Effects of Setting Regulators on the Efficiency of an Inorganic Acid Based Alkali-free Accelerator Reacting with a Portland Cement

Today, in the field of underground construction, alkali-free accelerators are commonly used during tunnel excavation to allow flash concrete setting. In this way, the cementitious sprayed material can firmly bond to tunnel walls, controlling the convergence (the tendency of the section to squeeze). Their efficiency may be related to parameters such as cement type, setting regulator, concrete composition, or working temperature. Nevertheless, the influence of such factors on accelerator performance has not yet been clarified. Accelerator efficacy is evaluated by actual spraying tests at the job site or, when only lab equipment is available, by measuring the final setting times of cement systems admixed with the accelerator. Several alkali-free flash setting admixtures are available on the market. They can be divided into 2 main categories both containing aluminium sulphate complexes stabilized either by inorganic or organic acids. In this paper, the influence of different setting regulators on the performances of an inorganic acid based alkali-free accelerator was analyzed. Portland cement samples were obtained by mixing clinker with gypsum, α-hemihydrate, β-hemihydrate, or anhydrite. The setting regulator instantaneous dissolution rates were evaluated through conductivity measurements. The setting time of cement pastes with and without the accelerator was measured. It was found that the shorter the final setting time (therefore the more efficient is the accelerator) the lower the setting regulator instantaneous dissolution rate. In order to understand this phenomenon, a comparison was performed between accelerated cement paste samples containing the setting regulator with the highest (β-hemihydrate) and the lowest instantaneous dissolution rate (anhydrite). The analytical work included morphological (Environmental Scanning Electron Microscopy–Field Emission Gun—ESEM–FEG), crystal–chemical (X-Ray Powder Diffraction—XRD), physical–chemical (hydration temperature profile), and chemical (Induced Coupled Plasma–Atomic Emission Spectroscopy—ICP/AES) evaluations. The results revealed significant morphological differences among the investigated samples.

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  • Supplemental Notes:
    • Abstract reprinted with permission from Elsevier
  • Authors:
    • Maltese, C
    • Pistolesi, C
    • Bravo, A
    • Cella, F
    • Cerulli, T
    • Salvioni, D
  • Publication Date: 2007-4

Language

  • English

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  • Accession Number: 01049838
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 22 2007 5:00PM