Mechanical Properties Geopolymer Concrete Based on Fly Ash PLTU Tanjung Jati B Jepara As An Alternative Material

Geopolymer concrete is a new material and has very good prospects because it does not use cement, where the material uses environmentally friendly materials and is energy-efficient, because it can use industrial waste materials and manufacturing processes. Geopolymer concrete does not require too much energy, as does the process from making cement which requires at least temperatures up for 800°C. The aim of this study is to evaluate and examine the worth of geopolymer concrete’s mechanical qualities. Compression tests, split tests, and flexural strength tests on geopolymer concrete are all part of the battery of mechanical properties tests. The trial study of geopolymer concrete was used to inform the mix design employed in the production of the test specimens. Merapi sand fine aggregate, 10-20 mm coarse aggregate, PLTU Tanjung Jati B Jepara fly ash from coal waste, Na2SiO3, 8M NaOH activator, and 2% fly ash superplasticizer were employed in this research. Three 15/30 cylinders are used to test concrete’s compressive strength, three 15/30 cylinders are used to test concrete’s split tensile strength, and three 15x15x60 are used to test concrete’s flexural strength in this study. After only 28 days, testing could begin. Compressive strength was found to be 31.746 MPa, split tensile strength was 3.920 MPa, and flexural strength was found to be 4.833 MPa for geopolymer concrete.


Introduction
There has been an advancement in geopolymer concrete, which utilizes eco-friendly and energyefficient materials due to its ability to incorporate industrial waste materials in its production.Unlike the production of cement, which requires temperatures of at least 800 o C, geopolymer concrete does not consume as much energy.It only involves heating at around 60 o C daily to produce high-strength concrete.Using geopolymer concrete, greenhouse gas emissions caused by cement production can be reduced by up to 20% [1].
Geopolymer technology stands out as the top solution, effectively converting waste into a valuable resource, addressing Indonesia's coal ash waste crisis.It is an eco-friendly material that minimizes CO2 emissions, offering numerous benefits such as fire resistance, corrosion resistance, and impressive strength [2].
A geopolymer material comprises inorganic components, specifically silicate (SiO4) and aluminum (AlO4), connected in tetrahedral structures as its primary constituents.To serve as a binding agent, an alkaline reactant is employed.To enhance its binding properties, it is necessary to incorporate additional chemicals like pozzolans, sodium hydroxide (NaOH), and sodium silicate (Na2SiO3).The silica oxide within this material will engage in a chemical reaction that leads to the creation of polymer connections 1321 (2024) 012038 IOP Publishing doi:10.1088/1755-1315/1321/1/012038 2 [3].Geopolymer gel combines coarse and fine aggregates to create GPC, a durable and enduring geopolymer.Thanks to its impressive compressive strength, minimal shrinkage, resistance to deformation over time, and resilience against sulfuric acid, geopolymer concrete holds great potential for applications in infrastructure The study was conducted at Universitas Semarang's materials and structures laboratory and test specimens at the Universitas Diponegoro Laboratory, Semarang.The objective of the research was to assess the mechanical characteristics from geopolymer concrete through the execution of tests measuring compressive strength, flexural strength, and split tensile strength followed by an analysis of the obtained data.Among the many investigations into Geopolymer Concrete's mechanical properties are: 1.
"Fly ash-based geopolymer concrete" [3] Geopolymer concrete has been found to possess exceptional compressive strength, making it an ideal choice for structural applications.Additionally, it has been observed that geopolymer concrete exhibits remarkable resistance to low creep, sulfate attack, and minimal drying shrinkage.2.
"Fly ash-based geopolymer concrete : study from slender reinforced columns" [4], utilizing ASTM Class F low-calcium fly ash as a component, geopolymer concrete is created.According to a research paper, geopolymer concrete paste is created by combining aluminum and siliconrich fly ash with a mixture of sodium hydroxide and sodium silicate solutions.Surprisingly, decreasing the load eccentricity increases the load-bearing capacity of the column.

"Sifat Mekanik Beton Geopolimer Berbahan Dasar Fly Ash Jawa Power Paiton Sebagai Material
Alternatif" [2], The greater the mass ratio between Sodium Silicate and Sodium Hydroxide solutions, the extended the duration of the initial binding time, albeit leading to a shorter overall binding process.The rapid setting time of geopolymer concrete poses significant challenges for on-site implementation.Consequently, an additive is required to delay the initial binding phase.4.
"Analisa Sifat Mekanik Beton Geopolimer Berbahan Dasar Fly Ash dan Lumpur Porong Kering Sebagai Pengisi" [5], Geopolymer-Mud concrete has very low workability with a slump value from 0 or close for 0. Compressive strength from binder and geopolymer-mud concrete in 28 days from age: the greater the molarity from the activator, the greater the compressive strength that the binder and concrete can achieve.The less water added to the mixture, the greater the compressive strength of the concrete.

Method
This research begins with a literature study forunderstand the topic forbe researched, find research gaps and research problems that have already been carried out.The implementation from sample making is divided inforseveral stages, namely 1. Preparation from material equipment including preparation from equipment & materials as well as material testing (sand and gravel) for obtain composition data for each material, 2. Making test objects, Test concrete using cylindrical test objects15 x 30 cm as many as 6 pieces for the compression test and tensile test and test objects in the shape of blocks of a certain size from 15 cm x 15 cm x 60 cm as many as 3 pieces.3. Treatment/curing from concrete, and 4. Testing carried out in 28 days old, carried out in the laboratory.5 The test outcomes are then analyzed.[3] The research is presented in Figure 1.Research Flow Chart is as follows: The materials used in the research as follows: a.The fly ash from PLTU Jepara in Central Java.b.The alkali activator is composed of a mixture containing both sodium hydroxide and sodium silicate.c.A solution from sodium hydroxide (NaOH) with an 8M concentration is being utilized.d.BE 52 consists of 31% silicon dioxide, 14% sodium oxide, and 55% water.e.The alkali activator maintains a weight ratio from 2.5, which is the proportion from sodium silicate for sodium hydroxide.Both fine and coarse aggregates are incorporated.f.Plastiment-VZ, a superplasticizer and water-reducing product manufactured by PT.Sika Indonesia, is utilized to reduce the water demand in a blend containing fly ash by as much as 2% by mass.g.The test set includes three cubes measuring 15 cm x 15 cm x 60 cm and six cross-sections of cylinders with a 30 cm diameter.h.In this analysis of geopolymer concrete, the main factors evaluated include the compressive strength, flexural strength, and split tensile strength.
The geopolymer concrete test specimens were created based on a trial analysis, ensuring they met the necessary criteria.The geopolymer concrete had a density of 2400 kg/m3, and the composition per cubic meter can be found in Table 1.An 8M NaOH solution was utilized in the process [7].

Result and Discussion
The research outcomes encompass various test results, which include examinations related to aggregate testing, compressive strength, concrete flexural strength, and split tensile strength [8][3] [9].This study investigates the characteristics from the material to be employed, with test findings encompassing both coarse aggregate (crushed stone) and fine aggregate (sand) [10].The outcomes of this comprehensive test encompass evaluations for aggregate quality, compressive resilience, split tensile durability, and concrete flexural capacity, offering valuable insights into the characteristics of the material intended for use [11][12] [13][14].
The compressive strength of concrete is ascertained through measuring the highest compressive stress (denoted as f'c) that a test specimen, aged 28 days, can withstand when subjected to a compressive strength.For this purpose, laboratory investigations employ the following equation for determine concrete's compressive strength: Table 2 showcases the results from the 28-day compressive strength testing conducted on geopolymer concrete.In this table, 'f''c stands for the concrete's compressive strength in megapascals (MPa), 'P' represents the compressive load in newtons (N), and 'A' signifies the cross-sectional area from the test specimen in square millimeters (mm²).Table 2 illustrates the 28-day curing results for the compressive strength from geopolymer concrete.Within the geopolymer concrete samples tested, the third sample weighing 12.78 kg demonstrates the highest compressive strength, registering at 33.958 MPa.It's worth noting that, as a general trend, geopolymer concrete typically achieves a compressive strength of 31.746MPa after a 28-day curing period.
The equation below can be used to get the value of the tensile strength at the point of fracture for a cylinder of concrete:  = 2 ⋅.Table 3 presents the findings from the split tensile strength assessment conducted on geopolymer concrete samples after a 28-day period.This table includes data for the split tensile strength (measured in MPa or N/mm²), the length (L) and diameter (D) of the cylinder specimens (both in millimeters).[14] Table 3 (2) Table 3 displays the outcomes of a split tensile strength assessment performed on geopolymer concrete after 28 days.Among all the geopolymer concrete specimens examined, the third one (weighing 12.58 kg) exhibited the greatest split tensile strength at 4.171 MPa.On average, when geopolymer concrete reaches the age from 28 days, its split tensile strength measures 3.920 MPa.
After conducting a power regression analysis and subsequently validating the findings with correlation analysis, we observed an R 2 value of 0.7476, which indicates a robust and strongly supported connection between f'c and ft.This relationship model in geopolymer concrete closely aligns with the overall behavior seen in geopolymer concrete.It follows a nonlinear exponential pattern with a positive coefficient, indicating that as compressive strength rises, split tensile strength also increases.This model is consistent with the well-established relationship observed in conventional concrete using cement.
When conducting flexural tests on concrete beams following the guidelines outlined in SNI 4431-2019 [15], if the crack or fracture region spans one-third of the mid-span under the influence of two loads, the flexural strength can be determined using the following formula: fr in megapascals (MPa), with P denoting the maximum load in kilonewtons (KN), while L, h, and b respectively signify the length, height, and width of the test specimen in millimeters The results from the concrete flexural strength test at 28 days are presented in Table 5.
3.4   The relationship model forthe compressive strength from geopolymer concrete and flexural strength from geopolymer concrete is presented in table 6 and figure 3 with the equation: Obtained from the results of a power regression analysis, the R 2 value in a validity test of correlation was 0.8654, indicating a robust connection between flexural strength and compressive strength.This strong relationship in geopolymer concrete resembles the overall non-linear exponential pattern observed in geopolymer concrete, where higher compressive strength correlates with higher flexural strength.This positive correlation is also consistent with the relationship model both compressive strength and flexural strength in conventional cement-based standard concrete.The results of the mechanical properties research obtained are still in line with the results of Diaz Loya's research [6], despite the fact that the material properties of the used fly ash base differ.Research Diaz Loya presents compressive strength ranges out from 10.34 for 80.37 MPa, this research have compressive strength 31.746MPa.Diaz presents flexural strength ranges out from 2.24 for 6.41 MPa, flexural strength 7-26% from compressive strength, this research 4.833 MPa, flexural strength 15% from compressive strength.

Conclusion
After conducting research in the materials laboratory at the Faculty of Engineering, Universitas Semarang, on the Mechanical Properties of Geopolymer Concrete Derived from Fly Ash at PLTU Tanjung Jati B Jepara as a Potential Substitute Material, the following findings can be inferred: concrete's compressive strength is 31.746MPa,the tensile strength of concrete when split is 3.920 MPa, concrete's flexural strength amounts to 4.833 MPa, An equation is provided to model the relationship between compressive and split tensile strength in geopolymer concrete: ft = 2.9959(f'c) 0.1261 , an equation is presented to represent the relationship both compressive strength and flexural strength in geopolymer concrete: fr = 4.2181(f'c) 0.0447

Figure 3 .
Figure 3. Model relationship both concrete compressive strength and flexural strength.

Table 2 .
Outcomes from Compressive Strength from Concrete Aged 28 Days.
Source: research results

.
Outcomes from Split Tensile Strength from Concrete Aged 28 days.
Source: research results

Table 4 .
Split Tensile and Compressive Strength from Geopolymer Concrete.

Table 5 .
Results from Flexural Strength of Concrete Aged 28 days.According to the information provided in Table4, it illustrates the outcomes of the 28-day flexural strength test conducted on geopolymer concrete.The greatest flexural strength among the geopolymer concrete samples was achieved by the second sample, which weighed 12.37 kg and exhibited a flexural strength of 4.925 MPa.On average, the flexural strength from the concrete after 28 days was 4.833 MPa.

Table 6 .
Compressive Strength and Flexural Strength from Geopolymer Concrete.

Table 7 .
Based on research data on compressive strength, concrete flexural strength, and split tensile strength, it can be summarized the mechanical properties from geopolymer concrete that are available at table 7: Mechanical Properties Test Outcomes Geopolymer Concrete.