Building with Earth: Design and Technology of a Sustainable Architecture

35 Properties of earth

pH-value

Clayey soil is usually basic, with pH-values

between 7 and 8.5. Nowadays, due to acid

rain, earth dug from industrial areas may be

slightly acidic just below the topsoil. The

basic state usually prevents fungus growth

(the favourable pH-value for fungus usually

lies between 6.5 and 4.5).

Radioactivity

Measurements of the radiation of beta and

gamma rays show that loam has values no

higher on average than concrete or baked

bricks. On the contrary, some bricks tested

by this author exhibited much more radia-

tion, probably caused by additives like fly

ash or blast furnace slag. Much more impor-

tant than the beta and gamma rays are the

alpha rays emitted by the radioactive gas

radon and its short-lived decay products.

The “soft” rays cannot penetrate the human

body as they are absorbed by the skin, but

can be inhaled by breathing and, therefore,

may cause lung cancer. The following table

shows the exhalation rate of radon given

by the OECD (1979) for Germany, measured

in m becquerel/kg h.

Natural gypsum

Cement

Sand

Baked clay bricks

Lime-sand bricks

Porous concrete

This shows that a clay brick from a clayey

soil discharges very little radon.

radiation Shelter against high-frequency electromagnetic

tromagnetic radiation

Illustration 2.43shows the differing degrees

of effectiveness of solid building materials in

screening (reducing) high-frequency electro-

magnetic radiation, as measured at the Uni-

versity of the Federal Armed Forces at

Munich.

In the area of 2 gigahertz frequencies at

which most cellular (mobile) phones are

working, a 24-cm-thick mud brick wall

creates a reduction of 24 dB (decibels),

whereas an equal tick wall of a lime-sand

stone only absorbs 7 dB.

Samples

Loam mortars

Abrasion in g

2.41

2.43

2.39 Field test to derive

the bond strength of

mud mortar

2.40 Apparatus to test

the resistance against

abrasion, BRL

2.41 Amount of abrasion

of different earth plasters

2.42 Apparatus to mea-

sure the strength of

corners against dynamic

impacts

2.43 Shelter effect of dif-

ferent building materials

against high-frequency

electromagnetic radiation

1 Vegetation roof with 16 cm of substrate, 20 cm

thermal insulation, 24 cm green bricks (earth blocks)

2 Vegetation roof as in 1, without green bricks

3 24 cm green bricks (1,600 kg/m^3 , 15 cm loam plaster)

4 2 cm lime plaster, 25 cm lightweight loam (800 kg/m^3 ),

1.5 cm lime plaster

5 10 cm lightweight loam block (1,400 kg/m^3 )

6 17.5 cm porous concrete (500 kg/m^3 )

7 24 cm hollow bricks (1,200 kg/m^3 )

8 24 cm lime-sand-stone (1,800 kg/m^3 )

9 1.3 cm tile

10 aluminium sunshade element

11 metal insect grid (1x1 mm mash)

12 double glazing, gold film covered

mobile network, 900 MHzGPS satellite navigationmobile network, 1760 MHzmobile network, 1950/2150 MHzradarradio link systemradio link systemradio link system

Frequency in GHz

Cushioning effect in dB / %

Reduction of high-frequency electromagnetic radiation

0.5 1.0 1.5 2.0 2.5 3.0 3.5

0.7

0.2

0.3

0.1

0.1

0.0

0.3

0.3

0.5

2.3

2.4

1.3

1.5

3.2

2.5

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

99.9999%^60

99.999%^50

99.99%^40

99.9%^30

99%^20

90%^10

0

25.2

57.6

54.0

5.0

13.3

18.0