Category:205 Modified Subgrade

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Contents

205.1 Construction Inspection Guidance for Sec 205

Description (Sec 205.1)

As specified.

Material (Sec 205.2)

As specified.

Construction Requirements (Sec 205.3)

As specified.

Application (Sec 205.3.1)

As specified.

Compaction (Sec 205.3.2)

As specified.

Method of Measurement (Sec 205.4)

As specified.

Basis of Payment (Sec 205.5)

As specified.

205.2 Laboratory Testing Guidelines for Sec 205

This article establishes procedures for Laboratory testing and reporting samples of hydrated lime, subgrade material, mixtures of subgrade material, hydrated lime and water.

205.2.1 Apparatus

The following apparatus is normally required in addition to that required by any AASHTO or ASTM test method referred to in this article:

(a) Sieves conforming to AASHTO M 92-70, sizes 1 1/2 in., 3/4 in., No. 60 and No. 270.
(b) Container suitable for submerging molded specimens in a water bath.
(c) Aluminum foil, plastic wrap or other suitable material to prevent moisture loss.
(d) Air tight containers (freezer cartons) for curing specimens.
(e) Compression machine.

205.2.2 Procedure

205.2.2.1 Preliminary Tests

The sample as received from the field shall be prepared in accordance with AASHTO T 87. Samples of raw soil shall be tested to determine gradation, liquid limit, plastic limit, pH, moisture-density relations, shrinkage limit, shrinkage ratio and soil classifications.

205.2.2.1.1 Particle Size

Particle size shall be analyzed in accordance with AASHTO T 88 with the following modifications:

(a) Add sieve sizes 1 1/2 in., 3/4 in. and No. 60.
(b) The hydrometer test shall be deleted and the dispersed sample, normally used for the hydrometer test, shall be washed on a No. 200 sieve. The fraction retained on the No. 200 sieve shall be dried and a sieve analysis made using the No. 40, No. 60, and No. 200 sieves.
205.2.2.1.2 Other Preliminary Tests

The liquid limit shall be determined in accordance with AASHTO T 89.

The plastic limit and plasticity index shall be determined in accordance with AASHTO T 90.

The pH shall be determined on a sample of the material passing the No. 40 sieve according to AASHTO T 26 by the electrometric method.

The moisture-density relations test shall be made in accordance with AASHTO T 99, Method C, with the following modifications:

(a) Soil for the moisture-density test shall be pulverized over a No. 4 sieve. If the sample contains material retained on the No. 4 sieve, an amount of the No. 4 to ¾ in. material, equivalent to the amount of No. 4 to 2 in. material in the original sample, shall be used in the sample for the moisture-density test.
(b) The weight (mass) of the sample used for the moisture-density test may vary from 5000 g, if all the material passes the No. 4 sieve, to 8000 g if there is coarse material.

The shrinkage limit and the shrinkage ratio shall be determined in accordance with AASHTO T 92.

The sample shall be classified according to ASTM D2487 and AASHTO M 145 except that a maximum group index of 20 is to be used.

205.2.2.2 Estimated Lime Requirements

The Geotechnical Section shall be consulted for an estimated median lime content for determining the moisture-density relations to be used as the basis for molding compressive strength specimens.

205.2.2.3 Tests on Soil-Lime Mixture

The soil-lime mixture shall be tested to determine moisture-density relations, unconfined compressive strength of molded specimens, gradation, liquid limit, plastic limit, pH, shrinkage limit, shrinkage ratio and soil classifications.

205.2.2.3.1 Moisture-Density Relations

The estimated percent, by oven-dry weight (mass), of hydrated lime shall be added to the portion of the raw soil sample passing the No. 4 sieve with the weight of the soil passing the No. 4 sieve corrected for hygroscopic moisture. The lime and soil shall be mixed thoroughly to a uniform color and water added to bring the mixture to within 3 to 4 percent below the anticipated optimum moisture content. If the soil sample contains material retained on the No. 4 sieve, this material is then added to the soil-lime mixture. The sample shall be placed in a pan, covered with aluminum foil or other suitable material to prevent moisture loss, and allowed to cure at room temperature for 18 hours. After the curing period, an additional 1 to 2 percent water shall be thoroughly mixed with the soil-lime mixture and a moisture-density test made in accordance with AASHTO T 99, Method C.

205.2.2.3.2 Unconfined Compressive Strength

Results of the moisture-density relations test are to be used for molding the test specimens. Two 4 in. diameter specimens shall be molded for each soil-lime mixture. Mixtures shall be prepared for the estimated lime requirement. In addition, mixtures shall be prepared at 1 percent below and 1 percent above the estimated requirement. Prior to molding the specimens, the soil-lime mixtures must be mixed and cured the same as the mixture for the moisture-density relations test, except for the amount of water to be added. The amount of water to be mixed with the lime-soil mixture should be 2 percent less than the optimum moisture content, as determined from the moisture-density relations test. The remaining 2 percent shall be added just prior to molding the specimens to act as a lubricant.

The specimens shall be molded by placing the mixture in the mold in three approximately equal layers and compacting each layer the same as for the moisture-density relations test except the top surface of the first two layers shall be scarified to obtain good bond between the layers. The specimen shall be weighed and the weight (mass) recorded. A moisture sample shall be obtained from the soil-lime mixture, the weight recorded and the sample dried in a 230 ± 9º F oven. The actual dry density of the specimen shall be determined using the results of the moisture sample. The moisture content of the specimen should be within plus or minus 1 percent of the optimum moisture and 3 pcf of the maximum density.

The specimen shall be extruded from the mold, wrapped in plastic wrap or similar material to prevent moisture loss, placed in an air tight container, and cured for 7 days in 100 percent moisture at room temperature.

After completion of the 7-day cure period, the specimens are to be tested for unconfined compressive strength. The specimens shall be compressed at a rate of 0.02 inch per minute until failure occurs and the average strength of the duplicate specimens shall be calculated in pounds per square inch (kPa).

205.2.2.3.3 Preparation of Sample for Particle Size Analysis

One of the broken compressive strength specimens from each lime content shall be used to obtain samples for the particle size analysis on the soil-lime mixture. The specimen shall be broken apart and a portion (approximately 200 g) of the material worked through a No. 10 sieve in a manner to avoid breaking the soil-lime particles into a size smaller than necessary. The material should be rubbed through the sieve by hand or by light rubbing with a trowel or similar object. Any material retained on the No. 10 sieve in the original sample should not be crushed to pass the No. 10 sieve.

205.2.2.3.4 Preparation of Sample for Physical Tests

Approximately 300 g of the material from the broken specimen used in paragraph EPG 205.2.2.3.3 of this Section shall be broken apart and allowed to air dry. The air dry material is to be worked through a No. 40 sieve by use of a rubber covered mortar and pestle.

205.2.2.3.5 Gradation of Soil-Lime Mixture

A 120 to 125 g sample of the wet material passing the No. 10 sieve shall be soaked in a dispersing agent for 18 hours (see EPG 205.2.2.1.1). The sample shall be stirred in a mechanical mixer for one minute and washed over a No. 200 sieve. The portion of the sample retained on the No. 200 sieve shall be dried and sieved over the No. 40, No. 60 and No. 200 sieves. The ovendry weight (mass) of the gradation sample shall be determined by obtaining a moisture sample (approximately 100 g) of the material passing the No. 10 sieve.

The granulation effect of the lime shall be determined by calculating a new gradation for the entire soil sample for each lime content. This does not change the percent passing the No. 10 and larger sieves. The new gradation through the No. 40, No. 60 and No. 200 sieves shall be calculated as follows:

New gradation = (S x L)/ 100
where,
S = Percent of original soil sample passing No. 10 sieve
L = Percent minus No. 10 soil-lime mixture passing desired sieve
205.2.2.3.6 Physical tests

The soil-lime mixtures for each lime content shall be tested for liquid limit, plastic limit, plasticity index, shrinkage limit, shrinkage ratio, pH and classification according to the methods in EPG 205.2.2.1.2.

205.2.2.3.7 Production Testing

The QC tests and frequencies for these materials are covered in the table below:

Type of Construction or Material Tests to be Made (if specified) Sampled Minimum Number of Tests
Modified subgrade (sand-soil base, soil-cement base or soil-lime base) Graduation SAA002WABefore compactionsOne per 5,000 tons (5,000 megagrams) or fraction thereof per specified graduation source. None required if less than 1,000 tons (1,000 megagrams) of a specified graduation.
Liquid Limit included with gradationBefore compactionsOne per project per specified graduation, per source. None required if less than 1,000 tons (1,000 megagrams).
PI included with gradationBefore compactionsOne per project per specified graduation, per source. None required if less than 1,000 tons (1,000 megagrams).

205.2.2.4 Hydrated Lime

Samples of hydrated lime, submitted to the Laboratory for source approval or destination check sample, shall be tested according to EPG 106.3.2.27 TM-27, Determination of Calcium Oxide and Magnesium Oxide in Hydrated Lime for chemical composition for Type N hydrated lime to determine compliance with ASTM C207 Sec. 2. Gradation shall be determined by the wet sieving process as outlined in ASTM C110.

205.2.2.5 Sample Record

The sample record shall be completed in SiteManager, as described in Sample Record General Information , and shall indicate acceptance, qualified acceptance, or rejection. Appropriate remarks, as described in EPG 106.20 Reporting, are to be included in the remarks to clarify conditions of acceptance or rejection. Test results shall be reported on the appropriate templates under the Tests tab.

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