Use of Fly Ash in Air Entrained Concrete

Project Number 210

For the production of concrete with high frost-thaw-resistance special requirements regarding the air content in concrete are given in the German concrete standard (DIN 1045). The standard comprises requirements on the geometrical form of the air void system created by air entraining agents. With air entraining agents additional air bubbles are produced in the concrete matrix which will compensate the increase in volume of water during freezing.

It was observed that the entrainment and the statibility of the artificial air void system is influenced by a number of factors regarding concrete technology, -transport and -environment. There are comments in publications regarding the influence of additions on formation and stability of the air void system. These publications have not described the interaction of raw materials, additions and additives.

Within this project a database will be created for the assessment of the impact of fly ash on the stability of artificially entrained air voids in concrete. Further a contribution to the interaction of raw materials, additions and additives with respect to reduced stability of air voids in concrete will be given. The project consists in the following actions:

  1. Selection of favourable and unfavourable mixtures with respect to the formation and stability of air voids in concrete; Use of different types of cement (CEM I und CEM III/A) and air entraining agents based on different active substances.
  2. Determination of the amount of air entraining agents of cement/fly ash/mixtures needed to form stable air void systems by a special procedure on binder suspensions, called "foam-index-test" (figure). This test is useful for the estimation of the amount of air entraining agents and can be used for the internal production control.
  3. Determination of the air content in mortars and concretes with and without fly ash with different air entraining agents.
  4. Determination of the most important granulometric, physical and chemical properties of the raw materials in order to evaluate correlations between air content or amount of air entraining agent and the stability of the air void system.