Research on effect of the quantity and aspect ratio of steel fibers on compressive and flexural strength of SIFCON

SIFCON (Slurry Infiltrated Fiber Reinforced Concrete) is a composite which occur hardening of the matrix phase, consists of cement, water, mineral additives, fine sand, water reducing plasticizer, and reinforced with high volume fiber (5–20%). The main difference from the high strength concrete (HSC) is the ductile behaviour at failure. However, the brittleness increases with the strength increase in HSC, SIFCON has a ductile behaviour because of the high volume fiber content, low permeability, high durability. Despite fiber content is 2-3% in fiber reinforced concrete, fiber content may be ten times more in SIFCON and ductility is gained. This concrete is suggested to be used in military buildings against explosion, industrial grounds, airports, and bridge feet. In this study, in order to investigate the compressive and flexural strengths of SIFCON, the aspect ratio and fiber volume of steel fibers were chosen as variable and the effects of these parameters on compressive and flexural strengths were investigated. In the study, steel fibers with aspect ratio of 40, 55, 65, and 80 were used in 0, 4, 8 and 12% ratios. The water/binder ratio was kept constant at 0.35. Silica fume is used 10% and water-reducing plasticizer is used 1.5% of cement by weight. 7 and 28 days cured samples were subjected to compressive and flexural tests and the results were compared. As a result of the tests carried out, increases in both the compressive and flexural strengths of SIFCON specimens were determined with increasing fiber volume up to 8%. Strength reductions were observed at higher ratios. In cases where the fiber volume is too high, it has been seen that the strengths were decreased. The reason of strength reduction can be explained by the difficulty of passing ability of mortar between the fibers. The highest strengths were obtained from fibers with the aspect ratio of 80. Increase in the aspect ratio as well as increases in compressive and flexural strengths have been found

Effect of basalt, polypropylene and macro-synthetic fibres on workability and mechanical properties of self-compacting concrete

In this study, the effects of different fibre types on the workability and mechanical properties of self-compacting concrete were investigated. Fresh and hardened properties of self-compacting concrete, different fibre content 0.90, 1.35 and 1.80 kg/m3 were evaluated using basalt, polypropylene and macro synthetic fibres with different fibre lengths of 24, 19 and 40 mm, respectively. The properties of fresh concrete were evaluated in terms of slump flowing, viscosity and flowability. In addition, compressive, flexural and splitting tensile strength were obtained from hardened concrete properties. To characterize mechanical properties 90 specimens were experimentally tested. The results show that the use of fibre reduces the workability of self-compacting concrete. On the other hand, tensile and flexural strength of the self-compacting fibre reinforced concrete increased with increasing fibre content, but it was determined that the fibre addition had no significant effect on the compressive strength

Flow tilt angles near forest edges - Part 2: Lidar anemometry

A novel way of estimating near-surface mean flow tilt angles from ground based Doppler lidar measurements is presented. The results are compared with traditional mast based in-situ sonic anemometry. The tilt angle assessed with the lidar is based on 10 or 30 min mean values of the velocity field from a conically scanning lidar. In this mode of measurement, the lidar beam is rotated in a circle by a prism with a fixed angle to the vertical at varying focus distances. By fitting a trigonometric function to the scans, the mean vertical velocity can be estimated. Lidar measurements from (1) a fetch-limited beech forest site taken at 48–175 m a.g.l. (above ground level), (2) a reference site in flat agricultural terrain and (3) a second reference site in complex terrain are presented. <br><br> The method to derive flow tilt angles and mean vertical velocities from lidar has several advantages compared to sonic anemometry; there is no flow distortion caused by the instrument itself, there are no temperature effects and the instrument misalignment can be corrected for by assuming zero tilt angle at high altitudes. Contrary to mast-based instruments, the lidar measures the wind field with the exact same alignment error at a multitude of heights. <br><br> Disadvantages with estimating vertical velocities from a lidar compared to mast-based measurements are potentially slightly increased levels of statistical errors due to limited sampling time, because the sampling is disjunct, and a requirement for homogeneous flow. The estimated mean vertical velocity is biased if the flow over the scanned circle is not homogeneous. It is demonstrated that the error on the mean vertical velocity due to flow inhomogeneity can be approximated by a function of the angle of the lidar beam to the vertical and the vertical gradient of the mean vertical velocity, whereas the error due to flow inhomogeneity on the horizontal mean wind speed is independent of the lidar beam angle. For the presented measurements over forest, it is evaluated that the systematic error due to the inhomogeneity of the flow is less than 0.2°. <br><br> The results of the vertical conical scans were promising, and yielded positive flow angles for a sector where the forest is fetch-limited. However, more data and analysis are needed for a complete evaluation of the lidar technique

The influence of elevated temperatures on the mechanical properties of polypropylene fiber reinforced concrete

This paper describes the strength of Polypropylene Fiber Reinforced Concrete (PFRC) exposed to the elevated temperatures. In the study, control specimens without any fibers and the concrete specimens with the ratios of 0.30, 0.60, 0.90 and 1.20 kg/m³ polypropylene fibers both in woolen and bar shape fiber have been produced. The specimens have been kept in the laboratory conditions for 28 days. Shortly after the curing period was completed, every group was heated at 23, 150, 300, 450, 600 and 750°C for two hours then the compressive strengths of them were determined. The maximum compressive strength was obtained by the specimens including 0.30 kg/m³ woolen polypropylene. For this group, the compressive strength increase was 8% according to the control specimens. The compressive strengths of bar polypropylene fiber concrete were higher than the wool fibers under elevated temperatures. On the other hand, more compressive strength values are obtained from the control specimens than fiber groups at 600°C temperature. Melting the polypropylene fiber at 500°C formed some pore spaces in concrete and caused reduction of the compressive strength

FRESH CONCRETE PROPERTIES AND COMPRESSIVE STRENGTH OF SELF COMPACTING CONCRETES WITH SILICA FUME AND FLY ASH

Kendiliğinden yerleşen betonlar (KYB), geleneksel betona oranla işlenebilirlik, işçilik maliyetindeki azalmalar ve yüksek dayanım gibi önemli faydalar sağlayan beton teknolojisindeki gelişmelerdendir. KYB üretiminde yüksek oranda su azaltıcı süperakışkanlaştırıcı kimyasal katkılar, fazla miktarda toz malzeme ve/veya viskozite düzenleyici katkı maddesi kullanılmalıdır. Kendiliğinden yerleşme yeteneği; doldurma yeteneği, ayrışmaya karşı direnç ve geçiş yeteneği olmak üzere 3 parametre ile karakterize edilebilir. KYB üretiminde toz malzeme olarak genellikle kireçtaşı tozu, uçucu kül, granüle yüksek fırın cürufu ve silis dumanı kullanılmaktadır. Bu çalışmada mineral katkı maddesi olarak çimento yerine ağırlıkça % 5, % 10 ve % 15 oranlarında silis dumanı ve % 25, % 40 ve % 55 oranlarında uçucu kül kullanılarak KYB üretilmiş ve taze beton özellikleri ile sertleşmiş betonların 3, 7 ve 28 günlük basınç dayanımları belirlenmiştir. silis dumanı ilavesi basınç dayanımlarında artışa yol açarken uçucu kül katkılı betonlarda dayanım azalmaları tespit edilmiştir. En yüksek basınç dayanımı değeri 88 MPa değeri ile %15 silis dumanı kullanılarak üretilen betonlardan elde edilmiştir.Self Compacting Concrete, is one of the developments in concrete technology, which have important benefitsas workability, labor cost reductions and high-strength, compared to traditional concrete. In SCC production, high-range water reducing super plasticizer chemical additives, powder material and/or viscosity regulators additive must be used. Self-settlement capability may be characterized with 3 parameters; filling ability, resistance to decomposition and, passing ability between reinforcement bars. Limestone powder, fly ash, granulated blast furnace slag and silica fume is used as a powder material in SCC production. In this study SCC were produced with using silica fume instead of cement by weight, by the ratios of 5%, 10% and 15%, and fly ash with the ratios of 25%, 40% and 55%. Fresh concrete properties and 3, 7 and 28 days compressive strengths were determined. While SF increased compressive strength, addition of fly ash, on the contrary, decreased it. The highest compressive strength was observed from the concrete specimens with using 15% silica fume, with the value of 88 MPa.&nbsp