Effects of Shrinkage-Reducing Admixtures, Mixing and Curing Conditions on the Shrinkage of an Ultra-High-Performance Fibre-Reinforced Concrete

Abstract of the technical paper / presentation presented at:
CSCE Annual Conference 2021
May 26-29, 2021

Prepared by:
Cédric Androuët, Canadian Nuclear Safety Commission
Jean-Philippe Charron, Polytechnique Montréal

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, which make them very interesting for various Civil Engineering applications. One drawback of UHPC is their very high autogenous shrinkage due to their very low water to binder ratio. Several options allow for the reduction of UHPC shrinkage, such as the use of Shrinkage Reducing Admixtures (SRA), Expansive Admixtures (EA) and Super Absorbent Polymers (SAP). Other factors related to curing conditions, such as humidity and temperature, also affect the autogenous shrinkage of UHPC. In this paper, 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 have been evaluated 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 shrinkage reductions 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 polyols-based SRA allowed for reductions of 69% and 63% of early-age and long-term shrinkages, respectively, while a powder polyols-based SRA provided a decrease of 47% and 35%, respectively.

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