Pore- and density-related characteristics of a lightweight aggregate

Porous lightweight aggregates are frequently used in civil engineering to produce low-density concrete. As individual particles contain air voids (micropores), when evaluating particle assemblies it is necessary to consider both micro- and macro-porosity. Micropores are important when assessing water absorbency as they affect cement–water ratios and can be used to store self-healing admixtures/agents for slow release during curing. The physical characteristics of ‘Lytag’ are investigated, namely particle density, porosity, water absorption and dry density. The apparent particle density, ρa, of Lytag particles at their manufactured size and shape (typically 4–14 mm) is about 2.00 t/m3 because of the presence of micropores. This value increases to a maximum, intrinsic, ρs, value of about 2.62 t/m3 as particle size is progressively reduced through grinding to minimise the effects of micropores. With apparent and intrinsic density values known, micro- and macro-pore porosity can be established. Water absorption, measured with time, under negative, atmospheric and elevated pressures, is compared with theoretical values. The role of capillarity on water absorption is assessed conceptually using the Young–Laplace formulation. Combined, these characteristics provide insights into the time-dependent absorbency capacity of lightweight porous particles, which is relevant when used in concrete, filtration beds and backfill.