Salts accelerating strength increase of coal fly ash–carbide lime compacted blends

Compacted coal fly ash–carbide lime (two industrial by-products) blends have great potential application in geotechnical earthworks such as sub-base and base of pavements, beds of pipelines and spread footings, embankments and in erosion control. Pozzolanic reactions occur between silica and alumina in amorphous phases (found in the fly ash) and Ca²⁺ (existent in carbide lime) in an alkaline environment. However, pozzolanic reactions are notoriously slow at ambient temperatures, requiring long curing periods for certain applications. Therefore, this study aims to verify the influence of application of distinct salts [sodium chloride (NaCl), magnesium oxide and potassium permanganate] in the acceleration of unconfined compressive strength (q_u) increase of coal fly ash–carbide lime blends. Results have shown that small amounts of certain salts allowed to accelerate q_u increase of coal fly ash–carbide lime blends. Among the studied salts, sodium chloride presented the best results after 28 days of curing. Coincidently, sodium chloride is also relatively cheap and of great availability, making it convenient for extensive use.