Effect of Superplasticizer Dosage on Mechanical and Durability Properties of Low-Volume Steel Microfiber Reinforced Self-Compacting Concrete.

This study investigates the effects of low-volume steel microfibers (0-0.4 vol.%) and superplasticizer (SP) dosage (0.8 wt.% and 1.5 wt.%) on the mechanical and durability properties of self-compacting concrete (SCC) for railing structures, with a constant water-binder ratio of 0.28. Fresh (slump flow), mechanical (compressive strength up to 90 days, 28-day flexural strength), durability (drying shrinkage, freeze-thaw resistance after 200 cycles), and microstructural (mercury intrusion porosimetry) properties were evaluated. SP enhances flowability while steel fibers reduce it. All mixtures except that with 0.8% SP and 0.4% fibers meet the workability requirements of Chinese standard JGJ/T 283-2012 for SCC. Compressive and flexural strengths generally increase with fiber content but decrease when the SP dosage rises from 0.8% to 1.5%. Steel fibers effectively reduce drying shrinkage and improve freeze-thaw resistance, as indicated by higher relative dynamic elastic moduli and lower mass loss after 200 cycles. Microstructural analysis reveals that the higher SP dosage (1.5 wt.%) significantly increases porosity, which explains the observed higher shrinkage and lower strength. Considering mechanical properties, durability, and castability, the SCC mixture with 0.3 vol.% steel fibers and 0.8 wt.% SP is recommended for railing structure applications.