Title: Effects of Prolonged Mixing and Retempering on Properties of Controlled Low-Strength Material (CLSM)

Author(s): Sarah L. Gassman, Charles E. Pierce, and Aaron J. Schroeder

Publication: Materials Journal

Volume: 98

Issue: 2

Appears on pages(s): 194-199

Keywords: compressive strength; controlled low-strength material; flowable consistency; mixing time; retemper; water-cementitious materials ratio (w/cm).

DOI: 10.14359/10203

Date: 3/1/2001

Abstract:
The effects of prolonged mixing and retempering on the fluid- and hardened-state properties of controlled low-strength material (CLSM) were examined in a controlled experimental program. This study investigated concerns regarding the quality of CLSM arising from prolonged mixing times experienced during construction delays, as well as excess water added by truck operators prior to discharge. These field practices were examined experimentally by adjusting the total mixing time, percent design water, and amount of water withheld for retempering in a control mixture. Changes in flowability, bleeding, time of setting, and 28- and 90-day unconfined compressive strengths were evaluated. The results of this study showed that extending the mixing time beyond 30 min decreases unconfined compressive strength and delays the time of setting. Sufficient flowability was always maintained with prolonged mixing. Retempering does not affect the 28-day strength; however, it does increase or decrease 90-day strength, depending on mixing time. Retempering does not significantly impact the material in its fluid state. Even though the observed effects on strength were measurable, neither prolonged mixing nor retempering altered the 28- and 90-day strengths to values outside the design range.