Optimization of fiber-reinforced concrete with polypropylene and basalt fibers using marble fillers

Introduction. One of the most promising materials for dispersed reinforcement of concrete is basalt fiber. It is characterized by high strength, thermal and chemical resistance, as well as environmental safety. The use of reinforcing fibers significantly increases the flexural and tensile strength of concrete and improves its water resistance and resistance to dynamic loads. A number of studies show that the introduction of basalt fiber contributes to an increase in the compressive and flexural strength of composites, as well as their crack resistance. With an optimal fiber content, a spatial reinforcing framework is formed, which increases the energy capacity of material fracture and its resistance to external influences. Methods and materials. Fiber-reinforced concretes were produced using the following technology: marble fillers of different fractions, reinforcing fibers, and Portland cement were first mixed in a dry state for 10 minutes, after which the required amount of water was added. The resulting mixture was stirred for 30 minutes and molded into special forms for physical and technical studies. After 24 hours, the samples were treated with water steam for 30 minutes, after which, after three days, tests for density, water absorption, and strength were carried out. According to the experimental plan of the Ha5 type, 27 compositions of fiber-reinforced concrete were obtained. Based on the experimental results, regression coefficients of models describing the studied properties of fiber-reinforced concrete with marble fillers were determined using the least squares method. Graphical representations of the experimental–statistical models were also constructed in the form of two-dimensional nomograms. Results. It was established that combined reinforcement with basalt fibers (BF) and polypropylene fibers (PF) is possible but requires optimization of their ratio. The most effective scheme is when the main reinforcing role belongs to basalt fibers (2–3%), while polypropylene fibers are introduced in small amounts (up to 1–2%) to control crack formation. The analysis of graphical regions and derivative functions showed the following optimal range of component contents: marble chips – 25–30%, marble powder – 10–15%, marble dust – about 12%, basalt fibers – 2–4%, polypropylene fibers – 0–2%. Conclusion. Basalt fibers are an effective means of increasing the strength characteristics of fiber-reinforced concrete at moderate content (about 2–3%). However, their excessive amount leads to a decrease in density and an increase in water absorption of the material. Polypropylene fibers in most cases reduce density and compressive strength and increase water absorption; therefore, their use should be limited to small doses and mainly applied to improve crack resistance. The best complex of physical and mechanical properties is achieved when marble dust is used in combination with basalt fiber.