Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements (2009)

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A-1 A T T A C H M E N T A Recommended Changes to AASHTO LRFD Bridge Design and Construction Specifications These proposed changes to AASHTO LRFD Bridge Design and Construction Specifications are the recommendations of the NCHRP Project 18-12 staff at the University of Sherbrooke. These specifications have not been approved by NCHRP or any AASHTO committee nor formally accepted for the AASHTO specifications.

A-3 C O N T E N T S A-4 A.1 Bridge Design Specifications A-4 A.1.1 Mixture Characteristics A-4 A.1.2 Code Provisions for Mechanical and Visco-Elastic Properties A-5 A.2 Construction Specifications A-5 A.2.1 Classification A-6 A.2.2 Material Constituents A-7 A.2.3 Mix Design and Proportioning A-9 A.2.4 Production, Handling, and Placement

A.1 Bridge Design Specifications A.1.1 Mixture Characteristics Clause 5.4.2 Normal and Structural Lightweight Concrete Clause 5.4.2.1 Compressive Strength A-4 This attachment presents the recommended modifications to AASHTO LRFD Bridge Design and Construction Specifications. These modifications are shown in underlined format. P(SCC) refers to self-consolidating concrete for use in precast, prestressed applications; SCC refers to self-consolidating concrete for use in general cast-in-place and/or precast applications. Specifications Commentary Minimum Cement Content Maximum W/C w/cm Ratio Air Content Range Coarse Aggregate Per AASHTO M 43 (ASTM D 448) 28-day Compressive Strength 56-day Compressive StrengthClass of Concrete pcy lbs. Per lbs. % Square Size of Openings (in.) ksi ksi P(SCC) 700* 0.45 As specified elsewhere (5.5 1.5% for severe freezing and thawing conditions). Higher air content may be required when using small MSA and/or HRWRA that can lead to relatively large air bubbles) ½ in. – No. 4 or ¾ in. – No. 4 (maximum) 6.0 to 8.0 8.0 to 10.0 * total cementitious materials Table C5.4.2.1-1. Concrete mix characteristics by class. Clause C5.4.2.1 Suggest the addition of a new Class of concrete to Table C5.4.2.1-1, as indicated below. A.1.2 Code Provisions for Mechanical and Visco-Elastic Properties Clause 5.4.2.3 Shrinkage and Creep Clause 5.4.2.3.2 Creep The creep coefficient may be taken as: in which: kvs = 1.45 − 0.0051(V / S) ≥ 0.0 where: H = relative humidity (%). In the absence of better in- formation, H may be taken from Figure 5.4.2.3.3-1. kvs = factor for the effect of the volume-to-surface ratio of the component k H k f k t f t hc f ci td ci = − + ′ = − ′ + 1 56 0 08 35 7 61 0 58 . . , . ⎛ ⎝⎜ ⎞ ⎠⎟ ψ t t k k k k t Ai vs hc f td i, . . . . ..( ) = ×−1 9 5 4 2 3 2 10 118 -( )

kf = factor for the effect of concrete strength khc = humidity factor for creep ktd = time development factor t = maturity of concrete (day). Defined as age of con- crete between time of loading for creep calculations, or end of curing for shrinkage calculations, and time being considered for analysis of creep or shrinkage effects ti = age of concrete when load is initially applied (day) V / S = volume-to-surface ratio (mm) f ′ci = specified compressive strength of concrete at time of prestressing for pretensioned members and at time of initial loading for nonprestressed members. If concrete age at time of initial loading is unknown at design time, f ′ci may be taken as 0.80 f ′ci (MPa) A = factor for the effect of cement type: 1.19 for Type I/II cement and 1.35 for Type III + 20% FA binder which may be used for P(SCC) Clause 5.4.2.3.3 Drying Shrinkage For steam cured concretes devoid of shrinkage-prone aggre- gates, the strain due to shrinkage, sh, at time, t, may be taken as: where: t = drying time (day) ks = size factor kh = humidity factor V / S = volume-to-surface ratio, and A = cement factor: 0.918 for Type I/II cement and 1.065 for Type III + 20% FA binder which may be used for P(SCC) A.2 Construction Specifications A.2.1 Classification Clause 8.2 CLASS OF CONCRETE Clause 8.2.2 Normal-Weight (-Density) Concrete Eleven classes of normal-weight (-density) concrete are provided for in these specifications as listed in Table 8.2.2-1. A new Class of concrete, P(SCC), is added to Table 8.2.2-1. ε sh s hk k t t A= − + ⎛⎝⎜ ⎞⎠⎟ × × (−55 0 56 10 3. steam-cured) = + + ⎡ ⎣ ⎢⎢ ( ) ( . . . . ) . 5 4 2 3 3 1 26 45 0 0142 - k t e t t t s V S ⎢⎢ ⎤ ⎦ ⎥⎥⎥⎥ − ( )⎡ ⎣⎢ ⎤ ⎦⎥ 1064 3 70 923 . V S Clause C5.4.2.3.3 The CEB-FIP MC90 modelA1 for drying shrinkage can also be used for P(SCC). The model takes into consideration rela- tive humidity, cement factor, compressive strength at 28 days, cross-sectional area, and perimeter, as well as age of concrete at testing and duration of curing before drying. P(SCC) proportioned with high binder content and low w/cm can exhibit autogenous shrinkage of 100 and 350 µstrain. Autogenous shrinkage is mostly affected by binder type and paste volume. A-5 Specifications Commentary A1CEB-FIP Model Code, Design Code 1990, Comité Euro-International du Béton (1990).

A.2.2 Material Constituents Clause 8.3.1 Cements For Class P(HPC), P(SCC), and Class A (HPC), trial batches using all intended constituent materials shall be made prior to concrete placement to ensure that cement and admixtures are compatible. Changes in the mill, brand, or type of cement shall not be permitted without additional trial batches. Clause 8.3.3 Fine Aggregate Fine aggregate for concrete shall conform to the require- ments of AASHTO M 6. Fine aggregate should be well-graded concrete sand. It may be beneficial to blend natural and man- ufactured sands to improve workability and stability, which is critical for P(SCC). Particle size fractions less than 0.005 in. (0.125 mm) should be considered as powder materials in pro- portioning P(SCC). Such fine content can have marked effect on water and admixture demand, as well as workability of P(SCC). Clause 8.3.4 Coarse Aggregate Coarse aggregate for concrete shall conform to the require- ments of AASHTO M 80. A-6 Clause C8.3.1 Selection of cement type depends on the overall require- ments for the concrete, such as compressive strength at release and ultimate age, visco-elastic properties, and durability characteristics. Type I/II or Type III cement can be used for P(SCC) designated for precast, prestressed bridge elements. Supplementary cementitious materials can be incorporated to replace part of the cement; for example, 20 percent Class F fly ash or 30 percent slag can be used as part of the total mass of binder for P(SCC) made with Type III cement. Clause C8.3.4 In the design of P(SCC), MSA values are typically smaller than those of conventional vibrated concrete. The MSA de- pends on the particular application, including reinforcement density, clear spacing between reinforcement and cover, and section minimum dimension. In general, MSA of 1⁄2 in. (12.5 mm) is recommended for P(SCC) designated for pre- cast, prestressed bridge elements. Minimum Cement Content Maximum w/cm Ratio Air Content Range Size of Coarse Aggregate Per AASHTO M 43 (ASTM D 448) Size Number Specified Compressive Strength Class of Concrete lb/yd3 lb per lb % Nominal Size Ksi at days P(SCC) 700* 0.45 As specified elsewhere (5.5 1.5% for severe freezing and thawing conditions). Higher air content may be required when using small MSA and/or HRWRA that can lead to relatively large air bubbles) ½ in. – No. 4 or ¾ in. – No. 4 (maximum) 7 or 67 6.0 to 8.0 at 28D or 8.0 to 10.0 at 56D * total cementitious materials Table 8.2.2-1. Classification of normal-weight concrete. Specifications Commentary

Clause 8.3.7 Air-Entraining and Chemical Admixtures Air-entraining admixtures shall conform to the require- ments of AASHTO M 154 (ASTM C 260). In the case of P(SCC), air-entraining admixtures may be used to increase the work- ability of the concrete and facilitate handling and finishing. The use of Type F or G HRWRA is essential to achieve P(SCC) fluidity. The HRWRA can be used in combination with water-reducing admixtures or mid-range water-reducing admixtures. Some mid-range water-reducing admixtures may be classified under ASTM C 494 as Type A or F, depending on the applied dosage rate. Viscosity-modifying admixture (VMA) can be used in P(SCC) to increase stability and robustness. In mixtures with low w/cm with sufficient stability, VMA may be incorporated at low concentration to enhance robustness. This can result in concrete less sensitive to small variations in mixture pro- portioning and material characteristics, including moisture content of sand, as well as mixing conditions and fresh con- crete temperature. If a shrinkage-reducing admixture is specified in the con- tract documents, verification of the air-void system in the hardened concrete is recommended. Clause 8.3.8 Mineral Admixture A.2.3 Mix Design and Proportioning Clause 8.4.1.1 Responsibility and Criteria For Class P(HPC), Class A(HPC), and Class P(SCC), such modifications shall only be permitted after trial batches to demonstrate that the modified mix design will result in con- crete that complies with the specified concrete properties. A-7 Clause C8.3.7 In some cases, high dosage rate of high-range water- reducing admixture (HRWRA), coupled with high fluidity, can make it difficult to ensure fine air-void system in the hardened concrete. Highly flowable concrete of marginal sta- bility can result in loss of entrained air voids and foaming at the surface. Air-entraining admixture that can stabilize small air bubbles should be used, especially in the case of P(SCC), whenever the concrete requires protection from frost action. Clause C8.3.8 Pozzolans (fly ash, silica fume) and slag can be used in the production of Class P(HPC), Class A(HPC), and Class P(SCC) concretes for improved durability and to extend the service life. Fly ash produced by plants that utilize the limestone injec- tion process or use compounds of sodium, ammonium, or sulfur, such as soda ash, to control stack emissions shall not be used in concrete. The carbon content in fly ash can affect air entrainment as it absorbs some of the air-entraining ad- mixture and adversely affects the ability to entrain air. Care should be exercised, and frequent tests should be conducted, to verify the presence of sufficient air voids in the concrete. Clause C8.4.1.1 Mix design of P(SCC) is vital for the performance of the material, both in the plastic and hardened stages. In designing P(SCC), a number of factors should be taken into considera- tion to a greater degree than when designing conventional vibrated concrete: • Properties of locally available raw materials, including min- eral, geometric, and physical properties of aggregates and cementitious materials Specifications Commentary

Clause 8.4.3 Cement Content The minimum cement content shall be as listed in Table 8.2.2-1 or otherwise specified in the contract documents. For Class P(HPC) and P(SCC), the total cementitious materials content shall be specified not to exceed 1000 lb/yd3 (593 kg/m3) of concrete. Clause 8.4.4 Mineral Admixtures Clause 8.4.2 Water Content The amount of water used shall not exceed the limits listed in Table 8.2.2-1 and shall be further reduced as necessary to produce concrete of the consistencies listed in Table 8.4.2-1 (a) at the time of placement. A-8 • Need for higher level of quality control, greater awareness of aggregate gradation, and better control of mix water and aggregate moisture • Choice of chemical admixtures and their compatibilities with the selected binder • Consideration of placement technique, configuration of cast element, and environmental conditions Clause C8.4.2 For P(SCC) member, workability characteristics shown in Table 8.4.2-1 (a) are recommended. Specifications Commentary Slump flow, in. Slump flow – J-Ring flow, in. Relative values 23.5–25 25–27.5 27.5–29 3–4 2–3 ≤ 2 Low Medium High Reinforce- ment density Small Moderate Congested Shape intricacy Shallow Moderate Deep Depth Short Moderate Long Length Thin Moderate Thick Thickness Low Medium High Coarse aggregate content 1 in. = 25.4 mm Shaded areas refer to recommended workability values. Table 8.4.2-1 (a). Workability characteristics for P(SCC). Clause C8.4.4 Mineral admixtures are widely used in concrete in the per- centages given. For Class P(HPC), Class P(SCC), and Class A(HPC) concretes, different percentages may be used if trial bathes substantiate that such amounts provide the specified properties. A 25-percent maximum of portland cement replacement is permitted for all classes, except for Classes P(HPC), P(SCC), and A(HPC), which have a 50-percent maximum portland ce- ment replacement.

A-9 Clause C8.5.5 It is essential to ensure that the delivery and placement of SCC be within the workability-retention period of the mix- ture. SCC can be transported by mixer trucks, tuckerbilts, sidewinders, clam buckets, pumping, or overhead cranes. Mixer trucks are suitable when transporting SCC over rough terrain or long transport distance. During transport, the loads in trucks may be limited to avoid spillage, or mixtures with lower flow can be shipped by holding back the mix water and the admixtures, which then can be added at the job site. Specifications Commentary For Class P(HPC), P(SCC), and Class A(HPC) concrete, mineral admixtures (pozzolans or slag) shall be permitted to be used as cementitious materials with portland cement in blended cements or as a separate addition at the mixer. In some cases, limestone filler may be used to replace part of the portland cement or to increase the powder content of SCC. Selected fillers should be uniform in chemical composition and physical characteristics and should not hinder the targeted performance of SCC (workability, strength development, and durability). The amount of mineral admixture shall be deter- mined by trial batches. The water-cementitious materials ratio shall be the ratio of the weight (mass) of water to the total cementitious materials, including the mineral admix- ture. The properties of the freshly mixed and hardened con- crete shall comply with specified values. A.2.4 Production, Handling, and Placement Clause 8.5.4 Batching and Mixing Concrete Clause 8.5.4.1 Batching The size of the batch shall not exceed the capacity of the mixer as guaranteed by the Manufacturer or as determined by the Standard Requirements of the Associated General Con- tractors of America. The batch size should be determined in consideration of the type of concrete, mixing efficiency of the mixer, volume of concrete to be transported, and shipping rate. The batch volume should be limited to 80 percent of the maximum capacity of the mixer for SCC. This value can be increased for concrete of relatively low fluidity, and final ad- justments to concrete deformability are made on site prior to casting. Clause 8.5.4.2 Mixing Mixing equipment and mixing sequence should be vali- dated during mix qualification testing of SCC. Necessary adjustments, such as time and energy of mixing, should be carried out until consistent and compliant results are obtained. Insufficient mixing could result in lower fluidity and could hinder the generation of adequate air-void system. Clause C8.5.5 Delivery

A-10 Clause 8.5.7 Evaluation of Concrete Strength Clause 8.5.7.3 For Acceptance of Concrete Except for Class P(HPC), Class A(HPC), and Class P(SCC) concrete, any concrete represented by a test that indicates a strength that is less than the specified compressive strength at the specified age by more than 0.500 ksi (3.5 MPa) will be re- jected and shall be removed and replaced with acceptable concrete. Such rejection shall prevail unless either: For Class P(HPC), Class A(HPC), and Class P(SCC) con- crete, any concrete represented by a test that indicates a strength that is less than the specified compressive strength at the specified age will be rejected and shall be removed and replaced with acceptable concrete. Clause 8.7 HANDLING AND PLACING CONCRETE Clause 8.7.3 Placing Methods Clause 8.7.3.1 General Because SCC is based on concrete placement without vi- bratory consolidation, an adequate construction plan should be formulated in consideration of the properties specific to SCC so that the proportioned concrete could be transported and placed while the required self-consolidation is retained. Under normal conditions, P(SCC) has an open time of 35 to 45 minutes (time after the end of mixing where the concrete still satisfies the stipulated flowability, passing ability, and sta- bility requirements). Delays in concrete deliveries between successive lifts may lead to surface crusting, formation of cold joints, and other surface defects given the lack of surface bleeding that is typically encountered in P(SCC). Clause C8.5.7.3 In the case of Class P(SCC) concrete, fresh concrete needs to be tested for its self-consolidating properties. It is recom- mended that the producer conduct workability tests and make necessary adjustments until consistent and compliant results are obtained. Given that in a precast concrete plant the manufacturing conditions are rather constant, the first three mixtures of a day can be subjected to more complete inspection and routine testing. Subsequent mixtures of similar compo- sition may be subjected to limited and less frequent quality control testing. Nonetheless, every batch should still be visu- ally checked before transportation, then tested for slump flow consistency and T-20 (T-50), and visually checked prior to casting. The Contractor may also elect to verify the passing ability on site by conducting a J-Ring test. In the case that the P(SCC) is air entrained, air volume should be evaluated as per Contract documents. Clause C8.7.3.1 Placement techniques of SCC can have a significant impact on the required fluidity level and flowing performance. For example, whenever a relatively high energy is available dur- ing SCC placement, a lower fluidity level could be possible to achieve the desired consolidation and filling capacity of the cast element. In the case of placement technique involving higher energy, extra care should be taken with regard to sta- bility characteristics. Some guidelines to the relative level of energy provided during different placement techniques are summarized in Table C8.7.3-1. Specifications Commentary

Placement of SCC in horizontal elements can be done by starting at one end of the mold, with the discharge point close to the form surface. It is recommended to discharge the SCC in the direction of desired flow to maximize the travel distance. To minimize segregation, the free-flow distance of the SCC should be limited to 10 and 33 ft (3 and 10 m), depending on section geometry and level of reinforcement. Clause 8.7.4 Consolidation All concrete, except concrete placed under water, Class P(SCC), and concrete otherwise exempt, shall be consoli- dated by mechanical vibration immediately after placement. Clause 8.11 CURING CONCRETE Clause 8.11.3 Methods Clause 8.11.3.5 Steam or Radiant-Heat Curing Method Clause C8.7.4 Mechanical vibration shall not be applied for the consolida- tion of Class P(SCC) except when delays occur between succes- sive lifts. In this case, extreme care must be taken to minimize any risk of segregation during mechanical consolidation. Clause C8.11.3.5 For Classes P(HPC) and P(SCC) concrete, temperature- sensing devices should be placed within the concrete to verify that temperatures are uniform throughout the concrete and within the limits specified. A-11 Specifications Commentary Placement Technique Discharge Rate Discharge Type Single Discharge Volume Flow Momentum Rating Truck Chute High Continuous High High Pump Medium/High Continuous Medium High/Medium Conveyor Medium Continuous High High Buggy Medium Continuous Low Low Crane and Bucket High Discontinuous Low Low/Medium Auger Low Continuous Medium Medium Drop Tube High Discontinuous High High Table C8.7.3-1. Relative placement energy associated with different placement techniques for SCC (Daczko and Constantiner, 2001).A2 A2Daczko, J. A., and Constantiner, D., “Rheodynamic Concrete.” Proceedings, 3rd Congresso Brasileiro do Concreto (IBRACON), paper IV-003, August, Brazil (2001), 15 p.