Abstract
Estimation of the mechanical properties of concrete in an existing structure is possible with the results of surface hardness and ultrasound tests (nondestructive tests (NDTs)). For both the use of correlation curves is necessary, it is established between NDT and the results of the compressive strength of test specimens or extracted from structure. The objective of this study is to produce correlations between the results of surface hardness and ultrasound NDTs and the compressive strength of the structural concrete in the bleachers of a soccer stadium in the city of Cianorte, which is located in the northwest part of the state of Parana, Brazil. This concrete structure, which is approximately 26 years old, has some defects, such as corrosion, concrete segregation and cracks. Concrete spalling in one of the slabs has recently raised some concern. Another significant issue is the absence of records regarding concreting of the bleachers’ structure. Therefore, mapping the reinforcement was initially performed according to the results of a surface hardness test, as recommended by standard [1]. An ultrasound test was simultaneously performed according to standard [2] for the same points employed in the surface hardness test. The concrete specimens were extracted according to the recommendations of standard [1] to determine compressive strength, perform the NDT and construct the correlation curves for the results. A total of 26 concrete specimens were obtained from all structures of the bleachers. From the methodology and the results of the study, highly reliable equations were obtained from the correlation curves among the compressive strength of the concrete specimens and the values of the surface hardness index and the ultrasound wave propagation velocity.
Highlights
The measurement of ultrasound and surface hardness comprises practical tests that do not damage a structure’s surface: the instruments are light and easy to handle and use
In the case of module 4, a correlation between the NDT that was directly performed on the structure and the results of the compression of the concrete specimens was not feasible for different reasons: excessive rebar concentration, the impossibility to perform the test in the direct transmission mode for the chosen points of the structure and
Ultrasound: A correlation between the results of the ultrasound tests of the concrete specimens collected from the stadium’s structure and the compressive strengths of the same specimens was established; The results indicated that the stronger the concrete was, the higher the wave propagation velocity was;
Summary
The measurement of ultrasound and surface hardness comprises practical tests that do not damage a structure’s surface: the instruments are light and easy to handle and use. Surface hardness is measured according to standard [3] to verify the uniformity of a concrete’s surface hardness to compare it with a reference concrete and to estimate its compressive strength. According to [3], a reliable correlation, which is obtained with local materials and with special attention to factors such as type of cement, type of aggregate, surface humidity conditions, carbonation and concrete age, must be available to have a direct assessment of a concrete’s compressive strength. The results of surface hardness measurement and ultrasound tests (nondestructive tests (NDTs)) enable the estimation of the mechanical properties of concrete in an existing structure. That estimation is performed using correlation curves that are established from the NDT results and the compressive strengths of specimens from the structure
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