Mixing water fit to drink has always been a basic requirement for good concrete. Yet all contractors know that this necessity can present major practical problems and often a financial burden. In developing countries, the construction boom is often seriously hindered by shortages of fresh water, which may need to be imported at great expense. A recently developed seawater concrete process may offer the opportunity to solve both the practical and financial difficulties imposed by water requirements.
The first major application was for a reinforced concrete containing wall around the Muroroa Atoll in the South Pacific. Built entirely with unwashed beach sands and sea-dredged aggregates and using seawater for mixing, the wall completely surrounds the atoll, which is 41 miles long and up to 3 miles wide. Construction of the atoll wall was made possible by use of the seawater concrete process.
The new process uses a chemically modified portland cement, obtained by mixing complex mineral constituents with a preselected cement in ratios that depend on the project specifications and the nature of the basic materials available at the site. Essentially, it allows hydration with water containing from 0 to 100 grams per liter of salts: this is a much greater proportion than the 32-grain-per-liter content of normal seawater. The following changes in properties of the concrete are also reported: reduced setting times; improved compressive strength; reduced porosity, shrinkage and cracking: and increased modulus of elasticity.