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