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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Effects of High Accelerator Dosages on the Physical, Chemical, and Morphological Properties of a Hydrating Portland Cement Paste
Author(s): C. Maltese, C. Pistolesi, D. Salvioni, A. Bravo, F. Cella, and T. Cerulli
Publication: Special Publication
Appears on pages(s): 201-214
Keywords: alkali-free accelerators; dosage; flash setting; sprayed concrete.
Abstract:Alkali-free flash setting accelerators are widely used in the area of underground construction as they allow a very rapid hardening of cementitious
systems. These chemicals are commonly intermixed with an air flow into a fluid
concrete which is rapidly projected on the rock wall to form a consolidating shield of variable thickness.
The typical accelerator dosages range between 6 and 8 % by cement mass.
Nevertheless, sometimes, due to concrete fluidity loss, low air flow pressure, or poor homogenisation of the concrete/accelerator system, a very high local accelerator concentration could result in the sprayed mixture. Practical experiences point out that these conditions could cause significant strength loss of the sprayed layer, thus compromising the safety of the tunnelling operations. In order to elucidate the influence of high accelerator concentrations on hydrating cement, setting time and mechanical strength development of cement paste samples, admixed with several dosages of different alkali-free accelerators, were measured. Furthermore morphological (ESEM-FEG) and crystal-chemical (TG/DSC, XRD) analyses were also performed to clarify the reasons responsible for these reduced mechanical strengths.
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