Toughness enhancement in steel fiber reinforced concrete through fiber hybridization

In recent years, an emerging technology termed, “High-Performance Fiber-Reinforced Concrete (HPFRC)” has become popular in the construction industry. The materials used in HPFRC depend on the desired characteristics and the availability of suitable local economic alternative materials. Concrete is a common building material, generally weak in tension, often ridden with cracks due to plastic and drying shrinkage. The introduction of short discrete fibers into the concrete can be used to counteract and prevent the propagation of cracks. Despite an increase in interest to use HPFRC in concrete structures, some doubts still remain regarding the effect of fibers on the properties of concrete. This paper presents the most comprehensive review to date on the mechanical, physical, and durability-related features of concrete. Specifically, this literature review aims to provide a comprehensive review of the mechanism of crack formation and propagation, compressive strength, modulus of elasticity, stress–strain behavior, tensile strength (TS), flexural strength, drying shrinkage, creep, electrical resistance, and chloride migration resistance of HPFRC. In general, the addition of fibers in high-performance concrete has been proven to improve the mechanical properties of concrete, particularly the TS, flexural strength, and ductility performance. Furthermore, incorporation of fibers in concrete results in reductions in the shrinkage and creep deformations of concrete. However, it has been shown that fibers may also have negative effects on some properties of concrete, such as the workability, which get reduced with the addition of steel fibers. The addition of fibers, particularly steel fibers, due to their conductivity leads to a significant reduction in the electrical resistivity of the concrete, and it also results in some reduction in the chloride penetration resistance of the concrete.

High-performance fiber-reinforced concrete: a review

In most cases, fiber reinforced concrete (FRC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overall properties of concrete, but may also result in performance synergy. The combining of fibers, often called hybridization, is investigated in this paper for a very high strength matrix of an average compressive strength of 85 MPa. Control, single, two-fiber and three-fiber hybrid composites were cast using different fiber types such as macro and micro-fibers of steel, polypropylene and carbon. Flexural toughness tests were performed and results were extensively analyzed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.

Hybrid fiber reinforced concrete (HyFRC): fiber synergy in high strength matrices

In most cases, fiber reinforced concrete (FRC) contains only one type of fiber The use of two or more types of fibers in a suitable combination has the potential to improve the mechanical properties of concrete, and result in performance synergy This combining of fibers, often called hybridization, is investigated in this paper under flexure and direct shear Along with a reference plain concrete mix, several single-fiber reinforced concrete mixes and two-fiber reinforced hybrid composite mixes were cast using diverse fiber combinations Two types of macro-steel fibers and a micro-cellulose fiber were examined Flexural and direct shear tests were performed and the results were analyzed to identify synergy, if any, associated with various fiber combinations The paper highlights the influence of load configuration on fiber synergy

Fiber synergy in Hybrid Fiber Reinforced Concrete (HyFRC) in flexure and direct shear

Rehabilitation of existing infrastructure has become a priority in recent years as an alternative to the daunting costs of rebuilding structures. Traditional repair methods have drawbacks, many of which can be overcome through the use of fibre reinforced polymer FRP laminates. However, the behaviour of FRP rehabilitated structures has yet to be conveniently and accurately modelled in many situations. For example, better understanding of their failure modes will allow for more precise designs that will balance safety andcost. To strengthen an RC beam or slab for flexure, FRP laminates are usually bonded externally on the structural element. A common failure mode encountered in initial tests was the laminate debonding from the surface. Here, the bond strength and modes of debonding between the FRP laminates and reinforced concrete members strengthened in flexure are reviewed. Current models for predicting the bond strength between the laminates and concrete are also scrutinized.

Bond Strength of FRP Laminates to Concrete: State-of-the-Art Review

Crack and strength properties of hybrid fiber reinforced concrete at early ages

A new phenomenon of decalcification of the cement concrete structure and dissolution of bitumen in bituminous pavement is described, caused by the surfactants included in the windshield washer fluid of automobiles. Decalcification occurs in cement concrete samples in the laboratory even at low concentrations of surfactant of 25ppm. Recently, foam with fine bubbles have been observed in the water on pavement just after rain worldwide. The decalcification reaction was identified as an ion exchange reaction between the calcium ions Ca2+ in the concrete and Na+ in the surfactants using the electron spectroscopy for chemical analysis (ESCA) method. Bitumen was also found in the decalcified cement concrete, from which the Ca component had dissolved out gradually with time.

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Decalcification of Cement Concrete Structures and Dissolution of Bitumen by Windshield Washer Fluid

Bond behavior and strength between fiber sheets and concrete

This research evaluated, from the ecological and economical points of view, the potential use of off-specification fly ash plus non-standard clinker ash (bottom ash or coal ash) in Controlled Low Strength Materials (CLSM) The effect of mixture proportions on the short-term as well as long-term compressive strength of CLSM is mainly investigated A wide range of fly ash/clinker ash ratio was evaluated in order to provide a cost effective mixture design for various material costs Two different sources of fly ash including off specification fly ash and three different sources of clinker ash were used with three levels of mixture combinations A total of 20 mixtures was tested for the flowability, bleeding and short-term and long-term compressive strengths (Strength developments up to 91 days were reported in this study) Test results showed that there is an optimum combination of fly ash to clinker ash ratio on the physical properties of CLSM Compressive strength improved with increasing the rate of replacement of clinker ash up to 50% in the case It is found that there was no disadvantage of using off-specification fly ash and non-standard clinker ash in the physical properties of CLSM CLSM with off-specification fly ash plus non-standard clinker ash showed excellent performance on the physical properties indicating the ecological and economical applicability to CLSM

Optimization of clsm mix proportion with combination of clinker ash and fly ash

It is a worldwide problem to build safer reinforced concrete (under-mentioned RC) structures on reflection of the great Hanshin earthquake disaster in 1995, Japan. The researches on the durability and the earthquake proof have advanced and the various countermeasures for these have been proposed. This paper deals with the specification of deterioration zones and its reliance, by using an external impact-acoustic detector, newly developed, which enables us to examine nondestructively the corrosive state of the inside of a concrete structure, and furthermore the verification with the natural potential method. The main experimental results concerning the building used in common are as follows:(1) The macroscopical corrosive degree of the RC structure can be evaluated by measuring the natural potential by means of the CuCuSO4 half cell and the effectiveness of the corrosion map. (2) “The external impact-acoustic method” can specify precisely the corrosive parts of reinforcement without the least damage on the RC structure, although the judgment of the corrosive grade is difficult; so, this disadvantage must be covered by using the natural potential method at the same time. (3)The relationship between the natural potential method and the external impact-acoustic one is quantitatively analyzed concerning an existing building.

Noboru Saeki

Papers

Crack and strength properties of hybrid fiber reinforced concrete at early ages

Decalcification of Cement Concrete Structures and Dissolution of Bitumen by Windshield Washer Fluid

Bond behavior and strength between fiber sheets and concrete

Optimization of clsm mix proportion with combination of clinker ash and fly ash

Evaluation of deterioration and specification of defect of RC structure by natural potential and external impact-acoustic methods