Correlation curves to characterize concretes used in Rio de Janeiro by nondestructive tests

Resumo

The nondestructive tests are an important tool for obtaining information about the properties of the concrete of the structure. However, the reliability of the evaluation of those properties depends on the experience of the professional that carries out the tests and the curves employed to correlate the measured values with the properties of the investigated concrete. The main objective of this study was to supply the engineers with correlation curves that make it possible to evaluate, by using nondestructive tests and in a more appropriate way than the one currently used, the compressive strength and the modulus of elasticity of the concretes used in Rio de Janeiro. In the first phase of the study, test specimens cast with concretes used in several constructions in Rio de Janeiro were tested, including concretes supplied by different ready-mixed concrete producers. These concretes had, in general, nominal fck value of 25 MPa or 30 MPa. In the second stage, aiming to include concretes with strength varying within a wider range and the two types of typical coarse aggregates of Rio de Janeiro, test specimens cast in the laboratories of two groups of ready-mixed concrete producers were tested. In these concretes, the water-cement ratio and the petrographic characteristic of the coarse aggregate were varied. In total, the following tests were carried out: 400 compressive strength tests, 400 ultrasonic pulse velocity tests (800 measurements of velocity), 400 rebound hammer tests (3600 measurements of rebound numbers) in standard cylindrical test specimens and 95 penetration resistance tests (380 shots) in prismatic test specimens, at the ages of the concretes of 3, 7, 14, 28 and 90 days. The correlation curves obtained from the analysis of the results of all those tests are presented herein and the use of combined nondestructive tests is discussed.