Concrete Durability in Marine Environment: Early Age Exposure of Standard and Self-Compacting Concrete to Chloride Ions

Lalousis, Calliope (2002). Concrete Durability in Marine Environment: Early Age Exposure of Standard and Self-Compacting Concrete to Chloride Ions B.Sc Thesis, School of Engineering, The University of Queensland.

       
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Author Lalousis, Calliope
Thesis Title Concrete Durability in Marine Environment: Early Age Exposure of Standard and Self-Compacting Concrete to Chloride Ions
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2002
Thesis type B.Sc Thesis
Supervisor P. Dux
Total pages 96
Language eng
Subjects 0905 Civil Engineering
Formatted abstract
The long-term durability of concrete structures is compromised as a result of exposure to marine environments. Chloride ions in concrete cause leaching which, results both in a loss in compressive strength and a loss of reinforcement protection. Chloride ions also greatly accelerate the corrosion of reinforcement. It costs the community millions of dollars to repair and replace damaged marine structures every year. Concrete structures are often exposed to marine environments without adequate curing. This exposure occurs at an early age, sometimes often immediately after casting.

Self-Compacting concrete has emerged in recent times as a possible solution to an ongoing concrete durability problem. Self-Compacting concrete is mostly used in situations where standard compaction is difficult to achieve. Self-Compaction is achieved using only the self-weight of the concrete.

Concrete blocks, made of standard and self-compacting concrete, were placed into tanks filled with salt water of similar concentration to ocean water. Other concrete blocks were moist cured for three days before exposure to the marine environment. The tanks were fitted with pumps in order to mimic the tide cycles experienced in the ocean. Blocks were placed into the tank immediately after casting or after curing. These blocks were placed at varying heights in the tanks so the period of submergence was varied. Samples were collected from the blocks using a hammer drill and samples were tested to determine total chloride concentrations present.

Several conclusions were reached during this work. Laboratory experiments showed that early age exposure of concrete to marine environment results in larger chloride concentrations in the surface layers of the concrete than concrete that was moist cured for three days. The theoretical equation representing the diffusion of chlorides into concrete was applied to experimental data and used to compare rates of chloride diffusion into concrete. This comparison showed that chlorides penetrate more rapidly into early age exposed concrete than cured concrete. This also showed that the most critical time for chloride penetration was the first three days of exposure to this environment.

Top and Bottom positioning of blocks in the tanks, to facilitate the dominance of two different chloride ion transport mechanisms, proved to be inconclusive. A comparison of self-compacting and standard concrete showed that self-compacting concrete should not be exposed to a marine environment at any early age, as the concrete was highly fluid at this early age and considerable fine material washed out of the concrete.
Keyword Concrete durability
Marine environment
Chloride ion

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
 
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Created: Tue, 06 Jan 2015, 11:02:32 EST by Ahmed Taha Siddiqui on behalf of Scholarly Communication and Digitisation Service