Silty loam (1900 kg/m3) (3)
0.32
3.7
3
Clayey loam (1940 kg/m ) (3)
1.6
Lightweight mineral loam (470 kg/m3) (3)
1.3
Lightweight mineral loam (700 kg/m3) (3)
2.8
Lightweight straw loam (450 kg/m3) (3)
2.4
Lightweight straw loam (850 kg/m3) (3)
3.6
Lightweight straw loam (1150 kg/m3) (3)
3.1
Spruce axial (2)
1.2
Spruce tangential (2)
0.2
Cement concrete (2290 kg/m3) (1)
0.27 0.13 0.15 0.20 0.26 0.29 0
0.2
0.4
(m3/m3)
1.8
Hollow brick (1165 kg/m3) (1)
8.9
Solid brick (1750 kg/m3) (1)
Shrinkage limit
The shrinkage limit (SL) is defined as the boundary between the semi-solid and solid states. It is the limit where shrinkage ceases to occur. With clayey soil, it can be identified optically when the dark colour of the humid mixture turns a lighter shade due to evaporation of water in the pores. Still, this is not an exact method of measurement.
25.1 0
2.19
10
20
30 2
Capillary action
0.5
w (kg/m h )
Water movement 2.19 Water absorption coefficient ‘w’ of loams in comparison with common building materials 2.20 Water absorption curves of loams
Water absorption w (kg/m2)
2.20
All materials with open porous structures like loam are able to store and transport water within their capillaries. The water, therefore, always travels from regions of higher humidity to regions of lower humidity. The capacity of water to respond to suction in this way is termed “capillarity” and the process of water transportation “capillary action.” The quantity of water (W) that can be absorbed over a given period of time is defined by the formula: W = w √t [kg/m2] where w is the water absorption coefficient measured in kg/m2h0.5 and t, the time in hours.
surface is operative. With loam samples, problems are caused by areas that swell and erode underwater over time. The BRL developed a special method to avoid this: to prevent the penetration of water from the sides as well as the swelling and deformation of the cube, samples are covered on all four sides by a glass-fibre reinforced polyester resin. To avoid the erosion of particles from the submerged surface, a filter paper is attached beneath and glued to the polyester resin sides. To preempt deformation of the weakened loam at the bottom during weighing, a 4-mm-thick sponge over an acrylic glass plate is placed underneath (see 2.18). A test with a baked brick sample comparing both methods showed that the BRL method reduced results by only 2%. The coefficient w of different loams tested along with the w-values of common building materials is listed in 2.19. Interestingly, the silty soil samples gave higher w-values than those of clayey soil. Surprisingly, comparison with baked bricks shows that loam has w-values that are smaller by a factor of 10. Water absorption in relation to time is also very interesting as shown in 2.20. Visible here is the amazing effect of a tremendous increase in absorption caused by adding small quantities of cement.
Determination of the water absorption
Time t (min) 1 2 3 4 5 6 7 8 9 10 11 12
Clayey loam + sand Clayey loam + 2% cement Clayey loam + 4% cement Clayey loam + 8% cement Lightweight mineral loam 650 Lightweight mineral loam 800 Lightweight straw loam 450 Lightweight straw loam 850 Lightweight straw loam 1150 Clayey loam Silty loam Sandy loam
coefficient
Capillary water capacity
According to the German standard DIN 52617, the water absorption coefficient (w) is obtained in the following way: a sample cube of loam is placed on a plane surface and immersed in water to a depth of about 3 mm, and its weight increase measured periodically. The coefficient (w) is then calculated by the formula:
The maximum amount of water that can be absorbed in comparison to the volume or mass of the sample is called “capillary water capacity” ([kg/m3] or [m3/m3]). This is an
w = W [kg/m2h0.5] √t where W is the increase in weight per unit surface area and t the time in hours elapsed. With this test, all four sides of the cube should be sealed so that no water enters from these surfaces, and only the bottom 27
Properties of earth
important value when considering the condensation phenomena in building components. Illustration 2.19 shows these values with the w-values. Water penetration test after Karsten
In Karsten’s water penetration test, a spherical glass container with a diameter of 30 mm and an attached measuring cylinder is fixed with silicon glue to the test sample so that the test surface in contact with the water is 3 cm2 (Karsten, 1983, see 2.21). The