EP1921209A1

EP1921209A1 - Cracking-inducing vehicle and method

Info

Publication number: EP1921209A1
Application number: EP07021816A
Authority: EP
Inventors: Warren Bently; Richard Needham
Original assignee: Aggregate Industries UK Ltd
Current assignee: Holcim Technology Ltd
Priority date: 2006-11-09
Filing date: 2007-11-09
Publication date: 2008-05-14
Also published as: US20080124172A1; GB0622338D0; GB2443612A

Abstract

This invention relates to methods and apparatus for inducing planes of weakness in hydraulically bound materials, for example roller compacted concrete. A crack inducer vehicle for fabricating pre-cracked hydraulically bound materials, the vehicle comprising: a groove former to form a groove in fresh hydraulically bound material prior to curing, said groove former having a first, lowered position for forming a groove in said fresh hydraulically bound material, and a second, raised position; and a system to apply a de-bonding agent into said groove such that when said hydraulically bound material has cured it preferentially cracks along a said groove.

Description

This invention relates to methods and apparatus for inducing planes of weakness in hydraulically bound materials, for example roller compacted concrete. Thus the invention relates to preparing concrete prior to curing so that it is prone to controlled cracking after curing.
Hydraulically bound materials (HBM), for example concrete, have a tendency to crack when they dry, due to shrinkage caused by a reduction in the volume taken up by water when the water evaporates. It is preferable to control the manner in which the concrete cracks, rather than allow uncontrolled cracking, as this could result in weaknesses in the concrete in highly stressed areas (for example, the areas of concrete supporting vehicles' tyres on a heavily used road), and increased likelihood of damage to the concrete in extreme weather conditions (for example, freeze-thaw frost shattering, due to rain water accumulating in cracks in the concrete and expanding when the temperature goes below freezing point). In the UK, the Specification for Highway Works (Volume 1, November 2004), clause 818, defines requirements for Induced Cracking of HBM:

(1) Where the HBM layer in the pavement construction comprises HBM with a strength class equal to or exceeding C 8/10, C 9/12 or T3 that layer shall have cracks induced during construction, as described below, at a maximum longitudinal spacing of 3 m ± 10%. Where any underlying pavement construction comprises cracked HBM the cracks in the overlying HBM shall align with cracks in the underlying construction.
(2) Cracks shall be induced in fresh material. The transverse cracks shall be induced by grooving the fresh material to a depth which leaves a vertical groove not more than 20 mm wide, between one half and two thirds the layer thickness after compaction, over the full width of the pavement. A de-bonding material [...] shall be inserted into the groove prior to final compaction, extending from the bottom of the groove to not less than half the height of the groove. During final compaction of the material, the groove shall be closed at the surface and the de-bonding material shall be fully encased and remain continuous within the closed groove.

It should be noted that the present invention is not concerned with cutting concrete after it has set (as described, for example, in US 2,673,725 , US 5,477,844 , US2006/0240753 , and US 4,175,788 ) - rather, the invention is concerned with preparing concrete before it has set so that it is prone to controlled cracking after curing.
Current practice to produce a joint in HBMs involves either the use of a hand shovel and application of a de-bonding agent from a watering can or similar, or operating a whacker plate with a metal fin attached to the underside (de bonding agent being applied in a similar manner). However, these methods have a number of disadvantages:

(a) Inconsistent joint width;
(b) Inconsistent introduction of the de-bonding agent;
(c) Carried out by a person on foot - only allows small areas to be covered at a time;
(d) Requires manual handling and repeated actions by operatives; and
(e) Potential health and safety issues relating to hand-arm vibration (HAV).

The last two points ((d) and (e)) are of key concern as part of the industry's continual improvement in health and safety. Such a factor can also be important at pre-tender stage for major contracts. There is a need for an apparatus and method for inducing cracks in HBMs that overcome the above disadvantages, and that are suitable for applications according to clause 818 above and other applications.
According to an aspect of the invention there is provided a crack inducer vehicle for fabricating pre-cracked hydraulically bound materials, the vehicle comprising: a groove former to form a groove in fresh hydraulically bound material prior to curing, said groove former having a first, lowered position for forming a groove in said fresh hydraulically bound material, and a second, raised position; and a system to apply a de-bonding agent into said groove such that when said hydraulically bound material has cured it preferentially cracks along a said groove.
According to a further aspect of the invention, there is provided a method of inducing a plane of weakness in a hydraulically bound material (HBM) the method comprising: using a vehicle as described above to form a groove in said fresh hydraulically bound material prior to curing of said hydraulically bound material; applying a de-bonding agent into said groove using said vehicle; and roller-compacting said hydraulically bound material using said vehicle to form a visibly continuous material including a plane of weakness; wherein said cured hydraulically bound material preferentially cracks along a said induced plane of weakness during shrinkage.
The de-bonding agent may be applied substantially simultaneously with, or a short time after, the forming of the groove.
There is described herein a vehicle used to provide a joint in paver-laid concrete also known as Roller Compacted Concrete (RCC) and Hydraulically Bound Material (HBM). This joint is then filled with a de-bonding agent (typically, but not exclusively, bituminous tack coat). The material is then roller compacted to form a visibly continuous material which will crack in a controlled manner along these induced planes of weakness during shrinkage. (RCC is concrete comprising a damp mixture of cement, sand, aggregate and water, having a consistency allowing it to be compacted with a heavy roller. It has a much drier (or stiffer) consistency than is usual, involves less slump, and generates less heat on curing).
In particular, the crack inducer vehicle according to the invention, or embodiments thereof, has the benefits of:

(i) Consistent joint width;
(ii) Consistent introduction of the de-bonding agent;
(iii) Mountable on a mobile device (e.g. small tandem roller) - enables large areas to be covered;
(iv) Elimination of manual handling/repeated actions by operatives; and
(v) Elimination of potential health and safety issues relating to hand-arm vibration.

Unless indicated otherwise herein, features of the aspects and embodiments of the invention described herein may be combined in any permutation.
Embodiments of these and other aspects of the invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a crack inducer mounted on a vehicle, according to the present invention;
Figure 2 shows a front view of a crack inducer mounted on a vehicle, according to the present invention;
Figure 3 shows a plan view of a crack inducer mounted on a vehicle, according to the present invention;
Figure 4 shows a perspective view of a crack inducer according to the present invention.
Figure 5 shows a front view of a crack inducer according to the present invention; and
Figure 6 shows a side view of a crack inducer according to the present invention;

Referring to the attached Figs 1 to 6, these illustrate, in accordance with embodiments of the invention, a vehicle incorporating or having mounted thereon a crack inducer (Figs 1 to 3), and the crack inducer in isolation (Figs 4 to 6). In the present disclosure, as will be appreciated by persons skilled in the art, where the context requires, the terms "groove", "channel" and "joint" are used somewhat interchangeably.
With specific reference to Fig. 1, this shows a side view of the crack inducer, mounted on a vehicle (in outline), in this case a road roller (18). A hardened steel cutting wheel (1), diameter 540 millimetres, is mounted on an arm (19), pivotally mounted on a support by means of a bearing (2). The support may form part of the crack inducer, or alternatively it may be on the vehicle.
The cutting wheel (1) is freely rotating. It need not be a grinding disk and thus need not have, for example, a diamond coating or a sharpened edge. The cutting wheel (1) produces a channel or groove (not shown) in loose, uncompacted, granular material, not by cutting but by pushing the material out of the way to either side. As the vehicle moves the cutting wheel (1) nestles in the groove and moves along.
Between the cutting wheel (1) and the bearing (2) is provided another pivot (3), here used to mount a hydraulic ram (4) between the support and the arm (19). A ram down pipe (5) and a ram up pipe (6) are provided to supply hydraulic fluid to the ram (4) to actuate the ram. A hydraulic 2-way directional control valve (7) may be used to control the actuation of the ram (4), and provide an up-down control over the position of the cutting wheel (1). A hydraulic pressure line (17) is provided to supply hydraulic fluid under pressure from the vibrator motor (not shown). A return hydraulic pipe (8) is provided to the hydraulic tank; the tank may be provided as part of the crack inducer, or the crack inducer may use a hydraulic tank from the hydraulic system of the vehicle, if one is available.
A nozzle (9), diameter 10 millimetres, is mounted near the cutting wheel (1), preferably behind the wheel in the normal direction of travel in operation, for clean injection of tack coat into the joint. The nozzle (9) is connected to a de-bonding agent application pipe (10). This carries de-bonding agent (11) from a pump (20).
A tap (12) is provided to control the flow of de-bonding agent in the crack inducer. This allows de-bonding agent, preferably a bituminous tack coat, to be applied to the joint when a joint is being cut, and for the amount of de-bonding agent applied to be controlled, and to stop the flow of de-bonding agent when the crack inducer is not cutting a joint. An existing on-board water tank (13) of the vehicle may be used to supply the de-bonding agent, or alternatively the crack inducer may include a separate tank (not shown). A suction pipe (14) is provided to the supply side of the pump (20) from the tank. The pump (20), here used to supply agent under pressure to the nozzle (9) to spray agent onto the joint, may be supported by a support welded to the existing framework (15) of the vehicle. A folded steel cover (16) may be provided for the de-bonding agent sprayer.
Figure 2 shows a front view of the crack inducer mounted on the vehicle (in outline). This shows the support unit welded to the existing chassis at the point (21). A folded sheet steel bracket (22) may be bolted to the existing bodywork to hold the 2 way directional control valve and de-bonding agent spray tap. It will be apparent to the skilled person that other attachment methods than welding and bolting are also suitable. Depending on the materials used, brazing or adhesive bonding may also be used.
Figure 3 shows a plan view of the crack inducer mounted on the vehicle (in outline). The nozzle may be held by a grub screw with a handle (31), which facilitates adjustment of the nozzle. The de-bonding agent sprayer (33) is shown from above. An example of the vehicle, in this case a road roller, is the Bomag 80 ADH 2, available from BOMAG (Great Britain), Ltd. of Aylesford, Kent. Other road rollers and other vehicles will also be suitable for mounting the crack inducer.
Figures 4, 5 and 6 show a visual layout of the crack inducer without the vehicle (roller) present, showing the spray injector, including nozzle (9), for thermal shrinkage cutting. Figure 4 shows a perspective view. The red pipes (spanning 402 to 404, 406 to 408, and 410 to 412) show the flow of de-bonding agent. Figure 5 shows a front view. Figure 6 shows a side view. The blue pipes (spanning 602 to 604, 606 to 608, 610 to 612 and 614 to 616) show the flow of the hydraulic fluid.
There is also described herein a crack inducer for fabricating pre-cracked hydraulically bound materials, the crack inducer being adapted mounting on a vehicle, the crack inducer comprising: a groove former to form a groove in fresh hydraulically bound material prior to curing, said groove former having a first, lowered position for forming a groove in said fresh hydraulically bound material, and a second, raised position; and a system to apply a de-bonding agent into said groove such that when said hydraulically bound material has cured it preferentially cracks along a said groove.
There is also described herein a method for fabricating pre-cracked hydraulically bound materials, the method comprising: forming a groove in said fresh hydraulically bound material prior to curing of said hydraulically bound material; applying a de-bonding agent into said groove; and roller-compacting said hydraulically bound material to form a visibly continuous material including a plane of weakness; wherein said cured hydraulically bound material will preferentially crack in a controlled manner along a said induced plane of weakness during shrinkage.
There is also described herein a joint cutter for cutting a joint in a hydraulically bound material, the joint cutter configured to be attachable to a vehicle, said joint cutter comprising: cutting means configured to have two configurations, a first configuration in which the cutting means is lowered to, in operation, cut the said joint in the said hydraulically bound material, and a second configuration in which the cutter is raised; and applying means for applying a de-bonding agent to the said joint.
Preferably, the hydraulically bound material comprises concrete, for example paver laid concrete or roller compacted concrete. Typically, the vehicle to which the apparatus may be attached comprises a road roller, for example a small tandem roller. Preferably the cutting means comprises a hardened steel disc or wheel. Other materials and shapes may also be used. The cutting means may be rotatably mounted on the crack inducer, or it may be fixed. The width of the disc may preferably be in the range 10 to 25 millimetres, more preferably 15 to 20 mm. The diameter of the disc may preferably be in the range 200 to 1000 mm, more preferably 400 mm to 540 mm.
Preferably, the applying means includes a nozzle for spraying the de-bonding agent into the joint. Preferably, the nozzle is coupled to a tank for storing the said de-bonding agent. Preferably, the cutting means is provided on an arm, preferably hydraulically actuated to provide the first and second configurations. The arm may be pivotally mounted on a support unit of the crack inducer. Alternatively, the arm may be mounted directly on the vehicle. Preferably, the applying means includes a pump or sprayer. Preferably, the de-bonding agent comprises a bituminous tack coat, for example a bitumen emulsion. Optionally, a crack-inducing agent may be used. In another aspect there is provided a crack inducing or joint cutting vehicle comprising a crack inducer or joint cutter according to the invention mounted to a vehicle.
There is also described herein a method of cutting a joint in a hydraulically bound material using a joint cutting vehicle according to the present invention, the method comprising: lowering the cutting means of the joint cutter of the vehicle to engage it with the hydraulically bound material; moving the vehicle in order to cut the hydraulically bound material with the cutting means; and applying a de-bonding agent to the joint thus formed.
No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

A crack inducer vehicle for fabricating pre-cracked hydraulically bound materials, the vehicle comprising:
a groove former to form a groove in fresh hydraulically bound material prior to curing, said groove former having a first, lowered position for forming a groove in said fresh hydraulically bound material, and a second, raised position; and

a system to apply a de-bonding agent into said groove such that when said hydraulically bound material has cured it preferentially cracks along a said groove.
A crack inducer vehicle as claimed in claim 1 wherein said vehicle comprises a road-roller to roller-compact said hydraulically bound material such that after passage of said vehicle said hydraulically bound material is compacted to form a visibly continuous material.
A crack inducer vehicle as claimed in claim 1 or 2 wherein said groove former comprises a freely rotating wheel.
A crack inducer vehicle as claimed in claim 1, 2 or 3 wherein said system to apply a de-bonding agent into said groove comprises a nozzle and a tap or pump to control application of said de-bonding agent into said groove.
A crack inducer vehicle as claimed in claim 4 wherein said de-bonding agent comprises bitumen.
A crack inducer vehicle as claimed in any preceding claim wherein said hydraulically bound material comprises Roller Compacted Concrete.
A method of inducing a plane of weakness in a hydraulically bound material (HBM) the method comprising:
using a vehicle as claimed in claim 2, or any of claims 3 to 6 when dependent on claim 2, to form a groove in said fresh hydraulically bound material prior to curing of said hydraulically bound material;

applying a de-bonding agent into said groove using said vehicle; and

roller-compacting said hydraulically bound material using said vehicle to form a visibly continuous material including a plane of weakness; wherein said cured hydraulically bound material preferentially cracks along a said induced plane of weakness during shrinkage.