ASTM C956-04(2019)
(Specification)Standard Specification for Installation of Cast-In-Place Reinforced Gypsum Concrete
Standard Specification for Installation of Cast-In-Place Reinforced Gypsum Concrete
ABSTRACT
This specification covers the minimum requirements for the installation of cast-in-place reinforced gypsum concrete over permanent formboard. Subpurlins shall be designed to support live and dead loads of the roof deck. Got-rolled and cold-rolled steel shapes other than bulb trees or truss tees shall meet the requirements of this specification. Mineral fiber formborad shall be tested in accordance with the transverse loading test. Hexagonal reinforcing mesh, rectangular reinforcing fabric, gypsum concrete, and expansion filler strip shall be fabricated in accordance to the specification. The subpurlins shall be placed transversely to the purlins and primary framing and shall be spaced to suit the size of the formboards. Cross tees shall be provided where formboard ends are supported by purlins or the primary framing. Formboards shall be located face down on the flanges of the supporting members and with the ends on top of the purlins. The mesh of wire fabric shall be located with the main longitudinal wires at right angles to the subpurlins and adjacent to the formboard at midspan between the purlins. Expansion filler strips shall be placed continuously against the walls, curbs, nailers, or other rigid surfaces that gypsum concrete will abut. Gypsum concrete mixing and placement shall be performed. Mixing shall be thorough but not overmixed.
SCOPE
1.1 This specification covers the minimum requirements for the installation of cast-in-place reinforced gypsum concrete over permanent formboard.
1.2 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered requirements of the standard.
1.4 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.
General Information
Relations
Standards Content (Sample)
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.
Designation:C956 −04 (Reapproved 2019)
Standard Specification for
Installation of Cast-In-Place Reinforced Gypsum Concrete
This standard is issued under the fixed designation C956; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope C11Terminology Relating to Gypsum and Related Building
Materials and Systems
1.1 This specification covers the minimum requirements for
C317/C317MSpecification for Gypsum Concrete
the installation of cast-in-place reinforced gypsum concrete
C726Specification for Mineral Wool Roof Insulation Board
over permanent formboard.
E72Test Methods of Conducting Strength Tests of Panels
1.2 The values stated in inch-pound units are to be regarded
for Building Construction
as the standard. The values given in parentheses are for
2.2 American Concrete Institute Standard:
information only.
ACI 318Building Code Requirements for Reinforced Con-
1.3 The text of this standard references notes and footnotes 4
crete
which provide explanatory material.These notes and footnotes
2.3 American Welding Society Standard:
(excluding those in tables and figures) shall not be considered
D1.1Structural Welding Code Steel
requirements of the standard.
1.4 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions shall be in accordance with Terminology
ization established in the Decision on Principles for the
C11.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3.2 Definitions:
Barriers to Trade (TBT) Committee.
3.2.1 primary framing, n—structural members provided to
support the reinforced gypsum concrete roof deck assembly.
2. Referenced Documents
3.2.1.1 purlin, n—a secondary structural member that spans
2.1 ASTM Standards:
the primary framing members and provides support for sub-
A82/A82MSpecification for Steel Wire, Plain, for Concrete
purlins.
Reinforcement (Withdrawn 2013)
3.2.2 subpurlin, n—a steel member applied transversely to
A185/A185M Specification for Steel Welded Wire
the primary framing and purlins to support the formboards and
Reinforcement, Plain, for Concrete (Withdrawn 2013)
to transmit the dead and live loads from the gypsum concrete
A568/A568M Specification for Steel, Sheet, Carbon,
slab to the primary framing.
Structural,andHigh-Strength,Low-Alloy,Hot-Rolledand
3.2.2.1 bulb tee, n—a subpurlin, hot-rolled formed steel,
Cold-Rolled, General Requirements for
rail-shaped section.
A653/A653MSpecification for Steel Sheet, Zinc-Coated
(Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed)
3.2.2.2 truss tee, n—a subpurlin fabricated from steel wire
by the Hot-Dip Process
and strip, tee-shaped section.
3.2.3 cross tee, n—asteeltee-shapedsectionusedtosupport
a formboard end at right angles to the subpurlins where a
This specification is under the jurisdiction of ASTM Committee C11 on
formboard end does not occur over the purlin or primary
GypsumandRelatedBuildingMaterialsandSystemsandisthedirectresponsibility
framing.
ofSubcommitteeC11.03onSpecificationsfortheApplicationofGypsumandOther
Products in Assemblies.
3.2.4 formboard, n—sheet material used as a permanent
Current edition approved Oct. 1, 2019. Published October 2019. Originally
form to support the gypsum concrete.
approved in 1981. Last previous edition approved in 2015 as C956–04(2015).
DOI: 10.1520/C0956-04R19.
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 AvailablefromAmericanConcreteInstitute(ACI),P.O.Box9094,Farmington
the ASTM website. Hills, MI 48333-9094, http://www.concrete.org.
3 5
The last approved version of this historical standard is referenced on Available from American Welding Society (AWS), 550 NW LeJeune Rd.,
www.astm.org. Miami, FL 33126, http://www.aws.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C956−04 (2019)
3.2.5 reinforcement, n—steel wire mesh or fabric used supported at the perimeter with a frame providing 1 in.
within the gypsum concrete slab to provide longitudinal and (25.4mm) bearing on ends and ⁄2 in. (12.7 mm) bearing on
transverse strength. edges and 7 in. (177.8 mm) nominal clearance from the bed of
the apparatus.
3.2.6 double-pouring, n—the application of gypsum con-
7.3.1.3 For formboards ⁄4 in. (19.0 mm) thick, test speci-
creteinmorethanonelayertocompletethefullslabthickness.
mensshallbe48in.(1200mm)longby24in.(600mm)wide.
See 8.7.4.3.
7.3.1.4 Forformboards1in.(25.4mm)thickorgreater,test
3.2.7 ribbon-pouring or strip-pouring, n—theapplicationof
specimens shall be 48 in. (1200 mm) long by 32 in. (800 mm)
narrow ribbons of gypsum concrete, about 10 to 12 in. (254 to
wide.
305 mm) wide by 1 to 1 ⁄2 in. (25.4 to 38.1 mm) deep, across
7.4 Reinforcement, Specification A82/A82M, shall be fab-
the width of the formboard at center of span between purlins.
ricated from zinc-coated (galvanized) welded or woven steel
4. Delivery of Materials wire mesh or fabric having an effective cross-sectional area of
2 2
not less than 0.026 in. (16.77 mm) per foot of slab width.
4.1 Materials shall be delivered in original packages,
Reinforcement shall be free of rust, scale, or other materials
containers, or bundles bearing the brand name and name of
that reduce bond to the gypsum concrete.
producer or seller. Bulk materials shall be delivered with the
7.4.1 Hexagonal Reinforcing Mesh,shallbefabricatedfrom
brand name and name of the producer or seller shown on the
2 in. (50.8 mm) hexagonal mesh formed of not less than
accompanying bills of lading.
0.0410in. (1.04 mm) diameter wires with longitudinal wires
not less than 0.0625 in. (1.59 mm) in diameter, spaced not
5. Storage of Materials
morethan3in.(76.2mm)oncenters.Steelwireforfabricating
5.1 All materials shall be stored in a manner that prevents
wire mesh and fabric—Specification A82/A82M.
damage before use. When stored under tarpaulins, ventilation
7.4.2 Rectangular Reinforcing Fabric, Specification A185/
shall be provided to prevent moisture accumulation under the
A185M, shall be fabricated from longitudinal wires not less
tarpaulin.
than 0.1055 in. (2.68 mm) in diameter spaced not more than 4
5.2 Formboard shall be stored flat and off the ground.
in. (102 mm) on centers and transverse wires not less than
Handling and stacking shall be done in such a manner to
0.0800 in. (2.03 mm) in diameter spaced not more than 8 in.
preventdamagetoface,ends,andedgesandkeepdryuntiluse.
(203 mm) on centers.
5.3 Whenitisnecessarytostoregypsumconcreteatthejob
7.5 Gypsum Concrete,SpecificationC317/C317M, ClassA.
site, the gypsum concrete shall be stored off the ground and
7.6 Water, shall be potable and free of substances that could
kept dry until use.
adversely affect the gypsum concrete.
6. Environmental Conditions 7.7 Expansion Filler Strip, shall be not less than ⁄4 in.
(19mm) thick and equal in height to the abutting gypsum
6.1 The minimum temperature at which gypsum concrete is
concrete and of the type specified by the producer of the
mixed and placed is not specified. Gypsum concrete shall not
gypsum concrete.
be mixed with water containing ice crystals.
NOTE 1—An exothermic reaction during setting ensures complete
8. Installation
hydration before freezing.
8.1 Installation of Subpurlins:
7. Materials 8.1.1 Installation, Normal:
8.1.1.1 Subpurlins—The subpurlins shall be placed trans-
7.1 Subpurlins:
versely to the purlins and primary framing and shall be spaced
7.1.1 Subpurlins shall be designed to support live and dead
tosuitthesizeoftheformboardsspecified.Subpurlinsshallbe
loads of the roof deck.
of sufficient length so that their joints occur over purlins or
7.1.2 Hot-rolledandcold-rolledsteelshapesotherthanbulb
primaryframing.Subpurlinjointsshallbealternatedsothatthe
tees or truss tees shall meet the requirements of this specifica-
joints are staggered one purlin space.
tion for subpurlins.
8.1.1.2 Subpurlins shall be welded to purlins and steel
7.2 Cross Tees, shall be not less than 1 ⁄4 in. (31.75 mm)
primary framing with ⁄8 in. (3.2 mm) fillet welds not less than
wideby ⁄2in.(12.7mm)high,fabricatedfromnotlessthan26
⁄2in.(12.7mm)longonalternatesidesofthesubpurlinateach
gage zinc-coated steel conforming to Specifications A653/
intersection with purlins. Except as otherwise specified, weld-
A653M or A568/A568M.
ing shall be in accordance with AWS D1.1. Where primary
7.3 Formboard: framing is of wood, nails not less than 16d shall be used on
7.3.1 Mineral Fiber Formboard, Specification C726, not each side of the subpurlins at each intersection.The nails shall
3 3
be bent over approximately ⁄4 in. (19 mm) to securely clinch
less than ⁄4 in. (19.0 mm) thick nor more than 3 in. (76 mm)
2 2
thick. It shall sustain a uniform load of 20 lb/ft (97 kg/m ). the flange of the subpurlin.
7.3.1.1 Mineral fiber formboard shall be tested in accor- 8.1.2 Installation Seismic:
dance with the transverse loading test of Test Methods E72. 8.1.2.1 Subpurlins—The subpurlins shall be welded at each
7.3.1.2 The test specimen shall be uniformly loaded and intersection with the purlins with ⁄8-in. (3.2-mm) fillet welds
supported at both edges and ends. The test specimens shall be not less than 1 in. (25.4 mm) long, on one side. Both sides of
C956−04 (2019)
the subpurlin shall be welded with ⁄8-in. fillet welds not less 8.7.3.1 Calcium chloride or other admixtures shall not be
than2in.(50.8mm)longwheresubpurlinjointsoccuroverthe added to the gypsum concrete.
purlin. Both sides of the subpurlin shall be welded with ⁄8-in.
8.7.4 Placement:
fillet welds not less than 2 in. long at shear transfer points and
8.7.4.1 General—To avoid exposure to inclement weather
at intersections with exterior frame.
and physical abuse, gypsum concrete shall be placed the same
8.1.3 Maximum Spans—Refer to X2.1.3.
day as the installation of the formboard and reinforcement
8.2 Cross Tees—Cross tees shall be provided where form-
materials.
board ends are supported by purlins or the primary framing.
(a) The deck shall be poured in sections of similar size.
8.3 Formboards—Formboards shall be located face down
8.7.4.2 Screeds Grounds—Screeds, such as metal bars or
on the flanges of the supporting members and with the ends on
wood strips, shall be spaced approximately 10 ft (3050 mm)
top of the purlins.
apart at right angles on top of the subpurlins at a height that
8.3.1 Gypsumconcreteshallnotbepouredoverformboards
will allow the gypsum concrete slurry to be leveled at the
which have been wetted by rain or snow.
specified thickness.
8.3.2 Thegypsumconcreteshallbepouredonthesameday
(a) Gypsum concrete cants, curbs, and drainage slopes shall
the formboards are installed.
be placed to the design thickness. Curbs around openings shall
8.4 Reinforcement—The mesh of wire fabric shall be lo-
be permitted to be formed with the formboard.
cated with the main longitudinal wires at right angles to the
8.7.4.3 Thegypsumconcreteshallbedischargedintoplace-
subpurlins and adjacent to the formboard at midspan between
ment equipment immediately after completion of mixing.
the purlins. Ends of the reinforcement shall be lapped not less
(a)The slurry shall be poured or discharged not more than
than 4 in. (102 mm) or one mesh, whichever is greater.
8.4.1 Edges shall be butted, not lapped, unless required for 24 in. (600 mm) off the formboard to minimize impact and
allowed to build to full thickness in one continuous operation.
fire rated or horizontal diaphragm construction. Reinforcement
shall be cut to fit at walls, curbs, and openings, folded over on Double pouring shall not be permitted.
to itself, and extended into all areas when gypsum concrete is (b)Assoonastheslurryhasstiffenedenoughtoholdafull
to be placed.
level, it shall be screeded to a true, even surface using a
smooth, rigid straight-edge.
8.5 Expansion Filler Strips—Expansion filler strips shall be
placed continuously against the walls, curbs, nailers, or other
8.7.4.4 Place gypsum concrete cants, curbs, and drainage
rigid surfaces that gypsum concrete will abut.
slopes to the design thickness. Curbs around openings shall be
permitted to be formed with the formboard.
8.6 Expansion Joints—Expansion joints shall be located at
expansion joints found in the main structure, at a maximum of
8.8 Roof Overhangs—Gypsum concrete shall not be placed
200 ft (61 m) on center in a direction parallel to the subpurlins
on roof overhangs, eaves, or other similar locations, on
on large buildings, at intersections of wings on L-, U-, T-, and
formboards unless the underside is protected against direct
H-shaped buildings and, wherever the roof framing changes
wetting by a suitable facia drip cap overhang.
direction. See X1.5.5.
8.9 Drying—Construction moisture shall be removed from
8.7 Gypsum Concrete Mixing and Placement:
the building to permit drying of completed gypsum concrete
8.7.1 General—All equipment, including mixers, pumps,
slab, providing heat and ventilation where required. See X1.3.
hoses, tools, and screeds shall be kept clean and free of set
gypsum concrete throughout the placement operation.
8.10 ProtectionofCompletedSlab—Gypsumconcreteisnot
8.7.2 Proportioning—Theratioofwatertogypsumconcrete
a finished traffic or weather protective surface. The top side of
shall be that specified by the producer of the gypsum concrete;
the completed gypsum concrete slab shall be protected with a
additional water is prohibited. Volumetric or metering devices
permanent waterproof covering.
shall be used to ensure accurate measurement.
8.7.3 Mixing—Mixing shall be thorough but not overmixed.
9. Keywords
The slurry shall be discharged into placement equipment
immediatelyaftercompletionofmixingtoavoidbuildupofset 9.1 calculation of diaphragm shear; gypsum concrete; gyp-
material. sum roof deck
C956−04 (2019)
APPENDIXES
(Nonmandatory Information)
X1. GENERAL INFORMATION
X1.1 Limitations of Use ventilation is inadequate, mechanical ventilation is required to
remove construction moisture from the building. When sus-
X1.1.1 Roof Shapes and Designs—Gypsum roof decks
pendedceili
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