Fly Ash and Fiber Waste As Principal Geopolymer Mortar Material: A Review

Geopolymer mortar is an innovative mortar using fly ash waste as an alternative to cement. The development of advanced fiber geopolymer mortar materials is an alternative solution to the weaknesses and shortcomings of conventional materials so that they have the ability to reduce and even absorb sound intensity and prevent noise propagation in overcoming noise problems in the field of building construction. Many factors can affect sound absorption, including the type of aggregate, modification of material composition that has a density level in fiber geopolymer mortar. The development of fiber geopolymer mortar can be developed in the construction field to reduce sound frequency and improve sound insulation. There are also different measurement mechanisms to determine the performance of the material in improving sound quality. This paper aims to review the performance of sound-absorbing fiber geopolymer mortar. This review is expected to provide insight into the development of fiber geopolymer mortar in building construction to improve comfort and reduce noise pollution.


Introduction
Research developments in the field of materials and engineering show a growing interest in the development of energy-efficient and environmentally friendly materials to support the construction industry.Geopolymers are formed when alumino silicate materials are mixed with basic reactant solutions.In addition to environmental sustainability, geopolymers also have excellent fire resistance, resistance to corrosive environments, good thermal and pressure strength, and low water permeability [1] [2].During the geopolymerization process, a chemical reaction occurs between the alkaline solution and the aluminosilicate material resulting in the dissolution of fly ash and straw ash [3].
Noise refers to unwanted sounds produced by various sources, such as people playing guitars, running machinery, vibrations from air conditioners, and various other machines.The difference between sound and noise is subjective and depends on the listener and the situation in which it occurs.Noise is one of the most common workplace health hazards.To reduce the negative impact of noise exposure, the noise level should be reduced to an acceptable limit.One of the best solutions to reduce noise is to adopt engineering modifications to the noise source itself and use sound insulation panels.Sound can propagate through walls by making them vibrate, so using sound insulation panels can help muffle it [4].

Composition of Geopolymer Mortar
Geopolymer mortar mix consists of fine aggregate, binder, alkali activator, water or distilled water.

a. Fine aggregate
Fine aggregate is the filling material of geopolymer mortar, where the sand used does not have a high mud content, it must be according to specifications and free of hazardous materials.

Figure 1.
Fine aggregate [5] b.Binder Binders used in the manufacture of geopolymers include fly ash, granulated blast furnace slag and metakaolin [6] in Figure 2 [6].Fly ash is waste from coal combustion, which contains silica and alumina which are good binders.Fly ash used as geopolymer mortar is 100% binder base material where fly ash passes sieve no.200 [7].d.The water used is clean water that is free from harmful organic substances, in the study [7] using aquadest.
In the manufacture of geopolymer mortar, there are several parameter variations that need to be considered, such as the ratio between Na2SiO3 and NaOH and the variant of activator and fly ash precursor.In addition, there are two variations of fine aggregate and fly ash precursor used.This mixture results in a chemical reaction that enables the formation of geopolymer, an innovative construction material that is environmentally friendly and has sufficient strength for a wide range of applications.
From previous researchers, in Table 1 that the average geopolymer mortar composition uses the same ingredients and alkali with different molarity and catalyst activator ratio.Fly ash NaOH Na2SiO3 10 1:1

Fiber Geopolymer Mortar
Geopolymer mortar is a product produced by mixing fly ash with an alkaline solution, which then undergoes a geopolymerization process.One of the common problems with geopolymers is their susceptibility to micro-cracks, which can affect the structural integrity of the material.To overcome the brittleness of geopolymers and improve their toughness and ductility, fibers are often added to the mix.The characteristics of fiber in mortar in Table 2.
The types of fibers in geopolymer mortars are diverse, varying in length and diameter.Moreover, the tensile strength of natural fibers may vary depending on their source and how they are used.Different researchers may report different results depending on the measurement method and data processing according to previous researchers.

Performance of Fiber Geopolymer Mortar
The performance of geopolymer mortar such as workability, density, porosity, strength, modulus of elasticity and ductility are affected by many factors such as type of binder, type of alkaline solution, ratio of solution to binder, ratio of sand to binder, temperature and curing duration [2].

Physics performance
Analysis of the physical performance of the material, including porosity, absorption, SEM (Scanning Electron Microscopy), density, and other parameters, was carried out to understand the characteristics of the geopolymer.The water absorption test involves comparing a control sample with a sample that has been treated.The physical performance of mortar properties in Table 3.The physical properties of geopolymer mortar where the greater the percentage of porosity and the smaller the absorption value the better the value, this is similar to research [2].From the results of previous studies, the density value is between 1770 and 1987 kg/m 2 .

Mechanical performance a. Compression strength
Compressive strength is the ability to withstand a given compressive load and one of the variables in mechanical performance.From Figure 5, it produces a higher compressive strength with a fiber percentage of 0,50%.b.Flexural strength Flexural strength is the ability of concrete beam to resist flexural collapse.Mechanical testing on fiber geopolymer mortar in Table 4.

Acoustic performance
The importance of natural fibers in the context of acoustics is receiving increasing attention.Natural fibers are becoming very attractive materials due to several advantages, such as low density, good mechanical properties, ease of processing, high stability, benefits to workers' health, ability to reduce friction, availability in large quantities, affordable price, and lower environmental impact during production.Some studies have also shown that natural fibers can have a positive impact on the environment through CO2 absorption during plant growth, which supports ecological sustainability.Therefore, natural fibers are not only an environmentally friendly option for acoustic products, but also open up the potential to reduce negative impacts on the environment, making them a more sustainable and efficient solution in acoustic applications [12].
The impedance tube is a tube designed to measure the acoustic parameters with a small test material size according to the size of the tube diameter.The impedance tube used in this study is made of iron pipe with a diameter of 8 cm and a length of 125 cm can be seen in Figure 8.This tube serves to propagate sound waves coming from the sound source (loudspeaker) to the material so that the propagating waves do not get interference from outside [12].Insulation tests are conducted to determine the acoustic properties of materials.Sound insulation is the reduction of energy from the transmission of sound through materials.Sound is transmitted through most walls and floors by making the entire structure vibrate.When sound reaches a surface, it is reflected, absorbed and transmitted.Good insulation is obtained with materials that have a light to heavy mass and are impermeable.Acoustic performance can be seen in Table 5.From the research [16] mentioned that the absorption of composites through several aspects.Polyester fibers exhibit good sound absorption properties but are chemically synthesized which is problematic in terms of environmental pollution and high cost.Wood fibers are used to partially replace polyester fibers because they reduce pollution and lower costs [16].

Conclusion
This paper presents a research summary of fiber geopolymer mortar.Geopolymer mortars are produced by mixing sand, alkaline solution, and binder.Based on the review of mechanical characteristics, the compressive strength of fiber geopolymer mortar depends on the composition of the geopolymer mortar, the type of fiber and the physical properties.There is little information available on durability properties with fiber addition.In the context of mortar, the optimal fiber dosage is a very important parameter to improve performance.Absorption by coconut fibers affects mortar properties by causing the fibers to expand.Natural fibers have great potential to replace expensive synthetic fibers in the manufacture of acoustic absorption materials due to their abundant availability, affordable cost and natural cellular structure.This structure allows natural fibers to absorb acoustic energy effectively, making them an attractive option in the development of efficient and environmentally friendly acoustic materials.

Table 4 .
Mechanical testing of fiber geopolymer mortar.