Avaliação experimental do deterioramento mecânico do concreto causado por perfurações

Abstract

The presence of holes in reinforced concrete elements, necessary for various purposes, is addressed by the ABNT NBR 6118:2023 standard, which serves as a reference for indicating special regions for drilling and dimensional limits for holes in structural elements. However, such interventions generate shock waves and vibrations that induce internal damage to the material, such as microcracks and spalling. In this context, this study experimentally investigates the loss of mechanical strength in beams subjected to drilling by impact equipment, such as hammer drills and rotary drills, through tests on concrete specimens. After preliminary tests, nine specimens were constructed in a prismatic shape with rectangular bases, approximately proportional to commonly used concrete beams in various civil construction projects, respecting the physical similarity rules between physical models. After drilling holes in the specimens using a hammer drill, mechanical alterations were evaluated using two distinct methodologies: ultrasound testing along the entire length of the specimens to measure differences in the dynamic modulus of elasticity before and after drilling; and analysis of variations in the natural frequencies of the tested specimens, as reductions in these frequencies are commonly associated with damage. The results indicated a maximum reduction of 17.5% and a minimum of 5.1% in the modulus of elasticity for the tested specimens, representing significant changes in the mechanical properties of the concrete. In the analysis based on natural frequencies, an average reduction of 12% in the obtained values was observed, reflecting stiffness reductions in the specimens. Finally, based on the obtained data, an equation was proposed to estimate the reduction in the modulus of elasticity as a function of drilling, in addition to recommending the type of drilling, among those analyzed, that causes the least damage to the specimens.