Research on the properties and mechanism of a fiber-reinforced alkali-activated lithium slag artificial lightweight aggregate

Lithium slag (LS), a by product of the rapidly expanding new energy industry, poses challenges in terms of environmental pollution, disposal difficulties, and high disposal costs. To achieve efficient, low-cost, and eco-friendly utilization of LS in the construction material field, this study examines the LS artificial lightweight aggregate (ALWA) produced by the cold-bonded method. The mass ratio of LS to granulated blast furnace slag (GBFS) in the aggregate is 7:3. Polyvinyl alcohol (PVA) fibers are used to modify the aggregates at various dosages. Macroscopic tests and microscopic characterizations are conducted to investigate the basic physical and mechanical properties and formation mechanisms of the aggregate. The results indicate that under the action of an alkali activator with a modulus of 1.5, high-quality ALWA with a density grade of 1000 and a compressive strength of 6.9 MPa is successfully prepared. Furthermore, a 0.1 % fiber dosage reduces the 28-day cylinder compressive strength of the aggregate due to the introduction of more macropores. An increased forming difficulty is observed at a 0.3 % fiber dosage. As the optimal dosage, 0.2 % fiber content decreases the aggregate density grade to 900 and increases the 28-day strength to 7.4 MPa, meeting the Chinese Standard (GB/T 17,431.1–2010) for high-strength lightweight aggregates. The microscopic results reveal that the reactive components in LS and GBFS participate in the reaction to form a geopolymer gel (N(C)-A-S-H), resulting in a dense aggregate structure. The aggregates without fibers have a porosity of less than 200 nm, accounting for up to 94.49 % of the aggregates. Although the addition of fibers physically increases the porosity of the aggregate, their bridging effect still optimizes the mechanical properties of the aggregate, especially in terms of early strength.