UNTREATED BASE COURSE (UTBC)
PART 1 GENERAL
1.1SECTION INCLUDES
A.Production, construction, and compaction of UTBC used for pavements,
shoulders, and incidental construction.
1.2RELATED SECTIONS
A.Section 01572: Dust Control and Watering
1.3REFERENCES
A.AASHTO T 11: Materials Finer than 75-µm (No. 200) Sieve in Mineral
Aggregates by Washing
B.AASHTO T 19: Bulk Density (“Unit Weight”) and Voids in Aggregate
C.AASHTO T 27: Sieve Analysis of Fine and Coarse Aggregates
D.AASHTO T 89: Determining the Liquid Limit of Soils
E.AASHTO T 90: Determining the Plastic Limit and Plasticity Index of Soils
F.AASHTO T 96: Resistance to Degradation of Small-Sized Coarse
Aggregate by Abrasion and Impact in the Los Angeles Machine
G.AASHTO T 180: Moisture-Density Relations of Soils Using a 4.54 kg (10
lb) Rammer and 457 mm (18 in) Drop
H.AASHTO T 193: The California Bearing Ratio
I.AASHTO T 255: Total Evaporable Moisture Content of Aggregate by
Drying
J.AASHTO T 335: Determining the Percent of Fracture in Coarse
Aggregate
Untreated Base Course (UTBC)
1.4DEFINITIONS Not Used
1.5SUBMITTALS
A.Written report for approval for each aggregate class and source, a
minimum of five working days before placement. Include the following:
1.Aggregate suitability. Refer to this Section, Part 2.
2.Name of supplier and location of source.
3.Maximum Dry Density and Optimum Moisture Content and
associated test result data. Refer to AASHTO T 180, Method D.
4.Job mix gradation including single values for each sieve size, No. 4
and finer. The target values must be within the gradation limits of Table 2.
B.Job-mix gradation changes
1.Refer to this Section, Article 3.2.
1.6ACCEPTANCE
A.Type I Placement – Pavement Section
1.Use Class A aggregate, Table 1.
2.The Engineer takes random samples from the grade and tests for
moisture, gradation, and laboratory density and performs in-place density determinations.
3.Meet gradation limits and applicable tolerances of Table 2 for each
gradation test.
a.Evaluate each sublot separately and do not average with
other sublots.
4.Meet minimum density test average of 97 percent of maximum
laboratory density with no test less than 94 percent.
B.Type II Placement – Incidental includes placement for Curb, Curb and
Gutter, Driveways, Pedestrian Access Ramps, Sidewalk, Waterways, Flatwork, and other items of work in the contract to which UTBC is included and not measured or paid for separately.
1.Use Class A aggregate, Table 1.
2.The Engineer takes random samples from the grade and tests for
moisture, gradation, and laboratory density and performs in-place density determinations.
3.Meet gradation limits and applicable tolerances of Table 2 for each
gradation test.
a.Each sublot will be evaluated separately and not averaged
with other sublots.
4.Meet minimum density test average of 95 percent of maximum
laboratory density with no test less than 92 percent.
Untreated Base Course (UTBC)
C.Type III Placement – Shoulder
1.Use Class A or B aggregate, Table 1.
2.Adjust moisture content before compaction .
D.Material not meeting the gradation requirements may be allowed to remain
in-place at the discretion of the Engineer provided density requirements are met.
1.Additional lots may not be placed until the deficiencies are
addressed and corrected.
E.Correct material that does not meet the specified criteria by scarifying,
placing additional material, re-mixing, reshaping, and re-compacting when determined by the Engineer.
F.Do not place additional material on any unaccepted layer.
PART 2 PRODUCTS
2.1AGGREGATES
A.Well-graded, clean, hard, tough, durable, and sound mineral aggregates
consisting of crushed stone, crushed gravel, or crushed slag, free of organic matter and contamination from chemical or petroleum products, according to Table 1.
Table 1 Aggregate Properties Aggregate Class A B Dry Rodded Unit Weight Not less than 75 lb/ft3 AASHTO T 19 AASHTO T 89 Liquid Limit/Plastic Index Non-plastic PI ≤ 6 AASHTO T 90 Aggregate Wear Not to exceed 50 percent AASHTO T 96 AASHTO T 11 Gradation Table 2 AASHTO T 27 CBR with a 10 lb surcharge 70% N/A AASHTO T 193 measured at 0.20 inch penetration Minimum Two Fractured Faces 50% Min N/A AASHTO T 335
Untreated Base Course (UTBC)
B.Establish the job mix (target) gradation for the ¾ inch sieve and finer
within the gradation limits.
1.The Job Mix Gradation Tolerance is the allowable deviation from
the job mix (target) gradation on the applicable sieves.
2.All other percents passing will be within the gradation limits. Refer
to AASHTO T 11 and AASHTO T 27.
Table 2 Gradation Limits Sieve Size Job Mix Gradation Job Mix Gradation Target Band Tolerance 1½ inch 100 1 inch 90 - 100 ±9.0 ¾ inch 70 - 85 ±9.0 ½ inch 65 - 80 ±9.0 ⅜ inch 55 - 75 ±9.0 No. 4 40 - 65 ±7.0 No. 16 25 - 40 ±5.0 No. 200 7 - 11 ±3.0 Percent passing based on total aggregate (dry weight) and fine and coarse aggregate with approximately the same bulk specific gravities.
PART 3 EXECUTION
3.1PREPARATION
A.Remove vegetation before Type III placement. Refer to Section 02231.
1.Protect existing delineators in place.
3.2INSTALLATION
A.Provide moisture content of ± 2 percent of optimum at the time of
placement. Refer to AASHTO T 180, Method D, AASHTO T 255, and
B.Procedures for Changing the Job-Mix Gradation
1.Submit changes in writing 24 hours before placement for approval
by the Engineer.
C.Place in layers of uniform thickness and compact each layer to a thickness
not to exceed a 6 inch depth.
1.Do not place on any frozen surface.
Untreated Base Course (UTBC)
D.Finish to a uniform line and grade with surface deviations no more than ⅜
inch in 10 ft in any direction.
1.Correct any profile deviations greater than ⅜ inch.
a.Rework minimum of 4 inch lift to achieve homogeneous
density.
b.Determine limits of correction based on extent of deviation.
c.Continue finishing until existing deviation is less than ⅜ inch.
E.Maintain optimum moisture content ± 2 percent during compaction, refer
to Section 01572.
1.Use appropriate compaction equipment adjacent to abutments,
backwalls, approach slabs, wing walls, retaining walls, and other structures.
2.Use a minimum of two passes with a roller for Type III placement or
as directed by the Engineer.
END OF SECTION
Untreated Base Course (UTBC)
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Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 428–432 of 1,331.
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