Method for improving load transfers between concrete slabs in zones at which joints are provided, and means for performing same

In order to improve load tranfers between concrete slabs in zones at which joints are provided between said slabs, an elongated connection member, formed in one piece is fitted in the joint over at least part of the height of the slabs, which connection member is substantially cylindrical, adapted to be deformed over its entire length by compression or by expansion in at least one direction of deformation perpendicular to its axis. The connection member is placed astride the location of the joint with its axis situated substantially in the plane of the joint. The opposite portions, located on either sides of the plane of the joint, of the peripheral surface of the connection member are adhesively connected to the surfaces of the slabs with which they are in contact so as to prevent any relative movement between the contacting portions of the connection member and of the slabs.

The present invention relates to a method for improving load transfers 
between sections of concrete pavements or slabs in zones at which joints 
or cracks are provided between said slabs. 
The invention is particularly applicable in the case of concrete slabs in a 
pavement subjected to strong stresses, such as highways, airport runways 
or even factory floors. 
Taking for example the case of a highway with a concrete pavement, it is 
known that it is of the greatest importance to ensure a load transfer from 
one side of each contraction joint or crack of the pavement to the other 
side, i.e. to ensure that there is not too much discontinuity at the 
joints level, in the transfer of any vertical deformations occuring in the 
pavement surface. 
Some discontinuous pavements exist wherein the joints between the slabs are 
not dowel-connected, the load transfer being ensured by the engagement of 
the lips of the crack which has formed under the joint and by the layer of 
support material situated immediately below the concrete pavement. The 
formation of open joints at building time, because of special atmospheric 
conditions, of localized defects in the support layer and of the wearing 
down of the lips of the cracks are amongst the main causes which 
contribute to a lowering of the quality of the load transfer. The presence 
of water between the slab and the support layer, combined with the absence 
of load transfer, slowly causes, over long periods of time, some permanent 
vertical displacements of the slabs relative to each other, as well as the 
formation of cavities under the slabs on either sides of the crack. The 
injection of different products under the slab, which is a conventional 
mode of repair in such a case, has but a limited effect due to the fact 
that the load transfer is only partly restored. Moreover, new cavities may 
often occur sooner or later under the injected product. 
When the pavement is a discontinuous pavement, constituted by reinforced or 
ordinary concrete slabs, the joints between the slabs predetermine the 
location of the cracks. 
Continuous vertical deformations from one side of a joint to the other may 
then be ensured by dowels which are set in place at the time of the 
construction and are embedded in the slabs adjacent the joint. However, 
dowel-connected pavements are not always free from defects affecting load 
transfers. These may come from cracks occurring outside the joints or from 
other intermediate joints which are not dowelled and which have been 
provided in order to adapt the pavement to new traffic conditions. Repairs 
generally consist then in demolishing the pavement on either sides of the 
crack in order to place the dowels and in rebuilding the cracked slab. 
This again means rather lengthy and costly operations necessitating 
interruptions of traffic for rather considerable lengths of time. 
When the pavement is a reinforced concrete continuous pavement, cracks 
occur at random and normally remain virtually closed because of the 
presence of the reinforcements. The mutual engagement of the lips of the 
crack ensure the load transfer. However, any manufacturing defect, or 
corroding of the reinforcement or any defect in the overlapping the 
reinforcements may result sooner or later in a widely opened crack which 
no longer ensures the transfer of the load, thereby accelerating the 
pavement degradation process. In order to be repaired, the pavement is 
normally demolished on either sides of the crack, so as to uncover the 
reinforcements, and to restore their continuity before rebuilding the 
slab. Such repairs are rather long and expensive, and necessitate a fairly 
long interruption of the traffic. 
Finally, it will be noted that in the case of a discontinuous pavement, it 
is necessary when the frequency and the amplitude of the degradations 
increase, to load up the structure either with a running layer, 8 to 12 cm 
thick, or with another carrying layer, 6 to 8 cm thick. Depending on the 
nature and importance of the traffic, such operations should be renewed 
after, 4 to 8 years' service and 8 to 15 years' service, respectively. 
It is therefore clear from the foregoing that the repair of a connection 
between concrete slabs adjacent a crack or a joint in order to restore the 
transfer of the load from one side of the joint to the other, is generally 
expensive and long, and its effect is limited. 
The object of the present invention is to provide a method for connecting, 
safely and rapidly, two concrete slabs separated by a crack or a joint, 
whilst ensuring a load transfer between said slabs. A particular aim of 
the invention is the simple and rapid repair of an old pavement at the 
zone of its joints or cracks, not however excluding the case of the 
building of new pavement composed of concrete slabs separated by joints. 
In the method according to the invention, at least one elongated connection 
member is provided, which is in one piece, and substantially cylindrical 
in its outer shape, adapted to be deformed over its entire length by 
compression or expansion in at least one direction, perpendicular to its 
axis, said connection member is placed astride the location of the joint 
so as to extend over at least part of the height of the pavement, it axis 
being situated substantially in the plane of the joint, and with the said 
direction of deformation situated substantially perpendicularly to the 
plane of the joint, and the opposite parts are caused to adhere, to the 
slab surfaces with which they are in contact so as to prevent any relative 
movement between the contacting portions of the connection member and of 
the slabs, the said connection member thus ensuring the transmission of 
any vertical deformations of the slabs from one side of the joint to the 
other whilst allowing any expansions or contractions of thermal origin in 
the slabs. 
When working with an already existing pavement, for example when repairing 
a cracked pavement, at least one cylindrical recess is drilled astride the 
joint, in which recess is introduced said connection element. 
In order to join the connection member to the slab faces adjacent the 
joint, the contacting surfaces of the connection member and of the slabs 
are, at least partly, adhesively connected. 
As a variant, or additionally, it is possible to deform the connection 
member by compression in the said direction of deformation in order to 
introduce it into the said recess thereby conferring to the connection 
member fitted in the recess a prestressing force in compression so as to 
join together at least partly by friction or engagement, the contacting 
surfaces of the connection member and of the said recess. 
Preferably, the cylindrical member is fitted in, substantially vertically, 
and in such a way that its upper end is situated below the pavement 
surface. 
It is a further object of the invention to provide connection means for 
joining two parts of concrete pavement or slabs at zones where cracks or 
joints may be found between said slabs in order to ensure a load transfer 
from one side of the joint to the other. 
Said means is according to the invention, constituted by at least one 
elongated connection member, formed in one piece, and substantially 
cylindrical, having on its periphery at least one indentation or a 
longitudinal lap, forming bellows, so that it can be deformed over its 
entire length by compression or expansion in at least one direction, 
perpendicular to its axis. 
The cylindrical element may be for example a tube with a constant 
cross-section which can be inscribed in a circle and which is provided 
with at least one inward fold.

FIG. 1 illustrates very diagrammatically two adjacent slabs 11 and 12 of 
the concrete pavement of a highway, resting on a support layer or 
substrate 13, between which slabs a joint 10 is formed. This joint was 
marked at construction time by a groove 10', formed right from the 
pavement surface and extended downwards by a crack 10". The load transfer 
from one slab to another, i.e. the transmission of the vertical 
deformations due to the forces exerted on the pavement surface, is ensured 
by the engagement of the lips of the crack 10" and by the substrate 13. 
In case of wearing down of the lips of the crack 10", of deterioration of 
the substrate 13, of too wide an opening of the joint 10, etc. . . . , the 
load transfer is no longer ensured. To restore it, the present invention 
proposes to fit at least one connection member 14 (FIGS. 2 and 3) astride 
the joint 10. 
The connection member 14 is constituted by a tube with a constant 
cross-section which can be inscribed in a circle. Said tube comprises two 
longitudinal inward indentations or folds 15, 16 which are symmetrical 
with respect to its axis, which indentations define bellows conferring to 
the tube a capacity of deformation under compression and expansion in a 
direction D perpendicular to the axis of the tube. 
The connection member 14 is fitted as follows: 
A recess 20 of a diameter substantially equal to that of the connection 
member is drilled astride the joint 10 and substantially vertically over 
the greatest part or over the totality of the height of the pavement. The 
peripheral surface of the connection member 14 and the inner wall of the 
bore 20 are adhesively joined with for example an epoxyde-type adhesive. 
The member 14 is introduced in the recess 20, the direction D being 
perpendicular to the plane of the joint, the bellows 15, 16 thus opening 
out into that plane which plane is that from side of which extend the 
surfaces of the slabs 11, 12 adjacent the joint 10 at the zone where the 
recess 20 is drilled. The axis of the member 14, is situated substantially 
in the plane of the joint. 
The adhesion between the portions of opposite faces of the slabs 11 and 12 
adjacent the recess 20 and the portions of the peripheral surface of the 
connection member, should be sufficient to withstand any thermal 
contraction has to be wholly absorbed by the expansion of the bellows 15 
and 16 of the connection member without the said slabs and connection 
member coming apart anywhere. It will be noted on this point that it is 
preferable for the ambient temperature not to be too high when the said 
connection member is fitted in. 
Once fitted in, the connection member 14 ensures the transfer of loads from 
one side of the joint 10 to the other because of its adhesion to the 
opposite faces of the slabs 11 and 12 and it absorbs any expansion and 
contraction of thermal origin occurring, due to its deformability in the 
direction D. In the case of highways, for example, such expansions and 
contractions have an amplitude of the order of one millimeter. 
Other similar connection members may of course be fitted on the same joint 
depending on the length of the latter and of the loads supported by the 
pavement. 
The connection member 14 is set in, substantially vertically, with its 
upper end below the pavement surface. Said upper end is advantageously 
provided with a cap 17 which seals it off thereby protecting the inside of 
the tubular member 14. The cap 17 is for example made from a soft plastic 
material cast directly on the end of the connection member. Two lugs 18 
(FIG. 3) may be provided at diametrically opposite parts of the cap to 
serve for example as reference points when fitting in the connection 
member 14, said lugs having, in the example shown, to be in alignment with 
the joint 10. 
Once the member 14 is fitted, a further sealing piece 19 may be placed in 
that part of the bore 20 which is situated above the cap 18. 
Although it has been, hereinbefore, considered to joint the member 14 to 
the opposite faces of the bore 20 by adhesive connection, said connection 
can be either replaced or completed by a frictional connection obtained by 
imposing upon the member 14, at fitting time, prestresses in compression. 
This may be produced for example by deforming under compression the member 
14 when this is being fitted, by means of a sleeve clamping said member 
and from which it is progressively freed by introducing it into the recess 
20. 
FIGS. 4 to 7 illustrate, cross-sectionally, variants of embodiment of the 
connecting member. 
The connection member 24 shown in FIG. 4 is a tube with two relatively 
deep, longitudinal indentations 25, 26 starting from zones on opposite 
sides of the periphery of the member 24. Said indentations 25, 26 extend 
substantially parallel and symmetrically with respect to the axis of the 
member 24, thereby giving the cross-section of the member 24 substantially 
the shape of an S. Said indentations 25, 26 constitute the bellows of the 
element 24, which bellows open out into zones that are symmetrical with 
respect to the diametrical plane containing the direction of deformation 
D. Just as the member 14, the member 24 has a peripheral surface which can 
be inscribed in a circle so as to be fitted in a bore drilled on a joint 
of a concrete pavement. 
FIG. 5 illustrates a tubular connection member 34, provided with two 
bellows 35, 36 which are symmetrical with respect to the diametrical plane 
containing the direction of deformation D. Said bellows 35, 36 are round 
in cross-section and open outwardly with close together lips 35a, 35b, 
36b, thereby giving the member 34 a cross-section substantially in the 
shape of an X. As in the foregoing, the connecting member has a 
cross-section which may be inscribed in a circle. 
The connection member 44 shown in FIG. 6 is similar in shape to that shown 
in FIG. 3, with two indentations or bellows 45, 46 which are symmetrical 
with respect to the diametrical plane containing the direction D and 
flaring outwardly. Said member 44 however, comprises an additonal fold 
45', 46', at the bottom of each bellows the effect of which is to split up 
said latter. 
FIG. 7 shows a connection member 54 which differs from connection members 
14, 25, 34 and 54 by the fact that it is constituted by a bar having a 
circular cross-section wherein two rather deep notches or grooves 55, 56 
have been made. Said notches constitute bellows arranged in the same way 
as those of the member 24 which is shown in FIG. 4, thereby giving the 
elememt 54 a substantially S-shaped cross-section. 
The connection members shown in FIGS. 3 to 7 may be metallic, of steel for 
example. That (14) shown in FIG. 3, may be produced by cold-drawing. The 
members (24,34) shown in FIGS. 4 and 5 may be obtained by hot or cold 
rolling or burnishing, and even by drawing, such as that shown in FIG. 6. 
Finally, the connection member 54 may be produced by machining a solid 
bar. 
As a variant, the connection members may be produced in plastics, 
reinforced for example by glass fibres. 
As already indicated in the foregoing, the connection member is adhesively 
and/or frictionally joined to the opposed sides of the slabs, between 
which it improves the transfer of the loads. 
In the case of a connection ensured at least partly by friction, it may 
prove advantageous to reinforce the stress exerted against the sides of 
the slabs by the connection member when said latter is deformed by 
compression. 
FIGS. 8 to 10 are diagrammatical cross-sections of connection members 
comprising each a tubular part with at least one longitudinal indentation 
forming bellows and means, inside the tube, for increasing the forces 
which can be called upon by elastic deformation of the tubular piece. 
The connection member 74 shown in FIG. 8 is constituted by a hollow and 
deformable tubular piece 72, for example of the type shown in FIGS. 3 to 
7. The inside volume 73 of said connection member is filled with a 
resilient material, such as an elastomer, which adheres to the inner wall 
of the piece 72. 
The piece 72 is provided with at least two longitudinal bellows 75, 76 
which can also be filled with elastomer, thereby further increasing the 
resilient return force generated after deformation of the member 74 along 
its direction of deformation D. 
Material in powder form, such as sintered materials, may be included in the 
elastomer in order to increase the apparent modulus, and possibly, reduce 
the necessary volume thereof. 
FIG. 9 shows, in cross-section, a connection member 84 constituted by a 
deformable tubular part 82 extended over its entire length along a 
direction D, such as for example a part of the type shown in FIGS. 3 to 7. 
On the inside 83 of the part 82 are introduced vertically one or more metal 
parts 81 which, by their shape and their nature, exert a resilient return 
force which is sufficient to ensure the connection between the member 84 
and the sides of the concrete slabs between which it is placed. Said metal 
parts 81 are forcefully introduced in the part 82 before or after the 
fitting of said latter into the pavement. They are for example constituted 
by cup springs or by thin slices of cylinder having, at least in the 
direction of deformation D, a dimension in the free state which is greater 
than that of the inside 83 of the part 82. 
The connection member 94 shown in cross-section in FIG. 10 is constituted 
by a plurality of deformable tubular pieces 92 deformable along a similar 
direction D such as those shown in FIGS. 3 to 7. Said pieces are 
similarly-shaped and fit longitudinally and possibly forcibly into one 
another. They are joined by welding or riveting together their contacting 
surfaces. The number of pieces 92 is determined by to the force to be 
exerted against the side of the slabs and in relation to the force which 
may be created in each one of them. 
The connection by adhesion and/or by friction between the member fitted in 
the pavement and the sides of the slabs may further be completed, 
vertically, by an engagement connection, using a connection member of the 
type 104 half of which is shown in longitudinal section in FIG. 11. 
The connection member 104 is constituted by a deformable tube provided with 
bellows, such as those shown in FIGS. 3 to 6, an having one or more 
circular bosses 107 on its outer surface. 
Said bosses 107, annular ones for example, are introduced in recesses 108 
of corresponding shape which are provided in the opposite sides of the 
concrete slabs 101, 102 between which the member 104 is fitted. The 
machining of the recesses 108 is done after drilling the hole 110 due to 
receive the member 104, the fitting in of said latter being produced with 
prior resilient deformation thereof under compression. 
The preceding description considers the fitting of a connection member in 
an already existing pavement for example to restore a transfer of load 
where a joint is open. It is clear that the method according to the 
invention shows, compared with already known methods of repair, some 
considerable advantages which are related to the simple and rapid way in 
which it can be performed. Indeed, there is no need to proceed to any even 
partial demolishing or rebuilding of the slab. It is sufficient to drill 
at least one hole astride the joint and to introduce therein the 
connection member. 
Nevertheless, the fixing of connection members similar to those described 
hereinabove, may also be considered when the pavement is being built, the 
connection between said members and the concrete being produced for 
example by way of an adhesive capable of adhering to the soft concrete. 
The connection with the soft concrete can even be further improved by 
providing annular and/or longitudinal projections, or grooves or bosses, 
on the periphery of the connection member, which projections are used for 
anchoring-in the slabs whilst the concrete is setting. 
Other modifications or additions may of course be made without departing 
from the scope of protection defined by the accompanying claims.