Influence of Crimped Steel Fibre on Properties of Concrete ...

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Abstract

This research was inspired by the growing global shortage of natural aggregates. Different types of waste ceramics (apart from recycled concrete) are the most popular materials for the production of waste aggregates as possible substitutes for natural ones. The aim of this research was to analyse the efficiency of different aggregate mixes composed of waste and natural materials focusing on two waste ceramic aggregates, which were prepared concrete mixes based on specifically composed aggregates (blend of natural aggregate, porous and iron oxide-rich (red) waste ceramic aggregate, and dense, kaolin-based (white) waste ceramic aggregate). All aggregates were thoroughly tested before utilisation for concrete mix creation. Altogether, four blends of aggregates were prepared in order to prepare concrete mixes using a simplex experiment design. The mixes were then modified by adding various amounts of crimped steel fibre. Such properties of hardened steel fibre-reinforced concrete (SFRC) such as density, compressive strength, shear strength, ultrasound propagation velocity, dynamic modulus of elasticity, and limit of proportionality during flexural testing were of special interest. Tests were conducted according to European and Japanese standards. The achieved fibre-reinforced concretes were characterised by satisfactory strength characteristics, thereby enabling the substitution of traditional reinforcement. Strength classes according to the fib Model Code 2010 were assigned.

Keywords:

aggregate, white ceramic, red ceramic, waste, fibre, SFRC

1. Introduction

A growing research effort exists globally to successfully harness different ceramic wastes in the construction industry [1,2,3], resulting in some successful applications of different types of waste ceramics as partial full substitutes of fine and coarse natural aggregates [4,5,6]. The type of waste ceramic most often considered for harnessing as a waste aggregate is red (porous, iron oxide-rich) ceramic [4,7], with multiple types of nonstructural concrete elements characterised by less demanding strength characteristics being cast using this kind of waste aggregate [8]. In order to utilise waste ceramic aggregates for the production of structural concrete, a new approach to composition is needed. Different waste ceramic aggregates could be blended together (e.g., red waste ceramic aggregate and white (dense, kaolin-based) waste ceramic aggregate) to achieve a new level of quality in sustainable concrete production, thereby enabling the shaping of aggregate properties to utilise their advantages and harness synergy. Red ceramic is characterised by limited compressive strength due to its porosity (usually between 10 and 15 MPa), but has the advantage of using an internal curing process [7]. White ceramic is characterised by “no porosity” and a much higher compressive strength red ceramic. This research was conducted to prove the proposed novel concept of using waste ceramic aggregates, in which red ceramic obtained from brick production waste and white ceramic obtained from local pottery factory production waste were used as waste aggregates. Both ceramics were processed using the same machinery and grinding procedure to achieve waste aggregates. As a reference, the properties of natural post-glacial aggregates commonly available in countries located along the southern shoreline of the Baltic Sea [9] were chosen. Utilisation of a mixture design was enabled using three aggregates, where the sum of the volume of all three ingredients was always equal to 100%. The mixture design allowed the visualisation of results in the form of ternary contour plots, which are commonly used in technology of binders [10] and concrete [11].

The research programme was divided into two stages. The first stage covered the testing of the geometrical and mechanical properties of the waste and natural aggregates. The second stage covered property testing of concretes made on the basis of the waste and natural aggregates that were tested during the first stage. Analysis of the possible replacement of natural aggregates by waste ceramic aggregates was subsequently conducted. Specific mixtures of both waste ceramic and natural aggregates were proposed for concrete production. The obtained four mixes were subsequently modified by the addition of steel fibres, which were added in volumes ranging from 0.5% to 1.5% (Vf). Altogether, 16 mixes of concrete were cast in order to test the properties of the concretes in a hardened state.

3. Experimental Design

An ordinary integral simplex design (also known as a mixture design) [21] was utilised in this research. The three types of aggregate were named as follows: X—red ceramic waste; Y—natural aggregate; Z—white ceramic waste. Due to the different specific gravity values of red ceramic waste, white ceramic waste, and natural aggregate, the materials were dosed by volume. The specific property of the mixture design was that the sum of the volume of all three ingredients was always equal to 100%. In this case, the three aggregates played the roles of the ingredients. The utilised design is described in detail in .

Table 3

Mix No.Aggregate (%)Natural AggregateWhite Ceramic WasteRed Ceramic WasteI10000II03367III67330IV343333Open in a separate window

The object of the experiment was considered to be a complex composite material. The internal structure of the material was unavailable (for unknown reasons) to observers, with only the “input” and “output” parameters known to observers [22,23]. All achieved experimental results were statistically processed. The Smirnov–Grubbs criterion was used to assess gross error of the values. The sequence of specific test realisations was decided using a digital random number generator to guarantee objectivity. All calculations associated with the execution of the research and graphic interpretation of the mathematical model were carried out using the Statistica 12 software suite. Contour plots were created using a polynomial fit with fitted functions characterised by a correlation coefficient of at least 0.80. This type of experimental design was successfully used numerous times in concrete technology, including concretes based on waste aggregates and steel fibre-reinforced concretes [21]. The number, shape, and size of specimens utilised for each test are presented in .

Table 4

Type of TestSpecimen Shape (cm)Number of SpecimensStandardIn One TestTotalDensityCube 15 × 15 × 15
Beam 70 × 15 × 153
396EN 12390-7:2011 *Compression strengthCube 15 × 15 × 15348EN 12390-3:2011 *Shear strengthBeam 70 × 15 × 15348JCI-SF6:1984 **Ultrasound propagation velocityBeam 70 × 15 × 15348EN 12504-4:2005 *Dynamic modulus of elasticity ***Beam 70 × 15 × 15348EN 12504-4:2005 *Flexural strength: LOP
(limit of proportionality)Beam 70 × 15 × 15348EN 14651:2007 *Open in a separate window

All specimens were tested after 28 days of curing (first day in a plastic mould covered by a polyethylene sheet, then 27 days in a water tank) in a temperature of 20 °C ± 0.5 °C. After curing, specimens were measured, weighed, and dried to avoid problems during the ultrasound velocity test [25]. The calculated density was a general quality test of the prepared specimens, with the value of density also useful for the ultrasound propagation velocity test and for computing the dynamic modulus of elasticity value. The shear strength test was performed on half of the beams that remained after the flexural test. Concrete mixes were modified by adding steel fibres to proportions of 0.5%, 1%, and 1.5%. The achieved results were subsequently compared with results obtained by other researchers working on steel fibre-reinforced concrete. Altogether, 16 concrete mixes were cast in order to test the properties of steel fibre-reinforced concrete (SFRC) in the hardened state.

5. Discussion

Four residual strengths (fR1, fR2, fR3, fR4) associated with particular CMOD values (0.5, 1.5, 2.5, and 3.5 mm) are not feasible for the direct design of an SFRC mix. There is general agreement among the global SFRC research community that the first residual strength fR1 is important in terms of service conditions, whereas the third residual strength fR3 is recognised as a key factor for the assessment of ultimate conditions. The “fib Bulletin 55, Model Code 2010” proposed the utilisation of the first and third residual strengths to calculate both the serviceability limit state (SLS) and the ultimate limit state (USL). Basically, the ratio fR3/fR1 was defined to describe the relationship between the behaviour of SFRC at ULS and SLS [32,33].

The proposed fib strength classification of SFRC consisted of two elements, i.e., strength interval (namely fR1) and post-cracking softening or hardening behaviour, which was described by a letter symbol from a to d directly referring to the fR3/fR1 ratio. Letter a represents the strongest softening and letter d represents the strongest hardening [34].

When the fibre reinforcement was efficient enough, substitution of traditional bar and stirrup reinforcement was enabled. Two following conditions were fulfilled simultaneously to pass the substitution threshold:

fR1 / fLOP > 0.4

(2)

fR3 / fR1 > 0.5

(3)

Calculated values of the above factors for tested concretes are presented in with the associated strength class and reinforcement substitution.

Table 5

Concrete Symbol fR3/fR1 fR1/fLOP fLOP (MPa)Strength ClassReinforcement SubstitutionI0.7830.9786.2166.0bEnabledII0.6960.5973.6533.0aEnabledIII0.7881.0055.4525.0bEnabledIV0.7611.0275.6585.0bEnabledOpen in a separate window

The achieved strength classes and enabled traditional reinforcement substitutions allowed for the utilisation of the tested concretes for structural applications. The wise use of different blends of ceramic waste and natural aggregates to shape the properties of cast concretes is possible. The proposed approach toward ceramic waste aggregates merged the advantages of internal curing and fibre reinforcement and was proven to be efficient.

6. Conclusions

The following conclusions can be drawn from the research described in this paper:

• It is possible to cast composites based on multiple waste aggregates;

• A blend of waste ceramic aggregates achieved a greater flexural strength of a cement composite than ordinary natural sand;

• The highest compressive strength was achieved using only natural aggregates;

• The compressive strength of the tested concretes was significantly influenced by the composition of the aggregate mix, as evidenced by the concrete with 1.5% fibre composition, whereby the values ranged from 17.5 MPa to 85.3 MPa;

• It is possible to partially or fully substitute natural aggregates with white or red ceramic wastes;

• The composites created on the basis of the white and red ceramic wastes are characterised by satisfactory mechanical properties, allowing for the assignment of standard strength classes according to both the EN and fib Model Code 2010;

• The research programme should be continued using greater specimens, focusing on more complicated mechanical characteristics (e.g., dynamic properties) of composites to enable full-scale modelling.

Acknowledgments

The authors would like to thank Katarzyna Maciejewska and Elzbieta Kuźmińska for their help in the preparation of the specimens and during some of the conducted testing procedures.

Author Contributions

Conceptualization, J.K. (Jacek Katzer); Data curation, J.K. (Jacek Katzer) and J.K. (Janusz Kobaka); Formal analysis, T.P.; Funding acquisition, T.P.; Investigation, J.K. (Janusz Kobaka); Project administration, T.P.; Software, J.K. (Janusz Kobaka); Writing – original draft, J.K. (Jacek Katzer); Writing – review & editing, J.K. (Janusz Kobaka). All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding

Conflicts of Interest

The authors declare no conflict of interest

Product Description

◆Description

Crimped steel fibers are low-carbon, cold-drawn steel wire fibers designed to provide temperature and shrinkage crack control, strengthen flexural reinforcement, increase shear strength, and improve crack resistance of concrete. Crimped steel fiber conforms to the standards outlined in ASTM C1116 (Standard Specification for Fiber Reinforced Concrete and Shotcrete) and ASTM A820 Type V (Standard Specification for Steel Fibers for Fiber Reinforced Concrete). These coarse steel fibers not only enhance impact resistance, shatter resistance, fatigue resistance, and abrasion resistance but also contribute to increasing the overall toughness of the concrete. The recommended dosage ranges from 25 to 100 lb/cubic yards (15 to 60 kg/m3), depending on the specific reinforcement requirements of the project.

Crimped steel fiber is widely used for buildings, road surfaces, bridges, tunnels, airport road surfaces, water conservancy projects, military engineering, and all kinds of building products.

 

◆Specification:

Name

Crimped Steel Fiber(milling)

Material

Carbon steel 

Length

30-60mm

Diameter

0.5-0.7mm

L/D

30-80

Tensile strength

>800Mpa

shape

wave

Standard

ASTM A820

 

◆User's guidance

● Dosage: depend on the application and general mixing amount is 0.1%-1% .

● Mixing: When pouring sand and aggregates into the hopper, mix an appropriate amount of loose steel fibers evenly, and then add cement. Put it in a mixing table, dry and mix for 2 minutes. If it is glued in rows of steel fibers, you need to add steel fibers after adding water so that the water can dissolve the bonding glue.

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● Put the evenly mixed fiber concrete into the conveyor and transport.

● Concrete pouring and laying should be compacted.

 

◆Reference standards

● EN 14889-1:2006

● EN 14651-2005

● ASTM A820

 

◆ Advantages

● Improvement of impact resistance, crack resistance and abrasion resistance of concrete

● Reduces segregation, plastic settlement and shrinkage cracking of concrete

● Provides three-dimensional reinforcement to prevent macro-cracking

● Improves overall durability, fatigue resistance and flexural toughness

● Reduces site costs compared to screens used for temperature/shrinkage crack control

● Easily added to concrete mixtures at any time prior to placement

 

◆Features

High strength

Strong toughness

Good ductility

long lasting Freeze-thaw resistance

Heat resistance Abrasion resistance

Cavitation resistance 

Corrosion resistance

Compression and impact resistance

 

◆ Application:

-Industrial and commercial floor

-Sprayed concrete ( Shotcreting ) in tunnels and mine

-Precast concrete products

-Bridges, Culverts and Hydrodynamic structures

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-Concrete/shotcrete

-Heavy equipment foundation.

 

 

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20kg per bag/carton or as your requirements, there are 50 bags or 1000kg in a pallet, 24tons per 20'container

 

 

◆ Certificate

CE,ISO9001, MA

 

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