Stability

Stability Sand

CONCRETE

3 Parts coarse aggregate 2 Parts sand 1 Part cement to achieve a mix with a minimum of air spaces

Very large quantities of water the course of a season, so the

CONCRETE

3 Parts coarse aggregate 2 Parts sand 1 Part cement to achieve a mix with a minimum of air spaces

SAND MIXES

OR Washed, closely graded grains (90% between 0.1 and 0.6 mm) to give high proportion of macropores

have to be applied to composts over materials chosen must have very good stability. Fine sand and silt soils collapse too quickly and reduce the size of the pore spaces. Even clay crumbs, unless reinforced with high humus content, collapse quite quickly. The sizes of the components used must be selected carefully to ensure that they create macropores, but also so that the gaps between the larger particles are not subsequently filled in by smaller particles ('fines'). This is most easily achieved by using closely graded coarse particles. The reverse is achieved when combining many different-sized particles, as one would in mixing concrete, where the object is to minimize the air spaces as shown in Figure 22.2 .

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