Alternative Cap Materials for Evaluating the Compressive Strength of Controlled Low-Strength Materials

This research investigated the influence of different capping materials on the compressive strength of controlled low-strength material (CLSM). These capping materials included a sulfur compound, gypsum capping compound, and neoprene pads with different durometer hardness values. Neoprene pads with Shore A durometer hardness values of 20, 40, 50, 60, and 70 were incorporated into the test program. A total of eight CLSM mixtures that covered a wide range of mixture compositions was included in this study. Sulfur capping compound was found to generate the most consistent compressive strength values and was thus used as a control in qualifying other capping materials. With a slightly modified ASTM C 1231 procedure, neoprene pads with a Shore A durometer value equal to or less than 50 were qualified to yield compressive strength values not less than 80% of the corresponding value from the sulfur mortar capping compound results at a significance level of 5%, as required in ASTM D 4832. At this same level of significance, the compressive values from CLSM cylinders capped with gypsum capping compound were found to be more than 92% of the control values from the sulfur mortar capped cylinder results. But, this capping procedure was found to be more time consuming than the neoprene pad testing. As such, sulfur capping compound and neoprene pads with a Shore A durometer value of not more than 50 are recommended to evaluate the compressive strength of CLSM cylinders.