370(h) Protecting and Curing: After finishing of the subgrade, no vehicles except sprinkling equipment shall be permitted on the subgrade for a curing period of 7 days or until the next course is placed, whichever is less. During the curing period, the subgrade shall be lightly sprinkled with water at frequent intervals to prevent the surface from drying out and cracking. The Contractor shall plan and execute the work in such a manner as to place the next course during the curing period. If the Contractor has not placed the next course by the end of the curing period, the Contractor shall apply liquid asphalt and cover material at the rate specified on the plans. Damage to the stabilized course attributable to other phases of construction by the Contractor shall be repaired at the Contractor’ s expense. At least one subsequent course shall be constructed on the stabilized course before hauling operations for the other phases of construction are permitted on the treated course. If the material loses the required stability, density, or finish before the next course is placed or the work accepted, it shall be recompacted and refinished at the Contractor’ s expense.
306.04 Measurement and Payment
Lime stabilization will be measured in tons of lime or fly ash, square yards of manipulation, and cubic yards or tons of aggregate material, complete-in-place, and will be paid for at the contract unit price per ton of lime or ton of fly ash, per square yard of manipulation, and per cubic yard or ton of aggregate ma - terial. Weighing shall be performed in accordance with Section 109.01 except that transporting vehicles shall be tared prior to each load. Manipulation shall include preparing the roadbed, scarifying, pulverizing, drying material, mixing, com - pacting, finishing, protecting, curing, and maintaining the completed course. Payment will be made under: ——————————————————————————Pay Item Pay Unit—————————————————————————— Lime Ton Fly ash Ton Manipulation (Depth) Square yard Aggregate material (Type) Cubic yard or ton—————————————————————————— SECTION 307—HYDRAULIC CEMENT STABILIZATION
307.01 Description
This work shall consist of stabilizing roadbed material as specified or as directed by the Engineer and constructing one or more courses of the pavement structure using a mixture of soil, or approved aggregates and hydraulic cement, on a prepared surface in accordance with these specifications and in conformity with the lines, grades, typical sections, and cross sections shown on the plans or as established by the Engineer.
307.02 Materials
a.Cement shall conform to Section 214, Type I, IP , or II. Cement shall be transported, stored, and otherwise protected in accordance with Section 217.03.306.03 371(b) Water shall conform to Section 216.
c.Asphalt used for curing or priming shall conform to Section 210 as applicable.
d.Aggregate shall conform to Section 205, Section 207, or Section 208 or other Contract requirements as applicable.
e.Select borrow shall consist of approved material having the specified CBR.
307.03 Field Laboratory
When a field laboratory is furnished by the Department, the Contractor shall move the laboratory to various points along the project as necessary.
307.04 Weather Limitations
The Engineer will not permit cement stabilization when aggregate or the surface on which the course is to be placed is frozen. The Contractor shall not start manipulation operations until the air temperature is at least 40 degrees F in the shade and rising. The Contractor shall protect the stabilized material from freezing for 7 days or shall cover the stabilized surface with the next pavement course within 4 hours after the cement stabilization has been finished as specified when material may be exposed to freezing temperatures during the first 24 hours of curing.
307.05 Procedures
If the Contractor elects to use full-width paving equipment in the subsequent placement of asphalt concrete base, the width of the stabilized course upon which the base will be placed may be extended 1 foot beyond the designed typical section on each side.
a.Preparing Existing Surface: When the roadbed is to be stabilized, its surface shall be cut or bladed to the approximate line, grade, and cross section; however, the Engineer will not require compaction of the roadbed for the depth of the material to be treated prior to application of cement. The Contractor shall prepare the surface of the roadbed in accordance with Section 305.03 as applicable when the course placed directly on the roadbed is to be stabilized. Additional material needed to bring the roadway surface into compliance with the required specifi - cations shall be obtained from within the limits of the right of way, if available. When authorized, the Contractor shall obtain such material from borrow pits as provided for in Section 303. The surface shall be sufficiently firm to support the construction equipment without displacement and shall be in such condition that the compaction can be obtained as specified herein. Soft, yield - ing, or wet areas shall be corrected and made stable before construction proceeds.
b.Preparing Materials: The Contractor shall scarify and pulverize the material to be treated prior to application of cement when the roadbed is to be stabilized. Pulverizing shall continue during mixing operations until at least 80 percent of the material, exclusive of coarse aggregate, will pass the No. 4 sieve. The Contractor shall remove any material retained on the 3-inch sieve and other objectionable objects.307.05 372Applying and mixing cement with material in place or aggregate material shall be performed in accordance with the following methods except that aggregate subbase, aggregate base course, select material, and select borrow specified on the plans shall be mixed in accordance with 2. herein. If the closest central mixing plant is located more than 30 road miles from the project, the Contractor may elect to mix cement with aggregate subbase, aggregate base, select material, and select borrow in accordance with 1. herein provided an additional 1 percent cement by weight is added to the in-place mixing operation and the cement is mixed to a depth of approximately 1 inch less than the depth of the course being stabilized. No additional compensation will be allowed for the changes described herein.
1.Mixed-in-place method: The Contractor shall blend any additional required material with the existing material prior to application of cement. The Contractor shall uniformly apply cement on the material to be processed. When bulk cement is used, the equipment shall be capable of handling and spreading the cement in the required amount. The moisture content of the material to be processed shall be sufficiently low to permit a uniform mixture of the aggregate material and cement. The Contractor shall replace spread cement that has been lost without additional compensation before mixing is started. Mixing shall be accomplished by means of a self-propelled or self-powered machine equipped with a mechanical rotor or other approved type of mixer that will thoroughly blend the aggregate with the cement. Mixing equipment shall be capable of ensuring positive depth control. The Contractor shall exercise care to prevent cement from being mixed below the depth specified. Water shall be uniformly incorporated into the mixture. The water supply and distributing equipment shall be capable of supplying the amount of water necessary to obtain optimum moisture in the material within 1 hour. 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 uniform mixture has been obtained for the full depth of the course. The Contractor shall remix any mixture that has not been compacted and remains undisturbed for more than 30 minutes. If rain adds excessive moisture to the uncompacted material, the entire section shall be reworked. If the Contractor is unable to finish the section within the same day, the section shall be reconstructed and an amount equal to 50 percent of the original amount of cement shall be added to the mixture at the Contractor’ s expense.
2.Central plant method: Material shall be proportioned and mixed with cement and water in an approved central mixing plant. The plant shall be equipped with feeding and metering devices that will introduce materials into the mixer in the specified quantities. Mixing shall continue until a uniform mixture has been obtained. Mixed material shall be transported to the roadway in suitable vehicles and spread on a moistened surface in a uniform layer by a self-propelled or other approved spreader. Not more than 60 minutes shall elapse between the start of mixing and the start of compacting the cement-treated mixture on the prepared subgrade.
a.Mixing aggregate subbase and base material: The cement content will be determined by the titration method as described in VTM-40. Sampling and testing for determining cement content will be performed at the plant. However, nothing herein shall be construed as waiving the requirements of Section 106.06 and Section 200.02.307.05 373The Engineer’ s acceptance for cement content will be based on the mean of the results of tests performed on samples taken in a stratified random manner from each lot. The rate of sampling shall be four samples per lot. A lot of material is defined as 2,000 tons, or 4,000 tons for contract items in excess of 50,000 tons. If the project requires less than 2,000 tons; the amount of material necessary to complete the project is less than 2,000 tons, or 4,000 tons when the contract item is in excess of 50,000 tons; a portion of the lot is rejected for deficient cement content; the job-mix formula for the aggregates is modified within a lot; or a portion of the lot is rejected for an excessive liquid limit or plasticity index then that amount or the rejected portion of the lot shall be defined as a lot. A lot will be considered acceptable for cement content if the mean result of the test(s) is within the following process tolerance(s) of the plan design for the number of tests taken: mean of two tests, –1.1 percent; mean of three tests, –0.9 percent; mean of four tests, –0.8 percent. However, no one sample shall have a cement content more than 1.6 percent below the design cement content. If an individual test result indicates that the cement content of the material represented by the test is deficient by more than 1.6 percent from the design cement content, the portion of the material represented by the sample will be considered a separate part of the lot and shall be removed from the road. If the value of the test results falls below the allowable process tolerance, a payment adjustment will be applied to the contract unit price at the rate of 1.0 percent for each 0.1 percent the material is outside the process tolerance. If the total adjustment is 8.0 percent or less and the Contractor does not elect to remove and replace the material, the contract unit price paid for the material will be reduced at the rate specified herein. The adjustment will be applied to the tonnage represented by the samples.
b.Mixing select borrow: Cement in the mixture shall not vary more than ±7.0 percent by weight from that specified. Feeders and meters for introducing cement into the mixer shall be of such design that the amount of cement can be accurately determined before cement is introduced into the mixer.
c.Compacting and Finishing: Prior to the beginning of compaction, the mixture shall be brought to a uniformly loose condition for its full depth. For subgrade stabilization, the mixture shall be compacted to a density of at least 100 percent of the maximum density as determined in accordance with VTM-1 or VTM-12. For subbase and base stabilization, the mixture shall be compacted to conform to the density requirements of Section 309.05. At compaction, the cement treated subgrade soil shall have a moisture content of not less than optimum or more than optimum + 20 percent of optimum. The cement treated subbase and base aggregate shall have a moisture content of not less than optimum or more than optimum plus 2 percentage points. Compaction equipment shall be subject to the Engineer’ s approval, and the number of such units shall be sufficient to ensure the specified density and completion of the processed section within 4 hours from the time the water is added to the mixture. Initial compaction of soil mixtures shall be accomplished with a tamping roller. After the mixture has been compacted, the surface shall be shaped to the required lines, grades, and cross sections.307.05 374If the material to be shaped is a type in which surface compaction planes will form, the Contractor shall lightly scarify the surface continuously with a drag harrow or similar equipment during the shaping operation. The surface shall then be rolled with steel wheel or pneumatic tire rollers, or both. The moisture content of the surface material shall be maintained at not less than the specified optimum during finishing operations. Compacting and finishing operations shall be completed within the specified time and carried out in a manner that will produce a smooth, dense surface, free from surface compaction planes, cracks, ridges, or loose material.
d.Construction Joints: Each day’ s operation shall tie into the completed work of the previous day by the remixing of approximately 2 feet of the completed course prior to the processing of additional sections. An amount equal to 50 percent of the original amount of cement shall be added to such transition sections. When the completed section remains undisturbed for more than 24 hours, a transverse construction joint shall be made by cutting back into the completed work to form an approximate vertical face.
e.Tolerances: The finished stabilized course shall conform to the specified thickness and density, subject to the following tolerances:
1.Density: The density of the completed work for each day’ s operations will be determined at representative locations. Any portion on which the density is more than 5 pounds per cubic foot less than that specified shall be removed and replaced.
2.Thickness: Thickness will be determined in accordance with VTM-38A. The Contractor shall remove and replace areas that are deficient in thickness by more than 1 inch or, with the approval of the Engineer; the Contractor shall correct sections on stabilized base courses that are deficient in depth by applying asphalt concrete at his own expense. Mixed-in-place areas that are excessive in thickness by more than 1 inch shall be removed and replaced. When the central plant method of mixing is used, acceptance of the course will be based on Section 308.04 except when the depth is deficient by more than 1 inch. In such cases of deficiency, correction shall be as specified herein.
f.Protecting and Curing: The next course may be placed after the cement stabilization has been approved. If the next pavement course is not placed immediately, the cement-treated aggregate course shall be moist cured continually or covered by the application of liquid asphalt to prevent surface drying until the next pavement course is placed. The Contractor shall endeavor to place the next pavement course within 7 days after cement stabilization is finished. If this is not possible and a liquid asphalt cover has not been applied, the Contractor shall either seal the cement-stabilized layer with approved cover material or continually maintain the surface of the cement-stabilized course with moisture until the next pavement course can be successfully applied. The surface of the cement-treated aggregate course shall be maintained in such a manner that the entire surface of the course remains in a moistened condition. If asphalt cover material is used, it shall be applied at the rate of approximately 0.25 gallon per square yard or as shown on the plans. The Engineer shall direct the exact rate of application necessary to produce full coverage without excessive runoff. If asphalt is used, it shall be applied with an approved pressure distributor as specified in Section 314.04 and the asphalt material shall be immediately covered with the specified cover material. Prior to placing the next course or applying asphalt cover material, the surface of the cement- stabilized layer shall be lightly moistened. In no case shall the cement-treated aggregate course be allowed to dry out completely or go uncovered through the winter. The stabilized course shall be tightly knit and free from loose and extraneous material.307.05 375The Contractor shall maintain the cement-stabilized course, including shoulders and ditches, within the limits of the Contract in a condition satisfactory to the Engineer from the time work first starts until the work is officially accepted. Maintenance shall include immediate repairs of defects that may occur either before or after cement is applied, which work shall be performed by the Contractor and repeated as often as is necessary to keep the course continuously intact. Repairs to the course shall be performed in a manner that will ensure the restoration of a uniform surface and stability of the area repaired.
307.06 Measurement and Payment
Hydraulic cement stabilization will be measured in tons of hydraulic cement, cubic yards or tons of aggregate, and square yards of manipulation in accordance with Section 109.01 and will be paid for at the contract unit price per ton of hydraulic cement, per ton or cubic yard of aggregate, and per square yard of manipulation for the depth specified. This price shall include furnishing and applying water for moisture curing and, when grading is not a pay item, restoring shoulders and ditches. Hydraulic cement-stabilized aggregate material or aggregate base material will be measured in cubic yards or tons and will be paid for at the contract unit price per ton or cubic yard. This price shall include furnishing and installing cement, aggregate, and moisture for curing and, when grading is not a pay item, restoring shoulders and ditches. Cement-stabilized select borrow will be measured in cubic yards, pit measure, in accordance with Section 109.01 and will be paid for at the contract unit price per cubic yard. This price shall include furnishing component and curing materials and hauling, placing, and curing the cement-stabilized material. When bulk cement is used, scales capable of weighing loaded cement transports or lesser loads shall be provided at locations approved by the Engineer. Weighing shall be performed in accordance with Section 109.01 except that transporting vehicles shall be tared prior to each load. Manipulation, when a pay item and the Contractor elects to centrally mix the materials, will be paid for in accordance with the quantity of manipulation shown on the plans. Manipulation will include only the mixing operation. Asphalt and cover material for curing will not be measured for separate payment. Payment will be made under: —————————————————————————— Pay Item Pay Unit—————————————————————————— Lime Ton Fly ash Ton Manipulation (Depth) Square yard Aggregate material (Type) Cubic yard or ton——————————————————————————307.06 376SECTION 308—SUBBASE COURSE
308.01 Description
This work shall consist of furnishing and placing one or more courses of mineral aggregate on a prepared subgrade in accordance with the required tolerances within these specifications and in conformity with the lines, grades, typical sections, and cross sections shown on the plans or as established by the Engineer.
308.02 Materials
a.Subbase material shall conform to Section 208.02(a) except where other types of aggregate material are specified in the Contract, in which case the applicable specifications governing the material shall apply.
b.Local sources shall conform to Section 106.03.
308.03 Procedures
Prior to placement of the subbase course, the subgrade shall be constructed in accordance with Section 304 and Section 305 as applicable. Subbase material shall be mixed in an approved central mixing plant of the pugmill or other mechanical type in accordance with Section 208.05. The Contractor shall place the mixed material on the subgrade by means of an approved aggregate spreader. The Engineer will not require the use of such spreader when the material is being applied solely for the temporary maintenance of traffic or where the width of the course shown on the plans is transitional and impracticable to place with a spreader box. The Contractor shall spread and compact the material in two or more layers of approximately equal thickness where the required thickness is more than 6 inches. The compacted thickness of any one layer shall be not more than 6 inches, however the Engineer may approve increasing the compacted depth of a single layer of the subbase course to 10 inches when vibrating or other approved types of special compacting equipment are used. Each layer of subbase course shall be compacted at optimum moisture, within ±2 percentage points of optimum. The density of each layer of subbase aggregate material, when compared to the theoretical maximum density as determined in accordance with VTM-1, shall conform to the following: % Material Retained on No. 4 Sieve Min. % Density 0-50 100 51-60 95 61-70 90 Percentages shall be reported to the nearest whole number.308.01
Source: Virginia Road and Bridge Specifications, 2020 Edition. Pages 398–403 of 1,065.