Award Date

12-1-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Committee Member

Samaan G. Ladkany

Second Committee Member

Nadar Ghafoori

Third Committee Member

Mohamed Kaseko

Fourth Committee Member

Ying Tian

Fifth Committee Member

Brendan O'Toole

Number of Pages

369

Abstract

The purpose of this study is to incorporate discrete, short, mechanically deformed, small diameter steel fibers into high strength concrete with f'c > 70 MPa (10 ksi) in an attempt to reduce and partially eliminate the need for steel rebar in concrete construction. By introducing steel fibers to high strength concrete mixture, the overall tensile, compressive and shear strength of the mixture can be improved immensely thus, replacing portions or major parts of the longitudinal, temperature and shrinkage reinforcements. The reduction or elimination of longitudinal and transverse reinforcements in the construction of structural or non-structural members can result in savings in manual labor time for the placement of longitudinal and transverse reinforcements and facilitating concrete pour without the need for vibration.

The research presents a two-phase study:

1. In the first phase, the fresh properties and behavior of high strength steel fiber reinforced flow-able concrete / self-consolidating concrete (HSSFRC) mixtures with different dosages of steel fibers, ranging from zero-to-4% by volume in 1% increments with variable high range water reducer (HRWR) are studied. The fresh properties of HSSFRC such as, flow-ability (spread diameter), pass-ability (J-Ring and U-Box test) and fill-ability (V-Funnel test) are presented for various steel by volume fractions. The effect of high range water reducing agent (HRWR) and viscosity modifying agent (VMA) on the fresh properties of HSSFRC are also studied. The research shows as well the effect of coarse-to-fine aggregate and water-to-cementitious ratios on the fresh and hardened properties of the HSSFRC mixtures.

In this phase, the mechanical properties and hardened behavior of high strength steel fiber reinforced concrete are also studied. The mechanical properties studied include: compressive strength, splitting tensile strength, modulus of elasticity for compression and beam modulus of rupture.

2. In the second phase, the unidirectional and bi-axial flexural properties, shear property, mode of failure and ductility of 0%, 1% and 2% high strength steel fiber reinforced concrete (HSSFRC) thin, < 32 mm (1.25 in), plate and shell structures are studied. The structures in phase two have the same concrete constituents, including HRWR, with the exception of steel fiber by volume fractions.

The structures studied include:

1. Square plates simply supported at all sides and subjected to a concentrated center load.

2. Square plates supported at two corners and subjected to opposite corner loads.

3. Long and short span rectangular plates under center line loads.

4. Circular plates supported at three discreet points and under a concentrated center load.

5. Circular cylindrical shells under concentrated center loads (pinching load).

6. Hyperbolic paraboloid shells simply supported at all sides and subjected to a uniformly distributed load.

The study in phase 1 shows that:

1. The addition of steel fibers to the concrete mixture results in the reduction of flow-ability, pass-ability, fill-ability and workability, which was mitigated through the adjustment of HRWR and VMA dosage.

2. Mixture with low coarse-to-fine aggregate ratio provided that other constituents of the mixture are kept the same, yielded more flow-able and workable mixtures.

3. A decrease in the water-to-cementitious materials ratio results in a loss of fresh mixture workability and increase in HRWR and at times VMA dosage in order to achieve SCC standards.

4. Substantial increase in the compression and tensile strength along with the modulus of elasticity of high strength steel fiber reinforced concrete.

The study in phase 2 shows that:

1. The ductility and capacity of plates and shells improved with the increase in steel fiber by volume fractions.

2. Flexural, shear and torsional capacity of plates and shells enhanced with the increase in steel fiber by volume fractions.

3. Effect of HRWR on the Poisson's ratio, modulus of elasticity, compressive and splitting tensile strength.

The research presents test results, comparisons and conclusion.

Keywords

Concrete – Mechanical properties; Fly ash; High steel by volume fraction; High strength concrete; Modulus of rupture; Rosette strain gauges; Silica fume; Thin plates and shells

Disciplines

Civil Engineering | Engineering | Mechanics of Materials | Structural Materials

Language

English


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