Lightweight aggregate modified with sewage sludge
The water absorptivity of the aggregates reaches 15.9% and is probably a consequence of the open porosity of the grains and heterogeneity of the grain shape. The saturation obtained is comparable to water absorptiveness of the commercial aggregates Lytag, which is equal to 17.55%. The apparent particle density of the Lytag aggregates is equal to 1340 kg/m3 and bulk density-730 kg/m3. The parameters obtained are slightly higher than the parameters of lightweight aggregates with sewage sludge.
The absorptivity of Aardelite aggregates produced from industrial waste and carbon dioxide is 21.2% and the apparent particle density is slightly higher and reaches the value of 2100 kg/m3 . The generally acceptable water absorption capacity based on 24-h soaking in water is lower than 20%. Therefore, lightweight aggregates produced with sewage sludge fulfill the above requirements. The resistance to crushing of the examined aggregates is 34.7%, and its relatively low value is probably a consequence of the high porosity of the aggregates and the presence of a glassy layer both inside the aggregates and at their surface, which leads to a decrease in the material strength.
Frost resistance does not exceed 1.0%. After examination, the aggregate grains do not show any cracks. Lightweight aggregates can be treated as the F1 category because the percentage mass loss is lower than the required maximum 1% for this category, according to the standard. Hence, they fulfill the frost resistance requirements.
The aggregate porosity is 68%. This value provides suitable moisture absorptivity, high water vapor diffusivity, but also suitable thermal insulation. With its advantages, the lightweight aggregate obtained should be successfully used in energy-saving construction, for example in production of lightweight concretes and wall blocks, as well as thermal insulation for floors or roofs.
The leachability measurements of chromium, cadmium, copper, nickel, lead, and zinc in water extracts showed that the presence of metals is much lower than the tolerable values (Table 3). This means that it is possible to use the tested aggregate with sewage sludge as a valuable ecological building material. Aggregates supplemented with sewage sludge additives, burnt at the temperature of 1150 °C, permanently bind the cations of heavy metals inside their structure.
In the mineral compound of the lightweight aggregate burnt at the temperature of 1150 °C, the glassy phase is present and is recognized by the characteristic rise in the background of the diffractogram within the angular extent 15°–30° (2 Theta) and mullite (d = 5.41, 3.43, 3.39, 2.88 Å). The mineral composition of the aggregates is supplemented by hematite (d = 2.70, 2.51 Å).
Suchorab, Z.; Barnat-Hunek, D.; Franus, M.; Łagód, G. Mechanical and Physical Properties of Hydrophobized Lightweight Aggregate Concrete with Sewage Sludge. Materials 2016, 9, 317.
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