Rheological and Mechanical Performance of High-Powder Self-Compacting Concrete with Limestone Filler: A Multifactor Experimental and Response-Surface Analysis

Self-compacting concrete (SCC) performance depends on the complex interactions between water availability, chemical dispersion, and powder characteristics. This study evaluates the rheological and mechanical behavior of high-powder SCC incorporating limestone filler as an additional powder constituent rather than as a cement replacement. A response surface methodology (RSM) experimental design comprising 28 mixtures was developed to evaluate the effects of the water-to-powder ratio (W/P), filler-to-cement ratio (Lf/C), superplasticizer dosage (SP%), and limestone filler particle size (DLf). Fresh-state properties were assessed through slump-flow, V-funnel, L-box, and segregation-resistance tests, while apparent rheological coefficients of the modified Bingham model were derived from torque–rotational speed measurements. The results showed that W/P was the dominant factor controlling the fresh-state behavior, followed by SP%; Lf/C mainly controlled compressive strength, whereas the effects of DLf, evaluated only for the filler-containing mixtures, were limited to slump flow and sieve segregation, with no significant effect on compressive strength when all six half-prisms of each mixture were used. The central formulation (W/P = 0.40, Lf/C = 0.35, SP = 0.9%, and DLf = 45 μm) is retained only as a reference composition within the studied domain: its four replicates showed consistent filling ability, but only one of them met both an L-box ratio of at least 0.80 and a sieve-segregation ratio of at most 15%. In a strength model that describes trends but has no predictive ability, limestone filler content had a significant positive effect on compressive strength that decreased at higher W/P, and SEM observations showed a more continuous fracture morphology; because the paste volume and the cement content per unit volume changed together with Lf/C, this effect cannot be attributed to a specific mechanism, and the SEM and XRD observations do not establish packing or nucleation effects. Overall, within the investigated domain, the fresh-state behavior of high-powder SCC depended mainly on water availability and admixture dosage and their interaction, whereas the effects of filler content and grade were smaller and partly confounded with the associated changes in paste composition.