403 SECTION 802
802.01 Mix Design
A.General.
1.Development. Develop a mix design based on the requirements of this section. Perform the specified aggregate and strength tests and submit the results with the mix design. Submit the completed mix design a minimum of 14 days before beginning concrete placement operations. Use materials slated for use on the project when developing and testing the mix design. If any material or material source changes, develop and submit a revised mix design and test results. Provide concrete that is air entrained. Concrete is divided into classifications as shown in Table 802 -01. Table 802 -01 Concrete Class Designation Cementitious Material Content (lbs) per CY Water -Cement Ratio (Max) AAE 600 – 650 0.44 AE 550 – 600 0.47 ASE 575 – 625 0.40 A numeral following the alphabetical designation for the class of concrete indicates the gradation of coarse aggregate to be used in the mix, based on Table 802-03. If a specific gradation is not designated, use any gradation from Table 802-03. For ASE concrete, use aggregate that meets the requirements of Section 802.01 C.4, “Well Graded Aggregate” .
2.Class AE and AAE Mixes. Design a mix that will attain a compressive strength of 3,000 psi within 7 days or a flexural strength of 450 psi within 7 days. Mix designs used for Section 550, “Concrete Pavement” will be required to attain both a compressive strength of 3,000 psi and a flexural strength of 450 psi within 7 days. Measure compressive strength according to AASHTO T 22 and flexural strength according to AASHTO T 97. Aa correction factor of 0.92 when using 4 inch x 8 inch concrete cylinders.
3.Class ASE Mix. Design a mix that will attain a minimum compressive strength of 3,000 psi within 30 hours or a minimum flexural strength of 450 psi within 30 hours. 404 Develop a maturity curve according to ASTM 1074. Use 6 inch x 12 inch cylinders or flexural beams for strength determination.
4.Certificate of Compliance. Submit a certificate of compliance for non-aggregate materials.
B.Cement. Provide cement as specified in Section 804.01 “Cement” .
C.Aggregate.
1.General. Base the aggregate content of the concrete mix on a saturated surface- dry condition of the aggregates. Determine the relative proportions of each stockpile and adjust the batch quantity of each aggregate as necessary to compensate for any free water on the surf ace of the aggregate or for any water that will be absorbed by the aggregate.
2.Coarse Aggregate. Provide coarse aggregate that meets requirements of Table 802-02 and the appropriate numerical designation from Table 802-03. Table 802-02 Miscellaneous Coarse Aggregate Properties Test Method Max. Percent by Weight of the Plus No. 4 fraction Shale NDDOT 3 0.7 Iron oxide particles NDDOT 3 4.01 Lignite and other coal NDDOT 3 0.5 Soft Particles (Excluding Shale, Iron oxide particles and Lignite and other coal) NDDOT 3 2.5 Thin or Elongated Pieces NDDOT 3 15
L.A. Abrasion AASHTO T 96 40.0 Soundness (Sodium Sulfate) AASHTO T 104 12 1 For concrete for spall repairs and bridge deck overlays, the maximum iron oxide particles shall be 2.0 percent. Table 802 -03 Coarse Aggregate Gradation Sieve Size Aggregate Size and Percent Passing by Weight 3 4 5 1-1/2 inch 100 1 inch 95 – 100 100 3/4 inch 90 – 100 100 1/2 inch 25 – 65 90 – 100 3/8 inch 15 – 55 20 – 55 40 – 70 No. 4 0 – 10 0 – 10 0 – 15 405 Table 802 -03 Coarse Aggregate Gradation Sieve Size Aggregate Size and Percent Passing by Weight 3 4 5 No. 8 0 – 5 0 – 5 0 – 5 No. 200 0 – 1.0 0 – 1.0 0 – 1.0
3.Fine Aggregate. Use fine aggregates that meet the gradation in Table 802-04 and the miscellaneous properties in Table 802- 05. Test fine aggregates in accordance with AASHTO T 21. If the results of the analysis are darker than the standard color, determine the compressive strength of mortar mixed using the aggregate in accordance with AASHTO T 71. If the results of the AASHTO T 71 test result in a relative strength less than 95 percent, do not use the fine aggregate. Table 802 -04 Fine Aggregate Gradation Sieve Size Percent Passing 3/8 Inch 100 No. 4 95 – 100 No. 16 45 – 80 No. 50 10 – 30 No. 100 0 – 10 No. 200 0 – 3.0 Table 802-05 Miscellaneous Fine Aggregate Properties Test Method Requirement Soundness (sodium sulfate) AASHTO T 104 10% max. Lightweight pieces in Aggregate ND T 113 2% max.
4.Well Graded Aggregate. Use a well graded aggregate that meets the gradation in Table 802-06 and the properties specified in Table 802-02 and 802-05. When testing material properties specified in Table 802-02 and Table 802-05, divide aggregate samples into course and fine aggregate on the No. 4 sieve. Table 802 -06 Well Graded Gradation Sieve Size Percent Passing 1-1/4 inch 100 1 inch 95 – 100 3/4 inch 90 – 100 3/8 inch 55 – 70 406 Table 802 -06 Well Graded Gradation Sieve Size Percent Passing No. 8 31 – 42 No. 16 18 – 35 No. 50 0.0 – 10 No. 200 0.0 – 3.0
D.Water. Provide water as specified in Section 812, “Water”. The water content of the mixed concrete includes the quantity of mixing water measured into the batch plus any free water on the surface of the aggregates, but does not include water absorbed by the aggregates. Use the minimum water content required to produce a workable, plastic mix having a consistency that permits a satisfactory rate of discharge, proper placement, and consolidation of the concrete.
E.Slump. If concrete is pumped from the mixer or truck, adjust the slump at the mixer to give the proper consistency at the point of deposit in the forms. Provide concrete that has a slump that meets the requirements in Table 802-07. Table 802 -07 Slump Requirements Concrete Application Min Max Inches Inches Pavements: Formed Paving 1.0 4.0 Slipformed Paving 0.0 2.0 Structures: Structural Concrete 1.0 4.0 Bridge Decks 1.0 3.0 Barrier Curbs 1.0 4.0 Barrier Curbs Slipformed 0.0 2.0 Box Culvert, Top and Bottom 1.0 4.0 Box Culvert, Sides 1.0 5.0 Applications not listed above 1.0 4.0
F.Admixtures.
1.General. Use admixtures as specified in Section 808 “Concrete Admixtures” .
2.Bridge Deck Concrete. Use a retarding admixture in Class AAE -3 concrete in bridge decks when the temperature of the concrete or the ambient air temperature at the time of placement exceeds 75°F. Provide a retarding admixture that meets the requirements of AASHTO M 194 and that are cl assified as Type B or D under ASTM C 494.
3.ASE Concrete. A non-calcium chloride accelerator may be used, but must meet the requirements of AASHTO M 194 and be classified as Type C under ASTM C 494. Accelerating admixtures are limited to a maximum of 2.0% by weight of cement.
G.Supplementary Cementitious Material (SCM).
1.Concrete Used in Bridges, Beams, and Box Culverts. When placing concrete under section 602, 604, 606, 622, and 650 ; use Class F Fly Ash meeting the requirements of Section 820.02 B. “Class F Fly Ash” Class F Fly Ash may replace cement on a 1:1 ratio, up to a maximum of 29 percent by weight.
2.ASE Concrete. Include SCM in the mix at a rate between 10 percent and 20 percent, by weight, of the cementitious material in the mix.
3.Other Concrete. SCM, meeting the requirements of Section 820, “Supplementary Cementitious Material (SCM) ”, may replace cement on a 1:1 ratio, up to a maximum of 35 percent by weight.
H.Air Content. Use one of the following methods to entrain air in the concrete:
1.Air-entraining cement;
2.A chemical admixture as specified in Section 808, “Concrete Admixtures” ; or
3.A combination of 1. and 2. Supply concrete with an air content between 5.0 and 8.0 percent of the volume of the concrete at the time of placement.
I.Tests on Concrete. Furnish the concrete necessary for the tests. Near the site of concrete placement, provide a level area protected from construction activities near the site of placement for the Engineer to conduct tests.
802.02 Equipment
Item Section Batch Plant 155.02 Mixer 155.03 Transporting 155.04 408 802.03 CONSTRUCTION REQUIREMENTS
A.Handling and Storing Materials.
1.Cement or SCM . Handle and store cement and SCM of different types, brands, or sources separately. Provide storage that protects the cement or fly ash against dampness. Do not use cement that contains caked lumps or is salvaged from spillage.
2.Aggregates. Handle and stockpile each separate aggregate component of different source or grading separately. Provide adequate equipment and material to ensure a continuous batching operation. Do not operate aggregate hauling equipment on the stockpile. Do not use material from the bottom one foot of the stockpile. The Engineer will reject aggregates that become intermixed with aggregates of different source or become contaminated by foreign materials. Remove rejected aggregate from the plant site. The Engineer will reject segregated aggregate unless the aggregate is uniformly remixed to meet the specified gradation. Allow washed aggregates to drain for at least eight hours before use to obtain stable and uniform moisture content. The Engineer will consider gravity drainage in the weigh hoppers or truck box es evidence that the moisture content is not stable. The moisture content is not uniform if the variations in moisture content of any aggregate component causes fluctuations in the consistency of successive batches of the mixed concrete. Store freshly was hed aggregates separately from the drained aggregates in use.
B.Batching of Concrete Materials.
1.General. When directed by the Engineer, test the batching operation accuracy on a certified scale. Weigh the batched ingredient on a platform scale. Perform the accuracy test at no additional cost to the Department. Stop mix production if the scale is out of tolerance. Fix and recertify the batching scale before continuing mix production.
2.Batching Cement and SCM . Batch bulk cement and SCM to a tolerance of 1 percent of the weight specified in the mix design.
3.Batching Aggregate. Batch aggregate components to a tolerance of 2 percent of the weight specified in the mix design. 409 4. Batching Water. Measure the mixing water for each batch by volume or by weight. Add the designated quantity of mixing water to each batch, within a tolerance of 1 percent.
C.Measuring and Dispensing Admixtures. Measure admixtures used in the concrete and dispense using the manufacturer’s recommendations to give a uniform distribution. Dispense admixture using a clean device that repetitively controls the batching of the admixture within a tolerance of 5 percent of the required volume of material or 1 fluid ounce, whichever is greater. Arrange dispensing equipment to allow convenient, visual observation of the volume of admixture dispensed. If using more than one admixture in the same batch, add the admixtures separately to prevent contact in their concentrated form.
D.Mixing and Transporting Concrete.
1.General. Mix the concrete at the site of placement or by a ready -mix method. Mix the concrete in the quantity required to provide continuous placement and finishing operations. Do not add water to reestablish the required consistency of concrete. Operate the mixer so successive batches of concrete do not merge or intermix during the mixing cycle. Mix all concrete until the cement, water, aggregates, and admixtures are uniformly distributed. Do not use materials containing frost or lumps of frozen material. If weather conditions begin damaging the work, stop concrete mixing operations.
2.Mixing. Measure the mixing time from the time all solid materials are in the drum until discharge of that batch begins. Charge the drum so a portion of the mixing water enters in advance of the aggregates and cement. Add all remaining water after charging the aggregate and cement and before 1/4 of the mixing time has elapsed. Include transfer time in multiple compartment mixers in mixing time. Use a minimum mixing time per batch of 60 seconds. Mix the concrete for a minimum of 90 seconds if temporarily operating the mixer under manual timing control or the mixer has a rated capacity of less than 10 cubic feet.
3.Transporting C oncrete. Deliver concrete to the site of placement in an agitating truck, in a truck mixer operated at agitating speed, or in approved non-agitating equipment. Do not exceed 30 minutes in non-agitating equipment or 60 minutes in agitating equipment, between introducing the cement to the mixture and the time the concrete has been completely discharged. 410 Limit the amount of time between introducing the cement into the mix and fully discharging the batch to: − 30 minutes for non-agitating equipm ent; or − 60 minutes for agitating equipment. The Engineer may reduce these time limits if weather conditions affect the concrete adversely. The Engineer may extend the 60 minute time limit to a maximum of 90 minutes if the ambient air and the concrete mix temperature at the time of mixing is less than 80°F, and if the mixed concrete meets the specified requirements for maximum water content and air content when discharged at the site of the work. The mix must be completely discharged within the 90 minutes. Do not add water to concrete after the 60 minute time limit. Only produce truck -mixed concrete after all equipment, facilities, and methods for handling and storing materials and for proportioning, mixing, and transporting the concrete have been approved. Discontinue the use of truck mixed concrete if the delivery of concrete is insufficient for continuous placement and finishing. Discontinue the use of truck mixed concrete if any properties of the concrete are not meeting specifications. Place a volum e of concrete in the truck -mixer that does not exceed the maximum capacity shown on the manufacturer’s rating plate. Clean the truck -mixer at periodic intervals to prevent accumulation of hardened concrete, and empty it of all free water before receiving any batch ingredients. After all ingredients are charged in a truck -mixer, rotate the mixer between 70 and 100 revolutions at mixing speed. If the batch volume is 90 percent or less than the rated mixing capacity, the Engineer may reduce the mix ing to a minimum of 50 revolutions. After mixing is complete, revolve the mixer at agitating speed. If water is added, mix an additional 30 revolutions at mixing speed after mixing has begun or been completed.
4.Temperature Control. After mixing, maintain the concrete temperature between 50°F and 90°F until placement. The Engineer will allow heating or cooling aggregates, mixing water, or both if required to maintain the temperature range. Apply the following restrictions: - Heat aggregates using indirect heat only and to temperatures not exceeding 150°F; - If the aggregate or the water is heated to a temperature exceeding 100°F, combine the aggregate and water before placing them in contact with the cement; - If heated by steam, drain aggregates as spec ified in Section 802.01 C, “Aggregate” before measuring it into the batches; and - Use heating methods that heat the materials uniformly. Section 804 411 SECTION 804 CEMENT AND LIME
804.01 Cement
Use one of the following materials: − Portland Cement that meets the requirements of AASHTO M 85, Type II; or − Blended Hydraulic Cement that meets the requirements of AASHTO M 240, Type IL(MS).
804.02 Lime
Use hydrated lime that meets AASHTO M 216.
Source: North Dakota Standard Specifications for Road and Bridge Construction, 2022 Edition. Pages 438–445 of 550.