Shrinkage and cracking of restrained ultra-high-performance fiber-reinforced concrete slabs at early age

In this study, the combined effect of shrinkage-reducing admixture (SRA) and expansive admixture (EA) on the shrinkage and cracking behaviors of restrained ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs was investigated. For this investigation, six full-scale UHPFRC slabs with three different thicknesses (h = 40, 60, and 80 mm) were fabricated using two different mixtures. Test results indicated that the combined use of 1% SRA and 7.5% EA is beneficial to improve the mechanical strengths and to reduce the free shrinkage strain of approximately 36-42% at 7 days. Regardless of SRA and EA contents, the slabs with the lowest thickness of 40 mm showed shrinkage cracking at a very early age, while the slabs with higher thicknesses of 60 and 80 mm showed no cracking during testing. However, the UHPFRC slab including 1% SRA and 7.5% EA exhibited a shallow crack with a very small maximum crack width of below 0.04 mm, while the slab without SRA and EA showed through cracks with a large maximum crack width of 0.2 mm.