Acta Polytechnica CTU Proceedings


doi:10.14311/APP.2017.13.0089
Acta Polytechnica CTU Proceedings 13:89–92, 2017 © Czech Technical University in Prague, 2017

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

DRYING CHARACTERISTIC OF RAMMED EARTH WITH
ILLITIC-KAOLINITIC CLAY CONTENT

Tereza 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. Clay is a traditional construction material which has got to background with introduction
of modern materials to building practice. There is no proper material available for clay constructions
design due to lack of proper examination of its mechanical properties. This paper focuses on drying
rate of rammed earth. Drying is a primary way in which clay gets its strength. It is thus essential to
know a duration needed to a construction to get dry. After pass of this time the maximum strength
is attained and it is possible to load a construction. Properties of unburned clay are dependent on
clay mix composition. In this contribution two sets of testing bodies with different composition are
presented. As a bonding agent an illitic-kaolinite clay was used. It was presupposed that amount of
used clay in clay mixture has major influence on the speed of drying and a final equilibrium moisture
content. This presumption was disproved.

Keywords: Clay, Rammed Earth, Drying Rate, Water Coefficient, Load-bearing Structure.

1. Introduction
An unburned clay was commonly used construction
material of the past. However, with the boom of new
modern construction materials, unburned clay was
pushed out from the business, and therefore the nec-
essary scientific research of unburned clay mechanical
properties was never performed [1–5].
These days unburned clay returns to focus again

generally for three reasons. First reason is reconstruc-
tion of already built clay buildings [6–8]. Second, the
unburned clay constructions are compatible with the
principles of sustainable development [9, 10]. Third,
unburned clay has a blessed impact on the internal
micro-climate of the building and consequent improve-
ment in the health of inhabitants [1, 3, 11].

One of the major methods of unburned clay manu-
facture is a ramming technology which this subscrip-
tion concerns of. A principle of the method is ramming
of earth layers into a framework. Rammed earth is
mostly used for load bearing constructions and for
that reason is important a knowledge of the earth
drying speed [1, 3].

The drying speed of unburned clay is important be-
cause drying is the only process with which unburned
clay gain its strength. It is thus necessary to know
drying speed to be able to estimate the time that
must pass from a manufacture to full construction
load [1, 3, 9, 12].
The clay mixture consists of three basic compo-

nents: sand, clay and water. The sand acts as a filling
agent. The clay has a function of a bonding agent
similarly as a cement in concrete. And water serves
for activation of bonding properties of the clay and
for proper processibility of clay mixture [1, 13–15].

The clay mixtures that were experimentally exam-
ined and described in this contribution contain just
these three basic components. No any additive nor
additional bonding agent such as cement or lime were
added to examined clay mixtures. The reason to ex-
clude the additives was our effort to properly describe
plain clay mixture.
It was proved that even plain unburned clay used

as a construction material features long lifespan. It is
true particularly for properly designed construction
details. In some cases it was discovered that by adding
of another organic bonding agents the result material
strength decreased. That is crucial for load-bearing
construction elements. Another reason why we con-
centrated on unburned clay without additives is a fact
that addition of a cement or lime reduces positive
influence of unburned clay to inner microclimate and
raises environment load [3, 16, 17].

2. Test mixture and test bodies
manufacture

Two types of clay mixtures were tested. The mixtures
differed in sand to clay ratio and in amount of used
water (water coefficient). The testing bodies were
manufactured by ramming technology. The published
results were measured minimally on six testing bodies
of each mixture.
The used clay mixtures are composed from a sand

(see Fig. 1), illitic-kaolinitic clay (see Fig. 2) and
water (common tap water). A sand to clay ratio
and water amount were prescribed for the both clay
mixtures.
The behaviour of the clay mixture during drying

and the speed of drying were studied in connection

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

Figure 1. Granularity curve.

Figure 2. Illitic-kaolinitic clay.

with clay content and water content in the mixture.
The clay mixture KRII contained 1/4 more clay (bond-
ing agent) than in the mixture KRIII. The mixture
KRII was manufactured with water coefficient 0.37.
The mixture KRIII was manufactured using water co-
efficient 0.4. The water coefficient is a ratio between
weight of water and weight of clay. The actual clay
mixture composition is declared in the Table 1.
The test bodies were rammed using electric power

hammer into steel moulds of size 40×40×160 mm.
Only the last layer was rammed manually (see Fig. 3).
Immediately after manufacture the testing bodies

were put out of mold and weighted. After that the test-
ing bodies were inserted into air-conditioned chamber,
where constant temperature (20 °C) and relative hu-
midity (60 %) are maintained (see Fig. 4). The testing
bodies were left in the air-conditioned chamber until
their humidity has settled (approximately 1 month).

3. Measured results
The test bodies were held in the air-conditioned cham-
ber and regularly weighted. Thus the decrease of their
mass was measured (see Table 2, Fig. 6). A frequency
of weighting was the highest in the first day after
manufacture (approximately once per one to three
hours). During the first day after manufacture the
highest drop in weight was measured (approximately
90 % from total drop of weight) (see Fig. 5, Table 2).

Figure 3. Production of the test bodies.

Figure 4. Test bodies in the air-conditioning chamber.

The equation 1 was used for calculation of weight
moisture content from the measured values. Initial
weight moisture content of the both test body sets
was 9.3 %. Time course of average value of weight
moisture content is introduced in the Table 3 and in
Figures 7 and 8.

w =
mw − md

md
(1)

It can be seen in the Figures 7 and 8 that equilib-
rium moisture of KRIII set is 1.6 % and thus higher
than moisture of KRII which is 0.8 % even though
that KRIII set contains less clay that KRII set (see
Table 1). This finding is surprising because it is gener-
ally believed that clay minerals bond water [1, 3, 13].
It was expected that equilibrium humidity of KRII
set will be higher.

The reason why the equilibrium humidity is higher
for clay mixture with lower clay ratio is probably
that KRIII set was manufactured with higher water
coefficient (see Fig. 9).
It can be further conclude from carried on experi-

ment that the speed of drying is independent on the
amount of used clay. For the both mixtures the 90 %
of moisture content (calculated from the total mois-
ture content drop) evaporated during the first 24 hours
after manufacture. Equilibrium moisture content was

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vol. 13/2017 Drying Characteristic of Rammed Earth ...

Set Clay Sand/clay ratio Water/clay ratio Number of test bodies

KRII illite-kaolinitic 75/25 0.37 6
KRIII illite-kaolinitic 80/20 0.4 6

Table 1. Composition of the clay mixture batches and number of test bodies.

Figure 5. Time course of the test bodies weight after
the first 30 hours from manufacture.

Figure 6. Time course of the test bodies average
weight.

reached after approximately 25 days. The form coeffi-
cient of test bodies defined by equation 2 was 0.8889.

Cs =
Vtb
Atb

(2)

4. Conclusion
The carried out experiment showed that the amount of
used water in mixture can have more substantial influ-
ence to resulting equilibrium humidity than amount of
used clay. However, it is necessary to verify this find-
ing and state the actual influence in detail. It should
be acomplished by testing another sets of clay mix-
tures that would be manufactured in wider range of
sand/clay ratio and water/clay ratio. It is also neces-
sary to focus on microstructure of tested material to
reliably describe influence of water and clay ratios on
unburned clay drying courses.

Figure 7. Time course of weight moisture content.

Figure 8. Time course of weight moisture content –
logarithmic scale of time

Figure 9. Ratio of the clay and water in mixture and
resultant equilibrium humidity.

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

Set
Time elapsed after manufacture [hour]

0 0.7 1.7 3 4 7 22 24 28 31 48 144 157 192 528 709

KRII 592 - - 582 - 564 - 551 - 550 - - 547 - - 547
KRIII 588 587 583 - 575 - 551 - 550 - 549 548 - 548 547 -

Table 2. Time course of the test bodies average weight [g].

Set
Time elapsed from test bodies manufacture [hour]

0 0.7 1.7 3 4 7 22 24 28 31 48 144 157 192 528 709

KRII 9.3 - - 7.3 - 4.1 - 1.6 - 1.3 - - 0.8 - - 0.8
KRIII 9.3 9.1 8.3 - 6.9 - 2.4 - 2.2 - 1.9 1.7 - 1.7 1.6 -

Table 3. Time course of the test bodies average weight moisture content [%].

The obtained results also indicate that the drying
speed is not dependent on the amount of the clay in
a clay mixture. For test bodies with form coefficient
of 0.8889 the drying was almost complete (reaching
of equilibrium humidity) after the first 24 hours.

List of symbols
w Weight moisture content [–]
mm Weight of damp sample [g]
md Weight of dry sample [g]
Cs Form coefficient [m]
Vtb Volume of test body [m3]
Atb Surface of test body [m2]

Acknowledgements
The financial support of this work by the Faculty of Civil
Engineering, Czech Technical University in Prague (SGS
project No. SGS16/201/OHK1/3T/11) is gratefully ac-
knowledged. 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 express thanks to HELUZ cihláhřský průmysl
v.o.s. for giving statistical data and information.

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	Acta Polytechnica CTU Proceedings 13:90–93, 2017
	1 Introduction
	2 Test mixture and test bodies manufacture
	3 Measured results
	4 Conclusion
	List of symbols
	Acknowledgements
	References