Properties of Underwater Concretes Containing Large Amount of Fly Ashes

The results of the testing of the underwater concretes, containing fly ashes from circulating fluidized bed combustion (CFBC) of the black coal, are presented in the paper. The concrete mixes were designed in such a way that the content of the binder was 400 kg/m3 and water to binder ratio w/b was equal to 0.48. Five mixes are prepared with the content of fly ashes: 0, 20, 30, 40 and 50 per cent of the cement mass, respectively. The consistence of the mixes was controlled by adding the suitable amounts of superplasticizer. The content of AWA admixture was constant for all mixes and equal to 1% of the binder mass. The following properties were tested for the concrete mixes: slump-flow, viscosity using V-funnel and passing ability using L-box. The wash-out losses were also determined. All tests of the concrete mixes were carried out immediately after mixing the components and after 60 minute after mixing. For the hardened underwater concretes, the following properties were determined: compressive strength after 7, 28 and 56 days of curing as well as the depth of water penetration under pressure and water mass absorbability. The best composition, regarding to the properties of the mix and hardened concrete, appeared that with 30% of the fly ashes.