Avaliação do tratamento de fibras curtas de sisal em matriz cimentícia

Abstract

Currently there are different solutions and technologies for the introduction of fibrous material in concrete, in order to health the deficiency that this material presents under tensile stress. The alternatives are linked to the introduction of a reinforcement that promotes decreased crack propagation, such as steel reinforcement, or synthetic and natural fibers. In view of this need, the present work seeks a sustainable alternative through the use of sisal fiber, added as reinforcement in the concrete matrix. However, natural fibers are subject to degradation in the alkaline medium of cement matrices, which results in the loss of their efficiency. In this sense, this work aims to study the behavior of concrete reinforced with short sisal fibers, impregnated with aqueous lignosulfonath solutions with 4% contents. For this, three different concrete mixtures were studied: (i) reference mixture (LI-REF), with fibers treated only with lignosulfonath; (ii) mixture with fibers treated with lignosulfonate plus rice husk ash (LI-CCA); and (iii) mixture with fibers treated with lignosulfonato and partial replacement of Portland cement by rice husk ash (LI+MCCA). The concretes were tested at 14 and 28 days, and their traction behavior in flexion, axial compression and water absorption by capillarity was analyzed. Through analysis with electronic microscopic scanning (MEV), it was verified that lignosulfonate was adhered to the fiber. However, there was no change in tensile results and fiber absorption capacity as a function of treatments. From the compression and traction tests in the flexion of the composites, it was observed that there was a loss of resistance from 14 to 28 days, except for the matrix with partial cement replacement, who did not suffer alterations between the ages analyzed. There was no reduction in water absorption by capillarity of composites containing rice husk ash. In short, the addition of the fibers showed improvementin the levels of tenacity of the concrete matrix, where the composite was able to deform after the opening of the first fissure. Studies of new treatments and older ages are recommended for certification of fiber performance in cementitious matrices. Keywords: sisal fiber; sodium lignosulfonate; rice husk ash; direct traction; traction in four-point flexion.