Influência de adições minerais e aditivo impermeabilizante interno no desempenho de telhas protendidas pré-fabricadas em concreto

Abstract

With the emerging precast concrete technology, the civil construction has acquired high agility, reducing construction time and greater quality control in execution. Among several precast pieces, tile in prestressed concrete is characterized by selfsupporting spans of up to 25 m, without the existence of an intermediate support structure. Being a slim product, requires an improvement in increasing the durability of the structure because of the steel corrosion and maintain their fitness for use. The objective of this research is to reduce the permeability of the precast tiles, and analyzing their influence in the durability of the concrete face of the aggressiveness classes constants in the NBR 9062/2006, that establish the a/c ratio up to 0,45 and minimum compressive strength characteristic of 40 MPa, positioning themselves as a class of environmental aggressiveness II - Urban. For this, were selected a few mineral admixture from Curitiba/Paraná and a waterproof internal admixture, comparing with the concrete mix pre-existing in production line. The concrete dosages were defined by packing particles and were analysed for mechanical compressive strength, water absorption by immersion and by capillarity and water penetration under pressure, in addition to tests of mercury intrusion porosimetry (MIP), carbonation and chloride ion penetration. About the mechanical compressive strength, the dosage reference showed the best results (due to lower water / cement ratio and higher cement consumption), followed by concrete with waterproofing admixture and metakaolin. For water absorption, all measurements fall as durable concrete, especially the metakaolin additive and filler + waterproofing. For the water absorption, all dosages presented low permeability. For the water penetration under pressure all fall as impervious to several conditions, especially with metakaolin and waterproofing admixture. The MIP test shows that the dosage with filler has a higher concentration of pores and the dosage with metakaolin has the smallest maximum diameter of pores, with a tendency towards refinement in smaller diameters. When analyzing the carbonation, the metakaolin showed the best results, allowing a smaller reinforcement cover for a lifetime of 50 years. As the penetration of chlorides ions, the metakaolin, showed a greater reduction comparing with other dosages for its pozzolanic activity, contributing to the concrete durability. In general, it is possible to improve the concrete impermeability with the addition of 8% of metakaolin by weight of cement, with 5,2% of cement reduction, showing good results also using 1% of waterproofing admixture. As for durability, the optimizing of aggregates granulometric curve and the use of metakaolin enables the use of prefabricated tiles in regions of class of environmental aggressiveness III - Industrial or Marine, observing the minimum concrete cover of reinforcement.