Estudo da energia de fraturamento em concretos com reação expansiva

Abstract

The durability and service life of concrete structures are of technical, economic, environmental and safety importance. Among the several types of pathological manifestations that can occur in a structure, there is delayed ettringite formation, a type of sulfate attack, which occurs when concrete during hydration process reaches temperatures greater than 65 °C. This reaction is expansive and causes cracking in the affected element. Considering that cracks can compromise structural integrity and be a gateway to other deleterious mechanisms, it is extremely important to understand the performance of concrete in this situation. For that matter, Fracture Mechanics researches concrete post-peak behavior and the propagation of cracks by calculating the fracturing energy. This work aimed to evaluate the fracturing energy performance of concrete with late ettringite formation. To do so, concretes with compressive strengths of 30 and 60 MPa were produced in the laboratory. In order to induce delayed ettringite formation, the concretes were exposed to a heat treatment with maximum temperatures of 65 and 85 °C during curing and stored at 38 °C and 96% humidity. The longitudinal variation of the samples was monitored weekly. The material was analyzed for its compressive strength, tensile splitting strength, static and dynamic modulus of elasticity, Stiffness Damage Test (SDT) and fracture energy at 28 days (without heat treatment) and at expansion levels of 0.05, 0.12 and 0.30%. The results demonstrated the influence of cement consumption and maximum curing temperature, in which the 60 MPa concrete cured at 85 °C expanded first, followed by the 30 MPa concrete cured at 85 °C and finally the 60 MPa concrete cured at 65°C. In the last level of expansion there was an increase in the compressive strength of the 60 MPa concrete of up to 18% and a 14% drop in the 30 MPa concrete in relation to 28 days. The tensile strength and elastic modulus maintained similar values and the SDT did not present conclusive results. Fracture energy had a greater drop in concrete treated at 85 °C compared to the 65 °C treatment and also in 30 MPa concrete, due to lower cement consumption, compared to 60 MPa concrete.