US3182109A - Method of making prestressed concrete pavement - Google Patents

Description

y 1965 a. G. GREULICH 3,182,109

METHOD OF MAKING PRESTRESSED CONCRETE PAVEMENT Filed Aug. 17, 1962 INVENTOR.

6264M G. GQEl/l/Cl/ United States Patent 3,182,109 METHOD OF MAKING PRESTRESSED CONCRETE PAVEMENT Gerald G. Greulicll, 3018 NE. 20th Court, Fort Lauderdale, Fla. Filed Aug. 17, 1962, Ser. No. 217,711 4 Claims. (Cl. 264-228) This invention relates to a method of making prestressed concrete pavements for highways, airport runways and the like, in which the prestressing tendons extend diagonally across the pavent.

Prestressed concrete pavements are those in which the concrete is held under high compression by rods, bars, cables or the like, called tendons herein, extending horizontally through the concrete and placed under great tension after the concrete has hardened. The advantages are many, including stronger and more durable pavements, which can be made from thinner slabs than otherwise would be the case and which are affected little by temperature changes and will not crack. Sometimes part of the tendons extend lengthwise of the slab and the rest extend at right angles to them across the slab, but such an arrangement produces considerable complication at the joints between the slabs because those joints have to be made wide enough to receive tensioning equipment and then they have to be filled with concrete later. It also has been proposed to extend the tendons diagonally across the pavement so that all of them project from its opposite sides. Advantages of this arrangement are that no anchors are necessary for the tensioning jacks because they can bear directly against the sides of the slab, and the tendons can be much shorter than if they extended lengthwise of the pavement, with the result that there is less friction between them and the slab while they are being stressed, so that the slab is compressed uniformly throughout its length. Nevertheless, heretofore transverse joints have always been required between the successive slabs, and the joints had to be filled after the tendons were stretched in the hardened concrete. Also, the joints have extended straight across the pavement, a condition that led to cracking of the concrete near the joints. Another disadvantage of known systems is that every slab has to move a considerable distance on the sub-grade as the slab is prestressed.

It is among the objects of this invention to produce a prestressed concrete pavement having tendons extending diagonally through the concrete, in which there are no transverse joints that have to be filled between adjoining slabs, in which there are no seams extending straight across the pavement, in which the concrete does not crack while the pavement is being constructed, and in the making of which very little movement of the concrete slabs occurs.

In accordance with this invention two lines of parallel forms are laid along the ground to define the sides of the pavement, and two layers of parallel tendon are placed between the forms, with the tendons in one layer crossing those in the other and with all of the tendons extending diagonally across the space between the forms and outward beyond them. A pair of V-shape forms are placed between the side forms at longitudinally spaced points, with the V-shaped forms converging from the side forms toward each other to points substantially midway between the side forms. One side of each V-shape form is substantially'parallel to the tendons in one layer and extends across some of the tendons in the other layer. The other side of the V-shape form is substantially parallel to thetendons in the second layer and extends across some of the tendons in the other layer. The space bounded by the forms then is filled with concrete to form a starting slab having fish tail ends and crossed tendons djhzid Patented May 4, 1965 extending diagonally through it. After the concrete has hardened, the forms are removed. Then, starting at approximately the middle of the slab and progressing toward both of its ends, the tendons that are embedded in the slab throughout its width are permanently tensioned to prestress the slab. A second slab is formed by pouring concrete in engagement with a fish tail end of the starting slab. The second slab has a fish tail free end and crossed tendons extend diagonally through it. After the concrete second slab has hardened, all of the tendons therein, except those projecting from its free end, are permanently tensioned, starting at the starting slab and progressing toward the free end of the second slab. Similar prestressed slabs are added onto the second slab in the same way in succession until substantially the desired length of pavement has been laid. While all of this is happening similar slabs may be laid in the same way at the opposite end of the starting slab.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a plan view showing the forms and tendons in place for my starting slab;

FIG. 2 is a plan view of the starting slab after the concrete has hardened and the forms have been removed, but before the tendons have been put under tension;

FIG. 3 is a plan view of the prestressed starting slab, with forms and tendons added to its opposite ends for forming the second slabs;

FIG. 4 is a fragmentary plan view of the prestressed starting slab, with the forms removed from the second slab and the tendons therein ready to be stretched; and

FIG. 5 is an enlarged fragmentary vertical section through a slab at the point where two tendons cross each other.

Referring to FIG. 1 of the drawings, two lines of side forms 1 are laid along the ground in spaced parallel rela tion a distance apart corresponding to the width of the concrete pavement that is to be laid. The forms are fastened securely in place in a well-known manner. Suitable tendons, such as metal rods 2, are laid across the space between the forms in two layers, generally half way between the top and bottom of the forms. They may be supported at intervals by small concrete blocks or the like (not shown) resting on the ground. The tendons in each layer are parallel and extend diagonally of the forms and outward through them. Usually they will be located closer together than indicated in the drawings. The tendons in one layer cross those in the other layer. Therefore, to make it possible to remove the forms from the crossed ends of the tendons after the concrete has hardened, the forms are split lengthwise into upper and lower sections so that the upper sections can be lifted off the tendons andthe lower sections pulled out from beneath their ends. The specific angle of the tendons to the longitudinal axis of the pavement will be determined by the direction in which it is desired to stress the concrete the most. The smaller the included angle between the tendons and the longitudinal axis of the pavement, the more the concrete will be prestressed lengthwise as compared with transverse prestressing. For each pair of projecting tendon ends at each side of the pavement, the adjoining form is provided with an outwardly projecting V-shape portion 3, the sides of which are substantially perpendicular to the tendons that extend through them. The reason for this will soon become apparent.

A pair of V-shape forms 4 also are placed between the side forms at longitudinally spaced points a predetermined distance apart. The V-shape forms converge from the side forms toward each other, with the apex of each V-shape form located substantially midway between the side forms. The angle of each V-shape form is such that one side of it will be substantially parallel to the tendons in one of the layers, while the other side of the form will be substantially parallel to the tendons in the other layer. Of course, it follows that each side of the form also extends across some of the tendons in one layer. The V-shape forms, like the side forms, are split lengthwise into upper and lower sections so that they can be removed after the concrete has been poured and has hardened.

The next operation is to pour concrete into the space bounded by the forms to fill that space and surround the tendons. Since the tendons are to be post-tensioned; that is, tensioned after the concrete has hardened, it is necessary that they not adhere to the concrete. That can be prevented, as is well known, by encasing each tendon in a tube or by coating it with asphalt or other separating material. Whether a tube or a coating is used, it is a bond-preventing sheath around the tendon.

After the concrete has hardened, the forms are removed from its sides and ends so that the first or starting slab 6 of concrete appears as shown in FIG. 2, with large V-shape notches 7 in its opposite ends so that those ends resemble fish tails, which they will be called hereinafter, It will be seen that in each triangular half of each fish tail there are a number of crossed tendons, some of which extend across the full width of the slab and others of which project from the sides of the notches. The slab also has a series of longitudinally spaced V-shape projections 8 along each side, from which the ends of the tendons extend in pairs. One end of each tendon is anchored against the adjoining projection. In the case of rods, this can be done by using rods with threaded ends and screwing nuts 9 onto them and up against the concrete, after which the surplus end of the rod can be cut off. To leave plenty of room for the post-tensioning operation that is to follow, it is preferred that two nuts engage each alternate projection 8 along each side of the slab, although other arrangements could be used without departing from this invention.

It is an important feature of this invention that when the slab is prestressed by placing the tendons under high longitudinal tension, the post-tensioning of the tendons is started approximately at the middle of the slab and proceeds progressively outward in opposite directions toward its ends. Thus, as shown in FIG. 2, a pair of tensioning jacks 11 of well-known construction are secured in a known manner to the projecting ends of the pair of tendons extending from the central concrete projection 8 at position A at one side of the slab. At the same time, another pair of jacks 12 may be secured to the ends of the pair of tendons extending from one of the two concrete projections closest to the center of the opposite side of the slab. The four jacks then are operated to stretch the four tendons to which they are connected, during which the ends of the tendons held by the jacks are anchored against the concrete, such as by nuts 13 (FIG. 3) that are tightened up against the sides of the slab. The next step is to remove jacks 11 and apply them and another pair to the projecting ends of the tendons at positions B at the opposite sides of position A, as indicated in dotted lines. At the other side of the slab, jacks 12 are moved to the dotted line position beside projection 8 at the other side of center. In positions C and D, to which the jacks are next moved in succession, they are not applied to the tendons that extend out of the sides of notches 7, because there would be nothing to anchor the opposite ends of those tendons. The jacks are moved progressively outward toward the opposite ends of the slab until all of the tendons that extend through the full width of the slab have been put under permanent tension to compress the slab lengthwise and transversely. During the tensioning, the ends of the slab are pulled toward its center, whereby the slab is shortened. The projecting ends of the tendons removed from the jacks can be cut off so that the starting slab appears as shown in FIG. 3.

By beginning the post-tensioning of the tendons at the middle of the slab and progressing toward its opposite ends, much less bodily movement of the slab occurs as it is shortened by the tendons than if the post-tensioning proceeded from one end toward the opposite end. Conse quently, friction between the slab and the sub-grade does not interfere so much with the prestressing operation. The fish tail ends of the slab also are very important ecause the two triangular areas forming each fish tail are prestressed to a considerable extent by some of the tendons therein, so that they are dragged along intact by the main body of the slab toward its center as it is shortened. On the other hand, if the slab had fiat or parallel ends, all of the large triangle of concrete that would fill the space now occupied by a notch 7 would not be prestressed at all because the tendons extending through it could not be tensioned at the time. This plain, uncompressed concrete could pull apart and crack as the ends of the slab were drawn toward each other during post-tensioning of the remaining tendons. Consequently, with my invention, there is a minimum of variation in prestressing throughout the area of the slab, and none of the slab is left unprestressed.

As shown in FIG. 3, the next step is to add side forms 15 to the opposite ends of the prestressed starting slab 6 and to place V-shape forms 16 between the side forms a distance from the starting slab which should be less than the length of the starting slab, so that the new slabs to be formed will weigh less than the starting slab. The V-shape forms point toward the starting slab in order that the new or second slab at each end of it will likewise have a fish tail end at its outer or free end. The untensioned tendons 2 that extend out of the ends of the starting slab extend across the space between the new side forms 15, and further tendons are added to continue the two layers of crossed diagonal tendons. The space bounded by each end of the starting slab and the adjoining side forms and V-shape form then is filled with concrete to form a second slab 17 (FIG. 4) containing crossed diagonal tendons. Concrete can be poured at both ends of the starting slab simultaneously in order to speed up the laying of the pavement. The new concrete will flow up against the ends of the starting slab, leaving no gaps. After the second slabs have hardened the forms are removed and, as shown in FIG. 4, nuts 18 are screwed on the ends of preferably alternate pairs of tendons along each side of the second slab. Then tensioning jacks 19 and 20 are attached to the two unstressed tendons at positions C beside the starting slab to stress them and thereby start to pull the second slab tightly into the fish tail end of the heavier starting slab. The jacks are moved progressively outward along the starting slab and the adjoining second slab to positions D, E, F and G in succession, so that the second slab is prestressed progressively from its inner or pointed end to its free or fish tail end and therefore it is pulled toward the starting slab.

A third and succeeding slabs are formed at the outer ends of the second slabs in the same manner, all prestressed from their inner toward their outer ends. This goes on until the desired length of pavament has been laid. Preferably, the last slab at each end of the pavement has a straight or flat free end rather than a fish tail end. In either case, shorter tendons must be used as the free end of the last slab is approached.

It will be seen that since all of the slabs are moved toward the starting slab during post-tensioning of the tendons, there are no joints or gaps between them that have to be filled later. All there are are tight V-shape seams 21 (FIG. 4), so the pavement is in effect a continuous, unbroken band of prestressed concrete. The

concrete at the seams is prestressed just as much as elsewhere along the pavement, with the result that the pavement is uniformly prestressed from end to end.

In case each slab is relatively long, then what is known as progressive prestressing may have to be resorted to. In such a method all tendons, starting from the center of the starting slab and progressing outward in opposite directions therefrom, and thereafter outward from the inner end of each succeeding slab, are tensioned by leaving all jacks along the slab in place and going outward along the jacks progressively several times to increase the prestress tensions by increments until the desired final tension in the tendons is reached. This procedure will insure progressive movement of the outer end of each slab towards the more tightly compressed portion thereof, and that no cracks will be formed as the outer ends of the slabs are dragged over the ground towards the previously highly compressed and shortened portions of the concrete.

According to. the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of making a prestressed continuous concrete pavement by post-tensioning, comprising laying two lines of parallel forms along the ground to define the sides of the pavement, placing two layers of parallel tendons having bond-preventing sheaths thereon between the forms with the tendons in one layer crossing those in the other and all of the tendons extending diagonally across the space between the forms and outward beyond them, placing a pair of V-shape forms between the side forms at longitudinally spaced points with the V-shape forms converging from the side forms toward each other to points substantially midway between the side forms,

one side of each V-shape form being substantially parallel to the tendons in one of said layers and extending across some of the tendons in the other layer, the other side of each V-shape form being substantially parallel to the tendons in said other layer and extending across some of the tendons in said one layer, filling the space bounded by said forms with concrete to form a starting slab having fish tail ends and crossed tendons extending diagonally through it, allowing the concrete to harden, removing the forms from the slab, starting at approximately the middle of the slab and progressing toward both ends to permanently tension all of the tendons that are embedded in the slab throughout its width, pouring in engagement with a fish tail end of the starting slab a second slab having a fish tail free end and crossed tendons provided with bond-preventing sheaths thereon extending diagonally through the second slab, allowing the concrete in the second slab to harden, starting at the starting slab end of the second slab and progressing toward its free end to permanently tension all of the tendons therein except those projecting from said free end, and adding onto said second slab in the same way similar post-tensioned prestressed slabs in succession until substantially the desired length of pavement has been laid.

2. The method of making a prestressed continuous concrete pavement by post-tensioning according to claim 1, in which said second slab is materially shorter than said starting slab.

3. The method of making a prestressed continuous concrete pavement by post-tensioning according to claim 1, including adding onto the last of said successive slabs a prestressed slab having a substantially fiat free end.

4. The method of making a prestressed continuous concrete pavement by post-tensioning, comprising laying two lines of parallel forms along the ground to define the sides of the pavement, placing two layers of parallel tendons having bond-preventing sheaths thereon between the forms with the tendons in one layer crossing those in the other and all of the tendons extending diagonally across the space between the forms and outward beyond them, placing a pair of V-shape forms between the side forms at longitudinally spaced points with the V-shape forms converging from the side forms toward each other to points substantially midway between the side forms, one side of each V-shape form being substantially parallel to the tendons in one of said layers and extending across some of the tendons in the other layer, the other side of each V-shape form being substantially parallel to the tendons in said other layer and extending across some of the tendons in said one layer, filling the space bounded by said forms with concrete to form a starting slab having fish tail ends and crossed tendons extending diagonally through it, allowing the concrete to harden, removing the forms from the slab, starting at approximately the middle of the slab and progressing toward both ends to permanently tension all of the tendons that are embedded in the slab throughout its width, pouring in engagement with the fish tail ends of the starting slab second slabs having fish tail free ends and crossed tendons provided with bondpreventing sheaths thereon extending diagonally through the second slabs, allowing the concrete in the second slabs to harden, starting at the starting slab ends of the second slabs and progressing outward toward their free ends to permanently tension all of the tendons therein except those projecting from said free ends, and adding onto said second slabs in the same way similar post-tensioned prestressed slabs in succession until the pavement has been extended substantially the desired distance in opposite directions from said starting slab.

References Cited by the Examiner UNITED STATES PATENTS ROBERT F. WHITE, Primary Examiner. ALEXANDER H. BRODMERKEL, Examiner.

Claims (1)

1. 4. THE METHOD OF MAKING A PRESTRESSED CONTINUOUS CONCRETE PAVEMENT BY POST-TENSIONING, COMPRISING LAYING TWO LINES OF PARALLEL FORMS ALONG THE GROUND TO DEFINE THE SIDES OF THE PAVEMENT, PLACING TWO LAYERS OF PARALLEL TENDONS HAVING BOND-PREVENTING SHEATHS THEREON BETWEEN THE FORMS WITH THE TENDONS IN ONE LAYER CROSSING THOSE IN THE OTHER AND ALL OF THE TENDONS EXTENDING DIAGONALLY ACROSS THE SPACE BETWEEN THE FORMS AND OUTWARD BEYOND THEM, PLACING A PAIR OF V-SHAPE FORMS BETWEEN THE SIDE FORMS AT LONGITUDINALLY SPACED POINTS WITH THE V-SHAPE FORMS CONVERGING FROM THE SIDE FORMS TOWARD EACH OTHER TO POINTS SUBSTANTIALLY MIDWAY BETWEEN THE SIDE FORMS, ONE SIDE OF EACH V-SHAPE FORM BEING SUBSTANTIALLY PARALLEL TO THE TENDONS IN ONE OF SAID LAYERS AND EXTENDING ACROSS SOME OF THE TENDONS IN THE OTHER LAYER, THE OTHER SIDE OF EACH V-SHAPE FORM BEING SUBSTANTIALLY PARALLEL TO THE TENDONS IN SAID OTHER LAYER AND EXTENDING ACROSS SOME OF THE TENDONS IN SAID ONE LAYER, FILLING THE SPACE BOUNDED BY SAID FORMS WITH CONCRETE TO FORM A STARTING SLAB HAVING FISH TAIL ENDS AND CROSSED TENDONS EXTENDING DIAGONALLY THROUGH IT, ALLOWING THE CONCRETE TO HARDEN, REMOVING THE FORMS FROM THE SLAB, STARTING AT APPROXIMATELY THE MIDDLE OF THE SLAB AND PROGRESSING TOWARD BOTH ENDS TO PERMANENTLY TENSION ALL OF THE TENDONS THAT ARE EMBEDDED IN THE SLAB THROUGHOUT ITS WIDTH, POURING IN ENGAGEMENT WITH THE FISH TAIL ENDS OF THE STARTING SLAB SECOND SLABS HAVING FISH TAIL FREE ENDS AND CROSSED TENDONS PROVIDED WITH BONDPREVENTING SHEATHS THEREON EXTENDING DIAGONALLY THROUGH THE SECOND SLABS, ALLOWING THE CONCRETE IN THE SECOND SLABS TO HARDEN, STARTING AT THE STARTING SLAB ENDS OF THE SECOND SLABS AND PROGRESSING OUTWARD TOWARD THEIR FREE ENDS TO PERMANENTLY TENSION ALL OF THE TENDONS THEREIN EXCEPT THOSE PROJECTING FROM SAID FREE ENDS, AND ADDING ONTO SAID SECOND SLABS IN THE SAME WAY SIMILAR POST-TENSIONED PRESTRESSED SLABS IN SUCCESSION UNTIL THE PAVEMENT HAS BEEN EXTENDED SUBSTANTIALLY THE DESIRED DISTANDE IN OPPOSITE DIRECTIONS FROM SAID STARTING SLAB.

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