Effect of the distribution of air entrained in superplasticized and high workability concrete for traffic areas

For obtaining a high degree of resistance to the action of frost and de-icing salts on concrete, it is essential to have an adequate content of air-filled micropores adjusted to the amount of fine-grained mortar in the mix. With QOI1ventional road concrete, correctly made, it can be presumed that if the minimum air voids content of the fresh concrete as specified in the standards and codes of practice is complied with and if an approved conventional air-entraining agent is used, the air entrainment criteria in the hardened concrete will be satisfied (spacing factor AF.0.20 mm, airfilled micropare content L 300 -1.5% by volume for 32 mm maximum aggregate particle size) and that this concrete will have a high frost/de-icing salt resistance. Concrete of high workability made with a superplasticizer (consistency K 3 according to Germanr standard DIN 1045, "flowing conclrete") must. also have a micropare content adjusted to the amount of finegrained mortat in order to achieve sufficiently high resistance. Widely varying information as to the frost/de-icing salt resistance of high-workability superplasticized concrete is given in the literature. Some authors report low frost/de-icing salt resistance of airentrained superplasticized concrete and assert that the superplasticizer adversely affects the entrainment criteria. Against this, other investigations showed air-entrained superplasticized concrete to have just as good a frost/de-icing salt resistance as that attained by corresponding air-entrained concrete without superplast:icizer. In road construction, especially when individual slabs have to be reinstated, the use of high-workability superplasticized concrete' can be advantageous because it requires less plant and equipment and is much simpler to work with. For this reason, the Research Institute of the Cement Industry, Düsseldorf, with financial support from the German Federal Minister for Transport, undertook research to clear up this problem. The results so far obtained are as follows: The nature and duration of the compaction applied to the concrete in the pressure vessel for determiniQ&the entrained air in superplasticized concrete have a decisive effect on the air content measured in the test. In general, the pores (air voids) in such concrete are somewhat larger than those in the corresponding initial concrete (non-superplasticized), so that, for equal air content, the superplasticized concrete has a somewhat larger spacing factor. With superplacticizers containing a powerfully acting antLfoam agent, it was not possible to attain a sufficiently high content of entrained air. However, such superplasticizers are not officially approved for use in concrete required to develop a high resistance to the action of frost and de-icing salts.