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Electrospun nanofibers are very popular in polymer nanocomposites because they have a high aspect ratio, a large surface area, and good mechanical properties, which gives them a broad range of uses. The application of nonwoven structures of electrospun nanofiber mats has historically been limited to enhancing the interlaminar responses of fiber-reinforced composites. However, the potential of oriented nanofibers to improve the characteristics of bulk matrices cannot be overstated. In this research, a multilayered laminate composite was created by introducing polyamide (PA6)-oriented nanofibers into an epoxy matrix in order to examine the effect of the nanofibers on the tensile and thermal characteristics of the nanocomposite. The specimens’ fracture surfaces were examined using scanning electron microscopy (SEM). Using differential scanning calorimetry (DSC) analysis, the thermal characteristics of the nanofiber-layered composites were investigated. The results demonstrated a 10.58% peak in the nanocomposites’ elastic modulus, which was compared to the numerical simulation and the analytical model. This work proposes a technique for the development of lightweight high-performance nanocomposites.

The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, at the same time increasing reliability and durability. Commonly accepted technology is exploiting randomly distributed in the concrete volume fibers with random each fiber orientation. In structural members subjected to bending, major loads are bearing fibers located close to outer member surfaces. The majority of fibers are slightly loaded. The aim of the present research is to create an SFRC construction with non-homogeneously distributed fibers. We prepared layered SFRC prismatic specimens. Each layer had different amount of short fibers. Specimens were tested by four point bending till the rupture. Material fracture process was modelled based on the single fiber pull-out test results. Modelling results were compared with the experimental curves for beams. Predictions generated by the model were validated by 4PBT of 100 × 100 × 400 mm prisms. Investigation had shown higher load-bearing capacity of layered concrete plates comparing with plate having homogeneously distributed the same amount of fibers. This mechanism is strongly dependent on fiber concentration. A high amount of fibers is leading to new failure mechanisms—pull-out of FRC blocks and decrease of load-bearing capacity. Fracture surface analysis was realized for broken prisms with the goal to analyze fracture process and to improve accuracy of the elaborated model. The general conclusion with regard to modelling results is that the agreement with experimental data is good, numeric modelling results successfully align with the experimental data. Modelling has indicated the existence of additional failure processes besides simple fiber pull-out, which could be expected when fiber concentration exceeds the critical value.

Traditional fiberconcrete structures have fibres in the mix oriented in all spatial directions, distributed in the struc­tural element volume homogenously, what not easy to obtain in practice. In many situations, structurally more effective is the insertion of fibres into the concrete structural element body by forming layers, with a predetermined fibre concentration and orientation in every layer. In the present investigation, layered fibre concrete is under investigation. Short steel fibres were at­tached to flexible warps with the necessary fibres concentration and orientation. Warps were placed into the prismatic mould separating them by concrete layers without fibres. Prisms were matured and tested under four-point bending. The bending-affected mechanical behaviour of cracked fibre concrete was simulated numerically by using a developed struc­tural model. Comparing the simulation results with experimental data, material micromechanical fracture mechanisms were analysed and evaluated.

In this research fiber reinforced concrete prisms with layers of non-homogeneous distribution of fibers inside them were elaborated. Fiber reinforced concrete is important material for load bearing structural elements. Traditionally fibers are homogeneously dispersed in a concrete. At the same time in many situations fiber reinforced concrete with homogeneously dispersed fibers is not optimal (majority of added fibers are not participating in load bearing process). It is possible to create constructions with non-homogeneous distribution of fibers in them in different ways. Present research is devoted to one of them. In the present research three different types of layered prisms with the same amount of fibers in them were experimentally produced (of this research prisms of non-homogeneous fiber reinforced concrete with dimensions 100×100×400 mm were designed. and prisms with homogeneously dispersed fibers were produced for reference as well). Prisms were tested under four point bending conditions till crack opening in each prism reached 6 mm. During the testing vertical deflection at the center of a prism and crack opening were fixed by the linear displacements transducers in real time.

Operative determination of consistence of self-compacting concrete mixes at plant or in construction conditions is an important problem in building practice. The Abram's cone, the Vebe's device, the U-box siphon, L-box or funnel tests are used in solving this problem. However, these field methods are targeted at determination of some indirect parameters of such very complicated paste-like material like concrete mix. They are not physical characteristics suitable for the rheological calculations of the coherence between the stress and strains, flow characteristics and the reaction of the concrete mix in different technological processes. A conical plastometer having higher precision and less sensitive to the inaccuracy of the tests in construction condition has been elaborated at the Concrete Mechanics Laboratory of RTU. In addition, a new method was elaborated for the calculation of plasticity limit τ0 taking into account the buoyancy force of the liquid or non-liquid concrete mix. In the present investigation rheological test of the concrete mix by use the plastometer and the method mentioned earlier was conducted for different self-compacting and not self-compacting concrete mixes.

As it has been found out, fiberconcrete has many positive attributes, which make that material a target of the numerous investigations. Traditionally fibers are homogeneously dispersed in the concrete volume. At the same time, in many situations fiber reinforced concrete with homogeneously dispersed fibers is not optimal (the majority of added fibers do not participate in the load bearing process). In the present investigation it has been demonstrated that the use of homogeneous fiberconcrete in eccentrically loaded and subjected to bending structures is not rational from mechanical and economical point of view. Fiber reinforced concrete prisms with homogeneous and layered fiber distribution inside them were elaborated. Prisms were tested under four point bending till macro-crack opening of 4mm and more was reached. Load bearing capacities at different load bearing stages of differently made prisms were compared.

Reinforcing cement-based composites with continuous fibers is one of the most efficient ways to obtain high performance materials. This paper studies the application of layers of knitted textiles with relatively simple fabric architecture used to strengthen fiberconcrete beams. The objective of this study was to evaluate glass knitted fabric as reinforcement for fiberconcrete. For this purpose fiberconcrete beams with textile reinforcement in the form of three plies of glass weft knitted fabric (jersey) were produced. Four point bending test was used to experimentally investigate the influence of textile plies on composite flexural strength. The obtained results were compared with the material without textile reinforcement. The fiberconcrete reinforced by textile layers showed better flexural performance compared to non-reinforced fiberconcrete samples.

This work had three stages. In the first stage was examined pull-out process for steel fiber was embedded into a concrete by one end and was pulled out of concrete under the angle to pulling out force direction. Angle was varied. On the obtained forcedisplacement diagrams were observed jumps. For such mechanical behavior explanation, fiber channel in concrete surface microscopical experimental investigation, using microscope KEYENCE VHX2000, was performed. At the second stage were obtained diagrams for load- crack opening displacement for breaking homogeneously reinforced and layered fiberconcrete prisms (with dimensions 10x10x40cm) subjected to 4-point bending. After testing was analyzed main crack. At the third stage elaborated prediction model for the fiberconcrete beam, failure under bending, using the following data: a) diagrams for fibers pulling out at different angles; b) experimental data about steel-straight fibers locations in the main crack. Experimental and theoretical (modeling) data were compared., {"references":["Cabrera G.J. (1996) Deterioration of Concrete due to Reinforcement\nSteel Corrosion. Cement and Concrete Composites, Vol.18, pp.47-59.","Kooiman A. (2000) Modeling Steel Fiber Reinforced Concrete for\nStructural Design. Ph.D. thesis. Delft University of Technology, CN\nDelft, Netherland.","Krasnikovs A., Kononova O., Khabbaz A., Machanovsky E.,\nMachanovsky A.. \"Post – Cracking Behavior of High Strength (Nano\nLevel Designed) Fiber Concrete Prediction and Validation\".\nNanotechnology in Construction 4th International Symposium\",\nAgiosNikolaos, Crete, Greece, May 20-22, 2012, pp.1-6","Krasnikovs, A, Kononova O., Eiduks M., Kalinka J., Kharkova G.,\nGalushchak A., Machanovsky A. \"Fiber orientation in viscous fluid flow\nwith and without vibration\". Journal of Vibroengineering. Volume12,\nIssue 4, ISSN 1392-8716,Lithuania, p. 523-532, 2010.g.","Naaman, A.E., Shah, S.P. Pullout mechanism in steel fiber reinforced\nconcrete, ASCE J Struct Div. – 102 (1976), pp.1537-1548.","Papenfuss, C., V´an, P., and Muschik, W. Mesoscopic theory of\nmicrocracks. Arch. Mech., 2003, 55(5–6), pp. 481–499.","Pupurs, A., Pakrasti\tš, L., Kras\tikovs, A. Stress-State Analysis ofFibre\nReinforced Concrete (Frc). Construction Science.Vol.7, 2006, pp.160-\n171.","Pupurs A., Varna J. Energy release rate based fiber/matrix debond\ngrowth infatigue. Part I: Self-similar crack growth, Mechanics of\nAdvanced Materials and Structures, In Press (2010).","Stahli P., Custer R., van Mier J.G.M. (2008) On Flow Properties, Fibre\nDistribution, Fibre Orientation and Flexural Behaviour of FRC.\nMaterials and structures, Vol.41., pp. 189 – 196.\n[10] VictorC.Li&Stang H., \"Interface Property Characterization and\nStrengthening Mechanisms in Fiber Reinforced Cement Based\nComposites\", Advanced Cement Based Materials, 6, pp.1-20, 1997.\n[11] Stroeven, P., 'The analysis of fibre distributions in fibre reinforced\nmaterials', J. Microscopy 111 1977 pp. 283-295.\n[12] http://www.lrpv.gov.lv/sites/default/files/media/vestnesis/20101220.pdf\n[13] http://www.keyence.co.uk/products/microscope/microscope /vhx2000/\nvhx2000_ specifications_1.php"]}

Fiber reinforced concrete is important material for load bearing structural elements. Usually fibers are homogeneously distributed in a concrete body having arbitrary spatial orientations. At the same time, in many situations, fiber concrete with oriented fibers is more optimal. Is obvious, that is possible to create constructions with oriented short fibers in them, in different ways. Present research is devoted to one of such approaches- fiber reinforced concrete prisms having dimensions 100mm ×100mm ×400mmwith layers of non-homogeneously distributed fibers inside them were fabricated. Simultaneously prisms with homogeneously dispersed fibers were produced for reference as well. Prisms were tested under four point bending conditions. During the tests vertical deflection at the center of every prism and crack opening were measured (using linear displacements transducers in real timescale). Prediction results were discussed., {"references":["N. Toropovs, D. Bajare, G. Shakhmenko, A. Korjakins, and J. Justs, \"Effect of Thermal Treatment on Properties of High Strength Concrete,\" in 4th International Conference CIVIL ENGINEERING`13 Proceedings, 2013, pp. 129–133.","J. Justs, G. Shakhmenko, D. Bajare, and N. Toropovs, \"Comparison of pozzolanic additives for normal and high strength concrete,\" in Proceedings of the 8th …, 2011, vol. I, pp. 79–84.","G. Shakhmenko, D. Bajare, I. Juhnevica, N. Toropovs, J. Justs, and A. Gabrene, \"Properties and Composition of Concrete Containing Diverse Pozzolanic Admixtures,\" in 4th International Conference CIVIL ENGINEERING`13 Proceedings Part I, 2013, pp. 122–128.","A. Krasnikovs, O. Kononova, A. Khabbaz, E. Machanovsky, and A. Machanovsky, \"Post-Cracking Behaviour of High Strength (Nano Level Designed) Fiber Concrete Prediction and Validation,\" in CD-Proceedings of 4th International Symposium on Nanotechnology in Construction, 2012, p. 6.","B. Schnütgen and L. Vandewalle, Eds., \"Test and Design methods for Steel fibre reinforced concrete – Background and Experiences. Preface,\" in Preface. Rilem Proceedings PRO 31, RILEM TC 162-TDF Workshop, 2003, p. 209.","M. Di Prisco, R. Felicetti, and G. A. Plizzari, Eds., \"PRO 39: 6th International RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004 (Volume 1),\" in PRO 39: 6th International RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004 (Volume 1), 2004, p. 753.","G. Campione and L. La Mendola, \"Behavior in compression of lightweight fiber reinforced concrete confined with transverse steel reinforcement,\" Cem. Concr. Compos., vol. 26, no. 6, pp. 645–656, Aug. 2004.","M. A. Mansur, M. S. Chin, and T. H. Wee, \"Stress-Strain Relationship of High-Strength Fiber Concrete in Compression,\" J. Mater. Civ. Eng., vol. 11, no. 1, pp. 21–29, Feb. 1999.","F. Bencardino, L. Rizzuti, G. Spadea, and R. N. 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One of the main constructive materials in the building sphere is a precast concrete and fiber concrete. It is well influenced by scientific research basis, development and implementation of progressive technologies. The fiber concrete it is an ideal material with practically unlimited number of shapes. A nomenclature of concrete articles increases, it is working on different shape formation and processing. While preparation for this document started with the concept fabrication, it is necessary to understand the methods of construction variable geometry formwork of concrete thin-shell surfaces, both past and present as a point of departure. An understanding of this background helps provide an essential foundation for the exploration of new potential advances in the field of thin-shell construction. Obviously that is the reason for fiber concrete to be the most widespread constructive building material all over the world. In the article are considered shell development technology features and is evaluated technical and economical effectiveness of concrete shells with thin walls. Now variable geometry systems from flexible materials are developing and improving, there is a great potential followed by modern events in concrete technology. The results of laboratory experiments have proved that the technology can be used for fibro concrete shell production and construction.