|M.Sc Student||Aziz Shany|
|Subject||Sensory Stainless-Steel Yarns for Detecting Water|
Infiltration through Cracks in Textile Reinforced
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Yiska Goldfeld|
Textile reinforced concrete, or TRC, is a type of reinforced concrete which uses thin high strength filaments as reinforcement. TRC elements are more sensitive to cracking than conventional reinforced concrete elements. Crack widths of up to 100 μm are defined as micro cracks, and are considered within the serviceability limit state design. Wider than 100 μm are defined as macro cracks and can indicate a structural damage. In water containing elements such as water tanks or pipes, a crack may cause leakage in to or out of the element. When TRC elements are used for water containing or moving, these phenomena unite and create an opportunity to detect the cracking using the water penetration.
The sensing concept in based on the electrical conductance of water. Two adjacent fiberglass rovings in the textile reinforcement mesh are replaced with stainless steel rovings during the standard manufacturing process. The stainless-steel fibers are connected to an electrical system that supplies current and measures the electrical properties of the circuit. Once cracking occurs, water penetration creates contact with the stainless-steel filaments along the crack width and allows current to flow due to the conductive properties of the water. This accordingly affect the electrical measurement readings to change. The current study aims to characterize the correlation between the change in the electrical behavior of the electrical circuit upon the contact of water with the fibers, and the wetted crack width. This correlation is then used to distinguish between micro and macro cracks by the water penetration to them, thus enabling the detection of structural damages as they form.
The study is based on experimental investigation to suggest and characterize a monitoring method. The study is divided into two main parts. First, the electrical behavior of water contact between two bare fibers was examined. This examination allows a simpler, more sterile case of the fibers and the proposed electrical setup. The filaments were submerged in water, in a controlled monitored manner, to create controlled changes in length of the water contact with the filaments. In the second part, the study case was wetting of cracks in TRC elements. Three textile reinforced concrete beams with different section thicknesses were used, and a controlled monotonic loading experiment was conducted on all of them. The loading allowed a varied cracking pattern to develop, one which includes both micro and macro cracks.
The study included examining the electrical behavior of water infiltration to different cracking patterns, and yielded several conclusions. In the case of bare rovings, an investigation was performed to select an adequate electrical scheme for the monitoring purposes, and Definable correlations were found between changes of the rovings' wetting length and the electrical changes measured. The examination demonstrated an ability to differentiate between wetting of micro cracks and macro cracks, based on the relative change in resistivity upon wetting. And finally, based on the investigation of the electrical mechanism of water infiltration to cracks in a TRC element, the study includes several conclusions and further research suggestions.