SECTION 208—SUBBASE AND AGGREGATE BASE MATERIAL
208.01 Description
These specifications cover material used to form a foundation for base or surface pavement.
208.02 Materials
a.Subbase material shall consist of mixtures of natural or crushed gravel, crushed stone or slag, and natural or crushed sand, with or without soil mortar.
b.Aggregate base material will be designated as T ype I or T ype II as follows: Type I shall consist of crushed stone, crushed slag, or crushed gravel, with or without soil mortar or other admixtures. Crushed gravel shall consist of particles of which at least 90 percent by weight of the material retained on the No. 10 sieve shall have at least one face fractured by artificial crushing. Type II shall consist of gravel, stone, or slag screenings; fine aggregate and crushed coarse aggregate; sand-clay-gravel mixtures; or any combination of these materials; with or without soil mortar or other admixtures.
208.03 Detail Requirements
a.Grading: Grading shall conform to the requirements of the job-mix formula selected from within the design range specified in Table II-9, subject to the applicable tolerances specified in Table II-10 when tested to verify acceptance in accordance with VTM-25. TABLE II-9 Design Range for Dense-Graded Aggregates Amounts Finer Than Each Laboratory Sieve (Square Openings1) (% by Weight) Size ASTM D4791 Flat & No. 2 in 1 in 3/8 in. No. 10 No. 40 No. 200 Elongated 5:1 21A 100 94-100 63-72 32-41 14-24 6-12 30% max. 21B 100 85-95 50-69 20-36 9-19 4-7 30% max. 22 --- 100 62-78 39-56 23-32 8-12 30% max. 1In inches, except where otherwise indicated. Numbered sieves are those of the U.S. Standard Sieve Series. TABLE II-10 Process Tolerances for Each Laboratory Sieve (%) No. Tests Top Size 1 in 3/4 in. 3/8 in. No. 10 No. 40 No. 200 1 0.0 ±10.0 ±14.0 ±19.0 ±14.0 ±8.0 ±4.0 2 0.0 ±7.1 ±10.0 ±13.6 ±10.0 ±5.7 ±2.9 3 0.0 ±5.6 ±7.8 ±10.6 ±7.8 ±4.4 ±2.2 4 0.0 ±5.0 ±7.0 ±9.5 ±7.0 ±4.0 ±2.0 8 0.0 ±3.6 ±5.0 ±6.8 ±5.0 ±2.9 ±1.4 208.03
b.Atterberg Limits: Atterberg limits shall conform to Table II-11 when tested to verify acceptance in accordance with VTM-7.
c.Soundness: Soundness shall conform to the requirements of Table II-4 when tested to verify accept- ance in accordance with AASHTO T103 or T104.
d.Abrasion Loss: Abrasion loss shall be not more than 45 percent when tested to verify acceptance in accordance with AASHTO T96.
e.Optimum Moisture: Material shall be produced at optimum moisture ±2 percentage points.
f.Admixtures: Admixtures shall conform to the applicable Specifications for the use specified.
g.Flat and Elongated Particles: Subbase and aggregate base materials to be used as a temporary riding surface during construction activities or as the final riding surface after construction shall contain not more than 30 percent by mass of aggregate particles retained on and above the 3/8-inch sieve having a maximum to minimum dimensional ratio greater than 5 as determined in accordance with the testing requirements of ASTM D4791.
208.04 Job-Mix Formula
The Contractor shall submit, or shall have the source of supply submit a job-mix formula for each mixture for the Engineer’ s approval through the “Producer Lab Analysis and Information Detail” (PLAID) website https://plaid.vdot.virginia.gov prior to starting work. The formula shall be within the design range specified in Table II-9. If unsatisfactory results or other conditions make it necessary, the Contractor shall prepare and submit a new job-mix formula for approval.
208.05 Mixing
Subbase or aggregate base materials shall be mixed in an approved central mixing plant of a pugmill or other mechanical type. Materials shall be blended prior to or during mechanical mixing in a manner that will ensure conformance to the specified requirements. Preparation of subbase and aggregate base material will be subject to Department inspection at the plant. The Contractor shall provide a laboratory as specified in Section 106.07. 208.03 TABLE II-11 Atterberg Limits Max. Liquid Limit Max. Plasticity Index Subbase and Subbase Sizes Aggregate Base Aggregate Base No. 21A, 22, and Type I and No. Tests Type I and II Aggregate Base Type II Subbase Size No. 19 1 25.0 6.0 3.0 2 23.9 5.4 2.4 3 23.2 5.1 2.1 4 23.0 5.0 2.0 8 22.4 4.7 1.7 During the initial setup and subsequent production, the Contractor shall have a certified Central Mix Aggregate Technician present at the plant.
208.06 Acceptance
The Contractor shall provide the quality assurance necessary for the Engineer to determine conformance to the required grading and Atterberg limits of subbase and aggregate base material. Sampling and testing for determination of grading, moisture, and Atterberg limits shall be performed by the Contractor. The Contractor shall provide such test results within 48 hours of sampling to the Department through “the Producer Lab Analysis and Information Details” (PLAID) website https:// plaid.vdot.virginia.gov. The Contractor shall maintain appropriate current quality control charts. The Department will perform independent monitor tests at a laboratory of its choice. If there is a statisti - cally significant difference between the two sets of results, an investigation will be made to determine the reason for the difference. If it is determined that the material does not conform to the requirements of the Contract, the material will be rejected or a payment adjustment will be made in accordance with Determination of gradation and Atterberg limits will be based on a mean of the results of tests performed on four samples taken in a stratified random manner from each lot. Lots of 2000 tons or 4000 tons may be used at the discretion of the Engineer when warranted by annual plant shipping quantity and past performance. Samples shall be obtained by methods approved by the Engineer. Any statistically accept- able method of randomization may be used to determine the time and location of the stratified random sample to be taken. The Department shall be advised of the method to be used prior to the beginning of production. A lot will be considered acceptable for grading if the mean of the test results is within the deviation from the job-mix formula specified in Table II-10. A lot will be considered acceptable for Atterberg limits if the mean of the test results is less than the maximum for the liquid limit and plasticity index specified in Table II-11. If the liquid limit exceeds 30 or the plasticity index exceeds 6 for Type I base material or No. 19 subbase material; or the plasticity index exceeds 9 for Type II base material or subbase materials No. 20, 21, 21A, 21B, or 22 on any individual sample; that portion of the lot from which the sample was taken will be considered a separate part of the lot and the Contractor shall remove that portion from the roadway. If either the amount of material in the lot is less than 2,000 tons (4,000 tons if applicable), the job-mix formula is modified within a lot, or the Engineer rejects a portion of the lot on the basis of individual test results, the mean test results of the samples taken will be compared to the job-mix formula with the tolerances given in Tables II-10 and II-11 for the number of tests performed. If a visual examination by the Engineer reveals that material in any load is obviously contaminated or segregated, the Engineer will reject that load without additional sampling or testing of the lot. If it is necessary to determine grading or Atterberg limits of material in an individual load, one sample (taken from the load) will be tested and the results compared to the job-mix formula with the tolerances given in Tables II-10 and II-11 for one test. Results obtained in the testing of a specific individual load will apply only to the load in question. 208.06
208.07 Referee System
If the Engineer determines test results obtained for one of the four samples taken to evaluate a particular lot is questionable, the Contractor may request that the results of the questionable sample be disregarded. The Contractor shall then perform tests on five additional samples taken from randomly selected loca - tions in the roadway where the lot was placed. If the Engineer determines that one of the four test results is questionable, the Department will perform tests on five additional samples taken from randomly se - lected locations in the roadway where the lot was placed. The Engineer will average the test results of the three original (unquestioned) samples with the tests results of the five road samples, and the mean of the test values obtained for the eight samples will be compared to the job-mix formula with the tolerances specified in Table II-10 and Table II-11 for the mean of eight tests. If the Contractor questions the mean of the four original test results obtained for a particular lot, the Contractor may request approval to perform additional testing of that lot. If the Engineer approves the Contractor’ s request for further tests, the Contractor shall sample and test the material in accordance with procedures approved by the Engineer. If the Engineer determines that the mean of the four original test results is questionable, the Department will perform additional testing of that lot. The Department will average the test results of the original four samples with the test results of the four additional samples tak- en from randomly selected locations in the roadway where the lot was placed, and the mean of test values obtained for the eight samples will be compared to the job-mix formula with the tolerances specified in Tables II-10 and II-11 for the mean result of eight tests. If the mean of the test values obtained for the eight samples conforms to the requirements for the mean of the results of eight tests, the Engineer will consider the material to be acceptable; if the mean does not conform, the Engineer will adjust the lot according to the payment adjustment rate specified in Section 208.08. The provisions of this Section will not apply to mixtures containing cement or other admixtures that alter the characteristics of the material.
208.08 Payment Adjustment System
If a lot of material does not conform to the acceptance requirements of Section 208.06, the Engineer will determine payment adjustment points as follows: Sieve No. Adjustment Points for Each 1% Grading Is Outside Tolerance Permitted in Table II-10 2 in 1 1 in 1 3/4 in 1 3/8 in 1 No. 10 1 No. 40 3 No. 200 5 Adjustment Points for Each 1% Atterberg Limits Exceed Atterberg Limits Maximum Permitted in Table II-11 Liquid limit 3 Plasticity index 7 208.07
Referenced in this section
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Source: Road and Bridge Specifications, 2020 Edition. Pages 183–186 of 1,065. View official source ↗