A comparison of the effect of steel and polypropylene fibers on the strength, frost resistance, abrasion, and corrosion resistance in an acidic environment of fiber-reinforced concrete for industrial floors and road pavements was carried out. Steel fibers with a length of 50 mm and a diameter of 1 mm and polypropylene fibers with a length of 36 mm and a diameter of 0.68 mm were used. The amount of steel fiber varied from 15 to 25 kg/m³, and the amount of polypropylene fiber varied from 2 to 3 kg/m³. It has been established that steel fiber more significantly increases the concrete compressive strength, and both types of dispersed reinforcement increase the flexural strength equally by 27–34%. Also, dispersed reinforcement reduces the concrete abrasion resistance by 15–35% and increases its frost resistance by 50 cycles, which helps to improve the durability of industrial floors and road pavements. The use of steel fiber in an amount of 20 kg/m³ and polypropylene fiber in an amount of 2.5 kg/m³ also increases the concrete corrosion resistance in an acidic environment. In general, dispersed reinforcement with both fiber types has approximately the same technological effect concerning the mentioned applications. However, the use of polypropylene fibers is economically more profitable since an increase in the cost of 1 m³ of concrete with steel fiber reinforcement is from $22.5 to $37.5, and an increase in cost with polypropylene fiber is from $10 to $15.

Feasibility of application of multifractal theory for evaluation of materials mechanical properties, cast iron in particular, has been considered. The proposed method enables evaluation of mechanical properties of materials based on...

High-early strength fiber-reinforced concretes are effective materials for the full depth repair of rigid highway and airfield pavements. A comprehensive study was carried out on the influence of the amount of steel anchor fiber and hardening accelerator on properties that are important for repairing concrete. A two-factor experiment was carried out, in which the influence of the hardening accelerator and fiber dosages on the strength, frost resistance, wear resistance and shrinkage of repaired steel-fiber-reinforced concrete for rigid pavements was studied. The investigated concretes contained 400 kg/m³ of cement and polycarboxylate plasticizer in the amount of 1.2% of the cement content. It has been established that the optimal concrete compositions are with the amount of Sika Rapid 3 hardening accelerator from 1 to 2% of the cement content and the steel fiber amount from 60 to 90 kg/m³. Optimal fiber-reinforced concrete compositions have a reduced shrinkage during hardening, and at the age of 2 days they have a compressive strength of at least 55 MPa and a flexural strength of at least 8.5 MPa. At the design age, the fiber-reinforced concrete compressive strength is 85–90 MPa, its flexural strength ranges from 15.5 to 17.5 MPa, it has a frost resistance of F200 and abrasion not higher than 0.24 g/cm². These properties ensure the high durability of the repair material.

The article is devoted to ranking of quality criteria for multiparameter, multicriteria production technology of lightweight concrete depending on their significancy using fractal formalism. The proposed approach allows to determine the operation area of stability of the physicomechanical properties of expanded clay concrete with preset technology parameters depending on the size of their self-similarity area and to control the technological process relative to the determine parameter - watertightness. For concrete thin-walled hydraulic structures watertightness is one of the main indicators of quality, ensuring the durability of structures. In the experiment conducted on 15 points optimal plan, 3 factors of the composition varied: sulfate-resistant portland cement, silica fume, water reducing admixture. Possibility of ranking the indicators of W/C and physicomechanical properties of expanded clay concrete depending on the variation of concrete mixture components is shown. Stability of physical and mechanical properties of expanded clay concrete is necessary to ensure its durability and accordance with design requirements. Expanded clay concrete similar to those described in this article can be used in reinforced concrete shipbuilding to reduce weight of structures.

The complex effect of the amount of cement, polypropylene fiber (the fiber length was 39 mm, and the diameter was 0.45 mm), and polycarboxylate superplasticizer on concrete properties for rigid pavement was determined using the methods of experiment planning and experimental–statistical modeling. The fluidity of all the mixtures was S1. The W/C of the mixtures depended on the composition of the concrete and variable from 0.32 to 0.46. It was found that, by increasing the amount of superplasticizer from 1% to 1.8–2%, the compressive strength of concrete increased by 4.5–6 MPa after 3 days and by 7–9 MPa after 28 days. The flexural strength in this case increased by 0.6–0.9 MPa. The use of polypropylene fiber in the amount of 1.5–1.8 kg/m³ increased the compressive strength of concrete by an average of 3 MPa, increased the flexural strength by 0.5–0.6 MPa, reduced the abrasion capacity by 9–14%, and increased the frost resistance by up to 50 cycles. When using a rational amount of superplasticizer and fiber, the compressive strength of concrete, even with a minimum cement amount of 350 kg/m³, was at least 65 MPa, its flexural strength was at least 6 MPa, its frost resistance was F200, and its abrasion capacity was not more than 0.30 g/cm². Concrete with such properties can be used for roadways of any type. Low abrasion capacity and high frost resistance provide the necessary durability of concrete for rigid pavement during operation.

The purpose of the research was to improve the strength and durability of shipbuilding expanded clay lightweight concrete by using modifiers, fibers and optimizing the composition of concrete. The four-factor experiment was carried out according to the optimal plan. The experiment varied, the amount of sulfate-resistant Portland cement, silica fume and polypropylene fiber. The content of expanded clay gravel in concrete also varied. Strength, watertighness, frost resistance and average density of ship-building expanded clay lightweight concrete of various compositions are investigated. The rational quantity of modifiers and fibers is determined. It is shown that shipbuilding expanded clay concrete has high watertighness and frost resistance, which ensures their durability when operating afloat. The use of lightweight concrete allows increasing the load carrying of floating structures and improving the working conditions of personnel. Normative documents for the production of concrete for floating reinforced concrete structures inUkrainehave been developed.