A new unbonded capping practice for evaluating the compressive strength of Controlled Low-Strength Material cylinders

Controlled Low-Strength Material (CLSM) is a low strength cementitious material often used for pipe bedding, backfill, void fills, and in some cases bridges approaches. Because of its low strength, handling of test cylinders, especially at early ages, is often not possible or results in significant damage to the samples. Sulfur-capped specimens require more handling than non-sulfur capped specimens. To minimize handling, a new material is proposed for use as an end pad for compressive strength testing. Similar to the approach used for conventional concrete cylinders, a new method is proposed that uses different pads for different CLSM compressive strength levels. Pads made of sorbothane viscoelastic polyurethane rubber, neoprene, and a combination of the two were used for compressive strength and variability. Results indicate that the sorbothane viscoelastic polyurethane rubber material should be used when the compressive strength of the CLSM is less than approximately 1 MPa and neoprene pads with a durometer value not greater than 50 should be used when the compressive strength is expected to be greater than 2 MPa. Either pad type can be used for CLSM mixtures having expected compressive strengths between 1.0 and 2.0 MPa.