ASTM D5516-18

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Designation: D5516 − 17 D5516 − 18
Standard Test Method for
Evaluating the Flexural Properties of Fire-Retardant Treated
Softwood Plywood Exposed to Elevated Temperatures
This standard is issued under the fixed designation D5516; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method is designed to determine the effect of exposure to high temperatures and humidities on the flexure
properties of fire-retardant treated softwood plywood. In this test method, plywood is exposed to a temperature of 77°C (170°F).
1.2 The purpose of the test method is to compare the flexural properties of fire-retardant treated plywood relative to untreated
plywood. The results of tests conducted in accordance with this test method provide a reference point for estimating strength
temperature relationships. This test method is intended to provide an accelerated test at elevated temperatures and controlled
humidities of plywood sheathing treated with the same chemical formulation(s) and processing conditions as plywood used
commercially.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions
to inch-pound units that are provided for information only and are not considered standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D9 Terminology Relating to Wood and Wood-Based Products
D1165 Nomenclature of Commercial Hardwoods and Softwoods
D2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
D3043 Test Methods for Structural Panels in Flexure
D4933 Guide for Moisture Conditioning of Wood and Wood-Based Materials
D6305 Practice for Calculating Bending Strength Design Adjustment Factors for Fire-Retardant-Treated Plywood Roof
Sheathing
E84 Test Method for Surface Burning Characteristics of Building Materials
E176 Terminology of Fire Standards
E2768 Test Method for Extended Duration Surface Burning Characteristics of Building Materials (30 min Tunnel Test)
2.2 Other Standards:
AWPA C-27 Plywood-Fire Retardant Treatment by Pressure Processes
AWPA U1 Use Category System: User Specification for Treated Wood
NFPA 703 Standard for Fire Retardant Impregnated Wood and Fire Retardant Coatings for Building Materials
This test method is under the jurisdiction of ASTM Committee D07 on Wood and is the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.
Current edition approved April 15, 2017June 1, 2018. Published June 2017August 2018. Originally approved in 1991 as ES 20 – 91. Last previous edition approved in
20092017 as D5516 – 09.D5516 – 17. DOI: 10.1520/D5516-17.10.1520/D5516-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American Wood Protection Association (AWPA), P.O. Box 361784, Birmingham, AL 35236-1784, http://www.awpa.com.
Available from National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471, http://www.nfpa.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5516 − 18
PS 1Voluntary Product Standard U.S. Product Standard for PS1 Structural Plywood
PS 2Voluntary Product Standard U.S. ProductPS2 Performance Standard for Wood-Based Structural Use Panels
3. Terminology
3.1 Definitions—Definitions used in this test method are in accordance with Terminologies D9 and E176 and Nomenclature
D1165.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 depth of beam—that dimension of the beam which is perpendicular to the span and parallel to the direction in which the
load is applied.
3.2.2 span—the total distance between the centerline of supports providing the reactions on which a beam is supported to
accommodate a transverse load.
3.2.3 span-depth ratio—the numerical ratio of span divided by beam depth.
4. Summary of Test Method
4.1 After preconditioning (see 6.5), matched specimens of treated and untreated plywood will be exposed to 77°C (170°F)
temperature and relative humidity equal to or greater than 50 %.
4.2 Flexural strength tests are conducted on exposed specimens removed after various time periods. Flexural strength results
shall include maximum moment, bending stiffness, and work to maximum load. Adjust the test results to 50 % relative humidity
using Practice D6305 procedures (see X1.1.)
4.3 The purpose of this test method is to determine the ratio of the treated mean to the untreated mean for the plywood and plot
the accelerated exposure strength data against exposure time.
5. Significance and Use
5.1 The flexural properties evaluated by this test method are intended to provide any one or all of the following:
5.1.1 Data on the comparative effects of fire-retardant chemical formulations and environmental conditions on the flexural
properties of plywood.
5.1.2 Data for use in developing modification factors for the allowable design properties of treated plywood when exposed to
elevated temperatures and humidities.
5.1.3 Data comparing variables, such as other plywood species and dimensions.
5.2 Results obtained from tests conducted and analyzed in accordance with the procedures of this test method may be used are
suitable for use with other information to establish recommended roof sheathing spans for fire-retardant treated plywood.
NOTE 1—Temperatures lower than the test temperature specified in this test method and the cumulative effects of the elevated temperatures and
humidity exposures expected to be encountered in service should be taken into account when recommended roof sheathing spans are established.
NOTE 2—Practice D6305can be used to extend the laboratory strength data obtained by this test method to design value recommendations. The test
data determined by this test method are used to develop adjustment factors for fire-retardant treatments to apply to untreated plywood design values. The
test data are used in conjunction with climate models and other factors.
6. Test Specimens
6.1 Material Selection:
6.1.1 Source panels for this test shall be selected from grade marked PS 1 or PS 2 commercially available 3, 4, or 5 ply panels
of a single thickness, grade, construction, and bond durability. The nominal panel thickness shall be between 12 mm ( ⁄32 in.) and
16 mm ( ⁄8 in.).
NOTE 3—Southern Pine (as defined in PS 1) is suggested as the test material because it requires higher fire-retardant chemical retentions to obtain the
same flame spread rating compared to other softwood plywood species. Because the bending strength of treated plywood correlates to the chemical
retention levels, Southern Pine plywood is believed to represent a worst case scenario for the same chemical formulation and treating/redrying procedures.
Thus, evaluation of other species of plywood by testing of that species, rather than by application of southern pine test results, are considered to be
indicative of that species only.
6.1.2 Select source panels that provide bending strength specimens after cutting with clear essentially straight-grained faces free
of scoring or other manufacturing defects. The inner plies shall be essentially free of voids, core gaps, and core laps (see 7.3.4.2).
Panels shall have generally uniform grain orientation and percent latewood along and across the panel faces. A minimum of six
sheets of plywood meeting this description is required. Alternate 610 mm0.61 m (2 ft) long sections to be treated and adjacent
untreated 610 mm0.61 m (2 ft) sections (see Fig. 1) shall have visually similar wood quality.
6.1.2.1 Specimens shall be inspected and the culling of specimens done as necessary in accordance with the criteria in 7.3.4.
NOTE 4—A minimum of six sheets of plywood is required but culling of specimens maycould require more sheets.
Available from the U.S. Department of Commerce, 1401 Constitution Ave., NW Washington, DC 20230, http://ts.nist.gov/Standards/Conformity/vps.cfm.
D5516 − 18
FIG. 1 Plywood Cutting Pattern
6.1.3 The specimen cutting pattern and numbering sequence is shown in Fig. 1. Each panel of plywood is to be labeled with
a number from 1 to 6. Cut each sheet crosswise to provide 610 mm by 1220-mm 0.61 by 1.22 m (2 by 4-ft) sections. Each section
is labeled with the sheet number and letter A, B, C, or D. The A and C sections of each of the six panels is to be treated, while
the B and D sections of the six panels are to remain untreated.
6.2 Treatment:
6.2.1 For applications requiring conformance to building code requirements for “fire-retardant-treated-wood” based on Test
Method E84 test extended to 30 min or Test Method E2768, pressure treat the A and C section of each of the six plywood panels
with the fire-retardant formulation being tested. The gage retention level of each charge shall not be less than the value midway
between the middle of the retention range and the maximum retention as specified by the agency certifying the surface burning
characteristics of the treated plywood. The retention range specified by the certifying agency shall result in specimens that provide
a flame-spread index of 25 or less and be reported as showing no evidence of significant progressive combustion throughout the
30-min period, and not allow progression of the flame front beyond a distance of 3.2 m (10.5 ft) beyond the centerline of the
burners anytime during the 30-min test.
6.2.1.1 Alternate methods or processes of imparting fire-retardant properties can be substituted for pressure treatment for
purposes of this test method since this method evaluates the impact of the fire retardant method on the properties of the underlying
plywood.
6.2.1.2 The provisions of 6.2.1 are not intended to prevent use of this test method when the fire-retardant treatments being
certified are for applications other than those requiring conformance to AWPA U1, NFPA 703, or similar code requirements for
“fire-retardant-treated wood” that require the Test Method E2768 or Test Method E84 test extended to 30 min. When alternative
performance criteria for the treatment are being certified, the test report on specimens of that treatment shall state clearly the
alternative performance criteria and that the treatment retention was limited to that required for the alternative performance criteria.
6.2.2 Weigh all plywood sections before and immediately after treatment to determine the chemical retention based on the
solution retained and the concentration of chemicals in the solution. Complete a treating report for each charge of material to
document the treating cycle, times, pressures, and plywood retentions.
6.3 Post-Treatment Drying:
6.3.1 After pressure treatment, kiln dry the twelve treated plywood sections to a maximum moisture content of 15 % following
the standard redrying procedures established for the treatment by the manufacturer. Redry the sections at the manufacturer’s
maximum specified dry bulb temperature with a minus 2°C (4°F) tolerance for 21 h of the first 24-h period. For the remainder of
the drying period, the tolerance shall be minus 3°C (5°F). There is no upper limit on the redrying temperature. Sticker all plywood
sections to obtain proper air flow across the panels and to provide even drying. If the manufacturer’s procedures permit double
stacking of panels intended for structural application, treated plywood test sections also shall be double stacked rather than
stickered individually.
NOTE 5—Research has shown that high kiln drying temperatures can adversely affect the structural properties of wood products. The AWPA and NFPA
standards for fire retardant treated wood products limit kiln dry bulb temperatures. AWPA C-27 requires that the dry bulb temperature of the kiln not
exceed 71°C (160°F) during any kiln drying of plywood treated with fire retardants. In the case of exterior fire retardants that require curing at higher
temperatures, curing after the moisture content is 15 % or less is permitted. However, such elevated curing temperatures must not exceed 99°C (210°F)
and the total curing time must not exceed 48 h. In NFPA 703, the dry bulb temperature must not exceed 71°C (160°F) until the average moisture content
of the wood has dropped to 25 % or less.
NOTE 6—To establish the worst-case flexural properties of treated softwood plywood, the laboratory must redry the test material within a small negative
tolerance of the maximum temperature used by the manufacturer. Therefore, there is no upper limit for the temperature used in the tests. If a manufacturer
desires to establish conservative property values or provide a basis for evaluating production material that exceeds the limit, the test material can be
redried at that temperature. A manufacturer then is allowed to determine the necessary production schedule for their treatment and equipment or
D5516 − 18
conditions. Thus, a stepped schedule (for example, 10 h at 54°C (130°F), 10 h at 60°C (140°F), 10 h at 71°C (160°F), etc.) is allowed by the standard,
provided the maximum temperature tolerance requirement is met. These provisions provide for air-drying production material provided the redry
conditions for the test materials are within the tolerance of the maximum temperature specified by the manufacturer.
6.3.2 Monitor the moisture content of the plywood sections during the drying cycle by individually weighing the sections.
Reduce as much as possible damage or warp during the drying process by adequately supporting the sections. Keep a
well-documented kiln charge report and kiln recorder chart detailing the drying cycle and parameters.
6.4 Specimen Preparation:
6.4.1 After drying, cut the treated and untreated 6100.61 by 1220-mm1.22-m (2 by 4-ft) sections into nominal 750.076 by
610-mm0.61-m (3 by 24-in.) test specimens as shown on Fig. 1. Alternatively, specimen sizes in accordance with Test Methods
D3043, Test Method A shall be used instead of this size. Number these specimens consecutively from 1 to 14, creating 168 treated
and 168 untreated specimens. Randomly select 20 of the 168 untreated and treated specimens as unexposed controls. The
remaining 148 treated and 148 untreated specimens shall be randomly assigned to 7 sets of 20 specimens for both the treated and
untreated material. These are subjected to exposure followed by strength testing. This results in 8 treated and 8 untreated specimens
not assigned to any set for testing (see Note 7).
NOTE 7—The 168 treated and 168 untreated specimens (6.4.1) are 48 more specimens than are needed to be tested. The resulting two extra sets of 20
can be saved as replacement sets if the number of specimens in a set drops below the minimum of 18 (7.3.4). Alternatively, the extra 48 specimens can
be used to increase the number of specimens in each set. A sample size of 28 allows one to estimate a 75 % confidence interval for the 5 % nonparametric
tolerance limit (see Practice D2915).
6.4.1.1 Alternatively, the variation in the mean response can be reduced by a blocked specimen selection where each treated
specimen is end-matched to an untreated specimen from the same original panel. If blocking is used and a specimen is eliminated
either before or after testing, then its mate shall also be eliminated (1).
6.5 Preconditioning—Equilibrate all sets of treated and untreated specimens at an ambient temperature and relative humidity
to achieve an equilibrium moisture content in the untreated specimens of 10 6 2 % (see Table X1.3 in Guide D4933). Specimens
are considered to be at equilibrium moisture content when a constant weight has been achieved. A constant weight is assumed when
two consecutive weighings at a 24-h interval differ by no more than 60.2 %.
7. Procedure
7.1 Specimen Exposure:
7.1.1 After preconditioning, test the unexposed controls (see 6.4.1) as described in 7.3 for initial, unexposed flexural properties.
7.1.2 Expose all the remaining treated and untreated specimen sets in a chamber controlled to 77 6 1°C (170 6 2°F) and a
minimum of 50 % relative humidity. The control of the relative humidity in the chamber shall be 64 % and average 61 % around
the set point.
7.1.3 The first set of 20 untreated and 20 treated specimens shall be s
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