Functional Variability and Interchangeability of Commercial Limestone Powders in Concrete: An Experimental and Multivariate Screening Approach

Commercial limestone powders marketed under the same general material designation may differ in composition and particle characteristics, raising questions about their functional interchangeability in concrete. This study combined experimental concrete testing with multivariate data analysis to compare six commercially available limestone powders in C12/15 and C20/25 concretes, with 50% or 100% replacement of the original fly-ash fraction. Slump, air content, 7- and 28-day compressive strength, and water penetration were evaluated relative to class-specific reference concretes. Robust screening, rank-based correlation, principal component analysis (PCA), and hierarchical clustering were used as exploratory tools. Individual 28-day strength-retention ratios ranged from 0.501 to 1.094, while water-penetration performance showed a different, matrix-dependent ranking. The first two principal components explained 81.26% of the total response variance. Ward clustering produced a descriptive two-group structure, C–D–E and A–B–F, with Powder F appearing separate in a three-cluster interpretation. Because each powder–class–replacement combination was represented by a single batch and the 24 observations were repeated evaluations of six powders under four related conditions, the results are interpreted as exploratory. Within the investigated conditions, commercial limestone powders should not be assumed to be functionally interchangeable, and qualification should consider multivariable response profiles in the target concrete matrix.