Preparation and application of environmentally friendly liquid alkali-free and fluorine-free accelerator for shotcrete

Abstract

A liquid accelerator is a key component in shotcrete; however, it often faces challenges such as high alkali content and insufficient long-term concrete strength. This study utilizes polyaluminum sulfate as the primary raw material to develop an environmentally friendly, alkali-free, and fluorine-free accelerator (FAF). Through orthogonal experiments and cement compatibility tests, the effects of FAF on setting time, 1 day compressive strength, and 28 days compressive strength ratio of cement paste were analyzed, leading to the determination of the optimal FAF mixing ratio. The coagulation-promoting mechanism of FAF was further examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) results. Additionally, concrete slab tests were conducted to assess the impact of different FAF dosages on concrete rebound rates and mechanical properties, with the optimal dosage range found to be 4–8%. Field trials indicated that, at a 6% FAF dosage, shotcrete rebound rates on tunnel arch walls and roofs were 10.3% and 13.5%, respectively. The composition of the FAF does not contain alkali metal salts, which reduces the risk of alkali-aggregate reactions in concrete and minimizes the potential health risks to construction personnel, aligning with the global trend towards sustainable construction practices.