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VOLUME 44
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NUMBER 1
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, January-April, 2021, 44-50
Preliminary characterization of the rice husk ash from the
Manabí province for its use in concrete
César M. Jarre Castro
1
* , René Antonio Puig Martínez
2
, Camilo Zamora-Ledezma
3
,
Ezequiel Zamora-Ledezma
4
1
Laboratorio de Hormigones, Universidad Técnica de Manabí (UTM), Ave. Urbina y Che Guevara, Portoviejo,
Manabí, Ecuador, CP.
2
Centro de Estudios de la Construcción y Arquitectura Tropical (CECAT), Facultad de Ingeniería Civil,
Universidad Tecnológica de La Habana “José Antonio Echeverría” (CUJAE), Ave. 114 No. 11901, Marianao
19390, La Habana, Cuba.
3
School of Physical Sciences and Nanotechnology, Yachay Tech University, San Miguel de Urcuquí, Hacienda San
José s/n, Project Yachay, 100119, Ecuador.
4
Facultad de Ingeniería Agrícola, Universidad Técnica de Manabí (UTM), Av. Urbina y Che Guevara, Portoviejo,
Manabí, Ecuador.
*Corresponding author: mjarre@utm.edu.ec
https://doi.org/10.22209/rt.v44n1a06
Received: 11 de agosto de 2020 | Accepted: 21 de octubre de 2020 | Available: 01 de enero de 2021
Abstract
This article describes the potentialities of ash from controlled burning of rice husks in the province of Manabi
(Ecuador), as a substitute for portland cement used in concrete, including selection and preparation of representative
samples of rice husk, quantitative and qualitative characterization of the husk, burning procedure and characterization of
the resulting ash. The procedures used in the characterization of the rice husk are evaluated, demonstrating the relevance
of using the nuclear absorption test to determine the percentage by weight of silica in the mass of the sample and the ash
Keywords: rice husk ash; amorphous silica; concrete; pozzolan.
Caracterización preliminar de la ceniza de cáscara de
arroz de la provincia Manabí, Ecuador, para su empleo en
hormigones
Resumen
Este artículo se describen las potencialidades de la ceniza proveniente de la quema controlada de la cáscara de
arroz en la provincia de Manabí (Ecuador), como sustituto del cemento Portland empleado en hormigones, incluyendo
la elección y preparación de muestras representativas de cáscara de arroz, caracterización cuantitativa y cualitativa de
la cáscara, procedimiento de quema y caracterización de la ceniza resultante. Se evalúan los procedimientos empleados
en la caracterización de la cáscara de arroz, demostrando la pertinencia de utilizar el ensayo de absorción nuclear, para
determinar el porcentaje en peso de sílice en la masa de la muestra, y se caracteriza la ceniza obtenida de la quema a
Palabras clave: ceniza decáscara de arroz; sílice amorfa; hormigón; puzolana.
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
45
Preliminary characterization of the rice husk ash
Introduction
Pozzolans are active silica-containing materials that
in themselves have little or no binding quality, but mixed
with lime in the presence of water, set and harden like
portland cement. In general, pozzolans can be divided into
two large groups: natural, such as volcanic ash and zeolites;
from stone coal and ashes from the burning of agricultural
residues [1].
lime mortars. Later the Romans not only used powdered
but also discovered that some volcanic soils mixed with
lime were excellent for producing hydraulic mortars.
This Roman experience continued to be applied with
different alternatives and at present, the use of pozzolans
in the production of cements and concretes constitutes
an international practice [2]. Researchs had shown a
continuity in the study on the use of pozzolans, of natural or
in the production of concrete. Bonavetti et al. [3] highlight
this experience in the production of self-compacting
concrete with high performance and durability, with a low
content of portland cement as a result of the addition of
natural zeolite as pozzolana.
A pozzolan investigated as a partial substitute
for portland cement in the production of mortars and
concretes, is the ash from the controlled burning of rice
husks. Yanguatin et al. concluded that the experienced
combinations of rice husk ash with portland cement,
allow substituting up to 30% of the cement by ash without
20%, thereby achieving an increase of around 20% in
the compressive strength, improvement in the chemical
stability of the concrete and an increase in its durability.
As a negative effect, there is an increase in the demand for
mixing water.
However, regarding the use of rice husk ash in the
production of mortars and concretes, there are not many
references in Ecuador. In this country, the rice husk is
currently has few applications, resulting in a voluminous
and polluting by-product. It is a material rich in silica
[1,3,9], which has attracted attention in the construction
industry as a partial substitute for portland cement used
in the production of concrete, but still without conclusive
results.
Therefore, in the present paper, a preliminary
characterization of the rice husk ash was carried out to
possible use in the production of concrete, through the
following suppositions:
First, the characterization of the rice husk from
the province of Manabí, in particular the determination
of its silica content by novel test methods to achieve
greater accuracy, comparing with international standards
and assessing its viability to be used for the production
of ash as a partial substitute for portland cement in the
production of concrete.
Secondly, the characterization of the ash resulting,
from burning for different temperatures and burning
Experimental
Rice production in Ecuador
In social and productive terms, rice cultivation is
the most important in Ecuador, occupying approximately
one third of the country’s transitory product area [4].
The behavior of the crop cannot establish a trend that is
increases as well as decreases, being a multivariate of
the highest participation in rice production are Guayas,
Los Ríos, Manabí, Loja and El Oro. Chronologically in terms
of yield, the national average during 2015 was 5.24 t/ha,
Loja being the province of higher yield, with an average of
6.75 t/ha. The province that showed the lowest yield was
El Oro, with an average production of 3.68 t/ha.
Already in 2016 the survey of surface and
that the national surface planted in that year was 385,039
366,194 thousand hectares were harvested, obtaining a
production of 1,534,537 t and sales of 1,432,318 t [5].
statistics due to local consumption omissions, the data
indicate that the main rice producing provinces are
Guayas, Los Ríos and Manabí, especially the former due to
its favorable soils and climatic conditions [6]. However, in
Ecuador there are usually increases in the rice production
but at the same time reductions in the areas dedicated
to cultivation because either they are dedicated to new
crops or they are rotation criteria, as can be seen in Table
1. It shows that the three aforementioned provinces have
a weight of 96.6% as a trend of the total stacked whole
rice in the country. It can also be seen, according to the
data obtained from MAGAP [7], that the rice production
of the province of Manabí in 2017 was the third most
important in the country, reaching 48,604 t. Although it
only represents 3.37% of national production, the volume
is close to the sum of the rest of the country’s provinces
except Guayas and Los Ríos.
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
46
Jarre et al.
Table 1.
Provinces
Years
2012 2013 2014 2015 2016 2017
Guayas 1,029,783 1,060,669 902,424 1,187,135 1,035,344 986,397
Los Ríos 444,330 359,569 410,850 383,106 421,483 356,687
Manabí 42,128 63,656 45,607 57,169 55,536 48,604
Others 49,294 32,151 21,073 25,383 22,174 49,179
Total (t) 1,565,535 1,516,045 1,379,954 1,652,793 1,534,537 1,440,865
Surface (ha) 371,170 396,770 354,136 375,117 366,194 286,189
Performance (t/ha) 4.22 3.82 3.90 4.41 4.19 5.03
In the province of Manabí, according to a report
from the Central Bank of Ecuador [8], it can be seen
that of the cantons of Olmedo, 24 de Mayo, Santa Ana,
Rocafuerte, Sucre, Portoviejo, Paján and El Carmen, with
94% of the total. Standing out that they adjoin Santa Ana,
24 de Mayo and Olmedo; and the same happens with the
cantons of Portoviejo, Rocafuerte and Sucre. This explains
the location of the main pile machines who perform the
husking of dry and clean paddy rice in these six cantons,
which are located in Santa Ana and Portoviejo. Precisely
the rice from Rocafuerte and Sucre is mostly brought to
the processing centers of Portoviejo; and to Santa Ana
the rice from the cantons of 24 de Mayo and Olmedo. In
the case of Pajan and El Carmen, the cultivated rice is
processed in pile machines in the same cantons.
This analysis allowed for the purposes of the
research to synthesize the four fundamental regions of
the province, detailing the average percentage production
and location of the main pile machine, for the purposes of
sampling the rice husk to be used in the trials:
Region 1: cantons of Santa Ana, 24 de Mayo and
Olmedo; 31% of the provincial production; main pile
machine in Santa Ana.
Region 2: cantons of Sucre, Rocafuerte and Portoviejo;
27% of the provincial production; main pile plant in
Portoviejo.
Region 3: to the south, only the Paján canton, 21% of
the provincial production; main pile machine in the
center of the canton itself.
Region 4: to the north, only the El Carmen canton;
16% of the provincial production; main pile machine
in the center of the canton itself.
For a better understanding, Figure 1 shows the
distribution of the four regions in the province of Manabí
and the location of the pile machines in them.
Figure 1. Location of the four large rice growing regions
and the pile machines in them [9]
It is also found in the specialized reports that within
each one of the synthesized regions the same variety
of rice to be cultivated prevails, which constitutes an
advantage that facilitates subsequent sampling aimed
at the physical and chemical characterization of the rice
husk. The most relevant data is the mean estimate of the
productive residuals. If rice production in the province
were to be maintained or increased, no less than 13.4
thousand tons of rice husk per year can be estimated
in the selected regions, which instead of polluting the
environment and with a well-directed policy, they can be
used as raw material for the production of concrete, as a
partial substitute for portland cement, fully justifying this
research and its industrial application.
For the purposes of this investigation, the production
of dry and clean paddy rice is of interest, since this is the
rice that reaches the mills for the husking process. The
consultation carried out allows us to synthesize that from
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
47
Preliminary characterization of the rice husk ash
the product of the grinding process, approximately 20%
of the weight of dry and clean rice husks constitutes the
husk, and given the high production volumes the regional
potential is high [10].
Determination of silica in the rice husk samples
The previous analysis about rice crop
distribution and processing in Ecuador, allowed
samples from Paján, Santa Ana, San Eloy, Rocafuerte
and Chone pile machines were selected for the tests,
guaranteeing representativeness in the north, center and
south.
The presence of silica within the structure of the
rice husk has been known since 1938. According to
referenced research, it oscillates around 20%, occurring in
a higher quantity with respect to the rice grain [9,10,11].
Regarding the type of structure, there are several silica
polymorphs: quartz, cristobalite, tridymite, coesite,
stishovite, lechatelierite and silica gel. Silica or silicon
dioxide (SiO
2
) as it is also known generally exists in two
forms, amorphous and crystalline [11].
For the percentage determination of silica
pile machines, the nuclear absorption technique was
applied, one of the most innovative and exact for these
purposes [12,13], sending them to the laboratories of the
Directorate of Chemical and Environmental Sciences, of
the Faculty of Natural Sciences and Mathematics of the
Escuela Politécnica del Litoral, Ecuador (ESPOL).
Rice husk calcination process
Once the characterization of the rice husk was
concluded, as the next step in the investigation, the analysis
of the controlled burning procedure and characterization
of the resulting ash was undertaken.
Rice husk, when subjected to a calcination process,
produces ash in the order of 13 to 29% of the initial
weight, composed mainly of silica in a variable proportion
between 87 and 97%, plus other amounts of inorganic
salts that can be eliminated.
Several authors document that depending on the
temperature range and the duration of combustion,
crystalline or amorphous forms of silica are obtained
of amorphous silica forms in the range of 600 to 800 °C,
while crystalline silica occurs above 900 °C [14]. The
crystalline and amorphous forms of silica have different
properties. For the application required in this research,
the relevance is towards ashes with an amorphous
structure, an aspect that is more prone to minimum
temperatures within the range, although the formation
of silica is slightly lower, the relationship being inverse
behavior [15,16].
Prior to the calcination process, a drying process
was carried out by placing the standard husk samples
at a controlled temperature of 105 ºC for 24 hours.
After achieving almost zero humidity, the burning
procedure was carried out in an oven with a Bartlett
brand digital temperature controller (Genesis LT3140
model), generating a total of 70 operating points in the
process of calcination of the rice husk, as can be seen in
Figure 2, where the vertical columns from left to right,
correspond to temperature increases from 600 to 875
ºC with a step of 25 ºC; vertically, from bottom to top,
burning times between 15 and 90 min, with a step of 15
min. The color changes in each range can be clearly seen.
Figure 2. Operational points in the rice husk calcination
process
According to Salazar [17], as silica ash is a by-product
of a natural compound, in this case rice husk, it requires
careful methods or procedures of characterization studies
to better understand its nature and be able to determine
silica to improve its properties, including adhesion to the
Chemical composition analysis of the rice husk ash
The experimental techniques are based on strictly
developed procedures to analyze the presence and
formation of silica in rice husk ash, highlighting among
them: nuclear magnetic resonance spectroscopy (NMR),
infrared (FTIR) and differential thermal analysis (DTA). In
the case of the present investigation, for the determination
technique [18,19], was used in the applied chemistry
laboratories of the cement company CURAZAO SA, of
the province of Artemisa, in Cuba; and for the structural
[20,21,22], carried out at the chemistry laboratories of the
Yachay Tech University, San Miguel de Urcuquí, Ecuador.
Results and Discussion
The nuclear absorption test on the rice husk samples
from the selected pile machines, allows knowing their
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
48
Jarre et al.
constitution in percentage of SiO2, as shown in Table 2.
The table shows that the results for the percentage of
silica from the husk samples are located around the ranges
internationally referenced [23]. Soares et al. [24] endorse
for international practice the presence in the rice husk
of an average chemical composition of silica between 16
and 20%. Although two of the reported values are slightly
lower in comparison to the rest, their volume is not
cantons of the volume of husk generated and the reported
value is only 1.7 and 1.0% of the lower limit of 16% of the
presence of silica referenced in the literature. This result
indistinct use of the husk from any of the cantons.
Table 2. Analysis of the percentage silica (SiO2) in rice
husk by NR
M.
Region %
Pajan 15.0
Santa Ana 18.0
San Eloy 15.81
Rocafuerte 17.26
Chone 14.30
Table 3.
Parameters
Samples
M1 M2 M3 M4 M5 M6 M7 M8 M9
Time [min] 60 75 90 60 75 90 60 75 90
Temperature [°C] 600 600 600 625 625 625 650 650 650
When initially evaluating the results of the
burning, the experience gathered in the international
literature was taken into account. In this sense, Ayhan
[25] documents that under complete combustion, the
rice husk ash with the highest proportion of amorphous
white; but that under partial combustion conditions a
black ash is produced, with a rather crystalline structure.
This result makes it possible to reduce the operating
points obtained as a result of controlled burning to nine,
selecting only those in which the coloration is gray/white,
corresponding to temperatures of 600, 625 and 650 ºC
and burning times of 60, 75 and 90 minutes, shown in
silica in the rice husk ash obtained has an amorphous or
crystalline structure [26,27].
of silica in the ash, can be seen in Table 4. In all cases, a
high SiO2 content is obtained, with the maximum value in
sample M8, corresponding to a temperature of 650 ºC and
a burning time of 75 min.
Table 4. Results for percent silica (SiO2) and alumina
(Al2O3) in rice husk ash samples.
Samples
M1 M2 M3 M4 M5 M6 M7 M8 M9
SiO
2
/Si
85.00 88.85 87.21 88.76 88.59 89.31 90.05 90.62 90.26
Mean Concentration 88.74 Max Concentration 90.62
Mean Concentration 85.00 DST 1.74
Al
2
O
3
/Al
1.05 0.86 0.89 0.87 0.99 0.92 0.84 0.84 0.85
Mean Concentration 0.90 Max Concentration 1.05
Min Concentration 0.84 STD 0.07
STD: standard total deviation
The mineralogical characterization of the rice husk
diffractograms, practically peakless, as can be seen in
Figure 3.
Figure 3. Overlapping diffractograms of rice husk ash
As recognized in the specialized literature [22,
25, 26], the abundance of sharp peaks correspond to a
crystalline or semi-crystalline silica, named cristobalite. In
the case of study this is not the case, so it is concluded from
the analysis of the diffractograms, that mineralogically the
structure of the different samples tested is predominantly
the research.
This allows, in order to give continuity to
the investigation, to select M6 as a sample with a
predominantly amorphous mineralogical structure,
corresponding to a temperature of 625º C and a burning
time of 90 min, which constitutes the main result of the
investigation in this part.
Rev. Téc. Ing. Univ. Zulia. Vol. 44, No. 1, 2021, January-April, pp. 04-58
49
Preliminary characterization of the rice husk ash
lished by Coordinación General del sistema de In-
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[9] Valverde-Arias O., Alberto J. & Tarquis A.: “Using Geo-
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Conclusions
industrial by-product of rice production in the province of
Manabí, the rice husk, complies with the SiO2 percentage
ranges reported in the international literature (between
15 and 18%), enabling this result to give continuity to the
investigation.
And secondly, that the controlled burning of it
in temperature ranges between 600 and 650 ºC and
burning times between 60 and 90 min, produces an ash
that is characterized by a predominantly amorphous
mineralogical structure, which supports its use as an
artificial pozzolan substitute for Portland cement in
the preparation of mortars and concretes and makes it
possible to proceed to the next stage of the investigation,
in this case, the design of dosages with different levels of
substitution of cement for ash, taking for this a burning
temperature of 625 ºC and time burning for 90 minutes.
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