Browsing by Author "Alami, Mohammad Musa"

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Develepment of a new test method to evaluate dynamic stability of self-consolidating concrete
(Izmir Institute of Technology, 2014-07) Alami, Mohammad Musa; Erdem, Tahir Kemal
Self-consolidating concrete (SCC) is a new generation of concrete with high performance. It is able to flow under its own weight and fills the formwork without any external vibration. Stability is the most important plastic and crucial property for successful application of SCC and it refers to segregation of constituent in fresh state. Dynamic stability is the segregation resistance of SCC during transportation and placement. Evaluation of dynamic stability is one of the most investigated topics of SCC. Many different test methods have been proposed to evaluate the dynamic stability of SCC. No single and widely accepted method exists for the evaluation of the dynamic stability of SCC. In this thesis a new apparatus for testing the dynamic stability of SCC was developed. The effect of different mix design parameters such as water-to-cement ratio w/c, slump flow diameter, coarse aggregate-to-total aggregate ratio (CA/TA), and maximum size of aggregate (Dmax) were evaluated on the dynamic stability of SCC. Several fresh concrete tests were carried out on the SCC mixtures: slump flow, T500 time, Visual stability index (VSI), V-funnel, L-box, static sieve segregation (GTM), rheometer, and new proposed method (DSST). Several correlations were established between the test results. It was found that the new proposed test is a suitable method to evaluate the dynamic stability of SCC. Limits were proposed for a dynamically stable SCC.
Properties of hybrid fiber reinforced concrete for impact loading
(Izmir Institute of Technology, 2021-07) Alami, Mohammad Musa; Saatçi, Selçuk; Erdem, Tahir Kemal; Izmir Institute of Technology
Concrete is a brittle material and does not have significant energy absorption capacity before its fracture. Adding fibers to a concrete mix increases its ductility. Recently, there is significant development in the concrete technology to produce a concrete that can exhibit deflection hardening and show high energy absorption capacity. In this thesis, two kinds of cement based composites with high energy absorption capacity were studied: 1. Engineered Cementitious Composites (ECC). This material can exhibit deflection hardening under bending and it is produced only with synthetic fibers and fine aggregate, 2. Hybrid Fiber Reinforced Concrete (HyFRC). This material can exhibit deflection hardening under bending. It was produced with fine and coarse aggregates and hybrid fibers (both steel and synthetic fibers). The experimental program of this study consists of two main stages. The first stage is to design these composites and test their basic properties in fresh and hardened states, such as compressive strength, flexural behavior, freezing-thawing resistance, chloride ion permeability and sorptivity. In the second stage, dynamic tests (drop tests on small size specimens and pendulum impact tests on real size new generation road concrete barriers with a selected HyFRC mixture) were carried out to determine their energy absorption capacities. Based on the ECC results, fly ash/cement ratio of 1.2 and 20% perlite replacement of sand were selected for HyFRC mixtures. According to the mechanical behavior and durability test results of HyFRC, ST3,0.75_P0.25_D16 mixture (steel fiber type= ST3, steel fiber volume=0.75%, PVA volume=0.25%, Dmax=16mm) was found to have the best performance, and accordingly, this composite was selected for the real-size barrier pendulum test. The same mixture without fibers was also tested under pendulum test as control normal concrete since the present road barriers in the market do not employ fibers. As a result of this study, the HyFRC barrier was found to perform higher impact resistance.