Method for repairing asphalt pavement

The present invention provides an improved method of immediately repairing multiple backfilled utility cut trenches, potholes, and other discontinuities in asphalt pavement, at any ambient temperature, in which the pavement discontinuity is bridged by layers of heated virgin bituminous concrete of different grades, each layer including aggregate stone mixed with a liquid asphalt binder. Alternatively, substantially non-polymerized thermoplastic bituminous concretes of different grades may be used to form the bridging layers, each layer including aggregate stone mixed with a liquid asphalt binder and preferably also containing fractions of n-pentane soluble asphalts and being repetitively softenable in response to repetitive applications of infrared radiation. Also provided is a self-contained mobile unit for heating, storage, and delivery of required asphaltic material comprising two asphalt reclamation units.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved method for repairing asphalt 
pavement roads containing utility cut trenches, potholes, and other 
discontinuities. 
Utility companies must frequently cut trenches into roads and sidewalks in 
order to place new utility lines or to repair existing defective utility 
lines. Such openings are commonly designated as "utility cuts." After 
placement or repair of utility lines, the trench must be backfilled with a 
material which will ultimately support a patch in the overlying pavement. 
Similarly, potholes and other discontinuities in roads and sidewalks 
require repair, sometimes frequently. Repair and maintenance of utility 
cuts, potholes, and other pavement discontinuities drain resources away 
from the responsible governmental authority and ultimately from taxpayers. 
When utility cuts are repaired, a "temporary patch" is generally placed 
over the backfilled trench. Commonly used backfills include the subbase 
materials excavated from the trench, light strength concrete, manufactured 
and natural gravel, soil cements, and the like. In prior art repair 
methods, gravel backfill must be compacted and soil cements must "set", 
i.e. consolidate or settle, prior to placement of the temporary patch. The 
underlying ground layer is allowed to consolidate or settle for a period 
of time, which may vary from about thirty days to about a year. All 
backfill materials may consolidate and/or settle over time. The temporary 
patch is then excavated, using a jackhammer, saw, or the like, and any 
surface irregularities, such as those resulting from settlement and/or 
consolidation which has occurred are corrected. The temporary patch is 
then replaced by a permanent patch. 
An improved method of patching asphalt pavement, useful only when compacted 
soil cement is the backfill material (the PatchMaster.TM. method), 
eliminates the need to excavate the temporary patch by setting the surface 
of the soil cement with heat, scarifying the surrounding patch and bonding 
additional (single gradation) asphalt concrete to the heated area. 
However, the PatchMaster.TM. method is limited in its utility. The amount 
of time required to set soil cement backfill by heat limits the size and 
number of utility cuts which can be repaired using known Mating equipment. 
Most bituminous concrete pavements are formed of base and top layers 
having separate and distinct gradations of bituminous concrete for each 
layer. The PatchMaster.TM. method does not restore the original structure 
of such asphalt pavements, i.e., the separate base and top layers. 
Moreover, the PatchMaster.TM. method does not compensate for consolidation 
and/or movement of the backfill and surrounding subbase formed by the 
earth or ground underlying the patch, which occurs as a normal result of 
thermal expansion and contraction, of shrinkage of the soil cement 
backfill, or of traffic on the pavement. 
Conventional temporary patches are installed directly over the backfilled 
trench. This practice is not substantially changed by the PatchMaster.TM. 
method. Consequently, the boundary of the patch substantially overlies the 
boundary of the trench and the patch has no contact with the undisturbed 
solid ground surrounding the excavated area. In such instances, the 
patching materials used in the patch bonds with the vertical edge of the 
existing asphalt pavement where the patch boundary and existing pavement 
interface, by virtue of the nature of asphaltic materials. In the 
PatchMaster.TM. method the existing vertical edge is merely heated and 
loosened. At a later date, the temporary patch may (or may not)be 
excavated and replaced with a permanent repair sometimes enlarging the 
interfacing area, occurring around the original perimeter of the temporary 
patch. When the temporary patch is not excavated, the interfacing area 
remains relatively small, occupying substantially the area over the 
original trench, representing an inherent structural weakness. Even when 
the gravel backfills are compacted, and/or soil cements are set, the 
possibility of further consolidation of the ground underlying the 
permanent patch remains, since it is not possible to compensate completely 
for the differential of movement in the backfilled area as opposed to the 
surrounding subbase or subgrade, resulting from the initial disturbance by 
excavation of the utility cut. The lack of contact between the patch and 
solid ground in such circumstances creates inherent weakness that is 
amplified by the use of single gradation bituminous concrete in 
conventional temporary and sometimes in permanent patches. 
The need remains, therefore, for improved temporary and/or permanent repair 
methods for asphaltic pavement which has been subjected to utility cuts or 
which contains potholes or other discontinuities. 
It is an object of the present invention to provide an improved method and 
apparatus for effecting repair of utility cuts, potholes, and the like in 
asphaltic pavement. 
SUMMARY OF THE INVENTION 
The present inventor has developed a way to immediately apply an asphalt 
patch in all climates, throughout the year, in such a manner that the 
patch includes at least one large aggregate (base) layer of a virgin or 
substantially non-polymerized bituminous concrete including relatively 
large aggregate which bridges the utility cut trench, pothole, or other 
pavement discontinuity, and at least one small aggregate (surface) layer 
of a virgin or substantially non-polymerized bituminous concrete including 
relatively small aggregate overlying the uppermost large aggregate layer, 
significantly strengthening the structure and stability of the patch and 
restoring the pavement approximately to its original condition. When 
asphalt pavement patches are made in accordance with the present 
invention, the need to excavate temporary patches and replace them with 
permanent patches is eliminated entirely, yielding a new category of 
"semi-permanent" patch which does not require re-excavation and which is 
substantially completely heat recyclable if further surface alteration is 
desired. The method of the present invention may be used with any kind of 
conventional backfill material. The method of the present invention 
further does not require that backfill be compacted prior to application 
of the patch, and thus is not limited to use of soil cement as backfill. 
The nature, depth, and strength of the materials used in the method of the 
invention render the repaired area "pothole proof" and allows for future 
surface heat recycling, if required. 
In one embodiment, the invention provides a method of repairing asphalt 
pavement over a trench containing backfill and characterized by a 
peripheral wall defining the trench, comprising the sequential steps of: 
a) cutting back the pavement to provide a region overlying the trench and 
extending beyond the peripheral wall; b) applying at least one large 
aggregate layer in said region, whereby the peripheral wall of the trench 
is bridged; c) applying at least one small aggregate layer overlying the 
uppermost large aggregate layer; and d) applying heat to the uppermost 
layer of at least one of said large aggregate layers and said small 
aggregate layers; said large aggregate layer being a heated virgin first 
bituminous concrete including relatively large aggregate mixed with a 
liquid asphalt binder, or a substantially non-polymerized thermoplastic 
first bituminous concrete including a relatively large aggregate mixed 
with a liquid asphalt binder containing n-pentane soluble fractions of 
asphalts and being repetitively softenable in response to repetitive 
applications of infrared radiation, and said small aggregate layer being a 
heated virgin second bituminous concrete including a relatively small 
aggregate mixed with a liquid asphalt binder, or a substantially 
non-polymerized thermoplastic first bituminous concrete including a 
relatively small aggregate mixed with a liquid asphalt binder containing 
n-pentane soluble fractions of asphalts and being repetitively softenable 
in response to repetitive applications of infrared radiation, whereby a 
patch is formed. The patch made in accordance with the invention 
essentially conforms with the original texture and contour of the 
surrounding pavement. 
In another embodiment, the invention provides a single mobile 
self-contained unit for heating, storage, and delivery of all asphaltic 
materials in any climate throughout the winter season (when conventional 
asphalt plants traditionally close in cold weather), which comprises two 
separate asphalt reclamation units.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a road in which pavement 10 overlies the ground 11. A hole 18 
in the pavement overlies a utility trench, excavated to perform repairs on 
a utility pipe 13. A utility cut trench is defined by peripheral walls 12 
after backfilling. Any conventional backfill material may be used in 
accordance with the present invention, including light strength concrete, 
soil cement, manufactured gravel, and the like. In accordance with the 
invention, the term "backfill" includes subgrade or subbase as those terms 
are understood in the art. The utility pipe 13 may be surrounded by a 
non-abrasive small particle bedding material 14, such as sand, over which 
backfill 15 can be placed. In accordance with the present invention, the 
bedding material 14 may also be comprised of backfill itself. The boundary 
16 of the hole in the pavement 10 overlies the peripheral walls 12 of the 
trench. In accordance with the method of the invention, the backfill 
material is not restricted to soil cements commonly referred to as 
Controlled Density Fill (CDF); however, gravel backfills are optimally 
compacted prior to the first step of the method. When the method of the 
invention is used to repair potholes or trenches in which subgrade 
consolidation has occurred, a preheating step may be included prior to the 
first step to thermally enhance the bonding of the bituminous concrete 
patch with the existing pavement. 
FIG. 2 shows the first step of the method of the invention, in which the 
pavement 10 has been cut back to provide a surface region 20 of solid 
ground 11 extending beyond the peripheral walls 12 of the trench. In 
accordance with the invention, region 20 may be bounded by walls 16 in the 
form of a substantially square vertical surface, or it may gradually 
incline from the point of cutback toward the surface of the pavement 10. 
The cuts in the pavement 10 are made to extend to the solid ground 11 
surrounding the trench, beyond the peripheral walls 12 of the trench so as 
to form a "bridge" of the binder layer across the trench. At a minimum, 
the cuts in the pavement are made to extend slightly beyond the peripheral 
walls of the trench, so long as formation of the "bridge" of binder layer 
across the trench is allowed. Preferably, the pavement 10 is cut back 
approximately 12 inches beyond the peripheral walls of the trench. In 
accordance with the invention, the binder layer is comprised of one or 
more large aggregate base layers and of one or more small aggregate 
surface layers. 
FIG. 3 shows the second step of the method of the invention, in which a 
large aggregate foundational or base layer 30 has been applied over the 
region 20 and across the backfill 15, in such a way that the peripheral 
wall 12 of the trench has been bridged. The large aggregate base layer 30 
is comprised of a coarse grade of a heated virgin bituminous concrete 
including relatively large particles of stone, i.e., relatively large 
aggregate, mixed with liquid asphalt binder (asphalt cement, emulsified 
asphalt, or the like). In accordance with the invention, the large 
aggregate contains particles of stone having a maximum dimension in the 
range of 0.5 to 2 inches. Alternatively, the large aggregate base layer 30 
is comprised of a substantially non-polymerized thermoplastic first 
bituminous concrete including relatively large aggregate as defined above, 
mixed with a liquid asphalt binder containing fractions of asphalts which 
are soluble in n-pentane, such as those described in U.S. Pat. No. 
3,162,101; incorporated herein by reference. It is believed that the 
n-pentane soluble fractions of asphalts such as those described in U.S. 
Pat. No. 3,162,101 retard oxidation of the asphalt during heating, and 
thereby permit increased numbers of heating/softening cycles compared with 
conventional asphalt. Other oxidation retardants (or anti-oxidants) might 
also be used. 
Any non-recycled thermoplastic large aggregate bituminous concrete may be 
used to form the large aggregate base layer 30. Preferably, a 
substantially heat-resistant thermoplastic large aggregate bituminous 
concrete is used to form the large aggregate layer 30. In accordance with 
the present invention, "heat-resistant" is defined as being repetitively 
softenable in response to repetitive applications of infrared radiation. 
Such materials are minimally damaged in thermoplasticity and are commonly 
described as being "recyclable." More preferably, a substantially 
heat-resistant thermoplastic virgin large aggregate bituminous concrete is 
used to form the large aggregate base layer 30. Most preferably, a 
substantially heat-resistant substantially non-polymerized thermoplastic 
large aggregate bituminous concrete mixed with ASTM D977 asphalt emulsion 
binder and preferably also containing n-pentane soluble fractions of 
asphalts such as those described in U.S. Pat. No. 3,162,101 which is 
capable of curing with or without heat treatment, such as large aggregate 
grade MARIMIX.TM., is used to form the large aggregate base layer 30. In 
accordance with the invention, the large aggregate bituminous concrete 
used to form the large aggregate base layer 30 is prepared by heating to 
about 300.degree. F. prior to installation, overlapping region 20. 
In this step of the method of the invention, for a 4.0 inch pavement, for 
example, the large aggregate layer 30 is first placed overlapping region 
20 to a depth of preferably about 1 to about 3.5 inches. More preferably, 
the depth of the large aggregate layer 30 is about 1.5 to about 3 inches. 
Most preferably, the depth of the large aggregate layer 30 is formed in 
layers of about 2 to about 2.5 inches, said layers being placed to within 
1.5 to 2.0 inches of the pavement surface. The large aggregate layer 30 is 
rough graded by luting or raking and mechanically compacted using known 
methods in layers not to exceed 2 inches in depth. The large aggregate 
base layer 30 may be further sealed by applying heated liquid asphalt 
materials, as is known in the art. Suitable sealant materials for use in 
the method of the invention comprise asphalt emulsions optionally 
containing n-pentane soluble fractions of asphalts, as disclosed, for 
example, in U.S. Pat. No. 3,162,101. 
FIG. 4 shows the third step of the method of the invention, in which a 
small aggregate surface layer 40 has been applied to the large aggregate 
base layer 30. The small aggregate surface layer 40 is comprised of a 
finer grade of a heated virgin bituminous concrete than the large 
aggregate layer 30, mixed with a liquid asphalt binder (asphalt cement, 
emulsified asphalt, or the like). The small aggregate layer 40 is 
comprised of virgin bituminous concrete including relatively small 
particles of stone, i.e., relatively small aggregate. In accordance with 
the invention, the small aggregate contains particles of stone having a 
maximum dimension less than 0.5 inch. Alternatively, the small aggregate 
surface layer 40 is comprised of a substantially non-polymerized 
thermoplastic second bituminous concrete including a relatively small 
aggregate (as defined above) mixed with a liquid asphalt binder containing 
fractions of n-pentane soluble asphalts such as those described in U.S. 
Pat. No. 3,162,101. Any non-recycled thermoplastic small aggregate 
bituminous concrete may be used to form the small aggregate surface layer 
40. Preferably, a substantially heat-resistant thermoplastic small 
aggregate bituminous concrete is used to form the small aggregate surface 
layer 40. More preferably, a substantially heat-resistant thermoplastic 
virgin small aggregate bituminous concrete is used to form the small 
aggregate surface layer 40. Most preferably, a substantially 
heat-resistant substantially nonpolymerized thermoplastic small aggregate 
bituminous concrete mixed with ASTM 977 asphalt emulsion binder and 
preferably also containing n-pentane soluble fractions of asphalts such as 
those described in U.S. Pat. No. 3,162,101 which is capable of curing with 
or without heat treatment, such as small aggregate grade MARIMIX.TM., is 
used to form the small aggregate surface layer 40. In accordance with the 
invention, the small aggregate bituminous concrete used to form the small 
aggregate surface layer 40 is prepared by heating to about 300.degree. F. 
prior to application to the large aggregate base layer 30. 
In this step of the invention, an amount of small aggregate bituminous 
concrete is placed on the large aggregate base layer 30 which is 
sufficient to make the total depth of the patch, large aggregate base 
layer 30 plus small aggregate surface layer 40, not less than 4 inches, or 
the depth of the pavement, whichever is greater. After the small aggregate 
surface layer 40 is placed on the large aggregate base layer 30, the small 
aggregate base layer is finish graded by luring or raking, compacted by 
mechanical means, and constructed to be consistent with the adjacent and 
surrounding surface of the existing pavement. The small aggregate surface 
layer 40 may be further sealed by applying heated liquid asphalt sealant 
materials, as is known in the art, before and/or after installation. 
Suitable sealant materials for use in the method of the invention comprise 
asphalt emulsions optionally containing n-pentane soluble fractions of 
asphalts, as disclosed, in U.S. Pat. No. 3,162,101. 
In accordance with the invention, additional large aggregate and small 
aggregate layers may be added to the patch, or additional grades of 
bituminous concrete may be added to form additional layers of the patch. 
The resulting uppermost layer may be reworked to re-establish the original 
surface plane of the roadway and thermally integrated by applying heat, 
preferably non-aspirated heat and more preferably infrared heat. 
Optionally, additional suitable bituminous concrete(s) may be introduced 
after the surface has been plasticized by the application of heat and 
scarified. The additional paving materials are reworked into the scarified 
area by finish raking or luting to the desired grade and by compacting the 
entire heated sections. A sealant material such as the n-pentane soluble 
fractions of asphalt described in U.S. Pat. No. 3,162,101, optionally 
mixed with compatible liquid asphalts, may be applied to the uppermost 
layer of the patch, and stone dust and mineral filler, or the like, may be 
added to minimize tracking. The perimeter between the patch and the 
pavement surface may also be sealed using a sealant material. 
An asphaltic pavement patch made in accordance with the invention can be 
applied year round within 24 hours, at any ambient temperature, and 
because of the added strength of the bridging of the large aggregate and 
small aggregate layers, will not require re-excavation, needing only 
infrared heat treatment if the underlying subgrade has moved resulting in 
a surface irregularity and/or depression. Elimination of the need for 
reexcavation is environmentally desirable, resulting in a significant 
efficiencies and cost savings. 
If additional processing of the pavement patch made in accordance with the 
invention is required, such processing may be made as described below. 
After a period of time has elapsed to allow for consolidation and/or 
movement of the underlying ground layers, the surface area containing the 
asphaltic pavement patch is heated together with the immediate adjacent 
pavement, to a depth of about one to one and one-half inches. The ultimate 
size of the heated area will correspond approximately to the dimensions of 
the area to be repaired and to that of the heater used. When a large patch 
is being processed, the processing is continuous and is performed in such 
a way that only small, overlapping areas are processed a section at a 
time, to allow surface thermal integration of the bituminous asphaltic 
materials of the patch and newly added bituminous asphaltic materials with 
the existing pavement. 
Preparatory to the patch being heated, a compensating petroleum product 
such as the sealant described above may be applied to the pavement 
surface. The patch is then heated using a non-aspirated heat such as 
infrared heat. An additional application of the sealant material may be 
utilized after the pavement has been plasticized. The softened area may 
then be appropriately scarified, thoroughly mixing in the sealing 
mixtures, establishing the surface area requiring additional bituminous 
concrete. The heated virgin or substantially nonopolymerized bituminous 
concrete, which may comprise one or more additional small aggregate layers 
as described above, is added to the scarified area to compensate for any 
surface depression which may have occurred. This bituminous concrete is 
re-graded by finish raking or luring, and mechanically compacted, 
restoring the original surface plane of the pavement. Preferably, all 
additional bituminous concrete(s) are obtained from thermostatically 
controlled containers at the site. The edges of the patch are then sealed 
as set forth above, and a final application of the sealant material may be 
utilized to densify the entire heat treated surface area. In this way, a 
semi-permanent patch, which only requires further attention if, or when, a 
surface irregularity occurs, may be recycled into a permanent patch 
without re-excavation. This comprehensive system is environmentally 
responsive. 
FIG. 5 shows a self-contained mobile unit 50 used to practice the method of 
the invention. This unit contains two thermostatically controlled asphalt 
reclamation systems 60 and 70. Single asphalt reclamation systems are 
described in U.S. Pat. No. 4,445,848, incorporated herein by reference. 
The first reclamation system 70 is used in accordance with the invention 
to prepare and/or store the large aggregate bituminous concrete for 
application of the large aggregate layer by heating the large aggregate 
bituminous concrete to about 300.degree. F. The second reclamation system 
60 is used in accordance with the invention to prepare and/or store the 
small aggregate bituminous concrete for application of the small aggregate 
layer by heating the small aggregate bituminous concrete to about 
300.degree. F. The presence and capacity of the two asphalt reclamation 
systems on one mobile unit allows preparation and/or storage of the 
different grades of bituminous concrete which form the large and small 
aggregate layers of the patch to be delivered immediately to the sites of 
multiple backfilled trenches, which has not previously been possible. Of 
course, additional reclamation units can be added to the mobile unit of 
the invention if greater capacity or additional grades of bituminous 
concrete are used in accordance with the method of the invention. The 
self-contained mobile unit of the invention may additionally include 
miscellaneous apparatus such as compaction equipment, liquid asphalt 
sealants, hand tools, and the like. 
Those of skill in the art will recognize that the invention may be embodied 
in other specific forms without departing from the spirit or essential 
characteristics thereof. The presently described embodiments are therefore 
to be considered in all respects as illustrative and not restrictive, the 
scope of the invention being indicated by the appended claims rather than 
by the foregoing description, and all variations of the invention which 
are encompassed within the meaning and range of equivalency of the claims 
are therefor intended to be embraced therein.