Setting controlling of lithium slag-based geopolymer by activator and sodium tetraborate as a retarder and its effects on mortar properties

摘要

In this work, lithium slag based geopolymer (LSG) mortar with excellent properties was successfully produced by a strategy of pre-calcination at room temperature curing, which eliminated the limits of application scenarios of geopolymer acquired elevating curing temperature. Meanwhile, the setting controlling of LSG was investigated by adjusting activator and addition of sodium tetraborate as a retarder. Lowering modulus and dosage of activator could prolong the setting time. However, solubility of sodium silicate limited the minimum modulus of activator although lower modulus favored the early strength development and lowered drying shrinkage. Decrease of alkali dosage was detrimental to strength development and exacerbated efflorescence. The preaddition of sodium tetraborate to activator led the formation of B-[4]-O-Si bonding which later modified by [AlO4](-) tetrahedral and translated to B-[3]-O-Al-O-Si bonding, as a consequence, retarding the condensation reaction and prolonging setting time. Although addition of sodium tetraborate comprised a little of mechanical strength of mortars, the rheological behaviors of LSG was improved. And it was meaningful in some cases that strength is not strictly acquired. Additionally, water retaining of borate also lowered drying shrinkage of LSG mortar. At controlling dosage (<= 5%), sodium tetraborate not only could be used as retarders but also a useful water-retainer.