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Investigation of alkali-reactive, sulphide-bearing and by-product aggregates

  • Oberholster R. E. 
  • Krüger J. E. 
Article

Abstract

Concretes which have expanded and cracked because of the alkali-aggregate reaction or because of sulphate attack caused by the use of sulphide-bearing aggregate both display white reaction products in the matrix and on fracture planes in the aggregates, but the reaction mechanism and reaction products are entirely different.

Petrographic microscopy clearly differentiates between potentially alkali-reactive siliceous and potentially expansive sulphidebearing aggregates and XRD and SEM both differentiate between the reaction products.

Burnt clay aggregate suffering from moisture expansion can cause concrete to expand and crack.

A test method employing a domestic pressure cooker for checking the presence of quicklime in by-product aggregate is mentioned.

Keywords

Quicklime Floor Slab Masonry Unit Burnt Clay Moisture Expansion 

Etude de l'alcali-reaction de granulats contenant des sulfures et de sousproduits

Résumé

Les bétons qui se dilatent et se fissurent à cause d'une réaction alcaline du granulat ou à cause d'une attaque par les sulfates causée par l'emploi de granulats contenant des sulfures montrent tous des produits de réaction blancs dans la matrice et sur les plans de fracture des granulats, bien que le mécanisme de réaction et les produits de réaction soient complètement différents.

La microscopie permet d'établir une distinction très nette entre les éléments siliceux potentiellement réactifs aux alcalis et les granulats contenant des sulfures potentiellement capables de dilatation; une diffraction X et une microscopie électronique permettent de différencier les produits de réaction.

Un granulat d'argile expansée qui se dilate sous l'action de l'humidité peut conduire le béton à se dilater et à se fissurer.

Cet article fait mention d'une méthode d'essai utilisant un auto-cuiseur pour contrôler la présence de chaux vive dans les granulats de sous-produits.

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References

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Copyright information

© International Association of Engineering Geology 1980

Authors and Affiliations

  • Oberholster R. E. 
    • 1
  • Krüger J. E. 
    • 1
  1. 1.National Building Research Institute-CSIRPretoriaSouth Africa

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