ACI 523.1R-92
Guide for Cast-in-Place Low-Density Concrete Reported by
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A CI
Committee 523
Leo A. Legatski Chairman
L. E. Rivkind Secretary
Theodore W. Bremner Hubert T. Dudley E. A. Fischer Richard Galer * Lester Gorsline George C. Hoff
Albert Litvin Henry N. Marsh, Jr. Robert S. Milanese Owen Richards Rudolph C. Valore, Jr.
Committee members voting on the 1992 revisions: Leo A. Legatski Chairman
Leo E. Rivkind Secretary
Theodore W. Bremner Hubert T. Dudley George W. Richard E. Galer Werner H. Gumpertz George C. Hoff
Albert Litvin Henry N. Marsh, Jr. Robert S. Milanese Manual M. Solis Rudolph C. Valore, Jr.
* Former Chairman Deceased This guide provides information on materials, properties, design, and proper handling of cast-in-place concrete s having oven-dry unit weights of 50 pcf (800 kg/m3 or less. These concretes achieve their low unit weight by incorporating low-density aggregates, air entrainment, or preformed foam. These concretes are most commonly used in roof deck systems, where their advantages include insulating value, the ability to be sloped-todrain, and improved fire resistance.
Chapter 2-Concrete materials, pg. 523.1R-2 2.l-Cement 2.2-Aggregates 2.3-Water 2.4-Foams 2.5-Admixtures 2.6-Fiber reinforcement
Keywords: accelerating agents; admixtures; aggregates; air entrainment; cellular concretes; compressive strength; concrete construction; fire Chapter 3-Concrete properties, pg. 523.1R-4 resistance; foaming agents; formwork (construction); insulating con3.1-Oven-dry unit weight cretes; lightweight aggregate concretes; lightweight concretes; modulus of elasticity; nailability; perlite; roofs; shrinkage; structural design; 3.2-As-cast unit weight thermal conductivity; thermal expansion; vermiculite.
CONTENTS Chapter 1-General, pg. 523.1R-2
l.l-Scope 1.2-Definition of low-density concrete 1.3-Types of low-density concrete AC I Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in designing, planning, executing, or inspecting construction and in preparing specifications. Reference to these documents shall not be made in the Project Documents. If items found in these documents are desired to be a part of the Project Documents they should be phrased in mandatory language and incorporated into the Project Documents. Copyright American Concrete Institute
3.3-Compressive strength 3.4-Modulus of elasticity 3.5-Drying shrinkage 3.6-Thermal expansion 3.7-Walkability 3.8-Nailability 3.9-Thermal conductivity
This report supersedes ACI 523.1R-67. The 1992 revisions became effective Mar. 1, 1992. They consisted of a few minor editorial revisions and the deleting of year designations of recommended references so that the current edition is the referenced version. Copyright 1986, American Concrete Institute. Al l rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.
ACI COMMITTEE REPORT
3.10-Fire resistance Chapter 4-Design considerat ions for roof deck s, pg.
portland cement, water, and air to form a hardened material which, when oven-dried will have a unit weight of 50 pcf (800 kg/m 3) or less.
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4.1-Load-bearing capacity 4.2-Expansion and contraction joints 4.3-Vapor pressure reduction 4.4-Standard roofing details Chapter 5-M ixing, handling, placing, finishing, and curing, pg. 523.1R-6
5.1-Storage of materials 5.2-Concrete designation 5.3-Mixing procedure 5.4-Conveying 5.5-Finishing 5.6-Curing 5.7-Weather Chapter 6-R oof deck applications, pg. 523.1R-7
6.l-Form systems 6.2-Roofing readiness
1.3-Types of low-density concrete
Low-density concrete is of three generic types: Concrete made predominantly 1.3.1 Aggregate type with either perlite or vermiculite mineral aggregates, other low-density aggregates, or with expanded polystyrene beads. 1.3.2 Cellular type Concrete made by forming a cement matrix around air cells that are generated by preformed or in situ foams generated from foam concentrates or gas-forming chemicals. 1.3.3 Cellular/aggregate type Low-density concretes made by combining foam and low-density aggregates to impart special properties to the mix. These properties may include, among others: improved strength, improved ability of the concrete to be cast on steeper slopes, and longer retention of additional water in the mix for curing in very dry climates. The cost of the concrete is also reduced.
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Chapter 7-R eferences, pg. 523.1R-7
7.1-Recommended references 7.2-Cited references
CHAPTER 2-CONCRETE MATERIALS 2.1-Cement
Th e
CHAPTER l-GENERAL l.l-Scope
This guide brings together pertinent data on the properties, uses, and application considerations for fieldplaced low-density concrete. The largest single use of these types of concrete is as a roofing base and thermal insulation for industrial and commercial buildings. The guide provides the engineer or architect with information on the types of raw materials and their properties, design considerations, and proper mixing and placing techniques for cast-in-place low-density concrete for thermal insulation and slope-to-drain roof decks. Only limited information is included on geotechnical applications for low-density concrete. These applications usually involve thick sections of material and the consideration of such things as retention of heat, thermal stresses, short-term and long-term water absorption, the ability to control density, and other unique site-specific aspects. Fill applications include replacement of poor soils; fills for abandoned mines, pipelines, and voids; and shock-energy absorbing installations. In these applications, the low-density concrete fills are often designed, mixed, and placed to meet specific job conditions and functional requirements. 1.2-Definition of low-density concrete
Low-density concrete, as used in this guide, is defined
cement should meet the requirements of ASTM C 150 (Portland cements) or C 595 (blended cements). Blended cements include portland blast furnace slag cement, Portland-pozzolan cement, and slag cement. Blended cements may result in slower rates of strength development during the first 3 to 5 days for these lowdensity concretes. High-early-strength cements (Type III) will produce low-density concrete with higher rates of early strength development. Manufacturers of polystyrene beads for use in concrete have recommended that under normal conditions of use, Type II cement (which is classified in ASTM C 150 Table 2A as a moderate heat of hydration cement and which has a lower heat of hydration than Type I or Type III cements) be used for placements of sections greater than 6-in. (152-mm) thickness, since excessive increases in temperature may cause further expansion of the beads. This recommendation may be modified to meet ambient temperature conditions, heat storage capacity of form media, type and content of aggregate, and other factors. 2.2-Aggregates 2.2.1 Perlite Perlite is a naturally occurring siliceous volcanic glass with a concentric layered structure. When heated above 1600 F (870 C), the crude rock expands as combined water (2 to 6 percent) vaporizes and creates numerous closed spheres in the heat-softened glassy particles. It usually expands to 4 to 20 times its original
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CAST-IN-PLACE LOW-DENSITY CONCRETE
crete has a loose, dry bulk density of 7 1 / 2 to 12 lb/ft3 (120 to 192 kg/m3) and should conform to ASTM C 332, Group I aggregates. Reference 1 provides further information on perlite. 2.2.2 Polystyrene Expandable polystyrene is made by polymerizing styrene. During the process, a hydrocarbon blowing agent is incorporated. The product is in the form of small beads, which soften and expand when heated with steam in special expanding chambers. The expanded beads are generally spherical in shape and have loose, dry bulk densities varying from 0.6 to 2 1 / 2 lb/ft3 (10 to 40 kg/m3). The expanded beads have a fine, closed cellular structure. The gradation of the expanded beads coming from a single expanding operation is narrow. At present, there are no gradation or density requirements for this material when it is used as concrete aggregate. Whether in expanded or unexpanded form, this aggregate must be considered combustible and safety precautions must be observed prior to its introduction into the mixture. 2.2.3 Vermiculite Vermiculite is the name given to platey micaceous minerals that are hydrous silicates of aluminum, magnesium, and iron. When heated to temperatures of 1200 to 2000 F (650 to 1100 C), the water trapped in the flakes of vermiculite ore turns to steam and forces the micaceous plates of the materials to exfoliate in an accordion-like fashion. This exfoliation of the thin plates causes the volume of the vermiculite to increase to up to 30 times the original volume. The air spaces formed in the aggregate are open or interconnected. The exfoliated vermiculite aggregate for use in concrete has a loose, dry bulk density of 6 to 10 lb/ft 3 (96 to 160 kg/m3) and should conform to ASTM C 332, Group I aggregates. Reference 1 provides further information on vermiculite. Other aggregates 2.2.4 Other low-density aggregates for use in low-density concrete may be prepared by expanding, calcining, or sintering various natural or artificial materials. When used, they should conform to ASTM C 332, Group II. 2.2.5 Sands Sands conforming to ASTM C 33 and ASTM C 144 are acceptable. Sands of other gradations may be used where their acceptability has been demonstrated.
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2.3 Water Mixing water should be potable and free of deleterious amounts of acids, alkali, salts, oils, and organic materials that would adversely affect the set time, strength, or performance of the concrete.
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2.4 Foams Preformed foam is produced 2.4.1 Preformed foam by diluting a foam concentrate with water, combining this foam solution with compressed air in predetermined proportions, and then passing this mixture through a blending device that expands the liquid up to about 30 times into the preformed foam. The density of the pre-
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and 64 kg/m3). This mechanical system is commonly referred to as a foam generator. The foam concentrate must have a chemical composition capable of producing stable air cells in the concrete which can resist the physical and chemical forces imposed during mixing, pumping, placing, and setting of the concrete. If the cellular structure is not stable, it may break down during mixing and/or placing resulting in increases in concrete density. Procedures for evaluating these concentrates in a standard mix for density, water absorption, and compressive strength are contained in ASTM C 796. The proprietary formulations of foam concentrates most commonly used are based on protein hydrolyzates or synthetic surfactants. For further details concerning these formulations and the need for stabilizers consult the manufacturer. The foam concentrate should conform to ASTM C 869. In situ foam is generated by high 2.4.2 In situ foam speed, high shear mixing in an open mixer. The concentrates are the same as noted in paragraph 2.4.1. The concentrate and water are most commonly mixed for a short period of time, usually before the addition of cement and aggregates (if any), to allow foam to form in the mixer. The air bubbles that are formed at first are reduced in size as mixing proceeds. The quantity of concentrate required is determined by trial and depends on the concentrate type, mixing time, mixer efficiency, batch size, and the density of concrete desired.
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2.5-Admixtures
Air entrainment is 2.5.1 Air-entraining admixtures normally used with the aggregate types of low-density concretes. The amount of air needed to develop a certain density concrete is a function of the type of low-density aggregate and the proportions of the mixture. It should be determined by a trial mixture or in accordance with the aggregate manufacturer’s recommendations. The airentraining agent may be prepackaged with the lowdensity aggregate or may be added at the mixer. Airentraining admixtures should conform to ASTM C 260. Small quantities of air can also be incorporated in the concrete using preformed foam or in situ foaming (Section 2.2). 2.5.2 Other chemical admixtures Other types of chemical admixtures have been used with low-density concretes. These include water-reducing and set-accelerating admixtures. Water-reducing admixtures may help in improving compressive strengths for special mixes or applications. Acceleration may be obtained with hot water, high-early-strength cement (Type III), and/or chemical accelerators. Many commercial accelerators contain chloride salts. Materials containing chloride ions should not be used in the concrete if it is placed on stayin-place steel forms or steel decking, if steel wire mesh is used for reinforcement, or if uncoated aluminum conduit or other aluminum members are embedded in the con-
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admixtures should conform to ASTM C 494 and should be used in dosages as recommended by the manufacturer or as determined by making trial mixes. Not all chemical admixtures are compatible with foam concentrates, and manufacturer’s recommendations should be followed. The compatibility of chemical admixtures and foaming agents expected to be used should be established by the trial batch method prior to being specified and used. In the pro2.5.3 Finely divided mineral admixtures duction of cellular concrete, finely divided mineral admixtures, such as ground quartz (silica flour) or pozzolans (fly ash), may be added as a filler or partial replacement of the cement. The use of finely divided mineral admixtures may reduce bleeding and segregation and may increase the strength of the concrete. Fly ash should conform to ASTM C 618. All of these mineral admixtures may differ considerably in composition, fineness, and other properties, but they must be compatible with the foam concentrate and other admixtures. The physical properties and amount of the mineral admixtures and their compatibility with the foam concentrates and other admixtures should be specified.
where Oc = Wda = Wct = = S 1.2Wct =
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2.6-Fiber reinforcement Various types of fiber reinforcement materials can be used to improve the flexural and tensile strengths and energy-absorption and spall-resistance properties of the low-density concretes.
CHAPTER 3-CONCRETE PROPERTIES 3.1-Oven-dry unit weight The oven-dry weight is commonly used to relate the physical properties of the various types of low-density concrete. Unit weight may be determined in accordance with the requirements of ASTM C 495 or C 513. 3.2-As-cast unit weight As-cast unit weight determinations are usually made at the point of placement, in accordance with Section 7.7 of ASTM C 796. In making this determination, the concrete should be consolidated by tapping the sides of the container, but never by rodding. The ratio of as-cast unit weight to oven-dry unit weight varies for the different types of low-density concrete due to different water content requirements. The as-cast unit weight of the particular concrete is an important jobsite quality assurance tool to control uniformity and density. The following formula adapted from ASTM C 567 is useful as a method for calculating approximate oven-dry unit weight when the batch quantities, moisture content of aggregates, and the batch volume of the concrete are known Oc =
approximate oven-dry weight, lb/ft3 (kg/m3) weight of dry aggregate in batch, 1 lb (kg) weight of cement in batch, lb (kg) volume of concrete produced by the batch, ft 3 (m3) weight of cement plus weight of water of hydration (considering water of hydration to be 20 percent of the weight of cement), lb (kg)
3.3-Compressive strength The compressive strength versus density relationships are important indicators of the quality of the concrete. Compressive tests for low-density concrete should be made in accordance with ASTM C 495. The compressive strength is related to the oven-dry unit weight of the concrete as indicated in Table 3.3. Table 3.3-Compressive strength ranges for low-density concrete Oven-dry unit weight pcf
kg/m3
20-25 25-30 30-35 35-40 40-50
320-400 400-480 480-560 560-640 640-800
Usual range of compressive strength at 28 days psi MPa 0.48-0.86 0.86-l.55 1.55-2.41 2.41-3.10 3.10-5.17
70-125 125-225 225-350 350-450 450-750
Low-density concretes with compressive strengths below 70 psi (0.48 MPa) have proven satisfactory for special applications such as pipe and wall insulation, tunnel and mine fills, energy absorption or shock mitigation applications, and as backfills in sewer and highway construction. Reference 2 presents many of these applications. 3.4-Modulus of elasticity- Relationship to compressive strength Data relating modulus of elasticity, compressive strength, and oven-dry unit weight are listed in Table 3.4. ` , , ` , ` , , ` , , ` ` , , , , , ` ` , , ` ` , , ` , , , , ` , ` , , , , , , , ` -
Table 3.4-Modulus of elasticity ranges for low-density concrete Oven-dry unit weight
Compressive strength
Modulus of elasticity
Concrete type
lb/ft3
kg/m3
psi
MPa
103 psi
GPa
Perlite Vermiculite Cellular (S)* Cellular Polystyrene
20-40 15-40 25-35 15-40 34-48
320-640 240-640 400-560 240-640 545-770
80-450 70-400 130-250 70-450 325-550
0.55-3.10 0.48-2.76 0.90-l.72 0.48-3.10 2.24-3.79
70-250 40-140 20-100 10-240 100-160
0.48-l.72 0.28-0.97 0.14-0.69 0. 07-l.65 0.69-1.10
*Cement-sand ratio = 1 (this silica sand should be 100 mesh or finer). + Neat cement.
+ 1.2
3.5-Drying shrinkage
CAST-IN-PLACE LOW-DENSITY CONCRETE
concrete is not usually critical in roof deck insulation and fill applications. For structural use, the shrinkage should be considered; it can be measured in accordance with ASTM C 157. Shrinkage after 6 months at 50 percent relative humidity and 73 F (23 C) is usually within the range shown in Table 3.5. The drying shrinkage varies inversely with density.
Table 3.5-Drying shrinkage ranges for low-density concrete
3.6-Thermal expansion Low-density concrete may be subjected to a wide temperature range. Thermal expansion should be considered by the designer in applications where placing and/or operating temperatures of the low-density concrete vary significantly. These applications may occur in insulating applications such as roof decks, power plants, ovens, steam lines, etc. The coefficient of thermal expansion varies directly with density. Coefficients of thermal expansion for low-density concretes are shown in Table 3.6.
Table 3.6-Thermal expansion ranges for low-density concrete Coefficient of thermal expansion
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out shattering or spalling. 2. The ability of the low-density concrete to hold the specialty roofing nail when a withdrawal force of 40 pounds (178 N) is applied to the nail.
3.9-Thermal conductivity The thermal conductivity k of low-density concrete may be measured by means of the Guarded Hot Plate (ASTM C 177) or the Heat Flow Meter (ASTM C 518) methods. Equations for thermal conductivity for lightweight concrete under varying moisture conditions have been developed. These are cited and discussed in Reference 3. The following equations from that reference are for thermal conductivity k in the oven-dry condition and the normally dry condition where the concrete is in moisture equilibrium at 50 to 60 percent relative humidity and room temperature. Oven dry, k
=
0.5
Eq. (1)
(k = 0.072 Normally dry, k
=
Eq. (1M)
0.6
Eq. (2)
(k = 0.087
Eq. (2M)
where is base of natural logarithms (= 2.718) and is 3 oven-dry density, pcf (kg/m ). Table 3.9 presents thermal conductivity values calculated from these equations.
Table 3.9-Thermal conductivity for low-density concrete Oven-dry unit weight
Thermal conductivity k Btu . in. /hr . ft2 . F
lb/ft3
W/m.K
Oven dry Normally dry Oven dry Normally dry kg/m3 [ E q . (1)] [Eq. (2)] [Eq. (1)] [Eq. (2)]
3.7-Walkability “Walkability” is a term that defines the ability of th e low-density concrete to sustain normal construction foot traffic without damage. It is best judged by examining the surface distress such as footprints left from normal foot traffic. Walkability improves with increasing density. For roof decks where heavy construction traffic (such as wheelbarrows, scaffolds, material storage, pathways, etc.) is expected, the surface of the concrete should be protected by protection boards or other means.
3.8-Nailability Nailability of low-density concrete is important when nailing is specified to attach roofing to the deck. Nailing within 7 days of concrete placement is desirable. Two properties should be considered: 1. The ability of the concrete to receive the nail with--`,,,,,,,`,`,,,,`,,``,,``,,,,,-`-`,,`,,`,`,,`---
3.10-Fire resistance A building element built from low-density concrete is of a given fire resistance if, in a standard fire test, for a period equal to the given fire resistance it is capable of 1) supporting the design load; 2) withstanding heat transmission in a sense specified by the test standard; and 3) withstanding the transmission of flame or hot gasses. References 4, 5, and ACI 216R provide information on the fire resistance of slabs of low-density concretes, and present charts that allow the estimation of the fire resistance of a variety of two-course floors and roofs. Fire resistance tests have been conducted on wall, floor, and roof assemblies constructed with low-density
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ACI COMMITTEE REPORT
galvanized steel decks, and wood structures. Some of these tests have employed expanded polystyrene insulation board sandwiched within the low-density concrete. Construction details are published by Underwriters Laboratories, Inc., Factory Mutual System, and other recognized laboratories.
tions are detailed. This evaluation is especially important in reroofing applications where all or a portion of the existing roof membrane, insulation, and/or structure is left in place, and over it is cast low-density concrete to provide drainage correction, additional thermal insulation, and/or as a solid base for a new single-ply or builtup roofing system.
CHAPTER 4-DESIGN CONSIDERATIONS FOR ROOF DECKS
4.4-Standard roofing details Generally accepted roofing details have been developed by the National Roofing Contractors Association (NRCA). These details may be obtained from Reference 6. A typical assembly is shown in Fig. 4.4.
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4.1-Load-bearing capacity Specific design requirements for low-density insulating concrete depend primarily on the type of installation. These installations may include form board-subpurlin systems, and the more common installations over wood, galvanized steel centering, and precast and cast-in-place concrete decks. The compressive strengths for these applications may range from 70 to 500 psi (0.48 to 3.45 MPa). The manufacturers of the foam concentrates and lowdensity aggregates have specific data on other structural considerations. These usually include ultimate load capacities from flexural loading and seismic diaphragm performance of various systems. 4.2-Expansion and contraction joints Low-density concrete may crack when placed in large monolithic pours such as roof decks. If shrinkage of the concrete is much greater than its thermal expansion, expansion joints are not necessary. However, some producers of aggregates used in low-density concrete recommend that expansion and contraction joints be provided at any changes in roof plane. For low-density concretes used in roof deck applications, expansion joints should be placed in the roof deck where there are expansion joints in the structural system and also where there are changes in the direction or type of substrate material.
CHAPTER 5-MIXING, HANDLING, PLACING, FINISHING, AND CURING 5.1-Storage of materials All materials should be stored in such a manner as to prevent deterioration and contamination by foreign matter. 5.2-Concrete designation
Consult with the specific low-density concrete manufacturer for specific mixture proportions, as-cast and oven-dry unit weights, and physical properties based on reliable test date for the particular application. 5.3-Mixing procedure All concrete should be mechanically mixed to produce a uniform distribution of the materials with a suitable consistency and the required as-cast unit weight. Excessive mixing should be avoided because of the possibility of changes in unit weight and consistency. In batch mixing operations, follow the manufacturer’s recommendations concerning the order of charging the mixer with the various ingredients. The as-cast unit weight should be monitored at the point of placement.
4.3-Vapor pressure reduction Moisture present in low-density concrete or moisture intrusion from external sources may, under certain temperature conditions, result in an increase in vapor pressure under roofing materials in a roof deck system. Methods for relief of this vapor pressure include nailing or strip or spot mopping the base sheet of the roofing materials to the roof deck coupled with either perimeter venting or stack venting. Perimeter venting may be achieved through the edge flashing detail. Stack vents, when necessary, should have a minimum diameter of 4 in. (100 mm), be cored through to the structural deck, and be placed at the frequency of one per 1000 to 2000 ft2 (100 to 200 m2) of roof deck. The rate of drying of low-density concrete is a function of type of insulating concrete, type of deck substrate, type of venting, and environmental conditions. The total roof deck system, the building’s use, and the climatic con- Fig. 4.4-A typicallow-densityinsulating concreteroof deck ditions should be evaluated before specific recommenda-
CAST-IN-PLACE LOW-DENSITY CONCRETE
Allowance should be made for any additional mixing that may result from the method of placement, such as mechanical or pneumatic pumping, and for any unit weight changes that may result from these methods. For continuous mixing operations, provision should be made for reasonably uniform (and continuous) rate of addition of all concrete components at appropriate positions in the mixing machine, and in the correct ratio, to assure uniformity and the required unit weight at the point of placement. 5.4-Conveying All equipment for conveying and placement, whether manual or mechanical, should be of such size and design as to insure uniform unsegregated concrete at the point of placement. 5.5-Finishing The low-density concrete should be finished to the proper slope and thickness as indicated on the drawings. The surface should be relatively smooth and be free from any large ridges. 5.6-Curing The surface of freshly finished low-density concrete should be protected from rapid drying. When rapid drying is anticipated, the use of water curing or a curing compound is advisable. The curing material should be compatible with the roof deck materials and the final roofing membrane. Traffic should not be permitted on the newly placed concrete until adequate walkability as described in Section 3.7 is demonstrated. 5.7-Weather When air temperatures between 30 and 40 F (-1 and 4 C) are predicted during the first 24 hours after placement, special precautions should be taken. These include the use of Type III high-early-strength cement or Type I cement with heated mix water. Heated mix water may be used to increase the temperature of the concrete to improve the setting time. Unless special techniques are used, low-density concrete should not be placed during freezing weather. Low-density concrete should not be placed during rain or snow, nor should it be placed on a deck or form when standing water, snow, or ice is present. ` , , , , , , , ` , ` , , , , ` , , ` ` , , ` ` , , , , , ` ` , , ` , , ` , ` , , ` -
CHAPTER 6-ROOF DECK APPLICATIONS
6.l-Form systems A common application of low-density concrete is for insulating roof deck fills. The roof deck system over which the insulating concrete is cast often is a permanent portion of the structure. Typical deck systems include: 1) corrugated or fluted galvanized steel deck, 2) nonstructural formboard, 3) structural concrete, and 4) wood decks.
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6.1.1 Corrugated galvanized steel deck The corrugated high-tensile or wide-rib steel deck should be galvanized to meet the requirements of ASTM A 446, Grade E, and coated to meet ASTM A 525 Class G-60 minimum. These steel decks are designed to carry both dead and live loads by varying the gage of the steel according to the span. The deck should be secured to the framing by either welding or mechanical fasteners, according to the individual manufacturer’s recommendations. The corrugated steel sheets may be vented at the sidelaps, have bottom slots with percent open area per square foot of roof, or not have any specified venting detail. Side lap embossments improve bond, which is important in seismic designs. A structural concrete base 6.1.2 Structural concrete for low-density concrete may be either cast-in-place or precast. For these concrete substrates, provision should be made for venting of moisture from the low-density concrete. This may be achieved by taking advantage of unsealed joints between precast structural concrete elements or by venting as described in Section 4.3. Low-density concrete is often cast 6.1.3 Wood decks over structural wood roof decks as drainage fill and insulation. A water-barrier type of membrane, such as an asphalt-saturated felt, should be securely fastened to the wood deck, lapping the edges, prior to installing the concrete fill. Provisions for expansion joints or venting should be made in accordance with the manufacturer’s recommendations.
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6.2-Roofing readiness Roofing can generally commence 2 to 5 days after the deck has been cast, if drying conditions have been favorable. The surface hardness should be adequate to withstand foot traffic and other light roofing operations without damage. The screeded surface of the low-density concrete should be relatively smooth and free from any finishing ridges that would affect the integrity of the roofing material. These ridges can be scraped flat. Nailing a roofing base sheet to the roof deck is a common method of attachment. If hot asphalt or pitch is used to attach the roofing membrane, the exposed concrete surface should be sufficiently dry so that hot mopped asphalt or pitch will go on smoothly without frothing and will adhere well to the surface. Solid mopping to the concrete surface is not recommended. Any other roofing attachment systems should be compatible with the low-density concrete and the structure to provide the required resistance to uplift.
CHAPTER
7-REFERENCES
7.1-Recommended references The ACI and ASTM documents referred to in this document are listed below with their serial designation.
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ACI COMMITTEE REPORT
American Concrete Institute
216R
Guide to Determining the Fire Endurance of Concrete Elements
AS TM
A 446
C 595 Standard Specification for Blended Hydraulic Cements C 618 Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete C 796 Standard Method of Testing Foaming Agents for Use in Producing Cellular Concrete Using Preformed Foam C 869 Standard Specification for Foaming Agents Used in Making Preformed Foam for Cellular Concrete
Standard Specification for Steel Sheet, ZincCoated (Galvanized) by the Hot-Dip Process, Structural (Physical) Quality A 497 Standard Specification for Welded Deformed Steel Wire Fabric for Concrete Reinforcement A 52 5 Standard Specification for General Requirements The above publications may be obtained from: for Steel Sheet, Zinc-Coated (Galvanized) by the American Concrete Institute Hot-Dip Process C 33 P.O. Box 9094 Standard Specification for Concrete Aggregates C 144 Standard Specification for Aggregate for MasonFarmington Hills, MI 48333-9094 ry Mortar ASTM C 150 Standard Specification for Portland Cement C 157 Standard Test Method for Length Change of 1916 Race Street Philadelphia, PA 19103 Hardened Cement Mortar and Concrete C 177 Standard Test Method for Steady-State Thermal 7.2-Cited references Transmission Properties by Means of Guarded 1. Wilson, H.S., “Lightweight Aggregates-VermicuHot Plate Pumice-for lite, Perlite, Insulating Concretes,” C 260 Standard Specification for Air-Entraining AdmixCANMET Report No. 81-15E, CANMET, Energy Mines tures for Concrete and Resources Canada, Ottawa, 1981, 28 pp. C 332 Standard Specification for Lightweight Aggre2. Lightweight Concrete, SP-29, American Concrete gates for Insulating Concrete Institute, Detroit, 1971, 321 pp. C 494 Standard Specifications for Chemical Admixtures 3. Valore, Rudolph C., Jr., “Calculation of U-Values for Concrete C 495 Standard Test Method for Compressive Strength of Hollow Concrete Masonry,” Concrete International: Design & Construction, V. 2, No. 2, Feb. 1980, pp. 40-63. of Lightweight Insulating Concrete 4. Abrams, M.S., and Gustaferro, A.H., “Fire C 49 6 Standard Test Method for Splitting Tensile Endurance of Two-Course Floors and Roofs,” ACI Strength of Cylindrical Concrete Specimens J O U R N A L, Proceedings V. 66, No. 2, Feb. 1969, pp. 92C 513 Standard Method for Securing, Preparing, and 102. Also, Re search and Deve lopment Bull et in N O . Testing Specimens from Hardened Lightweight 048.01B, Portland Cement Association. Insulating Concrete for Compressive Strength 5. Gustaferro, A.H.; Abrams, M.S.; and Litvin, Albert, C 518 Standard Test Method for Steady-State Thermal “Fire Resistance of Lightweight Insulating Concretes,” Transmission Properties by Means of the Heat Research and Development Bulletin No. RD004B, PortFlow Meter land Cement Association, Skokie, 1970, 12 pp. C 56 7 Standard Test Method for Unit Weight of Struc6. “The NRCA Roofing and Waterproofing Manual,” tural Lightweight Concrete Construction Details, National Roofing Contractors C 578 Standard Specification for Preformed, Cellular Association, Oak Park, 1983. Polystyrene Thermal Insulation ` , , ` , ` , , ` , , ` ` , , , , , ` ` , , ` ` , , ` , , , , ` , ` , , , , , , , ` -
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