This study aims to examine the use of low-calcium fly ash as a part of binder and residual soil in producing a soil-based controlled low-strength material (CLSM). In the mixtures, fine aggregate was made from a combination of sand and soil with the ratio of 4:6 by weight, while the binder dosage (cement + fly ash) was fixed at 100kg/m³. Different percentages of Portland cement replacement with fly ash (e.g., 0%, 15%, 30% and 45%) and water-binder ratios (e.g., 3.0, 3.2 and 3.4) were in turn selected for mix design. In addition, effect of 2% accelerating agent (CaCl₂) on the behavior of mixture was further investigated. Totally, 24 mixtures (12 mixtures without CaCl₂ and 12 mixtures with 2% CaCl₂) were prepared for the experiment. The engineering parameters of the CLSM including workability, settingtime,fresh density, unconfined compressive strength, ultrasonic pulse velocity (UPV), modulus of elasticity, and modulus of subgrade reaction were experimentally evaluated in accordance with the ASTM standards. Five groups of three 100×200mm specimens for each of these 24 mixtures were made for compressive strength test at 1-, 7-, 28-, 56-, 91-days. The testing results show that Class F fly ash substituted for cement of 30% or less may be acceptable for CLSM production. Also, increasing fly ash content in the mixture could  result in workability improvement, setting time extension, compressive strength and moduli reduction. Adding 2% CaCl₂ to the CLSM mixture effectively accelerated the strength development, especially at early ages. Moreover, based on the testing data, an empirical relationship between compressive strength and UPV was also provided with a high accuracy.

controlled low-strength material, fly ash, calcium chloride, workability, compressive strength, ultrasonic pulse velocity.