6-24-97

 LIME-KILN DUST MODIFICATION 
207-R-333

DESCRIPTION: This work shall consist of the upgrading of fine grained soils by uniformly mixing lime-kiln dust with the soils to aid compaction by drying out wet areas, and to provide a working platform for subsequent construction.

 MATERIALS: Materials shall be in accordance with the following:

             Hydrated lime.......................913.04.
              Water ................................913.01.

        Lime-kiln dust shall be in accordance with the following requirements:

  1. Total calcium and magnesium non-volatile oxides shall consist of a minimum of 60% lime-kiln dust.

  2. Available calcium hydroxide in accordance with ASTM C 25 and total magnesium oxide content calculated to be equivalent calcium hydroxide shall consist of 30% of lime-kiln dust.

  3. Sieve Analysis: Gradation shall be as follows:
Sieve
% Passing
4.75 mm (No. 4) 95-100
600 mm (No. 3) 90-95
150 mm (No. 100) 70-80

STORAGE AND HANDLING:

         Lime-kiln dust shall be stored in accordance with the manufacturer's recommendations so its chemical composition shall not be affected.

 MIXTURE COMPOSITION:

  1. Samples: The Contractor shall provide 50 kg (110 lb), minimum, samples of the soil to be modified, and 5 kg (11 lb), minimum, samples of the lime-kiln dust to be used at least 20 days prior to use of the lime.

  2. Mix Designs: Lime shall be proportioned as required by oven-dry test results of the mixture of lime-kiln dust and soil. The required proportion of lime-kiln dust will be established by the Engineer prior to construction, using samples of soil and lime-kiln dust modified soil. The Engineer will reserve the right to make such adjustments of lime-kiln dust proportioning as are necessary during the progress of the work within the range specified.

    The source or type of lime-kiln dust shall not be changed during the progress of the work without permission of the Engineer. However, the Engineer may choose, based on laboratory test results, to use different types of lime-kiln dust on different portions of the project limits. The different types of lime-kiln dust shall not be mixed in the same project portion.

 

CONSTRUCTION REQUIREMENTS:

  1. Temperature and Weather Limitations: Lime-kiln dust modification shall only be performed with a minimum soil temperature of 7E C (45E F), measured 100 mm (4 in.) below the surface, and with the air temperature rising. Lime-kiln dust shall not be mixed with frozen soils or with soil containing frost.

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

  3. Spreading of Lime: The subgrade shall be scarified or disked to the specified depth with a machine of such design that a visible indication is given at all times that the cutting is to the specified depth prior to distribution of the lime-kiln dust. The lime kiln dust shall then be distributed uniformly over the surface by means of a cyclone, screw-type, or pressure manifold type distributor. The Engineer may reject procedures which do not provide an uniform distribution of lime-kiln dust.

    Lime-kiln dust shall not be applied when wind conditions are such that blowing lime-kiln dust becomes objectionable to adjacent property owners or creates a hazard to traffic on adjacent highways.

    The spreading of lime-kiln dust shall be limited to that amount which can be incorporated into the soil within the same work day. If weather causes cessation of work, or exposure of the lime-kiln dust to washing or blowing, the Engineer may require additional lime-kiln dust to be spread.

  4. Mixing: The lime-kiln dust, soil, and water when necessary, shall be thoroughly mixed by rotary speed mixers or a disc harrow. The mixing shall continue until it has been determined by the Engineer that a homogeneous layer of the required thickness has been obtained, and such that 100% of the material, exclusive of rock particles, shall pass a 25 mm (1 in.) sieve and at least 60% shall pass a 4.75 mm (No. 4) sieve. The loose thickness of a single lime-kiln dust modified layer shall not exceed 200 mm (8 in.) if a disc harrow is used and 360 mm (14 in.) if a rotary speed mixer is used.

  5. Compaction: Compaction of the mixture shall begin immediately after mixing. If compaction is to be delayed, the surface of the lime-kiln dust modified soils shall be crown-graded and sealed immediately after mixing.

    Compaction shall be continued until the lime-kiln dust modified layer has a density of not less than 100% of the maximum dry density within the special subgrade treatment zone or 95% of the maximum dry density below the special subgrade treatment zone. Maximum dry densities will be determined in accordance with AASHTO T 99 or one point proctors in accordance with AASHTO T 272.

    If required density can not be achieved in the field, a one point proctor shall be performed to verify the target density. The standard dry density of the lime-kiln dust treated soil shall be obtained by one point proctor in accordance with AASHTO T 272. The field in-place dry density shall be obtained by the Engineer in accordance with AASHTO T 191 or T 239.

    Aeration by means of further mixing, or the addition of water and further mixing, may be required to achieve the required compaction.

  6. Finishing: When compaction of the lime-kiln dust modified soil is determined to be nearing completion, the surface shall be shaped to the required lines, grades, and cross section. Compaction shall then be continued until the specified compaction is obtained.

    The average compacted thickness of the modified subgrade constructed shall be within 10% of the specified thickness. However, the thickness at one given 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 means of coring, use of a phenolphthalein solution, or by other means. The Engineer will perform at least one test every 280 m2 (335 syds.) for each compacted lift to ensure that the lime is spread at the specified rate. All deficient areas shall be acceptably corrected.

METHOD OF MEASUREMENT

        The modified subgrade will be measured by the square meter (square yard) of the thickness specified. The width for measurement will be as shown on the plans. Water will not be measured.

        Lime kiln-dust will be measured by the megagram (ton). It may be weighed in either trucks or freight cars. If it is shipped in trucks, it may be weighed at the place of loading, at the place of unloading, or where otherwise directed by the Engineer. The Engineer may accept original signed bills in lieu of weighing.

        Contract Quantities: If the work is constructed to the lines, grades, or dimensions shown on the plans, and the Contractor and the Engineer have previously agreed in writing that the plan quantities are accurate, further measurement will not be required except when errors are discovered after work has been started. Corrective measurements will then be made.

        Should the method of construction require extra earth excavation or embankment due to the need for more than one lift to construct the lime-kiln dust modified soil layer as shown on the plans, such extra earth excavation and embankment will not be measured.

BASIS OF PAYMENT: The accepted quantities of modified subgrade of the thickness specified will be paid for at the contract unit price per square meter (square yard). Lime kiln-dust will be paid for at the contract unit price per megagram (ton).

Payment shall be made under:

Pay Item              

Metric Pay Unit Symbol
(English Pay Unit Symbol)


Modified Subgrade,_______mm
                      thickness

  ......................m2


Modified Subgrade, _______in
                      thickness

  ......................SYS


Lime-Kiln Dust

  ......................Mg (TON)

        The costs of removal of deleterious materials, scarification of the subgrade, spreading of lime, mixing of the lime and soil, sealing of the surface of the lime-kiln dust modified soils, compaction of the resultant mixture, shaping the subgrade, work required due to adjustments of lime-kiln dust proportioning made by the Engineer, additional lime-kiln dust required due to weather conditions, correction of lime-kiln dust deficient areas, water required for the modification process, required extra earth excavation and embankment due to method of construction, and cost of modified subgrade trimming as required shall be included in the costs of the pay items.