Conference Agenda

The tensile strength of concrete plays a vital role in the design of large concrete infrastructures. Further, the majority of these structures are subjected to cyclic loading, causing fatigue. Most of the properties under monotonic and fatigue loadings are obtained from tests conducted on smallsized specimens. Since concrete exhibits a strong size effect due to its heterogeneous nature, it is imperative to determine the properties of large specimens. This study aims to conduct a stable, direct tension test on 400 x 400 x 100 mm sized concrete prismatic specimens to investigate the differences in fracture mechanism under both monotonic and fatigue loading. The acoustic emission (AE) and digital imaging are used to capture the evolution of microcracking during the monotonic and fatigue tests. It is observed that the tensile strength of concrete is about 4-5% of the characteristic compressive strength, which is nearly half of the value considered in the literature. Further, the mechanism of microcracking is significantly different under monotonic and fatigue loadings.

Large concrete surfaces in industrial and parking areas, roads or highways, are typically designed with joints to mitigate constraint-induced stresses and uncontrolled crack formation. Thermal or hygric concrete deformations localize at these joints, which can vary in thickness from a few millimeters to several centimeters. To prevent the ingress of harmful substances into the concrete and its substrate, joints are typically sealed by flexible polymer sealants. However, the durability of these sealing systems is limited, despite being regularly maintained. Furthermore, the concrete in the joint areas often yields premature damage under combined mechanical loads and environmental exposures.

This paper presents an alternative concept consisting in overbuilding existing joints with a thin layer of carbon reinforced concrete (CRC). The CRC layers transform the joint deformations into multiple fine cracks over a predefined area, enabling an extended service life an enhanced traffic comfort. The work deals with the design of a large-scale testing facility including initial reference experiments on CRC joint systems. The experimental setup was developed to simulate both positive and negative, quasi-static and cyclic joint deformations at a full scale. It allows deriving the mechanical response of the system and analyze the damage development and crack formation by means of analogue and image-based techniques

The crack behavior of concrete needs to be revealed to properly evaluate the damage of concrete cores from in-service structures. Mechanical properties of heavily damaged concretes are unreliable due to variations in destructive behavior and damage localization. Supplemental indicator is necessary for damage evaluation of concrete considering crack propagation behavior. Against this background, the damage behavior of concrete with cracks of different orientations is investigated using Acoustic Emission in core tests. Concrete cores were drilled from a dismantled weir pillar of an RC structure. These concrete specimens were affected by freeze-thaw and salt damage because of severe serving environment. Each concrete has crack distribution with different orientation. Vertical and horizontal orientations are defined as the longitudinal or short directions of the concrete. In experimental procedures, X-ray Computed Tomography, ultrasonic and uniaxial compression test were performed. As the results of non-destructive testing, selected concrete specimens were served for uniaxial compression test. Pre-existing cracks are visualized and quantified based on their distribution and geometric features using X-ray CT. The geometric properties of crack are calculated in two-dimensional. Geometric properties include perimeter, angle and circularity. The number of AE events is estimated using machine learning based on the relationship between the geometric properties of neighboring elements. The influence of geometric properties on the number of AE events is investigated quantitatively.

Various important concrete structures are susceptible to imperfections, such as the presence of an interface. In some cases, the formation of an interface is an inevitable flaw, such as in the case of repair, dams and pre-cast concrete structures. These flaws can act as a weak link and could be responsible for the failure of the structures. One of the most widely used nondestructive techniques to monitor such damages in structures in real time is the acoustic emission (AE) technique. In this study, experimental tests are conducted on concrete-concrete interface specimens under four-point shear tests with different interface positions. The interfaces are formed between four different strengths of concrete on each side. The AE technique is used to monitor the crack growth. Based on the experimental results, A fracture criterion has been suggested based on simplified calculation of mode mixity ratio. Three different failure patterns have been identified depending on the mode mixity ratio, where cracks eventually kinked into the substrate material at a critical value of the mode mixity ratio.