Assessing the interactions of retarding admixtures and fine materials in long-term flowability of cement pastes

The incorporation of supplementary fine materials into mortars and concretes is a common strategy employed to enhance both their rheological and mechanical properties. While organic molecule-based admixtures are primarily utilized to regulate the setting time in pre-mixed concretes and mortars, their effects become more intricate in the presence of fine materials. This study delves into the interplay between flowability and setting times of cement pastes with 50 wt.% of fines (basalt filler, fly ash and quartz filler) in place of cement and three organic admixtures at 0.5 and 1.0% (wt.% of cement). The results unveil compelling insights: the incorporation of retarding additives proves notably advantageous, markedly decreasing viscosity and prolonging the initial stage of paste formation by as much as 305 hours. Nevertheless, the efficacy of these additives diminishes significantly in the presence of fine particles, especially when utilizing basalt filler. This prompts an in-depth exploration into the intricate interactions transpiring between the fine materials and the setting retardants. The implications of these interactions underscore their pivotal role in refining the application of retarding additives in scenarios involving fine materials.