Comparative assessment of OPC and portland composite cements on the rheology and strength of nylon fiber-modified self-compacting concrete

Abstract This study investigates the combined effects of Portland composite cement type and nylon fiber dosage on the fresh-property compliance and 28-day mechanical performance of self-compacting concrete (SCC). An empirical SCC proportioning approach was adopted. Four OPC-based trial mixes were first evaluated using slump flow diameter, t500, V-funnel, L-box, and visual stability criteria in accordance with EN 12350, ACI 237R-07, and JSCE guidelines, from which an optimally balanced SCC mixture was selected as the baseline. Using this reference mix, two composite cements (CEM II/A-M and CEM II/B-M) were investigated with nylon fiber contents of 0, 0.1, 0.25, and 0.5%. Fresh results show that increasing fiber content reduces slump flow and passing ability and increases flow resistance, confirming a workability–toughness trade-off; SCC compliance remained reliable up to ~ 0.25% fiber, while 0.5% approached or exceeded fresh-property limits in CEM II/A-M and remained borderline acceptable in CEM II/B-M. Under constant w/c and admixture dosage, higher SCM composite cement improved rheology and passing ability (CEM II/B-M > CEM II/A-M > OPC) but reduced 28-day strength, following clinker content (OPC > CEM II/A-M > CEM II/B-M). For mechanical performance, compressive and splitting tensile strengths increased to an optimum near 0.25% fiber before declining at 0.5%. Flexural behavior exhibited peak strength and toughness at approximately 0.25% fiber, whereas higher fiber contents primarily enhanced post-cracking ductility despite a slight reduction in total energy absorption. These results provide practical dosage guidance: fiber contents up to 0.25% ensure reliable SCC performance across cement types, while higher dosages require rheological re-optimization depending on placement constraints.