Self-compacting concrete (SCC) is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars. However, it is vital that SCC maintains its fresh state characteristics when its transportation phase is taken into consideration. Fiber reinforced in SCC affects the properties of fresh concrete negatively while it had a positive effect on its dynamic properties. In this study, the effect of steel fibers having different aspect ratios on the time dependent fresh properties and mechanical properties of self-compacting concrete mixtures was investigated. In addition to the control mixture without fiber, in the mixtures containing fiber, three different twin-hook steel fibers with aspect ratios of 54, 64 and 50 were used as 0.6% of total volume. In all of the SCC mixtures, the water/cement ratio, cement dosage and slump-flow value were kept constant. The time dependent rheological properties of the mixtures were investigated. The compressive, split-tensile and flexural strengths as well as fracture energy, the load deflection relation under flexural load and load-crack opening displacement, modulus of elasticity of SCC mixtures were also investigated. Besides, the water absorption capacity and depth of penetration of water under pressure of mixtures were measured. On the basis of the results, the fiber utilization and its aspect ratio had no significant effect on compressive strength and modulus of elasticity of the SCC mixtures. The split-tensile, flexural strengths and fracture energy of SCC mixtures increased by using fiber; the permeability properties of SCC mixture increased by fiber utilization.
In this study, the effect of silica fume and metakaolin on the strength, transport properties and ultrasonic pulse velocity of the mortar mixtures containing plain, binary and ternary cementitious systems were investigated comparatively. For this purpose, in addition to the control mixture containing no mineral admixture, three series of mixtures were produced by replacing silica fume and metakaolin with cement in different ratios. In the first and second series mixture, metakaolin and silica fume were used as 7.5wt% of the cement, respectively. In the third series, a mixture containing 15% of mineral admixture was prepared by replacing both silica fume and metakaolin with 7.5wt% of cement. In the all of mixture, the water/cement ratio, sand/binder ratio and flow values were kept constant. Water reducing admixture was used in different ratio for providing the desired flow values. The time-dependent flow value, compressive and flexural strengths, water absorption capacity and ultrasonic pulse velocity of the mixtures were determined. According to the test results, irrespective of utilization of mineral admixture, the time-dependent flow value, strength, permeability and ultrasonic pulse velocity of the mixtures were positively affected by using admixture. This effect was more pronounced by elapsing time. In the early ages, the metakaolin-bearing mixture with binary cementitious system showed better performance compare to the other mixtures. However, after 28 days, the mixture containing both metakaolin and silica fume with ternary cementitious system showed the most successful results.
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