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| 304.1 Construction Inspection for Sec 304==
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| '''Usage'''
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| Type 1 Base is specified for all light-duty pavements and all heavy-duty pavements unless a rock fill is specified. Each type of aggregate base has a specific function in a roadway pavement design.
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|
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| '''Drainability'''
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| Type 5 limits the amount of material passing the #200 sieve to 15 percent. By controlling
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| the amount of minus #200 material, the Type 5 becomes a drainable aggregate base. Type 1 base has no specified limit on the #200 sieve and is a non-drainable base.
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|
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| 304.0.3 Pavement Designs
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| 304.0.3.1 Light-duty Pavements. The pavement structure for light-duty pavements consists
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| of pavement and aggregate base. The earth shoulders are covered in most cases with either
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| Type 1 or 2 base. The function of the aggregate base is to serve as an interlayer between soil subgrade
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| and pavement. Since no under drains are specified for light duty pavements, little or no
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| drainage is realized.
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| 304.0.3.2 Medium-duty Pavements. For medium duty-pavements, the pavement structure
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| Division of Construction and Materials
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| 300-6 © Missouri Department of Transportation 2006
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| consists of the pavement, aggregate base and under drains. As under drains are specified, it is
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| imperative to have a drainable base.
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| 304.0.3.3 Heavy-duty Pavements. For heavy-duty pavements, with the exception of those
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| with rock fill, the pavement structure consists of the pavement, a stabilized permeable base,
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| aggregate base and under drains. For heavy-duty pavements the stabilized permeable layer serves
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| as the drainage layer in conjunction with the under drains. The purpose of the aggregate base is to
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| serve as an interlayer between the soil sub-grade and the stabilized permeable base. Since the
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| function of the base is to act as an interlayer, with the exception of those with rock fill, contractors
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| are allowed substitute Type 1 base in lieu of Type 5 base on active contracts with a price reduction
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| of at least $0.50 per square yard.
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| 304.0.4 Substitution
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| No substitution will be allowed on medium-duty pavements or heavy-duty pavements
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| with rock fill. If you have any questions, contact the Field Materials Director, at (573) 751-1037.
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|
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| ===304.1.1 Description===
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| Aggregate bases are used to provide additional structure and drainage.
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| 304.2 Material.
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| Production of aggregate base material is normally inspected by Materials inspectors. The
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| resident engineer will receive through SiteManager results copies of test reports showing quantity,
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| gradation, and plastic index (PI) of the material produced.
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| Construction personnel are responsible for QA inspection of material when it arrives on
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| the project and laying operations begin. Refer to GCM Section 304.4 in regard to QA testing
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| requirements. There will be times during base laying operations when Materials inspectors will
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| be on the project to take record samples of base. If difficulties are encountered with material
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| degrading, or varying appreciably in plastic index or gradation, the project inspector should not
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| hesitate to ask their assistance or advice.
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| 304.3 Construction Requirements.
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| Compaction and rolling requirements will be in accordance with Sec 304.3.5 of Standard
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| Specifications. Review the general construction requirements listed in Section 300 of this Construction
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| Manual.
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| 304.3.1 Field Laboratory.
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| Blank.
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| 304.3.2 Subgrade.
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| All subgrade on which the base is to be constructed shall be completed in accordance with
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| Sec 209 prior to placing base material. Aggregate base is not to be placed on frozen subgrade.
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| 304.3.2.1 Examine the subgrade to ensure that it has not deteriorated since it was tested.
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| Ensure that the material underlying the grading plane is firm, stable and unfrozen. A rutted surface
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| does not provide an acceptable surface.
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| 304.3.3 Placing.
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| Ensure Type 5 Aggregate Base is being spread without significant segregation. Normally,
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| General Construction Manual
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| © Missouri Department of Transportation 2006 300-7
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| you would observe segregation, but if problems persist, support your contractor corrective active
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| notice with a sieve analysis.
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| 304.3.3.1 A subgrade without cohesion and stability may need special considerations.
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| Frequent watering of a sand subgrade to obtain a stable surface may be necessary. If the subgrade
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| doesn’t stabilize, a material belt spreader may be necessary or the aggregate base may be dumped
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| in piles and spread ahead. It is important the base has sufficient moisture to minimize segregation.
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| Authorization to construct stabilized subgrade may be the only viable option.
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| 304.3.3.2 Aggregate base used for shoulders adjacent to rigid or flexible type pavement,
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| including pavement resurfacing, shall be simultaneously deposited and spread on the subgrade.
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| Because of segregation concerns and potential damage to the pavement, aggregate is not to be
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| deposited on the pavement and bladed or dozed into place.
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| 304.3.3.3 If earth subgrade is too low and the contractor elects to use base material to
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| bring it to grade, the cost of bringing it to plan subgrade elevation must be borne by the contractor.
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| Such work must be done before any base operations proceed in that area. When base material is
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| used, normal base manipulation is necessary to get required compaction. If the subgrade tolerance
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| encountered is excessive, the quantity of material required, the area effected and the contractor’s
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| time and equipment should be noted in the inspector's diary so there will be a record in case
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| of a later claim for additional costs. The production in linear feet / day in the area in question can
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| be compared to the contractor’s normal daily production to justify any additional costs.
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| 304.3.4 Shaping and Compacting.
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| Compaction operations usually follow immediately behind placing operations. It is
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| imperative that satisfactory moisture content be maintained during compaction operations if
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| proper density is to be obtained. Each layer shall be compacted to the specified density before
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| another layer is placed.
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| 304.3.4.1 Segregated surface areas constructed of Type 1 aggregate base may be corrected
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| by adding and compacting limestone screenings of such gradation and quantity as required
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| to fill the surface voids, and firmly bind the loose material in place. Type 5 aggregate base is
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| intended to provide drainage and must not be segregated. Trimmed Type 5 aggregate base may
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| not be reused until the material is verified as meeting the required specifications. Base material
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| contaminated to the extent that the material no longer complies with the specifications must be
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| removed and replaced with satisfactory material at the contractor’s expense.
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| 304.3.4.2 No visible consolidation shall be evident after the final rolling.
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| 304.3.4.3 If at any time the compacted aggregate base or subgrade becomes unstable, the
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| contractor, at the contractor's expense, shall restore the earth subgrade and the aggregate base to
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| the required grade, cross section and density.
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| 304.3.4.4 Density test is to be made at a minimum frequency specified. Additional tests
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| may be necessary to insure that minimum density requirements are being met.
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| 304.3.4.5 Density tests using the nuclear moisture / density gauges are documented with
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| Form C-709-ND.
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| 304.3.5 Substitutions for Aggregate Base.
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| If available, the contractor may substitute bituminous pavement cold millings or crushed
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| recycled concrete in lieu of aggregate base for any temporary surface, regardless of the type or
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| thickness of aggregate shown on the plans. If this option is exercised, the contractor shall notify
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| the engineer at least two weeks prior to using the millings or recycled concrete, and shall identify
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| Division of Construction and Materials
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| 300-8 © Missouri Department of Transportation 2006
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| the location from where the millings or concrete will be removed. The millings or recycled concrete
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| shall be installed to the same dimensions shown on the plans for the aggregate base. Millings
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| or recycled concrete shall be placed in maximum 4-inch (100 mm) lifts, and each lift shall be
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| compacted by a minimum of three passes with a 10-ton (9 Mg) roller.
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| 304.3.6 Maintenance.
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| The contractor is responsible to maintain the required density and surface condition of any
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| portion of the completed aggregate base until either the prime coat or a succeeding course or
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| pavement is placed. If a prime coat is specified in the contract, the contractor will be required to
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| apply the prime coat on any completed portion of the aggregate base as soon as practical, or as
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| otherwise specified. The contractor will not be permitted to apply prime if the moisture in the top
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| 2 inches (50 mm) of the aggregate base exceeds the higher of either (1) the average of the optimum
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| moisture as determined by the Standard Compaction Test and the absorption of the plus No.
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| 4 (4.75 mm) fraction, or (2) two-thirds of the optimum moisture as determined by the Standard
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| Compaction Test.
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| 304.4 Quality Control/Quality Assurance (QC/QA).
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| The contractor is responsible for density, thickness, gradation, deleterious and plasticity
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| requirements of the aggregate base. The frequency, documentation requirements and submittals
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| are specified in Spec Sec 304.4.
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| 304.4.1 Quality Control.
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| The contractor shall control operations to ensure the aggregate base, in place, meets the
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| specified requirements for density, thickness, gradation, deleterious, and plasticity index. Tests
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| shall be taken at random locations designated by the engineer at the frequency required by the
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| specifications.
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| 304.4.1.1 The contractor shall provide copies of the test results, including all raw data, to
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| the engineer the next business day following testing or sampling.
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| 304.4.1.2 The contractor or the contractor’s representative shall also determine the standard
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| maximum dry density and the optimum moisture content and supply all test data to the engineer.
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| 304.4.1.3 When density tests are less than specified or when thickness measurements
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| indicate the thickness is deficient by more than 1/2 inch (13 mm) from the plan thickness, additional
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| measurements will be taken at the frequency specified. Each measurement will be assumed
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| as representative of the base thickness for a distance extending one-half the distance to the next
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| measurement, measured along centerline, or in the case of a beginning or ending measurement,
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| the distance will extend to the end of the base section. Any deficient areas shall be corrected by
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| reworking or adding material within the limits of the deficiency.
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| 304.4.1.4 When two consecutive tests for gradation, deleterious material, or plasticity
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| index do not meet the specification limits, the material shall be removed beginning at the point
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| where the first test was conducted.
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| 304.4.1.5 The contractor shall retain the untested portion of the plasticity index, gradation
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| and deleterious sample for the engineer’s use.
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| 304.4.2 Quality Assurance.
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| A vital element in acceptance of aggregate base is the quality assurance. Material properGeneral
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| Construction Manual
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| © Missouri Department of Transportation 2006 300-9
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| ties are to be tested at the frequency stated in Spec Sec 304.4. Gradation, presence of deleterious
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| material and the PI need to be checked and documented. Test the compaction of aggregate base.
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| Observe the compacting operation to ensure the material forms a firm, stable base. Measure and
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| record the random thickness and template of the finished aggregate base for conformance with
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| specifications, in addition to any inspections performed on items that are not otherwise part of a
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| permanent record.
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| 304.4.2.1 The contractor’s QC test results and the engineer’s QA test results shall meet
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| the specifications and the following. The contractor’s compaction standard tests shall compare
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| within 3.0 pounds of the maximum density of the MoDOT determined compaction standard. For
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| retained samples, the contractor’s test results and the engineer’s test results shall compare within
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| the limits specified.
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| 304.5 Method of Measurement.
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| Final measurement of the completed aggregate base course will not be made except for
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| authorized changes during construction, or where appreciable errors are found in the contract
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| quantity. Where required, measurement of aggregate base course, complete in place, will be made
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| to the nearest square yard (m2). Where the aggregate base course extends to the inslope of the
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| shoulder, the pay limit of the aggregate base course will be measured from the mid-point of the
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| sloped portion. The revision or correction will be computed and added to or deducted from the
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| contract quantity.
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| 304.6 Basis of Payment.
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| The accepted quantities of aggregate base course of the thickness and type specified will
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| be paid for at the contract unit price for each of the pay items included in the contract. When bituminous
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| pavement cold millings or recycled crushed concrete are substituted for aggregate base,
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| payment will be made for the aggregate base quantity provided in the plans, regardless of whether
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| millings, recycled crushed concrete or the aggregate base is used.
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