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USDA Forest Service Forest Products Laboratory General Technical Report
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FIELD PERFORMANCE TESTING OF IMPROVED ENGINEERED WOOD FIBER SURFACES FOR ACCESSIBLE PLAYGROUND AREAS
Theodore L. Laufenberg |
Abstract
Some engineered wood fiber (EWF) surfaces on playgrounds
are soft and uneven, which creates difficulties for
those who use mobility aids, such as wheelchairs and walkers.
The outdoor field testing reported in this study is part of
an effort to stabilize EWF to improve accessibility. The
concept is to mix a binder with the upper surface of EWF to
create a stiff (firm) and scuff-resistant (stable) composite
overlayer. Latex, silicone, and polyurethane binders were
evaluated on small plots during a 6-month outdoor trial in
Wisconsin. Tests were performed at regular intervals to
provide a quantitative measure of accessibility. After
6 months of exposure, all the surfaces passed the existing
specifications for impact attenuation of playground surfaces.
Exposure changed impact performance of all systems except
the unsurfaced (without an additive) EWF. The latex and
polyurethane stabilizers consistently met accessibility requirements.
One polyurethane formulation produced a hard
brittle shell that became even harder with exposure and age,
which might increase the injury rate for falls on that surface.
The silicone system failed to maintain integrity adequately
during the rain/dry cycles of the test. Moisture measurements
indicate that the bonded surfaces retard drying of the underlying
EWF, which may have long-term implications for the
rate of decay for these systems.
Keywords: engineered wood fiber (EWF), accessibility,
playground surface, field performance testing
August 2003
Laufenberg, Theodore L.; Winandy, Jerrold E. 2003. Field performance
testing of improved engineered wood fiber surfaces for accessible playground
areas Res. Pap. FPL-GTR-138. Madison, WI: U.S. Department of
Agriculture, Forest Service, Forest Products Laboratory. 10 p.
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Acknowledgments
We gratefully acknowledge Bill Botten, U.S. Architectural
and Transportation Compliance Board, for guidance in
initiating phase II of the development of the stabilized EWF
concept; Ted Illjes and Doug Zeager of Zeager Brothers, Inc.
(Middletown, Pennsylvania), for donating EWF materials
and performing the ASTM F1292 impact tests; Denise and
Peter Axelson of Beneficial Designs, Inc. (Minden, Nevada),
for their support and project review; and Andrzej Krzysik,
Benjamin Henderson, Vicki Herian, Carl Syftestad,
Nancy Keen, Al Christiansen, Lloyd Currier, and other staff
of the Forest Products Laboratory for their assistance during
the project.
Field Performance Testing of Improved
Engineered Wood Fiber Surfaces
for Accessible Playground Areas
Theodore L. Laufenberg, General Engineer
Jerrold E. Winandy, Supervisory Research Wood Scientist
Forest Products Laboratory, Madison, Wisconsin
Background
Traditional engineered wood fiber (EWF) meets nearly all
safety-related expectations of a play surface. The primary
function of EWF playground systems is to prevent head and
limb injuries to playground users by absorbing impact energy.
One barrier to using EWF for playgrounds is the softness
and unevenness of the material, which creates difficulty
for those who use mobility aids, such as wheelchairs and
walkers. In our initial work (Laufenberg and others 2003),
processing techniques and binders were developed and
evaluated to produce wood.resin composite playground
surfaces. Our goals were to enhance user safety by providing
adequate absorption of impact-related energy and to improve
accessibility for users of wheelchairs and walkers. The
EWF.resin composite systems developed consisted of a
combination of a resin and EWF in a thin top surface layer
over unmodified EWF.
We identified designs using compatible resin (i.e., latex,
silicone, and polyurethane) binders and various species and
textures of EWF. Adhesive binders were chosen for their
inert or nontoxic nature and for the retention of a natural
look. Consideration was given to the need to add materials
and for the possibility of patching the surfaces to make them
level after a major impact event. A service life of 3 to
5 years for the playground surface was considered adequate
time for the binder to act prior to renewing the surface by
adding EWF. Because stabilized EWF systems had not been
used for playground surfaces, there was no guarantee or
warranty that they would function for that extended period.
The preliminary evaluation included laboratory testing of
energy absorption and surface firmness on trial surfaces in
0.5- by 0.5-m (18- by 18-in.) plywood boxes at a uniform
depth of 0.3 m (12 in.). In phase I studies (Laufenberg and
others 2003), seven systems were identified in the laboratory
as having reasonable performance. These systems were
evaluated in the phase II outdoor field evaluations, and the
results are reported here.
Present Study
Phase II research focused on outdoor evaluation of the
binder and fiber options identified as minimally acceptable
and promising in the phase I evaluations. In phase II, we
studied field durability and examined changes in long-term
performance by quantifying the impact safety and accessibility
of EWF surfaces after field exposure. Seven surface
treatments and a control surface were installed in a series of
outdoor test beds in Madison, Wisconsin. The binders
evaluated were (a) synthetic latex emulsion, (b) low
molecular weight silicone, and (c) foaming and nonfoaming
resilient polyurethane. Systems were evaluated
over a 6-month period.
Surfacing System Requirements
Stabilizing binders were applied on site or mixed with EWF
no longer than 1 h prior to placing the test surfaces on the
ground. Practical considerations evaluated were (a) cure/set
time prior to surface use, (b) range of EWF moisture and
temperature conditions acceptable for use, and (c) minimal
emission of fumes or odors, workable exotherms, and toxic
or other chemicals from the EWF.resin mixture.
The development guidelines require that a surfacing system
provide impact safety and good accessibility. The Americans
with Disabilities Act (ADA 1990) states that accessible
surfaces shall be stable, firm, and slip-resistant. These criteria
have not been defined adequately within the ADA Accessibility
Guidelines for measurement on any specific surface.
Currently, the only objective method suitable for assessing
the firmness and stability of playground surfacing systems is
the use of a rotational penetrometer (Axelson and Chesney
1999).
Impact safety is quantifiable by American Society for Testing
and Materials ASTM F1292 (ASTM 1999a) and F355
(ASTM 1995). Preliminary evaluation was conducted using
a portable impact test to determine the cushioning performance
of the stabilizing binder. The rotational penetrometer, a
portable measurement device that simulates the action of a
wheelchair caster, was used to assess the level of accessibility.
The portable test apparatuses and training in their use
were provided by two cooperators, Zeager Brothers, Inc.
(Middletown, Pennsylvania), and Beneficial Designs, Inc.
(Minden, Nevada).
The stabilized resin.EWF system needs to provide impact
safety and appropriate accessibility over a number of seasons.
It must retain the performance characteristics of impact
energy absorption and surface resiliency. Impact safety and
accessibility of the EWF surfaces were measured after a
6-month field exposure from April to October 2002 in Madison,
Wisconsin. Subsequent 12-month exposure performance
of each phase II EWF surface continues to be evaluated
while the surfaces are in place.
The stabilized resin.EWF system needs to be nontoxic to
users. Water should be able to drain from both the bonded
surface and unbonded interior of the mat system. This is
critical in reducing the biodeterioration potential of the wood
fiber and in maintaining its cushioning behavior during
subfreezing temperatures.
Materials and Methods
Bonded Impact/Cushioning Surfaces
Eight different test surfaces were formed with surface dimensions
of 1.2 m by 1.2 m by 0.3 m deep (48 in. by 48 in. by 12 in. deep)
(Fig. 1). Seven surfaces had a top layer of
bonded resin.EWF; one surface served as a full-depth control.
In addition, two surfaces (A1 and E1, Fig. 1) were
placed on a slope to assure drainage of the entire test surface.
All surfaces were made of EWF, as defined by ASTM
F2075.01 (ASTM 2001). All test surfaces were compacted
to simulate the finished surface of a play area. Because there
is no industry, governmental, or association definition or
standard for compacting EWF, we followed playground
industry installation practices.
Test surfaces for phase II (Table 1) were selected on the
basis of phase I results. Any phase I system shown to have
undesirable surface stability or resiliency was eliminated
from phase II testing. Phase II surfaces were fabricated from
EWF matched to phase I materials and obtained from a
commercial supplier (licensee of Zeager Bros., Oskaloosa,
Iowa). The baseline control test surface was made with
only EWF.
Four bonding systems were used to fabricate phase II
surfaces:
a. Silicone-based, waterproofing coating (AllGuard, Dow.
Corning Corp., Midland, Michigan)
b. Synthetic latex (Soil-Sement, Midwest Industrial Supply,
Canton, Ohio)
Figure 1. -- Overview of test surfaces in Madison, Wisconsin. See Table 1.
c. Foaming polyurethane (Franklin ReacTITE 8143, Franklin
International, Columbus, Ohio)
d. Non-foaming polyurethane (Vitriturf Vitricon, Polmer
Plastics Corp., Hauppauge, New York)
Table 1. Surfaces evaluated in phase II testsa
|
Surface |
Matrix adhesive |
Top surface thickness |
|
A1, A2 |
35 silicone |
51 |
|
B |
40 silicone |
38 |
|
C |
30 polyurethane |
38 |
|
D |
30 polyurethane |
25b |
|
E1, E2 |
Nonec |
Nonec |
|
F |
30 latex |
64 |
|
G |
25 latex |
51b |
|
H |
30 vitriturf |
38 |
b Single ply of lightweight polyolefin landscaping geotextile
placed between unbonded and bonded layers.
c Control.
An interfacial treatment was used for two surfaces (D and G,
Table 1, Fig. 1). A 1.2- by 1.2-m (48- by 48-in.) single-ply
layer of lightweight polyolefin landscaping geotextile was
placed between the unbonded and bonded layers of these
surfaces. The geotextile was intended to provide continuity
for the thinner bonded surface layers in the event of a fracture
through the entire thickness. Should this happen, the
layer could be thrust from its original position and become a
hazard on the remaining bonded surface.
Installation of Test Surfaces
In accordance with general EWF design and construction
practice, the full-depth surfaces were prepared to the requirements
for permanent playground surfaces (Fig. 2).
Installation began on February 27, 2002, and surfaces were
bonded within 6 weeks. Installation proceeded as follows:
1. Excavate area 380 mm (15 in.) in depth with a minimum
of 1% grade to ensure proper drainage. Remove roots,
stones, and vegetation.
2. Place diversion along slope above test area to ensure no
direct site drainage into surfaced area.
3. Cover entire subgrade with one layer of geotextile. Overlap
courses of geotextile by 125 mm (5 in.).
Figure 2. -- Representational cross-section of installed
surfaces. Note that EWF thickness includes thickness
of any stabilized EWF layer.
4. Cover excavated surface to 75-mm (3-in.) depth with
washed 18-mm (3/4-in.) stone.
5. Cover entire drainage bed with one layer of geotextile.
Overlap courses of geotextile by 125 mm (5 in).
6. Spread EWF to depth 1.5 times target depth and compact
uniformly, resulting in density 50% greater than bulk
(uncompacted) density.
7. Hand rake for smooth finished surface.
8. Install plywood retaining borders (15 mm thick by
100 mm wide, 0.6 in. thick by 4 in. wide) between
each pad.
9. Prepare and install top surface1
a. Place EWF in 60-liter (15-gallon) mixing bin. Measure
needed material by volume (1.5 × volume needed).
b. Measure EWF moisture content.
c. Measure binder as proportion of EWF dry weight.
d. Mix EWF and binder using a mixing paddle.
e. If required, place single layer of geotextile on EWF.
f. Immediately dump resin.EWF mixture onto target pad,
spread with hand tools to even thickness, and flatten
with 1.2-m by 1.2-m by 15 mm (4-ft by 4-ft by 5/8-in.)
piece of plywood using firm pressure to bring cushioning
pad thickness to full 0.3-m (12-in.) depth required
for unbonded EWF.
1 Operation requires monitoring of temperature. Most stabilizing binders require 24 h temperatures greater than 4°C (40°F) for proper curing.
Test Procedures
Accessibility
Figure 3. -- Rotational penetrometer in use on surface A2.
Periodically over the 6-month exposure and again after the
6-month impact tests, all surfaces were tested with a Beneficial
Designs rotational penetrometer (Figs. 3 and 4). This
device subjects the surface to a low-speed rotational bearing
test meant to simulate the weight and action of a front caster
wheel on a wheelchair. The procedures used were based on
the draft Rehabilitation Engineering and Assistive Technology
Society of North America national standard test method
for the firmness and stability of ground and floor surfaces
(RESNA 2000), with the exception that only one reading
was recorded instead of the average of five readings. This
test provides objective measures of firmness and stability of
surfaces. It has been correlated to the work measurement
done in ASTM F1951 (ASTM 1999b) for a wide array of
surfacing and floor coverings. The test was conducted
1 week after surface installation and each month thereafter
using the rotational penetrometer and protocol for assessing
the bearing/rotational indentation on each surface (Axelson
and Chesney 1999). Each surface was tested at a unique
location around its periphery.
Impact Attenuation
Impact tests were conducted by Doug Zeager and Ted Illjes
of Zeager Brothers, Inc. (Middletown, Pennsylvania). The
impact test was completed after the test surfaces had been
exposed for 6 months. ASTM F 1292.99 (ASTM 1999a)
test specifications and F355.95 (ASTM 1995) test methods
were used at a constant test drop height of 3.05 m (10.0 ft).
Three impact tests per test surface were run in sequence
according to the specifications. A tripod was erected to
center the impactor over each test surface (Fig. 5). Per
ASTM F355, the instrumented headform was mounted
on a magnetic release over the center of the surface.
Figure 4. -- Accessibility test with rotational penetrometer. Stability readings taken after caster wheel was rotated 360°.
(a) Poor stability of surface A2 indicated by amount
of silicone-coated EWF displaced by rotated caster wheel;
(b) good stability of surface G.
The first impact was ignored, and the data were collected
from the second and third impacts. Immediately after impact
testing, EWF samples were obtained from each surface for
moisture content determination.
Moisture Content and Durability
Figure 5. -- Impact attenuation test. A 4.5-kg (10-lb)
hemispherical impact head was installed 3 m (10 ft)
over surface D. Ted Illjes (on ladder) holds
instrumentation package connected to impactor by
coiled wire. Doug Zeager awaits arrival of impactor,
which will be caught on first rebound from surface.
The field systems were installed and exposed outdoors for a
minimum of 6 months. The intent was to expose the test
surfaces to a wide range of climatic conditions, freeze.thaw
cycles, and seasonal conditions (spring rain and summer
heat). Evaluation of the permeability of the surface and of
the entire mat was subjective. After the 6-month exposure
period, samples were taken from the surface layer and the
EWF just beneath the bonded surface. These samples provided
data on wood fiber moisture content and density. One
test surface was excavated through its entire 0.3-m (12-in.)
depth to determine the moisture profile of the resin.EWF
system. A 50-mm- (2-in.-) diameter observation pipe was
also inserted into this surface to monitor groundwater at the
test site.
Results and Discussion
Accessibility
Tests of surfaces using the rotational penetrometer began
1 week after installation and were performed monthly.
Measurements of firmness and stability taken with the rotational
penetrometer showed a considerable amount of variation
(Tables 2 and 3). Factors that may have contributed to
this variation include (a) inherent variability in the physical
composition of the EWF surfaces, (b) temperature-related
fluctuations in resin.EWF surface properties, and (c) the fact
that only single readings were taken in different locations.
In a previous study involving 39 human subjects, measurements
of surface firmness and stability taken with the rotational
penetrometer were shown to correlate with the amount
of wheelchair work as measured according to ASTM
F1951.99 (ASTM 1999b) and with the amount of energy
required to ambulate or wheel across the surface (Axelson
and Chesney 1999). Study participants, including wheelchair
users and those who ambulated with and without mobility
aids, negotiated long (400-m, 1,312-ft) test courses to determine
energy expenditure. The results of this study were used
to develop a classification system for levels of firmness and
stability based on rotational penetrometer readings.
Firmness
Firmness is defined as the depression of a surface when a
controlled load is placed on it. The categories of firmness
suggested by Axelson and Chesney (1999) are as follows:
- Firm.7.6 mm (0.3 in.) or less depression
- Moderately firm.more than 7.6 mm (0.3 in.)
but less than 12.7 mm (0.5 in.) depression - Not firm.12.7 mm (0.5 in.) or more depression
This classification system was deemed appropriate for our
study. Moderately firm and moderately stable were deemed
acceptable ratings for the short distances traveled. (Play
areas are considered short travel distances, whereas trails
and paths are considered long distances and would require
the rating of firm.)
In only one instance was a surface rated as not firm, the May
reading of the A2 surface (silicone binder). Most polyurethane
surfaces (C, D, and H) were rated as firm. During the
heat and dryness of summer, the polyurethanes as a class
were rated as moderately firm. From fall until the end of
testing, all three polyurethanes were rated as firm. All other
surfaces, including the EWF, were consistently rated as
moderately firm.
Table 2. Surface firmness as measured by rotational penetrometer
Surface firmness (mm) at various times
|
Surface |
1 week |
1 month |
2 months |
3 months |
4 months |
5 months |
6 months |
|
A2 |
9.7 |
12.2 |
14.2 |
9.9 |
10.2 |
10.7 |
9.9 |
|
B |
10.4 |
9.7 |
11.0 |
9.4 |
9.4 |
9.7 |
10.2 |
|
C |
5.1 |
5.1 |
5.1 |
7.4 |
7.9 |
4.6 |
3.8 |
|
D |
6.4 |
5.1 |
4.8 |
10.2 |
7.9 |
6.1 |
4.3 |
|
E2 |
10.2 |
8.6 |
9.1 |
8.1 |
10.7 |
10.4 |
7.9 |
|
F |
10.2 |
7.6 |
8.6 |
10.2 |
10.9 |
11.9 |
9.7 |
|
G |
9.7 |
8.4 |
9.7 |
11.9 |
8.6 |
8.6 |
8.6 |
|
H |
5.8 |
5.1 |
4.8 |
12.7 |
9.9 |
8.1 |
6.6 |
Table 3. Surface stability as measured by rotational penetrometer
Surface stability (mm) at various times
|
Surface |
1 week |
1 month |
2 months |
3 months |
4 months |
5 months |
6 months |
|
A2 |
15.2 |
262.6 |
258.8 |
23.6 |
24.9 |
20.1 |
24.9 |
|
B |
19.8 |
529.1 |
22.6 |
255.8 |
21.3 |
22.4 |
24.1 |
|
C |
5.6 |
6.4 |
5.8 |
8.6 |
9.4 |
6.6 |
5.3 |
|
D |
7.6 |
5.6 |
5.6 |
10.2 |
9.1 |
7.6 |
5.8 |
|
E2 |
19.1 |
19.1 |
18.0 |
18.3 |
19.5 |
20.1 |
19.6 |
|
F |
11.2 |
8.6 |
9.6 |
12.2 |
13.2 |
13.0 |
10.7 |
|
G |
10.4 |
264.2 |
11.2 |
13.7 |
12.2 |
12.4 |
11.4 |
|
H |
6.9 |
5.8 |
5.8 |
14.0 |
11.2 |
9.1 |
7.4 |
Stability
Stability is defined as depression of the surface by a simulated
wheelchair caster and the ability of the caster to resist
further erosion or indentation as a result of 360° rotational
movement. The categories of stability suggested by Axelson
and Chesney (1999) are as follows:
- Stable.12.7 mm (0.5 in.) or less indentation or erosion of
surface - Moderately stable.more than 12.7 mm (0.5 in.) and less
than 25.4 mm (1 in.) indentation or erosion of surface - Not stable.more than 25.4 mm (1 in.) indentation or
erosion of surface
In the 6 months of testing, the silicone surfaces (A2 and B)
were rated as moderately stable or even as not stable on
many occasions, whereas the other treatments were typically
rated as stable (Fig. 4). The unstabilized EWF surface (E2)
was consistently rated as moderately stable. In several isolated
instances, the latex and non-foaming polyurethane
surfaces were rated as moderately stable.
In summary, the polyurethane systems were rated as stable in
nearly all tests and conditions. The latex systems performed
much better than did the silicone and the control EWF surfaces.
Most noteworthy is that the silicone surfaces became
unstable within the first month and did not improve. The
silicone-coated wood elements became disassociated from
one another in the first month of the test. The silicone was
not able to bond the wood fiber in a matrix after the EWF
became wet. Within 2 months, the entire surfaces of A2 and
B, in which the top layer was composed of silicone-coated
wood fiber, became loose (unbonded).
Impact Attenuation
The results of impact testing are summarized in Table 4. The
specifications (F1292, ASTM 1999a, and F355, ASTM
F355) call for a maximum deceleration 200 g. Considering
the mode of falls on playgrounds, the maximum g was chosen
for the playground application to balance the cost of the
cushioning surface with the expectation for injury from falls.
As a relative comparison, it is useful to note that the U.S.
Department of Transportation standard test for motorcycle
helmets requires the helmet to bring an instrumented headform
to rest without exceeding 400 g.
All surfaces passed the existing specifications for impact
attenuation of playground surfaces. The significant observation
is that all the polyurethanes exhibited higher g values
overall, in comparison with EWF, silicone, and latex stabilized
EWF. Only the polyurethanes exceeded 100 g, but
none exceeded 140 g.
A similar observation can be made for the head injury criteria
(HIC). All the surfaces passed the existing HIC specifications,
that is, HIC is not to exceed 1,000. The HIC value of
1,000 is generally presumed to correlate with the impact
dynamics required to cause a brain concussion. Again, as
a group, the polyurethanes, both foaming and non-foaming,
had the highest HIC values of all the surfaces tested. The
minimum value was 472 and the highest 825. The HIC
values of all other surfaces ranged from 265 to 387. We
presume that an HIC of 825 will result in a higher percentage
of fall injuries than will a surface with an HIC of 400.
Table 4. Results of surface impact testing in study phases I
(no exposure) and II (6 months exposure) per ASTM F1292a
Deceleration (g) HIC
Drop 2 Drop 3 Drop 2 Drop3
|
Surface |
Phase I |
Phase II |
Phase I |
Phase II |
Phase I |
Phase II |
Phase I |
Phase II | |
|
A2 |
52 |
72 |
57 |
71 |
244 |
20.1 |
24.9 |
265 | |
|
B |
53 |
81 |
62 |
79 |
213 |
22.4 |
24.1 |
320 | |
|
C |
67 |
139 |
62 |
130 |
332 |
6.6 |
5.3 |
740 | |
|
D |
68 |
109 |
63 |
109 |
350 |
7.6 |
5.8 |
541 | |
|
E2 |
68 |
83 |
76 |
81 |
274 |
20.1 |
19.6 |
306 | |
|
F |
55 |
85 |
54 |
90 |
236 |
13.0 |
10.7 |
387 | |
|
G |
56 |
83 |
60 |
87 |
312 |
12.4 |
11.4 |
318 | |
|
H |
65 |
103 |
69 |
101 |
325 |
9.1 |
7.4 |
472 |
a ASTM 1999a.
A difference in behavior (Tukey tests, a = 0.25) differentiated
the polyurethane surfaces from the latex and silicone
surfaces. The impact performance of silicone, latex, and
unstabilized EWF was statistically indistinguishable. We are
able to state with some confidence that 6 months of aging
had a significant negative influence on impact performance
for all systems except the unsurfaced EWF.
Moisture Content and Durability
Because of the in-situ nature of the tests and the size of the
test surfaces, we did not have a means for nondestructively
evaluating moisture content or durability of these surfacing
systems. Thus, we relied on visual evaluation of the surfaces
during the 6-month exposure period; moisture content samples
were removed after the test period (Figs. 6 and 7). Data
on surface layer density and moisture content and EWF
moisture content just beneath the surface layer are shown in
Table 5 and Figure 8.
Moisture content measurements indicated that the bonded
surface layers, on average, were not as wet (by weight) as
the E2 surface (unstabilized EWF). The measurement of
moisture content is misleading because of the nonhygroscopic
properties of the binder. However, the EWF under
the stabilized surfaces was wetter than the bonded surface
layers. This suggests that the EWF.resin surface layer
retarded the drying process, which, in turn, saturated the
underlying EWF.
Another representation of EWF moisture content is shown
in Table 6 and Figure 9. The trendline fitted to the data of
the E2 moisture profile (Fig. 9) indicates that saturation
occurred at a depth of approximately 100 mm (4 in.) and
continued to the drainage bed. Additional study would yield
knowledge of the rate of decay under these very wet/ saturated
conditions. We have no quantified model for predicting
the loss (decay) of woody material under these moisture
conditions. We could easily presume that the development of
a stabilized resin.EWF system with reduced moisture content
in the unbound EWF would result in a beneficial reduction
of decay rate. This, in turn, would extend the life of
stabilized EWF in situ on playground surfaces.
Concluding Remarks
Impact Attenuation
- All surfaces passed existing specifications for impact
attenuation of playground surfaces. - Polyurethanes exhibited higher g values overall (in c
parison to g values of EWF alone, silicone-stabilized
EWF, and latex-stabilized EWF) and only the polyurethanes
exceeded 100, but none exceeded the maximum
allowed, 200 g. - All surfaces passed existing HIC specifications
(HIC < 1,000); polyurethanes, both foaming and nonfoaming,
had the highest HIC values of all surfaces tested. - Silicone, latex, and unstabilized EWF are not statistically
distinguishable (a = 0.05) in impact performance. - Six months of aging significantly (a = 0.25) changed the
impact performance of all systems except unsurfaced
(without an additive) EWF.
Figure 6. -- Removal of test sample for determination of
density and moisture content of surface layer and EWF
beneath surface.
Figure 7. -- Archeological-type excavation for
determining moisture profile of E2 surface. Note
gravel at bottom of 0.3-m (12-in.) excavation.
Accessibility
- Firmness
- Silicone surfaces were rated as moderately firm except
for one silicone surface, which was rated as not firm. - Polyurethane surfaces were usually rated as firm except
in summer, when the rating changed to moderately firm. - EWF and latex surfaces were consistently rated as moderately
firm. - Stability
- Polyurethane surfaces were rated as stable in nearly all
tests and conditions. - Silicone surfaces were rated as unstable early in the exposure
period. - EWF and latex surfaces were consistently rated as moderately
stable.
Table 5. -- Surface layer specific gravity and moisture
content and moisture content of EWF beneath surface
Surface Layer
|
Surface |
Dry |
Average moisture |
Moisture |
|
A2 |
0.265 |
22 |
131 |
|
B |
0.293 |
48 |
123 |
|
C |
0.438 |
45 |
160 |
|
D |
0.416 |
35 |
132 |
|
E2 |
0.206a |
24b |
76c |
|
F |
0.179 |
31 |
156 |
|
G |
0.149 |
18 |
82 |
|
H |
0.514 |
33 |
134 |
a Top 25 mm (1 in.).
b Top 12 mm (0.5 in.).
c Sampled at 25 mm (1 in.).
Moisture Content and Durability
- EWF beneath the stabilized surface was significantly
wetter than unsurfaced EWF. - Stabilized surface layers retarded the drying process for
the underlying EWF, saturating it. - Additional study should focus on moisture levels and rate
of decay under stabilized surfaces, which seem to exacerbate
EWF wet/saturated conditions.
Recommendations
We recommend that the next phase of development should
be to install larger surfaces in a working playground to
evaluate accessibility and durability. The stabilizers that
have met the requirements for this next phase include the
polyurethanes and latex systems. We believe it best to
choose one commercially available binder for each type of
adhesive system. From the standpoint of impact and accessibility
performance, the polyurethane Vitriturf and the latex
Soil-Sement are the best candidates. The polyurethane
ReacTITE produced a hard brittle shell that hardened even
more with age, which would increase the injury rate for
falls on the surface. The silicone AllGuard system did not
maintain its integrity adequately to bond EWF into a
contiguous mat.
Figure 8.Comparison of average moisture content of stabilized surface layers with moisture content of EWF immediately beneath surface.
Table 6. -- Moisture profile data for EWF
|
EWF |
Wet |
Dry |
Moisture |
Depth |
|
E1 |
23.8 |
13.5 |
76 |
2.5 |
|
E2 |
24.7 |
11.3 |
119 |
5.0 |
|
E3 |
25.8 |
10.7 |
141 |
7.5 |
|
E6 |
23.6 |
9.5 |
148 |
15.0 |
|
E9 |
25.9 |
10.4 |
149 |
22.5 |
|
E12 |
24.5 |
9.6 |
155 |
30.0 |
Before recommendations for public acceptance of any candidate
resin. EWF system or systems can be made, there is a
critical need for a full-scale phase III field assessment to
increase our understanding of the ongoing performance and
durability of the system. Using a larger pad than that used in
phase II would allow five repetitions to be performed with
the rotational penetrometer to reduce test variability and
edge effects. At minimum, a 3- by 3-m (10- by 10-ft) surface
should be installed on a working playground being accessed
regularly by children. System performance and moisture and
temperature profiles through the depth of the candidate
EWF.resin system or systems should be carefully monitored
during a 2-year field exposure. Industry leaders should be
consulted to identify two configurations of each of the two
binder systems.
Figure 9. -- Profile of moisture content through EWF of
surface E2 and trendline fitted through measurements.
ADA. 1990. Public law 101.336. Americans With Disabilities
Act, Public Law 336, 101st Congress, enacted July 26,
1990.
ASTM. 1995. Standard test method for shock-absorbing
properties of playing surface systems and materials. ASTM
F355.95, Vol. 15.07. West Conshohocken, PA: American
Society for Testing and Materials.
ASTM. 1999a. Standard specification for impact attenuation
of surface systems under and around playground equipment.
ASTM F1292.99. West Conshohocken, PA: American
Society for Testing and Materials.
ASTM. 1999b. Standard specification for determination of
accessibility of surface systems under and around playground
equipment. ASTM F1951. West Conshohocken, PA:
American Society for Testing and Materials.
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fiber. ASTM F2075.01, Vol. 15.07. West Conshohocken,
PA: American Society for Testing and Materials.
Axelson, P.W.; Chesney, D. 1999. Accessible exterior
surfaces. Tech. rep. Washington, DC: United States Architectural
and Transportation Barriers Compliance Board.
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playgrounds. FPL.GTR-135. Madison, WI: U.S.
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Laboratory. 15 p.
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firmness and stability. Working draft standard. Arlington,
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Society of North America. 11.20. info@resna.org
