BASE COURSE
307.01 Description. This item shall consist of a treated base
course, composed of a compacted mixture of existing subgrade or soil aggregate, Portland cement, and water, and sha ll be constructed according to these specifications and in substantia l conformity with the lines, grades, compacted thickness, and typical cross section shown on the plans. Unless otherwise provided, the Contractor may use e ither the travel plant or central plant method as described b elow.
307.02 Composition. The mixture shall be composed of existing
subgrade, base course and surface course materials, and/or an imported soil aggregate, with Portland cement and w ater added. The mixture shall contain not less than 4% cement b y volume of compacted mixture, 94 pounds (1420 kg) of cement be ing considered as 1 cubic foot (1 cu m ). At least 30 days before the beginning of stabilizing operations, adequate quant ities of soil and cement shall be supplied to the Materials Division for determination of cement requirements. The Engineer will specify, based on laboratory tests, the exact percentage of cement to be used. Specimens of soil aggregate, cement, and water shal l develop a compressive strength of a least 400 psi (2.7 MPa) i n 7 days.
307.03 Materials. The materials used shall comply with the
following requirements:
a.Water. Water used in mixing or curing shall be clean and free from injurious amounts of oil, salt, or other deleterious substances. Where the source of water is relativel y shallow, it shall 206 be maintained at such a depth and the intake so enc losed as to exclude grass, vegetable matter, or other foreign m aterials.
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. When cement is furnished in sacks, each sack shall contain not les s than 94 pounds (42.6 kg) of cement. Fly ash or slag cement shall comply with Subsection 501.02(f). Fly ash or slag cement may be used as a partial rep lacement for the cement. Replacement amounts, not exceeding 25% by weight, shall be determined through trial batch investigations us ing the specific materials proposed for the project. Mixtures with fly ash or slag cement shall meet the same requirements as mixtures without fly ash/ slag cement. All trial batches required by th is specification shall be accomplished by the Contractor, observed b y the Engineer, and approved by the Engineer of Materials. Mixing of Class C and Class F fly ashes will not be permitted. Fly ash w ill not be allowed as a substitute for high early strength or blended cements. For in-place stabilization, the fly ash/ slag cemen t and cement shall be blended to form a homogeneous mixture befo re application on the roadway. The use of cement salvaged from used or discarded s acks will not be allowed. Cement placed in storage shall be suit ably protected. Any loss of quality occurring during the storage pe riod will be cause for rejection. If the cement furnished shows errat ic behavior under the field conditions incident to the mixing and pla cing of the mixture, or in the time of the initial or final set , the Contractor will at once, without notice from the Engineer, cease th e use of that brand of cement and furnish material of such proper ties as to ensure quality work conforming to these specifications. 207 (c) Soil Aggregate. Soil aggregate shall meet the requirements of Subsection 302.02 for any class provided therein .
d.Asphalt.
1.Emulsified asphalt shall comply with Subsection 403 .03(d) for Grade CSS-1 or CSS-1h.
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 treated base course shall be at the option of the Contracto r, subject to the Engineer's approval.
307.04 Construction Requirements. Sufficient equipment shall
be available so that the work may proceed in proper sequence to completion without unnecessary delay. Equipment, t ools, and machinery used shall be maintained in a satisfactor y working condition. The application of cement and mixing of the cement and soil aggregate will be allowed only on an approved subgr ade, free of excess moisture. No work will be allowed on a froz en subgrade. The Contractor's operations shall be such as to pre vent the drifting of cement or dust off the right-of-way.
a.Preparation of the Roadbed. Prior to other construction operations, the existing roadbed, including the sho ulders, shall be brought to line and grade and shaped to the typical cross section of the completed roadbed and compacted to sufficient d ensity to prevent rutting under normal operations of construc tion equipment. All soft areas shall be corrected to provide unifor m stability. When soil aggregate is utilized, the subgrade shall be p repared according to Section 212.
b.Pulverizing. After shaping and compacting the roadbed, the material to be processed shall be scarified and pul verized before application of cement. Pulverizing shall continue during mixing operations until a minimum of 80% by weight of the material, exclusive of coarse aggregate, will pass a #4 (4.75 mm) sieve. Material retained on a 3" (75 mm) sieve and other u nsuitable material shall be removed. 208 (c) Application and Mixing of Cement. The application and mixing of cement with the aggregate material shall be performed according to one of the following methods:
1.Travel Plant Method. The specified quantity of cement shall be applied uniformly on the material to be pr ocessed, and shall not exceed that which can be processed the sa me working day. When bulk cement is used the equipment shall be capable of handling and spreading the cement in the require d amount. The moisture content of the material to be processe d shall be sufficiently low to permit a uniform and intimate m ixture of the aggregate material and cement. Mixing shall be accomplished by means of a self-pro pelled or self-powered machine equipped with a mechanical rot or or other approved type of mixer that will thoroughly blend t he aggregate with the cement. Mixing equipment shall be so cons tructed as to assure positive depth control. Care shall be exerc ised to prevent cement from being mixed below the depth specified. Machines designed to process less than the full width of bas e at a single pass shall be operated so that the full width of ba se can be compacted and finished in one operation. Water sha ll be uniformly added and incorporated in the mixture. T he water supply and distribution equipment shall be capable of supplying the total required amount of water to the section b eing processed within 3 hours. If more than one pass of the mixer is required, at least one pass shall be made before water is added. Mixing shall continue after all water has been applied until a u niform mixture of aggregate, cement, and water has been obtained f or the full depth of the course. The aggregate and cement mixture that has not been compacted and remains undisturbed more than 30 minu tes shall be remixed. In the event of rain adding excessive moisture to the uncompacted material, the entire section shall be r eworked. Should the Contractor be unable to finish the secti on within the same day, the section shall be reconstructed and an amount equal to 50% of the original amount of cement added to th e mixture at no cost to the Department.
2.Central Plant Method. When a central plant is used, the soil aggregate, cement, and water shall be mixed in a pugmill either of the batch or continuous flow type. The p lant shall be equipped with feeding and metering devices that wil l add the soil 209 aggregate, cement, and water into the mixer in accu rately proportioned amounts as determined by the laborator y design. Aggregate and cement shall be dry-mixed sufficientl y to prevent cement balls from forming when water is added. Mix ing shall continue until a uniform mixture of aggregate, ceme nt, and water has been obtained. The mixture shall be hauled to the roadway in truck s equipped with protective covers. Immediately before spreadi ng the mixture, the subgrade or foundation course shall be moistened and kept moist, but not excessively wet, until cove red by the mixture. The mixture shall be placed on the roadbe d in a uniform layer by an approved spreader or spreaders. No mor e than 60 minutes shall elapse between adjacent spreader r uns and not more than 60 minutes shall elapse between the time of mixing and the beginning of compaction. The layer shall b e uniform in depth, and in such quantity that the completed base will conform to the required grade and cross section. Dumping o f the mixture in piles or windrows will not be permitted.
d.Compaction and Surface Finish. The mixture shall be compacted to a density, as determined by AASHTO T 3 10, Direct Transmission, of not less than 95% of the maximum l aboratory density obtained by AASHTO T 134. The moisture con tent of the mixture during compaction shall not vary more than ±5% from the optimum moisture as determined by AASHTO T 134. The surface of the treated roadway shall be reshape d to the required lines, grade, and cross section after the mixture has been compacted. It shall then be scarified lightly to l oosen any imprints left by the compacting or shaping equipment and rol led thoroughly. The operation of final rolling shall include the us e of pneumatic tired rollers. The rolling shall be done in such m anner as to produce a smooth, closely knit surface, free of cracks, rid ges, or loose material, and conforming to the crown, grade, and l ine shown on the plans. The density, surface compaction, and finishing oper ation shall not require more than two hours. Water shall be added, if necessary, during the fini shing operation to maintain the mixture at the proper moisture cont ent for securing the desired surface. 210 Areas inaccessible to rollers or finishing and shap ing equipment shall be thoroughly compacted to the required densi ty by other approved compacting methods and shaped and finished as specified.
e.Joints. As soon as final compaction and finishing of a se ction has been completed, the base shall be cut back perp endicular to the center line to a point where uniform cement content with proper density has been attained and where the vertical fa ce conforms to the typical section shown on the plans. When the road mix method is used, a header shall be placed against the vertical face of the finished section and securely staked in place. Thi s header shall be left in place until all mixing operations on the ad joining section have been completed, after which the header shall be rem oved and the trench backfilled with processed material. This ma terial shall be compacted so that a well-sealed joint is formed and a smooth riding surface is obtained. As an alternate to using a header, the subsequent d ay's operation may be started by cutting back into the previously placed course to the extent necessary to obtain uniform grade and co mpaction.
f.Surface Test. The finished surface of the treated base course shall conform to the general surface provided for b y the plans. It shall not vary more than ¼" (6 mm) from a 10' (3 m) straightedge applied to the surface parallel to the center line of the roadway, nor more than ½" (12 mm) from a template conforming to the cross section shown on the plans. Excess material shall be disposed of as directed.
g.Protection and Cover. Immediately after the rolling and shaping has been completed, the surface of the trea ted base course shall be covered by a protective coating of asphalt to prevent loss of moisture during the curing period and to serve as a prime coat for the later application of wearing course. The aspha lt shall comply with the requirements listed herein and shall be ap plied by means of an approved pressure distributor at the rate of 0.1 to 0.3 gallon per square yard (0.4 to 1.1 L/sq m) to provide complete coverage without excessive runoff. The actual rate of appli cation will be determined by the Engineer. When used, emulsified asphalt shall be diluted with an equal amount of water before applic ation. At the time of application, the base shall be in a moist c ondition. The protective coating of asphalt shall be maintained u ntil the wearing surface is placed. If the condition of the protect ive coating is 211 satisfactory, no additional prime coat will be requ ired at the time of placement of the wearing surface. Furnishing and placing asphalt will not be paid for separately, but full compensation therefor will be considered inclu ded in the contract unit price bid for Processing Cement Treat ed Base Course. Finished portions of the roadway adjacent to constr uction that is traveled by equipment used in constructing an adjoi ning section shall be protected by means satisfactory to the Eng ineer. If earth covering is used on fresh bases, straw, hay, buildi ng paper, or similar material shall be placed under the earth so that the covering may be removed without damage to the base.
307.05 Maintenance. The Contractor shall, within the limits of
the Contract, maintain the treated base material in good condition until all work has been completed and accepted. Ma intenance shall include immediate repairs of any defects that occur . This work shall be done at no cost to the Department and repeated a s often as may be necessary to keep the area continuously intact. Faulty work shall be replaced for the full depth of treatment. The C ontractor shall construct the plan depth of cement treated base in one homogeneous mass. The addition of thin treated layers to provi de the minimum specified depth will not be permitted.
307.06 Seasonal and Temperature Limitations. Application of
cement will not be permitted when the surface tempe rature is below 40° F (5° C), nor shall it be applied before April 1. Application of cement shall be terminated sufficiently early to gi ve reasonable assurance that all mixing, spreading, rolling, and curing of the cement treated base course and the application of t he subsequent asphalt courses can be complete on or before the fo llowing dates, except by written permission of the Engineer: Asphalt Surface Treatment - Roadway September 30 Asphalt Surface Treatment - Shoulders October 31 ACHM Binder Course October 31 ACHM Surface Course October 31
307.07 Quality Control and Acceptance. Quality control and
acceptance shall be according to the provisions of Section 306 except the minimum frequency of testing shall be ba sed on a lot size of 12,000 square yards (10,000 sq m). 212 307.08 Method of Measurement. (a) Processing Cement Treated Base Course will be measured by the square yard (square meter) or by the station (metric station) for the d epth specified. When measurement by the station (metric station) is specified, roadways in each direction of a divided highway wil l be measured, and additional areas outside the normal roadway wil l be converted to the normal measurement on an equivalent area bas is. Water and asphalt will not be measured or paid for separately, but full compensation therefor will be considered inclu ded in the contract unit price bid for the item Processing Cem ent Treated Base Course.
b.Portland cement and/or fly ash will be measured by the ton (metric ton).
c.Soil Aggregate will be measured in place by the sq uare yard (square meter) or by the station (metric station) f or the width and depth specified, or in the pit by the cubic yard (c ubic meter) as determined in Subsection 109.01(a), or in trucks by the ton (metric ton) or cubic yard (cubic meter) according to Secti on 209.03, Method 2. When measurement by the station (metric station) is specified, roadways in each direction of a divided highway will be measured and additional areas outside the normal ro adway will be converted to the normal measurement on an equivalen t area basis.
307.09 Basis of Payment. Work completed and accepted and
measured as provided above will be paid for as foll ows:
a.Processing Cement Treated Base Course will be paid for at the contract unit price bid per square yard (square meter) or per station (metric station) for Processing Cement Trea ted 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 T reated Base Course.
c.Soil Aggregate will be paid for at the contract un it price bid per square yard (square meter), station (metric sta tion), cubic yard (cubic meter), or ton (metric ton) for Soil Aggrega te in Cement Treated Base Course. The contract unit prices mentioned above will be fu ll compensation for furnishing, hauling, and placing m aterials; for pulverizing, watering, mixing, compacting, finishin g, and applying asphalt; for performing quality control and accepta nce sampling and 213 testing; and for all labor, equipment, tools, and i ncidentals necessary to complete the work. Payment will be made under: Pay Item Pay Unit Processing Cement Treated Base Square Yard Course (__" [___mm] Uniform (Square Meter) or Thickness) Station (Metric Station) Cement in Treated Base Course Ton (Metric Ton) Soil Aggregate in Cement Treated Square Yard Base Course (__" [___mm] (Square Meter), Compacted Depth) Station (Metric Station), Cubic Yard (Cubic Meter), or Ton (Metric Ton)
Source: , Edition.