###### Abstract  
According to the sustainable development concept, it is necessary to solve the issue of replacing fiber from synthetic materials with natural, environmentally friendly, and cheap-to-manufacture renewable resources and agricultural waste. Concrete is the primary material for which fibers are intended. Therefore, the use of vegetable waste in concrete is an essential and urgent task. Coconut fiber has attracted attention in this matter, which is a by-product of the processing of coconuts and makes it relevant. This work aims to investigate the experimental base for the strength properties of dispersed fiber-reinforced concrete with coconut fibers, as well as the influence of the fiber percentage on the mechanical, physical, and deformation characteristics. The samples were made of concrete with a compressive strength at 28 days from 40 to 50 MPa. The main mechanical characteristics such as strength in compression (cubic and prismatic) and tension (axial and bending), as well as the material's compressive and tensile strains, were investigated. The percentage of reinforcement with coconut fibers was taken in the range of 0% to 2.5% with an increment of 0.25 wt.%. Tests were carried out 28 days after the manufacture. The microstructure of the resulting compositions was investigating using the electron microscopy method. The most rational percentage of coconut fibers was obtained at 1.75%. The increase in mechanical indicators was 24% and 26% for compression and axial compression, respectively, and 42% and 43% for tensile bending and axial tension, respectively. The ultimate strains in compression were raised by 46% and in tension by 51%. The elastic modulus was increased by 16%. concrete; fiber-reinforced concrete; sustainable concrete; natural fibers; coconut fiber +
Footnote †: journal: Applied Sciences
bar reinforcement does not practically influence the microstructure of the concrete matrix, in which many microcracks are formed already at the stage of hardening and shrinkage, which inevitably begin to develop during load application. Restraining the development of microcracks significantly increases the strength characteristics (SC) of the concrete itself as a material [1,2]. Traditionally, fiber-reinforced concrete (FRC) structures contain steel, polypropylene, cellulose fibers [3, 4, 5, 6, 7, 8, 9, 10, 11], and others. The use of fiber reinforcement made of coarse basalt fibers has a certain popularity [10]. Recently, the popularity of the use of glass and carbon fiber dispersed reinforcement of concrete (FDRC) has been growing [12]. The above materials have high tensile strength and other properties that have rightfully made them traditionally used materials for FDRC. However, their significant common disadvantages are their high cost and the need for production processes associated with high emissions of greenhouse gases into the atmosphere. Additionally, the obtained SC of FRC with fiber reinforcement from classic materials are often much higher than required for the normal operation of a particular FRC structure, and the cost of FRC in this case may not correspond to the required characteristics [1,2,8,10]. The above reveals the environmental and economic problem of FRC, which can be solved by using fibers that do not require separate production, which are a rapidly renewable natural material, or that are waste from the agricultural industry [13,14]. Thus, primary attention for the creation of environmentally friendly and relatively inexpensive FRC is attracted by natural fibers that do not require energy-intensive and environmentally unsafe production. The raw materials for such fibers are obtained by mechanical processing of plant parts, their cleaning, and drying. At the same time, plant fibers are often a by-product or waste of agriculture, and their use as a FDRC is one of the ways to obtain relatively waste-free agricultural processes, which corresponds to the concept of sustainable development [15, 16, 17, 18, 19, 20, 21, 22, 23, 24].