Marshalltown SG87SH SURFACE SHARK Floor Grinder - Manual (Page 27)

SG87Sh SuRFACE ShARK FLooR GRINDER PAGE 27
The highest degree of surface regularity is found
among the defined traffic floors. Defined traffic floors
allow the designer and contractor to focus on a limited
number of critical areas. When a defined traffic floor
is out of tolerance, it is relatively easy to identify the
defects for correction---usually by employing a grinding
process.
How to Define Surface Regularity.
Since the middle 1980s, new methods of defining
surface regularity have been adopted as national
standards. older methods will continue to be utilized,
although they are less effective. The following methods
will be discussed:
1) The F number system for random traffic floors
2) The TR34 system for defined traffic floors
both methods are not of equal value. For random
traffic floors, F numbers provide the most complete and
consistent system. For defined traffic floors, the TR34
system is superior.
The F number system utilizes a pair of numbers to
define surface regularity. The flatness number, oFF,
is based upon the curvature over a horizontal distance
of 24 inches. The levelness number, Fl, is based upon
the floor slope over a horizontal distance of 10 feet.
The standard test for F numbers is specified in ASTM
E1155 and/or most recent version.With both oFF and
Fl, higher numbers mean greater surface regularity.
Though the scale ranges from zero to infinity, almost
all floors have F numbers between 10 and 100 for both
flatness and levelness. Since the scale is linear, an
oFF50 floor is exactly twice as flat as an oFF25 floor.
Most F number specifications are written in a two
tier format. The overall F numbers apply to the floor
taken as a whole. The local F numbers apply to each
individual slab and are usually only one half to two
thirds the overall values.
The overall F numbers are not just simple averages.
ASTM E1155 covers how to combine F numbers.
The two tier format encourages contractors to achieve
good surface regularity while allowing for minor defects.
The attempt is to pour the entire floor to the specified
overall F numbers. If, for instance, the construction crew
has a bad day and fails to meet the specified overall
numbers for the slab, the slab can still be accepted
provided it meets the specified local numbers. Such
an occurrence serves as a warning to the crew that it
must strive for a better performance on later slabs, so
as to bring the overall F numbers up to the specified
values. If a slab fails to meet even the specified local
numbers, it must be repaired or replaced, but such
failures seldom occur if all parties understand what is
expected from the start.
Designers are not obligated to use this two tier format.
Some designers specify a single F number pair (oFF
and Fl) which applies to each individual slab. but this
also raises the risk that slabs will be rejected.
FIGuRE 21 depicts the overall and minimum F numbers
for various floor classes. The floor classification is
from the American Concrete Institute. Although the F
number system is only a few years old, it offers these
advantages:
a) The system controls both flatness and levelness.
b) There is a standard test method.
c) The system recognizes the statistical nature of
profile testing on random traffic floors.
d) The system is infinitely variable.
FIGuRE 21
one of the major limitations of the F number system is
that it does not control the surface regularity at joints.
because joints are statistical anomalies, the standard
test method forbids measurements within 24 inches.
The designer specifying by F number has two methods
to accommodate the problem. The first solution is
to locate joints at locations where surface regularity
is not important. The second solution is to design
specifications for the joints themselves.