Abstract
Abstract The Alkali-Aggregate Reaction (AAR) phenomenon in concrete structures is perceived via expansion and cracking, swelling of gel like material, causing damage and disruption in structural elements. Despite extensive standardization, AAR cases are still persistently occurring worldwide. The literature on susceptibility of concrete to AAR reported examples of false negative and positive results. Hence, long-term prediction is a problem still posing great challenge to engineers. The severity of AAR on the structural integrity can be mostly elucidated by the assessment of the historic of elastic properties. There is consensus that AAR causes decrease in the load capacity concrete, reflected by reduction of elasticity modulus due damage progresses. Non-destructive techniques are often used as first approach, as they can provide relatively fast assessment in situ as well as in large structural elements. Its data interpretation carries certain degree of complexity due intrinsic characteristic of many of these methods. This is the case of Ultrasonic Pulse Velocity (UPV), which have been considered to present several limitations for such purpose. This paper deals the potential use of the Longitudinal Resonance Frequency (LRF) method as tool to evaluate the elastic historic of AAR prone elements. The LRF possesses higher energy than UPV. Also, using modulation of frequency in input signal combined the test geometry, the LRF allow application to larger samples as well as to extract complementary information alongside the dynamic elastic modulus. This way, the LRF was applied to study concrete beams tested under controlled conditions for about 1.5 year. The independent variables to the tests are: time, frequency, aggregate type, cement content, alkali content and water to cement ratio. The dependent variables are: damping, loss factor and elasticity modulus. The analysis associate damage with vibration damping, confirming reduction of elasticity through damage with experimental validation and prediction of AAR under rheological model.
Highlights
CRITICAL LITERATURE REVIEWAlkali-Aggregate Reaction (AAR) is an expansion deleterious phenomenon that affects concrete’s long-term performance and durability
It's noticed an increase in Ultrasonic Pulse Velocity (UPV) over the time of the tests, in which the dynamic elastic modulus is proportional the pulse propagation velocity, it can be deduced that the concrete beams, including those affected by AAR (R # - beam affected by AAR), are gaining rigidity, when the beams with reactive material are undergoing degradation, as verified in the resonance tests and where Barreto [3] confirmed that the ultrasound is not sensitive to the detection of AAR
In the case in question, for Longitudinal Resonance Frequency (LRF) tests conducted by Barreto [3], longitudinal force of sinusoidal behavior with variable frequency was applied in a time interval of 8 seconds, by the logarithmic scanning system of the equipment used (AGILENT 33220A [8]), where the manufacturer (AGILENT TECHNOLOGIES) reports that logarithmic scanning is useful to cover a wide range of frequencies, which in low resolution could be lost with the linear scanning system
Summary
Alkali-Aggregate Reaction (AAR) is an expansion deleterious phenomenon that affects concrete’s long-term performance and durability. In recent years there has been an increase in the search for reliable techniques for dynamic non-destructive testing in the detection of damage to structures and materials (Butterworth et al [1]; Leśnicki et al [2]; Barreto [3]; Gutenbrunner et al [4]; among others). This is due to the fact that the damage causes changes in parameters such as damping, in stiffness, where the study of damping and its evolution over time can direct the effective methodology for detecting stiffness degradation in concretes submitted to AAR
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