Additives
In some industrialised countries, expanded clay is a low-cost and easily available additive. It has a bulk density of about 300 kg/m3, and is produced by burning loam in rotary ovens at temperatures up to 1200°C without any other additive for foaming. Foaming occurs due to the sudden heating, which causes the water of crystallisation and the pore water to evaporate, creating an expansion in the mass (similar to making pop-corn). The surface of these expanded clay balls melts and is sintered. Nearly all of the pores in these expanded clay balls are closed, and are therefore unsusceptible to water and frost. The equilibrium moisture content by volume is only 0.03%. Foamed glass has characteristics similar to expanded clay, but has a lower bulk density. It can be produced by recycling glass with additional foaming agents. Expanded perlite is produced from volcanic rock (found in Europe, on the Greek island of Milos and in Hungary). It contains 3% to 6% chemically bound water, and when it is heated up suddenly to 1000°C, this water evaporates and enlarges the former value 15 to 20-fold. The bulk density may be as low as 60 kg/m3, the k-value is 0.045 W/mK. The vapour diffusion resistance is about 2.7. The specific heat is 1000 J/kgK. With a material of bulk density 90 kg/m3, a k-value of 0.05 W/mK is achieved. The chemical composition of expanded perlite is: SiO2 (60-75%), Al2O3 (12-16%), Na2O (5-10%). Expanded lava is similar to expanded perlite of volcanic origin, except that its bulk density is higher. Pumice is a naturally porous stone that has already been “expanded” during its formation in a volcano. Its bulk density usually varies from 500 to 750 kg/m3. Mixing
While forced mixers are usually required to produce loam mixtures (see chapter 3, p. 37), lightweight mineral loam can be produced in an ordinary concrete mixer. There, aggregates can be placed in advance and 50
the loam slurry poured over it. The mix is ready in three to five minutes. The slurry needs to have a rich clay content and binding force. The production of loam slurry is described in chapter 3, p. 38. Grain size distribution
The grain size distribution of mineral aggregates affects the properties of lightweight mineral loam. For example, a density as low as 500 kg/m3 can be reached with expanded clay fractions of 8 to 16 mm diameter. The quantity of loam slurry has to be designed so that the volumes between aggregate particles are not completely filled, that is, the aggregates are only glued together at points of contact. This density of 500 kg/m3 can be reached if 2.5 parts of loam are added to 12 parts of expanded clay (8 to 16 mm). However, blocks of this mixture have a low edge and surface rigidity. A stronger mixture is obtained with 24 parts expanded clay (8 to 16 mm), 5 parts expanded clay (1 to 2 mm), and 5 to 7 parts loam. The density reached by this mixture will be 640 to 700 kg/m3. To achieve higher density, expanded clay fractions 4 to 8 mm can be chosen, adding enough loam to fill all spaces between the aggregates. In this case, it is advantageous to thin the loam with coarse sand. Handling
Lightweight mineral loam, unlike lightweight straw loam, can be poured or even pumped if the mix is chosen accordingly. The methods of preparing and handling this mixture are explained in greater detail in chapter 10. Thermal insulation
The thermal insulation properties of lightweight mineral loam depend mainly on its density and are equal to that of lightweight straw loam if the density is higher than 600 kg/m3. For mixtures below 600 kg/m3, the thermal insulation properties of lightweight mineral loams are somewhat better than those of lightweight straw loams, since straw has a higher equilibrium moisture content, and therefore more moisture, Improving the earth