IMPROVED CONCRETE QUALITY WITH COMBINATIONS OF FLY ASH AND SILICA FUME

Portland cement concretes and concretes with various combinations of cement (Types II and III), fly ash (Class F), and silica fume were tested to establish parameters for strength and chloride permeability. The effects of different curing temperatures and different durations of moist-curing were also determined. In general, the laboratory tests showed that in the temperature range of 23 to 38 C (73 to 100 F), concretes at a water-cement ratio of 0.40 to 0.45 with satisfactory 28-day strengths and good resistance to chloride-ion penetration at 28 days can be obtained with either type of cement and various combinations of fly ash and silica fume. Similar specimens cured at 6 C (43 F) generally did not develop an adequate early strength, and the chloride permeability was high. Combinations of the pozzolans with Type III cement yielded a higher strength and lower chloride permeability than did similar combinations with Type II cement.