Caracterização do módulo de elasticidade de concretos por meio de diferentes métodos e condições de carregamento

Abstract

The modulus of elasticity of concrete is a property that plays a fundamental role in the structural behavior of buildings. It is essential for understanding how concrete reacts under different loads and efforts, being especially important in large-scale works, such as bridges and dams, which will be exposed to extreme loads and adverse environmental conditions. In this context, the evaluation of the mechanical properties of concrete is crucial to judge the performance and durability of buildings. Standardized methods, such as the application of ultrasonic waves, estimation for design purposes based on mechanical resistance, or even the traditional static modulus of elasticity test, provide estimates that present divergences. The following work aims to analyze the variations in the modulus of elasticity obtained through different experimental techniques, in addition to identifying the damage to the material associated with the loading conditions and the discrepancy of these techniques in comparison to the model proposed by NBR 6118 (ABNT, 2023). For this, non-destructive tests were carried out (impact resonance and dynamic modulus through ultrasonic pulse speed) interspersed with static tests (at amplitudes of 30%, 20% and 10% of the concrete's ultimate strength - fc) and quasi-static tests (generating the viscoelastic property known as complex modulus) by varying the loading frequency. The results demonstrated that there was a reduction in the absolute value of the complex module |E*|, on average 2.4% ± 2.9% in UTM-25 and 2.3% ± 1.3% in UTM-30, between frequency of 25 Hz and 0.03 Hz, suggesting that concrete becomes less rigid as the loading frequency decreases. There was no significant difference between the measurements of the two Universal Test Machine (UTM) servo-hydraulic presses. For the loading amplitude, there was a reduction of 4.0% ± 1.0% in the resonant modulus of elasticity and in the dynamic modulus of elasticity, after the static modulus of elasticity test with 30% of fc, indicating the influence of loading in the value of the modulus of elasticity and possible damage to the material after applying the load. As for modulus prediction, through the proposal of NBR 6118 (ABNT, 2023) the calculated value, Eci=29.50 GPa, surpassed all measurements obtained with the tested methods. For the dynamic module, the adoption of the Poisson ratio suggested in NBR 6118 (ABNT, 2023), ν = 0.2, resulted in values 25% higher than the measurements of P-waves associated with S-waves.