Análise da resistência residual do concreto após exposição a altas temperaturas

Abstract

The concrete is known to has a good performance against high temperatures, since it has low thermal conductivity , is non- combustible and will not be release toxic gases . However , due to the heterogeneous composition of the material when exposed to situations such as fires , undergoes physical , chemical and mechanical changes that can compromise its structural integrity . Aiming to analyze the residual strength of concrete subjected to high temperatures, were performed uniaxial compression tests on bodies -specimens submitted to different temperatures ( 300 º C , 500 º C and 900 º C ) , exposure times ( 30 , 60 and 90 minutes) and cooling modes ( slow cooling and sudden cooling ) . The dosage was realizadada in order to meet the requirements of NBR 6118 and NBR 12655 , which proposed minimum values of water / cement ratio for concrete can meet the durability requirements of aggression exposed to strong structures . Afforded a concrete mix of 1 : 1.06 : 1.06 : 2.87 : 0.55 ( cement : sand natural , artificial sand : aggregates : water) to a characteristic resistance ( fck ) of 25 MPa. 76 bodies of the specimen of 5 cm in diameter and 10 cm high, exposed to fire conditions and broken after 7 days of curing were molded . For temperatures up to 300 ° C concrete presented losses of up to 40 % of initial strength , which increased to 50% at temperatures up to 500 º C, until a reduction from 80% to 90 % of the resistance to temperatures of 800 ° C. Furthermore , it was shown that the sudden cooling causes more damage to the concrete than the slow cooling , but there were few variations.