US3602115A

US3602115A - Paving apparatus

Info

Publication number: US3602115A
Application number: US858986A
Authority: US
Inventors: Raymond A Hanson
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-09-18
Filing date: 1969-09-18
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

A paving apparatus designed specifically for sidewalks, curbs, and similar concrete paving applications. Included is a paving head pivotally mounted to and trailed behind a mobile supporting unit. The mobile supporting unit includes a rigid frame that carries the paving head. Independent drive assemblies at each side of the rigid frame are mounted to it by a pivotal axle and adjustable suspension units.

Description

United States Patent 1 amen 15 [72] lnvemor Raymond A. in 2,393,954 2/1946 Baker .1 94/46 Box 19148 Spokane international Airport, 3,157,099 1 1/1964 Ulrich 94/46 Spokane, Wash. 99219 3,285,148 11/1966 Muryon 94/46 [21] App]. No. 853,986 3,363,524 1/1968 Catenacci 94/46 5? :f t d Primary Examiner-Jacob L. Nackenoff I 1 a e At!0rney Wells & St. John [54] PAVING APPARATUS 9 Claims, 10 Drawing Figs.

[52] US. Cl. 94/46 ABSTRACT: A paving apparatus designed specifically for [51] Int. Cl. IEUIC 19/48 sidewalks, curbs, and Similar concrete paving applications.

[50] Field of Search 94/44, 46 eluded is 3 Paving head pivotally mounted to and trailed References Cited hind a mobile supporting unit. The mobile supporting unit includes a rigid frame that carries the paving head. Independent UNITED STATES PATENTS drive assemblies at each side of the rigid frame are mounted to 2,864,452 12/1958 Guntert 94/46 X it by a pivotal axle and adjustable suspension units.

PATENTED mm 19?: 3502.115

SHEU 1 [1F 3 INVENTOR. Raymond )4. Hanson 7a f ll MM H Hys PATENTEU was] I97! 3, 02 115 sum 2 or 3 f1 44 INVENTOR.

- l5 BRYhymond R. Hanson //,m;'/A%ZJ PATENTEU AUGS] 19?:

SHEET 3 UF 3 INVENTOR.

H /s G by H H d ,R "MW V! RB Mobile paving machines have been available for many years for the paving of concrete highways and streets and, to a lesser extent, for the paving of sidewalks and curbs. Most such units in the past have required the contractor to first place longitudinal tracks along the desired grade, and then to move the machinery along the tracks. The processes involved were both expensive and cumbersome.

There has been development work within recent years relating to concrete highway paving machines which are self-supported by conventional crawler tracks. Most machinery of this type has been fabricated on the large scale needed for production highway work, and there has been little effort made to scale such machinery to meet the specific needs of sidewalk contactors.

The apparatus described and claimed herein is designed specifically for sidewalk contractors. It is capable of being applied to the layer of concrete sidewalks, curbs or even street configurations within a wide variety of widths. It provides a self-supporting mobile unit which is capable of automatic grade and steering control with a minimum of complication and expense. The suspension of the paving head is designed to provide maximum quality and consistency in the finished slab.

SUMMARY OF THE INVENTION The invention comprises the combination of a transverse paving head, including upright slipforms and a troweling pan, together with a mobile supporting unit. The supporting unit comprises a rigid frame that extends forwardly from the paving head. Two transversely spaced crawler track assemblies are mounted at each side of the supporting unit. The frame is pivotally connected to each of the crawler track assemblies about a common transverse axis. Suspension means is provided in the form of upright hydraulic cylinders at each side of the frame to selectively position the frame about this axis. The mounting apparatus for the frame with respect to the crawler track assemblies further includes means to pivot the frame about a longitudinal center axis between the crawler track assemblies to thereby provide cross leveling or a controlled incline on the finished concrete surface.

One object of the invention is to provide a novel supporting unit for an apparatus of this type including a minimum number of moving support elements.

Another object of this invention is to provide such an apparatus wherein the frame of the mobile unit and the equipment carried thereby move as a unit with respect to the supporting ground engaging devices.

Another object of this invention is to provide a trailing configuration fora concrete paving head to permit maximum adaptation of the machinery to the paving of concrete along curbed paths.

Another object of the invention is to insure proper support of the trailing paving head by provision of auxiliary groundsupporting devices. 1

These and further objects will be evident from a study of the following description and the accompanying drawings, taking into consideration minor mechanical variations which are readily adaptable to the mechanism described.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a side elevation view of the paving apparatus;

FIG. 2 is a top view of the apparatus shown in FIG. 1;

FIG. 3 is a front view of the apparatus shown in FIG. 1;

FIG. 4 is a rear view of the apparatus shown in FIG. ll;

FIG. 5 is a top view of the rigid frame for the mobile support unit;

FIG. 6 is an elevation view of the apparatus shown in FIG. 5;

FIG. 7 is a longitudinal sectional view through the paving head as seen generally along line 7-7 in FIG. 2 at an enlarged scale, showing the placement of a concrete slab;

FIG. 8 is a transverse fragmentary sectional view taken substantially along line fi-fl in FIG. 6, showing the track stabilizing apparatus;

FIG. 9 is an enlarged fragmentary sectional view taken along line 9-9 in FIG. 8; and

FIG. 10 is an elevation view of the rigid frame for the mobile supporting unit showing the pivotal support for the paving ead.

PREFERRED EMBODIMENT OF THE INVENTION The structure described herein is generally referred to in the contracting and paving industries as a slipform paver. It is self-supporting on a graded surface upon which the continuous concrete slab is to be poured. It requires no external forms, the concrete being finished by elements on the apparatus which move along the graded surface as concrete is poured within the space bounded by them. The present struc ture is designed specifically for the pouring of longitudinal concrete slabs having relatively small dimensions in comparison to slabs encountered in the construction of streets and highways. Specifically, it is designed for the pouring of sidewalks and curbs. Common curb configurations are 18 to 36 inches wide and common sidewalks are 4 to 6 feet wide. In modern residential areas it is not uncommon for sidewalks to curve, particularly where the streets are formed with culdesacs. In addition, curves are encountered normally at corner intersections.

The apparatus essentially comprises two machine sections. The first is the paving head 10, which receives and places concrete directed to it from a delivery truck or other source (not shown). The second is a mobile supporting unit 20 carried by transversely spaced crawler track assemblies 21. The paving head 10 is pivotally mounted to the rear end of the mobile supporting unit 20 and is both elevationally supported and guided longitudinally by the unit 20.

The paving head 10 comprises a rigid transverse frame that carries a pair of transversely spaced slipforms 11 (FIGS. 4, 7). Each slipform 11 is an upright rectangular metal plate. They are parallel to one another and together define the transverse bounds of the area within which concrete is to be placed on the graded surface as the forms move longitudinally along the path of motion of the machine. Extending across the slipforms 11 is a troweling pan 12 having a horizontal lower section 13 that is directed rearwardly. Pan 12 defines the upper surface of the poured concrete slab.

Located forward of the troweling pan I3 is a front retaining wall 14 bounded across its lower edge by a flexible rubber sheet 15. Sheet 15 prevents concrete from escaping in a forward direction as it is placed on the graded surface (indicated at 116).

INcoming concrete is directed across the paving head 10 from a receiving hopper 17 by action of a transverse feeder auger l8. Auger 18 operates within a trough 19 that opens downwardly into the space between the troweling pan 12, from retaining wall 14 and the slipforms 11. To provide control of the weight distribution on paving head 10, a ballast tank 22 is located across the paving head immediately above the troweling pan 12. Tank 22 can be selectively filled with water or other liquid, there being provided an inlet 23 and an outlet 24. Other suitable means can be utilized for weight distribution where desired.

Conventional concrete vibrators are illustrated at 25, each being extended into the concrete across the width of the machine. The operating vibratory heads are preferably located within the incoming concrete at an elevation below that of the lower section 13 of troweling pan 12 (FIG. 7).

The paving head 10 is supported and pivotally directed by the forward mobile supporting unit 20. This unit essentially comprises a rigid frame 26 which in turn is mounted by the transversely spaced crawler track assemblies 21.

The connections that exist between the frame 26 and the track assemblies 21 are best seen in FIGS. 3, 5, 6, 8 and 9. First, the frame 26 is connected to each track assembly 21 for ivotal movement about a common transverse axis. This is accomplished by means of a transverse main axle 27 at the front of unit 20. The outer ends of axle 27 are designated as 28, and are respectively journaled by the supporting framework 30 of each track assembly 21.

The axle 27 is movably connected to the rigid frame 26 by a longitudinal pin 31 which is carried by two transverse members within the rigid frame 26. These members are designated by the numeral 32 (FIG. The axis of pin 31 is a longitudinal axis located centrally between the track assemblies 21.

To prevent the rear ends of the track assemblies 21 from wandering from their required longitudinal positions, stabilizer assemblies are provided at each side of the rigid frame 26. As seen in F 8 and 9, each stabilizer assembly includes an upright pin 33 carried by upper and lower brackets 34 fixed to the respective track assembly framework 30. Encircling the respective pins are projecting horizontal rings 35 fixed to the rigid frame 26. Adequate tolerance is provided in the design of rings 35 to permit a limited amount of pivotal movement of frame 26 about the axes defined by the connections between the main axle 27 and the crawler track assemblies 21.

The rigid frame 26 is adjustably suspended about its longitu- 'dinal and transverse axes with respect to the crawler track assemblies 21. This is accomplished by a pair of upright hydraulic cylinder assemblies 36 shown located immediately rearward of the stabilizer units. The upper end of each cylinder assembly 36 is pivotally connected to the upper surface of rigid frame 26. The lower end of each cylinder assembly 36 is similarly connected to the framework of the respective crawler track assembly 21 associated with it. The respective connections at the ends of the cylinder assemblies 36 essentially constitute universal joints, permitting free pivotal movement of the cylinder assemblies 36 about both transverse and longitudinal axes, thereby permitting complete freedom of orientation of the rigid frame 26 with respect to its axes on the axle 27.

The pivotal support that exists between the rigid frame 26 'of the mobile supporting unit and the paving head 10 is best illustrated in F IGS. 5 and 10. Extending within rigid frame 26 to an intermediate pivot element 37, which is pivotally mounted by upright pins 38 on the frame 26. The pivotal axis of the pins 38 lies in a plane central to the rigid frame 26. This central upright plane also includes the axis of the previously discussed pin 31 that mounts axle 27. To provide additional support for the weight assumed by the pivot element 37, upper and lower sets of bearing rollers 40 are mounted to the rigid frame 26. The rollers 40 bear against the upper and lower surfaces of element 37 and serve as weight-supporting members. Fixed stops 41 are mounted to the rigid frame 26 in the pivotal path of the element 37 about the axis of the pins 38, serving to limit the amount of its pivotal movement within rather narrow confines. The purpose of this limitation will be discussed below.

The rear end of the pivot element 37 is hinged to the front end of the paving head 10 about pins 42. The axis defined by the pins 42 is parallel to the axis of the pin 38. When the apparatus is traveling in a straight forward direction, the axis of pins 42 will also be in the central plane that contains the axis of pin 31. The mounting bracket that connects these pins 42 and paving head 10 includes means to permit adjustment of the paving head 10 about a transverse axis with respect to the supporting unit 20. This includes a hinged plate 43 connected to the paving head 10 about the axis of a lower hinge pin 44, and an adjustable connecting bolt 45. Shims may be interposed between plate 43 and the paving head 10 to initially preset the trim" or attitude" of the troweling pan 12. This in turn affects the quality and condition of the finish applied to the concrete after passage of the apparatus.

At the rear of the paving head 10, and at each side of the slipforms 11 are auxiliary ground support units in the form of tracks 53. Each track 53 is movably carried by the paving head 10 by means of pivoting support arms 62. Their elevational position relative to the paving head 10 is controlled by individual cylinder assemblies 60 operatively connected between the paving head 10 and the framework of each track 53. Tracks 53 are preferably not powered, but simply idle as they frictionally engage the graded surface 16.

The purpose of the auxiliary tracks 53 is to provide positive support between the paving head 10 and the graded surface 16. A minimum amount of pressure is exerted on tracks 53 to partially counteract the weight of the paving head 10. This pressure serves also to prevent undesirable swinging of the paving head 10 about the axis of pins 42. The tracks 53 insure that the longitudinal path of movement of paving head 10 will be in a longitudinal direction trailing the unit 20. In some installations, tracks 53 can be replaced by skids each having the form of a ski. The skids can be fixed to the respective slipforms 11 and moved up and down relative to the graded surface 10 along with the slipforms 11.

The

cylinder assemblies

36 and 60 at each side of the machine are operated simultaneously by grade and cross leveling control units, whether automatic or manual. Thus, when the rigid frame 26 is raised at one side with respect to the crawler track assembly 21 at that side of the machine, the resulting lifting force on the paving head 10 will be counteracted by lowering of the track 53 at the side of the unit, enabling the track 53 to continue its desired support of the paving head 10 and its frictional engagement of the graded surface 16.

While many different power plants could be used with respect to the apparatus, it is preferably powered by a single engine 47, using hydraulic circuits to individually power the crawler track assemblies 21, and the operating elements of the paving head 10 and unit 20. All of these units can be controlled by a single operator located on an upper deck 48, using manual controls on an instrument panel 50.

The described apparatus readily lends itself to automatic grade and steering control units. Examples of such devices are illustrated in US. Pat. No. 3,247,771. An example of a crossleveling apparatus using a mercury level switch arrangement is described in US. Pat. No. 2,716,169.

As shown, the present apparatus can be controlled by a single string line 51, supported by longitudinally spaced posts 52. The string line 51 is preset by a survey crew to the next grade desired and extends parallel to the desired path of the machine. In a preferred operation, the same string line 51 will have been utilized in the trimming of the graded surface 16. As shown in FIG. 2, the width of the graded surface 16 is preferably at least as wide as the operating portion of the supporting unit 20 and paving head 10. Thus, the crawler track assemblies 21 and the supplementary supporting tracks 53 will be traveling on a surface prepared to grade specifications, minimizing the number and amount of correction movements required during paving operation. In the example shown in FIGS. 1 and 2, the width of the concrete slab 54 is slightly more narrow than the width of the graded surface 16. The width of track 54 can be readily varied using the same paving head, and moving the slipform 11 and replacing troweling pan 12 to meet particular paving specifications.

In the structure shown, a forward control unit 55 includes a sensor 56 that engages the side of the string line 51 and is utilized for automatic steering control by operation of the crawler track assemblies 21. Being located at the forward end of the mobile supporting unit 20, the unit 55 is capable of leading the rigid frame 26 and paving head 10 along the path directed by placement of string line 51.

At the rear of the paving head 10 is a second control unit 57 having a sensor 58 that contacts the underside of the string line 51. This unit 57 controls the

adjacent cylinder assemblies

36 and 60 at the side of the apparatus adjacent to the string line 51. This regulates the height of the working apparatus at that side of the machine.

Mounted across the rear portion of the paving head 10 is a cross level control device 61 of the general type shown in US. Pat. No. 2,7l6,l69. Essentially, such a device is preset in orientation across the paving head to relate the transverse orientation of the unit 61 to the transverse orientation of troweling pan 12. Unit 61

controls cylinder assemblies

36 and 60 at the side of frame to opposite to string line 51. If the unit 61 is mounted parallel to the lower section 13 of the troweling pan 12, the mercury switches or other leveling devices (such as a pendulum) will always seek this same level position and will therefore operate the cylinder assemblies to maintain troweling pan 12 at a horizontal condition. In such an instance, the

cylinder assemblies

36 and 60 at the side of the apparatus opposite to the string line 51 will make identical corrections to those assumed by the corresponding cylinder assemblies at the side near the string line 51.

When a transverse inclination is desired across the upper surface of slab 54 one or the other end of the unit 61 is lifted or lowered with respect to the remaining end, so that unit 61 is inclined relative to the lower section 13 of the troweling pan 12. Since unit 61 will continually seek a level position, one or the other side of the troweling pan 12 will be lowered or raised to maintain this preset transverse inclination. Thus, the apparatus can be automatically steered, held to grade and maintained at a preset transverse orientation by devices controlled from the single string line 51.

The purpose of the intermediate pivot element 37 is to minimize the transmission of lateral changes from the mobile supporting unit 20 to the paving head 111. Because of the extreme sensitivity of the sensors used for automatic steering controls, minor corrections in the steering of the mobile supporting unit 20 will occur at almost all times during operation.

These are such as to be within the limits of movement of the stops 41, and are essentially not transmitted back to the paving head 10, which thus smoothly follows the path of pulling power transmitted to it from the supporting unit 20. However, if the unit 20 is directed to turn, the stops 411 will be contacted by the pivot element 37, and the turning force will be immediately transmitted to the paving head to thereby enable the apparatus to be turned along a relatively short radius where a corner of other curved pavement section is to be formed.

Having thus described my invention, I claim: 1. In a concrete paving apparatus: a paving head comprising: a pair of laterally spaced upright slipforms; a troweling pan spanning the separation between the slipform; concrete delivery means for directing incoming concrete between the slipforms and forward of said troweling pan during longitudinal movement of the paving head along a graded surface; and a mobile supporting unit, comprising: a rigid frame operatively connected to the paving head; ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path; mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis; suspension means operatively connecting the rigid frame and said ground-engaging means for selectively locating the rigid frame about said transverse axis relative to said ground-engaging means; auxiliary ground engaging means at each side of the paving head for partially supporting the weight of the paving head by moving engagement of the graded surface during longitudinal movement of the paving head. 2. An apparatus as wet out in claim 1 further comprising: movable support means operatively connected between the paving head and said auxiliary ground engaging means for maintaining engagement of the graded surface bysaid auxiliary ground-engaging means. 3. In a concrete paving apparatus: a paving head comprising: a pair of laterally spaced upright slipforms; a troweling pan spanning the separation between the slip.-

forms;

concrete delivery means for directing incoming concrete between the slipforms and forward of said troweling pan during longitudinal movement of the paving head along a graded surface;

and a mobile supporting unit located forward of the paving head in the direction of intended longitudinal movement, comprising:

a rigid frame operatively connected to the paving head;

ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path, said paving head being pivotally joined to said rigid frame about an upright axis located centrally of the ground-engaging means;

mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis;

suspension means operatively connecting the rigid frame and said ground-engaging means for selectively locating the rigid frame about said transverse axis relative to said ground-engaging means.

41. An apparatus as set out in claim 3 further comprising:

means on said paving head for selectively varying the longitudinal inclination of the troweling pan relative to said upright axis.

5. in a concrete paving apparatus:

a paving head comprising:

a pair of laterally spaced upright slipforms;

a troweling pan spanning the separation between the slipforms;

and a mobile supporting unit, comprising:

a rigid frame operatively connected to the paving head;

ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path;

mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis and further permitting pivotal movement of the rigid frame about a central longitudinal axis relative to said ground-engaging means;

6. In a self-propelled paving apparatus for placement of a concrete slab along a graded longitudinal surface:

a paving head comprising:

a transverse troweling pan mounted to the paving head at an elevation above the graded surface;

a pair of upright longitudinal slipforms mounted to the paving head at the respective sides of said troweling pan, the lower edges of said slipforms being engaged with the graded surface;

and concrete delivery means on the paving head for directing incoming concrete between the slipforms and forward of the troweling pan during longitudinal movement of the paving head;

and a mobile supporting unit comprising:

a rigid frame operatively connected to the paving head;

ground-engaging drive units located alongside the respective sides of said rigid frame;

a rigid support'mounted to said rigid frame and pivotally journaled by said ground engaging drive units about a common transverse axis, said rigid support being further pivotally mounted to the rigid frame about an axis extending longitudinally along the centerline between the ground-engaging drive units; I

and adjustable means connected between the rigid frame and said ground-engaging drive units for selectively positioning said rigid frame relative to said ground engaging drive units about said common transverse axis.

7. An apparatus as set out in claim 6 further comprising:

ground-engaging means movably mounted at the respective sides of the paving head;

and means operatively engaged between the paving head and said ground-engaging means for maintaining them in frictional supporting contact with the graded surface.

8. In a self-propelled paving apparatus for placement of a concrete slab along a graded longitudinal surface;

a paving head comprising:

a pair of upright longitudinal slipforms mounted to the paving head at the respective sides of troweling pan, the lower edges of said slipforms being engaged with the graded surface;

and a mobile supporting unit comprising:

a rigid frame pivotally connected to the paving head by an assembly comprising a rigid intermediate element oriented longitudinally and pivoted at its forward end to said rigid frame about a central upright axis on said frame, and means pivotally joining said paving head to the rear end of said element about an axis on said element parallel to said upright axis;

a rigid support mounted to said rigid frame and pivotally journaled by said ground-engaging drive units about a common transverse axis;

9. An apparatus as set out in claim 8 wherein said paving head further comprises means for angularly adjusting the attitude of the troweling pan about a transverse axis.

Claims

1. In a concrete paving apparatus: a paving head comprising: a pair of laterally spaced upright slipforms; a troweling pan spanning the separation between the slipform; concrete delivery means for directing incoming concrete between the slipforms and forward of said troweling pan during longitudinal movement of the paving head Along a graded surface; and a mobile supporting unit, comprising: a rigid frame operatively connected to the paving head; ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path; mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis; suspension means operatively connecting the rigid frame and said ground-engaging means for selectively locating the rigid frame about said transverse axis relative to said ground-engaging means; auxiliary ground engaging means at each side of the paving head for partially supporting the weight of the paving head by moving engagement of the graded surface during longitudinal movement of the paving head.

2. An apparatus as wet out in claim 1 further comprising: movable support means operatively connected between the paving head and said auxiliary ground engaging means for maintaining engagement of the graded surface by said auxiliary ground-engaging means.

3. In a concrete paving apparatus: a paving head comprising: a pair of laterally spaced upright slipforms; a troweling pan spanning the separation between the slipforms; concrete delivery means for directing incoming concrete between the slipforms and forward of said troweling pan during longitudinal movement of the paving head along a graded surface; and a mobile supporting unit located forward of the paving head in the direction of intended longitudinal movement, comprising: a rigid frame operatively connected to the paving head; ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path, said paving head being pivotally joined to said rigid frame about an upright axis located centrally of the ground-engaging means; mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis; suspension means operatively connecting the rigid frame and said ground-engaging means for selectively locating the rigid frame about said transverse axis relative to said ground-engaging means.

4. An apparatus as set out in claim 3 further comprising: means on said paving head for selectively varying the longitudinal inclination of the troweling pan relative to said upright axis.

5. In a concrete paving apparatus: a paving head comprising: a pair of laterally spaced upright slipforms; a troweling pan spanning the separation between the slipforms; concrete delivery means for directing incoming concrete between the slipforms and forward of said troweling pan during longitudinal movement of the paving head along a graded surface; and a mobile supporting unit, comprising: a rigid frame operatively connected to the paving head; ground-engaging means at each side of the rigid frame for selectively propelling the rigid frame along a longitudinal path; mounting means operatively connecting the rigid frame and said ground-engaging means about a common transverse axis and further permitting pivotal movement of the rigid frame about a central longitudinal axis relative to said ground-engaging means; suspension means operatively connecting the rigid frame and said ground-engaging means for selectively locating the rigid frame about said transverse axis relative to said ground-engaging means.

6. In a self-propelled paving apparatus for placement of a concrete slab along a graded longitudinal surface: a paving head comprising: a transverse troweling pan mounted to the paving head at an elevation above the graded surface; a pair of upright longitudinal slipforms mounted to the paving head at the respective sides of said troweling pan, the lower edges of said slipforms being engaged with the graded surface; and concrete delivery means on the paving head for directing incoming concrete between the slipforms and forward of the troweling paN during longitudinal movement of the paving head; and a mobile supporting unit comprising: a rigid frame operatively connected to the paving head; ground-engaging drive units located alongside the respective sides of said rigid frame; a rigid support mounted to said rigid frame and pivotally journaled by said ground engaging drive units about a common transverse axis, said rigid support being further pivotally mounted to the rigid frame about an axis extending longitudinally along the centerline between the ground-engaging drive units; and adjustable means connected between the rigid frame and said ground-engaging drive units for selectively positioning said rigid frame relative to said ground engaging drive units about said common transverse axis.

7. An apparatus as set out in claim 6 further comprising: ground-engaging means movably mounted at the respective sides of the paving head; and means operatively engaged between the paving head and said ground-engaging means for maintaining them in frictional supporting contact with the graded surface.

8. In a self-propelled paving apparatus for placement of a concrete slab along a graded longitudinal surface; a paving head comprising: a transverse troweling pan mounted to the paving head at an elevation above the graded surface; a pair of upright longitudinal slipforms mounted to the paving head at the respective sides of troweling pan, the lower edges of said slipforms being engaged with the graded surface; and concrete delivery means on the paving head for directing incoming concrete between the slipforms and forward of the troweling pan during longitudinal movement of the paving head; and a mobile supporting unit comprising: a rigid frame pivotally connected to the paving head by an assembly comprising a rigid intermediate element oriented longitudinally and pivoted at its forward end to said rigid frame about a central upright axis on said frame, and means pivotally joining said paving head to the rear end of said element about an axis on said element parallel to said upright axis; ground-engaging drive units located alongside the respective sides of said rigid frame; a rigid support mounted to said rigid frame and pivotally journaled by said ground-engaging drive units about a common transverse axis; and adjustable means connected between the rigid frame and said ground-engaging drive units for selectively positioning said rigid frame relative to said ground engaging drive units about said common transverse axis.