COMPARISON OF STRENGTH AND DURABILITY OF CONCRETES MADE WITH SULFATE-RESISTANT PORTLAND CEMENT AND PORTLAND CEMENT WITH POZZOLANA ADDITIVE

In this study, a comparison of the strength and durability of concrete with sulfate-resistant cement and cement with pozzolana additive was performed. In assessing the concrete durability, three indicators were compared: sulfate resistance, water permeability, and frost resistance. All concrete mixtures were used without admixtures. The absence of chemical admixtures in the concrete mixtures was because of the need to compare properly the properties of concretes with different cements without the influence of modifiers, which may result in different efficiencies for different types of binders. The concrete compositions of grades C20/25 and C30/35 were presented. The use of Portland cement with pozzolana additive in concrete mixtures provided the necessary level of corrosion resistance and frost resistance of concrete, as well as higher water permeability and lower cement content in comparison with using sulfate-resistant Portland cement

Modified expanded clay lightweight concretes for thin-walled reinforced concrete floating structures

Reinforced concrete floating structures have much more durable metal structures and do not require frequent repairs. Heavy and lightweight shipbuilding concrete is used for these structures. Floating structures are operated in difficult climatic conditions. Properties of modified expanded clay concrete for thin-walled reinforced floating structures were investigated. The experiment was carried out according to the 3-factor optimal plan. Concretes with the strength of up to 43 Mpa, with water resistance up to W12 and the average density of up to 1750 kg/m3 were obtained. Due to the use of expanded clay lightweight concrete, the carrying capacity of a ship, in particular, the floating dock, is increasing, and the comfort of people and technological equipment is increasing. Regulations for the technology of manufacturing modified shipbuilding expanded clay lightweight concrete for the construction of thin-walled floating structures and floating docks were developed and approved. The results of the research were used in the development of the national standard of Ukraine "Shipbuilding Concrete"

FIBER-REINFORCED CONCRETE FOR RIGID ROAD PAVEMENTS MODIFIED WITH POLYCARBOXYLATE ADMIXTURE AND METAKAOLIN

Increasing the strength and durability of road surfaces is crucial. Therefore, the concrete compressive strength, flexural strength, frost, and abrasion resistance of fiber-reinforced concrete for rigid pavements are investigated in this study an experiment is performed based on an optimal plan, in which four factors of concrete composition are varied: the amounts of Portland cement, polypropylene fiber, metakaolin, and polycarboxylate type admixture. Experimental statistical models for investigating the effects of composition factors on concrete properties are established. It is discovered that owing to the use of metakaolin and a superplasticizer, the concrete compressive strength increases. Furthermore, the use of modifiers and fiber reinforcement increases the flexural strength, frost resistance, and wear resistance of concrete. X-ray phase analysis of the fiber-reinforced concrete structure confirm the effectiveness of the modifier effect, in particular the positive role of metakaolin as an active pozzolana. The developed fiber-reinforced concrete for rigid pavements with rational modifiers, depending on the Portland cement content, exhibits compressive strengths from 55 to 70 MPa, flexural strengths from 8 to 9.5 MPa, frost resistances from F350 to F450, and abrasion resistances from 0.3 to 0.4 g/cm2. Such properties ensure the high durability of fiber-reinforced concrete and allow it to be used on road pavements that support heavy loads and traffic

Method of material quality estimation with usage of multifractal formalism

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 determination of their sensitivity to dimensions of structure elements from the multifractal Renyi spectrum. Sensitivity of cast iron ultimate strength to informational dimension of carbides, ultimate bending strength to fractal dimension of carbides, impact strength to correlation dimension of carbides and hardness to fractal dimension of graphite have been determined. Fractal prediction models of quality characteristics of cast iron based on the analysis of the following its structure elements (carbides and graphite) have been received

Strength, Frost Resistance, and Resistance to Acid Attacks on Fiber-Reinforced Concrete for Industrial Floors and Road Pavements with Steel and Polypropylene Fibers

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