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Development of a general model of aggregate rebound for dry-mix shotcrete—(Part II)

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Abstract

A mechanical model previously developed is briefly described and linked to particle velocity versus size relationships experimentally obtained, allowing prediction of the energy of rebound of an aggregate particle during shooting. In addition, a failure criterion, based on the work necessary to debond a particle, is introduced in order to allow calculating the probability of rebound. The model shows good agreement with the experimental data in terms of predicting not only the overall rate of rebound but also its composition. This model provides a novel insight into the mechanisms involved in dry-mix shotcrete aggregate rebound and offers rational explanations to its dependence on aggregate size, cement content, shooting consistency and presence of silica fume.

Résumé

Un modèle mécanique précédemment élaboré est brièvement décrit et lié à la vitesse des particules par rapport à des relations de taille obtenues expérimentalement, permettant la prédiction de l'énergie de rebondissement d'une particule de granulat lors de sa projection. De plus, on introduit un critère de rupture, basé sur le travail nécessaire pour la décohésion d'une particule, ce qui permet de calculer la probabilité de rebondissement. Ce modèle s'accorde bien avec les données expérimentales en ce qui concerne la prédiction non seulement du taux global de rebondissement mais également de sa composition. Ce modèle fournit des éclaircissements nouveaux sur les mécanismes impliqués dans le rebondissement des granulats de béton à mélange sec projeté, et fournit des explications rationnelles concernant sa dépendance sur la taille des granulats, la teneur en ciment, la consistance de projection et la présence de fumée de silice.

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Abbreviations

a :

Radius of the contact area between the aggregate and the substrate

a * :

Maximum radius of the contact area between the aggregate and the substrate

A :

Mass percentage of aggregates in the mix

C :

Mass percentage of cement in the mix

σ and σ* :

Depth of penetration of the impactor and maximum depth of penetration

e :

Coefficient of restitution

ɛ pc :

Limit elastic strain of fresh concrete

г:

Aggregate diameter

ORR :

Overall rate of rebound by mass (rebounded material/total material shot)

p andp d :

Static and dynamic contact stress between the particle and the substrate

p i :

Percentage of aggregates from the combined gradation retained in the sieve sze i

r i andr c :

Rates of rebound for an individual sieve size i and cement rebound

R :

Aggregate radius

σ0 :

Adhesive strength of the aggregate to fresh shotcrete contact

V andV′:

Velocities of impact and rebound

V a :

Apparent volume dislocated (or penetrated) by the aggregate

W 1,W 2 andW D :

Impact, rebound and debonding energies

Y :

Yield stress of the substrate as determined from uniaxial stress conditions

References

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  2. Warner, J., ‘Understanding Shotcrete—The fundamentals’,Concrete International 17 (5 and 6) (1995) 59–64 and 37–41.

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  3. Armelin, H. S. and Banthia, N., ‘Mechanics of aggregate rebound in shotcrete—Part I’,Mater. Struct. 31 (206) (1998) 91–98.

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  4. Armelin, H. S., Banthia, N. and Mindess, S., ‘Kinematics of drymix shotcrete (submitted toThe ACI Materials Jourmal).

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  6. Armelin, H. S., Banthia, N., Morgan, D. R. and Steeves, C., ‘Rebound in dry-mix shotcrete’,ACI Concrete International 19 (9) (Sept. 1997) 54–60.

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Author information

Authors and Affiliations

  1. Civil Engineering Department, University of British Columbia, Vancouver, Canada

    Hugo S. Armelin Ph.D. Candidate

  2. Civil Engineering Department, University of British Columbia, Vancouver, Canada

    Nemkumar Banthia

Authors
  1. Hugo S. Armelin Ph.D. Candidate
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  2. Nemkumar Banthia
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Additional information

Editorial note Dr. N. Banthia is a RILEM Senior Member. He is a member of TC 148-SSC on “Test methods for the Strain Softening response of Concrete” and 162-TDF on “Test and Design methods for steel fibre reinforced concrete”.

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Armelin, H.S., Banthia, N. Development of a general model of aggregate rebound for dry-mix shotcrete—(Part II). Mat. Struct. 31, 195–202 (1998). https://doi.org/10.1007/BF02480400

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  • DOI: https://doi.org/10.1007/BF02480400

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