Estudo das propriedades mecânicas de uma matriz cimentícia com adição de cinza volante e reforçada com tecido de juta

Abstract

In this work the influence of jute fiber textile as reinforcement of cement mortar when submitted to direct tensile strength and at three points bending are discussed. To increase the fiber durability in alkaline environment a matrix with partial Portland cement replacement by 50% of fly ash was used. To evaluate if the developed matrix was able to control the degradation of fiber, the tests were done after six months of natural aging. For the characterization of the developed matrices, compression tests instrumented with strain-gages were performed. The ordinary Portland cement matrix obtained compressive strength of 79.21 MPa and modulus of elasticity of 37.29 GPa. The fly ash matrix achieved compressive strength of 58.61 MPa and modulus of elasticity of 29.25 GPa. However, in the three point bending and direct tensile strength tests, the matrices did not present a significant difference between the values of maximum strength. For the reinforced composites submitted to the three point bending test, the samples made from the matrix without the addition of fly ash presented better results. In this test, the reinforced specimens with three layers of fiber presented maximum tension higher than those with five layers, but the samples reinforced with five layers of fiber were able to maintain a higher percentage of tension after cracking. In the direct tensile test, the reinforced composites with five layers presented results better than those of three layers. For the composites without the mineral addition, only two samples presented strain-softening behavior, while in the composites with addition of fly ash this number increased to 6. Through the three point bending test and direct tensile test, it was realized that the use of jute reinforcement reduced the maximum stress, but bypassed the brittle behavior of the cementitious matrices. It is believed that the workability of the mortars produced was not adequate, which caused the existence of empty spaces and consequently caused the decreased of the composites maximum tensions. The partial replacement of Portland cement by fly ash was not enough to ensure fiber integrity and as a result of 6 months of natural aging the jute fiber was deteriorated at the test date.