Causes of failure in concrete elements buried in lagoon water

Abstract

The effect of salt attack on reinforced concrete structures in marine environment has become a source of concern to stakeholders in the construction industry. This trend has led to cracks and sometimes failure of structural members that are exposed to this environment. This study investigated the strength performance of concrete elements in lagoon water which is an offshoot of the Atlantic Ocean in Lagos State, Nigeria. A total of ten 150 mm cubes, and ten 150 mm × 150 mm × 600 mm reinforced concrete beams were cast using Portland limestone cement of 42.5-R at 28 days strength of 40 N/mm2 and cured in both fresh and Lagoon water with water-cement ratio of 0.45. Chemical analysis were carried out to determine the concentration of ions. Mechanical tests were also carried out on the concrete elements. The chemical analysis result showed that Calcium (Ca) was the predominant element having 61.62% in the concrete sample cured with lagoon water while concrete sample cured in fresh water had 51.77%. The flexural behaviour of reinforced concrete beams showed that the flexural stiffness of beams were 15.1 N/mm2 and 12.46 N/mm2 in the lagoon and fresh water, respectively. The compressive strength of concrete cubes cured in fresh water was 42.67 N/mm2 while that of lagoon water was 34.22 N/mm2. The preliminary results showed that concrete gained strength at the early stage for reinforced concrete beams buried in the Lagoon and reduced in strength at the early stage for concrete cubes buried in Lagoon. The result of the compressive strength showed that the high presence of salt could have contributed to the cracks and eventual spalling of concrete elements in marine environment.