Chloride Penetration Resistance and Service Life Prediction of Ultra-High-Performance Concrete With Supplementary Cementitious Materials in Marine Exposure Zones

This study investigates chloride penetration resistance, diffusion coefficients, and probabilistic service life prediction of UHPC mixtures with slag, fly ash, and silica fume in marine tidal zone exposure within the context of structural engineering and concrete durability, an area of growing scientific importance given its implications for marine bridge pier and coastal infrastructure design life extension, SCM optimization guidelines for UHPC, and probabilistic concrete durability modeling framework. Using NT Build 492 rapid chloride migration test, 36-month tidal zone field exposure (Huntington Beach pier), chloride depth profiles by acid digestion at 6-month intervals, and probabilistic service life modeling via Life-365 with Monte Carlo simulation, we examine pozzolanic reaction of SCMs consuming portlandite and forming additional C-S-H gel filling capillary pores, reducing effective chloride diffusion coefficient by 3-5 orders of magnitude vs. ordinary Portland cement; secondary effect of SCM reducing thermal cracking risk during curing in 8 UHPC mix designs (2 controls, 6 SCM variants with slag 20-40%, fly ash 10-20%, silica fume 5-15%) x 18 specimens per mix = 144 specimens total; n=3 specimens per destructive chloride profile at each 6-month interval drawn from Huntington Beach municipal pier tidal zone (tidal range 1.8 m, seawater Cl 19,400 ppm) for field exposure; Pacific Coast University concrete lab for accelerated ponding and migration testing. Results indicate that optimal 30% slag + 10% silica fume UHPC achieves Da = 0.24 x 10^-12 m2/s at 36 months (vs. 8.4 x 10^-12 for control OPC), P(depassivation) <5% at 100 years; service life >200 years at 95% confidence (p < 0.001), with Da 0.24 vs. 8.4 x10-12 m2/s; P<5% depassivation at 100 years; service life >200 years as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to structural engineering and concrete durability and carry actionable implications for the design of programs and policies targeting marine bridge pier and coastal infrastructure design life extension, SCM optimization guidelines for UHPC, and probabilistic concrete durability modeling framework.