Cengiz Özel

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.

Modeling of mechanical properties and bond relationship using data mining process

Reinforced concrete is a widely used construction material. Its properties depend on the bond between the reinforcing bar and concrete as much as the compressive strength or properties of the reinforcing bar because of component of construction expose to both flexural and bond together compressive loads. In this paper, the bond properties of concretes with different mix designs were investigated according to the results of compressive, flexural, bond, and flexural-bond tests. The data mining (DM) process was used to determine relationships among the test results and DM algorithms. Seventeen modeling techniques within WEKA were applied to the experimental data for the prediction of bond properties. The results show that the implemented models were good at predicting the bond properties. The best results were obtained from the RepTree algorithm for bond strength, the Multilayer Perceptron algorithm for flexural-bond strength, the MedSq algorithm for bond slippage, and the Pace Regression for flexural-bond deformation. Bond and flexural-bond can be easily predicted using the compressive strength, flexural strength and tensile stress of the rebar. Although a relationship is also existent between these and bond slippage and flexural-bond deformation, these relationships are weaker than the others. These results suggested that the DM algorithms can be used as an alternative approach to predict the bond strength using the results of compressive, flexural, bond, and flexural-bond tests as input parameters. The predictions of the bond slippage and flexural-bond deformation models poorly agreed with the experimental results. It can be obtained more successful results for these variables, when DM models with different inputs like the rebar-concrete interface stress together the measured parameters are used.

The relations between mechanical strengths and abrasive wear of concrete incorporating the hematite aggregate

Many concrete structures such as dams, canals, roads and floors are required to be abrasion resistant. Aggregates play an important role in the strength characteristics and abrasion resistance of concrete, and compressive strength has a decisive influence on abrasion. In this study, hematite was used as a replacement aggregate. However, very limited information on the properties of concrete containing hematite has been reported. Therefore, this study investigates the effects of different concentrations (10–50% replacement, by volume) of hematite on the mechanical properties of concrete. The water–cement ratio and cement content were kept constant as 0.42 and 400 kg/m3, respectively. It was observed that hematite will increase both compressive strength and wear resistance depending on the hematite content in the mixture. Concrete mixes with adequate workability were produced. Correlations between hematite content, mechanical properties and wear loss were made, and the equations representing the correlation between them were derived. The equations provide a high agreement with the experimental results.

PREDICTION OF ELASTIC MODULUS OF POLYPROPYLENE FIBER CONTAINING CONCRETE BY FUZZY LOGIC

In this study, the amount of polypropylene fiber was investigated that effect to physical (unit weight, air content) and mechanical (compressive strength and modulus of elasticity) properties of concrete. The different amounts of polypropylene fiber (0, 300, 600, 900, 1200 gr/m3) to prepared mixtures in three different cement dosage (350, 400 and 450 kg/m³) were added. According to experimental results, unit weight, compressive strength and modulus of elasticity decreases while the air content increases depend on the amount of fiber. Estimation model of the modulus of elasticity from the cement dosage, fiber content and air content is developed by using fuzzy logic. Also, It was investigated that relationships between experimental results with model results or analytical equations that proposed by the standards. As a result, proposed approaches by standards have been inadequate in determining modules of elasticity of the fiber containing concrete, the best results were obtained from fuzzy logic model (R2 = 0,988). It should be developed the new analytic equations for fiber containing concrete and fuzzy logic is used successfully to predict the properties of fiber concrete are usable.