The Frost and De-Icing Salt Resistance of Self-Compacting Concrete Containing Fly Ash

Project Number 215

Self-compacting concrete (SCC) shows the property that, until levelling is complete, it flows free of segregation, fills all cavities entirely and de-airs without any compacting work.

Concerning SCC numerous investigations have so far been conducted, but the resistance against the impact of freezing and de-icing salt has not sufficiently been investigated. At present, by order of VGB Powertech, the Institute of Building Materials Research (ibac) of the Aachen University is working on a research project regarding the resistance against the freezing and de-icing salt attack of vibrated concretes containing fly ash (project no. 203). In this project vibrated concretes made up according to exposure classes XF2 and XF4 (DIN EN 206-1 07.01 and DIN 1045-2 07.01) are investigated.

With regard to the resistance against the freezing and de-icing salt attack there is presently no technical experience concerning SCC that, depending on the mixture (powder-, combination- and viscosity agent type), features a powder content of more than 600 kg/m³ and thus a fly ash content of up to 350 kg/m³. As the first technical approvals of SCC containing fly ash have recently been made, questions arise regarding the durability of these concretes. Therefore, in addition to the current project "The influence of fly ash on the freezing and de-icing salt resistance of concrete", the resistance of significant SCC with a high content of fly ash against the freezing and de-icing salt attack is to be investigated.

In contrast to the vibrated concretes the following items have not sufficiently been investigated for SCC with a high fly ash content:

  • Interactions of the new generation of polycarboxylate-ether based superplasticizers with air entraining agents in mixtures containing fly ash.
  • Yielding of a sufficient air void stability and air pore content in SCC with a high fly ash content. The forming of micro air pores in concretes with a high consistency is impeded.
  • The influence of the storage conditions and the curing sensitivety of SCC with high amount of fly ash.
  • Long term behaviour of SCC with a high content of fly ash concerning the durability under attack of freezing and de-icing salt.

Thus, the results of this research project contribute towards obtaining confirmed knowledge, and fly ash SCC cannot be excluded from technical approvals for the exposure classes XF2 and XF4. Furthermore the results can be considered in the guideline "Self-Compacting Concrete" to DIN EN 206-1 07.01 and DIN 1045-2 07.01 of the German Commission for Structural Concrete (DAfStb).

In addition to the application of SCC in the precast element production, SCC with a high fly ash content is particularly suited for tunnel buildings because of the complexity of their production process. The resistance against freezing and de-icing salt attack is in this case of special interest.