Comparison Between Demand Of Superplasticizer of Admixture and and Strength Development of High Performance Concrete With Silica Fume and Residual Rice-Husk Ash

The use of high reactivity pozzolanas, such as silica fume in portland cement concrete, has increased significantly in the last two decades owing to improved resistance and durability of the concrete incorporating these materials. These properties were achieved through increased density of the cement paste generated by the micro-filler effect and pozzolanic reactions with calcium hydroxide liberated in hydration reactions of cement compounds. However, this beneficial effect on concrete properties involves a considerable cost increase due to the large use of superplasticizers necessary to confer the desired workability to concrete mixtures. A recently studied alternative pozzolana is rice-husk ash, which has been shown to present a performance compatible to that of silica fume, once it is produced under controlled conditions. Nevertheless, recent research in Brazil has shown that even residual rice-husk ash (a by-product of the cereal husk burning for energy production) presents excellent performances as a pozzolana. As part of that researth, this work has been carried out in order to compare silica fume performance with that of residual rice-husk ash in high-performance concrete. Both the demand of a superplasticizer admixture and strength development were investigated against a control concrete (without pozzolana). Three water/cementitious materials (keeping constant the absolute volume of cementitious materials) were studied. Residual rice-husk ash has been demonstrated to be a highly reactive pozzolana, ready for use in the production of high-performance concrete, and requiring less superplasticizer admixture than the concrete with silica fume. As to performance evaluation, concrete mixtures with silica fume showed greater strengths than other concretes. However, the results have shown an increase in residual rice-husk ash concrete strength from the 28th day on, reaching strength values close to those of silica fume at 90 days, an indication that the performance of both pozzolanas may be the same at later ages.