Abstract
Ultra-High Performance Concretes (UHPC) are cement-based materials with a very low water-to-binder ratio that present a very-high compressive strength, high tensile strength and ductility as well as excellent durability, making them very interesting for various civil engineering applications. However, one drawback of UHPC is their pretty high autogenous shrinkage stemming from their very low water-to-binder ratio. There are several options to reduce UHPC shrinkage, such as the use of fibers (steel fibers, polypropylene fibers, wollastonite microfibers), shrinkage-reducing admixtures (SRA), expansive admixtures (EA), saturated lightweight aggregates (SLWA) and superabsorbent polymers (SAP). Other factors related to curing conditions, such as humidity and temperature, also affect the shrinkage of UHPC. The aim of this paper is to investigate the impact of various SRA, different mixing and curing conditions (low to moderate mixing temperatures, moderate to high relative humidity and water immersion) as well as different curing starting times and durations on the shrinkage of UHPC. The major importance of the initial mixing and curing conditions has been clearly demonstrated. It was shown that the shrinkage of the UHPC was reduced by more than 20% at early-age and long-term when the fresh UHPC temperature was closer to 20 °C. In addition, curing by water immersion led to drastic reductions in shrinkage of up to 65% and 30% at early-age and long-term, respectively, in comparison to a 20% reduction for fog curing at early-age. Finally, utilization of a liquid polyol-based SRA allowed for reductions of 69% and 63% of early-age and long-term shrinkages, respectively, while a powder polyol-based SRA provided a decrease of 47% and 35%, respectively.
Highlights
Ultra High Performance Concrete (UHPC), characterized by a very high compressive strength, high tensile strength and ductility, with a very low water-to-binder ratio, is becoming more and more prevalent in the construction field [1]
Using shrinkage-reducing admixtures (SRA) or varying the mixing temperatures did not have any significant impact on the fresh state properties nor on the UHPC compressive strength measured at 28 days
Various options for mitigating earlyage shrinkage of UHPC have been considered in this research project, including the use of SRA as well as various mixing temperatures and curing conditions
Summary
Ultra High Performance Concrete (UHPC), characterized by a very high compressive strength, high tensile strength and ductility, with a very low water-to-binder ratio, is becoming more and more prevalent in the construction field [1]. Because of its very low water-to-binder ratio and very high quantity of binder, use of UHPC can be limited by its shrinkage behavior. High shrinkage is generally observed in UHPC specimens, resulting in a risk of cracking and deterioration [7]. Causing a concern to the dimension stability of UHPC elements, earlyage shrinkage (especially when restrained) might generate micro cracks which, along with the aging of concrete, increase vulnerability of UHPC structures to substance penetration, leading to further deterioration [7,9]
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