ASTM D4832 Standard Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cylinders

Scope:

In the ASTM D4832 test Typically, CLSM is utilized as a backfill material around structures, especially in constrained or small areas. Testing for compressive strength is done to help with mix design and to act as a control method while building. The standard mix design is based on construction control tests carried out seven days after placement and 28-day strengths. This ASTM D4832 method could be used to evaluate a wide variety of different mixtures of soil, cement, fly ash (cementitious or not), admixtures, or other components. Depending on the intended application, the availability of materials, and the placement criteria, the combinations would change.

Test Procedure: 

Apparatus:

• Single-Use Cylindrical Molds: Tight-fitting covers, 15 cm (6 in) in diameter by 30 cm (12 in) in height, plastic, single-use molds that adhere to Specification C 470. Molds of all sizes and shapes are acceptable as long as the length-to-diameter ratio is 2:1. The low material strength and the higher surface area of the cylinder ends make the 15 cm by 30 cm (6 in. by 12 in.) molds the ideal choice.

• Receptacle for Sampling and Mixing: A suitable heavy-gauge container, wheelbarrow, etc., with sufficient capacity to facilitate easy sampling and mixing, to prepare at least two cylinders, and to be utilized for other tests as outlined in Test Methods D 5971, D 6023, PS D6024, and D 6103, should be utilized for the receptacle.
• Storage Container: An airtight, insulated, well-braced wooden box with a cover or another appropriate container for storing CLSM cylinders on the construction site. The container should have the required equipment to keep the area around the cylinders between 16 and 27°C (60 and 80°F) at all times. The container should be brightly colored to prevent disruption and tagged for identification.
• Transport Container: A sturdy wooden box or other appropriate container designed to reduce shock, vibration, or other damage to the CLSM cylinders during transportation to the lab.
• Testing Device: The specifications stated in Test Method C 39 should be adhered to by the testing device.
• Curing Environment: A curing environment (water bath, moist sand, or fog chamber) that meets Method C 192’s requirements. The testing laboratory may choose to cure the cylinders in the same environment that is used to cure concrete cylinders.
• Small Tools: Items and tools that might be needed, such as trowels, buckets, shovels, and scoops.

Sample Preparation

• For each test specimen, CLSM samples should be collected, and the name of the depicted CLSM and the casting time should be noted by D 5971.
• To manufacture two cylinders, a minimum of 0.03 m3 (1 ft3) of sample must be extracted from the batch for each pair. To adequately reflect each sampling batch, a minimum of two compressive strength cylinders for each given test age should be constructed. When additional testing is required, as indicated in Test Methods D 5971, D 6023, D 6024, and D 6103, the prospect of requiring extra material should be considered. This assures that the testing procedure is complete and comprehensive, yielding dependable data for quality control and evaluation.

Place of Molding

• Mold specimens should be placed right away on a flat, level surface that is rigid and devoid of vibration and other disturbances. The preparation of the specimens should take place as close as possible to the site where they will be kept for the first four days.

Placing the CLSM

• The sampling and mixing container should be used for the thorough mixing of the CLSM.
• The CLSM should be poured into the cylinder mold by scooping through the center of the container with a bucket or pail. The mold should be filled repeatedly until it is full. Then, the mold should be covered with a lid.

Curing:

• The cylinders should be kept in the storage container at the construction site until the fourth day following their preparation.
• The cylinders must be kept in storage circumstances where the area around them is maintained at a temperature between 16 and 27 °C (60 and 80 °F). The cylinders need to be protected from freezing at all times. After the first day, the cylinders should be wrapped with damp burlap or another highly absorbent material to create a high-humidity environment.
• On the fourth day, the cylinders should be carefully transported in the transportation container to the location of the curing environment and placed in the curing environment.
• The cylinders are typically relocated to a curing environment after being left at the construction site for four days. If moving them on the fourth day would potentially cause damage to extremely low-strength CLSM (below 350 kPa), the cylinders must be stored at the construction site in a water storage tank with a temperature maintained between 16° and 27°C (60° and 80°F) until they can be transported without sustaining harm.

Capping the Cylinders

• On the day of testing, the molds should be carefully removed from the cylinders, and the cylinders should be allowed to air-dry for 4 to 8 hours before being capped. If the upper surface of the cylinder is not in a horizontal plane, it should be smoothed using a wire brush, and all loose particles should be brushed off. A cap for the cylinders should be provided by one of the following methods:
• The cylinders should be capped using sulfur mortar following Practice C 617
• The cylinder should be capped using gypsum plaster following Practice C 617
• Elastomeric pads, as per Practice C 1231, should be utilized. The qualification test results for acceptance of the caps must not show a reduction in strength of more than 20%, instead of the 2% as specified in Practice C 1231. Due to the less critical uses of CLSM, the higher discrepancy is deemed acceptable, and 20% is considered to be the intrinsic fluctuation in compressive strength results attributable to the lower strength levels, such as 350 kPa (50 psi).
• To prevent any variation in the test results caused by the utilization of multiple capping systems, a consistent capping method should be employed throughout each project.

Compressive Strength Testing

• Placing the Specimen—To place the specimen, the lower bearing block should be positioned beneath the upper bearing block, with its hardened face facing upward. The testing machine’s table or platen should have the upper bearing block spherically positioned on it. After cleaning, the bearing faces of both the upper and lower bearing blocks, as well as the test specimen, should be positioned. Care should be taken to ensure that the specimen’s axis is carefully aligned with the spherically seated center of thrust of the block. The spherically seated block should be brought into contact with the top of the specimen to ensure uniform seating, and the movable portion of the block should be rotated slightly by hand.
• Rate of Loading: The load should be continuously and smoothly applied without causing shocks. The load should be steadily applied in a manner that ensures that the cylinder does not fail in less than two minutes. The testing machine’s controls should not be altered while a specimen is undergoing rapid failure just before it is failed.
• The greatest load that the specimen could bear before the test failure should be recorded. The load should be applied until it leads to the specimen’s failure. The loading should be continued until the cylinder breaks enough to allow the inspection of the specimen’s inside for approximately one in ten cylinders.

Calculation:

To calculate the specimen’s compressive strength

C = L/[π(D²)/4]

where:

C = compressive strength, kPa (lbf/in.² )

D = nominal diameter of the cylinder (normally 15 cm or 6 in.)

L = maximum load, kN (lbf).

Video 01: ASTM C39 & C1231 – Compressive Strength with Unbonded Caps

Preferred Test Sample Size: 

Number of test Specimen: 1

Test Specimen Size: Typically 6″ x 12″ cylinders

Keywords: Flowable fill, CLSM (Controlled Low Strength Material), and CDF (Controlled Density Fill).

Conclusion: The ASTM D4832 method is used to determine the compressive strength of the hardened material which is a specialized construction material with low structural strength primarily used in backfill and trench applications.