A new lab study shows crushed limestone sand can be used in high-fluidity concrete without sacrificing flow or strength, while cutting embodied carbon by about 28% when 30% fly ash replaces part of the cement. The researchers tested mortar rheology and aggregate coating thickness to design mixes that reached slump flows up to 705 mm and 28-day compressive strengths up to 61.91 MPa. The work replaces broad trial-and-error batching with a mortar-centered method. By controlling initial yield shear stress, sand volume fraction, fly ash, silica fume, and rock powder, the authors set ranges that work for limestone sand. They stress the ranges need verification for other crushed sand sources, and the sustainability comparison covers raw materials only, not transport, durability, or full life cycle. For construction teams, the practical value is a clearer path to low-carbon, high-fluidity concrete using a material that is widely available as natural sand becomes scarce. The embodied energy savings of 25 to 26% also matter. Treat the results as a validated design framework, not a field trial.
