Methods for preparing natural and artificial structures

Voids in at least a part of an artificial or natural structures overlying a highly porous layer (e.g. a concrete road or airfield runway) adjacent an exposed surface of the structure are filled with a hardenable material by forming mutually spaced extractor and injector holes through said part and into said underlying highly porous layer; closely fitting a flexible fluid-impermeable covering over the exposed surface, the covering having adjacent its boundary edges an endless hollow wall that surrounds and opens towards the covered surface, and sealing boundary edges of the covering to the structure to form a substantially fluid-tight enclosure incorporating the hollow wall; evacuating air from the hollow wall and from each extractor hole and introducing hardenable material in a liquid or semi-liquid state into each injector hole; terminating evacuation of air from each extractor hole as hardenable material appears at the outlet of the hole and introducing hardenable material into the hole; and, when hardenable material is being introduced into all injector and extractor holes, gradually bringing evacuation of air to a stop as the hardenable material in the voids sets.

This invention relates to artificial and natural structures built up of or 
comprising a plurality of separately formed bodies of manufactured or 
natural material or consisting of a single body of concrete or of rock, 
granite or other material in its natural state. Structures fabricated from 
or comprising a plurality of separately formed bodies include the walls of 
buildings, the abutments and piers of bridges, chimneys, brick-lined 
tunnels, ducts, drains and sewers, retaining walls, foundations, 
monuments, sculptures, archaeological remains, and other structures built 
up of or comprising bricks, rocks, stones, granite, timber or other 
building materials with or without interposed mortar or other hardenable 
material. Single bodies of concrete or other materials include roads, 
airfield runways, foundations of heavy machinery, statues and sculptures. 
All such artificial and natural structures will, for convenience, 
hereinafter be referred to as "artificial or natural structures of the 
kind specified." 
Where an artificial or natural structure of the kind specified has cracks 
or voids in at least a part of the structure adjacent an exposed surface 
of the structure, such as the surface of a road or airfield runway, it has 
been proposed to introduce a hardenable material in a liquid or 
semi-liquid state into the cracks or other voids. Where a part of an 
artificial or natural structure of the kind specified, into cracks and 
other voids in which hardenable material in a liquid or semi-liquid state 
is to be introduced, overlies a highly porous layer, for example where 
concrete slabs of a road overlie a highly porous sub-grade of clinker, 
there is a risk that the liquefied hardenable material will soak away 
through the underlying highly porous layer over a wide area with the 
result that an unnecessarily large amount of hardenable material is 
required to fill the cracks and other voids, thereby rendering the process 
expensive, and, in some circumstances, the cracks and other voids are 
never completely filled. 
The present invention provides a method of introducing a hardenable 
material in a flowable state into cracks or other voids in at least part 
of an artificial or natural structure adjacent an exposed surface of the 
structure, which structure overlies a highly porous layer. 
According to the present invention, the method comprises drilling or 
otherwise forming at least one extractor hole through said part and into 
said underlying highly porous layer in the vicinity of at least one crack 
or other void into which hardenable material is to be introduced; drilling 
or otherwise forming at least one injector hole through said part and into 
said underlying highly porous layer at a position spaced from the crack or 
other void or from at least one of the cracks or other voids; closely 
fitting a flexible fluid-impermeable covering over the exposed surface, 
the covering having adjacent its boundary edges an endless hollow wall 
that surrounds and opens towards the covered surface; directly or 
indirectly sealing boundary edges of the covering to the structure to form 
a substantially fluid-tight enclosure incorporating the hollow wall; 
evacuating air and any other fluid from the hollow wall and from the or 
each extractor hole and introducing hardenable material in a liquid or 
semi-liquid state into the or each injector hole; as hardenable material 
appears at the outlet of the or each extractor hole, terminating 
evacuation of air and other fluid from this extractor hole and introducing 
hardenable material into the extractor hole; and, when hardenable material 
is being introduced into all injector and extractor holes, gradually 
bringing to a stop evacuation of air and other fluid as the hardenable 
material in said cracks and other voids sets. 
Since the spread of hardenable material from the part of the structure 
under treatment to the underlying highly porous layer is controlled and 
confined by the air and other fluid being drawn from the surrounding part 
of the highly porous layer, the cracks and other voids in the part of the 
structure under treatment will be substantially filled with hardenable 
material. 
Where a crack extends across the exposed surface of the structure, for 
example across a concrete road or airfield runway, preferably a plurality 
of extractor holes are drilled or otherwise formed at a plurality of 
spaced positions along the length of the crack. Preferably, also, two rows 
of mutually spaced injector holes are drilled or otherwise formed in said 
part of the structure, one row on one side of the crack and one row on the 
other side of the crack. At least one hollow wall that opens towards the 
covered surface and that is incorporated with the flexible 
fluid-impermeable covering may be positioned adjacent the row of extractor 
holes, air and other fluid also being evacuated from said hollow wall. 
To facilitate introduction of hardenable material into the or each injector 
hole and the evacuation of air and other fluid from, and subsequent 
introduction of hardenable material into, the or each extractor hole, 
preferably a flexible tube of rubber or plastics material is inserted into 
and protrudes from each extractor and injector hole, each flexible tube 
preferably being fitted with a sealing gland to prevent leakage of 
hardenable material between the tube and the wall of the hole. Preferably, 
at least the or each flexible tube fitted into and protruding from an 
extractor hole is of transparent material to enable the hardenable 
material to be seen as it approaches the outlet of the extractor tube. 
Where hardenable material is being drawn into the injector hole, or into 
one or more than one of the injector holes, at an undesirably high rate, a 
filler or fillers may be mixed with the hardenable material to render it 
less mobile and to reduce the risk of stress cracking when the hardenable 
material sets. The hardenable material is preferably a material that, when 
it sets, will adhere strongly to the boundary surfaces of the cracks and 
other voids. A material consisting of, or comprising as a major 
constituent, a synthetic resin being preferred.

Referring to FIGS. 1 and 2, a length 1 of concrete road has a crack 2 
extending transversely across the road dividing the road into slabs 3 and 
4, the road having cracked as a result of a void 5 that developed beneath 
the road between the road and an underlying highly porous layer 6 of 
clinker. 
In order to fill the void 5 and crack 2 with a synthetic resin that will 
bond to the surfaces of the slabs 3 and 4, including those surfaces 
bounding the crack, a plurality of extractor holes 8 are drilled through 
the concrete at spaced positions along the length of the crack and two 
transversely extending rows of mutually spaced injector holes 9 are 
drilled on opposite sides of, and spaced from, the crack. Transparent 
plastics tubes 8' and 9' are inserted, respectively, into the extractor 
holes 8 and injector holes 9 and protrude from the holes, the tubes being 
sealed in the holes by glands 15. A flexible, fluid-impermeable polythene 
sheet 10 having adjacent its boundery edges an endless hollow wall 11 is 
applied on the part of the road under repair so that the endless hollow 
wall surrounds and opens towards the covered surface, the tubes 8' and 9' 
passing through holes in, and being sealed to, the polythene sheet. The 
endless hollow wall also includes a transversely extending hollow wall 12 
which is positioned adjacent the row of extractor tube 8. Boundary edges 
of the polythene sheet 10 are sealed to the road by adhesive tape or 
mastic sealant 14. 
Air and any other fluid is evacuated from the void 5, porous layer 6 and 
crack 2 through the extractor holes 8 and associated tubes 8' and from the 
hollow walls 11 and 12 through an outlet 13 and synthetic resin in a 
semi-liquid state is introduced into the injector holes 9 through the 
associated holes 9'. As synthetic resin appears in the associated tube 8' 
of each extractor hole 8, evacuation of air and other fluid from this hole 
is terminated and synthetic resin in a semi-liquid state is introduced 
into the hole. When synthetic resin is being introduced into all injector 
holes 9 and extractor holes 8, as the synthetic resin filling the void 5 
and crack 2 sets, evacuation of air and other fluid through the outlet 13 
is gradually brought to a stop. Since, during introduction of synthetic 
resin, the part of the road under repair is completely bounded by the 
evacuated hollow wall 11, 12, any air or other fluid leaking through 
cracks and voids in the road that extend under the polythene sheet 10 from 
beyond its boundary edges will enter the evacuated hollow wall from where 
such air and other fluid will be evacuated. The polythene sheet 10, hollow 
walls 11 and 12 and protruding parts of the tubes 8' and 9' are then 
removed, synthetic resin being applied in any depressions in the top of 
the holes 8 and 9 and the crack. 
Since the synthetic resin, now setting, bonds to the surfaces of the 
concrete slabs 3 and 4, including the surfaces bonding the crack 2, the 
repaired part of the road 1 is at least as strong as the road itself. 
Where, as is shown diagrammatically in FIG. 3, the slab 4 has sunk so that 
its running surface is below the running surface of the slab 3, before the 
crack 2 is filled with synthetic resin, it is preferably to raise the 
sunken slab 4 so that 18 running surface is substantially level with that 
of the slab 3. Referring to FIGS. 4 and 5, this is done by drilling a 
plurality of holes 20 at spaced positions along the crack 2 and 
introducing into each hole an expendable claw 21 which is attached to a 
jack, winch or other lifting means and which has a pivotable arm 22, the 
arm being positioned to lie in the direction of introduction as the claw 
is introduced into the hole. After each claw 21 has been introduced into 
the hole 20, the arm 22 is caused to pivot and the claw is raised until 
the arm engages the undersurface of the sunken slab 4. The clamp 21 are 
then raised to lift the sunken slab 4 so that its running surface is 
substantially level with that of the slab 3 and to hold the slab 4 in this 
position whilst the filling operation described with reference to FIGS. 1 
and 2 is carried out. As a final step, the lifting mechanism is detached 
from the claws which are left in the holes 20, any remaining void in these 
holes being topped up with synthetic resin.