Compressive and tensile strength of reinforced сoncrete with basalt fiber

Досліджено міцність цементного каменю, дисперсно армованого базальтовою фіброю. Виготовлено дослідні зразки з різним об’ємним умістом фібри. Проведено експериментальні дослідження з метою встановлення впливу об’ємного вмісту фібри на міцність за розтягу та стиску композитного матеріалу. Відзначено значне зростання міцності на розтяг матеріалу зі збільшенням об’ємного вмісту армуючих волокон. Водночас міцність на стиск зменшується, що є несподіваним ефектом процесу армування цементної матриці.Nowadays the more often usage of concrete under extreme operating conditions requires invariably improvement of its properties such as: crack, frost, shock resistance and resistance before dynamic loads. It can be realised by means of reinforcement with fibers from steel, polymer, glass, basalt etc. As it is known, the reinforcement of concrete with fibers the Young’s modulus of which is higher than of matrix, contributes to increase of composite material strength. Among such fibers the basalt possesses high chemical and temperature resistance, as well as the necessary adhesion to concrete. In addition the basalt fiber has superior strength characteristics than concrete and steel. The tensile and compressive strength of reinforced cement stone with basalt fibers has been investigated. For determination of material strength at tensile bending the samples with dimensions 40×40×160 mm have been used, and for determination of compressive strength – 40×40×40 mm. The recipe of preparation of the mortar and the formation from them samples was as follows: water-cement ratio for all mortar equals 0,4 with plasticizer Berament TB-1 in amount 0,04% by weight of cement. The fiber with length 12 mm and with diameter of its filament 18 ± 2 microns has been used in studies. Basalt fiber volume content in mortar was changed from 0 to 2% with increments of 0,25%. The mortar was stirred was formed for 5 min. until a homogeneous suspension, after that during 3 min. it was densed on a vibration table to remove air bubbles and reduce the number of pores. The samples were tested after 28 days storage in the laboratory. With increase of fiber volume content in material the invariably enhance of its strength has been detected. It has been shown that for reinforcement concrete stone with fiber volume content 2% its compressive strength increases up in 2,22 times higher compared with the unreinforced material. At the same time the compressive strength with the addition of fiber decreases, which is an unexpected effect of reinforcing process cement matrix. We can suppose that this effect is associated with increase of porosity in process of mixture preparation from fine dispersed basalt fiber. For a final clarification the reason of this unexpected effect appropriate research will be performed in future

About short – and long – term strength of building constructions elements restored using injection technologies

Розроблено математичну модель деформування матеріалу в околі тонких тріщин, заповнених в’язкопружним матеріалом, та запропоновано методику визначення змінного з часом поля напружень і деформацій біля таких дефектів однорідної структури. Отримано розв’язки нових крайових задач, до яких зведені проблеми деформування навантажених довготривалими зусиллями розтягу або зсуву масивних тіл та пластин із тріщинами, що заповнені в’язкопружними матеріалами. Проаналізовано вплив повзучості та релаксації напружень на несучу здатність, пошкоджених тріщинами бетонних елементів конструкцій, які відновлені за ін’єкційними технологіями.The paper is devoted to the important scientific, technical and practical problems of predicting both service life time and strength of damaged structure elements over long-term operation, bearing capacity of which was restored using the injection technology. In practice there are engineering problems, for solving of which linear elastic media models are insufficient, serviceability estimation of prolonged use is often associated with the need to take account of the phenomenon of creep material. Therefore there is a need to develop models, which would take into account such complex material properties as reological properties. One of such examples is the technology of injecting strengthening of damaged structures. When restoring damaged cracked bearing capacity of long operation building structures the technology of filling defective areas with liquid material which hardens in some time, becomes very popular. A mathematical model of the material deformation in the vicinity of thin viscoelastic inclusions filled with cracks and determination of the stress-deformation field near the defects of its homogeneous structure has been developed. New solutions of the boundary value problems, which have been reduced to the problem of tensile or shear both loaded plates and massive bodies with cracks filled with the viscoelastic material have been obtained. In particular, a solution for the three-dimensional problem for an elastic space with filled elliptical cracks loaded at infinity by long-term uniform stresses has been found. The distribution of stress intensity factors along the contour of the elliptical crack in body or plate has been determined. The influence of reological properties of injecting materials on the time-varying stress-strain state of the body with a filled elliptical crack is investigated. The strength changing over time of these bodies has been obtained by using fracture mechanics criteria. The influence of creep and stress relaxation on the carrying capacity of damaged cracked concrete structural elements recovered by injection technology has been investigated

Design model for determination of the fiber-reinforced concrete strength

Розроблено модель міцності фібробетону за розтягу. На основі моделі встановлено формулу для оцінювання міцності фібробетону, яка враховує мікро тріщини і пори у структурі матеріалу і наявність армуючих волокон. Для підтвердження отриманої залежності проведено експериментальні дослідження з встановлення міцності цементного каменю, армованого фіброю різної природи і різного об’ємного вмісту. Теоретичний прогноз міцності фібробетону добре корелює з експериментальними даними.Structural material that is able to solve complex problems in the toughest construction industry is dispersed reinforced concrete (reinforced concrete). This is composite-based cement matrix reinforced with fibers of various nature (steel, glass, basalt, carbon, polymeric and others). Today three types of reinforcing fiber materials are mostly widely used: fibers in the form of short segments of thin steel wire, glass fibers and fibers based on polypropylene. The widespread use of reinforced concrete is caused by higher rates of strength, fracture toughness, impact strength, less micro cracking during hardening compared with classical concrete. The strength model for the tensile fiber-reinforced concrete was developed. Analytical dependence for strength assessing of material, which allows considering micro-cracks and pores in its structure and the presence of reinforcing fibers was obtained. For its verification experimental research has been carried out. In the research to prepare solutions the following materials were used: basalt fiber; Portland; plasticizer. On the basis of the prismatic component 40x0x160 mm size samples for tensile bending tests were made. Water-cement ratio was 0.4 with a plasticizer in an amount of 0.04% by weight of cement. The fiber (of 12 mm) length was used, which in unexploited state looks like bundles of filaments. The solution was stirred for 5 minutes until a homogeneous mixture was obtained, after which it was compacted on a vibration table to remove air bubbles and to reduce the number of pores. All series of samples for testing within 28 days were in the laboratory. According to the data obtained it follows that the composite tensile strength with 2% of fibre increases more than in 2 times compared with the base unreinforced material. Comparison of theoretical estimations of the composite strength with experimental data testifies high enough reliability of the predicted strength calculated for the scheme developed in the work