This document summarizes research on the effects of adding agave biomass ashes from different combustion temperatures to cement mortars. The researchers collected agave leaves and dried them to produce bagasse, which was then burned at temperatures from 500-900°C to produce ashes. The ashes were characterized and tested as partial replacements for cement in mortar mixtures. Compressive strength tests on the mortar mixtures showed that replacing 5% of cement with ashes burned at 700°C or higher increased compressive strength by up to 90% compared to a reference mixture without ash.

1. Small addition effect of agave biomass ashes in cement mortars
J.R. González-López ⁎, J.F. Ramos-Lara 1
, A. Zaldivar-Cadena 1
, L. Chávez-Guerrero 1
,
R.X. Magallanes-Rivera 1
, O. Burciaga-Díaz 1
Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León 66450, México
a b s t r a c ta r t i c l e i n f o
Article history:
Received 10 October 2014
Received in revised form 24 December 2014
Accepted 26 December 2014
Available online xxxx
Keywords:
Agave
Subproduct
Characterization
Biomass
The use of industrial waste for the production of biomass is a topic that has gained increasing interest. This is due
to the need to use plants that do not affect the food supply when used for power generation from biomass. Agave
salmiana residues meet these characteristics. It has now been proposed as a possible source of bioenergy produc-
tion because of its growth characteristics. Therefore, in this research, the effect of combustion temperature of the
A. salmiana as it could happen in the energy production was studied. In addition, the characteristics of these res-
idues were analyzed to serve as a basis for possible future applications in construction materials. Results indicate
that the ashes are mainly CaCO3 when calcined at below 700 °C, and CaO above this temperature. The apparent
particle size was between 25 and 32 μm. However, it is observed that it consists of much smaller particles of ap-
proximately 300 nm. This reduction in size is related to decomposition at higher temperatures and is reflected in
the increase of the specific area up to 70%. The compression strength at early ages was up to 90% higher than a
reference, when 5% cement replacement mixes were performed.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
Agroindustry is a sector that mainly serves the needs of food supply,
both animal and human consumption. It has been recently observed
that there is a great potential for some of these industries, such as
sugar, wood, and others to share part of their crops to the production
of biomass for power generation [1–3]. As a result, studies of how to
turn these plants into energy sources have constantly been done to
increase power energy efficiency. However, once the plants have been
burned to produce energy, the product of such combustion is a residue
with variable content of organic and inorganic material; these residues
are the biomass ashes (BA) and in most of cases those residues do not
have a defined application; thus, confinement is regularly practiced.
BA contains different features and their properties must be established
to determine the possible uses or final disposal. Currently, a unique
classification to relate the properties and/or applications of BA does
not exist. However, several researches have been conducted to classify
BA depending on their chemical composition and mineral phase to an
extensive number of different reported BA [4]. This classification
considered carbonaceous content, organic phases, inorganic material
composition and fluids contained in them, and possible uses were
established from the main chemical element groups that are often asso-
ciated [5].
Currently, between 8 and 12% of energy is produced through bio-
mass direct burning. The result of the widespread use of energy pro-
duction from biomass will be the increase of the residues which are
known as biomass bottom ashes. This form of energy production
will continue growing and the amount of waste would be even com-
parable to the fly ash that is currently produced by burning fossil
fuels [6]. This makes it urgent to establish the possible uses that
these BA might have.
BA properties would depend on the characteristics of the plants
used as biomass; temperature and time process; and the procedure
for its final disposal. Thus, it is necessary to emphasize the need
to analyze in the most elaborate way, a methodology for BA charac-
terization, which considers chemical composition, mineral phases,
size, and morphology of the BA to elucidate their potential uses
or the characteristics under which they shall be confined. The
chemical composition of the BA is based on the content of the
main components, having regularly as main elements: O, C, H, N
in the organic material; and Si, Ca, K and Mg in the inorganic mate-
rial [4,7].
Among the plants that are potential sources for generating biomass
with high power generation potential, is the Agave salmiana. Further-
more, the conditions where these plants grow are mostly arid regions;
therefore vast land that is uncultivable now could be planted. So, a
great potential for future energy production has been found [8,9].
Fuel Processing Technology 133 (2015) 35–42
⁎ Corresponding author. Tel.: +52 8183294000x7252.
E-mail addresses: rhodio@hotmail.com (J.R. González-López), ralf_89s@hotmail.com
(J.F. Ramos-Lara), azaldiva70@hotmail.com (A. Zaldivar-Cadena), guerreoleo@hotmail.com
(L. Chávez-Guerrero), rxmagallanes@gmail.com (R.X. Magallanes-Rivera),
oswaldo.burciaga@gmail.com (O. Burciaga-Díaz).
1
Tel.: +52 8183294000x7252.
http://dx.doi.org/10.1016/j.fuproc.2014.12.041
0378-3820/© 2015 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
Fuel Processing Technology
journal homepage: www.elsevier.com/locate/fuproc

2. Nowadays, most of the grown agave is intended for the mezcal produc-
tion industry, which is an alcoholic beverage produced in Mexico. An
advantage of using this plant as a possible raw material for power gen-
eration is that it does not compete with worldwide food production and
it can be grown on currently unused arid land. Arid and semi-arid areas
are expanding more because of climatic changes, and it has been found
that plants of the genus agave can grow in places where the total annual
rainfall (TAR) is as low as 427 mm. However, this affects their annual
productivity in 10 Mgha−1
and increasing to 34 Mgha−1
when the
TAR is 848 mm. Thus, it can be said that the conditions of higher produc-
tivity for the production of these plants are not fully established [10] and
the energy demand will develop this sector and consequently the waste
generation previously mentioned. Then, because of the large amount of
waste generated from biomass, some researchers have proposed to
integrate high volumes of biomass residues in products such as paper,
activated carbon and agglomerates, focusing mainly on the use of
bagasse and not to the ash resulting from its burning as biomass.
Agroresidues that have gone through this same process are olive and
sugarcane, which are mostly consumed to produce food, and more
recently for biofuel. The extensive use of sugarcane has led to character-
ize its waste and to use it in building materials. Researchers have report-
ed the possible use of different sugarcane wastes: for the manufacture of
fibers, in fiber-reinforced composite materials [11]; and ashes in ceram-
ic matrices, such as refractory materials [12]; or the effect of the sugar-
cane BA addition as supplementary material in cement[13,14] as an
alternative for construction in countries with emerging economies.
The reactivity of the ash is limited because it contains organic residues,
since the commonly used calcination temperature is not high enough to
reduce the content of organics [15].
For all the aforementioned, studies have been conducted on the
biomass waste decomposition conditions that would help to determine
their actual use, either as a mineral filler [16], material for cement
replacement [17,18], or as building materials [19–22]. In general, the
agroindustrial waste of sugarcane production, has been through a pro-
cess of assimilation of their capabilities and limitations to increase its
use [23]. Nowadays, applications are real, and this is the same process
that other agroindustrial residues, as rice husks, have been through
[24,25]. Studies related to the waste of agave industry are currently
focused on the characterization and use of the fibers of agave, and to
its potential use in applications of environmental engineering, either
as a source of calcium or chemical removal [24–29]. Thus, the calcina-
tion conditions for its use as fuel and how these residues can be used
within different industries, must be appropriately set, considering that
agave will be a biomass for energy production widely used in the future.
2. Material and methods
The plant leaves used in this work were obtained from Mexico in the
region located at 100°23′46.793″W 25°21′53.218″N which corresponds
to a semi-arid region. In this area, the plant is used for the production of
mezcal and it corresponds to the A. salmiana specie. This plant has a life
cycle of about 6 years and it can reach a size from 2 to 6 m depending on
species. These plants were obtained by manual labor and the removal of
material was not concentrated in the heart (piñas) of the plant, but in
the leaves.
As it was mentioned above, BA has been proposed to be used poten-
tially in building materials. However, the way agave biomass ashes
(ABA) are used is rarely studied in the literature, so, according to studies
consulted, a detailed description of the components of ABA will be
required to determine their possible use. The first parameter to deter-
mine the feasibility of using ABA is to know their chemical composition,
because the ashes of biomass are normally distinguished for having
carbonaceous material, highly crystalline materials, and a higher alkali
content than coal ashes [30]. Some researchers have reported that
these BA classifications are first determined by their main chemical
group. The chemical composition of ABA depends on the type of plant
species, soil and the conditions under which they were calcined, and
stored [1,31]. In this study, the combustion of dry A. salmiana bagasse
was conducted at different temperatures, and the resulting ashes were
characterized by thermogravimetric analysis (TGA), visual inspection,
chemical composition, X-ray diffractometry, particle size distribution,
morphology, and loss on ignition (LOI). Trying to use agroindustrial
waste in building material applications suggests that a very important
factor for their interaction in cement matrices is LOI content, i.e. the
amount of organics it contains [4]. But, there is no agreement of how
to determine the LOI in the BA ashes. The composition of the BA varies,
and some of the components can be decomposed at high temperatures,
so the analysis of the loss on ignition is complex because it is not only
related to the carbon-based organic material, but with the decomposi-
tion of carbonates, sulfates, phosphates and other elements. In this
study, recommendations of ASTM C311 standard were used to LOI mea-
surement. The resulting ABA from the ashing process proposed was not
subjected to a washing process; this to observe if the material obtained
would have a direct potential use in cement matrix.
The compressive resistance is an ideal parameter to analyze whether
the additions of these residues are feasible to be into the cementitious
matrix. As it has been mentioned, there is a consensus that the produc-
tion of energy from biomass will have an important participation in the
sector, so that the residues obtained will be of concern in their final dis-
position. Previous experiences with other BA have proven to be feasible
in the replacement and/or addition within the cementitious matrix, so,
using a similar methodology will help to investigate this possibility. In
this research, the compressive strength effect of the addition of ashes
burnt at different temperatures was evaluated to determine the conve-
nience of burning the ashes at high temperatures.
The procedures used to fabricate specimens and to evaluate the
addition of ABA in mortars were based on ASTM C311 standard, which
indicates the requirements to evaluate a fly ash and natural pozzolans
that could be used in Portland cement concrete. Strictly speaking,
biomass ashes are not classified according to the ASTM C618 standard,
which exclude this type of ashes due to their chemical composition.
Compressive strength tests in mortars were carried out according
to ASTM C109 and the proportioning mixtures used are shown in
Table 1, which was designed to evaluate the cement replacement by
ABA for each of the different combustion temperatures, and for a mix-
ture reference made only with Portland cement. ABA dry densities are
also reported for each combustion temperature according to ASTM
C188. After the 28 days of curing, samples were dried at 60 °C to con-
stant weight. Then, they were immersed in water and constant weight
was measured according to ASTM C642 to determine water absorption.
From results in Table 1, it was observed that the effect of adding ABA is
not very significant, and the values are very similar to the mortar refer-
ence. Water absorption is related to durability; thus, from the results it
could be said that the capillary absorption effect will be similar in all test
mortars. The amount of replacement was 5% mass, instead of 20% as rec-
ommended by ASTM C618 standard; because the mortar consistency
measured by ASTM C1437 remarkably decreased as shown in Table 1,
the consistency reduction is related to the ABA particle size and their
chemical and mineralogical composition. The cement used was an
ordinary Portland cement according to ASTM C150 and aggregate
used was standard silica sand, according to ASTM C778. The sand
cementitious ratio was 1:2.75 and a water/cement ratio of 0.484.
3. Experimental procedure
3.1. Bagasse collection and preparation
Agave leaves were removed directly from the plant and subsequently
its initial weight was determined. Once they were weighed, they were
subjected to a drying process during 120 h and the results show that
the dry sample (dry bagasse) is about 12% of the plant weight. The drying
process removes water that could interfere in the combustion process.
36 J.R. González-López et al. / Fuel Processing Technology 133 (2015) 35–42

3. 3.2. Ashing process
During the fermentation of the agave bagasse, alcohol is obtained
and the rest of the organic material is discarded or it can be used as
fuel, although currently most of these residues are just burned outdoors
because of the lack of adequate facilities to recycle them. The residue
remaining from burning bagasse is an ash with highly variable character-
istics and depending on these features are the applications for which it
can be used. For this work, the combustion of the dry agave bagasse
was performed in a muffle at 500, 600, 700, 800 and 900 °C during 3 h.
The temperature of ash generation is intimately related to the chemical
and mineralogical species reported [32,33], so this study aims to
determine how these chemical species evolve and to estimate how its
performance could be based on to their chemical composition. ABA was
subjected to different tests in order to determine the most feasible
temperature for its possible use in the building materials applications as
a cement replacement.
Exposure to different calcination temperatures resulted in the decom-
position of agave ash, which gave different color depending on the tem-
perature to which it was exposed; see Fig. 1. Samples were identified as
AA and after this identification the test temperature used is presented.
Above 500 °C all the carbonaceous material is expected to be gradually
eliminated and the inorganic content is expected to remain [4]. On the
other hand, in order to remove harmful durability compounds, such as
K and Cl salts, temperatures exceeding 1200 °C may be necessary.
4. Results and discussion
The first step was drying the samples in an air convection oven dur-
ing 120 h at 60 °C in order to focus on the dry solid waste. Subsequently,
the dried samples were calcined using a direct burning as a source of
partial combustion to incinerate them, as it would have been done to
burn the residue in the field. The partial combustion process was
performed during 10 min approximately, and its objective was to
reduce the volume of organic material. However, large amount of carbo-
naceous residues were observed, so the carbon matter combustion will
be completed with the combustion ashing process. Once the dry leaves
were partially burned, they were placed in a muffle at several controlled
temperatures (500–900 °C) to perform the combustion processes.
The result of burning dry bagasse reduced the sample masses between
85 and 90% of the dry mass, so that, the total quantity of ash is about 2 kg
per 100 kg of plant. Therefore, if 10% of the currently unused arid and
semi-arid lands were used to plant A. salmiana or one of its variations
to generate biomass, the amount of ash at an annual average rate of
20 Mgha−1
, would be around 140 million tons per year. So, this expecta-
tive supports the necessity to have fully characterized this residue and
compare it to other similar residues.
4.1. Chemical analysis
In this work, all procedures were performed under laboratory con-
trolled conditions, avoiding contamination of the samples; and in small
quantities to ensure the homogeneity of the resulting ABA. The chemical
composition of homogenized samples was obtained by XRF and they are
reported as oxides in Table 2. ABA mainly contain CaO in more than 64%
wt for all samples; this is because these plants are composed primarily by
oxalates and carbonates. Other elements found in large quantities are
MgO and K2O, so it will be important to determine whether these
elements affect the performance once the waste is integrated into a
cementitious matrix [34]. The MgO content is affected by the combustion
temperature used; even at 900 °C the content of MgO disappears due to
decomposition of the compounds that have been reported in other
studies. On the contrary, the content of K2O is approximately constant
over the entire range of combustion [32]. These elements are normally
associated with the growth conditions of the plants and their alkaline
nature. The system found is therefore CaO + MgO + K2O.
ABA chemical composition differs from most of the previously
studied BA; however, the main group of composition elements is similar
to some BA previously reported. According to the classification proposed
by Vassilev et al. [4,5], it is an alkaline ash mainly composed of CaO and
MgO. These characteristics may be suitable for applications in construc-
tion materials; however, the high content of MgO, K2O and SO3 should
be considered. Other trace elements that were found are P2O5, SiO2,
Fe2O3 and SrO. The sum of all these is about 5% for ABA burned a temper-
ature below 800 °C; and 2.5% for 900 °C. Therefore, their effect should be
Fig. 1. Coloring waste resulting from the agave bagasse burning. It can be observed that the ash tone changes when calcined from 500 to 900 °C.
Table 1
Proportioning of mixtures used for compression testing of agave ashes calcined at different temperatures.
Sample OPC (g) ABA (g) Sand (g) H2O (ml) w/b ABA density (g/cm3
) Mortar consistency (mm) Mortar H2O absorption (%)
Reference 500 0 1375 242 0.484 – 195 2.07
ABA 500 475 25 1375 242 0.484 2.64 168 2.31
ABA 600 475 25 1375 242 0.484 2.70 172 1.96
ABA 700 475 25 1375 242 0.484 2.65 166 2.31
ABA 800 475 25 1375 242 0.484 2.65 162 2.05
ABA 900 475 25 1375 242 0.484 2.67 156 1.82
37J.R. González-López et al. / Fuel Processing Technology 133 (2015) 35–42

4. considered in future researches related to the effect on the durability of
these ashes.
4.2. Thermal gravimetric analysis (TGA)
Agave decomposition depends on combustion ashing temperatures;
the decomposition of agave is reported in the thermogravimetric analy-
sis of Fig. 2, having used a sample of 10.93 mg with a heating tempera-
ture ramp of 10 °C in air atmosphere. The graphic can be divided in
different zones: loss of moisture for up to 150 °C; and decomposition of
organic products between, 185 and 347 °C; above this temperature, the
carbonaceous compounds will begin to decompose. The graphic shows
that burning at a temperature lower than 500 °C will leave a larger
amount of organic waste than burning above 500 °C, which leaves an
ash with a more homogeneous appearance and in which some thermal
changes were seen above 700 °C. The amount of ash obtained after
these calcination processes was about 7%, so handling a range between
500 and 900 °C will give an idea of what properties can be obtained
from this ash depending on their physicochemical properties, without
exposing the ABA at such unnecessary high temperature that would
melt them.
4.3. Loss on ignition
In this paper, the methodology of subjecting the samples to 750 °C ±
50 °C was applied during 2 h. Samples calcined at each of the tests
temperatures were placed in a crucible at 750 ± 50 °C during 2 h to deter-
mine the LOI. The results are shown in Table 3. From these, it was found
that the lower the calcination temperature, the higher the loss on ignition.
Therefore, the amount of organic waste in the ash could be up to 20%
higher at the lower temperature, in relation to the maximum ashing
temperature tested. The LOI values were not reported when the ashing
temperature was higher than the LOI test temperature. From these
results, it can be seen that the LOI of ABA previously burned, probably
only leading mainly to the decomposition of the CaO-based compounds.
However, a study using a different methodology by the law of LOI could
indicate what really is decomposing.
4.4. X-ray diffractometry
Agave plant decomposition, after ashing temperatures, left an ash
residue of approximately 1.6% compared to the leaves' weight. The
residues obtained by burning dried material show that they are mainly
composed of calcium carbonate, potassium phosphate oxide and mag-
nesite; see Fig. 3. However, carbonates, CaCO3 and Mg (CO3) began to
decompose at a temperature between 500 and 700 °C. Because of that,
a reduction in intensity for the peaks of this phase was observed in
the counts until the CaO becomes the largest mineralogical phase in
the ash when it is burned at 900 °C. All these compounds have been
reported in other studies that confirm the alkaline nature of the ABA,
and that they are composed of highly crystalline material and common
mineral phases. The content of ABA mineral phases is different from
other reported, such as BA sugar cane and wood waste, which could
have pozzolanic characteristics [35]. Temperature affects the type
of compounds that may exist due to different phenomena such as
Table 2
Chemical composition of the ABA in terms of ashing temperature.
%wt.
AA500 AA600 AA700 AA800 AA900
MgO 16.133 16.182 7.945 6.401 –
SiO2 1.452 1.451 1.416 1.468 1.341
P2O5 3.674 3.452 2.558 1.845 –
SO3 0.762 0.777 0.721 0.702 –
K2O 12.664 12.68 13.452 12.477 15.046
CaO 64.639 64.601 71.708 76.861 82.113
Fe2O3 0.239 0.198 0.157 0.541 0.845
SrO 0.111 0.110 1.153 0.143 0.167
Fig. 2. Thermogram of agave bagasse.
Table 3
Loss on ignition for each calcination condition.
Sample ID LOI (%)
AA 500 28.50
AA 600 26.00
AA 700 23.76
AA 800 –
AA 900 –
38 J.R. González-López et al. / Fuel Processing Technology 133 (2015) 35–42

5. oxidation, decarbonation, evaporation or fusion and, results agree with
the obtained from XRF chemical composition.
4.5. Scanning electron microscope (SEM).
4.5.1. Morphology and apparent particle size
The size and morphology of the BA particles are also critical variables
in determining a possible application in building materials. ABA could
be considered as semi-reactive compounds with some applications as
binders [36]. When ABA were prepared for SEM observation, they showed
a tendency to agglomerate, probably because of their size. This tendency
made it difficult to determine their individual particles. Immediately
before the SEM observation, the samples were subjected to agitation in
a dispersion of isopropyl alcohol ultrasonically during 30 min, and
subsequently they were deposited onto the slide. Fig. 4 shows that
agitate ultrasonically the samples dispersed in the solution is insufficient
to completely separate the particles, as they tend to agglomerate into
lumps of about 25 mμ.
The ashing process should affect the decomposition characteristics.
Thus, this decomposition is expected to result in a refinement of the
particle size, which was not possible to observe due to the agglomeration.
This decrease in particle size can be demonstrated by the higher specific
area reported in Fig. 5. The calcined samples were analyzed by gas
physisorption i.e. BET fineness, using a sample of 4 mg. The values report-
ed in the tests indicate that the specific area is increased depending on the
combustion temperature. The maximum values were increased to reach
14.0 m2
/g at a temperature of 800 °C and then they were subsequently
slightly reduced. These changes can be associated with the decomposition
of the original compounds or decarbonation process. As the temperature
increases there is a separation of particles, and at a higher temperature
than 800 °C there is an apparent agglomeration due to exposure to this
temperature.
Agglomerations observed at low magnifications by SEM, correspond
approximately to the determined average size by Laser Diffraction
Particle size, where at different ashing temperatures, the apparent
particle size was between 25 and 32 μm (see Fig. 4). In consequence,
the apparent particle size is the result of this agglomeration. However,
when observing at higher magnifications it was found that these
agglomerations are composed of individual particles with sizes ranging
from about 0.300 μm and up to 2.400 μm, as it can be seen in Fig. 6.
The use of compounds of this nature can be consistent within a
cement matrix hydrated phases. A way to evaluate the affinity of ABA
with an ordinary Portland cement matrix OPC is replacing the cement
with ABA and testing compressive strength development. However,
these tests are limited to the immediate response, so, other consider-
ations regarding the workability and durability must be addressed.
4.6. Compressive strength of mixtures with ABA additions
The results of performing additions of the ashes in an OPC matrix
and testing them in compression are shown in Fig. 7. From ABA chemi-
cal composition, it can be determined that the potential of pozzolanic
reaction is low because the contents of compounds forming CSH gel
are not significant (low content of SiO2) [35,37]. Therefore, the behavior
reported in studies in which the ashes mainly contain SiO2 and react
pozzolanically, is not expected [38]. However, other types of mecha-
nisms can be developed from the compounds of ABA; calcite is currently
used as filler in composite cements. Some researchers have observed
that adding calcite in low percentages can promote the reaction at
early ages of C3A and accelerate hydration of C3S [39–41]. The reactivity
of these additions depends on the particle size. When preparing the
mixtures, water demand should be taken into account, because the
surface area of these additions is very large, and it could cause complica-
tions to the workability of the sample.
The effect of adding ABA in the OPC matrix is very noticeable at early
ages where compressive strength at 7 days was 90% higher for the ABA
burned at 500, 600 and 700 °C than OPC mortar reference, as is shown in
Fig. 7. The ABA burned at 800 °C developed a resistance at 7 days 10%
lower than the reference days. This may be related to the decomposition
of carbonates and alkali presence in the ABA. At 900 °C the behavior was
similar to that at temperatures between 500 and 700 °C, even though
the main compound of the ABA 900 is lime which can act as nucleation
Fig. 3. Diffractograms of agave bagasse ash at different calcination temperatures. Q—calcium carbonate CaCO3, C—lime CaO, P—potassium phosphate oxide KPO3, and M—magnesite Mg (CO3).
Fig. 4. Agglomerates of CaCO3 in calcined ash at 600 °C.
39J.R. González-López et al. / Fuel Processing Technology 133 (2015) 35–42

6. Fig. 5. Specific surface area and average particle size of calcined ash residues.
Fig. 6. Images of reference and waste calcined at 500 °C, top left and right respectively; 600 °C middle right; 700 °C middle left; and, 800 °C and 900 °C bottom left and right respectively.
40 J.R. González-López et al. / Fuel Processing Technology 133 (2015) 35–42

7. site or portlandite source. Another possibility is that due to the fine
particle size of ABA 900 and to the high reactivity of CaO that compose
them, this could be easily carbonated and that is why the behavior is
similar to that reported in the ashes burned at lower temperatures.
For test formulations, 28 day strength development was about 10%
higher, around 55 MPa a 28 d in comparison to 7 d age, whereas, the
reference mixture exceeded 60 MPa at the same age. From these results,
it can be determined that the samples calcined at a lower temperature
have a similar behavior to the samples calcined at a higher temperature.
Therefore, 500 °C could be used as an ideal temperature for treating this
residue when added to an OPC cementitious matrix. However, the
mechanisms which determine the effect of compounds at different
temperatures should be clearly established and the effects of high alkalis
content should be investigated in both, fresh state, and durability of the
intended applications.
5. Conclusions
The A. salmiana use has been reported as a sustainable alternative for
energy production that does not affect resources for human consumption.
Hence, it was considered to have a detailed study of residue resulting
from the use of this plant as biomass. From the studies made in this
work the following is concluded:
• From the ashing process, the amount of ashes generated from the
dried plant is about 7%; therefore, if the tendencies reported in some
studies are used to estimate ABA, they could be comparable to those
reported in power coal generation industries. The loss on ignition in
this type of BA should be cautiously interpreted, because of the high
content of carbonates, sulfates, and phosphates. However, it must be
ensured that the amount of carbonaceous organic material is low.
• The calcination temperature affects the ash compounds, having main-
ly CaCO3 at temperatures below 800 °C and CaO at temperatures
above this value, besides Mg(CO3) and, KPO3 compounds. The chem-
ical composition of ABA, according to the classification given by other
authors, will be semi-reactive and would have possible applications as
cementitious in building materials. However, the effect of high
content of alkalis should be studied.
• The apparent particle size on average is between 25 and 32 μm for
all ashing temperatures. However, when observing in the scanning
electron microscope, the agglomerates are found to be formed by
particles as small as 300 nm and the disintegration of the larger
particles depends on the temperature. Because of this, the specific
area increases from 6.82 m2
/g to 14.00 m2
/g, and from 500 to
800 °C. It should be studied a mechanism to separate these parti-
cles, or to determine whether the difference in surface area affects
the performance of the possible applications, or if the apparent
particle size is the one that controls their behavior.
• The compressive strength of samples with additions of 5% in mass,
showed a strength development at 7 days 90% higher than OPC
reference. This strength development could be a consequence of
the semi-reactive characteristics of the ash components. However,
the subsequent strength development was only 10% at 28 days.
• The results suggest that the best ashing temperature is 500 °C because
apparently the prevailing mechanism is the same for higher temper-
atures. The ABA alkali content was high, so further studies should be
focused on its effect in the construction material durability.
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