APPARATUS AND METHOD FOR STRIATING CONCRETE
United States Patent 3846036
Disclosed is a tool for striating freshly placed concrete which is a broom-like device having a single course of closely packed bristles whose effective length varies about one-quarter to one-eighth inch, and whose overall length is about 26 inches. When drawn across wet concrete, the tool striates it without dragging concrete along the surface or pick-up of concrete. Depth of striations is controlled by angle of incidence of the tool and by bristle diameter.
US Patent References:
Brush
Hanson - July 1963 - 3099029
APPARATUS FOR FINISHING CONCRETE SURFACES
Jones - August 1971 - 3596578
/3605579.html
Heltzel - September 1971 - 3605579
Brush
Hanson - July 1963 - 3099029
APPARATUS FOR FINISHING CONCRETE SURFACES
Jones - August 1971 - 3596578
/3605579.html
Heltzel - September 1971 - 3605579
Application Number:
05/349935
Publication Date:
11/05/1974
Filing Date:
04/11/1973
View Patent Images:
Export Citation:
Assignee:
Roberts Supply, Inc. (Abilene, TX)
Primary Class:
Other Classes:
404/89, 15/160
International Classes:
E01C19/43; E01C19/22; E01C7/35
Field of Search:
404/89,93,118,72,75 15/235.4,166,183,160,200
Primary Examiner:
Byers Jr., Nile C.
Attorney, Agent or Firm:
Clegg, Cantrell & Crisman
Claims:
What is claimed is
1. Apparatus for striating freshly placed concrete comprising:
2. Apparatus in accordance with claim 1 in which the protrusion distance of said bristles is between about 20 inches and about 36 inches.
3. Apparatus in accordance with claim 1 in which the protrusion distance of said bristles is about 241/2 inches.
4. Apparatus in accordance with claim 1 and further comprising a reinforcing member extending across said course of bristles about midway of the length thereof.
5. Apparatus in accordance with claim 4 in which said reinforcing member is an adhesive tape.
6. Apparatus in accordance with claim 1 and further comprising mounting means for said head adapted to position said head at an acute angle to a concrete surface to be striated.
7. Apparatus in accordance with claim 6 in which said mounting means comprises a sled having floatation members slidable across a concrete surface, a frame mounted on said floatation members, and pivotable connectors between said head and said frame providing for movement of said head between two operative positions, one on either side of said frame.
8. Apparatus in accordance with claim 6 in which said mounting means comprises a work bridge.
9. Apparatus in accordance with claim 6 in which said mounting means comprises a swivel member attached to said head and an elongated handle attached to said swivel member and extending transversely of said head.
10. A method for striating freshly placed concrete to improve its tractive properties,
1. Apparatus for striating freshly placed concrete comprising:
2. Apparatus in accordance with claim 1 in which the protrusion distance of said bristles is between about 20 inches and about 36 inches.
3. Apparatus in accordance with claim 1 in which the protrusion distance of said bristles is about 241/2 inches.
4. Apparatus in accordance with claim 1 and further comprising a reinforcing member extending across said course of bristles about midway of the length thereof.
5. Apparatus in accordance with claim 4 in which said reinforcing member is an adhesive tape.
6. Apparatus in accordance with claim 1 and further comprising mounting means for said head adapted to position said head at an acute angle to a concrete surface to be striated.
7. Apparatus in accordance with claim 6 in which said mounting means comprises a sled having floatation members slidable across a concrete surface, a frame mounted on said floatation members, and pivotable connectors between said head and said frame providing for movement of said head between two operative positions, one on either side of said frame.
8. Apparatus in accordance with claim 6 in which said mounting means comprises a work bridge.
9. Apparatus in accordance with claim 6 in which said mounting means comprises a swivel member attached to said head and an elongated handle attached to said swivel member and extending transversely of said head.
10. A method for striating freshly placed concrete to improve its tractive properties,
Description:
BACKGROUND OF THE INVENTION
This invention relates to apparatus for striating freshly placed concrete and to a method for striating concrete.
Striated or grooved concrete is employed on selected sections of roadway where it is desired to provide improved traction for vehicles using the roadway, even at the expense of a "noisier" road surface. Typical locations where striated concrete pavement is used include bridge decks, banked highway curves, and entrance and exit ramps at interchanges. Striated concrete is also used in small patches at various locations to create noisy spots on the road to warn users of special conditions such as changes in the layout of traffic lanes, upcoming traffic islands, etc. In most instances, it is desired that the striations or grooves in the concrete run along the usual path of travel of vehicles using the roadway, but in some instances it is desired to have the striations run across the roadway.
In the past, concrete has been grooved after it has set up with the use of diamond wheel saws. This method of grooving is expensive and time consuming and involves the use of expensive equipment and skilled labor. In addition, as a practical matter, the grooves produced by this method are several inches apart.
Recently, those concerned with highway design have concluded that a better tractive surface is provided if the striations are both shallower and closer together than can be provided by the diamond saw technique. Hence, attempts have been made to roughen or striate the concrete while it is still wet to provide the desired surface of fine roughness.
The problem of roughening wet concrete surfaces appears at first to be a simple one. Wet concrete is plastic, and ought to take and retain the imprint of a rough object pulled or dragged across it. This straight-forward approach has been tried in the field. One expedient which has been used is to drag burlap or another rough textured cloth across the wet concrete. Use has also been made of street sweepers' brooms which have been pulled across the surface. Surprisingly, these simple approaches to the problem have not produced satisfactory results.
The results have not been satisfactory in several respects. Some roughening materials which have been tried have actually had the opposite effect, that of smoothing and polishing the concrete surface. Others, particularly the street sweepers' brushes mentioned above, pick up appreciable amounts of concrete in the course of use. As they pick up the concrete, such brushes become less satisfactory as roughening tools and accordingly must be frequently and repeatedly cleaned of the picked-up concrete. The picked-up concrete removed from such a roughening tool must be discarded, which is wasteful, or returned to the road surface, which is a difficult process to perform as a practical matter because of the difficulty of respreading such concrete uniformly. For example, if a worker is required to clean off his street sweeper's broom every six or eight feet and to respread the picked-up concrete onto the road surface in the vicinity where he has cleaned his broom, there will inevitably result a series of small humps or waves in the roadway surface at intervals of six or eight feet. These minute humps or waves can give a surprisingly rough and even dangerous ride to a vehicle moving along the roadway at high speed.
Another aspect of the unsatisfactory nature of prior expedients for striating or roughening wet concrete is that substantially all of them result in moving some of the concrete along the road surface in the direction in which the tool is dragged or moved, even if there is not an objectionable amount of concrete actually picked up by the tool. This movement of concrete is extremely objectionable because wet concrete, while plastic, is not a uniform material. It is made up of fine cement and sand, and relatively coarse aggregate or gravel. The part of the concrete which gets moved by prior roughening tools is the cement-sand mixture, and the large aggregate tends to remain in place. This phenomenon results in some of the aggregate being exposed at the roadway surface. This result is bad because the "feathered" thin regions of cement-sand compound around the edges of a piece of exposed aggregate wear very rapidly, and this wear leads to rapid deterioration of the roadway surface.
Since the above-mentioned adoption of a preference for shallow closely spaced striations in roadway concrete, highway engineers have been evolving standards for expressing that preference objectively for use in road construction specifications. One such specification for surface roughness is cast in terms of average width and depth of the grooves when spaced together as closely as practical. The actual measurement on a road surface is accomplished by pouring a specified amount of sand having a selected particle size distribution onto the surface, and brushing that amount of sand into a circular layer which just covers the concrete. The diameter of the circular layer of sand so formed has been empirically correlated with average groove size. It will be noted that this specification test can only be performed after the concrete roadway has cured or hardened, and this circumstance highlights the importance of striating the concrete correctly the first time. If the striated concrete is found after curing to be off specifications, a massive and exhorbitantly expensive rework job is necessary.
SUMMARY OF THE INVENTION
In accordance with the present invention, apparatus for striating freshly placed concrete is provided in the form of a broom-like structure having an elongated head in which are mounted bristles arranged in a single course. The bristles are preferably mounted side by side and are long enough that they tend to lay on the concrete surface to be striated when the head is held at an angle above the surface. Furthermore, the bristles are mounted so that while their ends establish a substantially straight line, preferably parallel with the head, there is a deliberate variation in the protruding length of the bristles so that no two adjacent bristles protrude from the head precisely the same distance. The desired variation in the protrusion distance is between about one-fourth inch and about one-eighth inch.
When a striating or roughening tool constructed in accordance with the invention is pulled across a freshly placed concrete surface, the bristles in their end regions penetrate into the surface and form a series of parallel grooves or striations therein. The width and depth of the striations is generally and approximately related to the bristle diameter; the depth of the striations can be controlled within this limitation by varying the angle at which the head of the tool is held above the concrete. Assuming other conditions to remain uniform, the greater the angle of the head, the deeper the striations or grooves will be.
The length variation of adjacent bristles mentioned above is of great importance to proper application of the invention. Such variation permits each bristle to form a groove without picking up or moving along the road surface any substantial quantity of concrete. This result is obtained because at the end of each bristle, which is the critical groove-forming region of the tool, the concrete on the shoulders of the groove being formed can displace laterally a slight but necessary distance without being thrown against or onto the adjacent bristle end. It is this lateral "micro-movement" of the concrete which prevents it from being dragged along with the tool or picked up by it.
In further accordance with the invention, several embodiments of supplementary support equipment for moving the tool across a freshly placed concrete surface are provided. In its method aspect, the invention involves an improved way to striate concrete by applying the striating force to each groove so that the concrete on the shoulder of the groove being formed can move laterally a short distance without encountering any part of a tool element forming an adjacent groove.
It is an object of the present invention to provide an improved apparatus for striating freshly placed concrete simply and efficiently, with no substantial waste of concrete and no deleterious side effects upon the quality of the concrete surface from the roughening.
It is a further object of this invention to provide a means and a method for striating freshly placed concrete surfaces with grooves of controllable size.
The manner in which the foregoing objects are achieved in accordance with the invention, together with other objects and purposes of the invention, may best be understood by a consideration of the detailed description which follows, together with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a striating tool constructed in accordance with the invention with the bristles shown on an enlarged scale for clarity;
FIG. 2 is a somewhat diagrammatic side view of a roughening tool of the invention mounted on a work bridge, which is shown in section;
FIG. 3 is a somewhat diagrammatic side view of a tool of the invention mounted on a handle for hand manipulation;
FIG. 4 is a side elevational view of a sled for conveying the roughening tool of the invention across a bed of freshly placed concrete;
FIG. 5 is a plan view of the sled of FIG. 4; and
FIG. 6 is a somewhat diagrammatic plan view of an area of concrete striated in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Attention is first directed to FIG. 1 from which it can be seen that the apparatus of the invention is a broom-like device having a head 10, which may be conveniently formed of oak or another light, strong material. Head 10 is elongated and is of any convenient length. As a practical matter, a length of about 6 feet is convenient and is not so long as to be clumsy in handling. When the width of a piece of concrete which is desired to be striated is greater than 6 feet, several separate devices may be mounted side by side to make up the required width. Thus, for example, when the apparatus of the invention is used in connection with a "work bridge" employed to span a bed of concrete 30 feet wide, five devices, each having a head 10 which is 6 feet long may be mounted side by side on such a bridge. On the other hand, if the tool is one which will be hand manipulated in use, head 10 may conveniently be made shorter, for example, 2 or 4 feet long. Head 10 is provided with a longitudinal slot 11 in the lower edge thereof. Slot 11 may conveniently be about 11/2 inches deep.
Bristles 12 are mounted in slot 11 in closely abutting side-by-side relationship. The bristles 12 are desirably formed of a tough plastic material such as polypropylene. This material has the desired properties of being wear resistant, flexible to the desired degree, and relatively non-adherent for concrete. The projecting length of bristles 12, that is, the distance from the lower edge of head 10 to the tip of any given bristle, is preferably about 241/2 inches. Some variation from this preferred length is permissible; however, if the bristles 12 have a projecting length less than about 20 inches, they tend to dig into the concrete surface objectionably when the head 10 is positioned at a convenient angle above the surface, and when the bristles are more than about 36 inches in projecting length they tend to be difficult to control during the striating operation.
From FIG. 1 it can be seen that the free ends of bristles 12, taken together, define or establish a generally straight line which is parallel to head 10. But in accordance with the invention, the projecting length of bristles 12 is not exactly the same from one bristle to another. A deliberate variation in such length from bristle to bristle is introduced so that the end of each bristle engages and grooves the concrete a little bit ahead of or behind its immediate neighbors. It is this variation which permits the before-mentioned "micro-movement" in a lateral direction, of the concrete being grooved, which results in the formation of grooves of controllable size and depth without objectionable pickup or longitudinal dragging of the concrete by the bristles. The desired variation in projecting length between adjacent bristles 12 is between about one-fourth and about one-eighth inch. Smaller variation does not permit the desired lateral movement of the concrete, and greater variation introduces control problems and a tendency for the last formed groove in a region to fill in adjacent earlier formed grooves.
The diameter of bristles 12 is generally and approximately related to the width and depth of the striations which are to be formed on the concrete. This relationship cannot be defined with precision because the condition of the concrete is an important parameter in the relationship, and the condition of the concrete is in turn dependent upon its makeup, the length of time it has been placed before striating, and the humidity, temperature and wind conditions prevailing at the site. Despite these factors which are not controllable by the design of the device, I have found that a bristle diameter which is approximately twice that of the depth of the groove desired to be formed is quite appropriate. At present, highway engineers prefer striations which are as close together as practical and of a depth between about 0.03 and about 0.05 inches. Thus, I prefer a bristle diameter of about 0.080 inches in a tool designed to produce striations meeting such specifications.
In accordance with one aspect of the invention, it is preferred to apply to the side of the course of bristles 12 a reinforcing member 13 at a point about midway of their projecting length. The reinforcing member may conveniently be woven glass fiber adhesive tape. While such a reinforcing member on the course of bristles is not absolutely necessary, it has been found that it aids in the controllability of the straightness and depth of the grooves being formed. It is also preferred to use such reinforcing tape to unite the bristle courses of tools which are mounted side by side, in the manner described above, to eliminate any discernable boundary between the work performed by one tool and that performed by another.
Head 10 is preferably rectangular in cross section and approximately 31/2 inches by 1 inch in width and thickness. Such proportioning makes it possible for those using the device to attach whatever fittings they find convenient for mounting the device on work bridges and other support apparatus. The groove 11 is desirably of a thickness approximately equal to the diameter of the bristles 12 so that a tight fit is accomplished. The bristles 12 may readily be secured in the groove by an adhesive which grips them and the material of head 10 tightly. For example, polymethyl methacrylate cement has been found to be a suitable adhesive for this purpose.
Attention is now directed to FIG. 2, where a work bridge 14 is shown somewhat diagrammatically positioned above a bed of concrete 15. Work bridge 14 is typical of structures employed by concrete workers laying roadways. Such bridges are lightweight steel trusses with a walkway for workmen across the top thereof, and mounting equipment (not shown) is furnished at each end to move the work bridge back and forth in the direction of the double headed arrow 16 over the bed of concrete 15. As can be seen from FIG. 2, the head 10 of the striating device is mounted at one side of the work bridge 14 at an acute angle with respect to the bed of concrete 15. The means of mounting are only diagrammatically indicated in FIG. 2 inasmuch as the exact mode of attachment forms no part of the invention and will vary depending upon the design of the work bridge. Bristles 12 extend downwardly and to the right to engage and lay upon concrete bed 15. It is preferred that the bristles 12 present a substantial surface to the concrete near their ends; preferably one to three inches of each bristle is in groove-forming contact with the surface. As FIG. 2 is drawn, the work bridge is displaced slowly to the left in the striating operation.
In FIG. 3 the striating tool of the invention is shown attached to a broom handle to form a hand manipulable tool. Thus, head 10 is attached to swivel member 17, which is shown only diagrammatically because its detailed structure forms no part of the present invention per se, and a variety of existing forms of such equipment may be employed. Swivel 17 is in turn connected to a broom handle 18. By this arrangement, a worker by manipulating handle 18 can position head 10 at a desired acute angle above a bed of concrete and draw bristles 12 across the bed to striate it.
In FIGS. 4 and 5, in accordance with the invention, there is illustrated a sled for supporting the striating device in applications where no work bridge such as that shown in FIG. 2 is employed and where the area to be striated is too large to be worked by hand tools such as shown in FIG. 3. As can be seen from FIGS. 4 and 5, the support device 19 is in the form of a lightweight sled having a pair of rectangular pads 20 which are large enough to give the sled 19 good floatation or bouyancy on the wet concrete bed. A light angle iron frame 21 is mounted above pads 20; the frame is triangular in end elevation. A ridge pole 22 extends across the width of the frame 21. Two or more straps 23 are fitted around ridge pole 22 and are connected to head 10. By this means head 10 rests against the legs 24 of frame 21 at an acute angle to a bed of concrete on which the sled 19 is positioned. The bristles 12 extend outwardly and engage the concrete surface in the manner described above. Each leg 24 is provided with one or more pull rings 25 to which a pull chord 26 of light twine is attached. Such a pull chord is provided at each side of sled 19.
In use, the sled 19 is pulled by pull chords 26 across a bed of freshly placed concrete by a worker located at the far side of the bed. When the sled is pulled all the way across the bed to the worker he then displaces it to a portion of the bed which has not yet been grooved, and flips the head 10 over the top of the sled so that it rests on the back pair of legs 24. A coworker then pulls the sled back across the wet bed of concrete, striating the portion which is in the path of the sled. The twine used to pull the sled 19 back and forth in the manner just described does not objectionably mar the striated surface of the concrete; if anything, it contributes to the striation. The marks, if any, left by the pads 20 of the sled are obliterated by bristles 12 striating the concrete behind pads 20.
In FIG. 6 there is shown somewhat diagrammatically, of necessity, a concrete surface 15 having striations 27 formed therein by the method and equipment of the invention. Also indicated on FIG. 6 is a pile of gauge sand worked into a circular pattern in the manner described above, to determine whether the striations meet the desired specifications. Such circle of sand is designated 28 in FIG. 6, and as explained above, its diameter gives a measure of the average depth of striations 27.
This invention relates to apparatus for striating freshly placed concrete and to a method for striating concrete.
Striated or grooved concrete is employed on selected sections of roadway where it is desired to provide improved traction for vehicles using the roadway, even at the expense of a "noisier" road surface. Typical locations where striated concrete pavement is used include bridge decks, banked highway curves, and entrance and exit ramps at interchanges. Striated concrete is also used in small patches at various locations to create noisy spots on the road to warn users of special conditions such as changes in the layout of traffic lanes, upcoming traffic islands, etc. In most instances, it is desired that the striations or grooves in the concrete run along the usual path of travel of vehicles using the roadway, but in some instances it is desired to have the striations run across the roadway.
In the past, concrete has been grooved after it has set up with the use of diamond wheel saws. This method of grooving is expensive and time consuming and involves the use of expensive equipment and skilled labor. In addition, as a practical matter, the grooves produced by this method are several inches apart.
Recently, those concerned with highway design have concluded that a better tractive surface is provided if the striations are both shallower and closer together than can be provided by the diamond saw technique. Hence, attempts have been made to roughen or striate the concrete while it is still wet to provide the desired surface of fine roughness.
The problem of roughening wet concrete surfaces appears at first to be a simple one. Wet concrete is plastic, and ought to take and retain the imprint of a rough object pulled or dragged across it. This straight-forward approach has been tried in the field. One expedient which has been used is to drag burlap or another rough textured cloth across the wet concrete. Use has also been made of street sweepers' brooms which have been pulled across the surface. Surprisingly, these simple approaches to the problem have not produced satisfactory results.
The results have not been satisfactory in several respects. Some roughening materials which have been tried have actually had the opposite effect, that of smoothing and polishing the concrete surface. Others, particularly the street sweepers' brushes mentioned above, pick up appreciable amounts of concrete in the course of use. As they pick up the concrete, such brushes become less satisfactory as roughening tools and accordingly must be frequently and repeatedly cleaned of the picked-up concrete. The picked-up concrete removed from such a roughening tool must be discarded, which is wasteful, or returned to the road surface, which is a difficult process to perform as a practical matter because of the difficulty of respreading such concrete uniformly. For example, if a worker is required to clean off his street sweeper's broom every six or eight feet and to respread the picked-up concrete onto the road surface in the vicinity where he has cleaned his broom, there will inevitably result a series of small humps or waves in the roadway surface at intervals of six or eight feet. These minute humps or waves can give a surprisingly rough and even dangerous ride to a vehicle moving along the roadway at high speed.
Another aspect of the unsatisfactory nature of prior expedients for striating or roughening wet concrete is that substantially all of them result in moving some of the concrete along the road surface in the direction in which the tool is dragged or moved, even if there is not an objectionable amount of concrete actually picked up by the tool. This movement of concrete is extremely objectionable because wet concrete, while plastic, is not a uniform material. It is made up of fine cement and sand, and relatively coarse aggregate or gravel. The part of the concrete which gets moved by prior roughening tools is the cement-sand mixture, and the large aggregate tends to remain in place. This phenomenon results in some of the aggregate being exposed at the roadway surface. This result is bad because the "feathered" thin regions of cement-sand compound around the edges of a piece of exposed aggregate wear very rapidly, and this wear leads to rapid deterioration of the roadway surface.
Since the above-mentioned adoption of a preference for shallow closely spaced striations in roadway concrete, highway engineers have been evolving standards for expressing that preference objectively for use in road construction specifications. One such specification for surface roughness is cast in terms of average width and depth of the grooves when spaced together as closely as practical. The actual measurement on a road surface is accomplished by pouring a specified amount of sand having a selected particle size distribution onto the surface, and brushing that amount of sand into a circular layer which just covers the concrete. The diameter of the circular layer of sand so formed has been empirically correlated with average groove size. It will be noted that this specification test can only be performed after the concrete roadway has cured or hardened, and this circumstance highlights the importance of striating the concrete correctly the first time. If the striated concrete is found after curing to be off specifications, a massive and exhorbitantly expensive rework job is necessary.
SUMMARY OF THE INVENTION
In accordance with the present invention, apparatus for striating freshly placed concrete is provided in the form of a broom-like structure having an elongated head in which are mounted bristles arranged in a single course. The bristles are preferably mounted side by side and are long enough that they tend to lay on the concrete surface to be striated when the head is held at an angle above the surface. Furthermore, the bristles are mounted so that while their ends establish a substantially straight line, preferably parallel with the head, there is a deliberate variation in the protruding length of the bristles so that no two adjacent bristles protrude from the head precisely the same distance. The desired variation in the protrusion distance is between about one-fourth inch and about one-eighth inch.
When a striating or roughening tool constructed in accordance with the invention is pulled across a freshly placed concrete surface, the bristles in their end regions penetrate into the surface and form a series of parallel grooves or striations therein. The width and depth of the striations is generally and approximately related to the bristle diameter; the depth of the striations can be controlled within this limitation by varying the angle at which the head of the tool is held above the concrete. Assuming other conditions to remain uniform, the greater the angle of the head, the deeper the striations or grooves will be.
The length variation of adjacent bristles mentioned above is of great importance to proper application of the invention. Such variation permits each bristle to form a groove without picking up or moving along the road surface any substantial quantity of concrete. This result is obtained because at the end of each bristle, which is the critical groove-forming region of the tool, the concrete on the shoulders of the groove being formed can displace laterally a slight but necessary distance without being thrown against or onto the adjacent bristle end. It is this lateral "micro-movement" of the concrete which prevents it from being dragged along with the tool or picked up by it.
In further accordance with the invention, several embodiments of supplementary support equipment for moving the tool across a freshly placed concrete surface are provided. In its method aspect, the invention involves an improved way to striate concrete by applying the striating force to each groove so that the concrete on the shoulder of the groove being formed can move laterally a short distance without encountering any part of a tool element forming an adjacent groove.
It is an object of the present invention to provide an improved apparatus for striating freshly placed concrete simply and efficiently, with no substantial waste of concrete and no deleterious side effects upon the quality of the concrete surface from the roughening.
It is a further object of this invention to provide a means and a method for striating freshly placed concrete surfaces with grooves of controllable size.
The manner in which the foregoing objects are achieved in accordance with the invention, together with other objects and purposes of the invention, may best be understood by a consideration of the detailed description which follows, together with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a striating tool constructed in accordance with the invention with the bristles shown on an enlarged scale for clarity;
FIG. 2 is a somewhat diagrammatic side view of a roughening tool of the invention mounted on a work bridge, which is shown in section;
FIG. 3 is a somewhat diagrammatic side view of a tool of the invention mounted on a handle for hand manipulation;
FIG. 4 is a side elevational view of a sled for conveying the roughening tool of the invention across a bed of freshly placed concrete;
FIG. 5 is a plan view of the sled of FIG. 4; and
FIG. 6 is a somewhat diagrammatic plan view of an area of concrete striated in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Attention is first directed to FIG. 1 from which it can be seen that the apparatus of the invention is a broom-like device having a head 10, which may be conveniently formed of oak or another light, strong material. Head 10 is elongated and is of any convenient length. As a practical matter, a length of about 6 feet is convenient and is not so long as to be clumsy in handling. When the width of a piece of concrete which is desired to be striated is greater than 6 feet, several separate devices may be mounted side by side to make up the required width. Thus, for example, when the apparatus of the invention is used in connection with a "work bridge" employed to span a bed of concrete 30 feet wide, five devices, each having a head 10 which is 6 feet long may be mounted side by side on such a bridge. On the other hand, if the tool is one which will be hand manipulated in use, head 10 may conveniently be made shorter, for example, 2 or 4 feet long. Head 10 is provided with a longitudinal slot 11 in the lower edge thereof. Slot 11 may conveniently be about 11/2 inches deep.
Bristles 12 are mounted in slot 11 in closely abutting side-by-side relationship. The bristles 12 are desirably formed of a tough plastic material such as polypropylene. This material has the desired properties of being wear resistant, flexible to the desired degree, and relatively non-adherent for concrete. The projecting length of bristles 12, that is, the distance from the lower edge of head 10 to the tip of any given bristle, is preferably about 241/2 inches. Some variation from this preferred length is permissible; however, if the bristles 12 have a projecting length less than about 20 inches, they tend to dig into the concrete surface objectionably when the head 10 is positioned at a convenient angle above the surface, and when the bristles are more than about 36 inches in projecting length they tend to be difficult to control during the striating operation.
From FIG. 1 it can be seen that the free ends of bristles 12, taken together, define or establish a generally straight line which is parallel to head 10. But in accordance with the invention, the projecting length of bristles 12 is not exactly the same from one bristle to another. A deliberate variation in such length from bristle to bristle is introduced so that the end of each bristle engages and grooves the concrete a little bit ahead of or behind its immediate neighbors. It is this variation which permits the before-mentioned "micro-movement" in a lateral direction, of the concrete being grooved, which results in the formation of grooves of controllable size and depth without objectionable pickup or longitudinal dragging of the concrete by the bristles. The desired variation in projecting length between adjacent bristles 12 is between about one-fourth and about one-eighth inch. Smaller variation does not permit the desired lateral movement of the concrete, and greater variation introduces control problems and a tendency for the last formed groove in a region to fill in adjacent earlier formed grooves.
The diameter of bristles 12 is generally and approximately related to the width and depth of the striations which are to be formed on the concrete. This relationship cannot be defined with precision because the condition of the concrete is an important parameter in the relationship, and the condition of the concrete is in turn dependent upon its makeup, the length of time it has been placed before striating, and the humidity, temperature and wind conditions prevailing at the site. Despite these factors which are not controllable by the design of the device, I have found that a bristle diameter which is approximately twice that of the depth of the groove desired to be formed is quite appropriate. At present, highway engineers prefer striations which are as close together as practical and of a depth between about 0.03 and about 0.05 inches. Thus, I prefer a bristle diameter of about 0.080 inches in a tool designed to produce striations meeting such specifications.
In accordance with one aspect of the invention, it is preferred to apply to the side of the course of bristles 12 a reinforcing member 13 at a point about midway of their projecting length. The reinforcing member may conveniently be woven glass fiber adhesive tape. While such a reinforcing member on the course of bristles is not absolutely necessary, it has been found that it aids in the controllability of the straightness and depth of the grooves being formed. It is also preferred to use such reinforcing tape to unite the bristle courses of tools which are mounted side by side, in the manner described above, to eliminate any discernable boundary between the work performed by one tool and that performed by another.
Head 10 is preferably rectangular in cross section and approximately 31/2 inches by 1 inch in width and thickness. Such proportioning makes it possible for those using the device to attach whatever fittings they find convenient for mounting the device on work bridges and other support apparatus. The groove 11 is desirably of a thickness approximately equal to the diameter of the bristles 12 so that a tight fit is accomplished. The bristles 12 may readily be secured in the groove by an adhesive which grips them and the material of head 10 tightly. For example, polymethyl methacrylate cement has been found to be a suitable adhesive for this purpose.
Attention is now directed to FIG. 2, where a work bridge 14 is shown somewhat diagrammatically positioned above a bed of concrete 15. Work bridge 14 is typical of structures employed by concrete workers laying roadways. Such bridges are lightweight steel trusses with a walkway for workmen across the top thereof, and mounting equipment (not shown) is furnished at each end to move the work bridge back and forth in the direction of the double headed arrow 16 over the bed of concrete 15. As can be seen from FIG. 2, the head 10 of the striating device is mounted at one side of the work bridge 14 at an acute angle with respect to the bed of concrete 15. The means of mounting are only diagrammatically indicated in FIG. 2 inasmuch as the exact mode of attachment forms no part of the invention and will vary depending upon the design of the work bridge. Bristles 12 extend downwardly and to the right to engage and lay upon concrete bed 15. It is preferred that the bristles 12 present a substantial surface to the concrete near their ends; preferably one to three inches of each bristle is in groove-forming contact with the surface. As FIG. 2 is drawn, the work bridge is displaced slowly to the left in the striating operation.
In FIG. 3 the striating tool of the invention is shown attached to a broom handle to form a hand manipulable tool. Thus, head 10 is attached to swivel member 17, which is shown only diagrammatically because its detailed structure forms no part of the present invention per se, and a variety of existing forms of such equipment may be employed. Swivel 17 is in turn connected to a broom handle 18. By this arrangement, a worker by manipulating handle 18 can position head 10 at a desired acute angle above a bed of concrete and draw bristles 12 across the bed to striate it.
In FIGS. 4 and 5, in accordance with the invention, there is illustrated a sled for supporting the striating device in applications where no work bridge such as that shown in FIG. 2 is employed and where the area to be striated is too large to be worked by hand tools such as shown in FIG. 3. As can be seen from FIGS. 4 and 5, the support device 19 is in the form of a lightweight sled having a pair of rectangular pads 20 which are large enough to give the sled 19 good floatation or bouyancy on the wet concrete bed. A light angle iron frame 21 is mounted above pads 20; the frame is triangular in end elevation. A ridge pole 22 extends across the width of the frame 21. Two or more straps 23 are fitted around ridge pole 22 and are connected to head 10. By this means head 10 rests against the legs 24 of frame 21 at an acute angle to a bed of concrete on which the sled 19 is positioned. The bristles 12 extend outwardly and engage the concrete surface in the manner described above. Each leg 24 is provided with one or more pull rings 25 to which a pull chord 26 of light twine is attached. Such a pull chord is provided at each side of sled 19.
In use, the sled 19 is pulled by pull chords 26 across a bed of freshly placed concrete by a worker located at the far side of the bed. When the sled is pulled all the way across the bed to the worker he then displaces it to a portion of the bed which has not yet been grooved, and flips the head 10 over the top of the sled so that it rests on the back pair of legs 24. A coworker then pulls the sled back across the wet bed of concrete, striating the portion which is in the path of the sled. The twine used to pull the sled 19 back and forth in the manner just described does not objectionably mar the striated surface of the concrete; if anything, it contributes to the striation. The marks, if any, left by the pads 20 of the sled are obliterated by bristles 12 striating the concrete behind pads 20.
In FIG. 6 there is shown somewhat diagrammatically, of necessity, a concrete surface 15 having striations 27 formed therein by the method and equipment of the invention. Also indicated on FIG. 6 is a pile of gauge sand worked into a circular pattern in the manner described above, to determine whether the striations meet the desired specifications. Such circle of sand is designated 28 in FIG. 6, and as explained above, its diameter gives a measure of the average depth of striations 27.