2462Precast Concrete

2462.1DESCRIPTION

This Work consists of producing, providing, placing, curing, and protecting wetcast precast Portland cement concrete in Structures, pavements, and Incidental construction.

2462.2MATERIALS

A Cementitious Materials Provide cementitious Materials from certified sources listed on the APL. Use Type I, I/II, IS, IL, IP, or Type III cement to produce Type 1 non-air-entrained concrete. Use Type I, I/II, IS, IL, IP, or Type III cement and an air-entraining admixture listed on the APL to produce Type 3 air-entrained concrete. A.5 Ternary Mixes Ternary mixes are identified as Portland cement or Type IL and two other supplementary cementitious Materials, Type IT blended cement, or blended cement (excluding IT) and one other supplementary cementitious Material. B Aggregates Provide Aggregates from sources listed on the Department Concrete Aggregate Properties list. Provide admixtures from the APL for concrete grades shown in Table 2462.2-4. D.1 Allowable Admixtures Use of any of the following admixtures are at the precaster’s discretion:

D.2 Use of Accelerating Admixtures The Materials Engineer may permit the use of Type C or Type E accelerating admixtures when the following conditions exist:

E Precast Concrete Mix Designs E.1 Classification of Concrete The Department will classify concrete by mix number to identify type, grade, consistency, Aggregate size, coarse Aggregate class and supplementary cementitious Material, if any, in accordance with Table 2462.2-1. Table 2462.2-1 Mix Number Identification First Digit Second Digit Third Digit Fourth Digit Additional Digits Type Designation Grade Designation Maximum Slump Coarse Aggregate Gradation Designation Additional Digits Allowed or as Specified E.1.a Type Designation Provide Type 1 or Type 3 concrete in accordance with Table 2462.2-2: Table 2462.2-2 Concrete Type Designation Concrete Type Target Air Content*, percent 1 2.0 3 6.5 * For concrete mix design purposes only. E.1.b Grade Designation The Department will designate concrete grade in accordance with Table 2462.2-4 using a letter to represent the following:

for Concrete” E.1.c Slump Designation The Department will designate the slump range as defined by the grade designation in accordance with Table 2462.2-4.

E.1.d Coarse Aggregate (CA) Designation Determine the coarse Aggregate designation in accordance with Table 2462.2-3 based on the intended use and the gradation requirements in 3137, “Coarse Aggregate for Concrete.” Table 2462.2-3 Coarse Aggregate Designation for Concrete Designation Coarse Aggregate Gradation 1 2301, “Concrete Pavement,” only 2 #67* 3 #7* 4 #89* 7 CA-70 8 CA-80 X No gradation required * Gradation sizes designated per ASTM C33/C33M, Standard Specification for Concrete Aggregates, Table 3. E.1.e Additional Concrete Mix Designation Digits Specialty concrete mixes require additional concrete digits in accordance with Table 2462.2-4. The precaster may add additional digits to the right of the required digits in the concrete mix number. E.2 Concrete Mix Design Requirements The precaster assumes full responsibility for the mix design and performance of the concrete. The Department defines the concrete mix design requirements for precast designed mixes in accordance with Table 2462.2-4. When specified, precast Bridge deck, precast pavement panels, and any other special precast product requirements are included in the Special Provisions of the Contract.

Table 2462.2-4 Precast Concrete Mix Design Requirements Concrete Grade Mix Number* Intended Useǁ Maximum W/C/ Ratio Cementitious Content (pounds/ cubic yard) Maximum percent SCM (Fly Ash/ Slag/ Ternary) Slump Range‡ Minimum 28-Calendar Day Compressive Strength, f’c # 3137, “Coarse Aggregate for Concrete” M 3M82 Concrete barrier 0.45 530 – 750 30/35/40 1 – 8 inches 4500 psi 2D.1 V 3V82 Retaining wall blocks, noisewall panels, Equipment pad, lightpole bases 0.45 605 - 850 30/35/40 1 – 8 inches 4000 psi 2D.1 W 1W82 Bridge girders 0.42 660 – 850 30/35/40 1 – 8 inches Design Strength Per Plan § 2D.1 3W82 Noisewall posts, box Culverts, Bridge girders† 0.42 660 - 850 30/35/40 1 – 8 inches Design Strength Per Plan § 2D.1 3W8X Pipe, manholes, inverts 0.45 470+ 30/35/40 1 – 8 inches Design Strength Per Plan § 2D.1 Z 3Z82 Thin panel retaining walls 0.45 605 - 850 30/35/40 1 – 8 inches 4000 psi 2D.2 * Unless otherwise modified in the Contract. ǁ If the intended use is not included elsewhere in the Specification or Special Provisions, design concrete mix 3W82. † Review the Plans to determine if the Bridge girders require air entrainment. ‡ Flowable slumps exceeding the designated slump range require approval of the Materials Engineer. # Requires strength cylinders in accordance with 2462.3G.4, “Test Methods and Specimens,” for determining shipping strength. § If design strength is not indicated in Plan, minimum 28-Calendar Day compressive strength is 5,700 psi for 1W82 and 5,000 psi for 3W82 and 3W8X. E.3 Precast Submittal Requirements At least 21 Calendar Days before initial placement of the concrete, submit a Precast Mix Design Submittal to the Concrete Engineer for review. Use the most current Precast mix design form, specific gravity, and absorption data available from the Concrete Engineering website. Design the concrete mix to an absolute volume of 27.00 – 27.27 cubic feet. MnDOT will review the Contractor’s proposed concrete mix design solely for compliance with the applicable mix design properties in Table 2462.2-4. The Department makes no guaranty or warranty, either express or implied, that compliance with mix design properties ensures compliance with any other requirements.

E.4 Precast Mix Design Adjustments The Department will allow mix design adjustments based upon the criteria as defined in Table 2462.2-5: Table 2462.2-5 Mix Design Adjustments Requirements Type of Change or Adjustment Mix Design Approval Resubmittal Requirements Admixture Dosage Rate Cement or SCM sources No Resubmittal Required Admixture Source Aggregate Source Any Cementitious or SCM Proportion Aggregate Proportions Resubmittal of Mix Design

2462.3CONSTRUCTION REQUIREMENTS

A Batching Equipment A.1 Mixer Requirements Provide stationary mixers or truck mixers. A.2 General Condition Maintain mixers as necessary to detect changes in condition due to accumulations of hardened concrete or mortar and examine to detect wear of blades. Replace or recondition pickup and throwover blades in mixers with a rated capacity less than 14 cubic feet showing a blade wear loss of greater than 1/2 inch, and pickup and throwover blades in mixers of greater capacity, showing a blade wear loss of no greater than 3/4 inch from the original factory dimensions. A.3 Manufacturer's Rating Plate Provide mixers that include the manufacturer’s rating plate, showing the following information:

A.4 Drum Speed for Stationary Mixers Operate the drum speed in the mixer as specified by the manufacturer or as directed by the Materials Engineer. A.5 Auxiliary Equipment Requirements Provide mixers equipped with the following:

each batching cycle

in increments no greater than 1/4 gallon in full view

A.6 Mixer Capacity Do not exceed the manufacturer’s rated capacity of the mixer when mixing a single batch of concrete. Batch concrete in volumes the mixer can accommodate without spilling, leaking, or segregating during the charging, mixing, or discharging operations . Provide mixers with a capacity of at least 1 cubic yard. A.7 Mixing Time For the purpose of the Work specified in section 2462.3A.7, “Mixing Time,” the Department defines the mixing time as the time period beginning when the cement and aggregates enter the mixer drum and ending when the discharge begins. Refer to the manufacturer’s recommended minimum mixing time for single drum and dual drum mixers. In the absence of manufacturer’s recommendation, the Materials Engineer will designate the minimum mixing time. The minimum mixing time for any concrete batch is 60 seconds. The precaster may reduce the manufacturer’s recommended minimum mixing time or the Materials Engineer designated mixing time if the precaster obtains uniform mixing in accordance with 2462.3E, “Mixing Requirements,” and as approved by the Materials Engineer, in conjunction with the Concrete Engineer. If there is evidence of inadequately mixed concrete (unmixed or partially mixed Materials) during concrete placement, the Materials Engineer may direct an increase in the mixing time. A.8 Turbine Type Mixers Provide turbine type mixers meeting the applicable requirements for conventional type mixers in accordance with 2462.3A.1, “Mixer Requirements,” through 2462.3A.7, “Mixing Time,” and this subsection. Maintain the mixer drum in a cylindrical shape within 3/4 inch from the original factory dimensions at any point. Maintain the mixer discharge gate in a mortar tight condition in the closed position. Replace or recondition mixer paddles showing a wear loss greater than 1/2 inch from the original factory dimensions. Add the mixing water to the batch Materials in a manner that distributes the water to the inner or central areas of the drum. Start the flow of water before introducing the solid batch Materials into the mixer drum. During mixing, operate the paddles at a speed between 20 revolutions and 30 revolutions per minute. After adding the batch Materials to the drum, mix the concrete for an additional 60 seconds. A.9 Horizontal Axial-Revolving Blade Type Mixers Provide horizontal axial-revolving blade type mixers in accordance with the applicable requirements for conventional type mixers in accordance with 2462.3A.1, “Mixer Requirements,” through 2462.3A.7, “Mixing Time,” and this subsection. Test the concrete uniformity as directed by the Materials Engineer. The Materials Engineer will use concrete uniformity tests to determine the minimum mixing time.

A.10 Counter-Current Pan Type Mixers Provide counter-current pan type mixers in accordance with Industry Standards and the applicable requirements for conventional type mixers in accordance with 2462.3A.6, “Mixer Capacity,” through 2462.3A.7, “Mixing Time.” The counter-current pan type mixer must have stationary side wall scrapers, a primary mixing motor, and a secondary mixing plow. Completely clean the pan of concrete before proceeding with the next batch. Maintain the pan and all working parts of the counter to current manufacturer’s recommended tolerances. Test the concrete uniformity as directed by the Materials Engineer. The Materials Engineer will use concrete uniformity tests to determine the minimum mixing time. B Transportation Units B.1 General Requirements Equip transportation units intended for both mixing and agitating with watertight revolving drums mounted and powered and fitted with properly designed mixing blades in accordance with 2462.3A.1, “Mixer Requirements,” through 2462.3A.7, “Mixing Time.” Provide units capable of combining the ingredients into a homogeneous mixture and designed to provide two drum speeds, one for mixing and the other for agitating. Provide units capable of delivering the concrete without segregation or loss of any of the batch Materials . Equip the mixer drum with a working counting device to record the number of revolutions. Equip dump trucks and agitator trucks with vibrators to aid in discharge, are mortar tight, capable of complete discharge of the concrete. B.2 Capacity of Transportation Units Refer to the truck mixer manufacturer’s certification plate attached to the unit for the maximum capacity of the unit. If the unit will not satisfactorily mix the maximum volume shown, reduce the batch volume to allow proper mixing or discontinue use of the mixing unit as directed by the Materials Engineer until the problem is corrected. C Handling and Storing Materials C.1 Batch Material Requirements Do not change the source, kind, or gradation of batch Materials after the start of concrete production for the Work unless otherwise approved by the Materials Engineer. If the Materials Engineer approves use of different Material, completely exhaust the supply on hand before changing to the different Material. If delivering freshly washed Aggregates to the batching plant, drain the Aggregates before using in the batching operation. If draining freshly washed Aggregates at the site of the batching plant, completely separate the drained Material from the undrained Materials, and provide for the disposal of water that accumulates from the drainage of Materials . Drain any excess water from the Aggregate hoppers before batching concrete. Provide smooth, firm, and well-drained stockpile sites cleared of vegetable and extraneous matter. Where the natural foundation is unsatisfactory, as determined by the Materials Engineer, construct the stockpiles on suitable platforms. Construct suitable bulkheads or partitions to separate different kinds of Aggregate, gradation, or water content. Construct stockpiles by methods that hold segregation and degradation to a minimum . If the Materials Engineer sees segregation or degradation, the Materials Engineer may designate that pile as unacceptable for use.

Do not use Aggregates used to construct runways for loading or hauling E quipment in concrete batches. Use of Aggregates from the bottom 1 foot of a stockpile placed on an unprepared surface in concrete batches is allowed only under the Materials Engineer’s direct supervision and if the Material meets requirements of 3126, “Fine Aggregate for Portland Cement Concrete,” 3131, “Intermediate Aggregate for Concrete,” and 3137, “Coarse Aggregate for Concrete.” Provide Aggregates in accordance with the specified gradation requirements. The Materials Engineer will consider Aggregates unacceptable if the variation in moisture content carried by any of the Aggregates causes a marked variation in the consistency of successive batches of the mixed concrete, and will suspend operations until corrected. C.2 Concrete Temperature Control Produce concrete at temperatures from 50°F to 90°F and maintain temperatures until deposited in the Work. If necessary to maintain placement temperature, uniformly heat or cool the water, Aggregates, or both, before introduction into the mixer. Control the temperature of the mixing water during heating or cooling. Use Aggregate at temperatures from 32°F to 130°F. Do not allow cementitious Material to contact other batch Material when the Aggregate temperature exceeds 130°F. Do not heat the cement, add salt, or add chemical admixtures to the concrete mix to prevent freezing. Use a heating system to heat batch Materials as approved by the Materials Engineer. Do not use steam jets to spot heat the Material as the Work progresses. Do not place mixer heaters intended for heating the batch Materials in the mixer drum. D Batching Requirements The Concrete Engineer will allow only large capacity Scale companies authorized by the Minnesota Department of Commerce, Weights and Measures Division to calibrate weighting E quipment and meters for Projects. A list of authorized companies is available from the Concrete Engineering Unit website. Calibration of weighing Equipment is required within three months prior to plant certification each calendar year. Calibrate weighing Equipment and perform spot checks in accordance with the Concrete Manual. D.1 Batching by Weight D.1.a Proportioning Methods Proportion concrete batch Materials by weight in a central plant or by volume as directed by the Materials Engineer, in conjunction with the Concrete Engineer. D.1.b Weighing Equipment and Tolerances Weigh or measure concrete mixture ingredients to within the targeted batch weight in accordance with the following:

D.1.c Batching of Mixing Water Measure the mixing water on Scales or water metering devices containing the following:

predetermined quantity

dating the time of the previous calibration and adjustment An authorized service agency will calibrate the water meter in accordance with the following:

Make adjustments as necessary before use meeting the requirements of the weighing procedure in the Concrete Manual. Check the water meter for accuracy at least once each month as the W ork progresses. D.1.d Batching of Cementitious Materials Weigh the cementitious Material independently of the Aggregates in separate compartments or on separate Scales. If the precaster weighs the cement first and then separately records the weights of each individual cementitious Material, the precaster may weigh the cementitious Materials cumulatively as approved by the Materials Engineer, in conjunction with the Concrete Engineer. D.1.e Batching of Aggregates If the precaster records each individual fraction weight of Aggregates separately, the precaster may weigh Aggregates cumulatively as approved by the Materials Engineer, in conjunction with the Concrete Engineer. D.1.f Admixture Proportioning If using two or more admixtures in a single concrete batch, add each admixture separately to prevent interaction of the different admixtures before mixing with other batch Materials. Agitate admixtures to ensure homogeneous concentrations in accordance with the manufacturer’s recommendations. Incorporate admixtures to the batch mix in liquid form. Maintain admixture solutions at a uniform concentration at all times. Use the solution concentration and proportions designated by the manufacturer. If using a mechanical dispenser for proportioning Class I or Class II admixtures, provide a site gauge or meter. Have the admixture manufacturer check admixture dispensers yearly to determine accuracy and ensure unobstructed flow.

D.2 Batching by Volume Proportion concrete for precast products by volume or as required by the C ontract. The Materials Engineer will approve methods and Equipment used in volumetric proportioning. Determine Material proportions and calibration settings on the basis of 100 pounds of cementitious Material. Provide and use only sacked cement in the original mill containers unless the p recaster calibrates the mixer for the specific Materials in use. Do not use previously opened sacks. Increase the cementitious content by 10 percent in the computation of volume proportions unless the precaster calibrates the mixer for the specific Materials in use. E Mixing Requirements The Materials Engineer may check the water measuring Equipment for accuracy before mixing operations begin and at any other time, the Materials Engineer considers necessary. Mix concrete by one of the following methods:

Do not allow the mixing batch to merge or intermix with the subsequent dry batch during mixing. Discharge water remaining in the drums before batching. Mix concrete to provide a mixture that is homogeneous and uniform in color . The Materials Engineer will reject concrete batches that show a marked variation in consistency or evidence of improper mixing as unacceptable Work in accordance with 1503, “Conformity with Contract Documents,” and 1512, “Unacceptable and Unauthorized Work.” After completely mixing the concrete, either in a central plant mixer or truck mixer, continuously agitate while in transit to the point of placement until the concrete is discharged from the unit, unless otherwise allowed by the Materials Engineer, in conjunction with the Concrete Engineer. Transport in non-agitating Equipment is exempt from this requirement. If the mixing does not appear uniform, perform slump tests at the 15 percentage point and the 85 percentage points during unloading. If the results show a slump variation greater than 1 1/2 inch, stop Work and correct the mixing unit. Produce concrete in such quantity and at such a rate as proper placement and finishing will permit. Do not retemper partially set concrete. Do not hand mix concrete. E.1 Mixing In Truck Mixer Charge the Materials into the truck mixer drum by introducing sufficient water before adding solid Materials. Perform charging operations without losing Materials. Leave the truck mixer at the plant site for a minimum of 5 minutes or 50 revolutions during the mixing period. Transport the concrete at agitating speed to the point of placement.

F Batch Ticket Provide a computerized or handwritten batch ticket for each batch of concrete . The Department defines computerized to mean a document that records mix design quantities from load cells and meters. Provide a batch ticket for each item of information, including the following:

Review and sign the first batch ticket for each mixer, each mix type, each day, for accuracy. G Concrete Placement Assume full responsibility for the acceptable production, placement, finishing, and curing of concrete under the conditions prevailing, regardless of the restrictions imposed . Provide any artificial lighting, rain, or cold weather protection necessary, including that directed by the Materials Engineer, at no additional cost to the Department. Place concrete after the Materials Engineer inspects and approves forms and falsework erection, placement of reinforcement steel, Materials, Equipment condition, and cold weather protection. Do not place concrete if portions of the form are frozen. Maintain the surface temperature above freezing for forms, steel, strands, inserts, brackets, and adjacent concrete that will come in contact with the poured concrete. Protect the concrete from freezing. Protect the concrete against damage from construction operations. The Materials Engineer will evaluate any defects in concrete or concrete surfaces resulting from weather conditions, inadequate lighting, or other causes in accordance with 1503, “Conformity with Contract Documents,” and 1512, “Unacceptable and Unauthorized Work.” G.1 Placement Temperatures Maintain concrete at a temperature from 50°F to 90°F until placement. Unless approved cold-weather Plans are in-place, do not place concrete when the air temperature is either of the following at the point of placement:

within the following 24 hour period G.2 Delivery Requirements Place concrete into the forms in accordance with the following:

the plant at the manufacturer’s recommended dosage rates listed on the APL

The precaster may transport Type 1 or Type 3 concrete in non-agitating Equipment if the concrete is discharged within 45 minutes of batching. Batch time starts when the batch plant or the transit mix truck adds the cement to the other batch Materials. G.3 Field Adjustments Mix the load a minimum of 5 minutes or 50 revolutions at mixing speed after addition of admixture or water. G.3.a Water Adjustments The Materials Engineer will allow water adjustments in accordance with the following:

Certificate of Compliance

stated on the Certificate of Compliance G.3.b Admixture Adjustments Approved admixture additions are allowed within 90 minutes from the initial batch time stated on the Certificate of Compliance. If the load of concrete has no available water to add, or the load is greater than 60 minutes old, the Materials Engineer will allow one admixture adjustment diluted with up to 2 gallons of water. G.3.c Consistency and Air Content Adjustments

accordance with the Schedule of Materials Control.

Control testing before the final test. Acceptance or rejection of the truck is based on the final test result.

above, and

trucks, increase verification testing rate to once per truck for acceptance for the remainder of the pour. G.4 Test Methods and Specimens Take samples randomly in accordance with ASTM D3665, Standard Practice for Random Sampling of Construction, Section 5, at a rate defined in accordance with the Schedule of Materials Control. Perform random sampling and testing in accordance with ASTM C172, Standard Practice for Sampling Freshly Mixed Concrete; ASTM C1064, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete; ASTM C231, Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method; ASTM C143, Standard Test Method for Slump of Hydraulic-Cement Concrete; ASTM C1611, Standard Test Method for Slump Flow of Self- Consolidating Concrete; and the Schedule of Materials Control. Furnish 4-inch by 8-inch cylinder molds, unless the maximum Aggregate size is greater than 1 1/4 inches, then furnish 6-inch by 12-inch cylinder molds.

Anyone fabricating concrete cylinders is required to hold either a current ACI Field 1 Technician Certification or a Department Field 1 Technician Certification. Anyone performing concrete strength testing of cylinders is required to hold one of the following current certifications:

G.4.a Strength Cylinders The precaster will cast strength cylinders to determine the following:

Cast cylinders used for determining strength at each stage for types of precast operations. Cure cylinders in the same location and under the same conditions as the concrete structure or unit involved meeting the requirements of ASTM C31, Standard Practice for Making and Curing Test Specimens in the Field. G.5 Consistency Test the concrete for consistency using the slump test during the progress of the W ork. If any test shows the slump outside of the slump range requirements, reject the concrete represented by that test. In order to bring the mixture back into the slump range requirements, the Materials Engineer will allow adjustments to the concrete in accordance with 2462.3G.2, “Delivery Requirements” and 2462.3G.3, “Field Adjustments. Adjust the slump not to exceed the slump range allowed to optimize both placement and finishing. Contact the Materials Engineer if encountering unusual placement conditions that render the maximum slump unsuitable. G.5.a Non-Conforming Material Only place concrete meeting the slump requirements in the Work. If the precaster places concrete not meeting the slump requirements into the W ork, the Materials Engineer will determine acceptance in accordance with 1512, “Unacceptable and Unauthorized Work.” G.6 Air Content Maintain the air content of Type 3 general concrete at the specified target of 6.5 percent (+2.0 percent and -1.5 percent) of the measured volume of the plastic concrete in accordance with 1503, “Conformity with Contract Documents.” Measure the air content at the point of placement but before consolidation. Make any adjustments immediately to maintain the desired air content. The Materials Engineer will reject concrete with a measured air content greater than 8.5 percent or less than 5.0 percent.

G.6.a Non-Conforming Material Only place Type 3 concrete meeting the air content requirements in the Work. If the precaster places Type 3 concrete not meeting the air content requirements into the Work, the Materials Engineer will determine acceptance in accordance with 1512, “Unacceptable and Unauthorized Work.”

2462.4METHOD OF MEASUREMENT - BLANK

2462.5BASIS OF PAYMENT

The Department will include the cost of precast concrete in accordance with 2405, “Prestressed Concrete Beams,” 2411, “Minor Concrete Structures,” and 2545, “Lighting Systems.”