Effects of Constituent Materials and Quantities on Water Demand and Compressive Strength of Controlled LowStrength Material

Controlled low-strength material (CLSM) is a self-compacting, flowable, low-strength, cementitious material used primarily as backfill, void fill, and utility bedding in lieu of conventional compacted fill. Potential advantages of CLSM include decreased labor requirements, faster construction speed, and potentially lower in-place cost. When considering CLSM as a construction material, two of the most important properties include flowability and compressive strength. The flowability of CLSM can directly impact productivity and human resource requirements for placing the material. Lower flowability may require more resources. In addition, compressive strength values are required as an indicator for performance and long-term excavatability. Minimum strength requirements are necessary for performance criteria, and maximum strength requirements are necessary for long-term excavation. This research investigated the effects of material properties on the water demand necessary to obtain minimum flowability values and a range of compressive strength values for CLSM. Three types of aggregate, three types of fly ash, and one Type I cement were used in this study. A total of 31 mixtures were developed and tested. The use of different aggregate types and sources was found to be the most significant factor affecting water demand in this investigation. Watercement ratio, aggregate sources, and fly ash type were influencing variables on the compressive strength of CLSM. Formulas were developed to predict the compressive strength development of CLSM for the materials used in this research program.