Influência das variáveis de ensaio nos resultados de resistência à compressão de concretos: uma análise experimental e computacional

Abstract

The performance of concrete is commonly evaluated through its compression strength. The results of this test, however, often displays a high dispersion, possibly associated with aspects such as the specimen geometry, dimensions and degree of compaction of the specimen, as well as the flatness and parallelism of the specimen faces and their orthogonality in relation to the specimen axis. Variables linked to the testing procedures, such as the load application rate and testing machine stiffness may also affect the dispersion in the test results. Reports can be found in the literature, covering the possible influence of the geometry and dimension of the compression specimens, but very few studies seem to have been completed with regard to the effect of the load application rate, testing machine stiffness and specimen base regularity (flatness, parallelism and orthogonality to the specimen axis). The speeds of application of the load, commonly, vary from 0,07 to 0,80MPa/s Several techniques have been employed in order to treat the regularity of the specimen bases: capping with various materials (attached or not to the specimen bases), mechanical preparation of the bases and special casting moulds for the concrete. The systems most frequently utilized in the regularization of the specimen bases are capping with sulfur, neoprene cushions and base grinding. Surface regularization employing cement mortar, epoxy resins, sand cushions and special moulds that would guarantee adequate specimen bases have also been reported. The present text analyses through experimental approaches and numerical modeling (through the Finite Element Method FEM) the influence of the effect of the load application rate, testing machine stiffness and specimen base regularity of three strength concrete classes. The dispersion of results is presented, mainly the base regularity variation.