Usefulness of Mercury Porosimetry to Assess the Porosity of Cement Composites with the Addition of Aerogel Particles

Today’s need to reduce the energy consumption of buildings makes it necessary to search for new material solutions. Such materials are, for example, cement composites with various types of additives, such as foamed-polystyrene granulates, cenospheres or aerogels, which are intended to reduce the composite’s thermal conductivity. The introduction of such additives to concrete composites may be an issue for the assessment of microstructural properties of these materials. This is because the microstructure of concrete and additives are completely different. This problem exist in the mercury porosimetry of cement composites with the addition of aerogel granulate. The Washburn equation, traditionally used in mercury porosimetry, gives false porosity results when applied to aerogels. This paper presents the problems and the method of determining the total porosity and integral and log-differential graphs for cement composites with addition of aerogels. Two types of composites based on lightweight aggregates were tested: expanded clay and sintered fly ash aggregate. In both variants, concrete was made with the addition of aerogel granulate, which accounts for 20% of the total composite volume. Also reference concretes of the same composition, but without aerogel were prepared. The paper presents a method of combining the results of mercury porosimetry using the classic Washburn equation, which is suitable for cement-based materials, and the Pirard equation showing the relationship between the pressure of injected mercury and the diameter of pores in compressed hyperporous materials. The study also provides cumulative and log-differential diagrams of pore distribution in tested concrete with aerogel addition. The values of thermal conductivity in dry state and the compression strength average values for composites after 28 days of curing are also presented.