Porosity determination of self-compacting concretes using combined forced saturation

The superplasticizers (SP) and high mineral addition contents used in Self-Compacting Concrete (SCC) can have an important effect on the porosity of the hardened mixtures, influencing their durability and mechanical strength. In this paper, a combination of forced vacuum and boiling saturation techniques is used to determine the influence of the composition of six SCC concrete mixtures on the open porosity. The mixtures differ by the type of addition (quartzite, fly ash and two types of limestone addition), the cement type (a CEM I 52.5 R HES Portland cement and a coarser CEM III/A 42.5 N LA blast furnace slag (BFS) cement) and the cement-to-powder ratio (C/P). A traditionally vibrated concrete (TC) mixture with an identical water-to-cement ratio (W/C) is tested as a reference. The tests are performed on one year old concrete core samples. The combination of the saturation techniques results in an improved, though somewhat lengthy open porosity determination. The results show a distinct influence of the addition type: a higher specific volume and Blaine fineness of the addition lead to significantly lower open porosities. This effect is most important for the fly ash addition, for which the pozzolanic reaction adds to the densification of the microstructure. Due to the old age of the samples, the expected higher porosity for the coarser BFS cement is not distinguishable: the secondary pozzolanic reaction has had the time to phase out any differences. The lower C/P logically yields higher porosities due to the smaller quantities of reactive materials and consequent higher W/C. Except for the latter, all SCC mixtures show reduced open porosities compared to the TC, which can be explained by the presence of the additions and the superplasticizer.