1
Systematic Mapping on Utilization of Rice Hull Ash as Cement Additive
Julianne Kate Y. Barra
1, Yvonne Kirsten N. Estrada
1,*, Karlaiah Simonne F. Ngo
1, and Arnel B.
Beltran
21 Senior High School, De La Salle University, Manila
2 Department of Chemical Engineering, De La Salle University, Manila * [email protected]
Abstract:
The amount of rice hull ash in the country continues to rise due to increased rice consumption, so using methods to repurpose these wastes would be advantageous to the environment. The approximate number of rice hull wastes in the Philippines for 2021 is 3.96 million metric tons. Moreover, rice hull ash can be used as a cement additive because of its amorphous silica and alumina content. The performance of rice hull ash in cement can be affected by incineration under controlled temperatures. Hence, this study aims to evaluate the application of rice husk ash as a cement additive by formulating a systematic mapping framework. Through this method, relevant papers were collected, organized, screened, and evaluated. The result showed that carbonation, compressive strength, and flexural strength influence the performance of cement. For the flexural strength, fine RHA with a percentage of 10 had the best result. Meanwhile, the temperature and time for incineration range from around 260°C-1500°C for 0.25-72 hours. Overall, the results indicate the increasing potential of rice hull ash as an additive to cement.
Keywords: rice hull ash; cement additive; systematic mapping; compressive strength; flexural
strength
1. INTRODUCTION
Rice hulls are agricultural wastes that generate in landfills. The disposal of rice hulls in landfills causes environmental pollution (Pode, 2016). Approximately 20 kg of rice hull is collected from 100 kg of rice (Baiyeri et al., 2019).
The computed projected rice hull waste for 2019, 2020, and 2021 were 18.64 million metric tons, 19.34 million metric tons, and 19.82 million tons, respectively. During the burning process of rice hulls, its evaporable components are lost and leave a primary residue called silicates. Rice hull ash can be effectively used as a constructional material to develop long- term strength for mortar and concrete (Pacheco-Torgal, 2014).
One study by Thomas (2018) utilized rice hulls by burning them at a controlled temperature of 500-700°C to produce the most reactive silica in rice hull ash. Furthermore, Ketov et al.
(2021) used rice hull ash to have lightweight ceramic bricks.
Another study regarding rice hull ash is about optimizing a geopolymer made up of a blend of coal fly ash (CFA), coal bottom ash (CBA), and rice hull ash (RHA). Geopolymers could be a sustainable substitute for ordinary Portland cement due to their properties; they are produced from waste materials, require less energy in production, and emit less CO2 (Kalaw et al., 2016). A systematic mapping approach was used to evaluate the relevance of the topic. The paper would be limited to determining its performance based on the significant results of existing studies in different sites. The sites used for the research were Scopus, Science Direct, and Google Scholar.
This study aims to evaluate the application of rice hull ash as a cement additive through a systematic mapping framework. It will concentrate on carbonation, compressive strength, and flexural strength to evaluate its performance in cement.
2. METHODOLOGY
2
2.1. Research Framework
Figure 1 Research Flow
The framework presented in Figure 1 consists of nine steps. First, research questions were formulated and defined.
Next, various search engines were utilized to collect multiple papers on the utilization of rice hull ash. Afterward, papers on rice hull ash as cement additive were screened and organized for data gathering. Then, significant results from various papers on the performance of rice hull ash as a cement additive were extracted. An analysis was made to identify the efficiency of rice hull ash as a cement additive. Finally, the performance of rice hull ash in cement was evaluated to determine its potential as an additive.
2.1.1. Research Questions
The following research questions were formulated to be answered by the systematic mapping approach for the application of rice hull ash as a cement additive:
1. What are the studies conducted for RHA as a cement additive?
2. What are the processes RHA should undergo to be used in cement additives?
3. What are the characteristics or properties of RHA to be an effective cement additive?
4. What is the performance of cement with RHA additive?
2.2. Paper Search and Screening
The relevant papers (from 2006-2021) related to the research questions were searched. The following search engines and databases were used: Scopus, Google Scholar, and ScienceDirect. The results were filtered based on their keywords during the initial paper search. The keywords such as rice husk, rice hull, rice husk ash, rice hull ash, and cement additive were chosen to filter papers relevant to this study.
2.3. Data Collection, Organization, and Analysis
The extraction of the relevant data was necessary to answer the research questions by checking the title and abstract of the study. Screening and data extraction was required to specifically answer the research questions and show the relevance of the paper review. The characterization of rice hull ash, specific utilization, processing of rice hull ash, temperature, and cement were extracted from numerous papers. Moreover, the papers were organized by journal title, journal name, author, year of publication, specific utilization, temperature and duration, characterization of rice hull ash, compressive strength, and flexural strength.3. RESULTS AND DISCUSSION
3.1. Trends of Papers on Rice Hulls or Rice Husks
Scopus, ScienceDirect, and Google Scholar were used to analyze the number of papers about rice hull ash. As shown in Figure 2, from 2006 to 2021, there was an increase in the total number of papers that study rice husks as cement.Through Scopus, ScienceDirect, and Google Scholar, the keyword “rice husk ash cement” in 2021 exhibited the highest count with a total number of 219 papers (Scopus), 945 papers (ScienceDirect), and 6,720 papers (Google Scholar) respectively. The significant increase in papers indicates the growing interest in rice hull wastes as a cement additive.
Figure 2
Historical Count of Rice Hull Ash Papers in Scopus, ScienceDirect, and Google Scholar Using Keyword Search
“rice husk ash cement”
3 Through Scopus, the number of papers per country with the keywords “rice hull,” “rice husk,” “rice hull AND cement,” and “rice husk AND cement” were compiled. As shown in Figure 3, for the keyword “rice hull,” China had the highest number of papers, totaling 501 research papers. From the obtained data, the Philippines was listed amongst the top countries studying rice hulls, with a total of 83 papers indicating the growing interest in these agricultural wastes. For the keyword, “rice husk,” India, China, and Malaysia have the highest paper count, with 2,514 papers, 2,257 papers, and 1,325 papers, respectively. To analyze the utilization of rice husk as cement additives, the combination of keywords used for the search was “rice hull” and “cement.”
Brazil had the highest count, with a total of 18 papers. The Philippines and U.S. were tied with a total of 11 papers. For the keywords “rice husk” and “cement,” India showed the highest paper count with 438 papers, followed by Malaysia and Brazil with 184 papers and 116 papers, respectively.
Figure 3
Paper Count for Top Countries for Keywords “rice” AND
“hull,” “rice” AND “husk,” “rice” AND “hull” AND
“cement,” and “rice” AND “husk” AND “cement.”
Overall, China, India, and Malaysia exhibit the most papers concerning rice hull and its utilization as a cement additive. This could indicate the continuous research of the countries towards the utilization of rice hulls, the significance of rice as a staple food, and the need of these countries to study applications of rice hulls for the reduction of waste. Moreover, the total number of papers per country focusing on the application of rice hulls as cement additive indicates its feasibility for specific utilization. Therefore, studies about rice hulls can provide a sustainable method that addresses waste reduction.
3.2. RHA Processing 3.2.1. Incineration
Rice hulls are burned at high temperatures and durations (Bie et al., 2015). The temperature and duration of the incineration process influence the performance of rice hulls as cement additives. In Figure 4, the temperature and duration ranges collected from the studies were 260°C to 1500°C and 0.25h to 72h, respectively.The most common temperature and time used in the collected studies was 700℃, and the specific duration of incineration that was commonly used in different studies was two h and three h. This contributes to the increase in the performance of RHA as a cement additive.
Figure 4
Duration and Temperature of Incineration from Multiple Studies
3.2.2. Rice Hull Ash Properties and Characterization
Some properties of rice hull ash are identified through various tests and analyses. In Figure 5, the paper count for the most utilized characterization was the X-Ray 05000 10000
2005 2010 2015 2020 2025
Paper Count
Year
Scopus ScienceDirect Google Scholar
0 2000 4000
Paper Count
Country
rice hull rice husk rice husk AND cement rice hull AND cement
4 Diffraction Analysis (XRD) with 38 papers. This was followed by Scanning Electron Microscopy (SEM), X-ray Fluorescence Analysis (XRF), and Fourier-Transform Infrared Analysis (FTIR), with a total of 24 papers, 11 papers, and six papers, respectively. XRD Analysis is widely used due to the information about RHA structure and average size (Bie et al., 2015). Moreover, SEM Analysis is mainly used to study the surface’s topography or microgeometry (Ferraro & Nanni, 2012). Additionally, XRF Analysis is used to determine the elemental composition of RHA (Al-Alwan et al., 2022).
Lastly, FTIR Analysis is used to identify compounds and is presented in a spectrum (Sonat & Unluer, 2019).
Figure 5
Paper Count for Rice Hull Ash Characterization
In Table 1, the most common characterizations of RHA concrete were gathered. The values of the characterizations were reviewed to determine the range of values for each component of the RHA concrete from numerous papers. It is essential to know its characterizations and values, decipher the ideal amount for RHA concrete, and thoroughly compare the differences each paper has with its concrete. The table was arranged from most to least-used components from the data gathering. The most common component gathered from the papers would be SiO2, with a range of 54.25% – 95.983% since RHA is rich in silica content.
With that, SiO2 has the highest values compared to the values of the other compositions, indicating that silica is a significant content of rice hull ash in cement.
Table 1
Composition of Rice Hull Ash
Composition Range of Values (%)
SiO2 54.25 – 95.983
Fe2O3 0.2 – 3.59
MgO 0.07 – 3.83
K2O 0.96 – 3.39
CaO 0.12 – 2.58
Al2O3 0 – 2.39
SO3 0.016 – 1.19
Na2O 0.03 – 0.97
3.2.3. Percentage Replacement in Cement
Prasittisopin and Trejo (2015) state that an increased RHA replacement decreases calcium ion concentration. As shown in Figure 6, percentage replacements of 0% to 100%
were presented. In descending order, 10%, 20%, 15%, and 5%
replacement were studied by the majority of the papers.
Moreover, the paper counts for each percentage replacement are 70, 61, 60, and 39, respectively. A total of 28 papers studied the cement with 0% replacement of RHA. In addition, the significant number of papers for each of these specific percentage replacements shows that the potential of RHA as a cement additive is gradually increasing due to the increase in papers about this topic. The percentage replacement of cement using RHA influences cement's overall performance (Bie et al., 2015).
Figure 6
Paper Count for Percentage Replacements of Rice Hull Ash
3.3. Performance of Cement with RHA Additive 3.3.1. Carbonation
0 10 20 30 40
XRD SEM XRF FTIR
Paper Count
Characterization
0 10 20 30 40 50 60 70 80
0 2.5 5 7.5 12 15 20 35 55
Paper Count
% Replacement of RHA
5 The depth of carbonation has a significant contribution to the strength of the concrete. To increase carbonation, the concentration of cement must be lower, and the porosity should be increased (Thomas, 2018). It has also been found that the degree of effect on carbonation depends on the pozzolans types (Chindaprasirt & Rukzon, 2009). Two papers were considered to have reliable results. Both papers used 20% of RHA as their partial replacement for cement and used the water-cement ratio of 0.5 and 0.65. As shown in Figure 7, the first paper had 7.50 and 14.14 mm results from the water-cement ratio of 0.5 and 0.65, respectively. The study said the carbonation depth decreased when 20% of RHA was used (Thomas, 2018). Meanwhile, the second paper had 34.47 and 24.47 mm results for the water-cement ratio of 0.5 and 0.65, respectively. Just like in the first paper, the carbonation depth was reduced because the content of RHA was 20%. The result was lower than concrete without RHA, making it not beneficial (Wang et al., 2021). Furthermore, Antiohos et al.
(2013) stated that the replacement level of 15% RHA produced the highest carbonation depths. Also, RHA being pozzolanic causes the reduction of alkalinity, which in turn increases carbonation.
Figure 7
Carbonation Depth for 20% RHA Percentage Replacement
3.3.2. Compressive Strength
A study by Bie et al. (2015) states that the duration of incineration affects the compressive strength of the cement mixed with RHA. However, the enhancement effect towards the compressive strength is only very slight. The results were taken for compressive strengths in megapascal (MPa) and respective percentage replacements within seven curing days.
Figure 8 shows the graph of the compressive strengths for each percentage of RHA. With age and time, the RHA concrete gradually increases compressive strength. RHA cement of up to 360 days demonstrates compressive strength development comparable to that of normal concrete of up to 270 days. The long-term strength development of RHA concrete contributes to the efficiency of a cement additive (Madandoust et al., 2011).
Figure 8
Compressive Strength for Respective RHA Percentage Replacement at 7 Days
3.3.3. Flexural Strength
Venkatanarayanan et al. (2015) state that the strength of concrete in flexure made with RHA relies on the method of grinding RHA, water-to-binder ratio, use of SP, and the ideal usage of RHA. The results in flexural strength are in Newton per square millimeter (N/mm2). Figure 9 shows the box- whisker plot of the flexural strengths of 0%, 5%, 10%, 15%, and 20% of RHA in concrete in 7 days. The lower dot signifies the outlier minimum. The usual water/cement ratios that were gathered were 0.4-0.6. Moreover, the water/cement ratio is inverse to flexural strength. This concludes the large gap between the flexural strength value of Gunduz et al. (2019) and the other flexural strength values in the graph resulting in an outlier minimum. Furthermore, Ahsan et al. (2018) state that the acceptable 10% RHA had the best result for flexural strength. Therefore, the further enhancement of concrete relies on the capability of fine RHA molecules that improve flexural strength.
0 50 100 150 200
0 5 6 7 7.5 10 15 20 25 30 40 50 55 Compressive Strength (MPa)
% Replacement of RHA
6 Figure 9
Flexural Strength for Respective RHA Percentage Replacement at 7 Days
4. CONCLUSIONS
The increase in rice hull waste production led to various methods to repurpose these wastes. Rice hulls can be burned through incineration, which turns them into rice hull ash. The numerous papers analyzed show that the ideal temperature and duration are 260°C to 1500°C and 0.25h to 72h, respectively. Rice hull ash is rich in silica, making it an ideal additive to cement for a more sustainable alternative.
Moreover, it has been found that the incineration process affects the compressive strength of the cement mixed with RHA. Furthermore, in terms of flexural strength, it has been discovered that a replacement level of 10% RHA had the best results. Additionally, the carbonation depth of RHA cement increases as the level of replacement increases, making them directly proportional to each other. Therefore, due to its sustainability aspects, utilizing rice hull ash gives off benefits to cement in terms of strength and the environment.
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