Effect of admixtures and PVA fiber on the mechanical properties of high strength cementitious grout

In order to seal the joints between the ultra-high-performance concrete (UHPC) permanent formworks, the high strength cementitious grout (HSCG) was investigated in the presented work. The water reducer content and the water to binding materials (W/B) ratio of the grout were modified to meet the grout fluidity requirement, and then the effects of three commonly used admixtures (i.e., hydrophobic powders (HP), expansive agents (EA), and redispersible polymer powders (RPP)) and PVA fibers on the compressive, tensile, flexural, and adhesive strengths of the HSCG were investigated. In addition to the normal condition, the adhesive strengths under the soaked condition and the thermal aging condition were also evaluated. The HP worsen all strength index, especially the adhesive strength, while the appropriate utilization of the EA could improve all strength indexes by more than 12%. With the addition of RPP, the adhesive strengths under the soaked and thermal aging conditions could be significantly enhanced by over 85%. The PVA fiber could also enhance the normal adhesive strength by 20.5%. Based on the experimental results, the recommended contents of the EA, RPP, and PVA fibers were 6%, 2%, and 0.3%, respectively, while the HP was not suggested for the HSCG due to its adverse effect on the mechanical performances.