Quantifying damage level to concrete specimens

• Main Author: Teoh, Chun Wei.
• Other Authors: Fan Sau Cheong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/53864
• Institution: Nanyang Technological University

Concrete is widely used in Singapore. Loading on concrete will induced micro-cracks, which are invisible to naked eyes, in the concrete. The propagation of micro-cracks might lead to failure of concrete and might cause disaster in the worst case scenario. Hence, study of the behavior of micro-cracks with respect to damage level of concrete is important to predict the failure mode of concrete. The objective of this research project is to quantify the damage levels of concrete specimen of 100mm cube in terms of crack surface-to-volume ratio through experimental investigation. The experimental results obtained from this research will then be used for another Final Year Project group which will correlate the damage level to the event of breakup upon impacting on ground through experimental investigation. The research was carried out by using special mould to cast the 100mm concrete cube with chamfered edges. The mixture proportion of concrete specimens was standardized to produce specimens with almost similar characteristics. The concrete specimens were then control damaged at three different strain levels at post-peak state by using displacement control machine. After which, the damaged concrete specimens were sliced into 5 slices in the direction that is perpendicular to the applied uniaxial compression loading on the specimens. Stereomicroscope was then used to capture the image of each slice and the images were analyzed through analysis software, Image J. Density for both micro-cracks and macro-cracks were obtained for each different damaged concrete specimen. The behaviors of the strain level with respect to the density of macro-cracks and micro-cracks were obtained through data analysis. Results show that as the damage level increase from lower strain value to higher strain value, the cracks density increases as well. Moreover, the increase of density of cracks across the strain level was due to the introduction of new micro-cracks and also the widening and propagation of existing macro-cracks. The graph of crack surface-to-volume ratio, λ over the strains, Ɛ was plotted to correlate with another research project which is working on the event of breakup upon impacting on ground of concrete specimens. Conclusively, propagation of macro-cracks was the main contributor to the increase of damage level across three different strain levels. The existence of micro-cracks was not significant to the overall crack density of the concrete specimens. Moreover, there is a linear relationship between the crack surface-to-volume ration, λ and the change in strain levels, Ɛ. Some limitations and recommendations were also provided to facilitate the future researchers on this project.