Osman Gencel

Mechanical properties of self-compacting concrete reinforced with polypropylene fibres

Abstract The properties of hardened concrete can be significantly improved by fibres. However, the addition of fibres to fresh concrete results in a loss of workability. Self-compacting concrete (SCC) is an innovative concrete that is able to flow under its own weight, completely filling formwork and achieving full compaction without vibration. In the present study, the workability and mechanical properties of SCC with fly ash reinforced with monofilament polypropylene fibres were investigated. Two cement contents at 350 and 450 kg m−3 were studied as well with four fibre contents at 3, 6, 9 and 12 kg m−3. The water/cement ratio, fly ash and superplasticiser contents were kept constant at 0·40, 120 kg m−3 and 1% of cement content respectively. Slump flow, J ring, V funnel and air content tests were conducted for evaluating the fluidity, filling ability and segregation risk of the fresh concretes. Unit weight, compressive strength, splitting tensile strength, flexural strength, pulse velocity and elasticity modulus of concrete were determined. The materials used in this study exhibit no problems with mixing or workability when the fibre distribution is uniform. The polypropylene fibres enhance the strength of SCC significantly, without causing well known problems associated with steel fibres.

Workability and Mechanical Performance of Steel Fiber-Reinforced Self-Compacting Concrete with Fly Ash

Steel fibers change the properties of hardened concrete significantly. However, addition of fibers to fresh concrete results in a loss of workability. Self-compacting concrete (SCC) is an innovative concrete that is able to flow under its own weight, completely filling formwork and achieving full compaction without vibration. We have studied composites of SCC with steel fibers for further property enhancement. Water/cement ratio and cement, fly ash and superplasticizer contents were kept constant at 0.40, 400, 120 and 6 kg/m3 , respectively. The fiber amounts were 15, 30, 45 and 60 kg/m3. Slump flow, J-ring and V-funnel tests were conducted for evaluating the fluidity, filling ability and segregation risk of the fresh concretes. There were no problems with mixing or workability while the fiber distribution was uniform. Steel fibers can significantly enhance toughness of SCC and inhibit the initiation and growth of cracks.

Effect of high temperature on mechanical and physical properties of lightweight cement based refractory including expanded vermiculite

Abstract Four different composite mixtures with varying amounts of expanded vermiculite were exposed to high temperatures of 300, 600, 900 and 1100°C for 6 h. Physical and mechanical properties including unit weight, porosity, water absorption, residual compressive strength, residual splitting tensile strength and also ultrasonic pulse velocity were determined after air cooling. Microstructures were investigated by scanning electron microscopy. Lightweight concrete with vermiculite shows a good performance at elevated temperatures. Expanded vermiculite is a significant lightweight aggregate for cementitious materials which are used for fire resistance applications. Concrete with vermiculite can be used as cement based refractory.

Investigation of neutron shielding properties depending on number of boron atoms for colemanite, ulexite and tincal ores by experiments and FLUKA Monte Carlo simulations

(241)Am-Be source and three samples including different amounts of boron atoms per unit volume called colemanite, ulexite and tincal were used in total macroscopic cross section experiments. Also FLUKA Monte Carlo code was used to simulate total macroscopic cross sections, absorbed doses and deposited energies by low energy neutron interactions. Besides half value layers of samples were calculated and compared to paraffin. As a result, ascending concentration of boron atoms can enhance neutron shielding property of samples.

X-Ray, Gamma, and Neutron Radiation Tests on Epoxy-Ferrochromium Slag Composites by Experiments and Monte Carlo Simulations

Radiation shielding effects of ferrochromium slag loading hardened epoxy resin samples were investigated. Five different samples including different percentages of epoxy resin and ferrochromium slag were produced. X-ray, gamma ray, and neutron particle transmission experiments were performed for epoxy-ferrochromium slag composites. Also, FLUKA Monte Carlo simulations were made to obtain absorbed doses. As a result, radiation shielding performance increases with increasing ferrochromium slag additive in epoxy.

Effect of metallic aggregate and cement content on abrasion resistance behaviour of concrete

Abstract Many concrete structures are required to have sufficient abrasion resistance, such as dams, canals, roads and floors. The abrasion resistance of concrete may be defined as its ability to resist being worn away by rubbing. Compressive strength and aggregate type are also important factors affecting the abrasive behaviour of concrete. However, very little information on the properties of haematite containing concrete has been reported. The authors report on the abrasion resistance of concrete with four different cement contents (300, 350, 400 and 450 kg m−3) and with haematite as a metallic aggregate with replacement ratios of 15, 30, 45 and 60% under 5, 10 and 15 kg loads. The water/cement ratio was kept constant at 0·40 to evaluate the effects of haematite and cement content. Slump tests were conducted to evaluate the workability of fresh concretes. For hardened concrete samples, mechanical tests such as compressive strength, splitting tensile strength, unit weight and wear resistance were performed. Along with the physical and mechanical properties of concretes, haematite was studied as a mineral. Increasing both cement and haematite content has substantial effects on the strength of the concrete. Polarising microscopy views of the interfaces show that haematite aggregates exhibit greatly improved bond strength. Wear loss of concrete decreases with increasing concentration of haematite, while it increases with increasing cement content. An equation representing wear as a function of cement content, compressive strength and also applied load provides virtually perfect agreement with the experimental results.

Processed wastewater sludge for improvement of mechanical properties of concretes

Two problems are addressed simultaneously. One is the utilisation of sludge from the treatment of wastewater. The other is the modification of the mechanical properties of concrete. The sludge was subjected to two series of treatments. In one series, coagulants were used, including ferrous sulphate, aluminium sulphate or aluminium polyhydroxychloride. In the other series, an electrochemical treatment was applied with several starting values of pH. Then, concretes consisting of a cement matrix, silica sand, marble and one of the sludges were developed. Specimens without sludge were prepared for comparison. Curing times and aggregate concentrations were varied. The compressive strength, compressive strain at yield point, and static and dynamic elastic moduli were determined. Diagrams of the compressive strength and compressive strain at the yield point as a function of time passed through the minima as a function of time for concretes containing sludge; therefore, the presence of sludge has beneficial effects on the long term properties. Some morphological changes caused by the presence of sludge are seen in scanning electron microscopy. A way of utilising sludge is thus provided together with a way to improve the compressive strain at yield point of concrete.

Application of Taguchi Method to Study Abrasive Wear Behavior of Ceramic-Coated Specimens with Plasma Technique.

Different types of ceramic powders were coated on the surface of middle carbon steel using a plasma method. Coated surfaces were tested experimentally with regard to their abrasive wear resistance. To evaluate test data obtained, an experimental design method, which is based on the Taguchi method, was used. By using the Taguchi method, influence of test parameters, such as normal load, abrasive grit size, and material on wear resistance of coatings by calculating signal-to-noise (S/N) ratio and analysis of variance (ANOVA), could be estimated. From analysis of test results, it was determined that load factor has the most effect on wear of coating.

Durability properties of concrete reinforced with steel-polypropylene hybrid fibers

Abstract In this study, some mechanical and durability properties of concrete specimens, with a water/cement (w/c) ratio of 0.47 and having a reference slump of 40 mm, produced by addition of steel fibers (SF) and/or polypropylene fibers (PF), were investigated. The additions of SF were 20 kg/m3 and 40 kg/m3 and PF additions were 0.3 kg/m3 and 0.6 kg/m3. Workability and unit weight tests were made on fresh concretes. Compressive stress, elastic modulus, and flexural tensile tests were performed on hardened concretes. Also, load-deflection curves and toughness indices were obtained during a three-point flexure tensile test. Freeze-thaw, abrasion and drying shrinkage tests were also carried out to determine the effects of SF and/or PF on some durability properties of concretes. It was observed that fiber inclusion to concrete decreases the workability and that the mechanical properties of concrete can be improved by the addition of fibers. Using hybrid fibers in the concrete both increases and decreases some mechanical properties of concrete. In order to see a greater effect of both SF and PF on the properties of concrete, different hybrid fiber volume fractions for different matrix strengths may be examined, since fiber type and fiber volume fractions are important parameters to be taken into account in the mix design of concrete for the performance

Prediction of restrained shrinkage crack widths of slag mortar composites by Takagi and Sugeno ANFIS models

Abstract Shrinkage is an important parameter affecting crack development of mortars and concrete. With the occurrence of shrinkage cracks, the concrete starts to be exposed to the corrosion which significantly decreases the durability of concrete or mortars. In this study, the results of free shrinkage tests determining the length changes and ring test determination of the restrained drying shrinkage cracks are used for predicting the crack widths of granulated blast furnace slag fine aggregate mortars using adaptive-network-based fuzzy inference system (ANFIS). Subsequently, replacement ratios, drying time and free shrinkage length changes are used as inputs and crack width as output in order to predict the shrinkage cracking of these mortar types. The experimental test and the prediction results from the ANFIS model are compared with each other. It is clear that ANFIS can be employed directly in the prediction or discussion of the drying shrinkage cracks.