Title: Effects of Additives on Properties of Rapid-Setting Controlled Low-Strength Material Mixtures
Author(s): Lianxiang Du, Kevin J. Folliard, and Thanos Drimalas
Publication: Materials Journal
Appears on pages(s): 21-30
Keywords: additives; aluminum sulfate; controlled low-strength material (CLSM); fly ash; gypsum; hemihydrates; rapid-setting CLSM
Rapid-setting controlled low-strength material (RS-CLSM) is a special type of CLSM that is characterized by rapid setting, hardening, and early-strength development, making it well suited for rapid repair and accelerated construction. RS-CLSM mixtures are typically comprised of ASTM C618 Class C fly ash, sand, and water. In this study, research was performed to evaluate the effects of different Class C fly ashes and dosages, and the addition of various additives on the fresh properties and early strength of RS-CLSM mixtures. Two Class F fly ashes were used as additives at replacement levels of 5, 10, 15, 20, 25, 30, and 35% of Class C fly ash. The results showed that they were not effective in extending the flowability time window of RS-CLSM. Gypsum was added to RS-CLSM mixtures at dosages of 1, 2, 3, 4, and 5%. No significant retarding effects were found with the dosing levels. By contrast, the addition of hemihydrate was found to be more effective in changing the fresh properties when the same dosages as gypsum were used. Aluminum sulfate was found to be the most effective to delay or even prohibit the hydration of Class C fly ash for up to 24 hours, when dosages of less than 5% were used. The addition of Type I portland cement at levels of 1, 2, 3, and 4% was also studied and the effects differed with the Class C fly ashes used. Different possible reactions to explain the results are discussed. In summary, this study found that RS-CLSM mixtures made of different Class C fly ashes possess different fresh properties and respond differently to various additives; such knowledge may be applied to the optimization of RS-CLSM for desired workability, setting, hardening, and early-strength development.