303In-Place Cement Stabilized and Treated Base

In-Place Cement Stabilized and Treated Base Courses

303.01DESCRIPTION. Scarify, pulverize, blend, shape, and stabilize

roadbed material with portland cement, blended hydraulic cement, or portland blast-furnace slag cement in accordance with the lines, grades, thickness, and sections established or shown on the plans. Cement stabilization and cement treatment is primarily for existing roadbed materials. When specified, furnish and place materials under different pay items to be stabilized or treated in accordance with this section. In areas that are inaccessible for mixing and compacting in turnouts and crossovers, and in other isolated or irregular areas, portland cement concrete complying with Section 901 or asphalt concrete complying with Section 502 may be used in lieu of the specified base course material with approval. If using asphalt or portland cement concrete, the top half of the base thickness shall be asphalt or portland cement concrete. If used, portland cement concrete shall be a minimum thickness of 6 inches. The remaining thickness shall be the same type and construction as the top layer of embankment, treated layer, or subgrade. Place, consolidate, finish, and cure concrete as directed in accordance with Section 706. Remove and satisfactorily dispose of existing materials as required to accommodate placement of the portland cement concrete or asphalt concrete at no direct pay. Dispose of excess material in accordance with 202.02. Submit a dust control plan to address weather, sight clearance, operational procedures, traffic control, and any other project specific concerns. Failure to maintain sight clearance will result in the engineer stopping contractor operations. The Department will identify dust sensitive areas in the plans. In these specific areas, the dust control plan must also include environmental requirements. Quality assurance requirements shall be as specified in the latest edition of the Department’s publication titled Application of Quality Assurance Specifications for Embankment and Base Course.

.1 Cement Stabilization: Cement stabilization is primarily

used for existing roadbed materials, typically 8.5 inches thick, unless specified otherwise. The design compressive strength criteria for cement stabilization shall be 300 psi as determined in accordance with DOTD TR 432, Method B or C.

.2 Cement Treatment: Cement treatment is primarily used

for existing roadbed materials typically 12 inches thick, unless specified otherwise. The design compressive strength criteria for cement treatment shall be 150 psi as determined in accordance with DOTD TR 432, Method B or C.

303.02MATERIALS. Materials shall comply with the following

sections or subsections: Portland Cement 1001.01 Blended Hydraulic Cement 1001.02 Ground Granulated Blast-Furnace Slag Cement 1001.05 Emulsified Asphalt Section 1002 Water 1018.01 Portland cement shall be Type I or II. Blended hydraulic cement shall be Type IP. Ground granulated blast-furnace slag cement shall be Type IS. The quantity of cement used shall be supported by proof of delivery. Portland blast-furnace slag cement shall contain a maximum of 50 percent ground granulated blast-furnace slag by weight. Pre-blending of Types I or II portland cement and ground granulated blast-furnace slag will be allowed if blended at an approved blending facility and mixed thoroughly to ensure a uniform blend. The ground granulated blast-furnace slag used in pre-blending shall be from the Approved Materials List and meet the requirements of 1001.05. Furnish soils or soil-aggregate combinations for cement stabilization or treatment in accordance with this section that comply with the requirements of 302.02.1. If an A-4 or A-6 Soil Group material is used for cement treatment, it shall meet the durability requirements of DOTD TR 432.

.1 Determination of Cement Rate:

.1.1 Predetermined (Plan Specified): For portland

cement, mix the roadbed material with the rate of cement by volume as shown on the plans.

.1.2 Non-Predetermined: If the percent cement has not

been predetermined, the District Laboratory will determine the percent of cement by volume in accordance with DOTD TR 432 from materials sampled in-place on the project. The Department will take samples for percent cement determination from isolated random areas selected by the project engineer, prepared for sampling by the contractor. Thoroughly pulverize and mix the sampling area to the satisfaction of the project engineer. Resurface sampling areas as directed after samples are taken and maintain to the satisfaction of the project engineer. Payment for resurfacing will be made under the appropriate asphalt concrete roadway or maintenance aggregate items. Depending on materials to be stabilized, normal testing time to determine the required cement content may require up to 21 calendar days.

.1.3 Contractor Selected Cement Type: If selecting

Type IP or IS as the cementitious material, determine the rate of blended cement prior to mixing using TR 432, Method B or C, whichever applies, using the design compressive strength criteria listed for treatment or stabilization. In addition, determine the durability of the base course mixture using Type IP or IS in accordance with DOTD TR 432 with the rate of cementitious material determined from Method B or C. Perform the laboratory testing specified above for Types IP or IS cement at no expense to the Department. The laboratory used must be approved by the Materials Engineer Administrator. Take samples, in the presence of the engineer, by methods described in

.1.2 above. Payment for resurfacing and subsequent maintenance to

the satisfaction of the engineer shall be at no expense to the Department. During sampling operations, obtain sufficient material to provide the District laboratory with approximately 200 pounds of the base material to be treated for verification testing. Take samples for verification from randomly spaced locations, determined by the engineer, throughout the project length. The engineer will take immediate possession of the verification samples. Also provide approximately 10 pounds of the selected cementitious material to the District laboratory. Provide materials for verification testing at no cost to the Department. Submit all design data used to determine the recommended cement rate to the District Laboratory Engineer for approval. Prior to approval of the design, the District Laboratory will perform verification testing. Verification testing by the District Laboratory will consist of molding, curing, and testing a minimum of three specimens in accordance with TR 432, at the percentage of cementitious material and at the optimum moisture determined by the contractor’s laboratory. The recommended cement rate will be considered verified if test results indicate that the minimum strength and durability criteria as specified have been met and that the optimum moisture are within 2 percent of that submitted by the contractor. Normal testing time for verification testing may require up to 21 calendar days. Do not begin construction operations until the design is approved.

303.03EQUIPMENT. Furnish and maintain the equipment necessary to

produce a finished base course meeting specification requirements. Equipment shall be approved prior to use. Pulverize using an approved in- place mixer. Use an in -place mixer equipped with a spray bar that can apply water across the full width of the cut and be adjusted to prevent overlap of water on adjacent paths. Distribute cement from transports using spreader bars approved by the engineer. The engineer may require the use of a cement spreader capable of width adjustment and equipped with a calibrated spreader box if a uniform cement spread cannot be achieved. The Department may verify the distribution of dry additives using DOTD TR 436, Method A. Perform initial compaction using a conventional sheepsfoot-type roller or a self -propelled tamping foot compactor-type roller. The spikes shall be sufficient in size and number to provide uniform compaction for the full width and depth of the base course. Perform finish rolling with a pneumatic tire roller.

303.04PREPARATION OF ROADBED. Unless otherwise designated

on the plans, remove all existing asphalt concrete surfacing except the bottom 1 inch in accordance with Section 509 prior to cement stabilization. During these removal and replacement operations, maintain the areas used by public traffic in a safe condition in accordance with 105.15. Scarify and pulverize materials to be stabilized for the full width and depth of the base course. Pulverize the remaining existing asphalt surfacing and uniformly mix it with materials below the surfacing. Do not prepare roadbed in excess of 2 miles in advance of roadway base course stabilization or treatment. When approved by the project engineer, the 2 -mile limit may be extended. However, when the 2 -mile limit is extended, the lag between preparation of roadbed and base stabilization or treatment shall not exceed 5 working days. When stabilizing or treating shoulders separately from roadway base, the 2-mile limitation will not apply to shoulders. Blend the scarified and pulverized material to achieve uniform blending. When existing material is not uniform across the full width to be stabilized, blend the material to form a uniform blend for the full width and depth of the base course. Scarify and pulverize the roadbed to at least 60 percent passing the No. 4 sieve in accordance with DOTD TR 431 prior to mixing with cement. Identify and remove existing concrete or asphalt concrete patches encountered during roadbed preparation operations. Remove patches and disposed of in accordance with 202.02. After the roadbed has been prepared as specified above, shape the roadbed to the required section and uniformly compact the roadbed material to at least 93.0 percent of maximum dry density prior to mixing with cement. Determine maximum dry density in accordance with DOTD TR 415 or TR 418. Determine in-place density in accordance with DOTD TR 401. Correct areas which cannot be compacted to 93.0 percent of maximum dry density at no direct pay.

303.05MIXING. The method of spread shall be such that the amount of

cement used can be readily determined when tested in accordance with DOTD TR 436. Uniformly spread and mix cement with the material. Make a minimum of two passes with the mixer (stabilizer). Shape the mixture to the required section. Add water as needed by means of the mixer and uniformly incorporate the mixture in amounts required to attain optimum moisture for the mixture. During the mixing process, add water only through the spray bar of the in - place mixer, adjusted to provide uniform coverage across the completed width of the roadway for the full depth of the base. Do not allow wet streaks or spots. Determine optimum moisture of the mixture in accordance with DOTD TR 415 or TR 418. Do not allow the percentage of moisture, determined in accordance with DOTD TR 403, in the mixture by dry weight to vary from optimum moisture by more than ±2 percent at the time of compaction.

303.06COMPACTING AND FINISHING. Uniformly compact the

mixture immediately upon completion of mixing to the specified depth and width shown in the plans. Complete initial compaction with an approved sheepsfoot-type roller or a self-propelled tamping foot compactor-type roller in such a manner that no internal laminations occur in the completed base course. Complete final compaction with a pneumatic tire roller. Keep the surface uniformly moist during compacting and final finishing. Continue compaction until each lift of base course has met the requirements of 303.11. At places inaccessible to rollers, such as edges adjacent to curb and gutter sections, compact the mixture using devices that will obtain the specified density without damaging adjacent structures. Begin mixing operations within one hour of placement. Complete compaction and finishing operations within three hours after initial mixing of cement with base course materials. Upon expiration of the three -hour period after initial mixing, only intermediate finishing (tight blading) of the base course surface will be allowed. Dispose of excess bladed material. Do not drift bladed material along the base. Use stabilized or treated material in the base course except that small amount necessary for tight blading. Excessive blading, exceeding 10 percent of the base thickness, to achieve plan depth will not be allowed. Complete operations, including tight blading, within 24 hours of mixing. The finished base course shall have a smooth, uniform, closely-knit surface, free from ridges, waves, laminations, or loose material. Do not spread cement within two hours before sunset, unless otherwise approved by the project engineer.

303.07QUALITY CONTROL. Control the preparation of roadbed,

selection and placement of materials, cement spread, mixing, compaction, moisture content, density, thickness, width, surface finish, grade, and cross slope so that the completed base course is uniform and conforms to plan dimensions and other acceptance requirements as provided herein. Control operations so that contamination, segregation, soft spots, wet spots, laminations, and other deficiencies are prevented. Take such tests as necessary to adequately control the work.

303.08PROTECTION AND CURING. Upon completion of final

finishing, immediately protect the base against rapid drying by applying an asphalt curing membrane in accordance with Section 506. Maintain complete coverage of curing membrane from the initial application until the placement of the next course. When allowing traffic, including construction equipment, on the base course, place at least the first lift of surfacing within 30 calendar days unless otherwise directed.

303.09MAINTENANCE. Protect the completed base course from

damage due to either public traffic or the contractor’s operations, and satisfactorily maintain the completed base course including asphalt curing membrane. Repair damaged base course at no direct pay. When requiring patching of the base course, in addition to removing damaged or unsound base course, remove a sufficient width and depth of base course to ensure satisfactory placement of patching material. Submit the proposed type of patching materials to the engineer for review and comment before use. Complete patching or other repairs of the base course to restore a uniform surface, conforming to the requirements of the material used, prior to surfacing operations. Do not allow public traffic or construction traffic on the completed base course for a 72-hour curing period. If conditions permit, route both public traffic and construction traffic off the completed base course onto shoulders or other suitable areas during the 72 -hour curing period. Traffic may be permitted on the base course during the curing period, if conditions warrant and if approved by the engineer. When permitting traffic to use the completed base prior to the construction of the surface course, further protect the base by additional applications of asphalt curing membrane in accordance with 302.10 as directed at no direct pay. Prior to surface course construction, clean the base course and apply and maintain additional asphalt curing membrane as directed at no direct pay. Correct any weak spots that develop. Keep the base course free from deficiencies and true to grade and cross section at no direct pay. When the surfacing is asphalt concrete, place the first lift of surfacing within 30 calendar days.

303.10WEATHER LIMITATIONS. Do not mix when the base course

material is frozen, when raining, when the ambient air temperature is below 35°F, or the temperature forecasted by the U.S. Weather Service is to be 25°F or less within the 24-hour period following placement.

303.11ACCEPTANCE REQUIREMENTS. The department will test

soils and aggregates from samples taken after preparation of the roadbed. Test cement spread rate in accordance with DOTD TR 436. Test the moisture content of the cement stabilized or treated mixtures for compliance with optimum moisture content in accordance with DOTD TR 403 at placement at least twice per day. Test the pulverization of the prepared roadbed in accordance with DOTD TR 431, and must be at least 60 percent passing the No. 4 sieve. Check the completed base course for determining acceptance in increments of 1000 linear feet per roadway or 2000 linear feet per shoulder constructed separately.

.1 Density Requirements: Upon completion of compaction

operations, determine in-place density in accordance with DOTD TR 401. The density requirement as based on DOTD TR 415 or TR 418 shall be 95.0 percent of maximum dry density. When the density test value for the section is below 95.0 percent, apply a payment adjustment in accordance with Table 303-1. Table 303-1 Density Acceptance and Payment Schedule Density Test Value (percent) Percent of Contract Unit Price 95.0 & Above 100 93.0 to 94.9 90 90.0 to 92.9 75 Below 90.0 50 or Remove 1 1 At the option of the Chief Engineer.

.2 Thickness Requirements: Determine the thickness of

the completed base course in accordance with DOTD TR 602. The completed base course shall not vary from plan thickness in excess of the tolerances in Table 303-2 as follows. Base course thickness deficiencies in excess of these tolerances shall be corrected as specified herein at no direct pay. Table 303-2 Base Course Thickness Tolerance Under-Thickness, Inches Over-Thickness, Inches 3/4 11/2 Isolate any failing area for purposes of correction. Correct base course thickness deficiencies in excess of the foregoing tolerances as follows. When not permitting grade adjustments, correct thickness deficiencies by restabilizing or retreating with cement or removing and replacing the full depth of base course in deficient areas with one of the following materials:

When permitting grade adjustments, deficiencies may be corrected by furnishing and placing a supplemental layer of asphalt concrete complying with Section 502 for the full width of base course in lieu of removing and replacing deficient base course. When approved, corrections may be made by restabilizing or retreating the existing material in accordance with this section and the cement content may be reduced from design contents with approval of the District Laboratory Engineer. Thickness of the supplemental layer of asphalt concrete shall be in accordance with Table 303-3 as follows. Table 303-3 Supplemental Asphalt Concrete Layer Thickness Under-Thickness, Inch Over-Thickness, Inch Minimum Thickness of Supplemental Asphalt Concrete 1, Inch 1 to 11/2 13/4 to 2 11/4 13/4 to 2 21/4 to 21/2 11/2 21/4 to 21/2 23/4 to 3 2 Over 21/2 Over 3 Remove and Replace 2 1 May be placed with subsequent lift of asphalt concrete. 2 At the option of the Department after investigation.

.3 Width Requirements: Determine the width of the

completed base course in accordance with DOTD TR 602. Do not exceed roadway base course plan width by more than 6 inches. Do not exceed shoulder base course plan width by more than 3 inches. Under-widths of shoulder or roadway bases are not allowed. When the base course for roadway and shoulders are constructed at the same time, the 6-inch width tolerance will be applied. Correct base course width deficiencies in excess of foregoing tolerances as follows at no expense to the Department.

.3.1 Over-Width: When not permitting grade adjustments,

the full depth and width of base course in isolated areas with over-widths in excess of the foregoing tolerances shall be re-stabilized or retreated full width with cement, and the cement content may be reduced from design contents with approval of the District Laboratory Engineer. Otherwise, remove and replace to the plan width with asphalt concrete complying with In lieu of removing and replacing over-width base course, allow areas of the deficient base course to remain in place at a payment adjustment of 90 percent of the contract unit price for the entire lot. When permitting grade adjustments, correct base course width deficiencies by removing and replacing as specified above, or by furnishing and placing a 1 1/4-inch thick supplemental layer of asphalt concrete complying with Section 502 for the full width of the roadway.

.3.2 Under-Width: Correct under-widths of base course in

excess of the foregoing tolerances to plan width by restabilizing or retreatment the full width with cement or by furnishing and placing additional materials; however, do not allow the width of the widening materials to be less than 12 inches. Materials used for widening the deficient base course shall be the same as specified for over-width correction in 303.11.3.1.

.4 Grade and Cross-Slope: The finished grade shall be

within ±1/2 inch of the established grade. Do not allow the cross slope to vary by more than ±0.003 foot/foot.

.5 Correction of Deficiencies: Correct deficiencies in

surface finish, grade, contamination, segregation, soft spots, wet spots, laminations, and other deficiencies at no direct pay. Correct deficiencies by removing and replacing or as directed.

303.12MEASUREMENT. The quantity of in-place cement stabilized or

treated base course for payment will be the design areas as specified in the plans and adjustments thereto. The design quantity is based on the horizontal dimensions of the completed base course shown on the plans. The design quantity will be adjusted if the engineer makes changes to adjust to field conditions, if design errors are proven, or if design changes are necessary. Removal of existing patches will be measured by the square yard . This measurement will be determined and documented jointly by the contractor and project engineer. If including items in the contract, measurement will be in accordance with 109.04.

303.13PAYMENT. Payment for in-place cement stabilized or in-place

treated base course will be made at the contract unit prices per square yard, adjusted as specified in 303.11 and the following provisions, which include furnishing required portland cement, water, and asphalt curing membrane, and performing necessary roadbed preparation. Payment for removing all existing asphalt concrete surfacing will be made under Section 509 except for the bottom 1 inch. No direct payment will be made for removal and disposal of the remaining bottom 1 inch of asphalt surfacing or maintaining the areas in safe condition for traffic. If the actual required percent of cement differs from that required by the contract documents, payment will be increased or decreased based on the difference in required quantity of cement at the price of cement shown on paid invoices (total of all charges). The contractor shall provide copies of paid invoices for this determination. If the contract documents do not specify a percent cement, 8 percent cement will be used for stabilized base course and 6 percent will be used for treated base courses for bid purposes. Removal of existing patches will be paid at the contract unit price per square yard or if no item is provided, in accordance with 109.04. However, no payment will be made unless the contractor identifies the patches and participates in the measurement and documentation. Payment adjustments will be applied for specification deviations of asphalt materials in accordance with Section 1002 based on the invoice price per gallon. The Materials and Testing Section will provide the payment adjustment percentage for properties of asphalt materials. Item No. Pay Item Pay Unit

303-01In-Place Cement Stabilized Base Course ___in

Thick Square Yard

303-02Removal of Existing Patches Square Yard

303-03In-Place Cement Treated Base Course ___in Thick Square Yard