Slabjacking: Concrete Leveling Techniques & Applications

Sawcutting at joints.
Inspection of slab settlement.
Drilling holes (left) and pumping
grout (right).
By Susan C. McCraven
C
racked, bumpy, and uneven
concrete surfaces can present
both minor and major problems. Does the neighborhood rollerhockey gang complain that your
jagged driveway prevents them from
playing like Gretzky? Do the forklift
operators ache like bronco riders after
a long workday on your warehouse
floor? Or are you worried about tripping hazards and liability issues because of uneven public sidewalks and
entranceways? Slabjacking may be
your answer.
Concrete leveling contractors and
pump equipment manufacturers point
out that slabjacking has many advantages over slab removal and replacement, and many good applications.
As early as the 1930s, pressure injection was used to raise deteriorated
slabs and roadways. J.W. Poulter is
believed to have developed the first
machine for what was then called
mudjacking for highway work. Early
grouts ranged from soils such as clay,
sand, and loam, to portland cement,
fly ash, lime, and casting plaster.
Though dangerous, even hot asphalt
was pumped into voids under roadways to prevent water penetration.
Selecting the proper pump and proportioning the grout are critical to success,
a lesson learned in the 50-year history
of slabjacking.
Slabjacking process
When approaching a new job, the
slabjacking contractor first assesses the
settlement of the concrete slab.
Slabjacking:
Inadequate subgrade compaction isn’t
the only cause for settlement of concrete slabs on ground. “While improper subgrade compaction prior to the
placement of a concrete slab can lead
to subsidence and cracking problems,
loss of soil support due to water seepage through joints is often the cause of
sinking concrete. You can look for the
telltale signs of water erosion after a
rain at the bottom of a sloped, sunken
concrete driveway. You’ll often see a
sand washout,” according to Darrel
Maute, sales manager with A-1 Concrete Leveling, Belleville, Mich.
If the sunken slab has to be isolated
from adjacent slabs or structures, the
contractor may use sawcuts at joints
(relief cutting) to relieve binding. Surveying equipment and grade and string
lines are used to establish the correct
p
U
t
I
p
Pum
Finish elevation.
A-1 CONCRETE LEVELING
Truck-mounted pump and slurry mixer.
elevations. Based on experience, the contractor custom drills a specific pattern of
holes in the existing concrete slab or
floor using a diamond bit or a percussion
drill with a carbide bit. Depending on
the pumping system that will be used,
these access holes range from 1 inch to 2
inches or more in diameter.
The contractor then hydraulically
pumps a grout mixture through the
holes and into the voids beneath the
concrete. If the subsided slab has adhered to the soil, the contractor may
have to create a void using air pressure
equipment. At pressures that vary
from 10 to 150 psi, the pumped grout
mixture fills the void, exerting pressure
on the concrete and the subsurface
material and lifting the slab. During
the lifting operation, the pump operator monitors both volume and pressure. The amount of pressure used depends upon the grout slump (stiffness),
the weight of the slab, and the area of
void space. Contractors decide on the
proper slump for a given application
based on years of experience.
Jim Sexton, manager at Airplaco
Equipment Co., Cincinnati, cautions,
“Trying to raise a slab too rapidly with
too much volume often can create
more problems than you are trying to
correct.” Slabjacking must be performed with controlled and even pressure grouting, as portions of the slab
may crack if subjected to significantly
different subgrade pressures. Once the
concrete is properly aligned and lev-
eled, the drill holes are patched.
Within about 24 hours, the grout mixture solidifies and forms a stable bearing surface for the slab. Special care is
taken to ensure that the slab slopes
properly to drain water away from
foundations.
Manufacturers of larger pumps
have equipment that can be adapted
for slabjacking. “While today’s jack
pump designs can discharge material at
volumes from 100 to 300 cubic feet per
hour and with line pressures up to 600
psi, slabjacking operations typically use
lower pressures and volumes,” according to Sexton. This article does not
address pumping equipment used for
similar pressure grouting applications
such as void filling, undersealing, and
tunnel injection repair.
and new slab construction.”
While driveways, sidewalks, pool
decks, and other residential repairs
remain the bread-and-butter work for
slabjacking contractors, commercial,
manufacturing, and roadwork are
often well suited to the advantages of
slabjacking. For example, Kent Concrete Lifting recently realigned a press
foundation that had settled due to
equipment vibration. “The plant managers could not afford to have the
press offline for any longer than necessary. We were able to get in, level up
Not just residential
Most people think of slabjacking
as a residential repair for driveways
and sidewalks that have settled and
tilted out of alignment. However,
Dean Stacer, division manager of Kent
Concrete Lifting, Redford, Mich.,
explains, “Slabjacking has many applications besides residential. Slabjacking
can be used for road leveling at intersections, realignment of bridge approaches, warehouse floor repair, and
equipment foundation stabilization in
manufacturing plants. When you are
looking for the shortest downtime,
slabjacking can provide concrete leveling in much less time than demolition
Slabjacking, often
called mudjacking,
is an economical
alternative to
costly replacement of sunken
concrete slabs
Before and after shots of slabjacking roadway repair.
DWYER MAGNUM PUMPS
the foundation, and patch the surface
in 8 hours. The equipment was back
online in 24 hours,” said Stacer.
Depending upon the municipality or state, safety regulations defining a legal tripping hazard can vary.
In nursing homes, flooring with a 1⁄ 2inch variation from level can constitute a tripping hazard. For public sidewalks, most municipalities consider 1
inch or more to be unacceptable.
Maintaining proper elevation is particularly critical for concrete entrances
to public buildings.
“We can repair the concrete entrance ways to commercial and business establishments and not inconvenience the tenants with building
closure and lost work time. There
are many advantages and applications where slabjacking is the best
alternative to the mess, noise, and
downtime of demolition work,”
advises Maute.
Advantages
The alternative to slabjacking for
restoring the levelness and proper elevation of a slab is to demolish the
existing concrete and construct a new
slab. Slabjacking has many advantages
over such drastic measures:
Low cost: Slabjacking can result
in significant cost savings. Prices in the
Midwest typically range from $1 to $3
per square foot for slabjacking, compared with $5 to $8 per square foot to
rip out and construct a new floor.
Maneuverability/access: The size
of pumping equipment makes the slabjacking pump plant highly maneuverable, enabling it to access fairly small
or congested areas. Most equipment
can pump up to 150 feet away.
Little
mess:
Cleanup is fast and
minimal compared
For more information
with the dust and
debris of demoliThe following companies manufacture pumping
tion. Drill hole
equipment specific to slabjacking:
patches are less
Hydraulic Mudpumps, Ernest Cvetezar,
noticeable than the
President, PO Box 1054, 4903 Vista Road,
color difference of
Manitowoc, WI, 54221-1054, 800-626-2464,
a newly placed slab
Fax: 920.684.9008, www.mudpumps.com, or
next to older concircle 1 on the reader service card.
crete.
Magnum Pumps, Dwyer Companies, Katie
M i n i m a l
Dwyer, Director of Advertising, 6083 Schumacher
downtime: Besides
Park Drive, West Chester, OH, 45069, 513-777the significant cost
1635, Fax: 513.777.5374, kdwyer@dwyercompa
savings, an
nies.com, or circle 2 on the reader service card.
owner’s greatest
Airplaco Equipment Co., James R. Sexton,
advantage is the
Manager, 4141 Airport Road, Cincinnati, OH,
minimal
down45226-1643, 513-321-2950, Fax: 513.321.8178,
t i m e .
[email protected], or circle 3 on the reader
Manufacturing
service card.
facilities can mini-
mize the time their equipment and
operations are offline.
Aesthetics: Instead of patched
drilled holes, concrete cores can be cut
out and grouted back into the holes
after pumping. This repair method
costs more but is a good alternative for
owners who are concerned with a
more uniform appearance in the repaired slab.
Landscaping: Today’s landscaping
costs (materials and labor) can be significant. Slabjacking operations do
little to no damage to landscaping
adjacent to the lifted slab, compared
with slab replacement.
Waste disposal: With slabjacking,
there are no disposal costs for demolished concrete.
Disadvantages
Not every aspect of slabjacking is
perfect. Here are some of the reasons
to proceed with caution:
Appearance/aesthetics: Some owners do not want a finish with noticeable
patches. While some contractors try to
match existing concrete color and
aggregates, or use cores, the patches are
still often noticeable. Over time, though,
the patched areas tend to blend in with
the surrounding concrete.
Underground utility lines: There
can be complications with existing
utility conduits or heating ducts in the
ground beneath the slab. Without
proper care, pressurized grout can create enough force to move existing utilities out of alignment or push grout
into pre-existing cracks in pipes or
lines. Utility lines must be identified
prior to slabjacking operations.
Cracking: While existing cracking
can be made less noticeable once the
Grout mixes, applications, cost, and pumps
Aggregate Fillers
Natural Soil
Lime
Fly Ash
(Mud) (Top soil/clay)
(Crushed limestone /
hydrated lime, lime
kilndust, etc.)
(Type F/C, C & F)
Binder (if any)
Properties
Cement
Cement
Cement
Cement
Variable consistency due to
raw materials such as
chunks of stiff clay, rocks,
plant roots, naturally occurring organic materials and
other. These materials offer
the greatest potential pumping, shrinkage, strength,
etc. Variations. Easily displaced/eroded with water,
vibration, freeze/thaw
cycles. Must use adequate
amount of binder.
Crushed limestone
dust/fines are typically
found in limited areas. This
material is dry, very
absorbent, irregular/rough
surface, yielding potential
pumping problems, high
shrinkage. Hydrated lime is
likewise very absorbent,
rough surface, varies in
chemistry causing consistency control problems.
Sand can be used as an
effective filler. Must use
adequate amount of binder
to avoid displacement,
as with the natural soil
materials.
Class F typically used, readily available with low
absorbency. Class C is
available and can be used
as a binder, filler, etc.
Depending on the chemistry
Class F/C can be D.O.T.
certified for state, city,
municipal projects. Class
C/F fly ash is very
pumpable and can offer
very stiff to flowable grouts.
This material can yield low
to medium compressive
strengths depending on the
needs. Available dry or wet
depending on source
and/or potential use. Binder
may prove optional depending on the basic chemistry.
Fillers may be used to take
up space in a grout to
minimize cost, minimize
shrinkage, provide higher
strengths, etc. Fillers generally consist of calcareous
sands, powders, coarse
aggregates, or special normal/lightweight materials.
Aggregates are often used
to improve mixing consistency from ready mixed
plants (especially dry
batched plants). Aggregates
are always used in combination with a binder (i.e., portland cement) and/or fly ash
or other fine filler materials.
Availability
of Materials
Materials are readily available, but can be expensive
due to screening and
shredding.
This material is not readily
available in most areas and
generally not economically
viable due to transportation
cost.
This material is readily
available (byproduct of the
elec. utility industry) and
extremely economical. Only
use silo and/or pugmill
(possible pond ash).
Natural aggregates/materials are readily available and
economical. Any materials
manufactured and/or modified drive the cost up (i.e.,
lightweight agg.)
Residential
Can be used, has greatest
failure rate/warranty-call
backs.
Can be used, but must use
binder to avoid displacement (erosion, etc.)
This material should be first
choice for good predictable
results/cost.
Rarely used, most often
used when large voids
dictate.
Light
Commercial
Can be used, has greatest
failure and potential problems.
Can be used, but must use
binder to avoid displacement (erosion, etc.).
This works very well with
good predictable results.
Sometimes used to offset
large volume cost and/or
speed up a project.
Municipal
Very rarely able to use,
most often specifications
prohibit use.
Can be used and often
acceptable under specifications, not best choice.
Most often specified and
works great.
Used often to speed up a
job with large volumes
and/or for best consistency.
Cost
Availability of consistent,
clean materials drives the
raw material and trucking
cost up as well as jobsite
problems to the point material is not cost-effective.
Availability of this material,
as well as the potential longterm problems, makes this
material not cost-effective in
most areas of the country
as compared with other
readily available materials.
This material is not only
readily available, but in
most cases is very costeffective. Using fly ash is a
very good use of a recyclable material.
Aggregates provide a costeffective filler and mixing
stimulator if pump can handle the material.
Rotor Stator
Consistent jams and inconsistency can be expected if
material is not screened
(very clean).
Works OK, but with high
water demand can cause
consistency problems.
This material offers little if
any concerns for jamming
up pump with consistency
in batching.
This pump design when
coordinated with maximum
size coarse aggregate.
Should pump well if
grout/concrete is designed
properly.
Ball Valve
Expect consistent problems in pumping and valve
jam-ups.
Works OK but with varying
water demands can cause
consistency problems and
jam-ups.
Must be batched and mixed
consistently, and ,if so, can
work OK with experience
and quality materials (no
bottom ash).
These pumps are extremely
sensitive to max. size
coarse aggregate and cementitious combination in
order to pump at all. Generally only good for rich grout.
Swing Tube
Expect very little if any difficulty pumping.
Expect very little if any difficulty pumping. Consistency
isn’t the concern here.
Expect no problems in mixing, pumping, and placing
this material.
Maximum size coarse agg.
is again important in
matching pump and materials design, but the swing
tube is least sensitive with
any materials.
3 6 Concrete Construction July
www.worldofconcrete.com
Information provided by DWYER MAGNUM PUMPS
Bulk/Filler
Materials
Before and after shots of slabjacking roadway repair.
DWYER MAGNUM PUMPS
slab is leveled, it is possible to cause
new cracks if one section of the slab is
raised too rapidly.
Slab drift: Slabs can drift laterally
during the slabjacking operation. If
the grouting material is unstable, the
material eventually can wash out,
leaving the slab without proper subgrade support.
Pumps and grout
According to Brian Dwyer, president of Dwyer Magnum Pumps of
Cincinnati, “Using the right concrete
pumping equipment and the right
grout mix can make the difference
between success and failure on slabjacking projects.” (See description of
Magnum’s newest pump in Product
Update, p. 62.) Most slabjacking
projects require grout mixtures with
low slump because of shrinkage concerns. Low slump grout can be more
difficult to pump, which means selecting the right pump for the project
is necessary.
The most common types of
pumps used for slabjacking or pressure grouting are rotor stator pumps,
ball valve pumps, and swing valve
pumps. Understanding the characteristics of a pump and the material to
be used is important because of variables like viscosity and curing time of
the mix, lifting pressures, live loads
on the slab, de-pressuring line requirements, and safety concerns.
Like other technologies today, slabjacking equipment is benefiting from
manufacturing innovations. With
over 20 years of manufacturing experience in the slabjacking industry,
Ernie Cvetezar, president of Hydrau-
lic Mudpumps, Manitowoc, Wis.,
says, “I have seen more progress in
functionality, convenience, and equipment capacity in the past 2 years
than ever before.”
Equipment costs vary. “A standard slabjack pump will range from
$5000 to $16,000, and a mounted
unit with pump and mixer can range
from $18,000 to $26,000,” according to Sexton.
Various types of pumps are used
in the slabjacking industry:
Rotor stator pumps: are capable
of handling only very fluid (high
slump) mixes containing little or no
aggregate; deliver materials at low
pressures. Typical mixes include very
lean cement and water. Rotor stator
pumps have no reverse pumping
capability and are suitable for smaller, lightweight slabjacking jobs.
Ball valve pumps: are capable of
handling medium to very fluid (medium to high slump) mixes with some
small aggregate; can handle a wider
range of mixes than rotor stator
pumps. Ball valve pumps have no
reverse pumping.
Swing valve pumps: are capable
of pumping a wide spectrum of material from extremely thick to very fluid
(very low to very high slump) mixes
with aggregates; are capable of pumping at very high pressure; have reverse
pumping capability, which allows for
depressurizing the lines safely and
cleanly; are well suited for a variety of
slabjacking projects. (For a handy reference, see the table on page 36, for
suitability of various pumps and
grouts for different job requirements.)
Training
Most slabjacking contractors provide their own training for employees
using manufacturers’ operation manuals and videos. Some equipment manufacturers also will provide training if
requested. Cvetezar had this to say
about training: “Slabjacking is often
believed to be more of an art than a
science. While HMI provides training
manuals for our equipment, our customers still prefer the expense of
sending their personnel to us for
training. It is always best to learn
from a master.” ■
Publication #C01G032
Copyright © 2001 Hanley-Wood, LLC
All rights reserved