Effects of prolonged mixing and retempering on properties of controlled low-strength material (CLSM)

The effects of prolonged mixing and retempering on the fluid- and hardened- state properties of controlled low-strength material (CLSM) were examined i n a controlled experimental program. This study investigated concerns regar ding the quality of CLSM arising from prolonged mixing rimes experienced du ring construction delays, as well as excess water added by truck operators prior to discharge. These field practices were examined experimentally by a djusting the total mixing time, percent design water; and amount of water w ithheld for retempering in a control mixture. Changes in flowability, bleed ing, time of setting, and 28- and 90-day unconfined compressive strengths w ere evaluated. The results of this study showed that extending the mixing t ime beyond 30 min decreases unconfined compressive strength and delays the time of setting. Sufficient flowability was always maintained with prolonge d mixing. Retempering does not affect the 28-day strength; however; it does increase or decrease 90-day strength, depending on mixing time. Retemperin g does not significantly impact the material in its fluid state. Even thoug h the observed effects on strength were measurable, neither prolonged mixin g nor retempering altered the 28- and 90-day strengths to values outside th e design range.