METHOD OF TEST FOR LABORATORY DESIGN OF SOIL-CEMENT MATERIAL
This method of test covers the procedures for making and testing hardened soil-cement samples prepared with portland cement. The laboratory maximum dry density and optimum moisture content are determined for samples at three different percentages of cement. Samples are then compacted in a mold before cement hydration to the established laboratory maximum dry density and optimum moisture content and tested for unconfined compressive strength.
The materials shall consist of the following:
Soil may consist of any combination of gravel, stone, sand, silt, clay, caliche, scoria, slag, sand-shell, cinders, ash, waste material from aggregate production plants, high-quality crushed stone and gravel base course aggregates, and failed bituminous surfaces.
2. Portland Cement
Portland cement shall comply with the latest ASTM, AASHTO, or CSA specifications for portland cement or blended hydraulic cements.
Water shall be free from substances deleterious to the proper hardening of the soil-cement material.
If used, pozzolans shall comply with the latest ASTM, AASHTO, or CSA specifications for fly ash, slag, and silica fume.
The apparatus shall consist of the following:
A cylindrical metal mold approximately 4.0 inches (100 mm) in diameter and 4.6 inches (115 mm) in height and having a volume of approximately 1/30-cubic foot (940 cc). This mold is fitted with a detachable base plate and a removable extension approximately 3.1 inches (80 mm) in height.
A metal rammer having a 2-inch (50 mm) diameter flat circular face and weighing 5.5 pounds (2.5 kg). The rammer shall be equipped with a suitable arrangement to control the height of drop to a free fall of 12.0 inches (300 mm) above the elevation of the soil sample.
The ¾-inch (19 mm) sieve shall conform to the “Standard Specifications for Sieves for Testing Purposes”, AASHTO Designation: M-92.
4. Sample Extruder
A jack, lever frame, or other device adapted for the purpose of extruding samples from the mold.
A balance or scale of at least 10,000 gram capacity sensitive to 1.0 gram.
6. Polyethylene Freezer Bags
Polyethylene freezer bags shall be the ordinary commercial type freezer bag of 1-quart (950 cc) capacity.
7. Moist Room
Moist room or a suitable covered container capable of maintaining a temperature of 73.4°F ± 3°F (23.0°C ± 2°C) and having a relative humidity of not less than 90 percent.
8. Testing Machine
The testing machine may be the hydraulic or screw type with sufficient opening between the upper bearing surface and the lower bearing surface of the machine to permit testing of the samples specified herein. The machine shall be capable of applying at least 20,000 pounds (9,070 kg) to within an accuracy of ± 1 percent of the total load.
A steel straightedge 12 inches (300 mm) long.
10. Large Pans
Pans of sufficient size to allow the thorough mixing of the material passing the ¾-inch (19 mm) sieve.
Scoops or other suitable devices for mixing and sampling the material passing the ¾-inch (19 mm) sieve.
12. Graduated Cylinder
Glass or plastic graduate of 1,000 ml capacity used for measuring the mixing water.
13. Small Pans or Dishes
Pie pans or evaporating dishes suitable for weighing the cement and/or other admixtures.
D. SAMPLE PREPARATION
Sieve a sufficient quantity of the soil material through the ¾-inch (19 mm) sieve to determine maximum dry density and optimum moisture content and to provide at least nine, 4.0-inch (100 mm) diameter by 4.6-inch (115 mm) high compacted specimens having a total volume of 1/30-cubic foot (940 cc). (Usually about 100 pounds (45 kg) of dry soil is required.)
1. Determine Maximum Dry Density and Optimum Moisture Content
a. Weigh out three 4,000 gram batches of dry soil.
b. Weigh out three batches of dry cement to represent 4 percent (160 grams), 6 percent (240 grams), and 8 percent (320 grams) of the batches of dry soil.
c. Place one 4,000 gram batch of dry soil plus the first percentage of dry cement (4 percent) in a large pan and mix the dry ingredients to uniform color.
d. Determine the laboratory maximum dry density and optimum moisture content for the soil-cement mixture by following ASTM D558 – Standard Test Methods for Moisture-Density Relations of Soil-Cement Mixtures.
e. Determine the laboratory maximum dry density and optimum moisture content for the 6 percent and 8 percent cement batches the same as in steps E.1.c. and E.1.d.
2. Prepare and Test Specimens for Unconfined Compressive Strength
a. Weigh out three 10,000 gram batches of dry soil.
b. Weigh out three batches of dry cement to represent 4 percent (400 grams), 6 percent (600 grams), and 8 percent (800 grams) of the batches of dry soil.
c. Place one 10,000 gram batch of dry soil plus the first percentage of dry cement (4 percent) in a large pan and mix the dry ingredients to uniform color.
d. Add sufficient water to bring the soil-cement mixture to optimum moisture as previously determined in step E.1.d. above. Mix until uniform moisture content is achieved throughout the entire batch.
e. Form a specimen by compacting the prepared soil-cement mixture, in three equal layers, in the mold following standard Proctor test procedures.
f. Extrude the sample from the mold and seal in a polyethylene freezer bag.
g. Prepare two more samples as in steps E.2.e. and E.2.f. from the batch of soil-cement mixture.
h. Prepare the 6 percent and 8 percent cement batches the same as in steps E.2.c. through E.2.g. and place all nine molded samples in the moist room for curing.
Three samples for each cement content are tested uncapped for unconfined compressive strength after 7 days curing in the moist room. These samples are vertically loaded in a testing machine at a loading rate of .05 in/min (1.25 mm/min) until failure.
Compressive Strength (PSI) = Load (lbs) at failure area of sample (in²)
Compressive Strength (kg/m²) = Load (kg) at failure area of sample (m²)
NOTE: No consideration is given to the length-diameter ratio (K-factor).