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Earth-Based Mortars: Mix Design, Mechanical Characterization
and Environmental Performance Assessment
R.L.M. Paiva1,a*, A.P.S. Martins1,b, L.R. Caldas1,c, O.A.M. Reales1,d,
R. Dias Toledo Filho1,e
1Programa de Engenharia Civil (PEC/COPPE), Universidade Federal do Rio de Janeiro (UFRJ),
Rio de Janeiro, Brazil
2Faculdade de Arquitetura e Urbanismo (FAU), Universidade Federal do Rio de Janeiro (UFRJ),
Rio de Janeiro, Brazil
email@example.com, firstname.lastname@example.org, email@example.com,
Keywords: Earth mortar, chemical stabilization, mechanical behavior, ACV
Abstract. The incorporation of sustainable materials in the civil construction sector has grown in
recent years to minimize environmental impacts. Among these materials, the use of earth, a local raw
material that does not require much energy for its processing, appears as an advantageous and
promising alternative. Earth mortars stabilized with natural binders, when compared to conventional
mortars, can have technological, economic and environmental advantages. The objective of this work
was to develop an earth-based mortar stabilized with mineral binders using a 1:3 binder to aggregate
mass proportion, and to evaluate its fresh and hardened state properties, as well as its environmental
impacts using Life Cycle Assessment (LCA) with a cradle to gate scope. The selected materials were
divided in four groups: (i) cement, hydrated lime, fly ash and metakaolinite (binders), (ii) natural sand
and coarse fraction of the earth (aggregates), (iii) calcium chloride and superplasticizer (additives)
and (iv) water. In the matrix formulation the clay fraction from earth constituted the majority of the
binder. The selection of supplementary cementitious materials as additional binders provided
improvements in workability and mechanical properties of the mortar. A mix design was carried out
using different cement (5; 7.5 and 10%) and fly ash (11; 13.5 and 16%) mass percentages. The
water/binder material ratio, superplasticizer content and calcium chloride content were 0.65; 2% and
1%, respectively. The results showed that an increase in fly ash content combined with a decrease in
cement content provided an increase in workability and a decrease in mechanical properties of
mortars. Nevertheless, the mechanical performance of the mortars remained above the minimum
values prescribed in Brazilian construction codes. From the results analysis it was concluded that
partial replacement of cement by fly ash provided greater workability in the fresh state and reduced
the environmental impacts of the earth-based mortar.
Buildings are responsible for around 33% of world energy consumption and about 30% of global CO2
emissions (IEA, 2019). A scenario projected by IEA (2019) identified the need of both reducing 30%
of the global energy demand by 2050, simultaneously with the doubling of the global built area, and
the maintenance of indoor air quality and thermal comfort. With regard to residential buildings, this
goal can only be achieved through the development of innovative and high-performance materials
and technologies, carbon and energy efficient, capable of passively regulating indoor temperature and
humidity, thus, minimizing the need for air conditioning.
Earth mortars have received increasing attention from the scientific community due to their eco-
efficiency characteristics (Santos et al., 2017; Melià et al., 2014). They have low embodied energy
and carbon because the energy required for extraction, transportation and preparation of raw material
is small when compared with conventional mortars (Santos et al., 2021). The referred mortars
normally don´t contain toxic compounds and are recyclable at the end of life (Santos et al., 2021).
Construction Technologies and Architecture Online: 2022-01-06
ISSN: 2674-1237, Vol. 1, pp 271-278
© 2022 Trans Tech Publications Ltd, Switzerland
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications Ltd, www.scientific.net. (#580846760-27/01/22,17:55:22)
Earth matrices with optimized mechanical resistance were produced by Perrot et al. (2018) using
different strategies : granular optimization, clay particles dispersion, addition of biopolymer and
textile reinforcement. From the combination of the strategies, composites with high compressive
strength and high deformability were produced. Santos et al. (2017) verified the influence of sand
granulometry and additions (fibers and hydrated lime) on the workability and physical-mechanical
properties of earth mortars. They concluded that a 5% lime addition improved the matrix workability.
The strength of earth mortars under compression and bending loads was investigated by Delinière et
al. (2014), which obtained average values of in the range of 1.3 to 2.1 MPa and 0.49 to 0.69 MPa,
respectively. Moevus et al. (2015) verified the influence of different dispersants on the properties of
earth mortars andfound a reduction in water consumption and an increase in the elasticity modulus
and compressive strength. The influence of the binder-aggregate relationship on the physical and
mechanical performance of earth mortars was investigated by Emiroglu et al. (2015). These authors
obtained an optimum ratio binder-aggregate between 0.43 to 0.66 (in mass), leading to the
maximization of the mechanical strength.
Santos et al. (2021) reviewed the Life Cycle Assessment (LCA) studies for mortars. They observed
that there is just small amount of studies using the LCA to assess the environmental benefits
associated with earth mortars. Melià et al. (2014) compared the environmental performance of earth
and conventional mortars, obtaining superior results for the first. Caldas et al (2020) compared the
potential environmental impacts associated with different earth mortars, with and without chemical
stabilizer (cement or lime). Earth mortars, even when stabilized, showed environmental gains of up
to 80% in the climate change impact category, compared to conventional mortars, considering the
same life cycle for both types coatings.
Although there are some studies in the literature addressing the performance of earth mortars, these
studies are still scarce, and it is necessary to expand knowledge regarding the mix design and global
performance. The objective of this work is the development of an earth mortar matrix with optimized
environmental credentials, which can serve as a basis for the production of durable composites with
high physical, mechanical and environmental performance, contributing effectively to a more
sustainable civil construction.
2 Materials and Methods
The binding materials used were the fine fraction of the earth (Eff = Ø <0.06 mm), hydrated lime
(HL), Brazilian Portland cement with high initial resistance (CPV), metakaolin (MK) and fly ash
(FA). The aggregates used were natural sand (NS) with a 850 µm maximum diameter of and the
coarse fraction of the earth (Ecf = Ø> 0.06 mm). The other constituents used were superplasticizer
Glenium 51 (SP), water (W) and calcium chloride (CaCl2) as an accelerator for cement hydration.
Table 1 shows the density values of the constituents used obtained by helium picnometry. The
granulometric curves of the binding materials were obtained using laser granulometry while
granulmetric curves of the aggregates were obtained by sieving following ABNT NBR 6457 (1986)
and ABNT NBR NM 248 (2003) standars. Results are presented in Figure 1.
Tab. 1: Density of materials
272 Bio-Based Building Materials
Fig. 1: Granulometric curves. (a) binding materials and (b) aggregates
2.2 Mortars preparation and specimens
For the production of earth mortars a binder materials:aggregates mass ratio of 1:3 was used. In order
to produce a mortar with low environmental impact the total binder materials were composed of a
fixed and a variable portion. The fixed portion contained 49% Eff, 10% MK and 20% HL. In the
variable portion three combinations of CPV and FA (5% CV+16% FA, 7.5% CPV+13.3% FA,
10% CPV+11% FA) were studied. The aggregate phase was composed of 17% Ecf and 83% NS.The
water-to-binder material ratio (w/bm) was fixed at 0.65, while 2% of SP and 1% of CaCl2 by mass
of binder were used as chemical additives.The composition of the mixtures produced in the present
study are summarized in Table 2. Nomenclature was abbreviated as earth based mortar (EBM)
followed by the x-y correlation where x corresponds to the percentage of CPV and y to the percentage
Mortars were prepared using a planetary mixed and poured in 50 x 100 mm (diameter x height)
cylindrical molds for uniaxial compression testing and 160 mm x 40 mm x 40 mm (length x width x
thickness) prismatic molds for three point bending flexural testing. The mortars were kept in the
molds, protected from moisture and demoulded after 48 hours. The curing of the specimens took
place in a controlled environment at a temperature of 23 ± 2 °C and a relative humidity of 55 ± 2%.
Tab. 2: Mixture composition (kg/m3)
EBM Binder materials Aggregates W SP CaCl2
23.09 73.87 92.34 46.17 226.24 235.47 1149.65 306.57 9.23 4.62
34.63 62.33 92.34 46.17 226.24 235.47 1149.65 306.57 9.23 4.62
46.17 50.79 92.34 46.17 226.24 235.47 1149.65 306.57 9.23 4.62
2.3 Mortars test methods
Mortars were characterized in fresh and hardened states. Fresh state testing included consistency
thorugh the flow-table method, according to ABNT NBR 13276 (2016), specific mass, according to
ABNT NBR 13278 (2005) and entrapped air content through the pressometric method, ABNT NBR
NM 47 (2002). For characterization in hardened state four specimens per sample were used after
28 days of curing. Uniaxial compression tests were performed in a universal testing machine
Shimadzu - 1000kN with displacement control at a constant deformatino rate of of 0.3 mm/min.
Compressive strength and the elastic modulus were determined according to Brazilian standard
ABNT NBR 5739 (2007) and ABNT NBR 8522 (2008). Flexural strength tests were performed
Construction Technologies and Architecture Vol. 1 273
according to Brazilian standard ABNT NBR 13279 (2005) using the universal testing machine
Shimadzu - 100kN with displacement control at a constant deformatino rate of of 0.3 mm/min.
2.4 Life Cycle Assessment (LCA)
The LCA was performed based on EN 15978 (CEN, 2011). The first two standards refer to the LCA
of any product, while the last deals specifically with building products. It was divided in: (1)
Definition of the objective, scope, and functional unit; (2) Life cycle inventory; and (3) Life cycle
The objective of this LCA is to compare the potential environmental impacts of three different mortar
mixtures developed in the laboratory. This study can be considered as a cradle-to-gate scope (CEN,
2011) and contemplates the following stages: raw material supply (A1), raw material transportation
(A2), and mortars manufacturing (A3). Firstly, the functional unit was defined as the volume of
mortars (in m³). Secondly, a mechanical performance indicator (in m³/MPa) for each environmental
impact category (e.g. for Climate Change in kgCO2-eq m-³/MPa) was adopted to verify the
differences between the compressive strength of the mortars and the environmental impacts. These
were denominated environmental intensity indicators, similar to the indicators used by Celik et al.
(2014) and Caldas et al. (2020).
For the Life Cycle Inventory (LCI) primary data was collected in the laboratory, while secondary data
was collected from Ecoinvent v. 3.6 and scientific literature. The electricity consumption of original
Ecoinvent data was adapted to the Brazilian energy mix and market transports. Transportation
distances were adopted for each material as follows: CPV and HL – 100 km, MK – 200 km, FA –
500 km, E – 10 km, NS – 50 km, CaCl2 and SP additive – 1000 km. Finally, for the mortar production
process (A3), ordinary processes that occur in a conventional mortar mixing plant were assumed
based on the Ecoinvent database. For the Life Cycle Impact Assessment (LCIA), the EN 15804 +A2
method version 1.00 was used. The assessment was performed with the SimaPro software. This
method was chosen since it is used in the last version of BS EN 15804 (CEN, 2012) that is the main
normative related with LCA applied to the building sector.
3.1 Characterization of fresh mortars
The fresh state characterization results of the earth based mortares are presented in Table 3. It can be
seen that all developed matrices presented consistency index values above the desired minimum value
of 180 ± 20 mm. It was also found that the aparent density remained approximateley constant (less
than 0.3% reduction), while the entrapped air content increased by up to 16%. The improvement in
the evaluated properties was found to be related with the increase in FA content, this as a function of
its physical characteristics (shape and sphericity); thus, providing better workability.
Tab. 3: Characterization of mortars in the fresh state
Total Air content
187 ± 0.20
1789 ± 1.25
4,2 ± 0.20
192 ± 0.21
1786 ± 0.20
4,3 ± 0.16
207 ± 0.24
1784 ± 3.82
4,9 ± 0.21
3.2 Characterization of mortars in the hardened state
Typical stress versus deformation curves obtined from compressive testing, and typical equivalent
flexural stress versus central deflection curves ontained from three point bending testing of EBM
5-16, EBM 7.5-13.5 and EMB 10-11 after 28 days of curing are presented in Figure 2.
Regarding compressive stregth results (Figure 2 (a)), all matrices developed an initial elastic linear
behavior followed by a nonlinear range, until reaching the maximum breaking strength. It was found
that the compressive strength was 3.89 ± 0.18 MPa, 1.92 ± 0.04 MPa and 1.67 ± 0.12 MPa and the
modulus of elasticity was 2.28 ± 0.42 GPa, 1.19 ± 0.22 GPa and 1.29 ± 0.08 GPa for EBM 10-11,
274 Bio-Based Building Materials
EBM 7.5-13.5 and EBM 5-16 for 28 days, respectively. Comparing the values obtained from EBM
10-11 with EBM 7.5-13.5 and EBM 5-16, a reduction of 50% and 57% is observed for the rupture
stress and 47% and 43% for the modulus of elasticity. A higher CPV content was found to be related
with higher strength, higher stiffness, and a more fragile and sudden rupture. Regarding flexural
testing results (Figure 2 (b)) it can be seend that for all matrices the initial stretch is linear elastic and
after the maximum tension peak it presents a sudden drop, indicating a low energy absorption
capacity. The flexural strength results were 1.57 ± 0.27 MPa, 1.08 ± 0.16 MPa and 0.75 ± 0.06 MPa
for EBM 10-11, EBM 7.5-13.5 and EBM 5-16 for 28 days, respectively. Comparing the values
obtained from EBM 10-11 with EBM 7.5-13.5 and EBM 5-16, a reduction of 31% and 52% is
observed for the rupture stress.
The stregth reduction found both in compressive and flexural testing can be can be asociated with the
increase in FA content and decrease of CPV. Due to its slow pozzolanic activity, replacing CPV with
FA makes the mortars stregth developement slower. Additinally, FA must compete with MK for the
available lime in the mixture, necessary for both pozzolanic reactions. It is worth mentioning that the
values obtained in the characterization in the hardened state for all the mortars developed meet the
minimum requirements established by Brazilian mortar standards.
Fig. 2: Mechanical characterization (a) uniaxial compression test and (b) flexion tensile test
3.3 Life Cycle Assessment (LCA)
LCA results are presented in Figs. 3-4. It was found that the binders (especially HL and CPV) were
materials with considerable impacts. The limestone calcination processes involved in their production
is significant for the climate change impact due to the CO2 release of from limestone decarbonation.
Most of the literature points out that the chemical binders are the main impactful materials in mortars,
including earth mortars, mainly for climate change impact (Santos et al., 2018; Galán-Marínet al.,
2015; Caldas et al., 2020). NS was also found to be another impactful material. Although the
production of sand (per kg of sand) does not have a great impact when compared to other
industrialized materials such as cement and hydrated lime, the highest participation in mass in the
mortar composition (more than 60%) results in considerable impacts, especially for land use,
particulate matter, eutrophication and photochemical ozone formation. The chemical additives, CaCl2
and SP were responsible for an important contribution in some impact categories, mainly: water use,
resources use (minerals), eutrophication (freshwater) and ecotoxicity.
The EBM 5-16 mortar presented smaller values for all impact categories, however with small
differences (reaching the maximum of 10% for some impacts) when compared with EBM 10-11.
When the mechanical performance is included in the analysis, the results lead to another direction in
terms of the choice of the mortar with the best environmental and mechanic performance (the EBM
10-11 presented the best results). We can see that it is better to use mixtures with more cement, since
this mixture presented lower values (with a difference superior than 100%) of environmental impacts
Construction Technologies and Architecture Vol. 1 275
for “m³.MPa”. Then, the replacement of Portland cement for fly ash in these proportions do not
represents a good strategy in terms of compressive strength.
Fig. 3: Environmental profile of the evaluated mortars. (A) EBM 5-16. (B) EBM 7,5-13,5.
(C) EBM 10-11
Fig. 4: Comparison of the environmental performance of mortars. (A) impacts per m³.
(B) impacts per m³.MPa
This work aimed to develop earth based mortars by obtaining behavior parameters in both fresh and
hardened states and evaluating their environmental performance. Three combinations of cement
(CPV) and fly ash (FA) (5% CPV+16% FA, 7.5% CPV+13.5% FA, 10% CPV+11% FA) were
studied, while the remaining components remained constant (hydrated lime - HL, metakaolin - MK,
natural sand - NS, additives and water). Based on the experimental results, the following conclusions
can be highlighted:
• In the fresh state, the matrix consistency index varied from 187 to 207 mm, with no segregation or
exudation, showing good flow properties. The density did not vary significantly for the three mixtures
• The matrix with higher amount of CPV and lower amount of FA (EBM 10-11) showed greater
compressive strength (3, 89 MPa), greater stiffness (2.28 GPa) and greater bending strength
• LCA showed that the binders (mainly HL and CPV) were the materials with the highest
environmental impacts, especially for climate change category. However, the mortar with highest
276 Bio-Based Building Materials
cement content also presented the best results when environmental and mechanical performance are
evaluated together. Therefore, the replacement of the cement for fly ash in the proportions evaluated
in this study do not represents a good strategy.
• The optimized earth matrix EBM 10-11 demonstrated good rheological, mechanical and
environmental properties, and can serve as a basis for subsequent research, with the production of
eco-efficient composites, contributing to a civil construction with low environmental impact.
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