Non-Destructive Evaluation of Micro-Cracked SCC by Ultrasonic Waves

. Self-Compacting Concrete (SCC) is an effective, reliable and safer technology to cast-in-place concrete structures. However, the large amount of paste required to achieve its high flowability may increase drying shrinkage at early age, due to the undesirable effects of curing conditions, producing micro-cracking and damaging concrete members. When this happens, an evaluation of the hardened SCC is necessary and Non-destructive testing techniques (NDT) can be suitable. Among NDT, Ultrasonic pulses (US) have showed to be very useful due to its portability, easiness of application and sensitivity to changes in material microstructure, porosity and presence of defects. In order to evaluate the applicability of ultrasonic (US) waves to better understand the relations among composition, microstructure, properties, curing conditions and micro-cracking, an experimental program using transmission P-and S-waves was carried out on SCC with limestone filler (LF), microsilica (MS) and nanosilica (NS), set and hardened under different curing conditions: 10, 20 and 30 °C and 40 and 80 % relative humidity. Free shrinkage and double displacement restrained slabs were tested and cracking potential due to Early Age Shrinkage was assessed. Ultrasonic transmission time and wave amplitude of the raw US signal were measured and Ultrasonic pulse velocity (UPV) and attenuation coefficient were calculated. In addition, some physical and mechanical properties of cracked and un-cracked samples were measured. The aim of this study was to compare US parameters to hardened properties of cracked and un-cracked SCC. Correlations for SCC micro-cracking based on US parameters were identified, demonstrating the potential of using transmission US P-and S-waves as an evaluation technique for micro-damaged SCC.