1

Efficiency of hydrophobic products regarding water

performance of compressed cement stabilized earth blocks

Isabel Maria Alves Gomes Marujo Lopes

Master in Civil Engineering

Instituto Superior Técnico, Universidade de Lisboa, Portugal Acronyms

• CEB – Compressed earth blocks

• PI – Plasticity Index

• OMC – Optimum Moisture Content

• SH – Surface Hydrophobe

• BH – Bulk Hydrophobe

1. Introduction

The use of earth as a building material is ancestral and, as a proof of that, constructions 5 000

years old can be seen nowadays (Pacheco-Torgal & Jalali, 2011), being the oldest records of earth

construction date back to 10 000 B.C. (Heathcote, 1995). Earth is an abundant resource and is usually

applied unbaked, being considered a self-construction material. Therefore, even though this material

had a decay due to the rising of the reinforced concrete and baked masonry, nowadays about 40% of

the world population still lives in unbaked earth constructions (UNCHS, 2015).

Several institutions were created to study possibilities of this material for construction, being

one of the most important the CRATerre, founded in France in 1979. Worldwide known architects

have been using unbaked earth in their projects and have proven that, with the right maintenance

these constructions are durable, being able to achieve structural and functional performances

compatible with the current standards and demands (Duarte, 2013). Though unbaked earth

constructions ara important in a wide range of regions dispersed throughout the globe, there is some

scarcity when it comes to normative documents that regulate the constructions, being the existing

ones developed by countries like New Zealand, Colombia, USA and Germany.

Portugal has a rich tradition regarding unbaked earth constructions, in large extent motivated

by the significant muslim influence, existing records of houses using more than 2 500 years ago

(Eusébio, 2001). The earth construction tecniques most common in Portugal are rammed earth,

specially in Alentejo, and adobe, typical of Aveiro region, both in the center and south of the country

(Parreira, 2007).

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The properties of unbaked earth constructions vary significantly depending on the quality of

the materials used and technic employed. However, one can identify general advantages of its use in

construction, such as good hygrothermal and acoustic performances, being reported energy savings

of 30% to 50% when compared to baked masonry (Krnjetin & Folić, 2004). Since earth is a dispersed

and abundant material, it has the potential to reduce drastically the overall cost, both encomical and

environmental, of the construction. Taking into account transformation, transport and application,

Krnjetin & Folić (2004) report energy savings of 5 to 10 times when compared to baked masonry. In

addition, it is relevant to mention that when non-stabilized or stabilized with natural products (e.g.,

lime), earth can be 100% recycled and reused (BSI, 1999; Burroughs, 2001; Little & Morton 2001). It is

also possible to identify a set of disavantages, such as the impossibility to build in height in seismic

areas, reduced performance when in contact with water and weak tensile strength (Pearson, 1992). It

is important to highlight that some of these disadvantages can be minimized through a careful

selection and application of the materials.

The main goal of this study is to analyse the efficiency of hydrophobic products used on non-

stabilized and cement stabilized compressed earth blocks (CEB) towards water. For that purpose, a

experimental campaign was carried out to evaluate the mechanical, physical and durability

performance of non-stabilized and chemically stabilized CEB. In addition to cement, the chemical

stabilizer most commonly used in CEB, commercial artificial and natural (linseed oil) hydrophobe

products were also tested applied in the surface (artificial and natural) and in mass (artificial). The

natural gravel in the CEB was replaced by recycled gravel from construction waste and the blocks

used in the study were produced in a factory in Montemor-o-Novo, ensuring that the diference from

the commercially available CEB is restricted to the composition.

2. Earth as construction material

Amongst the earth properties, some of the most relevant for its use as construction material

are the granulometry, density, plasticity and retraction, for the raw material, and the moisture content

and compression strenght, for the constrution product or building element (Neves et al., 2010).

Earth is basically made from gravel, sand (silica), clay and silts, and it should have a minimum

content of organic matter to be considered suitable for construction, hence its extraction is only made

from 50 cm deep (Lourenço et al., 2002). As a building material it can be compared with a mortar,

whereas the clay and silts are the binder, being responsible for the cohesion and resistance against

water and the sand is the aggregate. Due to its high retraction potential, clay content should vary

between 5% and 20%, in order to avoid the appearance of cracks while drying (Namango, 2006). The

granulometry of the aggregate (gravel and sand) needs to be carefully selected to minimize the voids

of the mix and enhace the mechanical resistance and durability. To use earth as a building material,

water needs to be added and its content needs to be balanced with the clay content to ensure a

proper workability and, particularly when mechanical stabilization (compression) is to be used, to

achieve the maximum compaction (Eusébio, 2001; Rigassi & CRATerre-EAG, 1985).

The various earth construction technics available have wide range of requirements for the

earth and can exhibit significant perfomance differences. Nowadays it is possible to observe earth

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construction approaches ranging from rudimentary traditional adobe or rammed earth to highly

sophisticated CEB, which can incorporate industrial, mechanized and automated processes (Lourenço

et al., 2002). Adobe bricks are made by laying the earth in plastic state, in a rectangular cast, in which

it will cure in air for 3 to 6 weeks (Duarte, 2013). Rammed earth is a monolithic system which consists

on the execution of big in-situ moulded earth blocks, compressed with pestles inside removable

formworks, which are removed once the earth has dried enough to sustain itself (Rufo, 2010).

According to Rigassi & CRATerre-EAG (1985), CEB are masonry blocks whose characteristics are

obtained through static or dynamic compression of the earth in a humid state in a cast, followed by

immediate cast release (Namango, 2006).

The earth naturally available rarely presents the desirable properties for its use as

construction material and the final product has some limitations. To overcome this issues, it is

common practice to stabilize the earth to enhance the strength and durability of the construction

(Burroughs, 2001). Stabilization of earth can be cataloged as physical, mechanical and chemical

(Namango, 2006; Duarte, 2013). Physical stabilization methods include granulometry correction and

the addition of fibers (e.g., straw), improving compression and tensile strength and preventing cracks

due to retraction. Mechanical methods involve the compression (static or dynamic) of the earth to

increase its compaction and density, resulting in higher compressive strenght and durability. Chemical

stabilization is achieved through the addition of products that improve the earth perfomance. The most

common chemical stabilizers act as binders, being the most typical cement or lime depending on the

earth’s particle size distribution, but they can have other purposes such as water repellents (Auroville,

2015; Rigassi & CRATerre-EAG, 1985; Cid-Falceto et al., 2012).

CEB usually combine the three types of stabilization, since compression is implicit in the

technic and granulometry correction and cement addition are commonly employed to enhance their

physical, mechanical and durability performance. Amongst the relevant physical properties, CEB are

characterized by their low thermal conductivity. In fact, Sampaio et al. (2014) tested the thermal

conductivity of several unstabilized mixes, presenting the reference one after 34 days of curing

exposed to variable humidity and temperature conditions, a conductivity of 0,60 W/(m.K). The

mechanical properties of CEB are limited and, even though there is a relationship between dry density

and compressive strength, CEB production process is highly variable, enabling the possibility of

exceptions (Walker, 1995). Falceto (2012) obtained average values of dry density of 1913 kg/m3 and

1933 kg/m3 for non-stabilized and cement stabilized blocks, respectively. These values are consistent

with Rigassi & CRATerre-EAG (1985), which reported density values between 1870 kg/m3 and 2200

kg/m3. However, these values are merely an indication since density is highly dependent of the

moisture content and the compressive strength of the used press. Australian documentation, as well

as authors like Walker (1995), state that stabilized blocks should have a minimum compressive

strength of 2 MPa in order for them to be considered suitable. Mechanical properties of CEB were

exhaustively studied by Morel & Pkla (2002) using compressive strength and 3-point bending tests,

concluding that there is a correlation between them when confinement effect on the blocks is verified.

The durability of CEB against water is one of the main concerns of whom uses this type of

construction (Lourenço et al. 2002). Falceto (2012) conducted a highly detailed study regarding CEB

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durability towards different interactions with water, in which several tests portrayed on documents from

Australia and New Zealand simulating soft and heavy rain exposure conditions were considered, as

well as conventional capillary and immersion absorption testes. Cement stabilized blocks obtained

capillary absorption coefficients between 5,0 and 6,2 g/(cm2.min0,5) and immersion absorption of 13%,

being this last value confirmed by Lima et al. (2012). As expected, cement stabilized CEB presented a

higher durability than the non-stabilized ones, considering that the latter did not perform satisfactorily

on the mentioned tests.

3. Experimental programme

The experimental programme was designed to link the CEB characteristics with its

perfomance and was divided into 3 stages: i) selection and characterization of the materials (earth and

recycled aggregate); ii) formulation of the mixes and production of the CEB; and iii) testing the CEB

performance both on the fresh and hardened states.

3.1. Materials selection and characterization

The materials used in the present research were earth, recycled aggregate, cement and

artificial and natural hydrophobes. The earth used was obtained from Herdade da Adua (Montemor-o-

Novo, Alentejo, Portugal) and the recycled aggregates from a construction and demolition waste

recycling unit, also in Montemor-o-Novo. The cement and hydrophobes used are commercially

available products.

The source of earth was selected because there is a factory producing CEB for commercial

purposes at Herdade da Adua, where the CEB used in this study were also produced. The recycled

aggregates were selected from a source close to the Herdade da Adua to evaluate their viability as an

alternative to the natural gravel required to correct the composition of the available earth.

For the purpose of producing CEB the relevant physical characteristics of the earth and

recycled aggregates are the density and the particle size distribution. Their characterization was

carried out following the portuguese standard document NP – 83 (1965), for the density, and the

technical National Laboratory for Civil Engineering (LNEC) specification LNEC E 239 (1970), for the

particle size distribution and the results are presented in Table 1. These tests are equivalent to the

ASTM D2937-10 (density) and ASTM D422-63(2007)e2 (particle size distribution), but the particle size

distribution was only obtained by seiving particles larger than 0.074 mm (sieve nº 200 of the ASTM

series).

Table 1: Relevant physical properties of the earth and recycled aggregates

Materials Density [kg/m3]

Particle size distribution [%]

≥2 mm (coarse sand)

2 mm>d≥0.074 mm (sand)

<0.074 mm (clay and silt)

Earth 2655 3% 50% 47%

Recycled aggregate 2645 15% 40% 45%

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The percentage of clay and silt of the earth (47%) was found to be higher than the

recommend by Pacheco-Torgal & Jalali (2011) (40%). As such, a mix of 80% earth and 20% recycled

aggregate, in weight, was used. Despite the content of particles smaller than 0.074 mm in the recycled

aggregates being also larger than 40%, due to their origin there is no clay or silt in its composition.

The mixture was tested to evaluate its suitability and the most adequate properties for CEB

production, namely the consistency limits (plasticity and liquidity limits and plasticity index) and the

optimum moisture content for compaction (Table 2).

Table 2: Characterization of the mix used to produce the CEB.

Test Proctor (OMC) wL wP PI

Result 12,5% 18% 15% 3%

The consistency limits where determined according to the portuguese standard NP – 148

(1969), which is equivalent to the ASTM D 4318 standard. These parameters, in particular the

Plasticity Index (PI) that translate the range of water contents in percentage by weight where the soil

exhibits plastic properties, indicate the suitability of the soil for stabilization. According to Burroughs

(2008), in order to obtain a stabilization success rate of over 80%, the Plasticity Index (PI) should be

lower than 15%, which is verified in this case.

The optimum moisture content (OMC) for compaction was determined using the Proctor

(Compaction) test according to the specification LNEC E 197 (1966), which is equivalent to the ASTM

D698. This is a crucial property for CEB production, since the water content of the mix during the

compression influences significantly the maximum density of the CEB that can be achieved.

The cement and hydrophobes characteristics were available from the producers. The cement

used was a CEM I 42,5 R, with a density of 3100 kg/m3. The hydrophobes used were Toupydro, an

artificial bulk hydrophobic product, Hydrofuge HS, an artifical surface hydrophobic product, and

linseed oil, a natural surface hydrophobic product. The bulk hydrophobe (Toupydro) was only used in

the stabilized mix because it requires the presence of calcium and sodium hydroxides to achieve its

performance. Since sustainability is one of the key advantages of earth construction, linseed oil was

chosen as a natural hydrophobic product based on the positive results obtained in other studies (e.g.,

see Duarte, 2013; Heathcote, 2002; Guillaud et al., 1995).

3.2. Mix proportions and production

For the production of the CEB, three mixes were considered: i) earth and recycled aggregate

(N); ii) earth, recycled aggregate and cement (C); and iii) earth, recycled aggregate, cement and bulk

hyrohobe (CBH). Egenti et al. (2014) and Lima et al. (2012) suggested that for the CEB to achieve its

maximum strength, the cement content should vary between 6% and 12%, of the dry weight of the

mix, so, a content of 8% was chosen. Non-stabilized (N) and stabilized (C) blocks were, after the

curing time, painted with surface hydrophobe and linseed oil, resulting in a total of seven composition

evaluated (Table 3).

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Table 3: Composition of the blocks

Mix Earth Recycled Aggregate

Cement (8%)*

Hydrophobe product

Bulk Surface

Toupydro Hydrofuge HS Linseed oil

N

80% 20%

- - - -

C x - - -

CBH x x - -

NSH - - x -

CSH x - x -

CL x - - x

NL - - - x * % in weight

The CEB were produced at Herdade da Adua (Montemor-o-Novo) using a manual press

Tersteram ApproTech R capable of providing a maximum of 3,6 MPa of compressive strength and

producing blocks of 29,5 x 14 x 9 cm or 22 x 10,5 x 6 cm, depending on the cast used. For this study

the smallest cast (22 x 10,5 x 6 cm) was chosen. The earth and the recycled aggregate were properly screened and milled separately. The

solid componentes were mixed by weightand water was added to the mix through a hose. The water

content is very hard to quantify with precision during the production phase since there is some

humidity in the earth and recycled aggregate, which is not quantified. The expedite method proposed

by in the NZS 4298 was used to ensure that the water content is close to the OMC. This method

consists in evaluating the splash pattern from hand throwing a small amount of the mix to the ground.

The splash of the pieces indicates if the mix is too dry, too wet or suitable for compression. Once the

water content is considered suitable, the mix is layed on the cast, placed on the press and

compressed (Figure 1).

a) b)

Figure 1: Mix in the cast: a) before compression; b) after compression.

After the compression, the blocks were labled according to their composition and mixing. One

block for each mixing was weighted in order to calculate its porosity. A sample of each mix was also

collected so that the precise water content could be determined.

The blocks were cured covered with a plastic canvas during the first seven days. The

stabilized compositions (C and CBH) were sprinkled with water in order for the cement to cure

properly. After the seven days of the initial cure, the blocks were transported to the IST Construction

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Laboratory, where they were exposed to variable conditions of temperature (19ºC to 26ºC) and

moisture (55% and 75% of relative humidity).

3.3. Performance evaluation tests

The CEB were characterized on the fresh state and hardened states. The former included the

moisture content, weight, density and porosity. The latter included the compressive and tensile

strength, ultra-sonic wave velocity, thermal conductivity, capillarity, immersion and low pressure water

absorption, and water dripping and spraying erosion resistance.

The moisture content test was carried out according to NP – 84 (1965) and basically it

consists on the determination of the moisture content of a soil. A sample was collected of each mix

produced. Each sample was weighted before being put inside the kiln long enough so that all the

water has exahled. Afterwards, the samples were again weighted and the moisture content calculated

by the difference of the two weights over the dry weight.

The density test was carried out according to NP EN 772 -12 (2002) and it determines the

weight per volumetric unit. Since one block of each mix was weighted immediately after compression

and the volume was known beforehand, it was only necessary to compute the quotient between the

weight and the volume. In addition, having this information, it was possible to estimate the porosity of

the blocks.The compressive strength test was carried out according to NTC 5324 (2004). This document

proposes that for each block tested, it is cut in half perpendicularly to its largest dimension, being one

half put on top of the other, having the cutted surfaces facing opposite ways (Figure 2). The two halfs

of each block are layed on a metal plate and the data acquisition is made through a load cell, instead

of the hydraulic press, due to the fact that expected strength values are quite lower than the ones of

concrete specimens. Three blocks of each composition were carried out for two different moisture

content (Saturated and Laboratory) and for two different ages (28 and 90 days). The compressive

strength is given by the quocient of the force value registered on the load cell and the area of the

smallest block half.The 3-point bending test was carried out according to NP 772-6 (2002) and since this

document normalizes the test for masonry blocks, it had to suffer some adjustments. Just like the

compressive strength test, a load cell was used for the same reasons. The block is layed on top of two

metallic cylinders 18 cm apart (≅ 3 times the height of the block) and another one is layed on top of

the block (Figure 3). There were 3 specimens of each composition tested. The tensile strength is

calculated using equation (1):

f!" =!×!×!!×!×!!

(1)

where F is the force registered by the load cell [N]; l is the span between the two bottom cylinders (180

mm); b is the width of the block (105 mm); and h is the height of the block (≅ 60 mm).

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Figure 2: Layout of the block just before Figure 3: Block after the 3-point bending

the compression test. test had occurred.

The ultra-sonic test was carried out according to the NP EN 12504-4 (2007) and it basically

measures the velocity that a certain sonic impulse takes to go from one end of the block to the other.

For this particular situation, it was used the direct method in order to maximize the emission and

receiving energy. Two blocks of each composition were tested, being presented dry, saturated and

exposed to the Laboratory conditions.

The thermal conductivity was determined following the ISO/FDIS 10456 (2007), using the

ISOMET 20114 equipment, in which the measurement probe is layed on a surface of the block until

the test is finished. Two blocks of each composition were tested under dry, saturated and Laboratory

environment conditions.The capillary absorption test was carried out according to the NP EN 772-11 (2002). This test

basically consists on the determination of the water absorption rate (sorptivity) of CEB by measuring

the increase in the mass of a specimen due to absorption of water as a function of time when only one

surface of the specimen is exposed to water. The exposed surface of the specimen was immersed in

5 ± 1 mm of water and the mass of the specimen was recorded 10, 20, 30, 60 minutes and 2, 6, 24

and 72 hours after the initial contact with water. For each composition, three dried specimens were

tested at 28 days. During the test, the specimens were covered with a bell-glass in order to avoid the

water evaporation. The water absorption and the absorption coefficient were calculated for each age.

The absorption coefficient was obtained from the slope of the linear regression line between 20 min

and 12 hours.

The immerson test was carried out according to NBR 8492 (1984) and it consists on the

determination of the absorption of the CEB, providing an estimation of their open porosity. The blocks

were layed on a tank full of water totally immersed for 48 hours and then weighted. In order to dry the

blocks out, they were put inside a kiln until all the moisture had evaporated and then weigthed. The

absorption is calculated through the difference of both weights over the dry weight. Three blocks of

each composition were tested.

The water absorption under low pressure was carried out according to Rilem (1980) and it

basically determines the time it takes for a certain area of a porous material (π×1,352) to absorve a

certain amount of water (4 cm3). In order to determine the water absorption coefficient Cabsi, [kg/m2.s],

it is necessary to build a graph of the amount of water absorved over time [s].

The water permeability test was carried out according to Costa (1997) and it basically

measures the amount of water per unit area that drains out of a porous material and the time it takes

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to do it, due to the imposition of a pressured water flow. For this test the blocks had to be covered with

an epoxy resin in all surfaces, except for two 5 cm diameter circles in opposite surfaces, where the

water would flow. The water had a pressure of 1 bar and the amount of water was measured for 1, 3

and 5 minutes of test. The permeability coefficent was calculated using equation (2):

k! = !.!!.∆!

(2)

being kw the permeability coeficiente [m/s]; Q the flow drained [m3/s]; l the thickness of the block [m]; A

the area of water penetration [m2]; and ∆P the water pressure [m.w.c.].

The dripping test was carried out according to the NZS 4298 (1998) and it measures the

erosion caused by the dripping of 100 mL of water, when dropped 400 mm above the surface of the

block, between 20 and 60 minutes. After the test is finished, the erosion on the block is measured and

it is broken in half so that the moisture penetration can be evaluated. This test pretends to simulate

soft rain.

The pressure spray method was carried out according to the NZS 4298 (1998) and it

measures the erosion on a covered surface of a block with a 105 mm diameter circle opening caused

by a water jact of 0,5 bar 470 mm apart from the block. This test takes an hour, occurring stops every

15 minutes in order to measure the erosion. After the test is over, the block is broken in half so that the

moisture penetration can be evaluated. If the block is totally eroded before an hour, the test is

considered finished. This test aims the simulation of heavy rain.

4. Results and discussion

4.1. Fresh state

On Table 4, one can observe the results of the tests performed on the fresh state. Table 4: Fresh density and porosity of the mixes.

Mix Water content [%]

Weight of the reference block [g]

Fresh density [kg/m3]

Fresh porosity [%]

N 10 2544 1967 32,6

CBH 10 2840 2084 29,4

C 9,5 2632 2035 30,7

The moisture content values observed on Table 4 were slightly lower than the OMC estimated

previously (12,5%), but are within the range of values indicated by some authors (10 a 13%) (Silva et

al., 2014; Jiménez Delgado & Guerrero, 2007).

As it can be seen, composition N presented the lower value of density. This was to be

expected since it did not contain any cement, which presented a density 15% higher than the earth

and recycled aggregate. The composition CBH presented a density marginally higher than C (about

2,5%), being this situation explained not by the presence of the hydrophobe product but due to the

slightly higher water content which promoted higher compaction strength. Still, according to Rigassi &

CRATerre-EAG (1985), the density of CEB should present a minimum of 1870 kg/m3, being 2200

kg/m3 the recommend value, so the values obtained were considered acceptable. From Figure 4 it

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can be concluded that the introduction of cement produced a higher net increment on the density than

the difference on water content.

Figure 4: Relation between weight and fresh density.

The porosity of a material is inversely related to the density, which was confirmed by the

presented values. It is also possible to claim that the stabilization reduces the porosity (Lourenço et

al., 2002; Duarte, 2013). As it is possible to see, the composition CBH presented the lower porosity,

and once again, it can be explained by the proximity of its water content to the OMC.

4.2. Hardened state

Physical and mechanical performance

The results of the physical and mechanical tests can be observed on Table 5.

Table 5: Results of the physical and mechanical tests.

Age RH Mix Ultra-sonic waves velocity [m/s]

Thermal conductivity [W/(m.K)]

Compressive strength [MPa]

Tensile strength [MPa]

28 days

Sat

C 2324 1,7 4,40 -

CBH 2171 1,76 4,96 -

CSH 2269 1,78 4,20 -

Lab

N 1227 0,72 1,98 0,37

C 1704 0,80 6,22 1,8

CBH 1592 0,75 6,77 1,63

CSH 1713 0,81 6,72 1,91

NSH 1410 0,77 1,65 0,45

Dry

N 1105 0,61 - -

C 1243 0,65 - -

CBH 1078 0,65 - -

CSH 1596 0,67 - -

NSH 1402 - - -

90 days Lab C - - 11,14 -

N

C

CBH

1960

1980

2000

2020

2040

2060

2080

2100

2500 2550 2600 2650 2700 2750 2800 2850 2900

Freshde

nsity

[kg/m

3 ]

Weight[g]

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The results of the compressive strength test confim that stabilized compositions present

higher mechanical resistance, about 3-3,5 times higher than the non-stabilized compositions, being

this situation was also reported by Aubert et al. (2013) and Falceto (2012). The decrease of the

strength between the blocks exposed to the Lab conditions and saturated is noticeable (about 20%),

being this reported by other authors as well (Riza et al., 2010). Due to the hydration of the cement and

variations inherent to the moisture content, at 90 days of maturation, the compressive strength of the

composition C increased about 80%. As it’s also observable, the values of the blocks of the

compositions having hydrophobic products don’t vary much from the reference ones, which implies

that these do not have influence in the compressive strenght of the blocks.

The stabilized compositions presented values of tensile strenght roughly 5 times higher than

the non-stabilized. Morel & Pkla (2002) using the same method obtained similiar results. Once again,

the compositions having hydrophobic products did not present tangible differences when compared to

the reference ones. Namango (2006) claims that the results from the compressive strength test were

about 6 times higher than the ones from this test. This trend was observed, however it was only about

4 times. It was possible to observe a clear trend between the ultra-sonic wave velocity and the

humidity conditions that the blocks were exposed before the test. The higher values are observed

when the blocks are saturated, as expected, due to the filling of the empty spaces with water,

promoting the propagation of the wave. However, when analysing them between compositions there

are several variations. This test can be subjected to deviations due to variations during the drying

process and in the blocks itself.

Similarly to the results of the ultra-sonic test, it is possible to verify a trend between the

thermal conductivity and the relative humidity of the blocks. The higher values of thermal conductivity

were obtained on the saturated blocks, which presented values over the double than the dry blocks.

On a closer look, one can observe that the values of the stabilized compositions are always higher

than the other compositions, for the same RH state. This situation is due to the higher thermal

conductivity value of cement when compared to the earth. Sampaio et al. (2014) obtained values

about 20% higher than the the ones presented regarding non-stabilized blocks exposed the variable

thermal and moisture conditions.

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Durability performance

On Table 6 there are layed the results of the water durability tests. Table 6: Results of the durability tests.

Mix Capillary

absorption [g/cm2.min0,5]

Immersion absorption

[%]

Low pressure

absorption [kg/(m2.s]

Permeability [m/s]

Dripping test Pressure spray method

Erosion depth [mm]

Moisture penetration

[mm]

Erosion depth [mm]

Moisture Penetration

[mm]

N - - 0,233 - 9,7 84,7 56 -

C 0,056 13,3 0,013 2,61E-07 0 58,3 0 56

CBH 0,034 11,8 0,006 2,52E-07 0 53,7 0 47

CSH 0,008 13,7 0,001 2,22E-07 0 0 0 49

NSH - - 0,002 - 0 0 56 -

CL 0,052 12,3 0,006 - 0 35,5 56 -

NL 0,131 12,9 0,009 - 0 38 0 35

As it was expected, the composition NL presented the highest water absorption coefficient

value, since it has the highest porosity. It is also possible to confirm that the incorporation of

hydrophobic products in cement stabilized compositions allow the achievement of lower values of the

capillary absorption coefficient than the reference one (C), thus proving their efficiency. The

composition CSH presents a drecrease of 85% compared to C, which suggests that SH provides a

capillary cut. In a general way, the linseed oil provides a very interesting outcome when applied to

non-stabilized blocks, since it allows them to finish the test, however on stabilized blocks, the

decrease of the coeffcient is marginal. The CBH compositions, besides having the hydrophobic

product, presented the lowest porosity value (Table 4), which can explain the result obtained.

Analysing the capillary absorption over time (Figure 5), it is possible to observe that the linseed oil had

a very effective performance during the first 30 minutes, presenting results near the ones achieved by

the composition CSH. However, for older ages, the latter continued to have an effective performance

while the composition CL performance approached the reference mix (C). This can be explained by

the fact that linseed oil creates a barrier on a block of about 5 mm that might have been destroyed

along the test.

Figure 5: Absorption of water over t.

0,00

1,00

2,00

3,00

4,00

5,00

6,00

0 10 20 30 40 50 60 70

Abs

orpt

ion

[g/c

m2 ]

Duration [min0,5]

NL

C

CL

CBH

CSH

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It is possible to observe that the immersion absoption achieved don’t vary much among

compositions, since this test only allows to estimate the level of porosity approachable to water. The

lowest level of absorption is achieved by the composition CBH, not being this fact necessarily

dependent of the existence of BH, but in part, due to its porosity. Falceto (2012) using the same

method, achieved values of 14% of absorption for stabilized compositions, which confirms the present

data. It is important to highlight the results of the composition NL, since only with the presence of

linseed oil was it possible for a non-stabilized composition to finish this test.

As it would be expected, the non-stabilized compositions present higher water absorption

under low pressure than stabilized compositions, being these results in accordance with the capillary

aborption test results. Regarding non-stabilized compositions, there are substancial reductions of the

coefficients when hydrophobe products are used, specially SH (99%). It is also visible that non-

stabilized compositions (NSH/NL) presente a similiar performance of the stabilized compositions

(CSH/CL), thus demonstrating the ability of the products to dissemble the seen different performances

between the reference compositions (N and C), as can be seen on Figure 6. Once again, the

composition CBH presented intermediate values between the compositions C and CL/CSH, as seen.

Figure 6: Water absorption under low pressure of stabilized blocks – a) and linseed oil protected blocks –b).

In general, all the compositions showed similar water permeability values, which suggests that

the hydrophobic products interfere essentially in the mechanism of transport related to capillary

suction, not having a significant effect on CEB permeability. The BH basically creates a gel that works

at a capillary cut level, not interfering in CEB porosity. When testing rammed earth walls, Delgado &

Guerrero (2006) obtained values of permeability of 10-8m/s, being this value higher than for CEB due

to the slightly higher content of clay.

Analysing the results from the dripping test, one can claim that only the composition N

suffered erosion of 9,7 mm. As it was expected, the stabilized compositions reveal much better results

than the non-stabilized ones. Analysing the moisture penetration values, it is easy to see that the

surface hydrophobe provides the best results, since it did not allow the water penetration, presenting

the other products an intermidiate behaviour between this and the reference compositions. Regarding

stabilized compositions, the SH, as seen, presents the best results, having the linseed oil reduced the

moisture penetration by 35%; the BH allowed a marginal reduction, so its contribution is not clear,

regarding this test.

From the pressure spray results, it is possible to say that only the stabilized compositions

would not be eroded by heavy rain, since the non-stabilized ones were totally eroded during this test.

Similar results were obtained by Falceto (2012). So, one can affirm that the hydrophobic products do

14

not have much influence on non-stabilized blocks when exposed to this test. After a more thorough

review of the moisture penetration results of stabilized compositions, it is clear that the hydrophobic

products increase the resistance to water penetration, being the best results portrayed by the CL

compostion. This situation can be explained due to the penetration of the linseed oil, which is about

6 mm whereas the penetration of the SH is only ≅1 mm. So, when exposed to a heavy rain situation,

the SH is washed away faster than the linseed oil, allowing the faster penetration of moisture. The BH,

as seen, works at a capillary cut level, which is not relevant to this test.

5. Conclusions

In the present study, the mechanical and durability behavior of non-stabilized and cement

stabilized compressed earth blocks having hydrophobic products were analysed. The following main

conclusions have been drawn:

• The moisture content of the mix before compression is extremely important, and it should be

as close to the OMC as possible, since it will allow the achievement of maximum densities.

The higher the density of the block is, the lower the porosity will be. As seen, compositions

having lower porosities present, in general, better mechanical performance as well as some

durability tests (capillary absorption and Water absorption under low pressure);

• The stabilization of the blocks increases about 3-3,5 times the compressive strength of non-

stabilized ones, for Laboratory moisture conditions. However, when exposed to saturated

conditions, the compressive strength increases 2,5 times, being verifies the sensitive of CEB

to moisture conditions;

• As expected, compositions having lower porosity present higher thermal conductivity

coefficients, not existing great differences between compositions considering the same RH

state;

• The linseed oil presented very interesting results when used on non-stabilized blocks, since it

allows them to resist direct contact with water (capillary absorption and immersion tests),

when it was only possible with stabilization;

• The surface hydrophobe presented the best results regarding capillary absorption test,

dripping test and water absorption under low pressure test, having the other products

intermediate results between these ones and the reference ones;

• When exposed to heavy rain conditions, the stabilization of the blokcs is a key element for

them to fulfill the requirements of the test;

• The composition CBH presented generally slightly better results than the C, but had always an

underchiement behaviour when compared to CSH;

• The performance of the hydrophic products was only tested on an early age, so it is important

to evaluate its durability over time;

• Hydrophic products do not present any influence on the blocks, regarding physical and

mechanical properties.

15

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