Effects of natural seawater and sea sand on the compressive behaviour of unconfined and carbon fibre-reinforced polymer-confined concrete

This article presents an investigation into the effects of natural seawater and sea sand on the behaviour of unconfined and fibre-reinforced polymer-confined concrete. The experimental programme covered compression tests of a large number of standard concrete cylinders, which were prepared from the following four series of concrete: (1) the reference normal concrete, (2) sea-sand concrete, (3) seawater concrete (SwC), and (4) seawater sea-sand concrete. The concrete cylinders were either unconfined or confined with externally wrapped carbon fibre-reinforced polymer jackets to be tested at various ages from the early to the long term. This article presents the results of the first-phase tests, which covered a total of 48 specimens from the four series of concrete, with a half of them tested in the unconfined condition at the ages of 7 and 28 days, and another half tested with either one-ply or two-ply carbon fibre-reinforced polymer jackets at 28 days. The results show that at the ages of 7 and 28 days, the unconfined concrete specimens prepared with seawater and/or sea sand developed a slightly higher compressive strength, as compared to those prepared from normal concrete. When confined with carbon fibre-reinforced polymer jackets, the compressive stress-strain responses of concrete with or without seawater and/or sea sand were very similar. The use of seawater and sea sand did not seem to have significant effects on the compressive strength, ultimate axial strain and stress-strain responses of confined concrete, and the ultimate strain capacity of carbon fibre-reinforced polymer jackets neither. The test results were also compared with the predictions of an existing analysis-oriented stress-strain model for fibre-reinforced polymer-confined concrete. It is shown that the compressive strength, ultimate axial strain, stress-strain responses and dilation behaviour of the carbon fibre-reinforced polymer-confined concrete with or without seawater/sea sand can be reasonably well predicted.