6-24-97

CEMENT STABILIZATION OF SOILS 
207-R-337

 DESCRIPTION: This work shall consist of stabilizing the soils by uniformly mixing portland cement with the soils. This may be used to stabilize the natural ground under embankments and to the subgrade under pavements.

 MATERIAL: The materials shall be in accordance with the following:

Portland cement, type II.......... 901.01(b)
Water......................... 913.01

        Asphalt material for curing seal shall be AE-150 Type I in accordance with 404.

 Reactive Soils are those soils which, when mixed thoroughly with at least 4 percent potland cement, compacted in accordance with AASHTO T 99 Method C, and cured for 48 hours at 49E C (120E F), shall show a strength gain of at least 345 KPa (50 psi) greater than that obtained for similarly prepared untreated control specimens.

EQUIPMENT: The machinery, tools and equipment necessary for proper execution of the work shall be available on the project site and approved by the Engineer prior to the commencing of construction operations.

STORAGE AND HANDLING:

  1. Portland cement shall be stored in weather protected conditions with adequate protection from ground dampness. The storage facility shall be approved by the Engineer prior to commencement of any cement work.

  2. Each shipment shall be accompanied by a bill of lading and by a certificate of compliance stating conformance to the applicable specification requirements.

  3. The Contractor's safety measures shall be in accordance with applicable OSHA standards.

MIXTURE COMPOSITION:

  1. Sample: The contractor shall provide 135 kg (300 lb), minimum, samples of the soil to be modified, and 20 kg (45 lb), minimum, samples of the cement be used at least 45 days prior to the use of the cement.

  2. Mix Design: Cement shall be applied at an approximate rate of 3% to 10% of the dry soil weight as determined by oven-dry test. The required proportion of cement shall be established by the Engineer prior to construction, using samples of soil and cement, and the Department's laboratory design procedure for soil stabilization. The Engineer reserves the right to make such adjustments of cement proportioning as are considered necessary during the progress of the work.

    The source or type of cement shall not be changed during the progress of the work without written permission of the Engineer. The Engineer may, based on laboratory test results, direct the use of different types of cement on different portions of the project. The different types shall not be mixed in the same project portion.

 

CONSTRUCTION REQUIREMENTS:

  1. Temperature and Weather Limitations: Cement modification shall only be performed with a minimum soil temperature measured 100 mm (4 in.) below the surface of 7E C (49E F), and with the air temperature rising. Cement shall not be mixed with frozen soils or with soil containing frost.

  2. Preparation of Existing Roadway: All deleterious material, such as stumps, roots, turf, etc. and aggregate larger than 75 mm (3 in.) shall be removed. All soft organic soils shall be removed as directed by the Engineer.

  3. Scarification and Pulverizing: The existing soils shall be scarified to the required depth with a machine of such design that a visible indication is given at all time that the cutting is to the required depth. Moisture shall be added if necessary.

  4. Cement Application: The specified quantities of cememt shall be uniformly spread. If bagged cement is used, the cement piles shall be leveled by hand raking or with a drag before mixing commences. Graders shall not be used for this purpose. The Engineer may suspend the spreading operation under windy conditions.

    The Department reserves the right to increase or decrease the quantity of the cement used based on test results, as directed by the Engineer.

    The cement application shall include a curing period of seven days if the specified gradation is achieved. Curing periods may be extended at the discretion of the Engineer, if the specified gradation is not achieved.

    All cement that has been exposed to the open air for a period of six hours or more before mixing will not be accepted unless approved by the Engineer.

    Cement which has been damaged by hydration due to rain prior to or during the mixing operations, which has been damaged while spreading contrary to the above mentioned requirements, or which has been displaced by the Contractor's equipment or other traffic, shall be replaced.

    Cement shall be spread only on that area where the initial mixing operation can be completed during the same working day.

    Heavy traffic or equipment shall not be permitted on the spread cement other than that required for spreading, watering, or mixing.

  5. Moisture Control: At the completion of the mixing operation, the moisture content of the mixture shall be between 3 percentage points below to optimum moisture content for sandy soils and between -2 to +1 percentage points of the optimum moisture content for silty and clayey soils.

  6. Test Section: The first section of each mixing operation shall be a test section to demonstrate the acceptability of the Contractor's equipment and methods, to provide a check of the resulting finish grade elevation, and the compacted thickness of the stabilized layer. Changes in equipment shall be made as needed based on the results of the test section. If changes in methods or requirements are made, additional test sections shall be constructed as directed by the Engineer. Additional test sections shall be constructed if recommended in the Geotechnical Report. Test sections may be waived by the Engineer. The length of the section shall be as long as necessary to use one truck of cement.

  7. Dry Mixing: Dry mixing of soil and cement is required when mixing equipment other than a traveling mixing plant is used. After the cement is spread, it shall be mixed with the pulverized soil. Mixing shall be accomplished with mixing devices approved by the Engineer and shall be continued until the resulting mixture is homogeneous and uniform in appearance. Cement shall not be mixed below the specified depth.

    When any part of the operations from the start of soil and cement mixing through final compaction are interrupted for any reason for more than 30 minutes, the entire thickness of the subgrade shall be thoroughly loosened, reprocessed, and shall be completed within the specified time limits for these operations. When the uncompacted soil-cement mixture is wetted by rain so that the average moisture content exceeds the specified limits at the time of final compaction, the portion being processed shall be reconstructed.

  8. Moist Mixing:
  1. With Equipment Other Than a Traveling Mixing Plant. Water shall be immediately applied and incorporated into the dry mixed soil-cement mixture in quantities which will produce the required moisture content for the soil-cement mixture.

    Water supply and pressure distributing equipment shall be provided which will ensure the application of all water required on the section being processed within 3 hours. Each application or increment of water shall be at least partially incorporated into the mixture, if necessary, to avoid excessive concentration of water on and near the surface.

    After the last increment of water has been added, mixing shall be continued until a uniform mixture of soil, cement, and water is obtained. The uniformity of the mixture shall be controlled by the cement-water application rate per square meter (square yard) for the specified depth. Satisfactory moisture distribution along the edges of the section and for the full depth of the treatment shall be obtained.

    When water application and moist mixing is completed, the moisture content, on the basis of dry weight, in the portion of the mixture passing a 25 mm (1 in.) sieve and 60% passing a 4.75 mm (No. 4) sieve, exclusive of gravel or stone retained on these sieves, shall be as specified under section e.

  2. With a Traveling Mixing Plant. After the cement is spread, it shall be mixed with soil and water with a traveling mixing plant. Mixing shall be at such rate that, or shall be repeated until, a uniform mixture of soil, cement and water is obtained. A satisfactory mixture along the edges of the section and for the full depth of treatment shall be achieved. At the completion of the mixing operation, the moisture content and gradation of the mixture shall be as specified. Mixing shall not be done below the specified depth.

    Prior to compaction, the cement stabilized soil mixture shall be pulverized so that 100% of the mixture passes a 25 mm (1 in.) sieve and 60% passes a 4.75 mm (No. 4) sieve, excluding the non-slaking fraction.

  1. Compaction: Compaction of the mixture shall begin immediately after the mixing process is complete. Prior to the beginning of the compaction, the mixture shall be in a loose condition for its full depth and width. The mixture shall then be compacted, using tamping rollers in conjunction with other compaction equipment for the entire width, to at least 100% of the maximum dry density of the cement stabilized mixture in accordance with AASHTO T 99 or one point proctor in accordance with AASHTO T 272 within the special subgrade treatment zone and to a least 95% of the maximum dry density of the cement stabilized mixture in accordance with AASHTO T 99 or one point proctor in accordance with AASHTO T 272 below the special subgrade treatment zone. The density of the soil-cement mixture will be determined by the Engineer near the end of the finishing operations. Any portion of the soil-cement mixture having density less than specified shall be corrected or removed and replaced. The in-place dry density will be determined by the Engineer in accordance with AASHTO T 191 or T 239.

    The average compacted thickness of the modified soil shall be within 10% of the specified thickness, except that the thickness at one place may be within 15% of that specified.

    The Department reserves the right to determine the actual thickness of the completed and cured layer by coring or other means. The Engineer will perform at least one test every 280 m2 (335 sys) for each compacted lift to ensure that the cement is spread at the specified rate. All deficient areas shall be corrected.

    Throughout this operation, the shape of the course shall be maintained by blading and the surface shall be sloped to the required lines, grades and cross-sections. Compaction shall be continued until the minimum specified density is obtained.

  2. Curing and Protection: After the treated area has been finished as specified, it shall be protected against drying for 14 calendar days. The surface shall be maintained in a moist condition by sprinkling for the above mentioned period or until a seal coat is placed, whichever occurs first. Equipment used to apply the curing seal and curing water shall be of a size and weight such that the treated area is not damaged.

    Heavy traffic or equipment other than curing equipment shall not be allowed on the finished area until completion of curing, unless permitted by the Engineer. A satisfactory curing day shall be any day when the temperature of the completed subgrade does not fall below 7E C (49E F). All damage occuring to the curing seal prior to completion of curing shall be immediately resealed.

    The curing seal shall consist of the asphalt material specified and shall be uniformly applied at the rate of approximately 1 kg/m2 (2 lb/syd) with approved distributing equipment. The actual rate and application temperature of asphalt material will be determined by the Engineer.

    If the asphalt material is tacky, a sand blotter material shall be applied at a rate by approximately 3 kg/m2 (5 lb/syd), when directed by the Engineer.

    Other acceptable curing material or methods may be used upon written permission of the Engineer.

    The treated area shall be protected against freezing for seven calendar days after placement.

    The stabilized subgrade shall be completely covered with the specified pavement courses before work is suspended for the winter months. When the stabilized subgrade is not completely covered by the specified pavement courses, the Contractor shall be responsible work necessary to protect and maintain the uncompleted work during the winter months. The Contractor shall perform all work necessary to repair or restore the uncompleted work before the beginning of spring paving operations.

  3. Maintenance: The Contractor shall maintain the entire cement stabilized soil mixture in a manner satisfactory to the Engineer. Maintenance shall include immediate repairs of any defective or damaged portions of the stabilized subgrade.

 

METHOD OF MEASUREMENT: Cement stabilized soils will be measured in square meters (square yards) of the thickness specified. The width for measurement will be as shown on the plans. Water will not be measured. Cement and the asphalt used as a curing seal will be measured in megagrams (tons).

         The cement may be weighed in trucks or freight cars. If the cement is shipped in trucks, it may be weighed at the place of loading, at the place of unloading, or at such other place as the Engineer may designate. The Engineer may accept original signed bills in lieu of weighing. 

        Contract Quantities: When the project is constructed essentially to the lines, grades or dimensions shown on the plans and the Contractor and Engineer have previously agreed in writing that the plan quantities are accurate, no further measurement will be made. If errors are discovered after work has been started, corrective measurements will be made.

         When the plans have been altered or when disagreement exists between the Contractor and the Engineer as to the accuracy of the plan quantities, either party shall, before any work is started which would affect the measurement, have the right to request in writing and thereby cause the quantities involved to be measured.

 BASIS OF PAYMENT: Cement stabilized soils will be paid for at the contract unit price per square meter (square yard) at the thickness specified, complete in place. Cement and the asphalt curing seal will be paid for at the contract unit price per megagram (ton).

 Payment will made under:

 

Pay Item              

Metric Pay Unit Symbol
(English Pay Unit Symbol)

Asphalt Curing Seal

 

......................Mg (TON)

Cement

 

......................Mg (TON)

Cement Stabilized Soils

 

......................m2 (SYS)

 

        The costs of replacing cement damaged by hydration due to rain prior to or during the mixing operations; the replacement of cement damaged by the Contractor's operations; the loosening and reprocessing of the soil and cement mixture when operations are interrupted for more than 30 minutes; the reprocessing caused by the average moisture content exceeding the specified limits at final compaction; the water necessary for moisture control or for the stabilization process; correction of deficient areas; repair of damage to the curing seal; furnishing and spreading the sand blotter; the extra materials, methods, and construction techniques required to protect, maintain, or repair portions of the uncompleted work left during the winter months; and all extra earth excavation or embankment due to more than one lift being required to construct the fly ash stabilized soil layer will be included in the costs of the pay items.