Influence of Superplasticizer on Porosity Structures in Hardened Concretes

One of the criteria used to achieve frost resistant concrete is to obtain appropriate parameters of porosity structure in the hardened concrete. Polish requirements in this regard are not defined by standards. There is only a requirement in terms of the Spacing Factor for air-entraining admixtures contained in EN 934-2. The standard EN 206 to ensure frost resistance of concretes requires in exposure classes XF2-XF4 air content in fresh concretes at least 4% without verification of the porosity structure in the hardened concrete. The technical specifications for paving concretes and bridges usually contain requirements for parameters of porosity structures based on international requirements. Air entraining process of concrete mixtures is complex and depends on many parameters. The analysis of porosity structures in hardened concretes, despite the required frost resistance of concrete, often do not give satisfactory results. Analysis of the results indicates that the reason is inadequate pores sizes in the concretes. Thus, an attempt of explanation of influences of one of the parameters affecting the air entraining process – consistencyof concrete mixes (quantity of superplasticizer) on the porosity structure in the hardened concrete. The research programme was performed on eight series of air-entraining and non-air-entraining concretes with a variable content of superplasticizer. The basic composition and air-entraining admixtures content in air-entraining concrete mixtures were constant. The results showed that with the increase of the content of superplasticizer (with increasing fluidity) air content decreases and the pores sizes changed.