BASE COURSE
308.01 Description. This item shall consist of a base course
constructed on the completed and accepted subgrade according to these specifications and in conformity with the lin es, grades, compacted thickness, and typical section shown on t he plans or as directed by the Engineer.
308.02 Composition. (a) Cement Content. The quantity of
cement, approximately 3 to 8% by weight, to be used with the aggregate and water shall be determined by the Engi neer. The moisture in the mix shall be maintained within a ra nge of ±1% of optimum.
b.Laboratory Tests. Specimens of aggregate, cement, and water must develop a compressive strength of at lea st 750 psi (5.2 MPa) in 7 days. At least 30 days before beginning base construction , adequate quantities of materials shall be supplied to the Ma terials Division for determination of mix proportions. The Department w ill determine 214 the quantity of cement, the optimum moisture, and t he maximum laboratory density and furnish this information to the Contractor.
308.03 Materials. Materials used in the mixture shall comply
with the following requirements:
a.Aggregate. Crushed stone shall comply with Subsection 303.02 for Class 7.
b.Cement. Unless otherwise specified, portland cement conforming to the requirements of AASHTO M 85, Type I shall be furnished. One of the following blended cements ma y be used in lieu of Type I: • Portland-Pozzolan Cement, AASHTO M 240, Type IP (20 % maximum) • Slag-Modified Portland Cement, AASHTO M 240, Type I S (25% maximum) Fly ash or slag cement shall not be substituted for blended cements. Cement shall be from sources that are lis ted on the Department’s Qualified Products List and that have executed a certification agreement with the Department. Fly a sh or slag cement , if used, shall comply with Subsection 307.03(b) .
c.Water. The water for the base course shall be clean, cle ar, and free from injurious amounts of oil, salts, or o ther deleterious substances and shall not contain more than 1000 ppm of chlorides. If the water is of questionable quality, it shall b e tested according to AASHTO T 26.
d.Asphalt.
1.Emulsified asphalt shall comply with Subsection 40 3.03(c) for Grade SS-1.
2.Medium curing cut-back asphalt shall comply with Subsection 403.03(b) for the grade selected by the Engineer.
3.Rapid curing cut-back asphalt shall comply with Subsection 403.03(a) for the grade selected by the Engineer. The type of asphalt used for protection and cover f or the cement stabilized base course shall be at the option of th e Contractor, subject to the Engineer's approval.
308.04 Construction Requirements. (a) Weather Limit ations.
The cement stabilized base shall not be mixed or pl aced while the 215 atmospheric temperature is below 40° F (5° C) or wh en the weather is rainy.
b.Equipment. Sufficient equipment shall be available so that the work may proceed in proper sequence to completi on without unnecessary delay. Equipment, tools, and machinery used shall be maintained in a satisfactory working condition.
c.Forms. When forms are required, they shall comply with Subsection 501.07.
d.Subgrade. The subgrade shall be prepared according to the typical sections on the plans before placement of b ase. When the subgrade is constructed under the same Contract as the base, the subgrade shall be prepared according to Section 212 . When the subgrade is constructed under a separate contract, preparation of the subgrade shall be according to Section 214.
e.Mixing. Mixing shall be accomplished at a central mixing plant by either batch or continuous mixing. The ag gregates and cement may be proportioned either by weight or by v olume. The plant shall be equipped with feeding and meteri ng devices that will add the aggregate, cement, and water into the mixer in the specified quantities. Aggregate and cement shall b e dry-mixed sufficiently to prevent cement balls from forming w hen water is added. Mixing shall continue until a uniform mixtu re of aggregate, cement, and water has been obtained. In all plants, cement shall be added in such a mann er that it is uniformly distributed throughout the aggregates dur ing the mixing operation. The charge in a batch mixer, or the rate of feed in to a continuous mixer, shall not exceed that which will permit comp lete mixing of all the material. To compute the mixing time in a continuous mixer, t he weight of its contents at operating level is divided by the w eight of the mixture delivered per second by the mixer: /g1839/g1861/g1876/g1861/g1866/g1859/uni0009/g1846/g1861/g1865/g1857/uni002C/g1871/g1857/g1855/g1867/g1866/g1856/g1871/g3404/g1842/g1873/g1859/g1865/g1861/g1864/g1864/uni0009/g1856/g1857/g1853/g1856/uni0009/g1855/g1853/g1868/g1853/g1855/g1861/g1872/g1877/uni002C/g1864/g1854/uni0009 /g4666/g1863/g1859 /g4667 /g1841/g1873/g1872/g1868/g1873/g1872/uni002C/g1864/g1854/uni0009/g4666/g1863/g1859 /g4667/uni0009/g1868/g1857/g1870/uni0009/g1871/g1857/g1855/g1867/g1866/g1856 The pugmill for the continuous mixer shall be equip ped with a surge hopper containing sufficient baffles and gate s to prevent 216 segregation of material discharged into the truck a nd to allow for closing of the hopper between trucks without requir ing shut down of the plant.
f.Placing and Compacting. The subgrade surface, if dry, shall be moistened but not to the extent of producing a m uddy condition at the time the base mixture is placed. Placing of the base course shall begin along the high point of the pavement on a crowned section or on the high side of a pavement sloping i n one direction. Proportioned and mixed materials shall be transport ed to the point of delivery in approved non-agitating equipme nt. Covers shall be provided for protection during transport. The material shall be spread on the prepared underl ying course to such depth that, when thoroughly compacted, it will conform to the grade and dimensions shown on the plans. The materials shall be spread by a self-propelled s preading machine or similar method approved by the Engineer. Sufficient equipment shall be provided to obtain full width sp reading of the base material. If, in the judgement of the Enginee r, full width placement is not desirable, the base shall be const ructed in partial widths. If the time elapsing between the placing o f adjacent partial widths exceeds 30 minutes, a construction joint sat isfactory to the Engineer shall be provided. Such joints shall be o ffset a minimum of 12" (300 mm) from a planned concrete pavement jo int. The equipment and methods employed in spreading the base material shall ensure accuracy and uniformity of de pth and width. If conditions arise where such uniformity in the sprea ding cannot be obtained, the Engineer may require additional equip ment or modification in the spreading procedure to obtain s atisfactory results. Immediately upon completion of the spreading operat ions, the base material shall be thoroughly compacted. Self- propelled rollers, in sufficient number, size, and type shall be provi ded to obtain the specified results. Care shall be exercised in rout ing construction equipment to avoid the formation of unnecessary rid ges due to wheel tracks or tractor treads. If necessary, the base material after compaction shall be trimmed by means of a self-prop elled motor grader to the grade and section shown on the plans. All material loosened in this operation shall be swept from the surface before any further rolling. Finishing operations shall contin ue until the surface 217 is true to the specified cross section and until th e surface shows no variations of more than ¼" (6 mm) from a 10' (3 m) straightedge laid in any location parallel with, or at right angles t o, the longitudinal axis of the pavement. No equipment or traffic shall be permitted on the f inished base course during the first 72 hours of the curing peri od, except for minor maneuvering to enable the Contractor to begin the next day’s work, not to exceed 25' (8 m). After the base course is 7 days old, one lane in ea ch direction may be used as a haul road, at the Contractor's own risk. Any damaged areas resulting from this operation shall b e removed and replaced at no cost to the Department. Loaded truc ks will be permitted to back onto the base to unload.
g.Construction Joints. At the end of each day's run a transverse construction joint shall be formed by a header or by cutting back into the compacted material to form a true transverse vertical face. These faces shall be protected by b anking damp earth against them or by other approved suitable methods. The protection provided for construction joints sha ll permit the placing, spreading, and compacting of base material without injury to the work previously placed. When a longitudinal construction joint is required in partial width construction, side forms shall be used or the joint shall be formed by cutting back into the compacted material to form a vertical edge. Suitable curing shall be provided for any exposed l ongitudinal edge. Joints shall be offset from a planned longitudinal pavement joint a minimum of 12" (300 mm). Care shall be exercised to ensure thorough compacti on of the base material immediately adjacent to all construct ion joints.
h.Protection and Curing. After the base course has been finished as specified herein, it shall be protected against drying for 7 days by the application of asphalt material. The c uring methods shall begin as soon as possible, but no later than 24 hours after the completion of finishing operations. The finished b ase course shall be kept reasonably clean and continuously moist unt il the curing material is placed. The asphalt material specified shall be uniformly a pplied to the moist surface of the completed base course at the r ate of 218 approximately 0.2 gallon per square yard (0.75 L/sq m) using approved heating and distributing equipment. The e xact rate and temperature of application to give complete coverag e without excessive runoff will be specified by the Engineer. Should it be necessary for construction equipment o r other traffic to use the asphalt covered surface before the aspha lt material has dried sufficiently to prevent pickup, sufficient gr anular cover shall be applied before such use. The curing material shall be maintained and applied as needed by the Contractor during the 7 day protection period s o that all of the base course is covered effectively during this peri od. Finished portions of base course that are used by e quipment in constructing an adjoining section shall be protecte d in such a manner as to prevent equipment from marring or dama ging the completed work. When the air temperature may be expected to drop to the freezing point, sufficient protection from freezing shall be given the base course for 7 days after its construction and until it has hardened.
i.Cold Weather Protection. During cold weather, when the air temperature may be expected to drop below 35° F (2° C), a sufficient supply of hay, straw, or other material suitable for cover shall be provided at the site. Any base that has b een damaged by freezing shall be removed and replaced at no cost t o the Department.
j.Tolerance in Base Thickness. The base course shall be constructed according to the typical sections on th e plans ±½" (12 mm) in thickness. Sections over ½" (12 mm) def icient in thickness shall be removed and replaced at no cost to the Department. No payment will be made for materials placed in excess of planned thickness.
308.05 Quality Control, Acceptance, and Adjustments in
Payment. (a) General. The Contractor shall furnish all personnel, equipment, and facilities necessary to perform the required sampling and testing. The Contractor's facilities shall be separate from any Field Laboratory and/or Field Office furnished unde r the Contract. The Contractor shall provide the Engineer with the opportunity to observe all quality control and acceptance sampling and testing. Quality control sampling and testing by the Contrac tor shall be performed in a qualified laboratory by a certified technician. 219 Requirements for technician certification and labor atory qualification are contained in the Department’s Manual of Field Sampling and Testing Procedures . Test reports shall be signed and copies made available to the Engineer.
b.Quality Control. Quality control of the Cement Stabilized Crushed Stone Base Course in regards to gradation, density, and plasticity index shall be according to the Quality Control and Acceptance provisions contained in Section 306. Th e density, as determined by AASHTO T 310, Direct Transmission, sh all not be less than 95% of the maximum laboratory density det ermined in the laboratory by AASHTO T 180, Method D. The Contract or shall conduct soundings to insure that the minimum specif ied depth is maintained.
c.Acceptance Testing. Acceptance testing by the Contractor for thickness, gradation, and compressive strength will be based upon lots. The standard lot size for acceptance wi ll be 4000 cubic yards (3000 cubic meters) of mix, with each standar d lot divided into four sublots of 1000 cubic yards (750 cubic me ters). The Engineer may establish partial lots at any time. T he Engineer will determine the size of any partial lots established and the number and size(s) of the sublots, if any. The minimum frequency of sampling and testing for t hickness, gradation, and compressive strength shall be one te st for each sublot. The Department will determine the location for each sample in the sublot by AHTD Test Method 465. For compressive st rengths, the Contractor shall obtain one core from each sublot a ccording to AASHTO T 24 and all core holes must be repaired by the Contractor using acceptable material approved by th e Engineer. The Contractor shall perform compressive strength testi ng on the cores according to AASHTO T 22. The Contractor shall cer tify to the Engineer that the calibration of the concrete cylin der compression testing machine has been verified. This verificati on shall be performed in accordance with AASHTO T 22 and T 67 u nder any of the following conditions and documented in accordan ce with AASHTO T 67:
1.After an elapsed interval of 12 months, not to exce ed 13 months since the previous calibration.
2.After original installation of the machine or follo wing relocation of the machine. 220 3. Immediately after repairs or adjustments.
4.Whenever there is a reason to doubt the accuracy of the results, without regard to the time interval since the last verification. Thickness determination shall be made from cores sa mpled for compressive strength tests. Acceptance of the aggr egate gradation shall be according to the Quality Control and Accep tance provisions contained in Section 306. In addition to the required acceptance tests, the E ngineer may require the Contractor to test any location that, b y visual observation, appears to be defective. The Departme nt may perform any sampling or testing to verify the Contractor’s testing equipment or procedures. The Contractor shall be required to make changes to the equipment and/or procedures if the Department i s unable to verify the Contractor’s test results. The Contractor’s acceptance sampling and testing pr ocedures, equipment, and results will be subject to independe nt assurance sampling and testing conducted by the Department. Independent assurance sampling and testing will be conducted at the frequencies indicated in the Department’s Manual of Field Sampling and Testing Procedures . The Contractor shall be required to make changes to the equipment and/or procedures used if the results of the independent assurance tests do not correlate with t he Contractor’s test results. The Department will obtain and test a minimum of on e sample taken at random from each lot, including partial lo ts, to be used both for verification and for acceptance. The location of the lot sample will be determined by the Department using AHTD Tes t Method 465. Verification testing will be conducted in acc ordance with Subsection 106.11 and the Manual of Field Sampling and Testing Procedures . Acceptance sampling and testing by the Contractor s hall be performed in a qualified laboratory by a certified technician. Requirements for technician certification and labor atory qualification are contained in the Department’s Manual of Field Sampling and Testing Procedures. Acceptance sampling and testing shall be accomplished in a timely manner. The Cont ractor shall maintain records of all samples taken and the resul ts of all tests performed. Signed copies of these records shall be furnished to the 221 Engineer on the next business day after the tests a re performed. The item of work being tested shall not be considered c omplete or accepted until all test reports are submitted to th e Engineer.
d.Acceptance and Adjustments in Payments. Acceptance and adjustment will be by lot. Acceptance of a standard lot shall be based on comp lying test results for thickness and gradation and the average compressive strength testing results meeting a minimum of 750 p si (5.2 MPa) in 7 days. The average result will include the sublot results of tests performed by the Contractor and the results of the lot test performed by the Department. For a lot or sublot to be considered for acceptance and adjustments, each core shall achieve not less than 70% of the minimum compressive strength specified at 7 days. In the sublot containing the Department’s lot test, if the result of either the Contractor’s sublot test or the Department’s lot te st is below the minimum compressive strength specified, the two res ults will be averaged and the average of the two test results us ed to determine acceptance or rejection. If the average compressive strength of the cores is less than the minimum compressive strength specified, adjustments will be made by reducing the contract price for the items of Agg regate in Cement Stabilized Crushed Stone Base Course, Cement in Cem ent Stabilized Crushed Stone Base Course, and Processin g Cement Stabilized Crushed Stone Base Course on a lot basis according to Table 308-1. Continuous production of material not qualifying for full payment will not be allowed. TABLE 308-1 Acceptance and Adjustments in Payments Average 7 Day Compressive Strength Pay 750 psi (5.2 MPa ) 100 % 750 to 675 psi (5.2 to 4.7 MPa) 90 % 675 to 600 psi (4.7 to 4.2 MPa) 80 % 600 to 525 psi (4.2 to 3.7 MPa) 70 % less than 525 psi (3.7 MPa) Remove and Replace 222 (e) Unacceptable Base Course. Any lot or sublot that is not accepted shall be removed and replaced by the Contr actor at no cost to the Department. Payment for lots where removal and replacement is required will be withheld or recover ed, and released after replacement has been acceptably completed. T he quantity and measurement of the quantity used in replacement ope rations will not be considered.
308.06 Method of Measurement. (a) Processing Cement
Stabilized Crushed Stone Base will be measured by t he square yard (square meter) of the thickness specified. The qua ntities shown on the plans will be considered as the final quantitie s and no further measurement will be made unless, in the opinion of the Engineer or upon evidence furnished by the Contractor, substant ial variations exist between quantities shown on the plans and act ual quantities due to changes in alignment or dimensions or to app arent errors.
b.The mix proportions in pounds per square yard (kilo grams per square meter) of aggregate and cement, as establish ed by the laboratory design, will be used in conjunction with the square yard (square meter) measurement to determine the quantit ies of crushed stone and cement. Quality Control and Acceptance sampling and testing of Cement Stabilized Crushed Stone Base Course will not be pa id for separately, but full compensation therefor will be considered included in the contract unit prices bid for other items in this Section. Water and asphalt will not be paid for separately, but full compensation therefor will be considered included i n the contract unit price bid for Processing Cement Stabilized Bas e Course.
308.07 Basis of Payment. Work completed and accepted and
measured as provided above will be paid for as foll ows:
a.Processing Cement Stabilized Crushed Stone Base Cou rse will be paid for at the contract unit price bid per square yard (square meter) for Processing Cement Stabilized Crushed Sto ne Base Course.
b.Portland Cement and/or fly ash will be paid for at the contract unit price bid per ton (metric ton) for Cement in C ement Stabilized Crushed Stone Base Course. 223 (c) Aggregate will be paid for at the contract unit pr ice bid per ton (metric ton) for Aggregate in Cement Stabilized Crushed Stone Base Course. The contract unit prices mentioned above will be fu ll compensation for furnishing, hauling, and placing m aterials; for performing quality control and acceptance sampling and testing; for pulverizing, watering, mixing, compacting, finishin g, and curing; and for all labor, equipment, tools, and incidental s necessary to complete the work. Payment will be made under: Pay Item Pay Unit Processing Cement Stabilized Crushed Stone Base Course Square Yard (Square Meter ) Cement in Cement Stabilized Crushed Stone Base Course Ton (Metric Ton) Aggregate in Cement Stabilized Crushed Stone Base Course Ton (Metric Ton)
Source: , Edition.