Farhad Aslani

Bond Behavior of Reinforcement in Conventional and Self-Compacting Concrete

Self-compacting concrete (SCC) can be placed under its own weight without compaction. In addition, it is cohesive enough to be handled without segregation and bleeding. Modification in the mix design of SCC can have a significant influence on the materials mechanical properties. Therefore, it is important to investigate whether all of the assumptions about conventional concrete (CC) design structures also valid for SCC construction. Bond behavior between concrete and reinforcement is a primary factor in the design of reinforced concrete structures. This study presents a bond strength model based on the experimental results from eight recent investigations of SCC and CC. In addition, the proposed model, code provisions, and empirical equations and experimental results from recent studies on the bond strength of SCC and CC are compared. The comparison is based on the measured bond between reinforcing steel and concrete utilizing the pullout test on the embedded bars at various heights in the mock-up structural elements to assess the top-bar effect on single bars in small prismatic specimens by conducting beam tests. The investigated varying parameters on bond strength are the: steel bar diameter, concrete compressive strength, concrete type, curing age of the concrete, and height of the embedded bar along the formwork.

Mechanical Properties of Waste Tire Rubber Concrete

AbstractThe consumption of waste tire rubber in concrete has gained more attention from the point of view of enhanced engineering properties of the product, and also sustainability. Numerous attempts have been stated on the use of waste tire rubbers for the replacement of fine and coarse aggregates in concrete but there is vital need to comprehensively investigate the effect of them on the mechanical properties of rubberized concrete (RC). The aim of this paper is to explore the effect of rubber types and rubber content on mechanical properties of concrete. The compressive strength, tensile strength, flexural strength, modulus of elasticity, strain at maximum strength, and compressive stress–strain curves of RC are studied. Extensive databases used for evaluating the mechanical properties of RC include the measured compressive strength of 298 mixtures, measured tensile strength of 90 mixtures, measured flexural strength of 93 mixtures, measured modulus of elasticity of 156 mixtures, and compressive stress...

Relationship between Deflection and Crack Mouth Opening Displacement of Self-Compacting Concrete Beams with and without Fibers

There are only a few research results for predicting the relationship between deflection and the crack mouth opening displacement (CMOD) of self-compacting concrete (SCC) beams with and without fibers. A series of bending beam tests on SCC, with different fiber types have been carried out. For this purpose, four SCC mixes—plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC—are considered in the test program. Based on the experimental results, a model for predicting the relation between the deflection and CMOD of SCC has been established per each mix. These models rely on the load–deflection relation and the load–CMOD relation of bending beam. A well agreement has been found between the suggested model and the test results. The results of this study indicate that the load–deflection diagram is very similar to that of the load–CMOD diagram, and there is a linear relation between the mid-span deflection and CMOD of SCC.

Flexural toughness characteristics of self-compacting concrete incorporating steel and polypropylene fibres

Fibre-reinforced self-compacting concrete (FRSCC) is a relatively new composite material which congregates the benefits of the SCC technology with the profits derived from the fibre addition to a brittle cementitious matrix. Fibres improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, and fracture toughness. Although the available research regarding the influence of fibres on the properties of FRSCC is limited, this paper investigates the fl exural toughness characteristics of SCC incorporating steel and polypropylene fibres. An extensive experimental program is carried out to monitor and record the flexural strength of SCC and FRSCC prism specimens under four point static flexural loading. For this purpose, four different SCC mixes including plain SCC, steel, polypropylene, and hybrid FRSCC mixes are considered in the test program. The flexural strength was tested after 3, 7, 14, 28, 56, and 91 days. The fl exural toughness parameters were obtained using procedure laid down in ASTM C 1018, JSCE, Banthia and Trottier and ACI 544 methods.

Cyclic constitutive model for high-strength concrete confined by ultra-high-strength and normal-strength transverse reinforcements

Abstract In this paper, a cyclic constitutive model is developed for high-strength concrete (HSC) confined by ultra-high-strength and normal-strength transverse reinforcements (UHSTR and NSTR), with the intention of providing efficient modeling for the member and structural behaviour of HSC in seismic regions. The model for HSC subjected to monotonic and cyclic loading, comprises four components; an envelope curve (for monotonic and cyclic loading), an unloading curve, a reloading curve, and a tensile unloading curve. It explicitly accounts for the effects of concrete compressive strength, Volumetric ratio of transverse reinforcement, yield strength of ties, tie spacing, and tie pattern. Comparisons with test results showed that the proposed model provides a good fit to a wide range of experimental results.

Thermal Performance Modeling of Geopolymer Concrete

AbstractGeopolymers are used for several applications due to their sustainability, low density, low cost, excellent thermal properties, and fire resistance. Geopolymer concrete (GC) may possess superior fire resistance compared to conventional concretes with ordinary portland cement (OPC). The proper understanding of the effects of elevated temperatures on the properties of GC is essential. In the research reported in this paper, relationships are proven for normal and high-strength GCs at elevated temperatures to establish efficient modeling and specify the fire-performance criteria for concrete structures. They are developed for unconfined GC specimens that consist of compressive strength, modulus of elasticity, flexural strength, thermal strain, prestressed thermal strain, and the compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results and available OPC relationships. These results are used to establish ...

Bond characteristics of steel fiber and deformed reinforcing steel bar embedded in steel fiber reinforced self-compacting concrete (SFRSCC)

Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of the self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fiber and SCC firstly. Based on the available experimental results, the current analytical steel fiber pullout model (Dubey 1999) is modified by considering the different SCC properties and different fiber types (smooth, hooked) and inclination. In order to take into account the effect of fiber inclination in the pullout model, apparent shear strengths (τ(app)) and slip coefficient (β) are incorporated to express the variation of pullout peak load and the augmentation of peak slip as the inclined angle increases. These variables are expressed as functions of the inclined angle (ϕ). Furthurmore, steel-concrete composite floors, reinforced concrete floors supported by columns or walls and floors on an elastic foundations belong to the category of structural elements in which the conventional steel reinforcement can be partially replaced by the use of steel fibers. When discussing deformation capacity of structural elements or civil engineering structures manufactured using SFRSCC, one must be able to describe thoroughly both the behavior of the concrete matrix reinforced with steel fibers and the interaction between this composite matrix and discrete steel reinforcement of the conventional type. However, even though the knowledge on bond behavior is essential for evaluating the overall behavior of structural components containing reinforcement and steel fibers, information is hardly available in this area. In this study, bond characteristics of deformed reinforcing steel bars embedded in SFRSCC is investigated secondly.