ASTM C956-97

Standard Specification for Installation of Cast-In-Place Reinforced Gypsum Concrete

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 shall not be considered requirements of the standard.

General Information

• Status: Historical
• Publication Date: 31-Dec-1996
• Technical Committee: C11 - Gypsum and Related Building Materials and Systems
• Drafting Committee: C11.03 - Specifications for the Application of Gypsum and Other Products in Assemblies

Relations

• Replaced By: ASTM C956-97(2002)e1 - Standard Specification for Installation of Cast-In-Place Reinforced Gypsum Concrete
• Effective Date: 10-Apr-1997

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 956 – 97
Standard Specification for
Installation of Cast-In-Place Reinforced Gypsum Concrete
This standard is issued under the fixed designation C 956; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope Building Construction
2.2 American Concrete Institute Standard:
1.1 This specification covers the minimum requirements for
ACI 318 Building Code Requirements for Reinforced Con-
the installation of cast-in-place reinforced gypsum concrete
crete
over permanent formboard.
2.3 American Welding Society Standard:
1.2 The values stated in inch-pound units are to be regarded
D1.1 Structural Welding Code Steel
as the standard. The values given in parentheses are for
information only.
3. Terminology
1.3 The text of this standard references notes which provide
3.1 Definitions shall be in accordance with Terminology
explanatory material. These notes shall not be considered
C11.
requirements of the standard.
3.2 Definitions:
2. Referenced Documents 3.2.1 primary framing, n—structural members provided to
support the reinforced gypsum concrete roof deck assembly.
2.1 ASTM Standards:
3.2.1.1 purlin, n—a secondary structural member that spans
A 82 Specification for Steel Wire, Plain, for Concrete Re-
2 the primary framing members and provides support for sub-
inforcement
purlins.
A 185 Specification for Steel Welded Wire Fabric, Plain, for
2 3.2.2 subpurlin, n—a steel member applied transversely to
Concrete Reinforcement
the primary framing and purlins to support the formboards and
A 499 Specification for Steel Bars and Shapes, Carbon
3 to transmit the dead and live loads from the gypsum concrete
Rolled from “T” Rails
slab to the primary framing.
A 525 Specification for General Requirements for Steel
3.2.2.1 bulb tee, n—a subpurlin, hot-rolled formed steel,
Sheet, Zinc-Coated (Galvanized) by the Hot-Dip Process
rail-shaped section.
A 568 Specification for Steel, Sheet, Carbon, and High-
3.2.2.2 truss tee, n—a subpurlin fabricated from steel wire
Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, Gen-
and strip, tee-shaped section.
eral Requirements for
3.2.3 cross tee, n—a steel tee-shaped section used to support
C 11 Terminology Relating to Gypsum and Related Build-
a formboard end at right angles to the subpurlins where a
ing Materials and Systems
formboard end does not occur over the purlin or primary
C 317 Specification for Gypsum Concrete
framing.
C 726 Specification for Mineral Fiber Roof Insulation
3.2.4 formboard, n—sheet material used as a permanent
Board
form to support the gypsum concrete.
E 72 Methods of Conducting Strength Tests of Panels for
3.2.5 reinforcement, n—steel wire mesh or fabric used
within the gypsum concrete slab to provide longitudinal and
transverse strength.
3.2.6 double-pouring, n—the application of gypsum con-
This specification is under the jurisdiction of ASTM Committee C-11 on
Gypsum and Related Building Materials and Systems and is the direct responsibility
crete in more than one layer to complete the full slab thickness.
of Subcommittee C11.03 on Specifications for Application of Gypsum and Other
See 9.7.4.3.
Products in Assemblies.
3.2.7 ribbon-pouring or strip-pouring, n—the application of
Current edition approved April 10, 1997. Published June 1997. Originally
published as C 956 – 81. Last previous edition C 956 – 96.
Annual Book of ASTM Standards, Vol 01.04.
3 8
Annual Book of ASTM Standards, Vol 01.05. Annual Book of ASTM Standards, Vol 04.07.
4 9
Annual Book of ASTM Standards, Vol 01.06. Available from the American Concrete Institute, P.O. Box 19150, Detroit, MI
Annual Book of ASTM Standards, Vol 01.03. 48219.
6 10
Annual Book of ASTM Standards, Vol 04.01. Available from the American Welding Society, 550 N.W. La Jeune Rd., P.O.
Annual Book of ASTM Standards, Vol 04.06. Box 351040, Miami, FL 33135.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 956
narrow ribbons of gypsum concrete, about 10 to 12 in. (254 to from zinc-coated (galvanized) welded or woven steel wire
305 mm) wide by 1 to 1 ⁄2 in. (25.4 to 38.1 mm) deep, across mesh or fabric having an effective cross-sectional area of not
2 2
the width of the formboard at center of span between purlins. less than 0.026 in. (16.77 mm) per foot of slab width.
Reinforcement shall be free of rust, scale, or other materials
4. Delivery of Materials
that reduce bond to the gypsum concrete.
4.1 Materials shall be delivered in original packages, con-
7.4.1 Hexagonal Reinforcing Mesh, shall be fabricated from
tainers, or bundles bearing the brand name and name of
2 in. (50.8 mm) hexagonal mesh formed of not less than 0.0410
producer or seller. Bulk materials shall be delivered with the
in. (1.04 mm) diameter wires with longitudinal wires not less
brand name and name of the producer or seller shown on the
than 0.0625 in. (1.59 mm) in diameter, spaced not more than 3
accompanying bills of lading.
in. (76.2 mm) on centers. Steel wire for fabricating wire mesh
and fabric—Specification A 82.
5. Storage of Materials
7.4.2 Rectangular Reinforcing Fabric, Specification A 185,
5.1 All materials shall be stored in a manner that prevents
shall be fabricated from longitudinal wires not less than 0.1055
damage before use. When stored under tarpaulins, ventilation
in. (2.68 mm) in diameter spaced not more than 4 in. (102 mm)
shall be provided to prevent moisture accumulation under the
on centers and transverse wires not less than 0.0800 in. (2.03
tarpaulin.
mm) in diameter spaced not more than 8 in. (203 mm) on
5.2 Formboard shall be stored flat and off the ground.
centers.
Handling and stacking shall be done in such a manner to
7.5 Gypsum Concrete, Specification C 317, Class A.
prevent damage to face, ends, and edges and keep dry until use.
7.6 Water, shall be potable and free of substances that could
5.3 When it is necessary to store gypsum concrete at the job
adversely affect the gypsum concrete.
site, the gypsum concrete shall be stored off the ground and 3
7.7 Expansion Filler Strip, shall be not less than ⁄4 in. (19
kept dry until use.
mm) thick and equal in height to the abutting gypsum concrete
and of the type specified by the producer of the gypsum
6. Environmental Conditions
concrete.
6.1 The minimum temperature at which gypsum concrete is
mixed and placed is not specified. Gypsum concrete shall not 8. Installation
be mixed with water containing ice crystals.
8.1 Installation of Subpurlins:
8.1.1 Installation, Normal:
NOTE 1—An exothermic reaction during setting ensures complete
8.1.1.1 Subpurlins—The subpurlins shall be placed trans-
hydration before freezing.
versely to the purlins and primary framing and shall be spaced
7. Materials
to suit the size of the formboards specified. Subpurlins shall be
7.1 Subpurlins: of sufficient length so that their joints occur over purlins or
7.1.1 Subpurlins shall be designed to support live and dead primary framing. Subpurlin joints shall be alternated so that the
loads of the roof deck. joints are staggered one purlin space.
7.1.2 Hot-rolled and cold-rolled steel shapes other than bulb 8.1.1.2 Subpurlins shall be welded to purlins and steel
tees or truss tees shall meet the requirements of this specifica- primary framing with ⁄8 in. (3.2 mm) fillet welds not less than
tion for subpurlins. ⁄2 in. (12.7 mm) long on alternate sides of the subpurlin at each
7.2 Cross Tees, shall be not less than 1 ⁄4 in. (31.75 mm) intersection with purlins. Except as otherwise specified, weld-
wide by ⁄2 in. (12.7 mm) high, fabricated from not less than 26 ing shall be in accordance with AWS D1.1. Where primary
gage zinc-coated steel conforming to Specifications A 525 or framing is of wood, nails not less than 16d shall be used on
A 568. each side of the subpurlins at each intersection. The nails shall
7.3 Formboard: be bent over approximately ⁄4 in. (19 mm) to securely clinch
7.3.1 Mineral Fiber Formboard, Specification C 726, not the flange of the subpurlin.
less than ⁄4 in. (19.0 mm) thick nor more than 3 in. (76 mm) 8.1.2 Installation Seismic:
2 2
thick. It shall sustain a uniform load of 20 lb/ft (97 kg/m ). 8.1.2.1 Subpurlins—The subpurlins shall be welded at each
7.3.1.1 Mineral fiber formboard shall be tested in accor- intersection with the purlins with ⁄8-in. (3.2-mm) fillet welds
dance with the transverse loading test of Methods E 72. not less than 1 in. (25.4 mm) long, on one side. Both sides of
7.3.1.2 The test specimen shall be uniformly loaded and the subpurlin shall be welded with ⁄8-in. fillet welds not less
supported at both edges and ends. The test specimens shall be than 2 in. (50.8 mm) long where subpurlin joints occur over the
supported at the perimeter with a frame providing 1 in. (25.4 purlin. Both sides of the subpurlin shall be welded with ⁄8-in.
mm) bearing on ends and ⁄2 in. (12.7 mm) bearing on edges fillet welds not less than 2 in. long at shear transfer points and
and 7 in. (177.8 mm) nominal clearance from the bed of the at intersections with exterior frame.
apparatus. 8.1.3 Maximum Spans—Refer to X2.1.3.
7.3.1.3 For formboards ⁄4 in. (19.0 mm) thick, test speci- 8.2 Cross Tees—Cross tees shall be provided where form-
mens shall be 48 in. (1200 mm) long by 24 in. (600 mm) wide. board ends are supported by purlins or the primary framing.
7.3.1.4 For formboards 1 in. (25.4 mm) thick or greater, test 8.3 Formboards—Formboards shall be located face down
specimens shall be 48 in. (1200 mm) long by 32 in. (800 mm) on the flanges of the supporting members and with the ends on
wide. top of the purlins.
7.4 Reinforcement, Specification A 82, shall be fabricated 8.3.1 Gypsum concrete shall not be poured over formboards
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 956
which have been wetted by rain or snow. 8.7.4.1.1 The deck shall be poured in sections of similar
8.3.2 The gypsum concrete shall be poured on the same day size.
the formboards are installed.
8.7.4.2 Screeds Grounds—Screeds, such as metal bars or
8.4 Reinforcement—The mesh of wire fabric shall be lo-
wood strips, shall be spaced approximately 10 ft (3050 mm)
cated with the main longitudinal wires at right angles to the
apart at right angles on top of the subpurlins at a height that
subpurlins and adjacent to the formboard at midspan between
will allow the gypsum concrete slurry to be leveled at the
the purlins. Ends of the reinforcement shall be lapped not less
specified thickness.
than 4 in. (102 mm) or one mesh, whichever is greater.
8.7.4.2.1 Gypsum concrete cants, curbs, and drainage slopes
8.4.1 Edges shall be butted, not lapped, unless required for
shall be placed to the design thickness. Curbs around openings
fire rated or horizontal diaphragm construction. Reinforcement
shall be permitted to be formed with the formboard.
shall be cut to fit at walls, curbs, and openings, folded over on
8.7.4.3 The gypsum concrete shall be discharged into place-
to itself, and extended into all areas when gypsum concrete is
to be placed. ment equipment immediately after completion of mixing.
8.5 Expansion Filler Strips—Expansion filler strips shall be
8.7.4.3.1 The slurry shall be poured or discharged not more
placed continuously against the walls, curbs, nailers, or other
than 24 in. (600 mm) off the formboard to minimize impact and
rigid surfaces that gypsum concrete will abut.
allowed to build to full thickness in one continuous operation.
8.6 Expansion Joints—Expansion joints shall be located at
Double pouring shall not be permitted.
expansion joints found in the main structure, at a maximum of
8.7.4.3.2 As soon as the slurry has stiffened enough to hold
200 ft (61 m) on center in a direction parallel to the subpurlins
a full level, it shall be screeded to a true, even surface using a
on large buildings, at intersections of wings on L-, U-, T-, and
smooth, rigid straight-edge.
H-shaped buildings and, wherever the roof framing changes
8.7.4.4 Place gypsum concrete cants, curbs, and drainage
direction. See X1.5.5.
slopes to the design thickness. Curbs around openings shall be
8.7 Gypsum Concrete Mixing and Placement:
8.7.1 General—All equipment, including mixers, pumps, permitted to be formed with the formboard.
hoses, tools, and screeds shall be kept clean and free of set
8.8 Roof Overhangs—Gypsum concrete shall not be placed
gypsum concrete throughout the placement operation.
on roof overhangs, eaves, or other similar locations, on
8.7.2 Proportioning—The ratio of water to gypsum con-
formboards unless the underside is protected against direct
crete shall be that specified by the producer of the gypsum
wetting by a suitable facia drip cap overhang.
concrete; additional water is prohibited. Volumetric or meter-
8.9 Drying—Construction moisture shall be removed from
ing devices shall be used to ensure accurate measurement.
the building to permit drying of completed gypsum concrete
8.7.3 Mixing—Mixing shall be thorough but not overmixed.
slab, providing heat and ventilation where required. See X1.3.
The slurry shall be discharged into placement equipment
8.10 Protection of Completed Slab—Gypsum concrete is
immediately after completion of mixing to avoid buildup of set
not a finished traffic or weather protective surface. The top side
material.
of the completed gypsum concrete slab shall be protected with
8.7.3.1 Calcium chloride or other admixtures shall not be
a permanent waterproof covering.
added to the gypsum concrete.
8.7.4 Placement:
8.7.4.1 General—To avoid exposure to inclement weather 9. Keywords
and physical abuse, gypsum concrete shall be placed the same
9.1 calculation of diaphragm shear; gypsum concrete; gyp-
day as the installation of the formboard and reinforcement
sum roof deck
materials.
APPENDIXES
(Nonmandatory Information)
X1. GENERAL INFORMATION
X1.1 Limitations of Use may be exposed to sustained relative humidity greater than
90 % or condensing moisture. The producer of the gypsum
X1.1.1 Roof Shapes and Designs—Gypsum roof decks
concrete should be consulted regarding limitations of use in
meeting this specification can be installed on flat, warped,
high humidity occupancies.
sawtooth, curved, or pitched roofs.
X1.1.3 Temperature Exposures—Where i
...