STRUCTURAL LIGHTWEIGHT CONCRETE
This Guide Specification has been prepared to supplement the Architect-Engineer's standard concrete specifications where structural lightweight concrete is to be used.
Part I - General | Part II - Products | Part III - Control | Appendix | Comments
PART I - GENERAL
1.1 REFERENCE STANDARDS
1.1.1 AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)
1. ASTM C 31, Standard Practice for Making and Curing Concrete Test Specimens in the Field
2. ASTM C 33, Standard Specifications for Concrete Aggregates
3. ASTM C 39, Standard Test Method for Compressive Strength of Cylindrical Specimens
4. ASTM C 94, Standard Specifications for Ready-Mixed Concrete
5. ASTM C 127, Standard Test Method for Density, Relative Density (Specific Gravity) and Absorption of Coarse Aggregate
6. ASTM C 138, Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete
7. ASTM C 143, Standard Test Method for Slump of Hydraulic Cement Concrete
8. ASTM C 150, Standard Specifications for Portland Cement
9. ASTM C 172, Standard Practice for Sampling Freshly Mixed Concrete
10. ASTM C 173, Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method
11. ASTM C 205, Standard Specifications for Portland Blast Furnace Slag Cement
12. ASTM C 260, Standard Specifications for Air Entraining Admixtures for Concrete
13. ASTM C 330, Standard Specifications for Lightweight Aggregates for Structural Concrete
14. ASTM C 331, Standard Specification for Lightweight Aggregates for Concrete Masonry Units
15. ASTM C 340, Standard Specifications for Portland-Pozzolan Cement
16. ASTM C 494, Standard Specifications for Chemical Admixtures for Concrete
17. ASTM C 567, Standard Test Method for Determining Density of Structural Lightweight Concrete
18. ASTM C 595, Standard Specifications for Blended Hydraulic Cements
19. ASTM C 618, Standard Specifications for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
20. ASTM C 845, Standard Specifications for Expansive Hydraulic Cement
21. ASTM C 989, Standard Specifications for Ground Granulated Blast-Furnace Slag for Use in Concrete and Mortars
22. ASTM C 1017, Standard Specifications for Chemical Admixtures for Use in Producing Flowing Concrete
23. ASTM C 1157, Standard Performance Specifications for Hydraulic Cement
24. ASTM C 1240, Standard Specifications for Silica Fume Used in Cementitious Mixtures
1.1.2 AMERICAN CONCRETE INSTITUTE (ACI)
1. ACI Manual of Concrete Inspection
2. ACI 211.2, Standard Practice for Selecting Proportions for Structural Lightweight Concrete
3. ACI 213, Guide for Structural Lightweight Aggregate Concrete
4. ACI 301 Specifications for Structural Concrete for Buildings
5. ACI 304.2 Placing Concrete by Pumping Methods
6. ACI 304.5R, Batching, Mixing, and Job Control of Lightweight Concrete
7. ACI 305R, Hot Weather Concreting
8. ACI 306R, Cold Weather Concreting
9. ACI 318 Building Code Requirements for Reinforced Concrete
1.2.1 Except as modified or exceeded by these specifications all cast in place structural lightweight concrete work shall conform to ACI 301.
1.3 STORAGE OF MATERIALS
1.3.1 Cement: Store in weather tight enclosures and protect against dampness, contamination and warehouse set in accordance with ACI 318.
1.3.2 Aggregates: Each gradation of lightweight aggregate as supplied, shall be stockpiled in separate bins or piles. Storage shall minimize segregation and prevent contamination.
2.1.1 CEMENT: ASTM C150 or C595. Air-entraining cement will not be permitted.
220.127.116.11 FLY ASH: Shall meet ASTM C618.
2.1.2 AGGREGATE: Expanded shale, clay or slate produced by the rotary kiln method and shall conform to ASTM C330. Natural sand shall conform to ASTM C33.
2.1.3 MIXING WATER: Clean and free from injurious amounts of oils, acids, alkalis, organic materials or other deleterious substances, in accordance with ACI 318.
18.104.22.168 AIR-ENTRAINING AGENTS: ASTM C260.
2.1.1 The effect and comparability of various combinations of cement, fly ash and/or admixtures is generally the same in expanded shale lightweight concrete as in normal weight concrete.
22.214.171.124 WATER REDUCING ADMIXTURES: ASTM C494.
Admixtures may be used, provided they have a proven satisfactory performance record with structural concrete and are approved by the Architect-Engineer. Admixtures shall be used in accordance with the manufacturer's recommendations.
126.96.36.199 Consistent with comment 2.1.1, high range water reducing admixtures have demonstrated satisfactory performance with
expanded shale lightweight concretes. You should consult the lightweight aggregate producer in your area for specific information
concerning the performance of his aggregate with high range water reducing admixtures.
188.8.131.52 ACCELERATING ADMIXTURE: ASTM C494. Admixtures may be used only with the approval of the Architect-Engineer.
184.108.40.206 RETARDING ADMIXTURE: ASTM C494. Admixtures may be used only with the approval of the Architect-Engineer.
2.2 CONCRETE PROPERTIES
2.2.1 Materials shall be proportioned to produce concrete with a minimum compressive strength of____ psi (____ Mpa) at 28 days.
2.2.2 Materials shall be proportioned to produce concrete with a maximum equilibrium density of _pcf (_kg/m3) at ___days age, as determined by ASTM C567.
2.2.3 Concrete shall be delivered at the minimum slump necessary for efficient mixing, placing and finishing. The maximum
slump shall be ___in. (___mm) with a tolerance of ± 1 in. (±25 mm).
2.2.4 The air content shall be percent by volume with a tolerance of ± 2 percent.
2.2.5 The Contractor shall furnish the mix design for the strength and density of concrete specified. The mix design shall be prepared
by a qualified testing laboratory and may be based upon the recommendations of the aggregate producer. The mix design
shall be subject to the approval of the Architect-Engineer.
2.2.6 The Concrete shall be batched and mixed in accordance with ASTM C94.
PART 3 — CONTROL
3.1 FIELD CONTROL
3.1.1 The control of the concrete shall be under the supervision of the Architect–Engineer.
3.1.2 Samples of concrete shall be obtained in accordance with ASTM C172, and shall be transported to a place on the site where tests can be made and cylinders stored without being disturbed for the first 24 hours. In addition, if the concrete is placed by pumping, samples shall be obtained from the end of the pump discharge line.
3.1.3 Compressive strength specimens shall be made in accordance with ASTM C31, with the exception that the curing requirement for the test specimens shall be 7 days of moist curing followed by 21 days of air drying. as detailed in ASTM C330. Section 8.1.1 for each of the following conditions:
220.127.116.11 Each day's placing;
18.104.22.168 Each type of concrete;
22.214.171.124 Each change of supplier or source;
126.96.36.199 Each 150 cu. yd. (115m3) of concrete and fraction thereof.
3.1.4 Compressive strength specimens shall be tested in accordance with ASTM C39.
3.1.5 Density. slump and air content of fresh concrete shall be determined from each batch of concrete sampled for compressive strength tests. Fresh density, slump and air content shall be determined by ASTM C138, C143, and C173 respectively. The fresh density of the concrete shall not exceed the design weight plus the weight loss factor determined from project trial mixes by ASTM C567.
The following is a list of ACI publications that will be of assistance to the Architect–Engineer when preparing specifications for the use of structural lightweight aggregate concrete.
• ACI 211.2 Recommended Practice for Selecting Proportions for Structural Lightweight Concrete.
• ACI 212.2R Guide for Use of Admixtures in Concrete.
• ACI 213R Guide for Structural Lightweight Concrete.
• ACI 301 Specifications for Structural Concrete for Buildings.
• ACI 302 Recommended Practice for Measuring, Mixing Transporting and Placing Concrete.
• ACI 305R Hot Weather Concreting.
• ACI 306R Cold Weather Concreting.
• ACI 318 Building Code Requirements for Reinforced Concrete.
• ACI 347 Recommended Practice for Concrete Formwork.
• ACI 311.5R Manual of Concrete Plant Inspection and Testing of Ready-Mixed Concrete
These Guide Specifications have been prepared following the 16 Division Format of the Construction Specifications Institute, Section 03313 Concrete. These comments are intended to help the Architect-Engineer set down limits in his specifications and to so write them that he can obtain the quality of structural lightweight concrete required by the design in an economical manner. The Standards that are listed under Reference Standards are the ones quoted in the specification. In the Appendix there is a list of ACl publications that will be of assistance to the Architect- Engineer when preparing his concrete specifications.
2.2 CONCRETE PROPERTIES
The requirements of this paragraph as well as those of 2.2.5 should be repeated in the specifications if more than one type of concrete is required by the design. 2.2.1 Expanded shale aggregate has been used in lightweight concrete for practically every type of structural application. It has been furnished at all compressive strength levels common to construction practice today, including high strength of 5000 and 6000 psi (34.4 - 41.4 MPa) or more when required 2.2.2 The weight of this concrete will range from 70 to 120 pcf (1120 to /1920 kg/m3) depending upon the strength, air content, aggregate density and mix proportions. The equilibrium density is normally from 5 to 10 pcf less than the fresh density of the concrete as placed. The amount of weight loss in curing is primarily affected by the moisture content of the lightweight aggregate when it is batched. Also, expanded shale lightweight concrete will gain strength and lose weight even after the classical 28 day requirement. This is due to the absorbed moisture, and is especially significant in pumped lightweight concrete. The concrete may gain 500-1000 psi (3.4-7 MPa) and may lose 2% or more in density, in a period between 28 and 98 days, at which time it approaches density equilibrium. If the design conditions will allow extending the time for strength and/or density requirements, it will allow a more economical mix to be used. Consult the lightweight aggregate producer in your area for specific information relating to his aggregate.
2.2.3 The Architect-Engineer should require that the mix be designed for the specified compressive strength and density with a slump which will enable the concrete to be placed and finished efficiently and economically. This slump should be specified. If the concrete is to be placed by pumping, certain considerations such as presaturation of lightweight aggregates, use of admixtures and minimum cement content may be necessary. The Aggregate Producer can supply the Architect–Engineer recommended mixes for special placing conditions. The workability of structural lightweight concrete is comparable with that of normal weight concrete having 1 to 2 in. (25 to 50 mm) greater slump. Shape and dimensions of forms, placement of reinforcement and other specified job conditions vary. However, the following are generally satisfactory; for slabs and beams 3 to 5 in. (80 to 130 mm). For columns and walls 2 to 4 in. (50 to 100 mm).
2.2.4 Air-entrainment in structural lightweight concrete, as in normal weight concrete, improves durability, workability and reduces bleeding. Generally the aggregate producer recommends air entrainment to achieve workability with minimum slump. For durability, 5 to 8 percent air is required; for workability, 4 to 6 percent is generally satisfactory. The Architect-Engineer should specify the amount of air content required for the most economical mix and for the specific application.
2.2.5 In establishing batch proportions, trial mixes should produce concrete with an average compressive strength higher than specified in 2.2.1. The aggregate producer generally follows one of the procedures that are outlined in ACI 211.2, Recommended Practice for Selecting Proportions for Structural Lightweight Concrete. The degree of over design required depends on variability of test results. See AC1318, Building Code Requirements for Reinforced Concrete, Section 4.4. It is recommended that the Architect-Engineer obtain from the aggregate producer a recommended economical cement content, slump, air content and density for the strength of concrete required by the structural design and for the finishing qualities desired.
2.2.6 In designing structural lightweight concrete mixtures, the question is often raised regarding the effect of aggregate absorption. Prewetting requirements in specifications to provide for this characteristic of the aggregate often lead to difficulty in control. Consequently, these specifications do not contain prewetting requirements. The mix and the control of the mix proportions should be established and maintained by the producer's quality control personnel or a qualified laboratory based upon the recommendations of the aggregate producer. With this approach, the variations that exist in batching arrangements, ready-mixed plant layouts, weather, as well as in aggregate properties, can be taken into account to produce the most efficient and economical procedure.
3.1.3 The modified curing cycle for lightweight concrete is reasonable due to the large amount of absorbed water in lightweight aggregate concretes as compared to normal weight concretes. This curing cycle is standard practice for the expanded shale industry, and is recognized in ASTM C330.
3.1.5 The density, slump and air content determinations at intervals specified enable the Architect-Engineer to maintain uniformity in the concrete mixture. As long as there is no appreciable change in the density, i.e., not more than 2 pcf (32 kg/m3) variation from the established fresh density, there is reasonable certainty that the correct proportions are being batched. Variations greater than 2 pcf (32 kg/m3) indicate that some change has taken place in air content, weight of aggregate or batch weights, thereby resulting in a variation of yield. When this occurs, proper adjustments in the mix should be made at once to bring concrete quality back to that specified.