Acta Polytechnica CTU Proceedings


doi:10.14311/APP.2018.15.0081
Acta Polytechnica CTU Proceedings 15:81–87, 2018 © Czech Technical University in Prague, 2018

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

DETERMINATION OF DRYING TIME OF THE RAMMED EARTH
WALLS

Tereza Plaček Otcovská∗, Barbora Mužíková, Pavel Padevět

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

∗ corresponding author: tereza.otcovska@fsv.cvut.cz

Abstract. The unburned earth is a building material with long history of use. Buildings made of
unburned clay are all over the world. But at present, unburned earth is minority building material and
its properties are not sufficiently investigated. The rammed earth is one of main kind of unburned earth.
This paper is focused on drying rate of the rammed earth of known composition. The significant part
of the paper is focused on principle of our own research and the main idea of our research is explained
here. The second part of the paper is devoted to drying rate experiment and measured results from
this experiment. Determination of drying time of universal rammed earth walls is the main result of
the experiment.

Keywords: Rammed earth, unburned earth, clay, sand, water coefficient, drying rate, drying time.

1. Introduction
Importance of the unburned earth in construction in-
dustry is minor, but there are a few reasons why the
research of this building material is important. Re-
cently, there has been a growing interest in unburned
earth which has resulted in a number of scientific
articles on this topic. The growing interest in this
historic building material is evident in construction
industry too (see Fig. 1). I can see in my practice of
civil engineer that more and more people choose the
unburned earth for build of their houses. The growing
interest is the first reason why carry out research in
the unburned earth (see Fig. 2) [1, 2].

Figure 1. Sales of unfired bricks by HELUZ cihlářský
průmysl v.o.s.

The second reason is a need for reconstruction of
historic buildings. There are many earth buildings in
the world and in the Czech Republic that need recon-
struction. It is very important to have the knowledges
of unburned earth properties for correct reconstruction
of this buildings [3–7].

Third, an earth building is a good way for sustain-

Figure 2. Building of family house from straw and
earth in Klášterecká Jeseň.

able development in the construction industry. The
energy needed for production of the unburned clay is
minimal and the energy for demolition of the earth
construction is small, because earth waste can be com-
pletely recycled and earth waste does not need to be
stored in a waste dump. A good indicator is primary
energy investment (PEI). PEI is an energy used during
live cycle of building materials [8–11].
The primary complication about the properties of

the unburned earth is in composition of the earth.
The properties depend on composition of the earth
and the composition of earth can be very variable.
Currently, a design of load bearing structures from
rammed earth needs a lot of civil engineer’s experi-
ences because norms or methodology does not exist
for the design of unburned earth constructions in the
Czech Republic. The reliable methodology is very im-
portant for easier design of the earth buildings. That
are reasons why is necessary to carry out the research
focused on the composition of earth mixture and prop-

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http://dx.doi.org/10.14311/APP.2018.15.0081
http://ojs.cvut.cz/ojs/index.php/app


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

Figure 3. The rammed earth.

erties of the final earth structures. The reliable dates
from the research should be used for the creation of
the methodology [3, 12, 13].
The earth constructions can be produced of the

earth mixture without or with inorganic binder. The
inorganic binder can improve water resistance of un-
burned earth. But the inorganic binders are not neces-
sary for the earth constructions. There are old historic
buildings and there are researches which proved that
unburned earth can be sufficiently resistant against the
moisture. The important reason for using unburned
earth without the inorganic binders is environment
and the sustainable development. The unburned earth
with inorganic binder is not possible to recycle easily.
This are the reasons why our research is focused on
the properties of unburned earth without additives
[3, 8, 14–16].
The earth construction can be produced from the

earth mixture in several ways. The elementary type
of the earth construction is the rammed earth. This
paper is focused on the rammed earth. The principle
of rammed earth technology is pressing down layers
of the earth mixture to a formwork (see Fig. 3). The
rammed earth walls are usually used like load-bearing
structures. That is the reason why the mechanical
properties and information about drying rate are very
important [3, 13, 17].

The main topic of this paper is the drying rate and
drying time. Information about the drying rate and
drying time are important, because the drying is the
main way how the unburned earth gains its final me-
chanical properties. The rammed earth construction
are usually load-bearing types and it is necessary to
know when the rammed earth construction is possible
to load.

2. The Idea of Our Research
As stated in the introduction, the norm or relevant
instructions about the earth building designing are
not available in the Czech Republic. The quality
research about the unburned earth have to be realized
for creating of this instructions. It is necessary to
analyse unburned earth properties in dependence on
its composition. This is the reason why we investigate

Mark of clay Kind of clay
GEM montmorillonite

AGL illite
KR illite-kaolinite

Table 1. Three basic kinds of clay.

Figure 4. The test bodies shape of block.

the behaviour and properties of the rammed earth
from earth mixtures of different composition.
The test earth mixtures are produced in our labo-

ratory from the three elementary components (clay,
sand, water). Clay fulfils a function of a binder, sand
fulfils a function of a filling agent and water serves
for an activation of clay bonding properties and for
good earth mixture processing. The composition of
the earth mixtures differ in kind of clay, amount of
clay or amount of mix water. The amount of water
is defined by the water coefficient (see Equation 1).
Three elemental kinds of clay were used (see Table 1).
The summary of the earth mixture which have been
made can be seen in Table 2.

W = mw/mc (1)

W - Water coefficient [-]
mw - Weight of water [g]
mc - Weight of clay [g]

Determination of dependence between the rammed
earth properties and the rammed earth composition is
our goal. Up to now, we have produced 19 types of the
earth mixtures and analysed their properties. We fo-
cused particularly on the tensile bending strength, the
compressive strength, Young’s modulus, moisture’s
properties, methylene blue test, shrinkage, creeping
and drying rate.
We used the test bodies of block shape of size

2/2/10 cm and 4/4/16 cm for majority experiments
(see Fig. 4). We used the test bodies of prism shape
with octahedron base and height of 7 cm for measure-
ment of creeping and shrinkage (see Fig. 5). We used
the test bodies of block shape of different heights with

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vol. 15/2018 Determination of Drying Time of The Rammed Earth Walls

Set clay Sand/clay weight ratio Water coefficient
GEMI montmorillonite 80/20 0.370

GEMII montmorillonite 75/25 0.370
GEMIII montmorillonite 75/25 0.295
AGLI illite 80/20 0.370
AGLI illite 75/25 0.370
KRI illite-kaolinite 80/20 0.370
KRII illite-kaolinite 75/25 0.370
KRIII illite-kaolinite 80/20 0.400
KRIV illite-kaolinite 85/15 0.295
KRV illite-kaolinite 85/15 0.370
KRVI illite-kaolinite 85/15 0.400
KRVII illite-kaolinite 80/20 0.250
KRVIII illite-kaolinite 80/20 0.290
KRIX illite-kaolinite 80/20 0.450
KRX illite-kaolinite 75/25 0.295
KRXI illite-kaolinite 75/25 0.400
KRXII illite-kaolinite 70/30 0.295
KRXIII illite-kaolinite 70/30 0.370
KRXIV illite-kaolinite 70/30 0.400

Table 2. Summary of the earth mixtures.

Figure 5. The test bodies shape of prism with octa-
hedron base.

aluminium moulds for measurement of drying rate
(see Fig 6).

2.1. The Production of the Test Bodies
The earth mixture is produced from three elemen-
tal components (clay, sand, water). The clay is fine
powder form (see Fig. 7). Size of sand grain is to
4 mm. The grain curve of the sand can be seen in the
Figure 8. The water was used from a water supply
line.
The three components were mixed and processed

into the earth mixture. The earth mixture was pressed

Figure 6. The test bodies for drying rate experiment.

down to the moulds (see Fig. 9). The test bodies
for mechanical properties experiments and moisture’s
properties experiments were demoulded a few minutes
after production and inserted to an air-conditioning
chamber. The test bodies for drying rate experi-
ments were left in the moulds and inserted to the
air-conditioning chamber. The test bodies were left in
the air-conditioning chamber until equilibrium mois-
ture content was reached. Relative atmospheric hu-
midity in the air-conditioning chamber was 50 % and
temperature was 20oC.

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

Figure 7. Montmorillonite clay.

Figure 8. The grain curve of the sand.

3. The Measure of The Drying
rate

The test bodies in the Figure 6 were used for the
measurement of the drying rate. The earth mixture
was pressed down to to the moulds of four sizes. Uni-
directional moisture flow of moisture was provided in
the test bodies because the test bodies could dry out
only by two opposite surfaces. The size of surface for
dry out of the test bodies was square shaped of 53 mm
long side. The height of the test bodies (moulds) were
5 cm, 6 cm, 7 cm and 8 cm (see Fig. 10).
The test bodies in the moulds were inserted to

the air-conditioning chamber and regularly weighed.
Weight decrease of the test bodies was monitored. The
moisture content was calculated from the weight of
the test bodies by the Equation 2.

w = (mws − mds)/mds (2)

w - Moisture content [-]
mws - Weight of a wet sample [g]
mds - Weight of a dry sample [g]

Research was focused on the dependence of the
drying rate on the thickness of the drying rammed
earth (see Fig. 10).

Drying rate was determined for the test bodies. The
points of interest in this paper are amount of moisture
50 % and 15 % from original value. From the values

Figure 9. The pressing down to the mould.

obtained the drying time from experiment start we
tried to determine the drying time of a universal wall.

3.1. The Measured Data
The set KRIII is the set of the earth mixture for this
drying rate experiment (see Table 2). Number of the
test bodies of every height were 3. Total of 12 test
bodies were used for the experiment.
The weighing interval was 15 to 60 minutes in the

first 12 hours after production of the test bodies. After
first 24 hours the weighing interval was extended.

The moisture content was calculated by Equation 2.
The shape of the moisture content curve in time is
shown in Fig. 11. A total time for this experiment
was approximately 7 day (exactly 167.25 hours). The
moisture content after 7 days were 0.6 % to 0.9 %
(approximate decrease by 85 % from original value
of the moisture content). The main decrease of the
moisture content was in the first 24 hours. The mois-
ture content after first 24 hours were 2 % to 2.9 %
(approximate decrease by 65 % from original value of
the moisture content).

The moisture content 50 % from original value was
reached after 8 to 16 hours depending on the height
of the test bodies (see Fig. 12). Dependence between
the drying rate and the thickness of the rammed earth
appears to be linear (see Fig. 13). Time to reach
50 % from original value of the moisture content of
different thickness rammed earth is possible determine
by drying coefficient fdry. The drying coefficient is
defined by Equation 3.

fdry =
∑n

i=1(ti/hi)
n

(3)

fdry - Drying coefficient [hour/cm]
ti - Time for drying out of the test bodies of a
particular size [hour]
hi - Hight of the test bodies of a particular size [cm]
n - Number of the test bodies heights [-]

The drying coefficient was calculated 1.8 hour/cm
from the moisture content values obtained. Base on

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vol. 15/2018 Determination of Drying Time of The Rammed Earth Walls

Figure 10. The diagram of the test bodies in the moulds for drying rate experiments.

Figure 11. The time course of the moisture content.

the values obtained is possible to predict that, for
example, a 30 cm thick rammed earth wall will dry
out from 50 % in approximately 2.25 days. This
prediction was done using Equation 4.

t50 = Ww.fdry (4)

t50 - Time for drying out of a rammed earth wall
[hour]
Ww - Thickness of a rammed earth wall [cm]
fdry - Drying coefficient [hour/cm]

The decrease of the moisture content from 85 %
from original value was reached after 70 to 123 hours
depending on the height of the test bodies (see Fig. 14).
Dependence between the drying rate and the thickness
of the rammed earth appears to be linear (see Fig. 15).

Figure 12. The decrease by 50 % from original value
of the moisture content.

From the time to reach 85 % of the original value of
the moisture content of different thickness rammed

85



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

Figure 13. The decrease by 50 % from original value
of the moisture content – linear dependence.

Figure 14. The decrease by 85 % from original value
of the moisture content.

earth is possible to determine the drying coefficient.
The drying coefficient for 85 % decrease of the

moisture content was calculated 14.9 hour/cm from
the moisture content values obtained (see Equation 3).
Base on the values obtained it is possible to predict
that, for example, a 30 cm thick rammed earth wall
will dry out from 85 % approximately 18.6 days. This
prediction was done using Equation 3.

4. Conclusions
The rammed earth structures are usually load-bearing
types and that is the reason why it is necessary to
know how long after their production the rammed
earth has its final properties (in particular mechani-
cal properties). Determination of drying time of the
rammed earth of the known composition (set KRIII,
see Table 2) was the goal of the drying rate experiment
described in this paper.

The decrease of the moisture content was calculated
from the measured values of weights of the test bodies.
The drying coefficient was determined for the calcu-
lation of the drying time of the different thickness
rammed earth walls.
The points of interest were 50 % decrease of mois-

ture content from original value and 85 % decrease
of moisture content from original value. The predic-
tion of drying time is determined by using the drying
coefficient.

From the obtained values was predicted that 30 cm

Figure 15. The decrease by 85 % from original value
of the moisture content – linear dependence.

thick walls will dry out from 50 % of the original
moisture content approximately in 2.25 days. The
drying coefficient for this value is 1.8 hour/cm.
The same walls will dry out from 85 % of original

moisture content approximately 18.6 days. The drying
coefficient for this value is 14.9 hour/cm.

List of symbols
W Water coefficient [–]
mw Weight of water [g]
mc Weight of clay [g]
w Moisture content [–]
mws Weight of a wet sample [g]
mds Weight of a dry sample [g]
fdry Drying coefficient [hour/cm]
ti Time for drying out of the test bodies of a particular

size [hour]
hi Hight of the test bodies of a particular size [cm]
n Number of the test bodies heights [–]
t50 Time for drying out of a rammed earth wall [hour]
Ww Thickness of a rammed earth wall [cm]

Acknowledgements
The financial support of this experiment by the Czech
Science Foundation (GAČR project NO. 18-10884S) and
Faculty of Civil Engineering, Czech Technical University
in Prague (SGS project No. SGS16/201/OHK1/3T/11) is
gratefully acknowledged.

We would like to express our thanks to LB MINERALS,
s.r.o. company for free supply of material necessary for
experimental measurement and we would also like to ex-
press thanks to HELUZ cihlářský průmysl v.o.s. for giving
statistical data and informations.

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	Acta Polytechnica CTU Proceedings 15:81–87, 2018
	1 Introduction
	2 The Idea of Our Research
	2.1 The Production of the Test Bodies

	3 The Measure of The Drying rate
	3.1 The Measured Data

	4 Conclusions
	List of symbols
	Acknowledgements
	References