EMPIRICAL MODEL FOR WATER PENETRATION OF SEA WATER TO PREDICT CONCRETE COVER

Abstract

Small docks play a vital role in supporting economic activities in Indonesia, where concrete is commonly used due to its perceived durability. However, exposure to seawater and wave action necessitates enhanced protection, as degradation of concrete in marine environments is ultimately unavoidable. This study examines seawater penetration into concrete at the Lempasing Fishermen’s Boat Pier in Lampung Province, Indonesia, over a 365-day period. The research employed 22.5 MPa PCC concrete, which met the standard penetration depth requirements for highly aggressive environments. Samples were cured in freshwater for 7 days before exposure to seawater. The findings show that penetration depth conforms to the empirical model y = a ln(bt) + c, aligning with existing literature (Yoo et al., 2011). Model projections estimate seawater penetration to reach approximately 8.5 cm over 50 years. Accordingly, a 13 cm concrete cover can serve as a sacrificial layer, effectively delaying the initiation of rebar corrosion and preserving reinforcement integrity for up to 50 years, with a safety factor greater than 1.5. Despite this protective strategy, the compressive strength of submerged concrete declined significantly to 7 MPa after 365 days. This deterioration was primarily due to continuous wave action and the chemical ingress of seawater, which triggered the formation of ettringite and pore expansion, resulting in cracking. Furthermore, the premature exposure of concrete—before achieving pore discontinuity—significantly contributed to the loss of strength.