326Portland Cement Concrete Subbase

326.1 General Description

This work includes constructing a subbase composed of a mixture of Portland cement and graded aggregate, or Portland cement, aggregate, and sand. Construct according to these specifications and to the lines, grades, and typical cross-sections shown on the plans or established by the Engineer. Apply the requirements of Section 300 to this work.

326.1.01 Definitions

General Provisions 101 through 150.

326.1.02 Related References

A. Standard Specifications Section 109—Measurement and Payment Section 300—General Specifications for Base and Subbase Courses Section 430—Portland Cement Concrete Pavement Section 500—Concrete Structures Section 800—Coarse Aggregate Section 801—Fine Aggregate Section 815—Graded Aggregate Section 830—Portland Cement Section 831—Admixtures Section 832—Curing Agents B. Referenced Documents ASTM C 94 AASHTO T 22 AASHTO T 126 GDT 26 GDT 27 GDT 28 GDT 32

326.1.03 Submittals

Prior to construction, submit a grade control plan for the Engineer’s approval.

326.2 Materials

Ensure that materials meet the requirements of the following Specifications: Material Specification Fine Aggregate 801.2.01 Portland Cement 830.2.01 Fly Ash 831.2.03 *Graded Aggregate 815.2.01 Coarse Aggregate 800.2.01 Air Entraining Admixture 831.2.01 Chemical Admixtures for Concrete Type A or D 831.2.02 Curing Compound—White, Wax Base 832.2.03 * The gradation requirements of graded aggregate are modified to require 30 to 45 percent by weight passing the No. 10 (2.0 mm) sieve.

326.2.01 Delivery, Storage, and Handling

General Provisions 101 through 150.

326.3 Construction Requirements

326.3.01 Personnel

General Provisions 101 through 150.

326.3.02 Equipment

Provide the equipment and tools necessary to perform this work, including the following. A. Concrete Batching Equipment Provide separate bins and weighing hoppers for aggregates and cement in the batching plant. Use separate scales to weigh cement and aggregate. The Engineer will inspect scales for weighing concrete materials and water measuring devices before their use. Ensure accuracy of scales and water measuring devices of plus or minus 1.0 percent throughout the operating range. Measure admixtures to an accuracy of plus or minus 3.0 percent. B. Slip Form Paver and Spreader To place the subbase mixture, use a self-propelled slip form paver equipped with tracks sufficient to prevent slippage and bogging when loaded. • Use the paver to strike off, consolidate, and float finish the fresh mixture—all in one pass. • Operate the paver from a string grade control, or a combination of string control and existing pavement control. • Use a self-propelled mechanical spreader to distribute the mixture on the grade.

326.3.03 Preparation

Before placing Portland cement concrete subbase, prepare the roadbed as required by the plans and the specifications.

326.3.04 Fabrication

General Provisions 101 through 150.

326.3.05 Construction

Produce Portland cement concrete subbase by combining authorized proportions of approved materials in homogeneous, uniform batches. Ensure that the grade immediately under the subbase does not contribute to deficient thicknesses of either the subbase or pavement. Employ methods to ensure that subbase placement equipment does not cause deficient thickness to areas supporting the equipment. Produce the subbase as follows: A. Mixing The Engineer will determine the design proportions of the required materials based upon mixes prepared in the laboratory or trials performed during construction. Determine the batch weights required to produce the necessary quantity. Measure the cement, aggregates, and water separately, to the accuracy specified above. Continue mixing until producing a homogeneous and uniform mixture. Mix concrete produced in a stationary central mix plant for a minimum of 60 seconds, after all materials have entered the drum. A reduction of mix time may be allowed if representative tests show that the concrete meets the requirements of ASTM C 94, Requirements for Uniformity. In all cases, mix for at least 50 seconds. Ensure that transit mixed concrete meets the requirements of Subsection 500.3.04.E.3. B. Placing Spread the mixture on the grade with minimum rehandling. Hand spread with shovels if necessary. Do not place Portland cement concrete on muddy, puddled, or frozen subgrade. NOTE: Do not allow workers to walk in fresh concrete with shoes coated with dirt or other foreign substances. C. Consolidating Consolidate the mixture by vibrating the full length, width, and depth of the section. Ensure that vibration does not produce puddling or excessive grout accumulation. If consolidation and density are not satisfactory, stop placement and furnish methods or equipment to produce subbase conforming to the specifications. D. Finishing Finish the mixture to the proper cross-section. Use equipment that produces a uniform surface free of irregular, rough, or porous areas. Use a tube float or other finishing device approved by the Engineer to provide a smooth surface. Unless the Engineer permits, do not add water to the surface to aid finishing. E. Forming Construction Joints Form a construction joint when mixture placement is interrupted for more than one hour. Construct joints according to Subsection 430.3.05 unless the Engineer waives the requirements concerning reinforcement. Ensure that the straightedge tolerance is 3/8 in. (10 mm) in 20 ft. (6 m). F. Curing Cure the mixture according to Subsection 430.3.05.L.1. Apply compound for the impervious membrane method at the rate of 200 ft.²/gal (5 m²/L) or less. Apply a second application of curing compound just before placing the pavement to act as a bond breaker. Apply the second application at the same rate as the first application. G. Preserving the Subbase Maintain the subbase until it is covered by the succeeding pavement course. 1. Place the pavement course on the subbase only after the mixture has cured for 7 days. 2. Operate the spreader and slip form paver on the subbase after 7 days, but do not use the subbase as a haul road for loaded trucks, equipment, or other vehicles for 14 days. a. Construct earth ramps and barricades to move traffic across the subbase. b. Remove and replace areas damaged by vehicles or equipment at no additional cost to the Department. H. Weather Limitations 1. Do not place the subbase mixture when the air temperature in the shade is less than 40 °F (5 °C) and falling. Wait until the air temperature is at least 35 °F (2 °C) and rising. 2. Protect the subbase from rain until the surface has sufficiently hardened to prevent marring. 3. Protect the subbase from cold weather according to Subsection 430.3.05.L.4.

326.3.06 Quality Acceptance

Check the finished surface transversely by a system of ordinates measured from a string line. Also check the surface with a 20 ft. (6 m) straightedge placed parallel to the centerline. Remove or correct deviations in excess of 3/8 in. (10 mm) in 20 ft. (6 m). If the Engineer permits, correct low areas by increasing the thickness of the surface course at no additional cost to the Department. A. Composition of Subbase Mixture The Department will determine the required proportions based on the test results of sample material. Secure and deliver a sufficient amount of materials to the laboratory for evaluation. An approved mixture shall conform to the following: 1. Aggregate Use aggregate that meets the requirements of Subsection 815.2.01. Use aggregates manufactured at the quarry or blended at the plant site to produce the desired results. Place aggregates in one or more stockpiles if the gradation is uniform at the time of batching. 2. Cement Use at least 275 lbs./yd³ (165 kg/m³) of Portland cement for Portland cement concrete subbase. Use fly ash as a partial replacement for Portland cement if: a. The quantity of cement replaced is 15 percent or less by weight. b. Cement is replaced by fly ash at the rate of 1.25 lbs. to 2 lbs. (1.25 kg to 2.0 kg) of fly ash to each pound (kilogram) of cement. Do not use Type IP cement in fly ash mixes. 3. Water-Cement Ratio The maximum water-cement ratio shall not exceed 1.3. Calculate the water-cement ratio based on the total cement material used, including fly ash. 4. Air Content Maximum design air content shall be 7.0 percent. 5. Slump Maximum design slump shall be 1.5 in. (40 mm). 6. Compressive Strength Ensure that the mixture is capable of demonstrating a laboratory compressive strength at 28 days of 1,000 psi (7 MPa) +.18R*. (*Where: R = the difference between the largest observed value and the smallest observed value for all compressive strength specimens at 28 days, for a given combination of materials and mix proportions prepared together.) Determine compressive strength from the results of six cylinders prepared and tested according to AASHTO: T 126 and T 22. B. Field Adjustment of Design Proportions The Engineer will determine changes in design proportions based on construction conditions and notify the Contractor in writing of the effective date and time of the changes. C. Mix Tolerances The Engineer will verify that the mix is proportioned according to the approved mix design. Assume responsibility for determining the required batch weights. Ensure that variations in consistency and air content of the mixture are within the following limits at the time of placement. 1. Consistency Slump shall not exceed 2 in (50 mm) as determined by GDT 27. 2. Air Content Air content shall not exceed 8.0 percent, as determined by the applicable test method in GDT 26, GDT 28, or GDT 32. D. Acceptance of Subbase Mixture The Department will accept the mixture based upon results required in the Sampling Testing and Inspection Manual for: • Slump • Air tests • Water-cement ratio • Surveillance of plant operations and mix production E. Thickness Determine thickness by taking probe measurements in the fresh mixture every 250 ft. (75 m) or less. Adjust the strike off to compensate for variations in thicknesses. Obtain cores to determine the boundaries of areas subject to thickness correction. A construction tolerance of plus or minus 0.5 in. (13 mm) from the Plan depth is permitted. 1. Deficient Thickness Correct areas deficient in thickness by more than 0.5 in. (13 mm) but less than 1 in. (25 mm) by increasing the surface course depth. Remove or correct areas deficient in thickness by more than 1 in. (25 mm) as the Engineer directs. The Engineer may base the decision to remove or correct the area on a Plan submitted by the Contractor detailing how to obtain the final pavement profile and grade. 2. Excessive Thickness Remove areas with excessive thickness when the Engineer requires. Removal is not required when the excessive thickness does not result in a surface course deficient in thickness.

326.3.07 Contractor Warranty and Maintenance

General Provisions 101 through 150.

326.4 Measurement

Portland cement concrete subbase is measured by the square yard (meter) as noted in Section 109, complete in place and accepted.

326.4.01 Limits

General Provisions 101 through 150.

326.5 Payment

Portland cement concrete subbase will be paid for at the Contract Unit Price per square yard (meter) for each specified thickness shown on the plans. This payment will be full compensation for: • Providing Portland cement and all other materials • Applying first and second applications of curing compound • Providing all equipment and labor • Mixing • Hauling • Providing other incidentals necessary to complete the Item • Replacing subbase when required Payment will be made under: Item No. 326 Portland cement concrete subbase ____ in. (mm) thick Per square yard (meter)

326.5.01 Adjustments

General Provisions 101 through 150.