Experimental Study Of Using Rice Husk Ash and Borax On The Compressive Strength of Geopolymer Concrete

The development of infrastructure in Indonesia is currently very increasing, The use of concrete is widely used to build dams, buildings, roads, bridges and others. Concrete is used because it has advantages over other materials, apart from having compressive strength, concrete is also a relatively inexpensive material. However, the increasing amount of cement used in the manufacture of concrete will cause an increase in global warming. Thus, geopolymer concrete was introduced as an alternative to reduce cement consumption in concrete work. The purpose of this study was to determine the effect of using rice husk ash and borax as an alternative material on the compressive strength of concrete and to determine the effect of using rice husk ash and borax as an alternative material to slow the setting time of geopolymer concrete. The variations in the use of rice husk ash 0%, 10%, 15%, and 20% with the use of 3% borax. From the results of the study, the use of rice husk ash and borax in the geopolymer concrete mixture had an effect on the compressive strength of concrete in this study, with the addition of rice husk ash there was a decrease in compressive strength when compared to normal geopolymer concrete or without a mixture of rice husk ash and borax. The use of 15% rice husk ash and 3% borax achieved the highest compressive strength values when compared to the use of rice husk ash as much as 10% and 20%. Furthermore, the more the use of rice husk ash with the use of 3% borax, the longer the setting time in geopolymer concrete.


Introduction
The development of infrastructure in Indonesia is currently increasing. The use of concrete is widely used to build dams, buildings, roads, bridges and others. Concrete is used because it has advantages over other materials, apart from having compressive strength, concrete is also a relatively inexpensive material.
The increasing development of construction in the field of construction has a very significant impact on concrete technology where its use is indeed very high in terms of cost, selection of good quality materials, with good compressive strength in concrete and reducing the risk of damage or porous in concrete. As you know, that in cement production contributes to global warming due to CO2 are quite is great. Increasing the amount of cement used in the manufacture of concrete will cause an increase in global warming, however, the continuous use of Portland cement itself will result in the raw material for making cement itself depleted (Simatupang, Partogi H.;SIR, Tri MW;Kurniaty, 2016).
Geopolymer concrete is introduced as an alternative to reduce cement consumption in concrete work. Geopolymer concrete is made from inorganic waste materials which contain a lot of silica and alumina. To speed up the chemical reaction in geopolymer concrete, it is necessary to mix silica and alumina with alkaline activator substances, namely NaOH and Na2SiO3, these materials are mixed with aggregates to form geopolymer concrete without using cement anymore (Mulyadi, 2014).
Previous research used rice husk ash as an alternative binder and fly ash in a review of the compressive strength of boton geopolymer, in this study it was concluded that the addition of rice husk ash decreased compressive strength compared to geopolymer concrete without a mixture of rice husk ash. . The optimum value for the compressive test on the addition of rice husk ash was 15%. This happened because the geopolymer concrete binder was reduced due to too little and too much addition of rice husk ash at a variation of 5%, 10% and 20%. (Anam, et al, 2018). And there is also a previous study using borax and calcium oxide on setting time You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 99 and compressive strength of geopolymer mortar based on type c fly ash, in this study, borax was shown to slow down the setting time and the more borax was added, the longer the setting time would occur. (Purwantoro, A., Suyanto, W., Antoni,. Hardjito, 2016). However, no studies have used rice husk ash as a binder and borax as an admixture to determine the compressive strength of geopolymer concrete. The husk ash is expected to be an alternative to binder and borax as admixture which can slow down the setting time reaction in the geopolymer concrete.
Therefore, it is interested to try to make research on the addition of rice husk ash and borax to the compressive strength of geopolymer concrete. With the hope that the use of rice husk ash and borax can produce good quality geopolymer concrete.

Method
Geopolymer concrete is concrete with natural materials as a binder. The binder material undergoes a polymerization reaction in the hardening process. The main basic material for making geopolymer concrete is the research method used, namely using an experimental method with a mixture of rice husk ash as a precursor and borax as an admixture with a different variation of rice husk ash composition and a 3% variation of the use of borax to obtain compressive strength data from research. this.
This research was conducted using a mix design that refers to journals about geopolymers. In this study there were variations in the percentage of fly ash 100%, 90%, 85% and 80%, variations in the percentage of use of rice husk ash 0%, 10%, 15% and 20% and variations in the percentage of use of rice husk ash 3% at the age of 3, 7. , 14 and 28 days for geopolymer concrete and concrete ages 7, 14 and 28 days for geopolymer mortar.

Materials
a. Geopolymer concrete forming materials:  The fine aggregate used comes from Belitung.  The coarse aggregate used comes from Maloko.  The alkaline activators used in this study were NaOH and Na2SiO3.  The precursor used in this study is fly ash in the PT. SBB and rice husk ash.  The admixture material used comes from borax. b. The specimen is used in the form of a cylinder with a diameter of 10 cm and a height of 20 cm with 5 variations, each totaling 3 samples. The specimen material for geopolymer mortar was in the form of a 5x5x5 cm cube with 5 variations, each of which amounted to 2 specimens. You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 100 c. Checking the compressive strength of concrete is carried out at PT. Concrete Material Solutions, at ages 3, 7, 14 and 28 days for geopolymer concrete and 7, 14 and 28 days for geopolymer mortar. Following are tables 1 and 2 for the needs of 1m 3 material requirements.

Sieve Analysis
Testing The aggregate test carried out in this study included sieve analysis, density, absorption, sludge content and organic content, this aggregate test used the reference method ASTM C136.
This stage aims to determine the grain size and grain composition (gradation) of fine aggregate (sand) and fine aggregate (gravel) based on the sieve number. So that it can determine the modulus of fineness of the sand and gravel material. The following are the results of the grading test for fine aggregate and coarse aggregate: The graphical results of the fine aggregate sieve analysis are shown in figure 2.  -12-1989-F, 1989). This fine aggregate gradation falls into the zone II sand group, namely slightly coarse sand according to SNI 03-2834-2000, n.d. The graphical results of the fine aggregate sieve analysis test are shown in You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 101 Figure 3. Graph of Coarse Aggregate Sieve Analysis In testing the analysis of the 25mm split sieve, according to the graph in Figure 4.2 there is an FM value of 7,262. Gravel with FM is declared good and qualifies as construction material.   Test for the organic content of this sand using a standard color comparison obtained color no.5 where the organic content in this sample sand has high levels. The maximum limit according to the color standard in ASTM is no.3.

Workability
Workability can be seen from the results of the slump flow value that occurs because it is a consistency parameter of the concrete mixture which describes workability, the higher the slump value, the easier the workability is. ADRI INTERNATIONAL JOURNAL OF CIVIL ENGINEERING VOLUME 6 │ NUMBER 1 │ FEBRUARY 2021 http://adri.journal.or.id/index.php/aijce/index ISSN: 2656-1174 (online) Attribution 4.0 International (CC BY 4.0) You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 102 Figure 4. Graph of Workability Based on the linear graph of Figure 4. the results obtained are the higher the use of rice husk ash percentage, then the higher the value of flow obtained with the use of alkaline activator and borax pesentase equal to the admixture.  Figure 5. the results are the increased use of rice husk ash with the use of 3% borax, the longer the initial binding time that occurs in geopolymer concrete 3.2.6. Density Based on linear graph Figure 6. the density for variations in the use of rice husk ash is 20% with the use of fly ash as much as 80% and 3% borax is the result of the lowest density among other variations, namely 2.37 g / cm3.

Gamba r 7. Graph of Geopolymer Mortar Density
Based on the linear graph of Figure 7. The density for the variation of the use of rice husk ash 20% with the use of fly ash as much as 80% and borax 3% is the result of the lowest density among other variations, namely 1.97 g / cm3.

Figure 8. Geopolymer Concrete Compressive Strength Test Results
In Figure 8, it can be seen that the development of the concrete compressive strength that occurs at the age of concrete from 7 days to 14 days of concrete, where the use of rice husk ash as much as 15% provides a higher compressive strength than with the addition of rice husk ash 10%, 20%. The difference between the use of 15% rice husk ash and 10% rice husk ash at 3, 7, 14 and 28 days is 0.4 MPa, 0.6Mpa, 1 MPa and 0.6 MPa. The difference between the use of rice husk ash 15% and the use of rice husk ash 20% at 3, 7, 14 and 28 days is 0.6 MPa, 0.9 MPa, 1.7 MPa and 1.2 MPa. In Figure 9. You can see the development of the compressive strength of concrete that occurs at 14 days of mortar age, where the use of rice husk ash is 10% gives a higher compressive strength compared to the addition of rice husk ash 15%, 20%. The difference between the use of 10% rice husk ash and 15% rice husk ash at 7, 14 and 28 days is 0.48 MPa, 0.58 MPa and 0.9 MPa. The difference between the use of 10% rice husk ash and 20% rice husk ash at 7, 14 and 28 days was 0.58 MPa, 0.48 MPa and 0.16 MPa.
The factor that causes this compressive strength is low because it does not use Na2SiO3 with a concentration of 55%, Na2SiO3 which is used to become a mixture when making soap with a concentration of 40%. The results of the compressive strength of geopolymer concrete and geopolymer mortar can be applied as non-structural concrete such as concrete brick (Paving Block) with a classification of quality concrete bricks D which can be used for plants and other uses with a minimum average compressive strength of 10 MPa and a minimum of 8, 5 Mpa (SNI 03-0691-1996, n.d.).

Conclussion
1. In this study, rice husk ash material can be used as an alternative material in a mixture of binder and borax as an alternative admixture in the manufacture of geopolymer concrete. The higher the use of rice husk ash used, the higher the slump value but the higher the use of rice husk ash, the smaller the density obtained. The addition of rice husk ash and borax to the geopolymer concrete mixture has an effect on the compressive strength of the concrete in this study, with the addition of rice husk ash there is a decrease in compressive strength when compared to normal geopolymer concrete or without a mixture of rice husk ash and borax. The use of 15% rice husk ash and 3% borax achieved high compressive strength values when compared to the use of 10% and 20% rice husk ash. This occurs because the geopolymer concrete binder is reduced due to too much and too little addition of rice husk ash. The use of 3% borax in the EBG1 code can reduce the compressive strength of concrete. 2. In this study, the use of rice husk ash and borax can affect the setting time of geopolymer concrete. The more the use of rice husk ash with the use of 3% borax, the longer the setting time for geopolymer concrete.