25 AGGREGATE SUBBASES
25-1 General
25-1.01 General
25-1.01A Summary
Section 25 -1 includes general specifications for placing aggregate subbase.
25-1.01B Definitions
Reserved
25-1.01C Submittals
Submit an aggregate subbase QC plan.
25-1.01D Quality Assurance
25-1.01D(1) General
Reserved
25-1.01D(2) Quality Control
25-1.01D(2)(a) General
Reserved
25-1.01D(2)(b) Quality Control Plan
Reserved
25-1.01D(2)(c) Qualifications
Reserved
25-1.01D(2)(d) Quality Control Testing
AS quality control must include testing the quality characteristics at the frequencies shown in the following table: QC Testing Frequencies Quality characteristic Test method Sampling location Minimum frequency R-value California Test 301 Stockpiles, transportation units, windrows, or roadways 1 test before beginning work and every 2 ,000 cu yd thereaftera Aggregate gradation California Test 202 Stockpiles, transportation units, windrows, or roadways 1 per 500 cu yd but at least one per day of placement Sand equivalent California Test 217 Stockpiles, transportation units, windrows, or roadways Relative compaction California Test 231 Roadway 1 per 500 sq yd on each layer aAdditional R -value frequency testing will not be required when the average of 4 consecutive sand equivalent tests is 4 or more above the specified operating range value.
25-1.01D(3) Department Acceptance
The Department accepts AS based on aggregate gradation, R -value requirements, and sand equivalent requirements specified in section 25 -1.02. The Department accepts AS based on percent relative compaction specified in section 25 -1.03E tested under California Test 231. The Engineer takes aggregate subbase samples for R -value, aggregate gradation, and sand equivalent from any of the following locations: SECTION 25 AGGREGATE SUBBASES
1.Windrow
2.Roadway For Class 1 –4 AS, if the aggregate gradation test results, the sand equivalent test results, or both comply with contract compliance requirements but not operating range requirements, you may continue placing AS for the remainder of the workday. Do not place additional AS until you demonstrate to the Engi neer the AS to be placed complies with the operating range requirements. For Class 1 –4 AS, if the aggregate gradation test results, sand equivalent test results, or both do not comply with contract compliance requirements, remove the AS or request a paymen t deduction. If your request is authorized, $2.00/cu yd is deducted. Each aggregate gradation and sand equivalent test represents no more than 500 cu yd of AS or 1 day's production, whichever is smaller.
25-1.02 Materials
25-1.02A General
Aggregate for C lass 1, 2, 3, and 4 AS must be clean and consist of any combination of the following:
1.Broken stone
2.Crushed gravel
3.Natural rough surfaced gravel
4.Sand
5.Reclaimed processed asphalt concrete, PCC, LCB, or CTB If Class 5 is specified, the locatio n for obtaining the material and gradation requirements is in the special provisions.
25-1.02B Class 1, Class 2, and Class 3 Aggregate Subbases
Aggregate gradation must be within the percentage passing limits for the sieve sizes shown in the following tab le: Aggregate Gradation Sieve size Percentage passing Class 1 Class 2 Class 3 Operating range Contract compliance Operating range Contract compliance Operating range Contract compliance 3" 100 100 100 100 100 100 2 1/2" 90–100 87–100 90–100 87–100 90–100 87–100 No. 4 35–70 30–75 40–90 35–95 50–100 45–100 No. 200 0–20 0–23 0–25 0–29 0–30 0–34 The aggregate quality characteristics must comply with the requirements for the classes shown in the following table: Aggregate Quality Characteristics Quality characteristic Requirement Class 1 Class 2 Class 3 Operating range Contract compliance Operating range Contract compliance Operating range Contract compliance Sand equivalent (min) 21 18 21 18 21 18 Resistance (R-value, min) -- 60 -- 50 -- 40
25-1.02C Class 4 Aggregate Subbase
Reserved
25-1.02D Class 5 Aggregate Subbase
Reserved SECTION 25 AGGREGATE SUBBASES
25-1.03 Construction
25-1.03A General
Apply water to the AS as needed for compaction.
25-1.03B Subgrade
Immediately before spreading the AS, the subgrade must comply with the specified compaction and elevation tolerance for the material involved and be free from loose or extraneous material. You may fill areas of the subgrade lower than the grade established by the Engineer with AS. Before placing biaxial geogrid, remove sharp objects that may come in contact with the material.
25-1.03C Placing Geosynthetics Materials
Geosynthetic materials include filter fabric and biaxial geogrid. If filter fabric is shown, place it on the subgrade. Place biaxial geogrid if shown:
1.Under manufacturer's instructions
2.Longitudinally along the roadway alignment
3.Without wrinkles Overlap adjacent edges of geosynthetic material at least 2 feet. Overlap the ends of the rolls at least 2 feet in the direction AS is spread. You may fold or cut geosynthetic material to conform to curves. If material is cut, overlap it at least 2 feet. You may hold the material in place with mechanical ties, staples, pins, or small piles of AS. Do not place stockpiles on geosynthetic material o r place more material than can be covered in 72 hours. Do not operate equipment or vehicles directly on filter fabric. Do not operate equipment or vehicles directly on geogrid unless one of the following conditions is met:
1.Vehicles and equipment are: 1.1. Equipped with rubber tires 1.2. Operated under 10 mph 1.3. Operated to avoid sudden braking and sharp turns
2.At least 0.35 ft of AS has been placed, spread, and compacted on the material Repair or replace any damaged geosynthetic material by placing a new piece of material over the damaged area with at least 3 feet of overlap.
25-1.03D Spreading
Deliver uniform mixtures of AS to the roadbed. Deposit AS in layers or windrows. Spread and shape the AS to such thickne ss that after watering and compacting, the completed AS is within the tolerances specified in section 25 -1.03E. When AS is spread and compacted the moisture content must be uniform and sufficient to obtain the required compaction. Avoid material segregatio n. AS must be free from pockets of coarse or fine material. Where the subgrade is cohesionless sand and if authorized, you may dump AS in piles and spread it ahead in sufficient quantities to stabilize the subgrade. Where the subbase thickness shown is 0.5 0 foot or less , you may spread and compact the AS in one layer. Where the shown thickness is more than 0.50 foot, spread and compact in 2 or more layers approximately equal in thickness. The compacted thickness of any one layer must not exceed 0.50 foot. At locations inaccessible to spreading equipment, spread and compact AS by any means that will produce the specified results. SECTION 25 AGGREGATE SUBBASES
25-1.03E Compacting
Compact each AS layer to at least 95 percent relative compaction. Where biaxial geogrid is shown, compact AS with either (1) a smooth -wheeled roller or (2) a rubber -tired roller. Do not use vibratory devices during compaction. The finished surface of AS not covered, or covered by material paid for by weight, must not vary more than 0.08 foot above or below the grade established by the Engineer. The finished surface of AS covered by material paid for by volume mu st not project above the grade established by the Engineer at any point. Correct areas of AS that do not comply with the thickness shown if an equivalent thickness of overlying base will not compensate or req uest a payment deduction. If your request is authorized, the Engineer calculates the deduction by multiplying:
1.Deficient thickness less allowable tolerance
2.Planned width
3.Longitudinal distance of the deficient thickness
4.$11.00/cu yd
25-1.04 Pa Yment
The payment quantity of aggregate subbase is determined by the dimensions shown. The payment quantity does not include the volume of aggregate subbase used to fill low areas of the subgrade.
25-2 25-10 Reserved
Source: California Standard Specifications, 2024 Edition. Pages 403–406 of 1,372.