US3915582A

US3915582A - Method of repairing concrete roads

Info

Publication number: US3915582A
Application number: US191857A
Authority: US
Inventors: Ronald Albert William Clarke
Original assignee: KLARCRETE Ltd
Current assignee: SHERIFF OF JUDICIAL DISTRICT OF OTTAWA-CARLTON
Priority date: 1970-01-09
Filing date: 1971-10-22
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

A method of repairing concrete roads in which the defective concrete is cut away and the recess in the road plugged by a preformed block of concrete bonded in position by a synthetic resin adhesive. When the repair is carried out at low temperature, the block is heated before being placed in the recess so as to heat up the resin and reduce the setting time. A machine for cutting away the concrete has a frame, a first carriage reciprocable in one direction on the frame, a second carriage reciprocable on the first carriage in a different direction, and a power driven hammer unit mounted on the second carriage and arranged to reciprocate a cutting member into engagement with the road and impart a succession of impact blows to the road. The two carriages are reciprocated in a pattern arranged so that the hammer unit traverses over the whole area to be cut away. An anchoring device for securing the machine to the road has a metal plate formed with a peripheral skirt, two concentric rubber rings bonded to the underside of the base plate and projecting below the skirt, and means for withdrawing air from the space surrounded by the inner ring. When the device is placed on a road and air is extracted from the chamber enclosed by the inner ring, the base plate and the road surface, the difference between the pressure of air in the chamber and atmospheric pressure clamps the device to the road.

Description

United States Patent 1 Clarke Oct. 28, 1975 METHOD OF REPAIRING CONCRETE ROADS [75] Inventor: Ronald Albert William Clarke,

London, England [73] Assignee: Klarcrete Limited, London, England 22 Filed: 0a. 22, 1971 [21] Appl. No.: 191,857

Related U.S. Application Data [63] Continuation-impart of Ser. No. 1,700, Jan. 9, 1970.

[52] U.S. Cl. 404/75; 404/34; 404/41 [51] Int. Cl. E01C 7/32 [58] Field of Search 94/22, 26, 25, 11, 13,

[56] References Cited UNITED STATES PATENTS 1,698,734 1/1929 Pye 404/73 2,128,480 8/1938 Wertz 94/24 X 2,396,808 3/1946 Abel 94/13 2,448,134 8/1948 Abel 94/8 2,657,153 10/1953 Russell 117/54 2,811,906 1l/1957 Chappell 94/22 3,008,387 1l/196l Wittenwyler... 94/22 3,217,620 1 H1965 Mindrum 94/39 3,238,855 3/1966 Clay 94/13 X 3,348,988 10/1967 Wagner... 404/73 X 3,386,252 6/1968 Nelson 94/13 X OTHER PUBLICATIONS Journal of the American Concrete Institute, October, 1960, pp. 467 and 468.

Primary Examiner-Nile C. Byers, Jr.

[5 7] ABSTRACT A method of repairing concrete roads in which the defective concrete is cut away and the recess in the road plugged by a preformed block of concrete bonded in position by a synthetic resin adhesive. When the repair is carried out at low temperature, the block is heated before being placed in the recess so as to heat up the resin and reduce the setting time. A machine for cutting away the concrete has a frame, a first carriage reciprocable in one direction on the frame, a second carriage reciprocable on the first carriage in a different direction, and a power driven hammer unit mounted on the second carriage and arranged to reciprocate a cutting member into engagement with the road and impart a succession of impact blows to the road. The two carriages are reciprocated in a pattern arranged so that the hammer unit traverses over the whole area to be cut away. .An anchoring device for securing the machine to the road has a metal plate formed with a peripheral skirt, two concentric rubber rings bonded to the underside of the base plate and projecting below the skirt, and means for withdrawing air from the space surrounded by the inner ring. When the device is placed on a road and air is extracted from the chamber enclosed by the inner ring, the base plate and the road surface, the difference between the pressure of air in the chamber and atmospheric pressure clamps the device to the road.

1 Claim, 13 Drawing Figures US. Patent 'Oct.28,1975 Sheetlof? 3,915,582

US. Patent Oct. 28, 1975 Sheet 2 of 7 3,915,582

H05. H06. JZL- 5 3a 37 1 67 66 67 Sheet 3 of 7 3,915,582

U.S. Patent 'Oct. 28, 1975 U.S. Patent Oct. 28, 1975 Sheet4of7 3,915,582

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US. Patent 'Oct.28, 1975 Sheet5of7 3,915,582

U.S. Patent Oct. 28, 1975 Sheet6of7 3,915,582

U.S. Patent 'Oct. 28,1975 Sheet 7 of7 3,915,582

mQNT Q ST m5 vm? -3 METHOD OF REPAIRING CONCRETE ROADS This application is a Continuation-in-part of my copending application Ser. No. 1700, filed J an. 9, 1970.

Concrete roads, runways, or other concrete tracks subject to heavy use usually suffer damage which causes crumbling and flaking off of parts of the top surface. Such defects, which generally occur at the corners or along the edges of a cast section or bay of a road, are usually referred to as spalling defects. Spalling in concrete roads has hitherto been repaired by cutting away all the defective part of the concrete and then filling in the resultant recess with either concrete poured in situ or with a synthetic resin filling which hardens when cured. A repair with liquid concrete poured in situ has the disadvantage that the concrete,

takes several days to harden and the repair section of the road cannot be used for this period. Also it is very difficult to vibrate the liquid concrete filling to displace any bubbles of air in the filling concrete or at the interface between the filling concrete and the original concrete. A repair with synthetic resin can be completed and the road ready for use in the short time required for the resin to act, usually 1 or 2 hours, but the resin is comparatively expensive.

The object of the invention is to provide a method of repairing a concrete road which can be carried out in a much shorter time than that required for a liquid concrete repair and at a cost not appreciably greater than that required for a liquid concrete repair.

This object is accomplished in accordance with the invention by cutting away the defective part of the road to form in the top surface of the road a recess having a predetermined contour and size, plugging the recess with at least one preformed block of hard wearing material of a size and contour conforming to that of said recess so as to be a loose fit therein, and securing said block in position in said recess with a layer of adhesive material disposed between and bonded to the adjacent walls of said recess and the block. The adhesive material is preferably a synthetic resin adhesive, for example an epoxy resin. The adhesive may be spread over the base and side walls of the recess before the block or blocks are fitted in the recess, but instead or in addition the sides and base of the block or blocks may be coated with the adhesive before they are fitted in the recess.

The setting time of many synthetic resin adhesives increases with decrease in temperature, and the setting time at C. may be so long as to preclude their use as adhesives at this temperature. In a case in which a repair must be carried out at low temperature, the block or blocks are heated before they are fitted into the recess in the road. Sufficient heat is retained in the block to heat up the resin after the block has been fitted in the recess and to hold the resin at an elevated temperature during the short period required for curing the resin at that temperature.

Several tie rods may be embedded in each block, the tie rods extending downwards below the block, and the base of the recess provided with vertical holes to receive the lower ends of the tie rods. The holes are preferably filled with the synthetic resin adhesive before the block or blocks are fitted in position.

The blocks are preferably formed of reinforced concrete moulded on a vibratory table to prevent any air bubbles in the concrete. The blocks are of course of a size that their top surface is level with the top surface of the remainder of the road after being fitted in the recess, and the top surface of the blocks which are left exposed can be provided with any desired pattern as an anti'skid surface. The sides and bottom of the blocks may be suitably treated to give a bush-hammered finish to provide a good bonding surface.

Where possible, the recess is preferably plugged by a single concrete block which is identical in shape but slightly smaller than the recess so as to be a loose fit therein. In a case in which the recess is too large to be plugged conveniently by a single block, the several blocks are secured to one another as well as to the wall of the recess by the synthetic resin. This is done by coating the opposing sides of each adjacent pair of blocks with the resin before the blocks are fitted in the recess.

The side wall of the recess cut in the top surface of the road is preferably curvilinear or straight throughout its length, that is devoid of sharp corners, to avoid concentrations of tensions and stresses which would otherwise occur at such corners. The recess may be semicircular in a case in which the defect is at an edge of a rectangular concrete bay, that is a rectangular cast section, or a quarter circle in a case in which the defect is at a corner of a rectangular concrete bay.

The defective part of a concrete road to be repaired by the method of the invention may be cut away by percussive tools mounted in a machine arranged to reciprocate the tools continuously over the area to be cut.

According to another aspect of the invention there is provided a machine for cutting away the top surface of a concrete road, comprising a main frame adapted to be mounted on the road to be cut, a first carriage movable along a track on the mainframe, a second carriage movable on the first carriage along a track extending in a different direction from that of the track on the frame, a power driven hammer unit coupled to the second carriage for movement therewith and having a cutting head adapted to engage the road surface, the hammer unit being operable to impart through the cutting head a succession of impact blows to the road, and drive means operable to reciprocate the first carriage along the track on the frame and to reciprocate the second carriage along the track on the first carriage so that the cutting head traverses over an area of the road surface to be cut. The hammer unit is preferably provided with a plurality of cutting heads and the drive means arranged to reciprocate the carriages in a predetermined sequence in each cycle of which the cutting heads traverse over the total area of the road surface to be cut away.

The hammer unit may be mounted in vertical guides on the second carriage so that it rests on the road surface to be cut. Alternatively, the hammer unit maybe supported on a hydraulic dashpot mounted on the second carriage and operable to lower the hammer unit at a controlled rate during cutting operations.

The hammer unit can be of conventional construction well known in the art. Thus the hammer unit may comprise a cylinder block having several cylinders arranged parallel to one another, each cylinder having an air-operated piston, a piston rod extending out of the cylinder, a cutting head rigidly secured on the end of the piston rod, and valve means for feeding compressed air alternately to opposite ends of the cylinders so as to reciprocate the pistons therein. In use, the cylinder block is positioned with the cylinders vertical and the cutting heads resting on the ground. When air is supplied alternately to opposite ends of the cylinders, the cylinder block floats above the road and the pistons reciprocate within the cylinders so that the cutting heads impart a succession of impact blows to the road. The cutting action on the concrete is due more to the speed and frequency of the impact blows rather than to the actual thrust exerted on the pistons.

Operation of the hammer unit causes the machine to vibrate. The machine is therefore preferably fixed to the road, or made sufficiently heavy, either by the weight of its components or by weighting down the frame, so that the vibrations do not cause any movement of the machine across the road. The machine may if desired be mounted on a large vehicle having means for lowering the machine into a cutting position and raising the machine into a position clear of the ground for transport to another site.

The frame of the machine may be secured to pegs driven into the bitument filling separating concrete bays of a road. The frame is however preferably provided with anchoring devices, each of which comprises a base member having a recess arranged to co-operate with the road to define a closed chamber, sealing means providing a substantially air-tight seal between the base member and the road surrounding said chamber, and means for extracting air from the chamber so as to cause a thrust to be exerted on the base member to clamp it against the road sue to the difference in pressure between the atmosphere and the air remaining in the chamber.

Such anchoring devices are suitable for rigidly securing to a road or wall any machine which vibrates in operation.

The accompanying drawings illustrate the method of repairing a concrete road according to the invention, and apparatus suitable for cutting the recess in the road. In the drawings:

FIGS. 1 and 2 illustrate a quarter circle repair at the corner of a concrete bay in the road,

FIG. 3 illustrates a rectangular block repair in the centre of a concrete bay,

FIG. 4 is a plan view of a machine suitable for cutting the quarter circle recess shown in FIG. 1,

FIG. 5 is an elevation view taken along the line V-V in FIG. 4,

FIG. 6 is a detail view along the line VI-VI in FIG.

FIG. 7 is a plan view of a machine suitable for cutting the rectangular recess shown in FIG. 3,

FIG. 8 is a view along the line VIII-VIII in FIG. 7,

FIG. 9 is a view along the line IX-IX in FIG. 8,

FIG. 10 is a perspective view of one of the anchoring pads of the machine of FIGS. 7-9 shown on an enlarged scale,

FIG. 11 is an elevational view of the pad of FIG. 10 partially cut away to show details of the construction,

FIG. 12 is a detail view of part of the anchoring pad before engagement with a road surface, and

FIG. 13 illustrates the pneumatic circuit of the machine of FIGS. 7-9.

Referring to the drawings, FIG. 1 shows a quarter circle repair in one corner of a concrete bay 10 in a road, the adjacent concrete bays l1, l2, 13 being separated from the bay l0 and from one another by the usual bitumen joints 14, shown more clearly in FIG. 2. The defective concrete at the corner of bay 10 is first cut away in layers to a uniform depth by the machine shown in FIG. 4-6, hereinafter described, until sound concrete is exposed. The machine is arranged on the road so that the quarter circle recess 15 cut in the bay extends across the corner, that is the arcuate edge of the recess terminates at the side edges of the bay, so that there are no sharp corners within the periphery of the bay. Three holes 16 are then bored in the base of the recess 15 to a depth of approximately one inch with the aid of a template (not shown). FIG. 1 also shows a precast reinforced concrete repair block 18 of a size to be a loose fit within the quarter circle recess 15. The block 18 has three tie rods 19 positioned to engage within the holes 16 in the base of the recess. The side walls and base of both the recess 15 and the concrete block 18 are coated with an adhesive 20, and the holes 16 are filled with the adhesive, and the block 18 inserted in position in the recess as shown in FIG. 2. One example of a suitable adhesive is the synthetic resin marketed by Dussek Bitumen & Taroleum Ltd. of Bromley-by-bow, London, under the trade name Dupoxy 010. Alternatively, a quick setting mortar may be used as the adhesive provided that the block is a very close fit in the recess so that the layer of mortar is very thin and will thus harden very quickly. The block 18 is of a size such that its top surface is level with the top of the road. The gaps between the outer side walls of the block 18 and the adjacent concrete bays are then filled with bitumen. The tie rods 19 may be omitted, particularly with large size repair blocks.

The recess 15 is of course cut to a shape and depth to fit the block 18 which is cast several days previously so that the concrete in the block has set hard. Two or more blocks 18 of the same shape but of different thickness can conveniently be held available and the recess 15 cut to the minimum depth at which sound concrete is exposed and then further out to a depth corresponding to the thickness of one of the blocks 18.

In a case in which a spalling defect is along an edge of the concrete bay, the concrete may be cut away by a machine similar to the machine of FIGS. 4-6 but arranged to cut a semi-circular recess, which can then be repaired with a semi-circular concrete block by the method according to the invention.

Circular holes can conveniently be cut in a concrete road by a machine having a hammer unit mounted on a turntable arranged to rotate continously at a slow speed, the hammer unit having cutting heads spaced at different radial distances with respect to the centre of the turntable and arranged so that the paths traced out by each cutting head overlaps or is contiguous with the paths traced out by other cutting heads on the hammer unit.

When the spalling defect is inside the periphery of a bay, the defective concrete may be cut away by the machine illustrated in FIGS. 7-9 which forms a recess in the shape of a rectangular 23 with rounded corners, and the recess plugged by a correspondingly shaped concrete block 24 bonded to the base and walls of the recess by an adhesive according to the method of the invention.

The machine shown in FIGS. 4-6 comprises a frame 30 mounted on the concrete bay 10 of the road to be cut, a turntable 31 mounted on the frame for angular movement about a vertical pivot pin 32 on the frame, a carriage 33 mounted on the turntable for radial movement towards and away from the axis of the pivot pin 32, a hammer unit 34 slidable in vertical guides on the carriage and having three cutting heads 36 spaced along a radial line through the axis of the pivot pin 32, a hydraulic piston and cylinder unit 37 for oscillating the turntable about the pivot pin 32, and a hydraulic piston and cylinder unit 38 for reciprocating the carriage and hammer unit on the turntable.

The frame consists of a continuous vertical rail 40 mounted on legs 41, the rail having two

arcuate portions

42, 43 interconnected by

straight portions

44, 45, the arcuate portions being centered on the pivot pin 32 and serving as tracks for the turntable. The pivot pin is secured in an aperture in the cross piece of an inverted U shaped bracket 46, the legs of which are secured to the two

straight portions

44, 45 of the rail.

The turntable comprises a square section tube 48, one end of which is provided with an arm 49 fitted with rollers 50 which run on the track 42 and the other end of which is provided with a lug 51 fitted with a roller 52 which runs on the track 43. The turntable is pivotably connected to the pivot pin 32 by an inverted U shaped bracket 53 having the legs thereof secured to the sides of the tube 48, the pivot pin 32 being rotatably mounted in an aperture in the cross piece of the bracket 53. The cylinder of the unit 37 is secured to a lug 55 on one side of the tube 48 and the piston rod is pivotally mounted on a pin 56 on the bracket 46 so that extention of the unit 37 swivels the turntable into the broken line position shown in FIG. 4. The upper and lower walls of the tube 48 are provided with

slots

57, 58.

The carriage 33 is mounted inside the tube 48 and comprises two side plates 60, 61 spaced apart by two

end plates

62, 63 and upper and

lower rollers

64, 65 mounted on the side plates in rolling engagement with the inside surfaces of the upper and lower walls of tube 48 respectively. The end plates extend upwards through the slot 57 and form the vertical guides for the hammer unit. The cylinder unit 38 has the cylinder connected to a lug on the tube 48 and the piston connected to the end plate 62 on the carriage. The hammer unit is mounted on the lower end of a support plate 66 which extends through the space between the plates 60-63 of the carriage. The upper end of the support plate is fitted with rollers 67 adapted to engage the tube 48 to limit downward movement of the hammer unit.

The machine is fitted with suitable control mechanism operable'to actuate the cylinder unit 38 at a much higher speed than the cylinder unit 37, and automatically to reverse the movement of both the cylinder units at the ends of their strokes. The carriage and hammer unit thus reciprocate several times during each movement of the turntable across the frame, as shown by the arrows in FIG. 4, so that the cutting heads 36 traverse over the area 70 shown in broken lines in FIG. 4 and corresponding in shape to the recess 15 in FIG. 1. The control mechanism may if desired include trip switches mounted on the rail 40 and adapted to actuate the cylinder unit 38 at given angular settings of the turntable so that the cutting heads follow a set pattern. The hammer unit, in use, slides down the vertical guides formed by the

end plates

62, 63 of the carriage as the concrete is cut away.

The machine shown in FIGS. 7-9 comprises a main frame fitted with two parallel slide bars 76, a main carriage 77 slidably mounted on the bars 76, the carriage 77 being fitted with two parallel slide bars 78 arranged perpendicular to the slide bars 76, an auxiliary carriage 79 slidably mounted on the bars 78, a hammer unit 80 supported on a hydraulic dashpot 81 on the carriage 79, and

cylinder units

82A, 83B, 83C operable to reciprocate the main carriage on the bars 76 and the auxiliary carriage together with the hammer unit on the bars 78. The main frame consists of two side members 85, and two cross members 86 interconnecting the ends of members 85, the slide bars 76 being mounted on brackets on the cross members 86. The main carriage 77 consists of two side members 88, two cross members 89 interconnecting the ends of the members 88, and two tubes 90 connected to the cross members 89 and receiving the bars 76 as a close sliding fit, the two slide bars 78 extending between the cross members 89. The auxiliary carriage 79 consists of two side members 91, two cross members 92, and two tubes 93, which are secured to the cross members and receive the slide bars 78 as a close sliding fit. The cylinder unit 82A has the cylinder thereof mounted on a bracket 92 on one of the cross members 86 of the frame and the piston rod thereof connected to one of the side members 88 of the main carriage. The cylinder unit 838 has the cylinder thereof mounted on a bracket 97 on one of the cross members 89 of the main carriage and the cylinder unit 83C has the cylinder thereof mounted on a bracket 98 on one of the side members of the auxiliary carriage, the cylinders of the two units 833 and 83C being coaxial and having their pistons mounted on opposite ends of a common piston rod 99.

The frame 75 is provided with legs 94 fitted with anchoring pads 95 adapted to secure the frame securely to a concrete road, as described hereinafter.

The

cylinder units

82A, 8313i, 83C are operated by air under pressure in controlled sequence, as hereinafter described, so as to reciprocate the

carriages

77, 79 along their slide rods in a predetermined succession of movements in which the cutting heads on the hammer unit traverse over the whole area to be cut, shown at 96 in FIG. 7, and also trace out paths which extend along the sides of the area 96 and across the ends of the area, so that the recess cut in the concrete has clearly defined straight edges. The cutting heads are circular so that the corners of the recess are rounded. The hydraulic dashpot 31 lowers the hammer unit at a predetermined rate during the cutting operation.

As shown in FIGS. 10-l2, each anchoring pad 95 comprises a horizontal circular metal plate 100 having the outside margin turned down to form a peripheral skirt 101, a thick outer ring 102 of soft foam rubber of rectangular section bonded to the underside of the plate 100 adjacent the skirt, and a thick inner ring 103 of relatively hard rubber of rectangular section bonded to the underside of the plate 100 adjacent the ring 102. In the unstressed condition as shown in FIG. 12, the outer ring 102 extends below the inner ring 103, and both rings extend below the skirt. An air extraction pipe 104 is sealed in a port in the plate 100 and opens into the space bounded by the inner ring 103.

In operation, the anchoring; pad is positioned on a road to which it is to be anchored, the weight of the machine on the pad being supported on the road by the inner ring 103, with the outer ring 102 of foam rubber compressed against the road surface. The outer ring 102 which is relatively soft and deformable conforms to the irregularities in the surface of the road and provides a seal between the surface of the road and the metal plate 100. The air extraction pipe is then connected to a vacuum pump (not shown) which is run continuously to withdraw air from the chamber formed between the plate 100, the inner ring 103 and the road surface. When the pressure in the chamber is reduced below that of the atmosphere, the differential pressure acting on the plate 100 forces it downwards to compress the inner rubber ring 103 against the road and engage the lower edge of the skirt 101 against the road. The inner ring 103 then provides a seal which reinforces that provided by the outer ring in restricting seepage of air into the chamber. The relative depths of the inner ring 103 and the skirt 101 are arranged so that the ring is subjected to a substantial compressive force before the skirt engages the road surface, so that the rubber inner ring is forced into any small cavities in the road surface and provides an effective seal. Upon further reduction of the pressure in the chamber, the lower edge of the skirt is forced hard against the road to provide a firm anchorage.

The outer ring 102 of the anchoring pad may be replaced by a thin-walled annular rubber tube mounted as a loose fit in the annular recess defined by the plate 100, ring 103 and skirt 101, the tube being inflatable so that its wall makes sealing contact with the walls of the recess and the road surface. The tube can conveniently be of the type used as the inner tube in a pneumatic tyre, the valve stem for inflating the tube extending through an aperture in the plate 100.

The hammer unit 80 on the cutting machine of FIGS. 7-9 is provided with two cutting heads 120 of equal diameter spaced apart a distance equal to the diameter of each head, and the

cylinder units

82A, 83B, 83C are operated in a predetermined sequence so as to move the hammer unit along paths MN, NO, OP, PR, RS, ST, TU UM as shown in FIG. 13, in which paths MN and RS and also paths OP and TU are spaced apart a distance equal to the diameter of each cutting head 120 and paths OP and RS are spaced apart a distance equal to three times the diameter of each cutting head, whereby the cutting heads traverse over the whole area to be cut. For this purpose, the cylinder unit 838 has a stroke equal to the diameter of each cutting head, the cylinder unit 83C has a stroke equal to three times the diameter of each cutting head, and the cylinder units are operated in sequence by the pneumatic circuit shown in FIG. 13. For convenience, the

cylinder units

82A, 83B, 83C are referred to hereafter as cylinders A, B, C respectively, the switches and operating cams for initiating expansion of the cylinders A, B, C are denoted in FIG. 13 by the references A+, B+, c+ respectively, and the switches and operating cams for initiating contraction of the cylinders A, B, C are denoted in FIG. 13 by the references A, B, C- respectively.

The pneumatic circuit comprises three

spool valves

121, 122, 123 controlling expansion and contraction of the cylinders A, B, C respectively, four

switchs

125, 126, 127, 128 operable by a single cam 129 and controlling movement of the spool of valve 121, two

switches

130, 131 operable by

cams

132, 133 respectively and controlling movement of the spool of valve 122, a switch 135 operable by

cams

136, 137 and a switch 138 operable by

cam

139, 140 the two

switches

135, 138 controlling movement of the spool of valve 123, a selector valve 142 for selecting one or other of the

switches

125, 126 and a selector valve 143 for selecting one or other of the

switches

127, 128.

Each of the

spool valves

121, 122, 123 comprises a valve body having an inlet port connected to a supply of air under pressure, two services ports connected one to each end of the associated cylinder, two exhaust ports, and two control ports one at each end of the valve body and connected by a switch either to a supply of air under pressure or to exhaust. Supply of air to one control port moves the spool to a first setting position in which a first of the service ports is connected to the inlet port and the second service port is connected to an exhaust port, and supply of air to the other control port moves the spool to the second setting position in which the second service port is connected to the inlet port and the first service port is connected to an exhaust port. Such valves are well known in the art. Each of the

selector valves

142, 143 comprises a valve body having an outlet port, two inlet ports and a control port in one end of the valve body, and a valve spool biased by a spring towards the control port. When the control port is connected to exhaust, the spring holds the spool in a first setting position, in which the outlet port is connected to one inlet port and the other inlet port is blanked off. Supply of air to the control port moves the spool against the action of the spring into a second setting position in which the outlet port is connected to the other inlet port and said one inlet port is blanked off. Such selector valves are also well known in the art.

The

switches

125, 126, 127, 128 are mounted on the frame and their cam 129 is mounted on the auxiliary carriage and arranged so that switch is actuated when the hammer unit is on path TU, the switch 126 is actuated when the hammer unit is on path OP, the switch 127 is actuated when the hammer unit is on path RS, and the switch 128 is actuated when the hammer unit is on path MN. The

switches

130, 131, 135, 138 are mounted on the auxiliary carriage 79 (the switches being shown separate from the auxiliary carriage 79 in FIG. 13 for clarity), and the

cams

132, 133, 136, 137, 139, are mounted on the frame and arranged so that the

switches

130, 138 are actuated when the hammer unit is at point U on its path of travel, the

switches

131, 138 are actuated when the hammer unit is at point P, and the switch 135 is actuated when the hammer unit is at point N and also when it is at point S.

The spool valve 121 has its two service ports connected by

lines

150, 151 to opposite ends of cylinder A, one control port connected by line 152 to the outlet port of selector valve 142 and the other control port connected by line 153 to the outlet port of selector valve 143, the two inlet ports of valve 142 being connected by

lines

154, 155 to

switches

125, 126 respectively, and the two inlet ports of selector valve 143 being connected by

lines

156, 157 to

switches

127, 128 respectively, the arrangement being such that actuation of

switches

125, 126 causes air to be suppled to cylinder A to contract it and actuation of

switches

127, 128 causes air to be supplied to the opposite end of cylinder A to expand it. The spool valve 122 has its two service ports connected by

lines

160, 161 to opposite ends of cylinder B, one control port connected by line 162 to the switch 130, and the other control port connected by line 163 to the switch 131, the arrangement being such that actuation of switch 130 causes air to be supplied to cylinder B to contact it and actuation of switch 131 causes air to be supplied to the opposite end of cylinder B to expand it. Line is connected by line 165 to the control port of selector valve 142, and line 161 is connected by line 166 to the control port of selector valve 143. The spool valve 123 has its two service ports connected by

lines

170, 171 to opposite ends of cylinder C, one control port connected by line 172 to the switch 138, and the other control port connected by line 173 to the switch 135, the arrangement being such that actuation of switch 138 causes air to be supplied to cylinder C to contract it and actuation of switch 135 causes air to be supplied to the opposite end of cylinder C to expand it.

When the cylinders A, B, C are fully contracted as shown in FIG. 13, the hammer unit is at point M and the control valves are in the setting positions providing the air flow shown by full lines in FIG. 13. Switch 128 is then actuated and air flows through line 151 and causes the cylinder A to expand and the hammer unit to travel along path MN. At point N, cam 137 actuates switch 135 to cause cylinder C to expand and the hammer unit to travel along path NO. At point 0, switch 126 is actuated to cause cylinder A to contract and the hammer unit to travel along path OP. It will be noted that, throughout paths MN, NO, the selector valve 142 is actuated by air from

lines

160, 161 to connect the switch 126 to valve 121 and block switch 125. At point P,

cams

133, 140

actuate switches

131, 138 to cause cylinder B to expand and cylinder C to contract so that the hammer unit travels along path PR. Air is also fed from line 161 through line 166 to actuate the selector valve 143 and thereby connect switch 127 to the valve 121. At point R, switch 127 is actuated to cause cylinder A to expand and the hammer unit to travel along the path RS. At point S, cam 136 actuates switch 135 to cause cylinder C to expand and the hammer unit to travel along path ST. During travel along the path ST, the hammer unit actuates the switch 126 at point but this switch is blocked by the selector valve 142. At point T, switch 125 is actuated to cause cylinder A to contract and the hammer unit to travel along path TU. At point U,

cams

132, 139 actuated

switches

130, 138 to cause both the cylinders to contract so that the hammer unit travels along path UM. During travel along the path UM, the hammer unit actuates the switch 127 at point R but this switch is blocked by the selector valve 143.

It will be appreciated that the paths NO and ST overlap, as do the paths PR and UM, but they have been shown spaceda small distance apart in FIG. 13 to avoid confusion.

The cutting machine illistrated in FIGS. 8-10 may be used to remove the skin on the top of a concrete road before resurfacing the road. This exposes the aggregate in the concrete and enables a good bond to be made between the concrete base and the resurfacing layer. For this purpose, the machine is preferably of large size and fitted with several hammer units so as to reduce the time required for treating each area covered by the machine.

The cutting machine may be connected to the anchoring pads by knuckle joints which enable the pads to be inclined relative to one another in a case in which the road surface is uneven.

I claim:

1. A method of repairing spalling defects in a concrete roadway, characterized by:

A. continuously advancing cutting means in a programmed sequence of motions over that part of the roadway containing said defects and bounded by a predetermined contour conforming to that of preformed repair block means, said sequence of motions being such that the entire area of the road surface bounded by said contour is traversed repeatedly by the cutting means;

B. while so advancing the cutting means, continuously moving the same up and down, with a reciprocating motion, into engagement with the road surface to impart a succession of impact blows thereto with every successive blow occurring at an area different than the preceding blow, the speed and frequency of said blows being such as to cause cutting away of the concrete in successive layers in an upper surface portion. of the roadway without disturbing the aggregate in the concrete matrix therebeneath, to thereby form in said upper surface portion of the roadway a recess having said contour and a substantially uniform depth at least equal to that of the defects in the roadway and corresponding to the thickness of said preformed repair block means;

C. and bonding into said recess preformed repair block means of hard wearing material, having said predetermined contour and a thickness substantially equal to the depth of said recess.

Claims

1. A method of repairing spalling defects in a concrete roadway, characterized by: A. continuously advancing cutting means in a programmed sequence of motions over that part of the roadway containing said defects and bounded by a predetermined contour conforming to that of preformed repair block means, said sequence of motions being such that the entire area of the road surface bounded by said contour is traversed repeatedly by the cutting means; B. while so advancing the cutting means, continuously moving the same up and down, with a reciprocating motion, into engagement with the road surface to impart a succession of impact blows thereto with every successive blow occurring at an area different than the preceding blow, the speed and frequency of said blows being such as to cause cutting away of the concrete in successive layers in an upper surface portion of the roadway without disturbing the aggregate in the concrete matrix therebeneath, to thereby form in said upper surface portion of the roadway a recess having said contour and a substantially uniform depth at least equal to that of the defects in the roadway and corresponding to the thickness of said preformed repair block means; C. and bonding into said recess preformed repair block means of hard wearing material, having said predetermined contour and a thickness substantially equal to the depth of said recess.