The Compressive Strength of Unfired Clay Brick with Sugarcane Bagasse Fiber (SBF) and Bio-Enzyme Reinforcements

The architecture and construction industries play an important role in achieving sustainable development goals, particularly environmental ones. These industries currently contribute to high carbon emissions and high energy consumption, as common building materials are among the leading causes of environmental damage. The production of earthen materials, namely clay brick, requires a great deal of energy and emits carbon to the atmosphere in the kiln-firing process. Previous studies have used natural fibers, such as sugarcane bagasse fiber (SBF), and fermented vegetable extracts as reinforcements for use in unfired clay brick. This paper aims to investigate the effects of SBF and bio-enzymes as reinforcements on the compressive strength of unfired clay brick. The experiment produced four types of specimens, each one with the same composition ratios but containing different ingredients. A total of 120 brick samples measuring 50 mm × 50 mm × 50 mm were produced manually. They were cured for 28 days at a room temperature of 28±2°C before their compressive strength was measured. The results showed that adding SBF to the samples increased their compressive strength. Moreover, adding both SBF and bio-enzymes led to the highest compressive strength measurements compared to the other specimens.

Bio-enzymes; Soil reinforcement; Soil stabilizer; Sugarcane bagasse fiber (SBF); Unfired clay brick

Clay brick, an earthen building material, has been used for a long time. The sun-dried brick has been first used circa 8000 B.C while the fired brick has been used circa 4500 B.C (Smith et al., 2016; Zhang, 2013). Clay brick is popular in wall construction, especially in developing countries. Thousands of years ago, sun-drying was the most common technique for producing clay brick; sometimes natural fibers, such as straw, were added to the clay mixture as a reinforcement. This method produces no carbon emissions and consumes little energy in the production process (Yetgin et al., 2008). Nowadays, the most common clay brick production method is kiln-firing following sun-drying. In 2013, 1.391 million units of brick were produced globally (Zhang, 2013). This amount is predicted to increase alongside the development of the construction industry and population growth (National Statistics, 2015). Brick is in demand because it is sturdy, relatively cheap (Hall and Djerbib, 2004), fire-resistant (Deboucha and Hashim, 2011), possesses desirable thermal and acoustic properties (Hall and Djerbib, 2004), and is easily obtained (Deboucha and Hashim, 2011).

The purpose of firing is to strengthen the clay soil to become as hard as stone. Unfortunately, the process of making per one fired brick emits 0.4 kg of CO2 and consumes around 2 kWhThe purpose of firing is to strengthen the clay soil to become as hard as stone. Unfortunately, the process of making per one fired brick emits 0.4 kg of CO₂ and consumes around 2 kWh (Munoz Felasco et al., 2014). Previous studies related to unfired clay brick production have included added materials as reinforcements to create what is commonly known as reinforced brick. Some of the studies used natural plant fibers, including straw (Binici et al., 2005), sisal (Njau and Park, 2015), coir (Danso et al., 2015), and sugarcane (Saccharum officinarum) bagasse fiber (SBF) (Danso et al., 2015; Salih et al., 2020). The use of cement as an additive in clay brick is also common because of its mechanical strength, but it is less environmentally friendly given the high energy costs and CO₂ emissions that accompany cement manufacturing (Zhang, 2013; Marcelino-Sadaba et al., 2017; Joglekar et al., 2018). The production of one tonne of cement consumes around 5.6 GJ of energy and emits approximately one tonne of CO₂ that contributes 7% of emissions to the atmosphere (Shubbar et al., 2018). A more environmentally friendly reinforcement or stabilizer is thus required to produce unfired clay brick.

The use of sugarcane bagasse in the form of ash as a reinforcement has been examined in several studies because it contains SiO₂ which acts as a binding agent when fired. However, even so, the study of sugarcane bagasse in the form of fiber is not often conducted despite the material’s high cellulose content, which adds strength to a material. Moreover, SBF is relatively cheap and abundantly available in Indonesia in the form of waste (Agunsoye and Aigbodion, 2013). The addition of SBF to unfired clay brick improved compressive strength when the SBF was cut to an optimum length of 15 mm and comprised 5% of the total clay mixture. Generally, the compressive strength values ranged from 1.82 MPa–3.98 MPa (Salih et al., 2020). Another study was also conducted using SBF in which optimum compressive strength was obtained using 80 mm-long fibers that yielded ranges between 1.07 MPa–1.13 MPa (Danso et al., 2015).

Bio-enzymes have also been tested as a soil stabilizer in road construction (Vedula et al., 2007). A bio-enzyme is a non-toxic and natural liquid extracted from vegetables (Rajoria and Kaur, 2014). Bio-enzyme directly affects organic matter in soil, as well as biodegradable minerals and nutrients. Bio-enzyme works effectively in soil containing organic material that has not been sterilized. It attaches to microbes contained within soil and cause them to bond with each other. After that, the microbes reduce the surface tension of the water in the soil, which encourages rapid and thorough penetration of moisture. This leads to a cementation process whereby smaller soil particles combine to fill gaps in the soil, thus forming a dense layer (Chatrada, 2009).

Another study employed liquid bio-enzyme from fermented vegetables to be added to a unfired clay brick mixture (Dzulkifli et al., 2018). Five types of vegetables were used in this experiment: cucumber (Cucumis sativus), spinach (Spinacia oleracea), water spinach (Ipomoea aquatica), cabbage (Brassica oleracea), and cowpea (Vigna unguiculata). These vegetables were chosen for their soil-stabilizing minerals: calcium, iron, and silica. Besides the extraction of fermented vegetable juices, the researchers added eggshell powder as a calcium additive to encourage bio-cementation. The results showed that the compressive strength of the mixture reached 0.062 N/mm². By combining bio-enzymes from fermented vegetable extracts with SBF as an organic material in clay mixtures, it is hoped that compressive strength can be improved and meet the standards of conventional brick or fired clay brick.

The present research is focused on the mechanical properties, specifically the compressive strength, of the proposed brick mixture to determine its load carrying capacity and sustainability in wall construction. This research aims to investigate the effects of SBF and bio-enzymes on the compressive strength of unfired clay brick and thus contribute to the literature on building material technology. This paper is also relevant to researchers who work in the field of sustainable building material development.

The addition of a bio-enzyme and SBF to an unfired clay brick mixture increases the resulting brick’s compressive strength. Compressive strength increases by adding a bio-enzyme alone, but not significantly so. By adding SBF, the compressive strength of the Y samples increased. However, the samples with both a bio-enzyme and SBF (XY) demonstrated the highest compressive strength out of all other samples. These results highlight how added reinforcements, particularly SBF and bio-enzymes, have the potential to strengthen unfired clay brick. This material is not only lighter compared to fired brick, but it is more environmentally friendly because it requires no kiln-firing.

        While improvements in compressive strength have been noted through this study, further research is required to test whether other physical properties of unfired clay brick made with bio-enzymes and SBF, such as water absorption, meets construction standards. Additionally, greater variations in the types of soil used, SBF fiber lengths, curing time, raw material ratios, raw material pre-tests, and SEM tests are recommended in further research.

    This research was funded by Universitas Indonesia through Publikasi Terindeks Internasional (PUTI) Prosiding 2020 research grant no. NKB-1161/UN2.RST/HKP.05.00/2020.

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