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Compressive strength testing of compressed earth blocks


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As with other masonry units, compressive strength is a basic measure of quality for compressed earth blocks. However, as compressed earth blocks are produced in a great variety of sizes the influence of block geometry on measured strength, primarily through platen restraint effects, must be taken into account. The paper outlines current methodologies used to determine compressive strength of compressed earth blocks, including direct testing, the RILEM test and indirect flexural strength testing. The influence of block geometry (aspect ratio), test procedure and basic material parameters (dry density, cement content, moisture content) are also discussed. Proposals for the future development of compressive strength testing of compressed earth blocks are outlined.
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Compressive strength testing of compressed earth blocks
Jean-Claude Morel, Département Génie Civil et Bâtiment, URA 1652 CNRS, Ecole Nationale des
Travaux Publics de l’Etat, Rue Maurice Audin, 69518 Vaulx en Velin cedex, FRANCE.
Abalo Pkla, Département Génie Civil et Bâtiment, URA 1652 CNRS, Ecole Nationale des Travaux
Publics de l’Etat, Rue Maurice Audin, 69518 Vaulx en Velin cedex, FRANCE
Peter Walker, Dept. Architecture & Civil Engineering, University of Bath, Bath, BA2 7AY, UK.
Tel: 01225 386646; Fax: 01225 386691; Email:
As with other masonry units, compressive strength is a basic measure of quality for compressed earth
blocks. However, as compressed earth blocks are produced in a great variety of sizes the influence of
block geometry on measured strength, primarily through platen restraint effects, must be taken into
account. The paper outlines current methodologies used to determine compressive strength of
compressed earth blocks, including direct testing, the RILEM test and indirect flexural strength testing.
The influence of block geometry (aspect ratio), test procedure and basic material parameters (dry
density, cement content, moisture content) are also discussed. Proposals for the future development of
compressive strength testing of compressed earth blocks are outlined.
Keywords: Compressive strength testing; Compressed earth blocks; Aspect ratio
Corresponding author
1. Introduction
Plain masonry elements, such as loadbearing walls, arches and vaults, have developed to take
advantage of the material’s relatively high compressive strength. The capacity of masonry in
compression is strongly related to the compressive strength of the masonry units (stone, brick, and
block), as well as mortar strength, bonding pattern and many other factors. Though other parameters,
such as density, frost resistance and water absorption, may be specified in design, compressive
strength has become a basic and universally accepted unit of measurement to specify the quality of
masonry units. The relative ease of undertaking laboratory compressive strength testing has also
contributed to its universality as an expression of material quality.
For many centuries hand moulded unburnt mud blocks, adobes, have been used for loadbearing
masonry structures. Though adobes are most used for lightly loaded single and two-storey residential
building, adobes have also been used to construct 10-storey high buildings in Yemen [1]. Over the past
fifty years compressed earth blocks have developed and been increasingly used, especially in
developing countries such as Mayotte [2,3]. In that case, earth is a clayey soil with variable quantity
and quality of clay depending of the building site. The clay fraction is less than adobe, and usually less
than 25% of dry wet. The considerable variation of the composition of earth makes more important the
measurement of the compressive strength of compressed earth block and skilled masons to find the
optimum compsition during the block manufacture.
Compaction of moist soil, often combined with 4-10% cement stabilisation, significantly improves
compressive strength and water resistance in comparison with traditional adobe blocks. Dimensional
stability and tolerances are also much improved, allowing construction procedures similar to fired clay
and concrete block masonry, rather than the wet hand moulded method generally used for adobe.
Quality control strength testing of compressed earth blocks has often followed procedures developed
for fired clay and concrete block units [4]. However, the suitability of these procedures has largely not
been checked by scientific study. The compressive strength of compressed earth blocks can be many
times lower than similar fired bricks. Resistance is also significantly influenced by moisture content.
Previous studies have reported on the compressive strength characteristics of compressed earth blocks
[5-13]. Strength is improved by compactive effort (density) and cement content (generally linear
correlation), but reduced by increasing moisture content and clay content (cement stabilised blocks).
National and international standards have also developed for compressed earth block test procedures
[4, 14-16]. However, unlike other masonry units, there is little general consensus on test procedure for
compressed earth blocks. Should blocks be tested wet or dry? How should dimensional effects, such as
aspect ratio, and platen restraint be taken into account?
This paper reviews the current situation and seeks to inform the on-going debate on the development
of compressive strength test procedures for compressed earth blocks. A number of the different test
procedures currently in use are described and, where possible, compared. Results of experimental
studies are also presented. The compressive strength of blocks measured by differing tests is also
compared with other parameters, such as three-point bending strength.
2. Outline of compression test procedures
2.1 Background
Experimental compressive strength of materials such as concrete, stone, fired and unfired clay is a
function of test specimen dimensions. Load is normally applied uniformly through two stiff and flat
hardened steel platens. As compressive stress increases the test specimen expands laterally, however,
due to friction along the interface between the platen and test specimen, lateral expansion of the
specimen is confined. This confinement of specimens by platen restraint increases apparent strength of
the material. As the distance between the platens, relative to the specimen thickness (aspect ratio),
increases the platen restraint effect reduces.
In materials that are readily cast, such as concrete and mortar, the enhancement in compressive
strength is accommodated by specifying a standard test specimen size and shape, usually cube or
cylinder. Though test results are not true (unconfined) values for compressive strength of the material,
by adopting a standard geometry comparison between different samples and specified requirements is
readily achieved. However, when testing preformed, rather than cast, specimens of varying size, such
as masonry units, the effects of specimen geometry on unit strength is not as easily accommodated.
The approaches adopted in testing of fired clay, concrete and compressed earth block testing are
discussed within the following section.
2.2 Compressive strength testing fired clay and concrete masonry units
The compressive strength of both fired clay and concrete masonry units is determined by load testing
single units in a compression testing device, in a manner similar to the testing of cast concrete and
mortar cubes. To accommodate surface unevenness units are either temporarily capped with either 3-4
mm thick plywood or similar sheeting, or capped with a thin layer of cementitious or gypsum based
mortar. Units satisfying dimensional requirements can generally be tested between temporary
cappings. Bricks containing frogs and other recesses are generally filled in with a suitable strength
mortar, though cellular and hollow units are usually tested with the voids unfilled and strength
expressed as a function of gross, rather than net, cross-sectional area. In countries, such as Australia,
where hollow concrete blocks are laid on two parallel thin beds of mortar along their faces (face shell
bedding), unit compressive strength is correspondingly determined by applying the test load through
the two face shell capping strips [17].
In countries where fired clay bricks are generally manufactured in one standard size, such as the UK
where nearly all bricks are nominally 215 x 102.5 x 65 mm, geometrical effects on apparent brick
strength are ignored as specimen geometry is uniform, as with concrete cube or cylinder testing.
Similarly in having a standard test geometry design values for material properties, expressed as a
function of concrete cylinder or unit brick strength, are readily obtained.
Concrete masonry blocks come in a much greater variety of sizes and formats (solid, cellular and
hollow). Consequently in the current British Standard for masonry [18] the effects of unit geometry are
catered for in determination of design compressive strength of concrete block masonry by expressing
values as a function of both apparent block strength and geometry. Alternatively in the draft Eurocode
for structural masonry, block strengths are normalised by applying a shape factor to account for aspect
ratio effects [19]. In Australia similar geometrical variations in both fired clay and concrete blocks are
also catered for by applying a geometrical correction factor. The empirically based aspect ratio
correction factor [20] seeks to remove the influence of platen restraint by converting test values to
unconfined strengths (defined as that achieved by specimen with an aspect ratio of at least 5). For
standard Australian fired clay brick, measuring 230 x 110 x 76 mm, the aspect ratio correction factor is
0.60, for example.
2.3 Compressive strength testing compressed earth blocks
2.3.1 Direct unit strength
The procedure adopted in many national standards and codes of practice is similar to that used for fired
clay and concrete blocks [4]. Individual units are capped and tested directly between platens. Block
surfaces are usually sufficiently flat and parallel that only thin plywood sheet capping is necessary. As
blocks are also typically solid preparation of recesses and voids is not necessary. Blocks are generally
tested in the direction in which they have been pressed which is also the direction in which they are
generally laid. Test samples generally comprises between 5 and 10 blocks.
There are a few internationally recognised standard compressed earth block sizes, such as 295 x 140 x
90 mm, corresponding to the type of block press in use. However, in general block sizes vary widely
[1,15]. The method of production, in general non-industrial, enables the manufacturer to vary block
size, and shape, to suit requirements by using mould inserts.
Geometrical effects on individual block compressive strength are generally treated in one of two ways.
In many cases standard test procedures make no attempt to correct test result for platen confinement.
Average or characteristic compressive strength is simply expressed following statistical manipulation
of individual test results [4]. In an alternative approach, used in both Australia [15,21] and New
Zealand [14], platen restraint effects are catered for by factoring test values with an aspect correction
factor. Correction factors used, Table 1, are generally the same as derived for fired clay units, though
other work has suggested alternatives believed to be more appropriate to compressed earth blocks [22].
In some cases cubes cut from solid blocks have been tested in direct compression instead. However,
comparative strength testing of blocks and cubes of same material show poor direct correlation, though
in this case cubes were pressed separately rather than cut from the blocks [13]. By testing cubes effects
of geometry on compressive strength might be readily accommodated. However, the effects of
material non-uniformity arising from the manufacturing process require further investigation.
2.3.2 RILEM test
In an attempt to directly measure unconfined compressive strength of compressed earth blocks RILEM
Technical Committee 164 has proposed the test set-up shown in figure 1 [23]. To double the
slenderness ratio of the test specimen, blocks are halved and stacked bonded using an earth mortar bed
joint. The earth mortar joint replicates masonry construction and enables even and uniform stress
transfer between stacked blocks. To enable even transfer of stress between platens and blocks the
specimens are capped with a layer of neoprene. A sheet of Teflon is also placed between the platen and
specimen at each end to minimise friction. Half blocks may be prepared following splitting strength
test, an indirect tensile strength test similar to the Brazilian test performed on concrete cylinders.
In development of this test results have been compared with those from cylinder tests of similar
material. The test seeks to replicate compressive strength developed by cylinder of aspect ratio 1.5:1,
which is seen as giving unconfined strength value [9,23]. Compressive strength test results using the
RILEM procedure have been independently checked by three research laboratories in France and
North Africa [9,12,24]. Compressive strengths using this procedure are compared with values obtained
from cylinder tests or testing half blocks (with Teflon sheeting in place to reduce friction) in figure 2.
All the CEB are made with manual press (most popular) and that is why the compressive strength is in
a range of 2-3MPa, higher values need hydraulic press or higher content of cement which is often too
Results are from materials with and without cement stabilisation, each point representing an average of
between 2 and 13 repeat tests. On average the RILEM test under-estimates the unconfined
compressive strength of blocks or cylinders. Variation between the RILEM and cylinder test result is
in part due to variations in material dry density between the two different methods of manufacture.
The inclusion of a mortar joint in the test specimen alters the specimen format and behaviour. The test
is no longer simply on an individual masonry unit, but effectively on a simple stacked bonded masonry
prism. The mortar joint, even if made from identical material, is weaker and less stiff than the blocks,
due to higher initial moisture content and lack of compaction. In compression greater lateral expansion
of the mortar joint places the blocks in a state of compression and biaxial lateral tension [25], whereas
restraint of the blocks places the mortar joint in a state of triaxial compression. Inclusion of mortar
joint introduces a further variable into the test set-up, with performance of specimens also dependent
on the quality of work in combining half blocks and mortar joint.
2.3.3 Indirect tests
A small number of indirect compressive strength tests have been developed, primarily in order to allow
in-situ quality control testing of materials in the absence of laboratory testing facilities. The most
widely quoted indirect test methodology is the three-point bending test. Blocks are subject to single
point loading under simply supported conditions through to failure. Forces required to induce failure in
this manner are typically 80-150 times lower than that required to induce failure under uniform
compression and as such are normally quite achievable under site conditions, without resort to
sophisticated equipment. Flexural failure stress is calculated assuming pure bending (maximum
moment divided by elastic section modulus), ignoring the other potentially significant effects such as
shear and compressive membrane action (arching). Correlation between compressive and three-point
bending strength has been established experimentally by a number of workers; results show
considerable scatter but there is widely considered to be sufficient evidence to enable lower bound
prediction of compressive strength based on flexural strength [26]. Design guidelines and standards
have adopted this approach. Disadvantages of the test method include susceptibility to defects in the
blocks (shrinkage cracks). Another, less widely accepted, indirect test method is the splitting test, akin
to the Brazilian test used for concrete, in which the block is loaded in compression through two thin
steel bars along opposing faces. This induces indirect tensile stress, causing the block to split along the
line of the load. The advantage of this methodology is the greatly reduced forces required to induce
failure. Blocks from this test can also be used in the RILEM compression strength test, enabling direct
correlation between the two measured results.
3. Compressive strength characteristics of compressed earth blocks
3.1 Influence of specimen geometry
As previously discussed the geometry of test blocks has a significant influence on the value of
measured compressive strength using the standard test methodology described in section 2.3.1. The
apparent strength enhancement due to platen restraint depends on the ratio of height to thickness
(aspect ratio) of the block. As previously outlined one approach adopted is to correct measured
strength by a single aspect ratio correction factor. The distinct advantage of this approach is that it
enables a variety of different block sizes to be used, but of course it relies on accurate correction
To date, the correction factors in use were established for fired clay masonry rather than weaker and
non-uniform compressed earth blocks. Geometric effects on compressive strength of compressed earth
blocks stem not only from platen restraint, but also influence of friction during block manufacture.
Density of blocks produced using single acting ram presses is not constant, but reduces with height
away from the ram face due to friction along the mould sides. Experimental studies have confirmed
that the apparent unconfined compressive strength value is achieved when the aspect ratio reaches 5
[11,20]. However, beyond an aspect ratio of 1.5 the compressed earth block material is unlikely to be
homogeneous, due to friction during manufacture [23,27]. Though confined strengths have shown
significant scatter at lower aspect ratios, the correction factors proposed by Krefeld [20] would seem to
provide a reasonable improvement of the data.
Walker [28] has also reported on the influence of block geometry on RILEM test results. For varying
sized blocks, made from the same material, results of the RILEM test procedure do not correspond to
the results of direct block tests. Under direct (confined) compression block strength increased from 8.5
N/mm2 (aspect ratio 125/140) to 16.0 N/mm2 (45/140) despite a 3% reduction in density of the thinner
block. The experimental skew in apparent strength due to geometry is at least 88% of the measured
performance. When the same blocks were tested using the RILEM test the thinnest block produced the
least compressive strength, 2.26 N/mm2 compared to 3.14 N/mm2 for the 125 mm high block. In this
case the geometric effect is reversed (lowest strength for the thinnest block), and much reduced in
comparison with the direct strength test, with the experimental skew only around 28% of the measured
data. Geometric effects are least evident when aspect ratio correction factors are applied to the
confined direct block values, yielding strengths of 5.7 N/mm2 (125/140) and 6.4 N/mm2 (45/140)
respectively. However, considering all dry densities for these corrected data still leads to a coefficient
of variation of 26%.
The influence of block geometry on RILEM test strength is expected from classical masonry behaviour
[25], as the single mortar bed joint remained approximately 10 mm thick throughout. For thinner
blocks the 10 mm mortar joint has had a significantly greater effect on prism strength, figure 3. The
geometric effect could, perhaps, be mitigated by adjustment of mortar joint thickness in accordance
with varying block height, and warrants further investigation. It should also be noted that in practice
the variation in compressed earth block geometry is not as extreme as described above, but it is
possible to extend this work to adobe where the variation in block geometry can be even greater.
3.2 Influence of test procedure
Compressive strengths derived from differing test procedures or specimens have been compared in
experimental studies. Correlation between the RILEM test and adjusted strength values from direct
testing whole blocks is shown in figure 4. The correlation between the adjusted block strengths and
prism test results is similar to that shown in figure 2 above, though prism strengths are around 300%
lower than the corresponding adjusted block strength. Unlike the previous correlation there is no direct
parity between adjusted block strength and the RILEM test strength. This disparity might suggest,
together with the results in figure 2, that the Krefeld aspect ratio correction factors are incorrect.
3.3 Influence of dry density
Compressive strength of compressed earth blocks is strongly related to dry density achieved in
compaction. Compressive strength of individual blocks consistently increases as dry density increases,
figure 5. This relationship between strength and density has been consistently proven by test data over
the past 20 years [1]. In India block compressive strength is controlled through density [13]. Prior to
production the density and compressive strength of prototype blocks are determined in the laboratory.
Subsequently block density, for given a compactive effort, is ensured by carefully measuring, by mass,
the quantity of material added to the mould.
3.4 Influence of cement content
Cement is added to compressed earth blocks to improve durability and, indirectly, wet compressive
strength. Data produced by various researchers show strong, often linear, correlation between
compressive strength and cement content. Data shown in figure 6 is typical of the relationship between
direct compressive strength and cement content.
3.5 Influence of moisture content
Moisture content of blocks at testing has a significant influence on resultant compressive strength.
Blocks are typically tested at oven dry or ambient air dry moisture conditions, reflecting that under
service conditions. Strength reduces as moisture content increases due to the softening of binders by
water and development of pore water pressures. For plain soil, unstabilised, blocks compressive
strength when saturated is zero. Though there is some variation, depending on soil properties and
cement content, compressive strength of cement stabilised blocks following water saturation is
typically around 50% of that measured under dry conditions [10]. Moisture contents of unstabilised
materials at testing should ideally reflect in-service conditions. Testing cement stabilised blocks
following saturation allows minimum strength to be determined under easily controlled and replicable
moisture conditions, though conditions unlikely to be experienced in practice. The inclusion of mortar
joint in the RILEM test makes strength determination under saturated conditions difficult, and more
typically testing is undertaken under ambient air-dry conditions.
4. Three-point bending test
The three-point bending test has been recommended and used as a simple indirect means to measure
compressive strength of compressed earth blocks [26, 29]. Flexural modulus of rupture is determined
assuming simple, pure, bending. However, recent research has proposed alternative formulation in
recognition of the arching action that is postulated to occur in the blocks as a result of the small span to
depth ratios that inevitably occur [30]. The equivalent compressive strength σcif is given by:
cif 24
where P is failure load of the three-point bending test, L span between two roller supports, e the height
of the block, l the width of the block and ho a characteristic height, taken as 23 mm for typical sized
compressed earth blocks [30].
In both cases, classical bending [26] or with formula (1) [29], there is a linear relationship between
direct compressive strength and the strength given by the three-point bending test. Figure 7 based on
both the RILEM test procedure and that derived indirectly from three-point bending test using equation
(1). Though for only a few test results the correlation may be considered encouraging. Whereas the
correlation is poor with unconfined direct unit compression test.
5. Summary and conclusions
Compressed earth blocks are produced in a greater variety of unit sizes than many other masonry
blocks. If compressive strength is to remain a meaningful and general characteristic defining quality
and suitability of compressed earth blocks, the influence of unit geometry on performance needs to be
accommodated in a reliable and consistent manner.
To date, the most recommended compressive strength test procedure used for compressed earth blocks
undertake direct, confined, tests on single units. To accommodate geometric variation aspect ratio
correction factors, developed for fired clay masonry, have been adopted. Test results show wide
variation and suggest that at the low aspect ratios typical for most blocks, the current aspect ratio
correction factors may not be suitable. Cutting standard shaped specimens from solid blocks, such as
cubes, might be an alternative solution to this problem, though the effects of material non-uniformity
needs to be further evaluated.
RILEM Technical Committee 164 has proposed an alternative test method that represents a radical
departure for testing masonry units. Blocks are tested together with a mortar joint in a prism. Though
results have shown that the test performance is less dependent on variation in block geometry, the test
procedure may provide an unconfined masonry strength rather than block strength. The RILEM test is
also dependent on mortar performance and quality of work in preparation of the prism.
Indirect testing, such as the three-point bending test, can provide an indication of relative strength.
However, the test results are subject to considerable scatter. Recent developments in stress analysis of
three-point test performance could improve reliability of this simple test, but further work is required
to assess its generality, including the effects of material type, block geometry and method of
manufacture on performance.
In conclusion, further research work is required to investigate the influence of geometric effects on
compressive strength performance if a generalised test procedure is to be developed and widely
accepted. Direct testing of blocks needs to correlate unconfined performance with confined for a
variety of block sizes and materials. As effects such as manufacture procedure are likely to have a
significant influence, a single universal relationship may not be forthcoming. The significance of
mortar properties (materials, thickness) and block height on RILEM test needs further investigation
before the test can be universally accepted. However, as fundamentally the direct block test and
RILEM test measure two different parameters, it might be that in the future the two test procedures
will co-exist alongside each other.
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Table 1. Aspect ratio correction factors
Aspect ratio
Krefeld’s correction factor
(use linear interpolation)
Heathcote & Jankulovski’s correction factor
(non linear)
Figure 1 RILEM test set-up
y = 1,1339x
R2 = 0,7332
0,0 1,0 2,0 3,0 4,0
RILEM prism compressive strength (N/mm2)
Compressive strength (N/mm2)
data from pkla 2002, Half block test
data from hakimi 1996, Cylinder test
data from olivier 1994, Cylinder test
Figure 2 Comparison of unconfined block or cylinder strengths and RILEM prism compressive
strength, manual compaction press.
R2 = 0.7029
R2 = 0.985
40 60 80 100 120 140
CEB height (mm)
Compressive Strength (Mpa)
corrected= unconfined value
procedure (a)
Figure 3 Effect of block height on RILEM test compressive strength, the correction is made
following sample aspect ratio with Heathcote data (table 1)
y = 3.0338x
R2 = 0.5957
0.0 1.0 2.0 3.0 4.0
RILEM compressive strength (N/mm2)
Block compressive strength (N/mm2)
Figure 4 Comparison between RILEM prism strength and direct block strength
1.7 1.8 1.9 2.0
Dry density (Mg/m3)
Compressive Strength (N/mm2)
soil with bentonite and 4% cement
soil with kaolinite with 4% cement
soil with kaolinite, no cement
Figure 5: Relationship between dry density and compressive strength
0 2 4 6 8 10 12 14
Cement content (%)
Compressive Strength (N/mm2)
Guettala 1997
Walker 2000
Figure 6 Effect of cement addition on CEB compressive strength.
R2 = 0.8193
R2 = 0.5507
0 2 4 6 8
Compression strength from 3 point bending
test (Mpa)
Compression strength (MPa)
Rilem test
Direct unit compression corrected
with Heathcote
Figure 7 Comparison between RILEM test and bending strength estimation of compressive
strength from formula (1)
... Compressive strength and lime content have a strong, often linear, correlation. Lime added to compressed soil increases its durability and, thus, wet compressive strength (Morel et al., 2007). ...
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Remedial action for heavy metal-contaminated soils is imperative for preventing heavy metal leachability and minimizing environmental risks. This study evaluated the use of limekiln dust (LKD) as a heavy metal stabilization agent for Ghanaian gold mine oxide ore tailing material. Heavy metal-laden tailing material (Fe, Ni, Cu, Cd, and Hg) was collected from a tailing dam site in Ghana. Stabilization was done using acid neutralization capacity (ANC) and citric acid test (CAT) while all chemical characterization was done using X-ray fluorescence (XRF) spectroscopy. Various physicochemical parameters including pH, EC, and temperature were also measured. The contaminated soils were amended with LKD in doses of 5, 10, 15, and 20 wt.%. The results revealed that the contaminated soils had concentrations of heavy metals above FAO/WHO stipulated limits of 350, 35, 36, 0.8, and 0.3 mg/kg for Fe, Ni, Cu, Cd, and Hg, respectively. After 28 days of curing, 20 wt.% of LKD was found to be appropriate for the remediation of the mine tailings of all the heavy metals studied except Cd. Ten percent of the LKD was noticed to be enough in remedying soil contaminated with Cd since the Cd’s concentration reduced from 9.1 to 0.0 mg/kg with a stabilizing efficiency of 100% and a leaching factor of 0.0. Therefore, remediation of contaminated soils of Fe, Cu, Ni, Cd, and Hg with LKD is safe and environmentally friendly.
... The study performed by Morchhale et al. [21], showed that the bricks made of copper tailings stabilized with cement, are characterized by good strength supported by the low water absorption. Many studies [22,23] have shown the effect of cement stabilization on the increase of mechanical strength of bricks. Lasisi and Ogunjide [24], have demonstrated that increasing laterite/ cement rations reduces the strength and increasing the grain size fines increases compressive strength. ...
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Huge volumes of phosphate waste rock are generated during the extraction of sedimentary ores, and deposited around the mining site, covering large surfaces and causing many environmental problems. This study presents a cost-effective and environmentally friendly solution allowing the valorization of phosphate waste rock (PWR) to produce eco-friendly compressed stabilized earth bricks-CSEB. CSEB is one of the earthen building materials family, offering many advantages in terms of insulation and thermal properties, good mechanical performances, use of local raw materials, and low embodied energy… For the soil classification, PWR was first characterized using chemical, mineralogical, and geotechnical properties. Then, various mixtures were formulated at the laboratory scale using PWR with cement as a stabilizer and red marl employed to enhance the cohesion and brick’s consistency. The objective was to investigate the role of cement and red marls additions, curing conditions, and brick shapes on different CSEB properties. The optimal formulation that satisfied the requirements of the international standards was adapted to the pilot scale, using hollow and solid brick forms with a size of (250*125*75) . The laboratory results showed that the use of 10% cement with 10% red marl seems to be the most adequate. The pilot scale findings revealed that the addition of cement and red marl improves the compressive strength that reaches 5.70 and 2.56 MPa, for hollow bricks in dry and wet states, respectively. For solid blocks, 4.51 and 2.44 MPa were obtained in both states, respectively. The obtained water absorption coefficients respect the requirements of the standards. The thermal conductivity values are acceptable; 0.44 and 0.51 The TCLP test of the elaborated bricks showed that the concentrations of leached contaminants (Pb, Cd, As, Cr) are below the requested limits.
... Compressed Earth Blocks (CEBs) are currently being used to construct earthen buildings [6]. CEBs are traditionally stabilized with 5-10% cement [7,8]. Furthermore, the production of cement necessitates high-temperature heating, which produces greenhouse gas emissions that contribute to global warming [9]. ...
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Soil stabilization is usually used to enhance the soil properties and characteristics. Cement or supplementary cementitious materials (SAMs) are used for soil stabilization. Stabilized soil can be used in several civil constructions and structures such as roads bed, roadside stability and slop, and subgrade layers for pavement structures. Also, developing countries use stabilized soil for building houses due to low-cost, energy-efficient, and environment benefits. In this study, compressed earth blocks (CEBs) stabilized with Rice Husk Fiber without the use of cement are utilized to evaluate the effects of Rice Husk Fiber on the soil properties and behaviors. Different percentages of rice husk fiber (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0%) are blended into the moist clay and pit sand mixture. The CEBs were extracted from the soil mixture and dried. CEB cube crushing strength and modulus of rupture were determined in laboratory tests. The effect of rice husk fiber on the fundamental structural properties of CEBs was studied and compared to those that did not contain rice husk fiber. The results show that increasing the amount of rice husk fiber reduced shrinkage, drying time, cube crushing strength, and modulus of rupture by half (50%) as well as load-carrying capacity by 25%. According to existing guidelines, the compressive strength and modulus of rupture of the CEBs presented in this study are sufficient for use in earth buildings.
... Observations show that, unlike soil cohesion, biochar generally decreases the compressive strength of soil samples that were compacted at OMC, regardless of the DOC. While it has been established that ρ d (or DOC) and water content (or S r ) control soil compressive strength by affecting the void ratio and matric suction (Consoli et al., 2007;Li et al., 2015;Morel et al., 2007), the attention in the case of BAS remains limited. ...
Use of biochar as a soil amendment for climate change mitigation and environmental remediation has been intensively studied over the past decade, yet the growing interest in biochar for geo-environmental applications is primarily motivated by its active interactions with soil in terms of engineering properties. The addition of biochar can significantly alter the physical, hydrological, and mechanical properties of soils, but the diverse biochar characteristics and soil properties lead to the fact that a generalized conclusion on the impact of biochar on soil engineering properties is difficult to reach. Considering that the effects of biochar on soil engineering properties at multi scales could also potentially affect the applications of biochar in other fields, this review intends to provide a comprehensive and critical overview of biochar implications for soil engineering properties. Based on the physicochemical properties of biochar pyrolyzed from varying feedstocks and pyrolysis temperatures, this review analyzed the physical, hydrological, and mechanical performances of biochar-amended soils and the underlying mechanisms. Among others, the analysis releases that the initial state of biochar-amended soil requires special attention when evaluating the effect of biochar on soil engineering properties, yet it is usually neglected in the current studies. The review closes with a brief overview of the potential impacts of engineering properties on other soil processes, and future needs and opportunities for further development of biochar in geo-environmental engineering from academia to practice.
... During the curing process, the rate of gained strength is higher at the 12 beginning and reduces with age later, while the precise prediction about the age required for stabilization is not 13 established in worldwide standards [21]. The after-cured strength of CSRE has been predicted with the empirical 14 equations proposed by some authors by considering the effect of water-cement ratio [29], 28-day strength (time) [30], 15 and the combined effect of water-cement ratio and time [31], or water-cement ratio, time and dry density [32] at 16 laboratory curing conditions. 17 Furthermore, during the hydration process, the accumulated hydration products fill part of the pores in the earth 18 material by consuming water, which increases the dry density and suction, and decreases the porosity. ...
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To understand the general coupled chemo-thermo-hydro-mechanical (CTHM) behavior of CSRE, this work reviews the cement hydration process in CSRE and its influence on the thermo-hydro-mechanical (THM) behaviors of CSRE materials. It has been observed that the unconfined compressive strength of CSRE increases with material dry density. Compared to other factors such as grain size distribution, dry density, and water content, the effect of cement hydration on the variations of the soil water retention curve (saturation-suction scale) and thermal conductivity is not significant. The free water consumed in the hydration process exists in the form of chemically reacted water and gel water. Moreover, cement hydration increases the mechanical resistance of CSRE over time and is influenced by the curing conditions. The characteristics of CSRE vary considerably among different experimental works reported in the literature. The combined effect of initial water content, initial dry density, initial grain size distribution, initial cement content, curing conditions and curing time needs to be considered together from the design stage of CSRE material. The lack of a global view of all types of CSRE materials poses great difficulties in making a worldwide acceptable standard for CSRE materials. Consequently, based on the experimental results from literature review, a finite element numerical framework is proposed to reproduce a typical CSRE material as well as to globally explain the complex coupled CTHM properties of CSRE from the design stage.
... Similarly, earthen building codes from around the 5 world, e.g., those developed by the International Code Council [57,58], Standards New Zealand [51,60], and Indian Standard [61], depend heavily on established methods for ordinary masonry and reinforced concrete structures when providing guidance on engineering analysis of earthen structure [62,63]. In recent years, most of the research studies focused on understanding the engineering characteristics of the CSEB components [22,23,[69][70][71][72][73][74][75][76][77][78]24,[79][80][81][82][83]26,43,[64][65][66][67][68]. Only few studies have been performed to investigate the mechanical behavior of CSEB masonry systems at the structure level [21,[84][85][86][87][88][89][90]. ...
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Earthen masonry has been used since prehistoric times to build structures primarily made from soil. In the modern era of concrete and steel, earthen structures have seen a significantly reduced usage, because of their relatively low strength and lack of standardization. However, they are once again getting attention because of their low cost, low carbon footprint, energy efficiency, use of indigenous materials, and inherent simplicity. In particular, compressed and stabilized earth block (CSEB) construction is appealing as a viable response to the lack of affordable housing in the US and worldwide, as over two billion new houses will be needed in the next 80 years. Currently, only few building codes in the US allow the use of CSEB construction through a prescriptive approach adapted from ordinary masonry. As a result, earthen buildings represent only a small fraction of the building inventory in the US, even in places where this type of construction is historically established and culturally appreciated. The CSEB construction is even rarer in locations with humid and rainy climates such as the US Gulf Coast, because of the poor resistance to degradation experienced by traditional earthen construction and its widespread perception as a substandard structural choice under extreme wind loads. Therefore, the present research aims to engineer modern earthen construction by: (1) demonstrating the feasibility of CSEB masonry housing in the US Gulf Coast region; (2) enhancing the properties of CSEBs using sugarcane bagasse fibers, an agricultural by-product; (3) developing a computationally efficient and robust interface element’s constitutive model for simulating the mechanical behavior of masonry; (4) investigating the capabilities and limitations of finite element (FE) simplified micro-modeling techniques that are frequently used for simulating the behavior of ordinary masonry; and (5) developing an FE detailed micro-model specifically tailored for earth block masonry systems. The results of this research represent an advancement in the engineering knowledge necessary for (1) promoting CSEB construction that can endure humid climate and hurricane wind, and (2) understanding the structural behavior of CSEB masonry, which is ultimately required for developing material-specific design standards of CSEB masonry systems.
[Document available at:] This doctoral thesis presents a thorough analysis of the mechanical, structural and seismic behavior of rammed earth structures, aimed at encouraging the use of this technique in modern construction. Rammed earth is a traditional construction technique that has been used all over the world since antiquity, but today it is attracting renewed interest as an environmentally sustainable building solution. However, the lack of national and international standards based on the structural knowledge of this kind of constructions, makes it difficult for designers and builders to adopt this technique in new constructions. In this regard, as a first step, this thesis presents a detailed compilation of the most relevant results obtained by several researchers about the mechanical and physical properties of rammed earth, including the laboratory tests used to measure these properties and the additives and reinforcements that can be used to improve the material behavior. An experimental testing campaign is carried out to evaluate the mechanical properties of rammed earth stabilized with one of the most relevant additives, lime, focusing on the effect of increasing lime contents and the strength development process, two factors that are essential to build constructions with this technique and that have not been thoroughly studied yet. Compression tests and nondestructive ultrasonic pulse velocity tests are performed. For unstabilized rammed earth, the uniaxial compression tests are combined with diagonal compression test in order to assess also the shear behavior of the material, essential to understand its failure mechanisms (particularly under extreme loads such as a seism). This data is used to develop a numerical model of the material based on the concrete damage plasticity model in the FEM software Abaqus. The proposed behavioral model is evaluated by replicating with finite elements the diagonal tests carried out in laboratory. Considering the vulnerability of rammed earth structures under the action of an earthquake and the numerous areas of earth construction with a significant seismic hazard, in the last part of this study the seismic behavior of this kind of structures is evaluated. The state of the art about this topic is presented and analyzed, including the scientific research about the structural behavior of rammed earth walls subjected to horizontal loads, potential seismic reinforcements, and requirements and recommendations indicated in the existing standards and guidelines about earth construction in seismic areas.
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La terre crue est un matériau de construction ancestral qui a fait ses preuves en termes de résistance et de durabilité. Les édifices anciens en terre, dont certains sont classés dans le Patrimoine Mondial, sont encore là pour en témoigner. C'est un matériau local écologique par excellence en vertu de ses performances thermiques et acoustiques, mais aussi parce qu'il nécessite beaucoup moins d'énergie pour sa production que les matériaux conventionnels, et qu’il ne génère pratiquement pas de déchets lors de son élaboration puisqu’il est parfaitement recyclable. Ces arguments font de la terre crue un matériau de construction prometteur surtout dans une époque où l’intérêt pour le développement durable et le respect de l’environnement ne cessent de grandir. Au Maroc, le pisé, l’adobe et la brique de terre comprimée sont les techniques de construction en terre les plus pratiquées. Cependant, les procédés appliqués pour leur mise en œuvre restent, pour une large part, des procédés artisanaux qui s’appuient sur un savoir-faire local en voie de disparition. Cette disparition est d’autant plus justifiée que les références techniques normatives concernant la construction en terre sont peu nombreuses voire inexistantes. C’est dans ce contexte que cette thèse a été initiée afin de contribuer à l’émergence d’un travail de recherche et développement pour la standardisation de la construction en terre au niveau national. Ainsi, deux problématiques majeures se posent : la normalisation des essais de caractérisation du matériau et le développement de modèles de calcul des ouvrages en terre. Ces deux problématiques ainsi que celle de la durabilité du matériau terre ont d’abord été discutées dans le cadre de l’étude bibliographique faisant partie de cette thèse. Ensuite, une approche expérimentale a été adoptée afin de mettre au point une procédure générale pour la formulation et la caractérisation en laboratoire de la terre comme matériau de construction. Ainsi, plusieurs mélanges de terre crue, de granulats et de stabilisants (ciment, chaux, paille d’orge et fibres de palmier dattier) ont été testés pour évaluer leur comportement mécanique en compression et en traction. Les résultats de ces tests, réalisés suivant l’approche expérimentale adoptée, montrent qu’il est possible d’améliorer les caractéristiques de la terre, comme matériau de construction, rien qu’en optimisant sa distribution granulométrique. Ces résultats montrent également qu’avec un dosage optimal en fibres végétales, on peut atteindre quasiment les mêmes résistances mécaniques que peut apporter une stabilisation au ciment ou à la chaux, et ce tout en rendant le matériau plus élastique et plus ductile. L’analyse des résultats des essais de compression uniaxiale conduit à l’établissement de corrélations à tendance polynomiale de deuxième degré entre les contraintes et les déformations avant la rupture, et ce pour l’ensemble des mélanges testés, y compris la terre seule. Il a été également établi que cette corrélation est d’une tendance presque linéaire pour les mélanges terre-fibres, mais pas pour les autres mélanges.
Lightweight concrete (LWC) panels are becoming popular in buildings because of being lightweight, which allows easy transportation, handling, and installation. They provide the opportunity for modular construction. They also have insulating properties with thermal conductivity of 0.026-1.0 W/m-K. However, they have low thermal mass, which causes overheating during the heatwave period in Mediterranean and temperate climates. Therefore, Phase Change Materials (PCM) are integrated into LWC panels to increase thermal storage, mitigate overheating, and increase energy efficiency. However, the integration of PCM in LWC panels also increases their thermal conductivity, which is not favorable for a sustainable building. There is a need to reduce the thermal conductivity of PCM-integrated LWC panels. Thus, this study aimed to develop new lightweight heat-resistive and thermal storage panels (HRSPs) using porous fillers and PCM for energy-efficient building applications. First, the optimum PCM melting point for cool temperate climates of Melbourne was identified through parametric analysis considering a typical Victorian house as a case study. The result showed that the optimum PCM melting point for free-running and air-conditioned houses is 30°C and 25°C, respectively. Based on these findings, capric acid (CA) PCM with a 29-32°C melting point was selected. The integration of PCM in cementitious composites may suffer from leakage issues during mixing with cement and other aggregates. The leaked PCM, such as fatty acids, may acidify concrete and reduce its compressive strength. The traditional leakage test proposed by previous researchers was insufficient to identify the microscopic leakage of PCM and its potential acid attack on concrete. Moreover, the conventional Form Stable PCM (FSPCM) synthesis procedures are energy-intensive, increasing the embodied energy of FSPCM. This study proposed a new FSPCM synthesis procedure to reduce energy use, eliminate acid attacks and increase PCM absorption capacity in porous material for energy-efficient buildings. The proposed method was energy-efficient, with CA absorption of 75% in porous hydrophobic expanded perlite (HEP). However, due to acid attack, the compressive strength and thermal conductivity at 75% CA absorption were lower than one with 60% CA. Hence, the absorption of PCM should not be the only criterion for developing FSPCM. More indicators should be considered to develop an optimum FSPCM. This study proposed six indicators, including absorption, thermal conductivity, strength, thermal inertia, latent heat storage, and thermal storage, to select the best porous materials to absorb PCM. American Society for Testing and Materials (ASTM) standards were adopted to measure proposed indicators. A comparative study was conducted to select the best porous materials amongst Silica Aerogel Granules (SAG), Hydrophobic Expanded Perlite (HEP), Nano-clay (NC), Recycled Expanded Glass (REG), and Silica Fume (SF) to absorb CA and develop FSPCM. In this study, the FSPCM-integrated concrete panels were named thermal energy storage panels (TESP). The comparative analysis revealed that SAG-based TESP was meeting all five indicators accept compressive strength (3.66 MPa), which was lower than the minimum compressive strength (4.14 MPa) criteria for non-structural applications. However, HEP-based TESP had acceptable compressive strength and thermal conductivity with the second-best thermal inertia and heat storage, making it a suitable porous material for absorbing polar PCM for buildings. However, the thermal conductivity of TESPs was still higher than LWC because of the higher thermal conductivity of PCM and concrete, although the TESPs have higher thermal storage. Thus, there is a need to develop a TESP with high latent heat storage, low thermal conductivity, and acceptable mechanical properties. To reduce the thermal conductivity of TESP, sand was volumetrically replaced with SAG to prepare Heat Resistive and Storage Panels (HRSP) using the proposed particle-density-based approach. The developed SAG-based HRSP had lower thermal conductivity than TESP with similar thermal storage. Although HRSP had higher thermal conductivity than SAG-based LWC, it resulted in higher energy savings (9%), emission (24%), and comfort than SAG-based LWC because of higher thermal inertia and storage. Moreover, the HRSPs had lower embodied energy and carbon than SAG-based LWC. However, the SAG-based HRSP still had higher embodied energy than normal concrete panels. Consequently, the SAG was replaced entirely with REG particles to develop eco-friendly HRSP for buildings. Results revealed that REG based HRSP had 27% lower thermal storage then SAG-based HRSP due to high thermal conductivity and slightly lower latent heat storage. The compressive strength of REG-based HRSP (17.77 MPa) was very close to the minimum compressive strength for the structural application of concrete. Applying REG-based HRSP in a building envelope had slightly higher discomfort hours than SAG-based HRSP, and it also reduced annual energy use and CO2 emission by 8.24% and 20% lower than SAG-based HRSP in a typical Victorian house, respectively. In conclusion, the REG-based HRSP was the best eco-friendly material for buildings with acceptable structural properties and moderate energy savings potential. However, the SAG based HRSP was the most energy-efficient material with acceptable mechanical and thermal properties of the non-load-bearing structure.
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Nous fabriquons un treillis composé de deux bielles et un tirant, qui a un comportement à la rupture analogue à celui d'un bloc de terre comprimée (BTC) lors d'un essai de f lexion en trois points. On exprime simplement que la rupture peut se produire en compression dans les bielles ou en traction dans le tirant. La modélisation habituelle considère que le BTC est un solide poutre élastique linéaire sollicité en f lexion simple. Les données expérimentales de différents auteurs montrent que la modélisation simplifiée par bielles en compression et par tirant en traction, que nous proposons, est adaptée au cas des BTC. ABSTRACT. A lattice made of two struts and a tie is studied, having a behavior at failure close to that of a compressed earth block (CEB) during a 3 points bending test. Usually this test is modelled by considering that the CEB is an elastic linear beam under bending, at failure a tensile stress is then calculated. In this paper, by considering the failure occurring in the strut in compression or by traction in the tie, the failure stress is expressed simply as a compression strength or a tensile strength. MOTS-CLÉS : bloc de terre comprimée, compression, maçonnerie, f lexion, essai in situ.
This paper deals with an experimental study on the influence of soil composition on the strength and durability characteristics of soil-cement blocks. A brief summary of earlier studies on soil-cement has been presented. Effect of soil grading/composition on the strength of soil-cement blocks has been discussed in detail. Durability characteristics of soil-cement have been examined through tests such as alternate wetting and drying and expansion due to saturation. It has been found that sandy soils are best suited for cement stabilisation showing better strength and durability characteristics. The paper concludes with recommendations indicating the limits for soil grading and expansion due to saturation.
Indigenously stabilised black cotton soil (BCS) deposits exist in the BCS zones of India. Such soils have been designated as ash-modified soils (AMS). This paper deals with the investigations on the AMS soils for the production of stabilised mud blocks (SMB), used for masonry. Studies were earned out to understand the influence of stabilisers like cement and lime content, block density and curing period on the strength characteristics of SMB's using ash modified soils, a BCS soil and a red loamy soil. Long-term strength of SMB's has also been monitored over a period of 2 years. The results indicate that wet compressive strength of SMB's using AMS soil is very sensitive to density and stabiliser content. Stabiliser to clay ratio of 1.0 gives stable long-term strength for SMB's using AMS soils. These studies clearly show that AMS soils can be utilised for the production of stabilised mud blocks.