An attempt to quantitatively and qualitatively differentiate the pore structure originating from air naturally present in hardened concretes and introduced by an air-entraining admixture

The new generation superplasitcizers affect air-entraining stability and, consequently, the air void characteristics in hardened concrete. As part of research 6 air entrained and 6 non air entrained concretes with a variable water-cement ratio liquefied, using modified polycarboxylates. The air void characteristics in hardened concretes were determined using the automatic RapidAir 457 system according to EN 480-11. Porosity structure parameters change with the w/c ratio and were described by mathematical relationships. Water-cement ratio does not affect the content of favourable pores from air entraining, however is responsible for entrapped air (above 300 µm) content. The most favourable pore structure was obtained in concrete, which has the optimal viscosity allowing to escape large pores during compaction and preventing coalescence of fine pores, as well as the superplasticizer content that does not cause additional air entraining.