International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 3, Issue 1, January 2014
ISSN 2319 - 4847
Study of sulphate attack on earth stabilized blocks
Sihem Chaibeddra1, Fattoum Kharchi2
1,2
University USTHB-FGC-LBE, BP 32 Bab Ezzouar, Algiers- ALGERIA
ABSTRACT
This work investigates the behavior of stabilized earth blocks opposite to sulphate attack. The first part consists in a brief
description of earthen blocks manufacturing process; it’s followed by an analysis of weathering processes due to continuous
cycles of immersion in water and in a sulphated solution dosed at 3 ℅ followed by drying in an oven. Weight losses in both media
are estimated and compared based on the type of treatment and dosage incorporated.
Keywords: earth blocks, stabilization, sulphate attack.
1. INTRODUCTION
The construction with stabilized earth blocks is particularly prevalent in rural areas and in Sahara. This technique allows
the realization of collective dwellings, houses, schools, agricultural buildings, bus shelters ... etc. The architecture used is
suitable for the material that must work in compression [1].The material has good thermal characteristics and allows the
economy of energy and protecting the environment. It is product at different scales: manual presses, hydraulic or
electrohydraulic presses. The origin of stabilized earth blocks is connected to the unstable behavior of land used in
construction. This latter, because of the presence of clay, reacts with moisture by swelling when water is absorbed, and by
shrinking when the soil dries. Such a mechanism causes surface cracks which accelerate erosion and therefore involve
structural damage. The stabilization of the soil or the incorporation of stabilizer products such as lime, cement, asphalt...
will effectively remedy the problems of instability of the clay due to the changes in humidity. Compacting the mixture
significantly improves the mechanical strength. The principle is therefore, the best use of the land and to confer it
qualities that it does not possess. However, when treating land for construction, the reactions that occur between the
binder and the ground are very sensitive to the ambient environment and the conditions of implementation. Many
chemical elements are identified in the literature as disruptive elements of soil treatment. Most of the time, the
disturbances are attributed to the following compounds: sulfates, organic matter, clay minerals, phosphates, nitrates,
chlorides…etc. Failures are often the result of the presence in excess of these disruptive elements in the soil [2]. These
failures are manifested with insufficient mechanical properties or sensitivity to water, which affects the durability of the
material. Our work investigates the sustainability of stabilized earth blocks to erosion, particularly the behavior of the
blocks opposite to sulphates attack.
2. Materials and methods
Concerning the choice of materials, land used is a land available locally. The binders used for stabilization are a CEMII
CPJ cement and a lime. Some properties are listed in Table 1. The manufacturing steps are as follows: the extracted soil
is dried, crushed and passed through a 5mm sieve. Sieving is essential to ensure complete mixing of the components.
Land is then stabilized with cement, lime and a cement-lime mixture (at 50 ℅ 50℅). Stabilizers are incorporated in
weight percentage of dry land. Dosages vary from 5 to 10 ℅. Regarding the addition of cement-lime mixture, lime is first
incorporated, followed by cement with a rest time of one day between the two incorporations because pretreatment with
lime will dry wet materials that which decreases the plasticity for a better incorporation of the cement, as this latest
provides a rapid rigidification. The amount of mixing water corresponds to the optimum proctor (℅ 19) for cementitious
mixtures, and to the optimum proctor +3℅ for lime mixtures because lime requires more water to hydrate. After
compaction and demoulding, the blocks undergo cure which consists of water spraying for one week and a humid
preservation for 14 days in order to avoid premature drying of the material and to allow to stabilizer to harden. After
curing period and hardening (28 days for cement and 42 days for lime), the blocks are totally immersed in a water bath
and in a sulphated bath at 3℅ (Na2SO4 solution). This protocol simulates a general case of sulphated attack during
hydration of a soil already containing sulphates, or when sulphates come from an extern environment. The immersion
time is 5 hours. The blocks are then drained and dried in an oven at 71 ° C for 42 hours. After drying and cooling for 2
hours, the blocks are brushed and weighed to determine the weight losses in both media and then immersed again in the
baths and so on.
Table.1 soil, cement and limes properties
1.71
23
Organic matter (%)
0.31
Value of methylene blue
3. 25
Chloride (%)
0.017
Soil
characte
ristics
Maximum dry
density(g/cm3)
Plasticity index
Volume 3, Issue 1, January 2014
Chemical analysis
Mineralogical analysis
Montmorillon
ite (%)
51.73
Page 184
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Kaolinite (%)
21.80
Illite (%)
26.45
Optimum water(%)
19
Carbonate (%)
24.12
PH
Specific
surface
area [cm2/g]
Time of
initial
setting
[mn]
8.25
Final
setting
time
[mn]
Sulphate (%)
Expansion
Loss on
"Le
ignition
Chatelier"
[mm]
Traces
SiO2(%)
3900
Fe2O3(%)
155
CaO(%)
260
K2O(%)
1
Na2O(%)
8.48
MgO(%)
17.52
SO3(%)
4.63
chlorides
2.99
62.54
0.66
0.04
1.98
2.32
0.016
Al2O3(%)
Lime characteristics
Cement
characteristics
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 3, Issue 1, January 2014
ISSN 2319 - 4847
CaO %
44.24
Al2O3%
1.12
S2O3%
0.4
SiO2%
4.3
SO4%
0.83
3. Results and discussion:
Cycles of water Immersion / drying have led to significant weight loss exceeding 10 ℅ of dry weight (max tolerated in a
dry climate) even faster than the cement dosage is low. Blocks stabilized with lime and cement + lime mixture, seem
slightly more resistant. The protocol of "immersion in the sulfated solution / drying" has accelerated the deterioration of
the blocks and their damage. Blocks stabilized with cement showed a greater fragility, given the pronounced losses of
materials incurred before the total ruin. Blocks stabilized with lime and cement + lime mixture have a slightly better
performance compared to those stabilized with cement, which allows us to deduce that the lime has a favorable effect on
the resistance to erosion. Indeed, the weight losses of lime stabilized blocks are the lowest in water.
Figure1. Weight losses of blocks stabilized with cement, subjected to cycles of immersion in water and in sulphated
solution
Figure2. Weight losses of blocks stabilized with lime, subjected to cycles of immersion in water and in sulphated solution
Volume 3, Issue 1, January 2014
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 3, Issue 1, January 2014
ISSN 2319 - 4847
Figure3. Weight losses of blocks stabilized with cement&lime, subjected to cycles of immersion in water and in sulphated
solution
We can interpret this as follows: when a block of earth is contacted with water, it tends to absorb and retain it. The high
affinity that have clay minerals to water, promotes this absorption. In addition, moisture weakens the van der Waals
forces between the surface of the sand particles and the cement hydrates. When the block is in the saturated state, it is
subject to internal pressures that develop inside the pores. The accumulation of these forces can lead to a stress discharge
which is accompanied by a dispersion of the unassembled particles, or particles that are partly affected by the
stabilization. It leads also to the dissolution of the calcium hydroxide contained in the hardened cement paste. The
dissolution process is irreversible, the phenomenon of leaching can occurs [3]. An intense leaching increases the porosity
of the material and makes it more permeable (Neville, 1995) cited in [4].
On the other hand, vulnerability of blocks to water is due first to their composition. Indeed at least 90% of a block
consists of the ground, with 10% or less, consists of binder. In the matrix of a stabilized block, the cement stabilization
process does not affect all components of the block (Herzog & Mitchell, 1963; Houben & Guillaud, 1994) [4].The
fineness of the clay and silt particles and their large specific surface hinder the stabilization process. Because of their
greed water, these particles consume a portion of the mixing water necessary for hydration of cement (Van Olphen, 1977)
[4]. In addition, they cover the surface of the coarse fraction of soil (fine gravel and sand) thus inhibiting the effect of
cement on particles. Furthermore, the hydration reaction between portland cement and water, which is responsible for
binding created in the block, also produces soluble products, such as calcium hydroxide Ca(OH)2 (Illston, 1994 in [4])
which can easily contribute to the disintegration of wet block in time. The disintegration of blocks is then due to the
irreversible phenomenon of leaching of soluble products and to the lubrication of the contact surfaces between the grains
leading to the dispersion of particles unaffected by stabilization.
The integral destruction of the blocks in the sulphated solution is due to the loss of cohesion of the materials constituting
the blocks. Sulphates affect the hardened matrix binder and destroy it. The moisture sensitivity is then increased.
According Kerali [5], the soluble salts such as sulfates and chlorides penetrate into the pores and crystallize inside.
Germination and growth of crystals can lead to the development of internal stresses which cause bursting. In the case of
sodium sulphate, reaction with the calcium hydroxide present in the hydrated cement, products soluble hydrates:
Na2SO4 + Ca(OH)2 + 2H2O
2NaOH + CaSO4.2H2O
In addition, the presence of SO42- anions in the solution tends to accelerate the solubility of calcium ions and leads to the
decalcification of C-S-H [6]. The dissolution of calcium hydroxide and decalcification of C-S-H increases the porosity of
the surface of the material and decrease its resistance to the penetration of ions. The leaching mechanisms have negative
impact on the connectivity of the pore structure of the material (increase the diffusivity of ions) [7]. Mixing lime with
cement attenuate these effects due to the supplementary addition of calcium hydroxide. Calcium provided by the lime can
reduce decalcification of C-S-H [8].
The following figures show sample images of blocks observed using a scanning electron microscope SEM. The tested
samples were taken from blocks having undergone erosion in water and in the solution sulfated. A third reference sample
was also observed.
Volume 3, Issue 1, January 2014
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 3, Issue 1, January 2014
ISSN 2319 - 4847
Figure4. SEM observation: undamaged material; damaged due to water; damaged due to suphated solution respectively
We can see from the pictures above that the internal structure of the block has been modified in both environments.
Indeed, links appear to be destroyed in water resulting in the loss of compactness and the formation of new pores between
solid particles (dark areas of the image). These pores are probably due to leaching of soluble products Ca(OH)2 formed
during the hydration reaction of binder, or the dispersion of particles unaffected by stabilization. These effects are even
more pronounced in the sulphated solution as the structure seems much more dispersed.
4. Conclusion :
From the test results obtained we can conclude that the behavior of the blocks differs depending on the treatment and
dosage incorporated. Total immersion in water followed by drying is very destructive to the blocks. They accuse
significant weight losses in a very short time. Blocks stabilized with cement are the most fragile. Total immersion in a
sulphated solution followed by drying accelerates the destruction of blocks. The material completely loses its cohesion and
rigidity. However, these effects are lessened with the dosing of binder. The incorporation of the lime is slightly beneficial.
In general, we can consider the mixture cement + lime as the most suitable treatment for the land used, from the point of
view of durability of the blocks.
REFERENCES
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maçonneries « BTC-Mortier de terre ». Thèse de doctorat, France INSA de Lyon.
[2] Le Borgne.T (2010). Caractérisation et quantification des éléments perturbateurs devprise lors du traitement des sols.
Thèse de doctorat. France, INPL.
[3] J. Morris, Q. Booysen, “Earth construction in Africa, Strategies for a Sustainable Built Environment”, Pretoria,
August 23-25 (2000).
[4] A-G. Kerali, “Durability of compressed and cement-stabilized building blocks”. A thesis submitted in partial
fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering. Warwick Univ, School of
Engineering, 2001.
[5] Kerali.A.G. “Destructive Effects of Moisture on the Long-term Durability of Stabilised Soil Blocks”. WP 52 Durability of SS Blocks, Development technology unit DTU. Working Paper No.52, 2000.
[6] Sunil Kumar and C.V.S. Kameswara Rao. Harcourt Butler. “Effects of sulfates on the setting time of cement and
strength of concrete”. Journal of Cement and Concrete Research, Vol. 24, No. 7, pp 1237-1244, 1994.
[7] Marchand.J, Dale P Bentz, Samson.E and Maltais.Y (2001). “Influence of Calcium Hydroxide dissolution on the
transport properties of hydrated cement systems”. Materials Science of Concrete: November 1-3, Holmes Beach,
Anna Maria Island, Florida, pp 113-129, 2000.
[8] Bakhareva.T, Sanjayan.J.G, Cheng.Y.-B. “Sulfate attack on alkali-activated slag concrete”. Monash University,
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AUTHOR
Sihem Chaibeddra; Sihem Chaibeddra; civil engineer 2009 and Magister 2012 from the university of science and
Technology HOUARI BOUMEDIENE of BAB EZZOUAR, Algiers. Currently prepares a doctoral thesis in civil
engineering on the durability of stabilized earth concrete.
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