Influence of limestone filler and viscosity-modifying admixture on the porous structure of self-compacting concrete

The objective of this experimental work is to study porosity in self-compacting concrete (SCC) made without adding limestone filler, comparing the results with other SCC and with normally-vibrated concrete (NVC). Several types of concrete were made, keeping the w/c ratio constant. The results show that the air content in SCC depends on the flowability and viscosity of the material, putting a forward an expression to estimate the air content in accordance with these two parameters. SCC shows a finer and more tortuous porous structure than NVC, leading to lower permeability to water under pressure. Nevertheless, in the absence of pressure, when water penetrates by capillary action, the results obtained from the different types of concrete were very similar, with differences below 3.5%. This is due to the fact that the content of pores over 0.5 μm is practically the same in SCC and NVC, but for smaller pore sizes, which are therefore only accessed when water under pressure is applied, the differences in porosity between the different samples is more pronounced. On the other hand, it was observed that the use of more fluid mixtures permitted more impermeable concrete to be obtained. The use of viscosity-modifying admixture on SCC as a replacement for limestone filler does not affect the total volume of pores, but generates a slightly more coarse porous microstructure, thereby leading to concretes in which water penetration depth under pressure is a little higher (around 4 mm).

► We study porosity in SCC made without adding limestone filler.
► The air content in SCC depends on the flowability and viscosity of the material.
► SCC have a finer pore structure than NVC but content of pores over 0.5 μm is similar.
► More fluid mixtures permitted more impermeable concrete to be obtained.
► VMA in SCC as a replacement for filler produces a coarser porous microstructure.