Soil materials

'Soil materials' is a collective name for fine-particled materials that have originated from mineral or organic, decomposed products from animals and plants. Seen in the larger lifecycle, these eventually return to a solid form such as rock. During this process, soil materials with a large organic content can form the basis for the creation of coal or oil, which are mostly plant deposits crushed geologically over a very long timespan. Within these states of continuous degradation and regeneration, a wide spectrum of raw materials has been used for building construction throughout history (Table 8.1).

As well as being the starting point for all of the Earth's food production, soil materials have many different uses in the building process: sand and gravel as aggregate in concrete, clay mixed with earth which can be rammed for solid earth construction and clay for production of bricks, ceramic tiles and expanded clay pellets (Table 8.2).

In contrast to minerals, soil materials are defined by their physical properties rather than their chemical properties. Physical properties include grain size and form (see Table 8.3).

Different types of aggregates derive their names from the predominant size of material they contain - a minimum of 60%. The remaining

Table 8.1 Soil materials in the building industry

Material

Areas of use

Clays and silts

Earth constructions; plasters; claddings and flooring; production of bricks, ceramics and expanded clay pellets

Sand

Sound insulation in floors; aggregate in concretes, plasters and mortars

Gravel

Aggregate in concretes

Table 8.2 Basic materials

Material

Main constituents

Areas of use

Bricks, roof tiles

clay, sand, slag, fly ash, lime, fossil meal

Structures; wall cladding; flooring; roof covering; moisture buffering

Ceramic tiles

clay, kaolin, pigments, glazing

Flooring; wall cladding

Expanded clay pellets

Loose materials containing clay

Thermal insulation; sound insulation; aggregate in lightweight concrete products

Table 8.3 Soils defined by grain size

Material

Grain size (mm)

Clay

Less than 0.002

Silt

0.002-0.06

Sand

0.06-2.00

Gravel

2.00-64.00

percentage, if more than 20%, is used to define more closely the quality of that material; for example, 'gravelly sand'. They can have a quite pure mineral content, or they can be mixed with organic substances such as peat and mud, mostly mould and plant material, known as humus. Soil material that is well-suited to cultivation is not suitable for building, as it contains organisms and humus acids which have negative effects on both earth construction and concrete.

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