Acta Polytechnica CTU Proceedings


doi:10.14311/APP.2017.13.0085
Acta Polytechnica CTU Proceedings 13:85–88, 2017 © Czech Technical University in Prague, 2017

available online at http://ojs.cvut.cz/ojs/index.php/app

WATER ABSORPTION CAPACITY COEFFICIENT AND MASS
MOISTURE OF RAMMED EARTH MATERIAL

Barbora Mužíková∗, Tereza Otcovská, Pavel Padevět

Czech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7, 166 29 Prague 6, Czech
Republic

∗ corresponding author: barbora.muzikova@fsv.cvut.cz

Abstract. This article presents the development of mass moisture of rammed earth material and
determines the water absorption capacity coefficient for rammed earth with illite-kaoline clay. Specimens
of two prescriptions were rammed in the moulds. They were settled in the box with soft foam that was
moistened. The level of moistening was kept constant. The specimens were regularly measured and
weighted. Two measuerements were carried out – one of montmorillonite clay during 13 days and one
of illite-kaoline clay during three hours. The development of moisture increase was captured and the
water absorption capacity coefficient for illite-kaoline clay was determined and compared to coefficients
of common building materials.

Keywords: Rammed earth, illite-kaoline clay, mass wetness, water absorption capacity coefficient.

1. Introduction
This article presents earth material as a modern build-
ing material based on the long history of using, but
in last centuries it was replaced by modern mate-
rials. The material characteristics were never fully
researched due to the replacement. The demand for
the earth material is increasing nowadays following the
principles of sustainable buildings development [1, 2].
The main advantages of using earth as a building

material are good air humidity balance, lower costs for
material and construction, and also the fact that the
earth based material has a positive effect on human
health. Rammed earth is accessible, environmentally
friendly and suitable for low-cost building in person.
According to the sustainable buildings development
not only the mechanical properties are important in
the structure design. The quality of building material
is also given by economic and socio-cultural crite-
ria. For example the rammed earth primary energy
consumption connected with production of building
material is about 44 kWh/m3. This is 18× less than
for prefabricated concrete material [3–6]. The increas-
ing interest in unburned earth material can be seen in
the sales of unburned clay bricks in portfolio of Heluz
company shown in Table 1 [7].
The mechanical properties of the unburned earth

depend mainly on the composition and the method
of processing. The basic methods of using earth are
mudwalls, rammed earth, earth bricks, earth infill
in a timber frame construction etc. The material
which the research is focusing on is rammed earth.
Rammed earth walls are constructed by the compact-
ing (ramming) of moistened subsoil into place between
temporary framemwork panels.

The process of building is shown in Figure 1. First
of all, the reinforced plywood framework is built and
then the first layer moist earth (mixture of sand, gravel

Year Sold unburned bricks [pcs]

2010 700
2011 8,600
2012 19,800
2013 21,500

Table 1. Number of sold unfired bricks of Heluz
company [7].

Figure 1. The process of building rammed earth wall.

and clay) is filled in. Secondly, the layer of moist
earth is compressed by a pneumatic backfill tamper.
Thirdly, next layer of moist earth is added and then
succesive layers of moist earth are added and com-
pressed. Finally, the framework is removed leaving
the rammed earth wall with visible layers of com-
pacted earth. When dried, the result is a dense, hard
monolithic wall [4–6].

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B. Mužíková, T. Otcovská, P. Padevět Acta Polytechnica CTU Proceedings

Figure 2. The production of rammed earth specimens.

2. Testing of unfired earth
material

2.1. Rammed earth and water
The rammed earth material is considered for building
bearing walls of construction so that the material is
often exposed to rain and moisture of external condi-
tions. All materials with open porous structures like
loam are able to store and transport water within their
capillaries. Water always travels from regions of higher
humidity to regions of lower humidity. The value of
the water absorption coefficient w is known for com-
mon building materials, some of them are shown in
Table 2. In the research the value for rammed earth
with illite-kaoline clay was searched for to be compared
with values of other building materials. The premise
was that the value of the water absorption coefficient
w for rammed earth would be higher than for common
building materials.

2.2. Preparing material
Prescriptions for the specimens were designed of clay,
sand and water. There were two prescriptions GEM I
and GEM II of montmorillonite clay and AGL I and
AGL II of illitic-kaolinite clay. Prescriptions I and
II differed in the sand/clay ratio. The amount of
the components was expressed by the weight percent.
The amount of water was settled as a water/clay ratio,
same at both prescriptions, all prescriptions are shown
in Table 3.

Figure 3. Specimens in the climatic chamber.

Material
w ρ

[kg/m2
√

hour] [kg/m3]

Silty Loam 3.7 1900
Clayer Loam 1.6 1940
Cement Concrete 1.8 2290
Hollow Brick 8.9 1165
Solid Brick 25.1 1750

Table 2. Water Absorption Capacity Coefficient of
common building materials [5].

First of all, the sand was well mixed with two thirds
of water. Secondly, the clay and the rest of water was
added. It was mingled by a drilling machine with
a special ending. Specimens of size 40×40×160 mm
were prefabricated for the testing in the laboratory.
The production was made by ramming into moulds
by hand and by drilling machine. The moulds were
wiped by oil and the earth was rammed in four to
five layers. Layers were compresed by a mechanical
tamper and the last one was always compresed by
hand. Produced specimens are shown in Figure 2.
Specimens were tested after four weeks from pro-

duction. By this time the humidity from the pre-
fabrication is stable and is not changing any more.
The hardening process of clay is based only on the
drying out the mixed water. During these four weeks
the specimens were settled in constant condition of
temperature 20 °C and moisture 50 % in the climatic
chamber (specimens in climatic chamber Figure 3).

2.3. Practical tests
Firstly, specimens were put in the covering of nylon
to avoid the erosion of particles from the submerged
surface. Secondly, they were weighted and finally set-
tled in the box with soft foam that was moistened.
The level of moist was constant, the water was added
during the test. The specimens were regularly mea-
sured and weighted. Some of the specimens were
broken during the test, they were removed from the
testing and not evaluated.

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vol. 13/2017 Water Absorption Capacity Coefficient of Rammed Earth Material

Prescription Type of used clay Sand [%] Clay [%] Water/clay ratio [-] Bulk density [kg/m3]

AGL I illite-kaoline 80 20 0.37 2191
AGLII illite-kaoline 75 25 0.37 2159
GEM I montmorillonite 80 20 0.37 2073
GEM II montmorillonite 75 25 0.37 2040

Table 3. Prescriptions of used specimens and bulk densities of final specimens.

Twenty specimens of GEM and ten specimens of
AGL were tested. The test of GEM was 14 days long
and the AGL was evaluated for three hours of the test
beginning.

3. Evaluation of the measurement
3.1. Mass moisture development
The mass moisture mw was calculated from measured
weigh using relation:

mw =
m−md
md

. (1)

The mass moisture mw was calculeted as a weight
of the wet specimen m minus the weight of dry speci-
men md and then it was divided by the weight of the
dry specimen md (the weight of the specimen in the
beginning of the test) and it was multiplied by 100 to
transform it to percentage of weight. The data of spec-
imen with different starting weight can be compared
with the mass moisture.

The data represented the specimens that were not
broken during the whole testing. They had the same
conditions at the same time. The mass moisture
increase is shown in the Figure 4. The mass moisture
in percent is shown on the vertical axis and the time
(in hours or days) is shown on the horizontal axis.

3.2. Water absorption capacity
coefficient

The water absorption cofficient w determines the abil-
ity of material absorp water by an area in defined
time period. The formula for its calculation is:

w =
W
√
t
. (2)

Units of w are kg/m2
√
t. The quantity of water W

that can be absorbed by an area A is defined by the
formula:

W =
m−md

A
. (3)

Units of weight of the wet specimen m and weight
of the dry specimen md are in kg and the time t is
measured in hours.
The weights were measured in a time period of

one hour for AGL prescriptions. The absorbing area
of specimens is 40×40 mm. The coefficient w was
calculated for prescription AGL I and AGL II.

Figure 4. Mass moisture development of prescrip-
tions AGL and GEM.

4. Discussion
The mass moisture development of AGL (blue column)
and GEM (red column) is shown in Figure 4. The mass
moisture development of AGL I rose to 1.39 ± 0.28 %
and of AGL II to 1.32 ± 0.16 % after four hours.
The biggest increase was in the first hour of testing
then the mass moisture rose quite slower.

The specimen of GEM I rose to 14.89 ± 0.13 % and
of GEM II to 16.70 ± 0.92 % after 14 days. The trend
of development was simillar to the first measurement,
the biggest change was in the first days then it slowed
down.
The coefficient w was calculated to

2.80±0.55 kg/m2
√
t for AGL I and

2.70±0.30 kg/m2
√
t AGL II. The calculated

values were compared to known characteristics of
common building materials as it is shown in Figure 5.
The coefficients w for two types of loam, cement
concrete and two types of bricks were compered to

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B. Mužíková, T. Otcovská, P. Padevět Acta Polytechnica CTU Proceedings

Figure 5. Water absorption capacity coefficient of common building materials and tested rammed earth AGL.

illitic-kaolinite rammed earth material. The results
of made tests AGL are between the values of silty
and clayey loam. The coefficient w for AGL I is only
1.56× higher than for cement concrete.

The value of AGL I is 0.11× lower in comparation
to the solid brick. The value above 10 kg/m2

√
t is con-

sider to be not so good for building material. Non of
the prescriptions exceeds this limit, so in the point of
view of the coefficient w, the rammed earth material
with illite-kaoline clay is competitive to other common
building material.

5. Conclusion
The rammed earth material properities in relation to
mass moisture and water absorption capacity coef-
ficient was observed. Two kinds of specimens were
prepared, one prescription of illite-kaoline clay and
the other of montmorillonite clay.

The increasing of mass moisture in rammed earth of
illite-kaoline clay in three hours and montmorillonite
clay in forteen days was observed. The progress of
mass moisture increasing was fastest in the beginnig
of moistenig for both cases.
The other observed value was the water absorp-

tion capacity coefficient w for rammed earth with
illite-kaoline clay (prescriptions AGL I and AGL II).
The calculated values are comperative to other buiding
material as cement concrete and they are according
to the values found in literaterature [5] for silty loam
and clayey loam. From that point of view, rammed
earth have better properities than for example the
solid brick.

Generally the calculated values of water absorption
capacity coefficient are lower than it was expecting in
the begining of the test.

Acknowledgements
This research was financial supported by the Faculty of
Civil Engineering at CTU in Prague (SGS project No.
16/201/OHK1/3T/11).

Authors gratfully aknowledge free supply of material
necessary for experimental measurement to LB Mine-
rals, s.r.o. company.

References
[1] P. Suske. Hlinené domy novej generacie. First
printing. Alfa Bratislava, 1991.

[2] P. Suske. Nepalena hlina v moderni architekture.
Dokument ERA21: ekologie, realizace, architektura
(2):69–70, 2004.

[3] B. Little, M. Morton. Building with Earth in Scotland:
Innovative Design and Sustainability. First printing.
Scottish Executive Central Research Unit, 2001.

[4] J. Norton. Building with Earth, A Handbook. First
printing. Intermediate Technology Development Group
Limited, 1986.

[5] G. Minke. Building with Earth - Design and
Technology of Sustainable Architecturer. Second printing.
Birkhauser Publishe, 2006.

[6] I. Zabickova. Hlinene stavby. First printing. Era
vydavatelstvi, 2002.

[7] I. Zabickova, T. Otcovska. Compressive strength of
unburned clay masonry. Applied Mechanics and
Materials pp. 31–34, 2016.

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	Acta Polytechnica CTU Proceedings 13:86–89, 2017
	1 Introduction
	2 Testing of unfired earth material
	2.1 Rammed earth and water
	2.2 Preparing material
	2.3 Practical tests

	3 Evaluation of the measurement
	3.1 Mass moisture development
	3.2 Water absorption capacity coefficient

	4 Discussion
	5 Conclusion
	Acknowledgements
	References