Drying shrinkage cracking characteristics of ultra-high-performance fibre reinforced concrete with expansive and shrinkage reducing agents

摘要

Ultra-high-performance fibre reinforced concrete (UHPFRC) exhibits remarkable compressive strength and ductility which, when applied to structural members, enable significant reduction of the cross-section. However, the very low water-to-binder ratio and high fineness admixture used for the fabrication of UHPFRC provoke large shrinkage strain at early age. If such shrinkage strain is restrained by the form or the internal reinforcement, UHPFRC may become highly vulnerable to the occurrence of shrinkage cracks caused by the subsequent reduction of the section. Therefore, this study intends to propose a solution for reducing the risk of shrinkage cracks in UHPFRC by mixing a combination of expansive and shrinkage reducing agents. The appropriateness of such a solution is estimated by evaluating the mechanical and restrained shrinkage behaviour. The experimental results show that the admixing of 7·5% of expansive agent and 1% of shrinkage-reducing agent reduces the total free shrinkage by approximately 80% after 1 day. The results of the drying shrinkage crack test indicate that the admixing of expansive and shrinkage reducing agents prevents the occurrence of shrinkage cracks. Accordingly, it appears that significant reduction of the risk of shrinkage cracking in UHPFRC can be achieved by increasing the section of the member or by adopting a combination of expansive and shrinkage reducing agents.