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Title: Impact of Chemical Admixtures on Time-Dependent Workability and Rheological Properties of Ultra-High- Performance Concrete

Author(s): Flavia Mendonca and Jiong Hu

Publication: Materials Journal

Volume: 118

Issue: 6

Appears on pages(s): 383-394

Keywords: admixture; consolidation; flow; fresh properties; rheology; stability; time; ultra-high-performance concrete (UHPC)

Date: 11/1/2021

Abstract:
Ultra-high-performance concrete (UHPC) is a new class of cementitious material with unique characteristics, including self-consolidation, and excellent mechanical and durability properties. To achieve the desired properties, a very dense internal structure and a very low water-binder ratio (w/b) are necessary. Due to the very different mixture design compared to conventional concrete, it is critical to incorporate different types of chemical admixtures to achieve appropriate fresh concrete behavior of UHPC. To ensure the successful placement of UHPC, it is important to have a good understanding of the workability and rheological characteristics of UHPC with different types and dosages of chemical admixtures. This paper presents a detailed study of the impact of high-range water reducer, workability-retaining admixture, and anti-foaming admixture on the workability and rheological characteristics over different mixture elapsed times. Besides the flowability, both Bingham and modified Bingham models were used to obtain key rheological parameters, including yield stress, viscosity, and thixotropy. Furthermore, the authors developed stability indexes to assess the fiber stability of UHPC in both fresh and hardened states. Based on the experimental results, the paper presented suggested criteria to ensure appropriate flowability and fiber stability for UHPC placement.


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