## 1 Introduction  
Asbestos is a fibrous material with remarkable technical characteristics that has been used in the manufacturing of numerous building materials since its discovery. It has two types--serpentine and amphiboles. Because of its sound absorption capabilities, strength, fire resistance, heat resistance, electrical resistance, chemical resistance, and low cost, asbestos was prominent in the late nineteenth century. Some of its applications have come onto the market, such as asbestos cement particles, asbestos yarn cord and fabric, asbestos joint and millboard, and water and sewage pipes [1]. However, the movement of asbestos fibers through the atmosphere in plants can lead to a bad effect on human health. Breathing asbestos-containing air particles causes severe respiratory difficulties [2]. As a result, the development of raw materials for asbestos must be taken into account in order to protect public health and the environment. Coconut is a significant food and industrial product found mostly in Thailand's coastal areas due to its tropical environment. Coconut fiber may be extracted by hand or machine from the coconut husk and is readily accessible for use as a raw material in fiber-cement products due to its abundance, low cost, appropriate mechanical qualities, non-toxicity, and chemical reactivity. Coconut fiber (CF) is typically 350 mm long, 0.12-0.25 mm in diameter, and 1250 kg/m\({}^{3}\) in density. Coconut fiber has the strongest lignin coating of any natural fiber, making it stronger than most others: only banana fiber has a higher tensile strength. It is also unusual in its resistance to microbial deterioration and salt water [3]. Researchers focus on composite materials reinforced with natural fibers, as these composites combine good mechanical properties with low density. These compounds offer several advantages, such as cost, availability of renewable natural resources, and biodegradability [4]. [PERSON] et al. [5] produced fiber-cement boards (FCBs) using pretreated coconut coin and oil palm fibers at 5%, 10%, 15%, and 20% by weight. The results indicated that the addition of natural fibers led to a reduction in density, compressive strength, and flexural strength. However, the natural fibers improved sound insulation performance. Coconut fibers also outperformed oil palm fibers in both physical and mechanical properties in FCBs. [PERSON] et al. [6] investigated the physical and mechanical properties of concrete produced with shredded coconut fiber at volumes of 0.6% and 1.8%. The results showed a decrease in compressive strength as the fiber content increased. Coconut fiber-concrete exhibited higher water absorption compared to conventional concrete, suggesting that coconut fiber has potential for use in lightweight concrete. However, [PERSON] et al. [7] incorporated treated and untreated coconut fibers into concrete and subjected the concrete cubes to elevated temperatures of 250 \({}^{\circ}\)C and 150 \({}^{\circ}\)C for 2 h. The results indicated an increase in compressive strength compared to the control. The compressive strength improved by 3.88% with up to 0.5% fiber replacement. Beyond 0.5% fiber content, the compressive strength began to decrease. [PERSON] et al. [8] produced concrete reinforced with coconut fiber in proportions of 0.5%, 0.75%, and 1%. Concrete containing 0.75% fiber exhibited a significant reduction in crack propagation on the slab surfaces, as well as a decrease in crack depth caused by plastic shrinkage during the early stages of curing. [PERSON] et al. [9] studied the improvement in mechanical characteristics in normal-weight concrete by varying the proportion of coconut fiber from 0% to 2.5% with increments of 0.25 wt.%. The obtained results revealed that the most appropriate proportion of coconut fibers was 1.75% with compressive strength of 40-50 MPa and axial tensile strength of 3-4.3 MPa. Coconut fibers in the range of 2-2.5 wt% can reduce strength properties.