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The First Year in the
Life of Your New Floor
What to expect in the First Year After
Construction of Your New Industrial Floor...
What to Do When the Expected Occurs
As the owner of a new industrial facility, you are probably still
settling in, working the bugs out of your operations. Although
you may not have noticed, your floor is also adjusting to its
environment. How your floor settles in over the next year, and
how you respond can have a significant effect on the long term
durability of your floor. You need to realize that the durability
of your floor will forever affect your operations and
productivity.
The purpose of this article is to give you a condensed view of
what is going on with your floor during its first year. Consider
this an abbreviated owner's manual without technical jargon or
complicated formulas. Just a simple explanation of a very complex
object.
CRACKS
As much as you are displeased to hear it, all concrete cracks.
There are many causes of cracking, but most of them are rooted in
the fact that all concrete shrinks.
The standard concrete mix contains far more water than is needed
to hydrate (harden) the cement. This excess water, used mostly to
make the mix workable, will evaporate slowly over a long period
of time. As the moisture leaves the slab actually shrinks in
mass. This causes stress buildup, friction with the base the slab
rests upon and lifting of the ends of the pour. All of these
results can cause cracks. Other causes include restraint at fixed
objects such as docks, improper joint spacing, late joint
cutting, etc.
The question for you as the floor owner is not whether you have
cracks. You definitely do. The important questions to ask are:
1. What caused the cracks?
2. How many do I have?
3. How wide are they ; how deep?
4. Have they significantly weakened the floor?
5. Will they get worse?
6. Will they affect my operations?
7. Can they be permanently corrected?
8. Should they be corrected?
JOINT
DETERIORATION
In the traffic-bearing areas of your floor you have two types of
joints: construction and control joints. Construction joints are
those joints at the ends of pour sequences. Control (contraction)
joints are joints within each pour designed to induce the
anticipated cracks to crack in a straight line. Generally, you
will find joints at intervals from perhaps 12 to 25' grids.
Joints are affected by shrinkage. Conventional concrete shrinks
at a rate of approximately 1/8' or more in each 20'. This means
that over the one-to-two year period during which concrete
shrinks, your joints may open an additional 1/16 to 1/4Ó. This
can have a dramatic effect on any joint filler that is used.
Joints in traffic bearing surfaces should always be filled. The
function of a filler should be to protect (support) the joint
edges from damage caused by hard wheel impact. This damage is
called 'spalling'. Once spalls occur they continually get wider
and deeper. Spalls damage vehicle wheels, result in bumps that
material handling vehicles (MHV) drivers slow down for and
eventually costs $$$ to repair.
To be effective, the filler should be fairly stiff, like a very
hard rubber. This means it will not expand as the joint opens.
There are only two ways to overcome this dilemma: (1) install the
filler late in the schedule to allow for as much of the shrinkage
as possible; and (2) provide for repair or replacement of the
filler after the shrinkage seems to have stabilized, usually
after the first full heating season.
If you are experiencing joint filler separation (adhesive or
cohesive), contact the manufacturer of the filler for their
recommended corrective procedures.
If you are already experiencing joint edge spalling, don't delay
in reacting. Identify the cause and take appropriate action
before the spalls become too severe for simple correction.
There are many causes of joint edge spalling for you to consider,
including the following:
1. Joints are not filled.
2. Filler was too soft to support traffic.
3. Filler was installed too early and separated badly as
joints opened wider.
4. Filler was installed too low in joint to protect edge.
5. Filler was installed too shallow to support hard wheel
load (filler should be full depth in saw cut joints, 2'
deep in construction joints).
6. Filler was of poor quality, deteriorated with time.
7. The concrete edge itself was weak.
8. The joint was higher on one side, leaving it
vulnerable to wheel impact.
JOINT EDGE CURL
Joint condition #8 in the preceding paragraph (higher on one
side) could be caused by a phenomena known as 'curl'. Concrete
shrinks at a faster rate on its top surface because it is exposed
to the air. As shrinkage occurs the ends of each pour curl
upward. (You can see the same effect by examining dried mud). To
determine if you have a curled joint, simply lay a straightedge
across the joint and see if it rocks. Another is to listen for a
'thump' as vehicles cross, or visually watch for slab deflection.
Curl can leave joint edges at different elevations, leaving the
high one vulnerable to wheel impact. But curl can cause even
worse problems than that.
As the top edge of a slab curls upward, the bottom of the slab
may actually lift up off the ground. As MHV's cross, the two
adjacent slab segments may actually "rock" as they
deflect under load. This means that both slabs may be the exposed
high point at given times in the vehicles progress. The rocking
effect also causes any joint filler used to debond and become
worthless. Generally, replacing the filler will not solve the
problems of rocking.
Curl is a natural phenomena that is almost impossible to avoid
although, it can be minimized. The important questions for you,
the owner, are:
1. How severe is the curl with
regard to joint edge elevation? Will it affect my operations?
2. Do the slab ends "rock"? How much?
3. Can the rocking be eliminated easily or are more
sophisticated measures necessary?
4. Is the rocking in my floor "normal" or did
faulty design or construction practices contribute to the
problem?
SURFACE
DEFECTS
The surface is obviously the most critical part of any floor.
Surface defects can also be the most difficult floor problems to
repair since it is subject to constant abrasion, wear and impact.
For the purposes of brevity, this article will cover only a few
of the more common surface defects.
DUSTING
Dusting is a condition that usually occurs as a result of poor
finishing techniques and/or poor curing. This dusting indicates
that the surface is relatively soft and weak. There is no sure
cure for correcting this weakness, but treating the floor with a
liquid hardener will reduce dusting and improve wearability.
DELAMINATION
(Scaling)
This condition is where the top 1/16' or 1/8' of the surface
comes off, leaving the underlying aggregate exposed to wear. The
causes are usually improper finishing, although certain
aggregates can cause popouts that yield a similar appearance.
The correction of this condition requires that the entire surface
be stripped away down to sound concrete, often 1/4' to 3/8'. The
surface is then replaced with an epoxy or polymeric grout
overlay. The cost of this procedure is high, the results seldom
100% successful and special equipment is almost always advisable.
CRAZING CRACKS
Crazing is a defect that looks like a series of cracks in the
surface resembling a chicken wire pattern or a map. Crazing is
seldom a serious problem, especially if the cracks remain tight
and relatively shallow.
The typical cause of crazing is rapid drying of the surface
caused by wind, heat, poor curing, etc. If there is concern as to
the long term durability/wearability of the surface, a treatment
with a high solids sealer is usually appropriate. If the floor
starts to delaminate, resurfacing may be required.
There are many additional problems that can befall a new floor
besides those discussed in this abbreviated article. We hope you
will contact us if you need help or even just information on any
of them. There is never a charge nor any obligation for any
technical assistance we provide via phone or fax. Your new floor
is vital to the productivity of your operations. We hope you will
consider Metzger/McGuire as your floor resource center.
Copyright Metzger/McGuire 2001
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