Mix Proportion–Performance Relationships in 3D-Printed Concrete: A Literature-Based Evidence Analysis

Mix proportions for 3D-printed concrete must satisfy requirements for transport, extrusion, interlayer stability, and hardened performance. Heterogeneous raw materials, equipment, and test conditions often prevent direct use of published mixtures. This study analyzed mixture evidence from 1003 deduplicated publications at three levels: cross-study associations, within-study comparisons, and linked printability–mechanical evidence. Among mixtures with an explicit forming method and source-reported printability, 476 mixture-level aggregate units from 157 studies showed a negative association between the water-to-binder ratio and 28 d compressive strength. The pooled coefficient, paper-equally-weighted coefficient, and median within-study coefficient were −0.493, −0.422, and −0.516, respectively, supporting the use of the water-to-binder ratio as a priority screening variable rather than as a universally transferable strength predictor. Observed interquartile ranges in the cement-containing subset described the concentration of reported proportions. Scatterplots and sensitivity analyses for 12 variables showed that zero handling and sample boundaries affected the direction of some associations between mass concentrations. Five studies provided 28 comparable within-study results across 27 condition groups, each containing only one independent study. Four studies linked successful printing to mechanical specimens from the same mixture and process, yielding seven pairs; one included a four-mixture comparative series. Prediction data for nine printability outcomes and four strength ages failed all three eligibility scenarios. Thus, current evidence supports initial variable screening and study-specific material hypotheses, but independent replication and more complete process–specimen linkage are needed for transferable prediction and resource-efficient mixture research.