Shard characteristics
Clay materials for buildings. Properties and products

Before talking about products, let's talk about the properties of ceramic shards. Ceramic shards are agglomerates of grains of different origins:

• residual crystals of quartz, potassium feldspars or soda-lime feldspars (plagioclase) and mica from the original rocks;

• new small crystals formed during firing: quartz, mullite, hematite, calco-aluminum silicates (e.g. pyroxene, gehlenite).

These crystals are bound together by the glassy matrix of the melting elements. The theoretical density of this material is around 2,600-2,750 kg/m³ (the density of quartz is 2,650 kg/m³, but that of hematite is 5,250 kg/m³).

In practice, however, this material is porous over a wide range: porosity varies between 15 and 48%, although the most common porosity is around 35%. Pore diameters range from 0.1 to 3 µm, most...