Experimental Study on Workability of Alkali-Activated Red Mud-Based Controlled Low-Strength Materials
摘要
This study aims to optimize the mix design of alkali-activated red mud-based controlled low-strength materials (CLSMs) to enhance their applicability in road engineering backfilling. The effects of red mud content (20%‒50%), water-to-solid ratio (0.30‒0.36), sand-to-soil ratio (7∶3‒4∶6), polycarboxylate superplasticizer (PEC) dosage (0%‒2.1%), and fly ash to mineral powder ratio (5∶1‒0.5∶1) on the flowability and bleeding resistance of the materials were systematically investigated. The results are as follows: ① The water-to-solid ratio significantly influences flowability. Increasing it to 0.32‒0.34 improves flowability by 39%‒78%, but when the ratio exceeds 0.34, the bleeding rate increases significantly (up to 4.89%); ② When the red mud content is 30%‒40%, the high specific surface area adsorption and alkaline hydration synergistic effect balance flowability (200‒300 mm) and bleeding resistance (bleeding rate ≤5%); ③ When the sand-to-soil ratio is optimized to 5∶5, the grading effect of manufactured sand reduces the water absorption impact of fine-grained soil, enhancing slurry stability; ④ PEC dosages of 1.4%‒2.1% significantly improve flowability through electrostatic repulsion and free water release mechanisms. However, excessive addition (>2.1%) leads to increased bleeding rate due to insufficient water film thickness; ⑤ When the fly ash to mineral powder ratio is ≥ 2∶1, the spherical particle effect of fly ash reduces frictional resistance and suppresses bleeding. Based on the synergistic effects of multiple factors, the optimized mix design is recommended as follows: red mud content of 30%, water-to-solid ratio of 0.32, sand-to-soil ratio of 5∶5, PEC dosage of 1.4%‒2.1%, and fly ash to mineral powder ratio of 2∶1. This mix achieves high flowability (flow diameter of 200‒300 mm) and low bleeding rate (2-hour bleeding rate ≤ 5%). This study provides key technical parameters for the low-carbon application of red mud-based CLSM and promotes the resource utiliza