out from the slab  14 . Other rebar (s)  30  is (are) positioned, or laid down, inside the gap  16  along the width direction, so that the other rebar(s)  30  is (are) perpendicular to the length direction of the rebar  24  and/or  28 . Then, the pour strip  18  is formed around the rebar  24 ,  28 ,  30  filling in the gap  16 . 
     Referring back to  FIG. 1 , in a multi-level building construction having one or more floors, the floor construction  10  can be placed above another floor. These floors are connected to and accessible via a construction elevator  30 . Generally, there is only one (or very few) construction elevator  30  that is used during the construction of the building. Accordingly, during the construction of the floor construction  10 , the slab  12  area can be accessed via the elevator  30 . However, the slab  14  area cannot be accessed easily when a gap  16  four feet and more exists between the slabs  12 ,  14 . That is, construction equipment cannot easily be moved to slab  14  from slab  12 . Thus, generally, the construction process requiring access to slab  14  waits the twenty to thirty days until the pour strip  18  is poured to splice the slabs  12 ,  14  together. Further, the gap  16  allows significant weather conditions to intrude into the floor beneath the floor construction  10 . Such weather conditions can also prevent work from being performed in the floor underneath the floor construction  10 . Despite these disadvantages of having long gaps in post-tension concrete construction, waiting and time delay are generally an accepted part of the-process in the field of construction. 
     BRIEF SUMMARY 
     Devices, systems, and methods for connecting post-tensioned concrete slabs in new floor construction reduce the distance (e.g., length) of the gap between the post-tensioned concrete slabs as compared to conventional construction. Accordingly, the devices, systems, and methods disclosed herein advantageously reduce project construction time by reducing the time delay in accessing the floor underneath the slabs due to, for example, safety and/or weather conditions. 
     An embodiment of this concrete construction includes a first post-tensioned concrete slab, a second post-tensioned concrete slab, and a cavity-forming device. The first post-tensioned concrete slab and the second post-tensioned concrete slab have respective upper surfaces that are generally aligned. The first post-tensioned concrete slab includes a plurality of first rebars installed therein. The second post-tensioned concrete slab includes a plurality of second rebars installed therein. The first post-tensioned concrete slab and second post-tensioned concrete slab are separated by a gap so that the concrete material of the first post-tensioned concrete slab is not in contact with the concrete material of the second post-tensioned concrete slab. The cavity-forming device forms a cavity. The cavity-forming device is installed in the first post-tensioned concrete slab, wherein the cavity contains a portion of one of the second rebars. 
     In an embodiment of the concrete construction, the cavity-forming device has an end which is connected to an end portion of one of the first rebars, wherein the end has a threaded surface which mates with a threaded surface of the end portion of the one of the first rebars. 
     In an embodiment of the concrete construction, a portion of one of the first rebars is also contained in the cavity. 
     In an embodiment of the concrete construction, the cavity-forming device has a pair of tubes extending upwardly through the first post-tensioned concrete slab and providing air access from above the post-tensioned concrete slab to the cavity, the cavity being filled through one of the tubes with a binding material which fixes the one of the second rebars in the cavity. 
     In an embodiment of the concrete construction, the cavity-forming device has a pair of tubes extending upwardly through the first post-tensioned concrete slab and providing air access from above the post-tensioned concrete slab to the cavity, the cavity being filled through one of the tubes with a binding material which connects together the one of the first rebars and the one of the second rebars so that the portion of the one of the first rebars and the portion of the one of the second rebars are substantially parallel with each other. 
     In an embodiment of the concrete construction, the cavity-fomiing device has a pair of tubes extending upwardly through the first post-tensioned concrete slab and providing air access from above the post-tensioned concrete slab to the cavity, the cavity being filled with a binding material which connects together the one of the first rebars and the one of the second rebars so that the portion of the one of the first rebars and the portion of the one of the second rebars are substantially inline. 
     An embodiment of the concrete construction further comprises a second cavity formed by a second cavity-forming device installed in the second post-tensioned concrete slab, wherein the second cavity contains a portion of another of the plurality of the first rebars. 
     In an embodiment of the concrete construction, the gap has a longer dimension for one side-to-side and a shorter dimension for another side-to-side, the shorter dimension being three feet or less. 
     In an embodiment of the concrete construction, the gap has a longer dimension for one side-to-side and a shorter dimension for another side-to-side, the shorter dimension being twelve (12) inches or less. In some embodiments, the distance of the shorter dimension is from two to six inches. In some embodiments, the distance of the shorter dimension is from two to seven inches. In some embodiments, the distance of the shorter dimension is from two to eight inches. In some embodiments, the distance of the shorter dimension is from two to nine inches. In some embodiments, the distance of the shorter dimension is from two to ten inches. In some embodiments, the distance of the shorter dimension is from two to eleven inches. In some embodiments, the distance of the shorter dimension is from two to twelve inches. 
     An embodiment of the concrete construction further comprises a strip of non-shrink material being in the gap, wherein the strip has a compressive strength that is greater than or equal to the compressive strength of the concrete material of the first and second post-tensioned concrete slabs. 
     An embodiment of a concrete construction includes a first post-tensioned concrete slab, a second post-tensioned concrete slab, and a cavity-forming device, the first post-tensioned concrete slab and the second post-tensioned concrete slab having respective upper surfaces that are generally aligned, the first post-tensioned concrete slab including a plurality of first rebars installed therein, the second post-tensioned concrete slab including a plurality of second rebars installed therein, the first post-tensioned concrete slab and second post-tensioned concrete slab being separated by a gap so that the concrete material of the first post-tensioned concrete slab is not in contact with the concrete material of the second post-tensioned concrete slab, the cavity-forming device forming a cavity which together with the device form a volume, the cavity-forming device being installed in the first post-tensioned concrete slab, wherein one of the second rebars connects with the volume, the cavity being filled with a binding material which connects together the first post-tensioned concrete slab and the one of the second rebars, the gap having a longer dimension for one side-to-side and a shorter dimension for another side-to-side, the shorter dimension being twelve (12) inches or less, the gap being filled with a strip of non-shrink material, wherein the strip has a compressive strength that is greater than or equal to the compressive strength of the concrete material of the first and second post-tensioned concrete slabs. 
     In an embodiment of a method for making a concrete construction including a first post-tensioned concrete slab and a second post-tensioned concrete slab separated by a gap, the method includes the steps of forming the first post-tensioned concrete slab with a plurality of first rebars, wherein the first post-tensioned concrete slab includes a cavity-forming device with a cavity having an opening towards an end of the first post-tensioned concrete slab; prior to pouring a second concrete slab, positioning one of a plurality of second rebars for the second concrete slab so that a portion of the one of the plurality of second rebars is inside the cavity; pouring the second concrete slab; forming the second post-tensioned concrete slab by tensioning the second concrete slab, thus forming the gap between the first post-tensioned concrete slab and the second post-tensioned concrete slab, wherein the gap has a longer dimension for one side-to-side and a shorter dimension for another side-to-side; and after forming the second post-tensioned concrete slab, securely fixing the portion of the one of the plurality of the second rebars in the cavity. 
     An embodiment of the method, the step of securely fixing the portion of the second rebar in the cavity includes also securely fixing a portion of the first rebar in the cavity. In an embodiment of the method, the shorter dimension is three feet or less in length. 
     An embodiment of the method further comprises the step of forming a strip of material in the gap with a non-shrink material, wherein the strip has a compressive strength that is greater than or equal to the compressive strength of the concrete material of the first and second post-tensioned concrete slabs. 
     In an embodiment of a method for making a concrete construction including a first post-tensioned concrete slab and a second post-tensioned concrete slab separated by a gap, the method comprises the steps of forming the first post-tensioned concrete slab, wherein the first post-tensioned concrete slab includes a first rebar installed therein, and an end portion of the first rebar extends into a space that will become the gap; before a second post-tensioned concrete slab has been formed, positioning a cavity-forming device having a cavity at an end portion of the first rebar so that the end portion of the first rebar is inside the cavity, but not securely connecting the cavity-forming device to the end portion of the first rebar; pouring the second concrete slab; forming a second post-tensioned concrete slab by tensioning the second concrete slab, thus forming the gap between the first post-tensioned concrete slab and the second post-tensioned concrete slab, wherein the gap has a longer dimension for one side-to-side and a shorter dimension for another side-to-side; and after forming the second post-tensioned concrete slab, securely fixing the end portion of the first rebar in the cavity. 
     An embodiment of the method includes, prior to forming the second post-tensioned concrete slab, positioning a second rebar inside the cavity but not securely connecting the cavity-forming device to the second rebar; and in the securely fixing the portion of the first rebar in the cavity step, also securely fixing a portion of a second rebar of the second post-tensioned concrete slab in the cavity. 
     An embodiment of the method further includes the step of forming a strip of material in the gap with a non-shrink material, wherein the strip has a compressive strength that is greater than or equal to the compressive strength of the concrete material of the first and second post-tensioned concrete slabs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-2  show plan and elevation schematic diagrams, respectively, of a floor construction according to a generally known process using post-tensioned concrete. 
         FIG. 3  shows an enlarged, elevational schematic view of a portion of the floor construction shown in  FIG. 2 . 
         FIGS. 4-5  show plan and elevation schematic diagrams, respectively, of a floor construction according to an embodiment of the present invention. 
         FIG. 6  shows a schematic side view of a floor construction according to an embodiment of the present invention. 
         FIG. 7  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 8  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 9  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 10  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 11  shows a schematic perspective view of the floor construction shown in  FIG. 10 . 
         FIG. 12  shows a flow chart of an embodiment of a process for constructing the floor construction with reduced gap design. 
         FIGS. 13-18  show schematic side views of floor constructions being constructed according to an embodiment of the process. 
         FIG. 19  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 20  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 21  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 22  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 23  shows a schematic side view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 24  shows a schematic plan view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 25  shows a schematic plan view of an embodiment of a floor construction according to an embodiment of the present invention. 
         FIG. 26  shows a schematic plan view of an embodiment of a floor construction according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The systems, devices, and methods disclosed herein are directed towards reducing the gap between post-tensioned concrete slabs in a floor construction, so that time delay caused by the existence of conventional gaps in the floor construction can be reduced and/or eliminated. 
       FIGS. 4-5  show schematic diagrams of a floor construction  100  according to an embodiment.  FIG. 4  shows the “width” direction indicated by “W” and the “length” direction indicated by “L” ( FIGS. 5-11 and 13-26  also show the length direction indicated by “L”). The floor construction  100  includes post-tensioned concrete slabs  102 ,  104 .  FIG. 4  shows a top-down plan view of the floor construction  100 . The floor construction  100  includes post tensioned slabs  102 ,  104  separated by a gap  106 .  FIG. 5  shows a side view of the floor construction  100 , also showing the slabs  102 ,  104 , and the gap  106 . The distance of the gap  106  is substantially less than the conventional gap. For example, it is possible that the gap  106  is less than three feet in distance. In a preferred embodiment, the gap  106  is a foot or less in distance. 
     Accordingly, the floor construction  100  can advantageously reduce the overall construction time of the construction project associated with the floor construction  100 , because the time delay in accessing the floor underneath the floor construction  100  due to, for example, safety and/or weather conditions, is substantially reduced or eliminated. Further, in a multi-level building construction having one or more floors, the floor construction  100  can be placed above another floor. These floors are connected to and accessible via a construction elevator  108 . Accordingly, during the construction of the floor construction  100 , the slab  104  area can be accessed via the elevator  108  because the gap  106  has a distance that is small (or short) enough that the gap  106  can be crossed over, and/or the gap  106  can be covered with small piece of material such as, for example, a sheet of metal or a plank of wood, to serve as a short bridge between the slabs  102 ,  104 . Accordingly, the construction equipment can be easily moved between slab  104  and slab  102 . Thus, the generally required twenty to thirty day waiting period for accessing areas of the floor that cannot be reached due to the conventional gap ( 16  shown in  FIG. 1 ) can be eliminated. In a multi-level building construction and/or very large building construction having large square footage floors, the reduction or elimination of the twenty to thirty day waiting period per gap compounds to an enormous reduction in the overall construction time required for the project. 
     Further, the gap  106  can substantially reduce or prevent weather conditions to intrude into the floor beneath the floor construction  100 . Thus, weather conditions no longer prevent work from being performed in the floor underneath the floor construction  100 . Therefore, waiting and time delay associated with weather conditions can be reduced or eliminated from the construction process. 
       FIG. 6  shows a schematic side view of a floor construction  200  according to an embodiment. The floor construction  200  includes a floor  202  formed by joining two post-tensioned concrete slabs with a pour strip filled into a gap between the two post-tensioned concrete slabs. The first post-tensioned concrete slab includes at least one rebar  204  that is connected to a cavity-forming device  206 . Preferably, the cavity-forming device  206  is less than a foot in length. The second post-tensioned concrete slab includes another rebar  208  that is connected to the cavity-forming device  206 . The rebars  204 ,  208  can be aligned substantially parallel with each other and/or aligned to be continuous along the length (axial) direction. Although not shown in the schematic view, it will be understood that the floor construction  200  can include a plurality of rebars in the first post-tensioned concrete slab, wherein each of the rebars is fixed with respect to cavity-forming devices. Further, a plurality of rebars in the second post-tensioned concrete slab are each fixed with respect to the respective cavity-forming device, so that each cavity-forming device fixes the rebar of the first post-tensioned concrete slab with respect to the rebar of the second post-tensioned concrete slab. After a grout (a binding material) is inserted into the cavities of the cavity forming devices to fix the respective rebars in the cavities, the cavity-forming devices provide structural integrity to the floor and becomes the force and/or tension transferring devices. That is, force and/or tension can be transferred through the cavity-forming devices to and/or from the rebars. Preferably, the grout is stronger than the concrete slab. 
       FIG. 7  shows a schematic side view of an embodiment of a floor construction  300 , which is similar to the floor construction  200  shown in  FIG. 6 . The floor construction  300  can include similar components as the floor construction  200  of  FIG. 6 . The floor construction  300  includes a floor  301  formed by joining two post-tensioned concrete slabs with a pour strip filled into a gap between the two post-tensioned concrete slabs. The first post-tensioned concrete slab includes at least one rebar  204  that is connected to a cavity-forming device  304  having a cavity  306 . The second post-tensioned concrete slab includes another rebar  208  that is inserted into the cavity  306  of the cavity-forming device  304 . During the process of forming the floor construction  300 , the end portion of the second rebar  208  is allowed to move within the cavity  306  of the cavity-forming device  304  during the tensioning of the second slab. After the second post-tensioned concrete slab is formed, the cavity  306  of the cavity-forming device  304  is filled with, for example, grout material, to bind (e.g., fix and/or connect) the end portion of the second rebar  208  that is in the cavity  306  to the cavity-forming device  304 . Accordingly, the cavity-forming device  304  becomes connected to both the first rebar  204  and the second rebar  208 . The rebars  204 ,  208  can be aligned substantially parallel with each other and/or aligned to be continuous along the length (axial) direction. Although not shown in the schematic view, it will be understood that the floor construction  300  can include a plurality of rebars in the first post-tensioned concrete slab, wherein each of the rebars is connected to cavity-forming devices. Further, a plurality of rebars in the second post-tensioned concrete slab are each connected to the respective cavity-forming device, so that each cavity-forming device fixes the rebar of the first post-tensioned concrete slab with respect to the rebar of the second post-tensioned concrete slab. The force and/or tension can be transferred through the cavity-forming device  304  to and/or from the rebars  204 ,  208 . 
       FIG. 8  shows a schematic side view of an embodiment of a floor construction  310 , which is similar to the floor construction  300  shown in  FIG. 7 . The floor construction  310  includes the first post-tensioned concrete slab  312  and the second post-tensioned concrete slab  314 , and the pour strip  316  filled into the gap  318  that is between the two post-tensioned concrete slabs  312 ,  314 . The first post-tensioned concrete slab  312  includes at least one rebar  204  that is connected to a cavity-forming device  304  having a cavity  306 . The cavity-forming device  306  is positioned in the first post-tensioned concrete slab  312  so that the cavity  306  is provided as a part of the first post-tensioned concrete slab  312 . The end portion of the second rebar  208  is positioned in the cavity  306  of the cavity-forming device  304 . 
     During the process of forming the floor construction  310 , the end portion of the second rebar  208  is allowed to move within the cavity  306  of the cavity-forming device  304  as the second post-tensioned concrete slab  314  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  314  is formed, the cavity  306  of the cavity-forming device  304  is filled with, for example, grout material to bind the end portion of the second rebar  208  that is in the cavity  306 , and thus fixing the second rebar  208  with respect to the cavity-forming device  304 . 
       FIG. 9  shows a schematic side view of an embodiment of a floor construction  320 , which includes a first post-tensioned concrete slab  322  and a second post-tensioned concrete slab  324 , and a pour strip  326  filled into a gap  328  that is between the two post-tensioned concrete slabs  322 ,  324 . The first post-tensioned concrete slab  322  includes a plurality of rebars  326 ,  328  that are connected to respective cavity-forming devices  330 ,  332 , wherein each of the cavity-forming devices  330 ,  332  has a cavity  334 ,  336 . The cavity-forming devices  330 ,  332  are positioned in the first post-tensioned concrete slab  322  so that the cavities  334 ,  336  are provided as parts of the first post-tensioned concrete slab  322 . End portions of a plurality of rebars  338 ,  340  of the second post-tensioned concrete slab  324  are positioned in the respective cavities  334 ,  336 . During the process of forming the floor construction  320 , the end portions of the rebars  338 ,  340  are allowed to move within the respective cavities  334 ,  336  as the second post-tensioned concrete slab  324  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  324  is formed, the cavities  334 ,  336  are each filled with, for example, grout material to bind the end portions of the rebars  338 ,  340  to the respective cavity-forming devices  330 ,  332 . 
       FIGS. 10 and 11  show an embodiment of a floor construction  350 .  FIG. 10  shows a schematic side view of the floor construction  350 .  FIG. 11  shows an enlarged schematic perspective view of the floor construction  350 . The floor construction  350  includes a first post-tensioned concrete slab  352  and a second post-tensioned concrete slab  354 , and a pour strip  356  filled into a gap  358  that is between the two post-tensioned concrete slabs  352 ,  354 .  FIG. 11  does not show the pour strip in the gap  358 . The first post-tensioned concrete slab  352  includes a plurality of rebars  360 ,  362 . The second post-tensioned concrete slab  354  includes a plurality of rebars  364 ,  366 . At least one  362  of the rebars  360 ,  362  of the first post-tensioned concrete slab  352  is connected to a cavity-forming device  368  having a cavity  370 , wherein the cavity-forming device  368  is positioned at least partly within the material of the first post-tensioned concrete slab  352 . Preferably, the cavity-forming device  368  is positioned completely within the material of the first post-tensioned concrete slab  352 . An end portion of the rebar  366  of the second post-tensioned concrete slab  354  is positioned within the cavity  370 . During the process of forming the floor construction  350 , the end portion of the rebar  366  is allowed to move within the cavity  370  as the second post-tensioned concrete slab  354  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  354  is formed, the cavity  370  is filled with, for example, grout material to bind the end portion of the rebar  366  to the cavity-forming device  368 . Further, at least one  364  of the rebars  364 ,  366  of the second post-tensioned concrete slab  354  is connected to a cavity-forming device  372  having a cavity  374 , wherein the cavity-forming device  372  is positioned at least partly within the material of the second post-tensioned concrete slab  354 . Preferably, the cavity-forming device  372  is positioned completely within the material of the second post-tensioned concrete slab  354 . An end portion of one of the rebars  360  of the first post-tensioned concrete slab  352  is positioned within the cavity  374 . During the process of forming the floor construction  350 , the cavity-forming device  372  is allowed to move as the second post-tensioned concrete slab  354  is formed by tensioning of the concrete material. Accordingly, while the end portion of the rebar  360  is contained in the cavity  374 , during the tensioning of the concrete material in forming the second post-tensioned concrete slab  354 , the volume change of the concrete material moves the cavity-forming device  372  with respect to the rebar  360 . After the second post-tensioned concrete slab  354  is formed, the cavity  374  is filled with, for example, grout material to bind the end portion of the rebar  360  to the cavity-forming device  372 . 
       FIG. 12  shows a flow chart of an embodiment of a process  400  for constructing the floor construction with reduced gap design. The process includes a step  402  of positioning one or more rebars for a first concrete slab, prior to pouring the concrete material. Then, in step  404 , cavity-forming devices are positioned at near where an edge of the concrete slab would form. Preferably, the cavity-forming devices are splice devices connected to and/or positioned at ends of the rebars. If desired, the cavity-forming devices can be connected, attached, and/or secured on to the rebars of the first slab at this time. This particular step can depend on the particular features of the cavity-forming device used. The process  400  includes a step  406  of forming the first concrete slab, wherein the first concrete slab includes one or more rebars and one or more cavities (and cavity-forming devices and/or splice devices). Preferably, the cavities are elongated and generally cylindrical in shape. Further, the cavities are positioned near the end of the first concrete slab. It is preferable that the cavities are formed by and/or defined by one or more cavity-forming devices. It is preferable that the end portion and/or near the end of one or more rebars is connected to a respective cavity-forming device at or near an end portion of the cavity-forming device. It is possible that the end portion of one or more rebars is positioned inside the cavity that is defined by the cavity-forming device, but not yet directly connected to the cavity-forming device. Further, it is possible that the ends of one or more rebars are positioned to extend out from an edge of the first slab. It is preferable that these ends of the rebars do not extend more than six inches beyond the edge of the first slab. It is more preferable that these ends of the rebars do not extend more than two inches beyond the edge of the first slab. It is even more preferable that the ends of the rebars of the first concrete slab do not extend out from an edge of the first slab. The process  400  includes a step  408  of forming a first post-tensioned concrete slab by tensioning the concrete material of the first concrete slab. The process  400  further includes a step  410  of positioning the rebars for the second concrete slab so that their ends are positioned within respective cavities (e.g., inner chambers of the cavity-forming devices) of the first post-tensioned concrete slab. This step  410  is performed prior to pouring the concrete for the second concrete slab. These rebars are positioned so that they can move with respect to the cavities (e.g., cavity-forming devices, splice devices, and/or the edge of the first post-tensioned concrete slab). That is, for example, the rebars for the second concrete slab are not secured to the cavity-forming devices at this stage of the process. It is preferable that the positioning of the rebars for the second concrete slab with respect to the cavity-forming devices are done after the first concrete slab has been tensioned (e.g., using the wire strand system that is included in the concrete slab) and has gone through the volume change, becoming the first post-tensioned concrete slab. Thus, the positioning of the rebars for the second concrete slab can be done with a desired gap space in mind. That is, after the first post-tensioned concrete slab has formed, the length change along the length direction of the rebars would have been completed. Thus, the length of the gap can be estimated and/or substantially determined. It is preferable that this estimated and/or substantially determined gap distance is less than a foot. It is even more preferable that this gap distance is less than six inches. Further, at this stage in the process  400 , the cavities are open to where the gap between the first and second concrete slabs will exist when the second concrete slab is formed. The process  400  includes a step  412  of pouring and forming the second concrete slab. The second concrete slab includes one or more rebars that have end portions positioned within the cavities of the first post-tensioned concrete slab and/or any additional cavity-forming devices that have been placed for forming additional cavities within the second concrete slab. The process  400  includes a step  414  of forming a second post-tensioned concrete slab by tensioning the concrete material of the second concrete slab. In step  414 , the second concrete slab is shortened along the length direction of the rebar by and due to tensioning of a wire strand system in the second concrete slab. Because the rebars for the second concrete slab are not secured to the cavities of the first post-tensioned concrete slab, the rebars can and do move with respect to the cavities during the tensioning of the second concrete slab. Likewise, if there are any additional cavity-forming devices that have been positioned to be within the second concrete slab, and these cavities contain ends of the rebars of the first post-tensioned concrete slab, the additional cavities move with respect to the rebars contained therein during the tensioning and forming the second post-tensioned concrete slab. After the volume changes due to tensioning of the second concrete slab has been completed, the second concrete slab is the second post-tensioned concrete slab. The process  400  includes a step  416  of connecting and/or securing the rebars of the second post-tensioned concrete slab to the cavity-forming devices. In addition, if in the step  404  the cavity-forming device was not secured to the rebar of the first concrete slab, then, in step  416 , the cavity-forming device can be secured to the first rebar of the first post-tensioned concrete slab. Accordingly, in the step  416 , both of the first and second rebars of the first and second post-tensioned concrete slabs can be secured (e.g., fixed or connected) within the cavity of the cavity-forming device (e.g., this particular step can depend on the particular features of the cavity-forming device used). At this stage in the process  400 , the gap between the first post-tensioned concrete slab and the second post-tensioned concrete slab is generally fixed. Accordingly, the gap distance is generally known. The gap distance of three feet or less is possible. Preferably, the gap distance at this stage is one foot or less. Even more preferably, the gap distance is less than a foot. The process  400  includes a step  418  of filling in the gap between the first and second post-tensioned concrete slabs with material to form a pour strip. When the pour strip is formed in the gap, the cavity-forming devices connected to the rebars of the first and second post-tensioned concrete slabs are covered by the pour strip. It is preferable that the cavity-forming devices positioned in the gap are completely covered by the pour strip. 
       FIGS. 13-18  show schematic side views of floor constructions  500   a - f , respectfully, being constructed according to the process  400  described above and shown in  FIG. 12 . Like elements are referred to with the same reference numerals. The floor constructions  500   a - f  show cavity-forming devices  502 ,  504  having the same features. Each of the cavity-forming devices  502 ,  504  has a generally cylindrical shape. In some embodiments, the cavity-forming device has an elongated shape with a geometric base (e.g., circle, oval, ovoid, triangle, square, rectangular, hexagon, octagon, etc.). The body  506  of the cavity-forming device  502  defines a cavity  508 , and the body  506  has an opening  510  at one of the ends that allows access to the cavity by a rebar ( 530  shown in  FIGS. 15-18 ). The cavity  508  is configured to allow the rebar ( 530  shown in  FIGS. 15-18 ) to move with respect to the cavity  508  and/or the splice device  502  during tensioning of a concrete slab which includes the rebar ( 530  shown in  FIGS. 15-18 ). The body  506  also has another end  512  opposite from the opening  510  along the length direction of the body  506 . The end  512  includes a connector  514  configured for connecting and securing to an end of a rebar  522 . For example, the connector  514  can be a threaded chamber, wherein the inner side surface of the connector  514  is threaded to mate with matching threads of the rebar. Accordingly, the rebar  522  that is used to connect at the end  512  of the cavity-forming device  502  requires matching threads at the surface of the rebar  522 . The cavity-forming device  502  includes grout material for connecting the rebars  522 ,  530 . The cavity  508  can be accessed (e.g., for filling in the cavity with the grout material in order to secure a portion of the rebar to the cavity-forming device) via an inlet  516 . The splice device  502  can also include an outlet  518 , wherein the air in the cavity  508  can be evacuated out via the outlet  518  during the filling of the cavity  508  with the grout material. Additionally and/or alternatively, the air in the cavity  508  can be evacuated out via the opening  510  during the filling of the cavity  508  with the grout material. After the grout material fills in the cavity  508 , the rebars  522 ,  530  are connected or fixed securely via the cavity-forming device  502 . 
       FIG. 13  shows the floor construction  500   a , wherein a first concrete slab  520  is formed with rebars  522 ,  524  therein (see steps  402  and  404  in the process  400  of  FIG. 12 ). End portions of the rebars  522 ,  524  are connected to respective cavity-forming devices  502 ,  504 . It is possible that the cavity-forming devices  502 ,  504  are positioned to not extend beyond the end of the first concrete slab  520  and into a location  526  where a gap will exist when a second concrete slab is formed. Optionally, the opening  510  can be covered with a sheath during the pouring of the concrete material when the first concrete slab  520  is being formed to prevent the concrete material from entering into the cavity  508 . Further, the inlet  516  and the outlet  518  can have elongated tubes to extend towards and out from the surface of the first concrete slab  520  to prevent the concrete material from entering into the cavity  508 . 
       FIG. 14  shows the floor construction  500   b , wherein the first concrete slab ( 520  shown in  FIG. 13 ) has been tensioned and has become a first post-tensioned concrete slab  528 . The volume of the first post-tensioned concrete slab  528  has changed from the volume of the first concrete slab  520 , and a length of the first concrete slab  520  along the length direction of the rebars  522 ,  524  has been reduced by the tensioning, indicated by ΔL 1  (see step  406  in the process  400  of  FIG. 12 ). Accordingly, the first post-tensioned concrete slab  528  includes cavities  508 ,  509  for receiving and containing ends of the rebars ( 530 ,  532  shown in  FIGS. 15-18 ) of the second concrete slab. 
       FIG. 15  shows the floor construction  500   c , wherein additional rebars  530 ,  532  of the second concrete slab  534  are positioned so that each of the rebars  530 ,  532  has an end portion inside the respective cavities  508 ,  509  of the first post-tensioned concrete slab  528  (see step  410  in the process  400  of  FIG. 12 ). The rebars  530 ,  532  can be aligned in a length direction of the rebars  522 ,  528  guided by the cavity-forming devices  502 ,  504 . The second concrete slab  534  is poured to include the rebars  530 ,  532  (see step  412  in the process  400  of  FIG. 12 ). Because the cavities  508 ,  509  in the first post-tensioned concrete slab  528  accommodate the ends of the rebars  530 ,  532  and allow the rebars  530 ,  532  to move during the tensioning of the second concrete slab  534 , the edge of the second concrete slab  534  can be positioned closer to the edge of the first post-tensioned concrete slab  528  than conventional floor constructions. For example, it is possible that the distance from the edge of the second concrete slab  534  to the edge of the first post-tensioned concrete slab  528  is three feet or less. Preferably, the distance from the edge of the second concrete slab  534  to the edge of the first post-tensioned concrete slab  528  is one foot or less. 
       FIG. 16  shows the floor construction  500   d , wherein the second concrete slab ( 534  shown in  FIG. 15 ) has been tensioned and has become a second post-tensioned concrete slab  536  (see step  414  in the process  400  of  FIG. 12 ). Thus, the volume of the second post-tensioned concrete slab  536  has changed from the volume of the second concrete slab  534 , and a length of the second concrete slab  534  along the length direction of the rebars  530 ,  532  has been reduced by the tensioning, indicated by ΔL 2 . Where the gap  538  now exists, it is possible that the gap  538  is three feet or less. Preferably, the gap  538  is one foot or less. The cavity-forming devices  502 ,  504  are not yet secured to the rebars  530 ,  532 . Thus, during the change in volume and length of the second concrete slab, the rebars  530 ,  532  are allowed to move with respect to the cavities  508 ,  509  and/or the cavity-forming device  502 ,  504 . For example, shown in  FIG. 17 , as the length of the second concrete slab is reduced in the floor construction  500   e , thus lengthening the location between the first post-tensioned concrete slab  528  and the second concrete slab to form the gap  538 , the rebars  530 ,  532  may move (e.g., slide) away from the respective cavity-forming devices  502 ,  504  in the direction of the length change indicated by ΔL 3 . In embodiments, ΔL 2  is equal to, the same as, or substantially similar to ΔL 3 . The length change ΔL 3  does not move the end portion of the rebars  530 ,  532  so much that the length change ΔL 3  prevents the rebars  530 ,  532  from being connected and/or secured to the respective cavity-forming devices  502 ,  504 . This prevention is predetermined in the positioning of the rebars  530 ,  532 , for example, in step  410  in the process  400  of  FIG. 12 , and/or structural features included in the cavity-forming devices  502 ,  504 . After the volume change due to tensioning has been completed and the second post-tensioned concrete slab  536  has formed, the gap  538  between the first post-tensioned concrete slab  528  and the second post-tensioned concrete slab  536  is substantially defined. 
       FIG. 18  shows the floor construction  500   f , wherein the cavity-forming devices  502 ,  504  have been securely connected to the end portions of the respective rebars  530 ,  532  (see step  416  in the process  400  of  FIG. 12 ). The connection can be accomplished by filling the cavities  508 ,  509  of each of the cavity-forming devices  502 ,  504  with grout material for securely binding the end portions of the respective rebars  530 ,  532  to the cavity-forming devices  502 ,  504 . The floor construction  500   f  is positioned substantially horizontal with respect to the earth, and the floor construction  500   f  includes the first post-tensioned concrete slab  528  and the second post-tensioned concrete slab  536  separated by the gap  538 . The cavity-forming devices  502 ,  504  are secured to the respective rebars  522 ,  524 ,  530 ,  532  with sufficient strength for structural applicability for connecting the two post-tensioned concrete slabs  528 ,  536  for structural purposes. The gap  538  has been filled in with a material to form a pour strip  540  (see step  418  in the process  400  of  FIG. 12 ). The pour strip  540  covers the gap  538  sufficiently for structural purposes. Preferably, the gap  538  (e.g., edge to edge between the slabs  528 ,  536 ) is completely covered by the pour strip  526 . 
       FIG. 19  shows a schematic side view of an embodiment of a floor construction  600 . The floor construction  600  can include similar components as the floor construction  200  of  FIG. 6  and/or the floor construction  300  of  FIG. 7 . The floor construction  600  includes a floor  601  formed by joining two post-tensioned concrete slabs with a pour strip filled into a gap between the two post-tensioned concrete slabs. The first post-tensioned concrete slab includes at least one rebar  204  that is inserted into a cavity  602  of a cavity-forming device  604 . The second post-tensioned concrete slab includes another rebar  208  that is inserted into the cavity  602  of the cavity-forming device  604 . During the process of forming the floor construction  600 , the end portion of the second rebar  208  is allowed to move within the cavity  602  during the tensioning of the second slab. After the second post-tensioned concrete slab is formed, the cavity  602  is filled with, for example, grout material, to bind the end portions of the first and second rebars  204 ,  208  that are in the cavity  602  of the cavity-forming device  604 . Accordingly, the cavity-forming device  604  becomes fixed or connected to both the first rebar  204  and the second rebar  208 . The rebars  204 ,  208  can be aligned substantially parallel with each other and/or aligned to be continuous along the length (axial) direction. Although not shown in the schematic view, it will be understood that the floor construction  600  can include a plurality of rebars in the first post-tensioned concrete slab, wherein each of the rebars is fixed with respect to cavity-forming devices. Further, a plurality of rebars in the second post-tensioned concrete slab are each fixed or connected with respect to the respective cavity-forming device, so that each cavity-forming device connects the rebar of the first post-tensioned concrete slab with respect to the rebar of the second post-tensioned concrete slab. 
       FIG. 20  shows a schematic side view of an embodiment of a floor construction  610 , which is similar to the floor construction  600  shown in  FIG. 19 . The floor construction  610  includes the first post-tensioned concrete slab  612  and the second post-tensioned concrete slab  614 , and the pour strip  616  filled into the gap  618  that is between the two post-tensioned concrete slabs  612 ,  614 . The first post-tensioned concrete slab  612  includes at least one cavity-forming device  620  having a cavity  622 . Accordingly, the cavity-forming device  620  forms the cavity  622  in the first post-tensioned concrete slab  612  having an opening  630  towards the gap  618 . The end portions of the first and second rebars  204 ,  208  are positioned in the cavity  622 . During the process of forming the floor construction  610 , the end portion of the second rebar  208  is allowed to move within the cavity  622  as the second post-tensioned concrete slab  614  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  614  is formed, the cavity  622  is filled with, for example, grout material  624 , to bind the end portions of the first and second rebars  204 ,  208  that are in the cavity  622  to the cavity-forming device  620 . The cavity-forming device  620  includes an inlet  626  for directing the grout material into the cavity  622 , and an outlet  628  for directing flow of air and other fluids and particles to aid in the grout material from entering and filling up the cavity  622 . Optionally, the cavity-forming device  620  may include a lid at an opening  630  of the cavity for preventing cement material or other materials from entering into the cavity  622  when such prevention is needed and/or desired. For example, when pouring the concrete materials around the rebar  204 , it may be desirable to prevent the concrete materials from entering into the cavity  622 . The lid can be placed at the opening  630  to prevent the concrete materials from entering into the cavity  622 . Further, the inlet  626  and the outlet  628  can be configured to have an elongated tube shape having a height that is sufficient to extend to a top surface of the concrete slab  612 . The force and/or tension in the floor construction  610  can be transferred through the cavity-forming device  620  to and/or from the rebars  204 ,  208 . 
       FIG. 21  shows a schematic side view of an embodiment of a floor construction  650 , which is similar to the floor construction  600  shown in  FIG. 19 . The floor construction  650  includes the first post-tensioned concrete slab  652  and the second post-tensioned concrete slab  654 , and the pour strip  616  filled into the gap  618  that is between the two post-tensioned concrete slabs  652 ,  654 . The second post-tensioned concrete slab  654  includes at least one cavity-forming device  620  having a cavity  622 . Accordingly, the cavity-forming device  620  forms the cavity  622  in the second post-tensioned concrete slab  654  having an opening  630  towards the gap  618 . The end portions of the first and second rebars  204 ,  208  are positioned in the cavity  622 . During the process of forming the floor construction  610 , the end portion of the second rebar  208  is allowed to move within the cavity  622  as the second post-tensioned concrete slab  614  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  614  is formed, the cavity  622  is filled with, for example, grout material  624 , to bind the end portions of the first and second rebars  204 ,  208  that are in the cavity  622  to the cavity-forming device  620 . The cavity-forming device  620  includes an inlet  626  for directing the grout material into the cavity  622 , and an outlet  628  for directing flow of air and other fluids and particles to aid in the grout material from entering and filling up the cavity  622 . Optionally, the cavity-forming device  620  may include a lid at an opening  630  of the cavity for preventing cement material or other materials from entering into the cavity  622  when such prevention is needed and/or desired. For example, when pouring the concrete materials around the rebar  208 , it may be desirable to prevent the concrete materials from entering into the cavity  622 . The lid can be placed at the opening  630  to prevent the concrete materials from entering into the cavity  622 . Further, the inlet  626  and the outlet  628  can be configured to have an elongated tube shape having a height that is sufficient to extend to a top surface of the concrete slab  654 . An embodiment of a floor construction includes both the configuration shown in  FIGS. 20 and 21 . 
       FIG. 22  shows a schematic side view of an embodiment of a floor construction  700 . The floor construction  700  can include similar components as the floor construction  200  of  FIG. 6 , the floor construction  300  of  FIG. 7 , and/or the floor construction  600  of  FIG. 19 . The floor construction  700  includes a floor  701  formed by joining two post-tensioned concrete slabs with a pour strip filled into a gap between the two post-tensioned concrete slabs. At least one of the post-tensioned concrete slabs includes at least one rebar  708  that is inserted into a cavity  702  of a cavity-forming device  704 . During the process of forming the floor construction  700 , the end portion of the rebar  708  is allowed to move within the cavity  702  during the tensioning of the associated concrete slab. After the post-tensioned concrete slab is formed, the cavity  702  is filled with, for example, grout material, to bind the end portions of the rebar  708  that is in the cavity  702  to the cavity-forming device  704 . Accordingly, the cavity-forming device  704  becomes connected to the rebar  708 . Although not shown in the schematic view, it will be understood that the floor construction  700  can include a plurality of rebars in the first post-tensioned concrete slab, wherein each of the rebars can be connected to cavity-forming devices. Further, a plurality of rebars in the second post-tensioned concrete slab can be connected to the respective cavity-forming device. 
       FIG. 23  shows a schematic side view of an embodiment of a floor construction  710 , which is similar to the floor construction  700  shown in  FIG. 22 . The floor construction  710  includes the first post-tensioned concrete slab  712  and the second post-tensioned concrete slab  714 , and the pour strip  716  filled into the gap  718  that is between the two post-tensioned concrete slabs  712 ,  714 . The first post-tensioned concrete slab  712  includes at least one cavity-forming device  720  having a cavity  722 . Accordingly, the cavity-forming device  720  forms the cavity  722  in the first post-tensioned concrete slab  712  having an opening  730  towards the gap  718 . The cavity-forming device  720  can include a corrugated outer surface  740  that increases a surface area of the cavity-forming device  720 . The increased surface area of the outer surface  740  can advantageously increase areas of contact between the cavity-forming device  720  and the concrete material of the concrete slab, and can enhance the structural strength in this region of the floor construction. Further, the corrugated material making up the cavity-forming device  720  can be made from corrugated metal sheets, which can significantly reduce cost. The end portion of the rebar  708  of the second post-tensioned concrete slab  714  is positioned in the cavity  722 . During the process of forming the floor construction  710 , the end portion of the rebar  708  is allowed to move within the cavity  722  as the second post-tensioned concrete slab  714  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  714  is formed, the cavity  722  is filled with, for example, grout material  724 , to bind the end portion of the rebar  708  in the cavity  722  to the cavity-forming device  720 . The cavity-forming device  720  includes an inlet  726  for directing the grout material into the cavity  722 , and an outlet  728  for directing flow of air and other fluids and particles to aid in the grout material from entering and filling up the cavity  722 . Optionally, the cavity-forming device  720  may include a lid at the opening  730  of the cavity  722  for preventing cement material or other materials from entering into the cavity  722  when such prevention is needed and/or desired. For example, when pouring the concrete materials around the cavity-forming device  720 , it may be desirable to prevent the concrete materials from entering into the cavity  722 . The lid can be placed at the opening  730  to prevent the concrete materials from entering into the cavity  722 . Further, the inlet  726  and the outlet  728  can be configured to have an elongated tube shape having a height that is sufficient to extend to a top surface of the concrete slab  712 . 
       FIG. 24  shows a schematic side view of an embodiment of a floor construction  750 , which is similar to the floor construction  700  shown in  FIG. 22 . The floor construction  750  includes the first post-tensioned concrete slab  752  and the second post-tensioned concrete slab  754 , and the pour strip  716  filled into the gap  718  that is between the two post-tensioned concrete slabs  752 ,  754 . The second post-tensioned concrete slab  754  includes at least one cavity-forming device  720  having a cavity  722 . Accordingly, the cavity-forming device  720  forms the cavity  722  in the second post-tensioned concrete slab  754  having an opening  730  towards the gap  718 . The end portion of the rebar  204  of the first post-tensioned concrete slab  752  is positioned in the cavity  722 . During the process of forming the floor construction  710 , the cavity-forming device  720  is allowed to move with respect to the end portion of the rebar  204  that is inside the cavity  722  as the second post-tensioned concrete slab  714  is formed by tensioning of the concrete material. After the second post-tensioned concrete slab  714  is formed, the cavity  722  is filled with, for example, grout material  724 , to bind the end portion of the rebar  204  that is inside the cavity  722  of the cavity-forming device  720 . The cavity-forming device  720  includes an inlet  726  for directing the grout material into the cavity  722 , and an outlet  728  for directing flow of air and other fluids and particles to aid in the grout material from entering and filling up the cavity  722 . Optionally, the cavity-forming device  720  may include a lid at an opening  730  of the cavity for preventing cement material or other materials from entering into the cavity  722  when such prevention is needed and/or desired. For example, when pouring the concrete materials around the cavity-forming device  720 , it may be desirable to prevent the concrete materials from entering into the cavity  722 . The lid can be placed at the opening  730  to prevent the concrete materials from entering into the cavity  722 . Further, the inlet  726  and the outlet  728  can be configured to have an elongated tube shape having a height that is sufficient to extend to a top surface of the concrete slab  754 . An embodiment of a floor construction includes both the configuration shown in  FIGS. 23 and 24 . 
       FIG. 25  shows a top-down plan view of an embodiment of the floor construction  800 , wherein the floor construction  800  has all of the cavity-forming devices  802  in one of the first or second post-tensioned concrete slabs  804 ,  805 . The cavity-forming devices  802  can be the same as the cavity-forming device ( 720  shown in  FIGS. 23 and 24 ) described above. It is possible that the rebars  806  of one of the post-tensioned slabs are not directly connected to the cavity-forming devices  802 . Nevertheless, the rebars  806  of one of the post-tensioned slabs are fixed in the slabs relative to the cavity-forming devices  802 . The rebars  808  have end portions that are contained within the respective cavities  810  of the cavity-forming devices  802 . 
       FIG. 26  shows a top-down plan view of an embodiment of the floor construction  900 , wherein the floor construction  900  has the cavity-forming devices  902  in both of the first or second post-tensioned concrete slabs  904 ,  906 . The cavity-forming devices  902  can be the same as the cavity-forming device ( 720  shown in  FIGS. 23 and 24 ) described above. It is possible that the rebars  908  of one of the post-tensioned slabs are not directly connected but are fixed in the slabs relative to the cavity-forming devices  902 . It is also possible that the rebars  908  of one of the post-tensioned slabs  904  are connected to the cavity-forming devices  902 . The rebars  910  have end portions that are contained within the respective cavities  912  of the cavity-forming devices  902 . 
     Applications of the embodiments disclosed herein include all aspects of construction, including, but not limited to, buildings, towers, floating terminals, ocean structures and ships, storage tanks, nuclear containing vessels, bridge piers, bridge ducts, foundation soil anchorages, and virtually all other types of installations where normally reinforced concrete may be acceptable. 
     Preferred embodiments have been described. Those skilled in the art will appreciate various modifications and substitutions are possible, without departing from the scope of the invention as claimed and disclosed, including the full scope of equivalents thereof.