The Effect of Seawater on The Compressive Strength and Split Tensile Strength in Self Compacting Geopolymer Concrete

Article History : Article entry : 2021-10-11 Article revised : 2021-11-04 Article received : 2021-12-09 Fly ash is a kind of trash that may degrade the quality of the air. As a result, it is critical that it be used as an ecologically beneficial material. The aim of this research was to evaluate the strength of self-compacting geopolymer concrete (SCGC) cured in seawater, as well as to compare SCGC with and without saltwater. In this research, a cylindrical specimen with a diameter of 10 cm and a height of 20 cm was utilized as the specimen. Fly ash is used in proportion to fine and coarse aggregates at a ratio of 1: 0.65: 1.5. Using a 0.4 activator to binder ratio. The molarity ranges utilized were 11 M 15 M. Compressive strength and split tensile strength tests were conducted on 28-day-old concrete. The findings indicated that when the molarity of SCGC treated with seawater increased from 11 to 15 M, the compressive and split tensile strengths increased. Compressive strength values were greatest in SCGC treated at room temperature when an activator of 13 M was used, and compressive strength values dropped in SCGC treated at room temperature when an activator greater than 13 M was used.

Fly ash is a kind of trash that may degrade the quality of the air. As a result, it is critical that it be used as an ecologically beneficial material. The aim of this research was to evaluate the strength of self-compacting geopolymer concrete (SCGC) cured in seawater, as well as to compare SCGC with and without saltwater. In this research, a cylindrical specimen with a diameter of 10 cm and a height of 20 cm was utilized as the specimen. Fly ash is used in proportion to fine and coarse aggregates at a ratio of 1: 0.65: 1.5. Using a 0.4 activator to binder ratio. The molarity ranges utilized were 11 M -15 M. Compressive strength and split tensile strength tests were conducted on 28-day-old concrete. The findings indicated that when the molarity of SCGC treated with seawater increased from 11 to 15 M, the compressive and split tensile strengths increased. Compressive strength values were greatest in SCGC treated at room temperature when an activator of 13 M was used, and compressive strength values dropped in SCGC treated at room temperature when an activator greater than 13 M was used.

Introduction
The communities is the SDGs' eleventh objective, with ten targets to be met worldwide. The aim is to create inclusive, safe, resilient, and sustainable cities and settlements. One approach to achieve environmentally friendly sustainable urban development is to minimize the usage of cement in building projects by using renewable resources that may perform the function of cement.
Using X-Ray Fluorescence (XRF) analysis, previous research on fly ash from the Bosowa Ernergi Jeneponto PLTU revealed that the four highest chemical compositions of fly ash are silicate (SiO 2 ), aluminum (Al 2 O 3 ), iron (Fe 2 O 3 ), and lime (CaO) [1]. According to ASTM C 618-96, PLTU Energi Bosowa Jeneponto's fly ash is classified as a class C type, with a CaO content of 23.52 percent. Apart from being cement, the fly ash from the Bosowa Jeneponto PLTU Energi has pozzolanic properties. This is because the fly ash from the Bosowa Jeneponto PLTU Energi contains a high concentration of CaO. The use of fly ash from the Bosowa Jeneponto PLTU Energi power plant in the manufacture of geopolymer mortar has been investigated, and the results indicate that fly ash can be used in place of cement in mortar due to its high strength for construction. [1]- [4].
Numerous studies on fly ash-based concrete have been conducted, one of which examined the Utilization of Coal Fly Ash as a Partial Substitute for Cement in Concrete Mixtures by varying the amount of coal fly ash added to PLTU Jeneponto as a substitute for PCC cement by 15%, 30%, and 45 percent. At 28 days, the compressive strength of 15% fly ash concrete increased by 1.2 percent, while at 90 days, the compressive strength of 15% and 30% fly ash concrete increased by 1.28 percent and 3.8 percent, respectively [5].
Geopolymer binders emit carbon dioxide at a rate of 5-6 times that of Portland cement [6]. Through industrial usage of geopolymer concrete and its by-products, hazardous materials are converted into necessary building materials. Alkaline activation of alumino-silicate minerals derived from geological sources or by-products such as metakaline, fly ash, husk ash, and silica fumes results in the formation of geopolymer concrete. Although the mechanism of alkali activation is unknown, the chemical composition of the source material and alkaline activator has a significant influence in the formation of geopolymer products.
Geopolymer is mostly composed of industrial waste fly ash, which is rich in the elements alumina (Al) and silica (Si). The silica and alumina components in fly ash are dissolved in an alkaline solution. The alkaline solution is composed of sodium hydroxide (NaOH), sodium silicate (Na 2 SiO 3 ), and distilled water (H 2 O), all of which are necessary components of the synthesis. Geopolymer concrete synthesis is extremely reliant on the state of the raw materials, namely the type and content of the fly ash, the concentration of alkaline solution, and the geopolymerization process [7].
SCC is a self-compacting concrete with a rather high slump. SCC does not need vibration throughout the volume placement and compaction processes, like conventional concrete does. SCC has a high flow capacity, which enables it to flow, fill the formwork, and achieve its maximum density on its own [3]. The impact of superplasticizer (SP) and active sodium hydroxide (NaOH) molarity on the workability, compressive strength, and microstructural characteristics of self-compacting geopolymer concrete was investigated [8]. After 48 hours of treatment, specimens were examined to determine the optimal SP dosage and necessary SCGC molarity. Because 6% was chosen as the optimum concentration, the SP dosage of 6% and the concentration of 12 M NaOH provided acceptable performance. The compressive strength rises as the concentration of NaOH solution increases from 8 M to 12 M. At the age of 28 days, a dosage of 6% SP and a concentration of NaOH 12 was able to generate a concrete compressive strength of up to 51.52 MPa [8].
The strength of structures in a maritime environment will be lowered due to the weight on the structure and an aggressive environment that contains chloride ions in seawater that enters the concrete [9]. The high salt concentration of seawater can have an impact on the strength and durability of concrete. This is because seawater contains chloride, which has an aggressive effect on concrete. Fresh water is used to make concrete mixtures, however seawater will invariably infiltrate the concrete mixture when buildings are cast in a harsh environment. Because casting in building projects takes place in an aggressive environment, such as on the edge/top/on the sea, seawater will invariably infiltrate the formwork before the concrete sets. The chlorides have a complicated history in cement; on the one hand, they have long been employed to speed up cement hydration and strength, while on the other hand, they deprive embedded steel of the corrosion protection that occurs in chloride-free cement environments [9]. Because of the problem of corroded concrete caused by chloride in seawater, it is required to add additives to the concrete mixture to reduce chloride entrance and ensure the safety of the concrete reinforcement. Chloride can be prevented from infiltrating concrete by using fly ash. As shown in previous studies, the addition of fly ash reduces chloride ion precipitation and decreases the chloride ion diffusion coefficient as fly ash replacement increases, and fly ash encourages chloride binding in concrete [10].
This research is very useful in utilizing waste to be used as environmentally friendly materials. It is hoped that this research can be used as a construction material, especially in construction buildings in an aggressive environment (sea area).
The compressive strength and split tensile strength of seawater-cured SCGC concrete and air-cured SCGC are discussed in this research. SCGC was synthesized utilizing NaOH and Na 2 SiO 3 as activators, an alkali modulus of 2, and molarity fluctuations between 11 and 15 M.

Literature Review
Geopolymer is a green substance that may be used in place of Portland cement in construction as a concrete repair material or as a structural element in overall building.
SCGC is a relatively new idea and may be regarded the most significant advancement in the area of concrete technology. SCGC is a novel kind of material that does not need vibration to be placed and can be created by eliminating regular Portland from the mix [11].
The binder is the primary factor that distinguishes geopolymers from conventional concrete. When producing conventional concrete, coarse and fine particles are bound together using Portland cement and water [12]. In geopolymer concrete, the silica and alumina in fly ash react with an alkaline liquid to create a geopolymer paste capable of bonding coarse aggregate, fine aggregate, and other components. The glue will harden as a result of the polymerization process. One of the distinctions between geopolymer and ordinary concrete is the way the concrete is treated [12].
Geopolymer is an ecologically friendly substance that may be used in place of Portland cement in construction as a concrete repair material or as a structural element in the overall structure. Geopolymers are inorganic synthetic polymers that generate threedimensional polymer chains during alkaline chemical processes. The chemical composition of the raw materials and alkaline fluids controls the formation of the final geological polymerization product's microstructure and mechanical characteristics. Fly ash-based polymers are a new kind of binder that has a reduced environmental effect and increases the sustainability potential of concrete buildings [13].
According to the SCC EFNARC standard [3], if the following criteria are fulfilled, the workability or fatigue of a new concrete mix may be referred to as SCC concrete: Where sodium hydroxide concentrations ranging from 8M to 14M are used in the study.
The findings of the tests indicate that changes in the sodium hydroxide concentration have This research looks at the strength of concrete at 28 days if it has been polluted with saltwater and is continuing in the hydration process.

Research Method
The technique employed in this study is the laboratory experiment. The stages in this study are as follows: a) A literature review collects secondary data from a range of sources, such as books, research journals, scientific papers, and testing standards.
b) Laboratory examination and testing of samples with the goal of obtaining primary data that will be utilized to analyze the findings of the study conducted.
c) Using an excel program, the sample's experimental data will be evaluated to identify the difference between SCGC curing saltwater and SCGC curing fresh water.
d) The data analysis technique utilized in this research is descriptive analysis, which gives an overview of the data collected from the results of utilizing fly ash as a geopolymer concrete material with seawater and air curing procedures.

Tools
The following tools were utilized in this study: 2) Water is measured using measuring cups with capacities of 2000 ml and 50 ml.
3) Stirrer for mixing an alkaline activator solution. 4) A stainless steel cup or tray is required to store the components and alkaline activator solution.

5)
A brush is used to remove any leftover debris from the utilized equipment.
6) The time spent stirring was recorded using a timer. 7) Bucket for storing the remainder of the mixture and water. 8) Purpose: material movement from one place to another. 9) A soaking tub for soaking concrete.

Materials
Fly ash, coarse aggregate (gravel), fine aggregate (sand), sodium silicate (NaOH), and sodium hydroxide (Na 2 SiO 3 ) were utilized in this study. The inspection of fine and coarse aggregate is governed by the Indonesian National Standard, which is summarized in Tables   1 and Table 2.

Fabrication and Curing of Sample
The production of test items is based on the findings of mixed design, and this study is divided into the following stages:

1) Prepare a solution of alkaline activator (leave it for 24 hours)
2) Preparation of a SCGC fly ash concrete mix.  6) For 28 days, the test item is submerged in a bath of seawater.

Mix Design of SCGC
Prior to sampling, a mix design was performed utilizing the EFNARC technique.
The specimens were produced with varying molarities (11M, 12M, 13M, 14M, and 15M) and alkaline modulus 2, the water used to cure seawater and air-cured specimens, respectively. Prior to placing the mixture in the cylinder, SCC fresh concrete is evaluated

Data Analysis
The

Characteristic of Aggregate
Aggregate testing for both fine and coarse aggregates was conducted in accordance with SNI standards at Fajar Makassar University's Civil Engineering Laboratory. The results of testing the aggregate material produced indicate that the properties of fine aggregate and coarse aggregate meet the requirements for self-compacting geopolymer concrete component materials. Table 5 and Table 6 provide the test results for fine and coarse aggregate, respectively.   have an adverse effect on the quality of the concrete.

Slump Flow
To evaluate the workability of the SCC concrete mix, a Slump Flow test is performed. Workability refers to the ease with which the SCC concrete mix may be mixed, carried, poured, and compacted without producing segregation of the concrete components.
The degree of workability is determined by the mixture's composition, physical properties, and the kind of mixing medium used. As shown in Figure 1, the slump flow test at a molarity of 11-15 fulfilled the EFNARC criteria but did not satisfy them at a molarity of 13-15 because the self-compacting geopolymer concrete underwent fast bonding throughout the flow and therefore did not achieve the diameter limit. The EFNARC requirement is between 650 and 800.

The Compressive Strenght
At the age of 28 days, the compressive strength test was performed. The load is applied until the test item cracks or the load is no longer able to be applied. It is shown on the UTM tool by a pointer. For comparison, Figure 2 displays the compressive strength of seawater-cured SCGC and air-cured SCGC. The compressive strength of seawater-cured SCGC is compared to that of air-cured SCGC in Figure 2. Seawater curing has a significant impact on the compressive strength of SCGC concrete. This is shown in Figure 2, where nearly all of the compressive strength was lost owing to saltwater curing. However, a rise in the compressive strength of the seawater-cured SCGC was associated with an increase in the activator's molarity.

The Split Tensile Strength
The split tensile strength of split concrete is determined when it is subjected to the maximum load. Split tensile strength is then computed using the resultant data in accordance with Indonesian National Standard (SNI 2491-2014). The split tensile strength test results are shown in Figure 3.
The compressive strength of seawater-cured SCGC is compared to that of air-cured SCGC in Figure 3. Seawater curing has a significant impact on the split tensile strength of SCGC concrete. As shown in Figure 3,

Conclusion
The following conclusions are drawn from the study's findings: and 15 M were used, the split tensile strength of sewater-cured SCGC was greater than that of water-cured SCGC, increasing by 2.49 and 12.61 percent, respectively.

A similar investigation of the mechanical characteristics of SCGC concrete immersed
in saltwater for an extended period of time is required.

2.
It is essential to investigate the optimum value of the alkaline modulus in selfcompacting geopolymer concrete immersed in saltwater, as well as the variation of additional materials (viscocrete and retarder).