CRC 528-B5: Bond & CRC 528-B1: Load bearing behaviour of TRC
Table of contents
Project data
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Titel | Title |
Link to the project website
http://sfb528.tu-dresden.de/b5/index.html
Report in the yearbook 2010
Small Wave – Great Effect
Wave in the yarn.
The unit- and biaxial load-bearing behaviour of textile reinforced concrete (TRC) had to be examined to use TRC as an efficient strengthening method for reinforced concrete elements. In some tensile tests with carbon reinforced specimens a distinct separation of the concrete cover occurred before they were destroyed. This process called delamination was not noticed in similar tests with specimens reinforced with textiles made of alkali-resistant glass. The question was: why is the load-bearing behaviour of the textiles different despite nearly identical geometry and fabrication?
The wave in the yarn
During the textile fabrication a certain undulation of the yarns could not be avoided. The textiles are produced from two layers of yarns that are stitched together. At the points of intersection the individual yarn axes do not lie in the middle of the textiles. In between they do lie in the middle and therefore they are wavy. Under tensile loads these yarns are pulled straight. But if the textiles are embedded in fine concrete, the matrix constrains the pulling straight of the yarns. That’s why forces affect the concrete and the textiles in the cross direction. With increasing tensile loads on the yarns these deviation forces are rising and this can even lead to a spall of the concrete cover delamination occurs.
The strength makes the difference
The concrete transfers a part of the tensile loads acting on the composite material until it reaches its tensile strength. Then the concrete begins to crack and the textile reinforcement is more and more involved into the load transfer. Once the crack formation is completed the textile assumes the tensile loads on it’s own until its maximum strength is also reached. Then the specimen fails. The deflection forces in specimens with textiles made of alkali-resistant glass don’t become large enough to spall the concrete cover before the specimen fails. The strength of carbon is approximately 2.5 times higher than of alkali-resistant glass. Consequently the loads from the undulation of the yarns can rise until these loads can lead to delamination.
The spalling of the concrete cover is naturally not a desired behaviour of TRC. Because of the described effect the fabrication of textiles were further developed and the undulation of the yarns – and also the risk of delamination – was significantly reduced.