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.