Utilization of Fly Ash and Bottom Ash Waste of PLTU Jeranjang on Geopolymer Paving

Waste is produced as fly ash and bottom ash from coal-fired power stations. PLTU in West Nusa Tenggara uses 13,000 tons of coal in one month, so it can be estimated that Fly Ash waste will be produced around 1,950-2,210 tons. Geopolymer concrete utilizes fly ash as an adhesive to replace Portland cement. Fly ash is used to make geopolymer concrete, which is created by polymerization reactions caused by alkali-aluminosilicate reactions that result in materials with strong structures. In this study, the ratio of the composition of the weight ratio of paste (fly ash and alkaline solution) with aggregate was 35:65. The aggregates used are sand and bottom ash. The test object is a prototype paving block with a specific dimension of 10cm x 21cm x 6cm. Mechanical testing using compressive strength and water absorption testing with a specimen life of 7, 14, 21, and 28 days. Testing of bottom ash and fly ash characteristics in the form of XRF testing. The XRF test results found that the bottom ash and fly ash of PLTU Jeranjang belonged to class F. The average test result of compressive strength at the age of 28 days for mix designs A, B, and C was 8.54 MPa, respectively; 10.29 MPa; and 16.10 MPa. Quality geopolymer paving can be applied to gardens and other interiors used. Another result of the absorption value of Mix design C of 8% shows the addition of fly ash can be utilized in place of some of the used cement in paving blocks that satisfy SNI 03-0691-1996 Quality C criteria.


Introduction
Currently one of the most extensively utilized kinds of building materials is paving.Paving is very strong and easy to make and use in the field.In addition, the price is relatively cheap compared to other types of pavement layers such as asphalt and concrete.In addition, the shape and size of paving can be designed easily according to the function and purpose for which it is intended to be used.Paving can usually be used for roads, sidewalks, parking lots, parks, and roads in residential areas.The installation of paving helps national and international green campaigns because it increases water absorption and maintains groundwater balance [1].
In Indonesia, Fly ash is still added in modest amounts to cement, and only a few national power plants have been permitted to use fly ash and bottom ash.These include PLTU Suralaya in 2017, Labuan in 2018, and Indramayu in 2019 (Indonesian Minister of Environment and Forestry, 2017, 2018, 2019).Fly ash, which is waste from coal combustion residues or coal powder (ASTM C.168), can be used instead of cement.The properties of pozzolanic contained are predicted to raise the geopolymer paving's compressive strength.
Geopolymer paving blocks are made of a mixture of aggregate, water, and fly ash as a binder, which is added with an alkaline activator solution with a certain resistance.This substance is favorable to the environment, that can be used as a substitute for cement [2].
Geopolymer paving itself is made without cement.The mechanical properties of geopolymer concrete will be affected by the alkaline solution of the activator used as a binder.The alkaline solution of the activator consists of a solution of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH).Alkaline solutions of activators are made with a certain ratio [3].
The utilization of bottom ash is still much lower than fly ash in studies that combine fly ash and bottom ash in geopolymer paving blocks, where bottom ash serves as a binder and fly ash as a substitute for sand.Efforts are needed to optimize waste materials which called Bottom Ash (BA) and Fly Ash (FA) produced from coal production.A composition of 10 M NaOH was used in geopolymer paving blocks, with a ratio of 0.4 for alkaline activator solution to fly ash and 2.5 for Na2SiO3 to NaOH.Bottom ash variations range from 0%, 25%, 50%, and 75% by sand weight at room temperature curing.Paving block testing with 25%-75% Bottom Ash substitution shows good performance in various aspects, with the exception of compressive strength, including porosity, abrasion resistance, sulfate resistance, and absorption.Paving block performance is influenced by the properties, shape, and gradation of Bottom Ash.Paving blocks that do not use Bottom Ash meet paving D quality standards [4].
Based on the above problems, research was conducted on using bottom ash and fly ash in geopolymer paving with the aim of utilizing more and more coal waste and protecting the environment from coal pollution.

Geopolymer
Geopolymers were discovered by Prof. Davidovits.It is an inorganic form of aluminum silica made from materials containing Silica (Si) and Alumina (Al), which are of natural origin or from industrial by-materials [5].Geopolymer concrete is made from the rest of the inorganic industry and does not use Portland cement as a binder.Geopolymer materials consist of aluminum silicates, which have the ability to react chemically with alkaline liquids at certain temperatures to produce a mixture resembling cement.Today, fly ash is the most frequently used material.Alkaline solutions used as solvents for silicon and aluminum allow chemical reactions to occur.To bind geopolymer concrete material, binders consisting of fly ash and alkaline activators are needed, more specifically, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) [6].

Paving block
Paving blocks can be made whether or not additional additions that don't degrade the concrete bricks' quality by combining Portland cement or other hydraulic adhesives, water, and aggregates.The compaction system or paving press with manual power causes a decrease in the quality of mechanical characteristics in the form of compressive strength, wear tests, and water absorption in geopolymer paving [7].According to SNI 03-0691-1996, the quality of paving blocks is classified into 4 types.The load per unit area that causes the specimen to crumble when loaded with a specific force of compression, created by the press, is known as the paver's compressive strength.The following formula can be used to calculate the paving press: Compressive strength = P / A (1) with: P = Press load (N) A = Press field area (mm 2 )

Fly Ash
Fly ash is the solid material used in this study.Fly ash is a type of industrial waste and is one of the remaining results of the coal combustion process at Steam Power Plants (PLTU).This material is widely used as an additional material in order to enhance the performance of concrete.Fly ash can react chemically with alkaline liquids at certain temperatures to form mixtures that have cement-like properties.Fly ash falls into the category of "pozzolan", which is a siliceous or aluminous material that has little or no cementitious material, such as Portland Cement.

Bottom Ash
The residue left over after burning coal in a steam power plant's boiler (PLTU) is called bottom ash.In the combustion furnace, bottom ash sinks to the bottom because it is larger than fly ash in size.The workability of mixes containing bottom ash is less favorable than that of combination containing fly ash and cement due to the higher particle size of fly ash.The coal ash pozzolan reaction, according to [8], is typically linked to fineness of the particles; in this instance, fly ash is finer and has smaller particles than bottom ash, which is assumed to be the reason why the Pozzolan reaction is inefficient.The bottom ash utilized in this investigation came from PLTU Jeranjang in the West Nusa Tenggara district of Lombok.

Purpose and Benefits of Research
The goal from this research was to calculate the strength in compression of geopolymer paving made of fly ash and bottom ash of PLTU Jeranjang.These pavings are stored at room temperature for 7, 14, 21, and 28 days.The benefits obtained from this study, namely: a. Indicates that fly ash from PLTU Jeranjang can be used in place of cement in paving making.b.Get information about the geopolymer paving's compressive strength using fly ash from PLTU Jeranjang.c. Know the details of the process of making geopolymer paving made of bottom ash and fly ash.

Fly Ash
The study's use of fly ash came from PLTU Jeranjang, West Lombok, and West Nusa Tenggara.High Calcium obtaining fly ash type F from PLTU Jeranjang.The study's use of fly ash composing the amount of more than 70% (SiO2 + Al2O3 + Fe2O3) and 10% of CaO.The substance compositions of this material are listed within Table 2.

Aggregates
Before mixing the pavement, the aggregates were ready to be in the saturated-surface-dry (SSD) state.
In this investigation, 35% of the bottom ash was employed as a binder combined with 65% of river sand.Bottom ash was obtained from PLTU Jeranjang with the makeup of its chemical components this material is displayed in Table 2. Locally available river sand and bottom ash were derived from the moisture content and absorption tests as specified in ASTM C127 [10] and ASTM C566 [11], correspondingly.

Preparation of Specimens
Geopolymer and cement paving was carried out with the assumption that the particular gravity of the geopolymer concrete was 2200 kg/m 3 [7] with a ratio of binder and pasta of 65: 35.The mix design of geopolymer paving was prepared using 14 M of NaOH with a ratio of NaOH/NA2SiO3 2,5.The addition of water was conducted for this investigation.The ratio composition and water addition were added according to the outcomes of the prior research [7] and [12].Furthermore, water-made paving geopolymer when mixed in good workability in two variations of mix design.Mix design of paving with cement, fly ash, and water as pasta was conducted in this investigation to compare the result of geopolymer paving.The ratio of the mixture composition and percentage of geopolymer and cement paving appears in Table 4. Mixing pasta and binder was conducted with a hand mixer.The components were inserted into the bucket by hand with SSD condition and were cleaned.The base material fly ash was first mixed with river sand and bottom ash.Additionally, Alkali activators were mixed together.The manufacture and molding of the specimens are carried out by a hydraulic paving block machine.The mixture was cast measuring 21 cm by 10 cm by 6 cm using a paving molding machine and then cured at normal temperature until the age of the test.The testing method for specimens was strength of compression tests at 7, 14, and 28 days of age, and absorption on samples aged 28 days refer to SNI-03-0691-1996 as shown in Figure 1.The test of geopolymer and cement paving was performed by compressing the testing machine.The load was applied until the failure of specimens was observed.

Result and Discussions
The characteristic properties of paving geopolymer were not determined within this research.Fly Ash's Bottom Ash's chemical formula are according to the X-ray fluorescence (XRF) result analysis.Based on ASTM C 618-19 which divides pozzolans into three classes, namely class N, Class F, and C as shown in Figure 2. In this study, fly ash was used in class F because the total number of SiO2 + Al2O3 + Fe2O3 compounds was more than 70% and CaO more than 10% meaning high calcium and was indicated cementitious material.
The XRF analysis result showed the composition of bottom ash less silica and alumina.River sand and bottom ash were used as fine aggregates with a specific gravity of 2,422 and 2,262 respectively.The particle distribution of bottom ash and river sand in gradation Zona 2.

Compressive Strength
The result of the compressive strength of geopolymer and cement paving at 7,14,21 and 28 days is shown in Figure 4.The strength of compaction increases due to the increasing paving age.The result of 10,29 MPa compressive strength of geopolymer paving in mix design A showed in 28 days with added 3/35 water of total alkali activator composition.The water addition of 5/35 in Mix Design B decreased the strength of compaction of geopolymer paving.In contrast, the value of the strength of compression of the two mixed designs didn't show a significant result.The Highest Compressive strength showed 16,10 MPa in Cement and fly ash as based pasta materials in Mix design C. The reason for the rise in compressive strength is the use of cementitious material.In addition, 35% of fly ash was used to reduce the total of cement in the pasta composition of cement paving in this research.It is clearly proved that fly ash can be added as base pasta material of Paving geopolymer and reducing the use of total cement composition as pasta material in cement paving.

Conclusion
The compressive strength and absorption testing were investigated in this study.The variation of mix design for geopolymer and cement paving were examined with the summary of the conclusion from the experimental result: a. Compressive strength decreases as increasing addition of water in the ratio of total alkali activator used.b.Compressive strength of cement paving was higher than geopolymer paving.c. Fly ash and Bottom Ash of PLTU Jeranjang qualified for Geopolymer paving based on SNI 03 0691-1996 and qualified for replacing a few of cement compositions in pasta of cement paving.

Acknowledgment
The authors greatly acknowledge Universitas Islam Al Azhar's support of the research as HIBAH PDP Universitas Islam Al-Azhar 2022.Contribution of PLTU Jeranjang for Waste material (Fly Ash and Bottom Ash), Retas Green Concrete East Java, and Institute Technology Sepuluh Nopember (ITS) conducted the XRF Testing in Sucofindo.

Figure 2 .
Figure 2. Specimens after test of compressive strength.

Table 2 .
[9] components that make up fly ash (%).Activators used in the mixture are sodium hydroxide (NaOH) and sodium silicate (NA2Sio3).Sodium silicate accelerates the polymerization reaction, and sodium hydroxide reacts with the elements Al and Si in fly ash, allowing the formation of strong polymer bonds.The concentration of NaOH used in 14 M. NaOH was made by combining flakes with distilled water.NaOH contains 18,5% of Na2O, 36,4 % of SiO2, and 45,1 % of H2O[9].The mass ratio of Na2SiO3 to NaOH was maintained at 2.5 [3].
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