DIVISION 7 STRUCTURES

Transcription

1 DIVISION 7 STRUCTURES Section 701. PORTLAND CEMENT CONCRETE FOR STRUCTURES Description. Proportion structural concrete according to this section for the various grades of concrete required on the project. Unless otherwise specified, provide air-entrained concrete. The term sack refers to a 94-pound sack of cement Materials. Use materials meeting the following: Cement FlyAsh Ground Granulated Blast-Furnace Slag Coarse Aggregate 6A, 6AA Fine Aggregate 2NS, 2SS Concrete Admixtures Water Use coarse aggregate according to Table for the grade of concrete specified. Stone sand 2SS is permitted only in structure concrete not exposed to vehicular traffic. Ground granulated blast-furnace slag may be used as a portion of the cementing material with Type IA or Type I Portland cement. Do not use concrete accelerators containing calcium chloride in concrete for bridges or where the concrete will contain embedded aluminum or galvanized steel General Requirements. A. Equipment. Use equipment meeting subsection B. Mixing Concrete. 1. General. Produce and deliver ready mixed concrete as central mixed or truck mixed concrete. Central mixed concrete is concrete completely mixed in a central mixer and transported to the project site in a truck agitator, a truck mixer, or in approved non-agitating equipment. Truck mixed concrete is concrete completely mixed in a truck mixer with an approved revolution counter, at the plant site. 355

2 Table Concrete Structure Mixtures Cement Types (1)=IA Minimum (2) = IS-A, I(SM)-A Slump, in Strength of Concrete (f) (3) = IP-A, I(PM)-A S1 (1)(2)(3) Cement Content, Type A, Type MR, F, or G Flexural, Compressive, (per cyd) D or no Admixtures (g) psi psi (b) (c) Admixtures Grade of Concrete Fly Ash, Before After Admixture After (e) lb/cyd Admixture (Type MR) Admixture Day Day Day Day Day Day lb sack (Type F or G) (Design (Design Strength) Strength) D(a) 658 (d)(1)(2)(3) T S2(a) (d)(1) 611 (1)(2)(3) 545 (d)(1) 564 (1)(2)(3) 526 (d)(1)(2)(3) 517 (1) 480 (d)(1)

3 Table Concrete Structure Mixtures (continued) Cement Types (1)=IA Minimum (2) = IS-A, I(SM)-A Slump, in Strength of Concrete (f) (3) = IP-A, I(PM)-A S3 (d)(1)(2)(3) a. Unless otherwise specified, use Coarse Aggregate 6AA for exposed structural concrete used in bridges, retaining walls, and pump stations. b. Concrete mixtures containing Type IS-A, I(SM)-A, IP-A, or I(PM)-A cement, or containing ground granulated blast-furnace slag or fly ash, will not be permitted for use on projects in the Lower Peninsula between October 15 and April 1 nor in the Upper Peninsula between October 1 and April 15, except this restriction does not apply to Grade S1 concrete used in foundation piling below ground level, and Grade T concrete used in tremie construction. c. Non-air-entraining cement corresponding to the types of air-entraining cement listed may be used with an approved air-entraining admixture to produce the specified air content. d. Use admixture quantity as indicated in the Qualified Product List to provide reduction in mixing water. Admixture use is required for Grade D concrete and Grades S1, S2, S3 and T having reduced cement content. The admixture used in Grade D concrete must be a water-reducing retarding admixture at dosage required to provide the necessary retardation of setting. When the air temperature is not expected to exceed 60 F for the day, the Contractor has the option of using a water-reducing admixture or a water-reducing retarding admixture. Grade D concrete used in concrete diaphragms shall contain either a waterreducing admixture or a water-reducing retarding admixture. e. The mix design basis for bulk volume (dry, loose) of coarse aggregate per unit volume of concrete is 68% for Grade S1; 70% for Grades D, S2, T, and S3. f. Flexural strength may be used for determining when to remove forms. Compressive strength must be used for acceptance in all other situations. g. MR = Mid-range. Cement Content, Type A, Type MR, F, or G Flexural, Compressive, (per cyd) D or no Admixtures (g) psi psi (b) (c) Admixtures Grade of Concrete Fly Ash, Before After Admixture After (e) lb/cyd Admixture (Type MR) Admixture Day Day Day Day Day Day lb sack (Type F or G) (Design (Design Strength) Strength) 517 (1)(2)(3) 489 (1) 451 (d)(1)

4 Provide communication service from the project site to the batching plant and make it available to the Engineer during the concreting operations. Completely empty the mixer drum and truck mixers after each batch before recharging. Do not exceed the capacity of the mixer as shown on the metal plate attached to the truck. Do not exceed the manufacturer s recommended batch size for maximum agitating capacity of agitating units and truck mixers used to transport central mixed concrete. 2. Batch Mixing. Rotate the drum or blades at the speed, or within the speed range, recommended by the manufacturer and shown on the metal plate attached to the mixer. Mixing time is measured from the time all cement and aggregates are in the drum until the start of discharge of the concrete. For multi-compartment mixers the mixing time includes the transfer time between drums. Charge the ingredients into the mixer so that some water will enter before cement and aggregate, and substantially all the water is in the drum before one-third of the specified mixing time has elapsed. a. Central Mixed Concrete. Mix each batch of central mixed concrete 45 seconds for turbine mixers and 60 seconds for revolving drum and pugmill mixers. Mix revolving drum and pugmill mixers with a capacity of 1 cubic yard or less for a minimum of 90 seconds. b. Truck Mixed Concrete. Mix each batch of truck mixed concrete for more than 70 revolutions at mixing speed. 3. Elapsed Time. Do not exceed the time shown in Table between charging of the mixer and complete discharge of the concrete into the work. Charging begins when the cement comes in contact with the mixing water or damp aggregates. Continuously agitate the concrete when the time between charging and completion of discharge may exceed 30 minutes. 358

5 Table Maximum Time Interval Between Charging Mixer and Placing Structural Concrete (a) Type of Unit Temperature of Concrete (ASTM C 1064) <60 F F >85 F Closed Top Agitating Units and Truck Mixers Closed Top Agitating Units and Truck Mixers with Concrete Containing Water Reducing Retarding Admixture (b) a. All times shown in table are in minutes. b. Does not apply to superstructure concrete. (Superstructure concrete must meet the time limits for closed top agitating units and truck mixers.) 4. Additional Water at Placement Site. Add water to concrete transported in truck mixers only if additional mixing water is required to obtain the specified slump and the truck mixer is not loaded in excess of its rated mixing capacity. After all water is added provide a minimum of 30 revolutions of the truck mixer drum at mixing speed before discharging any concrete. Add this additional water and provide additional mixing at the project site within the maximum time interval specified in Table Except for fog curing, do not add water to the concrete during discharge or placement. In particular, do not add water in truck chutes or in pump or slipform hoppers. 5. Volumetric Batching and Continuous Mixing. Where volumetric batching and continuous mixing methods are used, proportion, mix, and discharge concrete according to ASTM C 685. C. Cold Weather Requirements. 1. Heating Ingredients for Concrete. Heat the ingredients for concrete whenever necessary to produce concrete having a temperature of not less than 45 F. When heating the concrete ingredients, do not exceed a concrete temperature of 80 F; do not exceed 70 F when concrete is placed in insulated forms. Heating the water or aggregates, or both, is permitted. Do not heat aggregates over 150 F. Mix the water with the aggregates before adding the cement. Use aggregates that are free of ice and frozen lumps at time of batching. Heat aggregates in stockpiles or bins using steam or hot 359

6 water coils, live steam, or by indirect hot air. Do not use direct flame to heat coarse aggregate. Compensate for accumulated condensation from heating during batching operations to maintain slump within allowable limits. D. Concrete Temperature Limitations. Concrete must be between 45 F and 90 F at the time of placement. E. Determining Volume of Concrete Used. The Engineer will determine the volume of concrete used each day or fraction of a day, or for each pour, based on the number of batches placed in the work and the nominal volume of concrete per batch. The Engineer will compare this quantity to the estimated plan quantities of concrete. If the volume of concrete used overruns the plan quantity by six percent or more, or underruns the plan quantity, check all factors that may affect the quantity of concrete and correct all irregularities. F. Concrete Mixture Requirements. 1. General. The Contractor is responsible for quality control for concrete on all projects according to subsection 604. The Contractor is responsible for concrete quality assurance, including mix design, according to subsection 605 when the corresponding concrete quality assurance pay items are shown on the plans. The Engineer will provide the mix design requirements on all other projects based on the Contractor s choice of materials from approved sources. Mixture proportions will be designed to provide concrete that meets the requirements in Table Immediately correct concrete production and placement methods if the requirements are not met. The Engineer will designate the quantity of cementitious materials, fine aggregate, coarse aggregate, and the quantity of water required per cubic yard of concrete. Modification of the Department s mix design is restricted to increasing coarse aggregate content or decreasing water content. All costs associated with Contractor modification of Department mix designs will be borne by the Contractor. 360

7 2. Mixes Using Fly Ash or Ground Granulated Blast-Furnace Slag (GGBFS). Use of fly ash in the concrete mixture according to Table is permitted. Use of a greater quantity of fly ash and GGBFS is permitted, if approved by the Engineer, subject to the following: a. The mixture must be designed by a testing laboratory conforming to ASTM C The laboratory must verify that the mix design produces concrete with 28-day compressive strength that exceeds the values in Table by at least 500 psi. Verification must consist of making and curing concrete according to ASTM C 192, with a minimum of three batches made and tested according to the grade of concrete. Submit this verification, with the mix design, to the Engineer. Submit new laboratory data for all subsequent changes in mixture constituents to the Engineer for approval before making the change. b. Use Type I or IA Portland cement. c. Reduce the quantity of cement shown in Table only up to 25 percent for fly ash substitutions and up to 40 percent for GGBFS substitutions. d. The weight of fly ash or GGBFS added must be equal to the weight of the cement reduction. e. If fly ash and GGBFS are used in the same mixture, the cement reduction may not exceed 40 percent and the fly ash portion of the substituted material may not exceed 15 percent. 3. Air Content. Do not use defoaming (air-detraining) admixtures. Furnish concrete containing 6.5 ± 1.5 percent entrained air, except as follows: a. For concrete containing Type F or Type G admixtures, provide an entrained air content of 7.0 ±1.5 percent. b. For concrete furnished for placement by slipform methods and having a slump of inches or less, provide a minimum entrained-air content of 4.5 percent. c. Provide an entrained air content of 6.5 ±3.0 percent for cast-inplace concrete slope paving and related headers. 361

8 d. Air content less than 5 percent for concrete that lies in the finished work at least 3 feet below the surface of the ground or entirely under water will not be cause for rejection. e. Non-air-entrained concrete for concrete placed in steel shell piles not subject to freezing is permitted. Use the Department s modification of ASTM C 231 or ASTM C 173 to determine the air content of freshly mixed concrete. Take samples according to MTM 207. Use the volumetric method, ASTM C 173 to determine the air content of freshly mixed concrete containing slag or other highly porous coarse aggregate. Take samples according to MTM 207. If the quantity of air-entraining admixture used per sack of cement or per batch of concrete is adjusted, record the new quantity on the first delivery ticket following the adjustment. If concrete having low air content is received at the project site in truck mixers, additional air-entraining admixture may be added at the site, with additional mixing as necessary, until adjustments at the batching plant are made. 4. Water-Reducing Admixtures. Concrete mixtures containing a waterreducing admixture must meet the requirements for strength, slump, and air content required for the respective grade of concrete without an admixture. Use water reducing admixtures according to the manufacturer s recommendations. The dosage rate must not be less than that shown on the Qualified Products List. Base admixture dosage rates on the total cementitious material in the concrete (cement plus fly ash or ground granulated blast-furnace slag when used). When a concrete mixture containing a Type A, D, or mid-range (MR) admixture requires retempering due to loss of slump, restore the consistency according to subsection B.4. When a concrete mixture containing a Type F or G admixture requires retempering due to loss of slump, restore the consistency only by the further addition of Type F or G admixture. This additional admixture may be added manually. Turn the mixing drum a minimum of 45 revolutions at mixing speed after addition of the admixture. 362

9 5. Slump. Determine the slump of concrete mixes according to ASTM C 143 slump cone test, except take the samples according to MTM 207 at the project site. Do not exceed the slump of the concrete shown in Table 701-1, for the grade and usage specified. G. Strength of Concrete. 1. Quality Assurance. Refer to section Non Quality Assurance-Strength of Concrete. The Contractor is responsible for supplying all material for test specimens and the labor for molding, curing and transporting them to the designated testing laboratory. The Engineer will furnish molds and testing equipment for specimens. Make concrete test specimens at frequent intervals, from the concrete being incorporated into the work. Flexural strength may be used as a basis for removal of forms. Compressive strength will be used for acceptance in all other situations. Use concrete technician(s) (Michigan Level I or II) certified through a program approved by the Michigan Concrete Association or through the Michigan Concrete Paving Association (Level I-three year certification) for all concrete sampling and testing. Furnish the name(s) and credentials of the concrete technician(s) to the Engineer before concrete placement begins. Make test specimens according to AASHTO T 23. Cure test specimens according to section 9.2 or 9.3 of T 23. Concrete cylinders will be tested according to AASHTO T 22. The use of unbonded caps is allowed by the annex of AASHTO T 22. If unbonded caps are used, MTM 206 will be followed. Flexural strength will be determined according to Department procedures that are based on a modification of ASTM C 293. If compressive strength is determined on beam ends according to ASTM C 116, that strength will be reduced by 20 percent to provide results comparable to results that would be obtained on a cylinder having a height-to-diameter ratio of 2:1. 363

10 If the average strength from compression tests on two companion cylinders is less than the 28-day strength shown in Table 701-1, the Engineer may take any of the following actions. a. Require the Contractor to remove and replace the concrete at no cost to the Department. b. Determine if the concrete has sufficient structural strength; if so, prorate the unit price for affected pay items and quantity represented based on the following formula with strength equal to the minimum strength of concrete shown in Table Adj. Unit Price = Tested Strength (Unit Price) Formula Strength c. Allow the Contractor to submit a corrective action plan for approval. If the plan is approved, all costs associated with the corrective work will be at the Contractor s expense. If the plan is not approved, either option (a) or (b) may be applied. 3. Work Progress Specimens. Determine the strength of structure concrete for opening to construction traffic or regular traffic; for removing shoring and forms; or for other similar purposes by one or more of the following methods, as determined by the Engineer. Refer to subsection for requirement for opening to construction traffic. Concrete containing ground blast-furnace slag or fly ash may gain strength at a slower rate during early stages (before 28 days) than if only Portland cement was used. Adjust operations as necessary for staging activities to conform with the actual strength gained by the concrete. a. Test Cylinders or Beams. Make a series of test cylinders or beams and cure them in environmental conditions similar to the pavement or structure. Test these specimens in the presence of the Engineer. b. Non-Destructive Tests. Conduct non-destructive tests on the structure at locations designated or approved by the Engineer. Perform non-destructive tests according to ASTM C 803 or C 805. Perform testing for calibration and for determination of strength in the presence of the Engineer. Calibrate nondestructive test equipment between the strength of flexure or 364

11 compression test specimens at various stages of curing, and rebound number measured by a concrete test hammer, or penetration resistance. Calibrate for a given instrument and for the specific materials and concrete mix. Make and test occasional cylinders or beams to verify the calibration. H. Furnishing and Handling Aggregates. Furnish, stockpile and handle fine and coarse aggregates to prevent segregation. Place fine aggregates, coarse aggregates and aggregates secured from different sources in separate bins or stockpiles. Place stockpiles on firm, level ground from which all foreign material has been cleaned. If paved areas are not used for aggregate storage, do not use the bottom one foot of the stockpile. Do not use frozen aggregate lumps. Do not use equipment that causes contamination or degradation. Keep the aggregate moisture content uniform throughout each day s run without evidence of surplus water. Keep stockpiles of slag or other highly absorptive aggregates continuously wet to maintain a uniform moisture content. Store fine and coarse aggregates to be used in work for the Department separately from piles or bins of aggregates to be used in other work. When the coarse aggregate consists of a blend of two more gradations, stockpile each gradation separately. I. Furnishing and Handling Cement, Ground Granulated Blast-Furnace Slag, and Fly Ash. Store cement, ground granulated blast-furnace slag, and fly ash furnished in bulk form in separate weatherproof bins. Do not use wet or contaminated material. If the source or type of cement, source or class of fly ash, or source or grade of ground granulated blast-furnace slag changes, empty the bin to within the quantity used for two batches of concrete before refilling with new material. Record the material change on the first ticket (see subsection A.4) for concrete delivered to each project. Furnish the Engineer with a copy of the shipment notice showing the quantity of cement, ground granulated blast-furnace slag, or fly ash in each shipment and containing a certification that the material meets Department requirements Measurement and Payment. Structure concrete mixtures, associated materials, equipment and labor are included in other contract items (pay items). 365