Coal Fly Ash–Carbide Lime Admixtures as an Alternative to Concrete Masonry Blocks: Influence of Ash Grounds

Compacted blocks of coal fly ash and carbide lime (two industrial by-products) have a great potential as building products. This admixture can be used as an alternative to weight-bearing or nonstructural concrete masonry blocks due to the pozzolanic reactions occurring between silica and/or alumina in amorphous phases (found in the fly ash) and ${\mathrm{Ca}}^{++}$ (existent in carbide lime) in an alkaline environment. However, pozzolanic reactions are notoriously slow at ambient temperatures, requiring long curing periods to achieve the necessary strength for certain applications. Therefore, this study aims to verify the influence of coal fly ash ground towards the increase of unconfined compressive strength ($q_u$) in fly ash–carbide lime blends. Results have shown that the ash grounds allowed an increase in $q_u$ for coal fly ash–carbide lime admixtures. It was found that coal fly ash ground for a short period of time (up to 2 h) increases the specific area of the fly ash grains by about 50%, while the strength at ambient temperature increases by about 200%. Ground specimens cured at 23°C for 7 days follow similar increase tendencies of $q_u$ values as the ones presented by the rising of curing temperature on nonground specimens from 23 to 40°C for a 7-day curing period. Finally, it can be concluded that grounds might be a convenient alternative for extensive use to increasing curing temperature or to be used combined with higher curing temperatures in order to increase strength of coal fly ash–carbide lime blocks in a short curing period.