Evolução da resistência com o tempo de concretos convencionais e com sílica ativa confeccionados com materiais locais.

Abstract

High performance concrete has been rarely used in Paraiba because the knowledge about this material is not enoth in the Region. This work try to show that using local material it is possible to have durable concrete with compression strength higher than 50 MPa. To prepare this kind of concrete, in general, it is necessary the use of mineral additions. Here, microsilica was employed. Two initial mixes without addition were obtained and the effect of partial cement replacement by silica, in the rates of 5, 8 and 12%, was verified. The strength development from 1 to 91 days was checked. Esperimental data were compared with those from theorical expressions from CEB and ACI. Two cosrse aggregates were tested: granite fom stone crusher and sand stones. The ultrasonic pulse velocity was measured in several concrete. Results showed that: partial cement replacement by silica improve strength, even when low rate was used; the silica fume did not change significantly the law of increasing strength, with age, and good agreement with theorical data was found; granite as coarse aggregate had better performance than sand stone; ultrasonic velocity was sensible to water/cement ratio and it is difficult to obtain a general correlation between pulse velocity and compression strength.