EVALUATION AND COMPARISON OF MECHANICAL CHARACTERISTICS AND DURABILITY OF CONCRETE WITH DIFFERENT CEMENT REPLACEMENT LEVELS BY FLY ASH

摘要

To determine the activity index of different types of fly ash, mortars with 25% cement replacement by fly ash were made. At 90 days the compressive strength was similar for the mortars with only cement as hydraulic binder and for the mortars with low-calcium fly ash from the combustion of coal and twice as high as the compressive strength of the mortars made with Municipal Solid Waste Incineration fly ash. After 90 days the splitting tensile strength for the mortar with MSWI fly ash was significantly lower than for the two other mortars. Secondly concrete samples with 10%, 40% and 60% replacement of cement by fly ash were produced, using an appropriate amount of (super)plasticizer to obtain good workability. The compressive strength of the mixes at young age decreased with increasing cement replacement level. Inclusion of 40% fly ash allowed to halve thickness changes in lactic/acetic acid, weight loss in sulphuric acid and chloride diffusion coefficients during accelerated experiments. The resistance to frost/thaw cycles was similar for fly ash and reference concrete (without air entrainments agents). The carbonation depth after 9 weeks in a 10% CO_2 environment was much higher for the 60% fly ash mixture. High volumes fly ash decreased the resistance against the combined action of frost and de-icing salts (3% NaCl solution).