Nondestructive Evaluation of Plain and Polymer Concrete

Abstract

Nondestructive measurement of the concrete strength is an important topic of research. Among different nondestructive testing (NDT) methods the ultrasonic pulse velocity (UPV) technique is the most popular method for concrete strength estimation. The device which is commonly used for finding this property is called "PUNDIT". Many studies have been conducted to find the relationship between the concrete strength and its UPV (ultrasonic pulse velocity) using this device. The purpose of this study is to gain a better understanding of nondestructive evaluation of plain and polymer concretes to determine their properties using a new method. To achieve this goal, instead of using PUNDIT an alternative method has been used to generate the ultrasonic waves. The main difference of this new method in comparison to the earlier methods followed by other researchers is that in this method a linear chirp signal with different frequencies is transmitted through the material unlike the single frequency signal as PUNDIT does. This new method is applied to both plain and polymer concrete samples. While measuring concrete strengths by the UPV method almost all researchers have neglected the effect of applied stress or load on the concrete member. When the specimen is tested under stress, its behavior is quite different from when it is tested without any load. In this investigation attempts have been made to properly incorporate the effect of the applied load on the strength prediction of plain and polymer concrete specimens from the UPV generated values. After applying the load on the specimen in multiple steps - at 20%, 40%, 60% and 80% of its failure strength - the time of flight (TOF) was measured for every loading step. From regression analyses the best equations which can be used to find the applied stress on the structure from the velocity values have been derived. Under cyclic loadings pre-existing cracks inside both conventional concrete and polymer concrete may grow and cause catastrophic failure of the structure. Structural failure under cyclic loading is also known as the fatigue failure. Another aim of this study is to investigate the behavior of plain and polymer concretes under the cyclic loading or fatigue. The specimens used for this study were subjected to compressive loads for different numbers of cycles. The applied load was gradually increased. After the loading- unloading cycles, nonlinear impact resonance acoustic spectroscopy (NIRAS) test was carried out on the samples using instrumented impact hammer. The degree of nonlinearity in the concrete specimens was measured by recording the shift in the resonance frequency as the impact energy increased. Experimental results from the conventional plain concrete and polymer concrete specimens were compared to investigate which type of concrete exhibits more nonlinear behavior under fatigue.