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Materials and Structures

, Volume 30, Issue 8, pp 473–479 | Cite as

Properties of fresh concrete incorporating a high volume of fly ash as partial fine sand replacement

  • Dan Ravina
Scientific Reports

Abstract

The use of fly ash in concrete is very common nowadays, mainly as a partial replacement for cement. However, the amount actually used in many countries is only between 15 to 25 percent. Disposal of unusable fly ash raises severe ecological problems and is quite expensive, not to mention the difficulty of finding dumping sites. Increased utilization of fly ash is thus, in many countries, in the national interest.

A research program was initiated on the utilization of large quantities of fly ash Class F of marginal-quality in concrete as partial fine-sand replacement. The present paper studies the effect of such replacement on the properties of fresh concrete. The mechanical properties of the hardened concrete will be presented in another paper.

The workability of most fly-ash mixtures was better than that of the reference mix (without fly ash). The water requirement of the fly-ash mixtures was either the same, or higher by about 9 percent, as compared with the reference mix. The rate and volume of bleeding were rather similar for the fly ash and the reference mixes. However, a significant reduction in bleeding by the fly-ash was found in the concrete mixtures with the chemical admixtures water reducer and retarder and high-range water reducer. Setting was delayed by the fly-ash, but the additional delay, that beyond the effect of the chemical admixture proper, was much less in the mixtures with the water reducer and retarder and negligible in the mixtures with the high-range water reducer.

Keywords

Portland Cement Water Requirement Fresh Concrete Chemical Admixture Final Setting Time 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Résumé

L’utilisation de cendres volantes dans le béton est courante de nos jours, principalement en remplacement partiel du ciment. Cependant, la quantité actuellement utilisée dans beaucoup de pays n’est que de 15 à 25%. Se débarrasser des cendres volantes inutilisables pose de sérieux problèmes écologiques et coûte cher, sans parler des difficultés à trouver des décharges. Une utilisation accrue des cendres volantes est donc d’intérêt national dans de nombreux pays.

Un programme de recherches a été entrepris sur l’utilisation de grandes quantités de cendres volantes de qualité marginale (classe F) en remplacement partiel de sable fin. Cet article étudie les effets de tels remplacements sur les propriétés du béton frais. Les propriétés mécaniques du béton durci seront présentées dans un autre article.

La maniabilité de la plupart des mélanges de cendres volantes était supérieure à celle du mélange de référence (sans cendres volantes). Les besoins en eau des mélanges aux cendres volantes étaient égales ou supérieures d’environ 9% au mélange de référence. Les taux et les volumes de ressuage étaient similaires pour les deux. Par contre, une diminution significative des ressuages par les cendres volantes a été constatée dans les mélanges ayant des adjuvants chimiques réducteurs d’eau-retardateurs et plastifiants-hauts réducteurs d’eau. Le temps de prise a été retardé par les cendres volantes, mais pour les mélanges avec adjuvants chimiques le retard, au-delà des effets des adjuvants eux-mêmes, était bien moindre avec le réducteur d’eau-retardateur et négligeable avec le plastifiant-haut réducteur d’eau.

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Copyright information

© RILEM 1997

Authors and Affiliations

  • Dan Ravina
    • 1
  1. 1.National Building Research Institute, TechnionHaifaIsrael

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