Scholarly article on topic 'Effect of Change in Micro Steel Fiber Content on Properties of High Strength Steel Fiber Reinforced Lightweight Self-Compacting Concrete (HSLSCC)'

Effect of Change in Micro Steel Fiber Content on Properties of High Strength Steel Fiber Reinforced Lightweight Self-Compacting Concrete (HSLSCC) Academic research paper on "Civil engineering"

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Procedia Engineering
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{"self-compacting concrete" / "lightweight concrete" / "high strength concrete" / "fiber reinforced concrete" / superplasticizer / "course aggregate" / "fine aggregate."}

Abstract of research paper on Civil engineering, author of scientific article — Shahid Iqbal, Ahsan Ali, Klaus Holschemacher, Thomas A. Bier

Abstract As known, with addition of fibers to concrete, the properties of concrete are altered. Steel fiber is one of the common fiber used in concrete. Using lightweight concrete is extremely important for reducing the self-weight of structures, especially in heavy ones, like high rise buildings. It enables to decrease additional loads in case of renovation or/strengthening of existing structures. Moreover, self-compaction avoids using vibrations for compaction of concrete in existing structures. Therefore the present study is aimed at investigating the effect of change in micro steel fiber content on the properties of high strength steel fiber reinforced lightweight self-compacting (HSLSCC). For this reason slump flow test was conducted to find workability of the fresh concrete mixture. Further compressive strength, splitting tensile strength, modulus of elasticity and flexural strength of the hardened concrete were tested. Four concrete mixes of HSLSCC with different fiber contents were prepared to study the change in its fresh and hardened properties. Results show that there is strong influence on workability of SCC with steel fiber content of 1% or more. There is around 7% reduction in compressive strength, 18% and 70% increase in splitting tensile strength and flexural strength respectively, with increase of steel fiber content from 0.5% to 1.25%, while the modulus of elasticity remains almost the same.

Academic research paper on topic "Effect of Change in Micro Steel Fiber Content on Properties of High Strength Steel Fiber Reinforced Lightweight Self-Compacting Concrete (HSLSCC)"

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Procedía Engineering 122 (2015) 88 - 94

Procedía Engineering

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Operational Research in Sustainable Development and Civil Engineering - meeting of EURO working group and 15th German-Lithuanian-Polish colloquium (ORSDCE 2015)

Effect of change in micro steel fiber content on properties of High strength Steel fiber reinforced Lightweight Self-Compacting Concrete

(HSLSCC)

Shahid Iqbala,b,*9 Ahsan Alia,b, Klaus Holschemachera, Thomas A. Bierb

aFaculty of Civil Engineering, University of Applied Sciences (HTWK), Leipzig, Germany. Institute of Ceramics, Glass and Construction Materials, Technical University, Freiberg, Germany.

Abstract

As known, with addition of fibers to concrete, the properties of concrete are altered. Steel fiber is one of the common fiber used in concrete. Using lightweight concrete is extremely important for reducing the self-weight of structures, especially in heavy ones, like high rise buildings. It enables to decrease additional loads in case of renovation or/strengthening of existing structures. Moreover, self-compaction avoids using vibrations for compaction of concrete in existing structures. Therefore the present study is aimed at investigating the effect of change in micro steel fiber content on the properties of high strength steel fiber reinforced lightweight self-compacting (HSLSCC). For this reason slump flow test was conducted to find workability of the fresh concrete mixture. Further compressive strength, splitting tensile strength, modulus of elasticity and flexural strength of the hardened concrete were tested. Four concrete mixes of HSLSCC with different fiber contents were prepared to study the change in its fresh and hardened properties. Results show that there is strong influence on workability of SCC with steel fiber content of 1% or more. There is around 7% reduction in compressive strength, 18% and 70% increase in splitting tensile strength and flexural strength respectively, with increase of steel fiber content from 0.5% to 1.25%, while the modulus of elasticity remains almost the same.

© 2015Publishedby ElsevierLtd. This isan openaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-reviewunderresponsibilityof the organizing committeeoftheOperationalResearch inSustainableDevelopment and Civil Engineering - meeting of EURO working group and 15th German-Lithuanian-Polish colloquium

* Corresponding author. Tel.: +49 341 30768821; fax: +49 341 30766461. E-mail address: shahid.iqbal@stud.htwk-leipzig.de

1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the Operational Research in Sustainable Development and Civil Engineering - meeting of EURO working group and 15 th German-Lithuanian-Polish colloquium doi: 10.1016/j.proeng.2015.10.011

Keywords: self-compacting concrete; lightweight concrete; high strength concrete; fiber reinforced concrete; superplasticizer; course aggregate; fine aggregate.

1. Introduction

Self-compacting concrete (SCC) is highly flowable, non-segregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement without any mechanical consolidation. It doesn't require any vibration for compaction and can flow through narrow spaces without segregation and excessive bleeding [1]. Similar to the normal vibrated concrete (NVC), SCC mixtures consist of aggregate, cement, water, admixtures and some mineral additions. Unlike NVC, SCC has high quantity of fillers (eg. silica fume, fly ash, limestone powder etc.) and superplasticizers added to improve its flowing property.

As SCC flows under its own weight without or very little use of vibration, it results in saving a lot of labor effort and bring economy to the concreting.

As per ACI committee report [2] for structural light weight concrete, structural light weight aggregate concrete is the concrete having minimum 28 day compressive strength of 17 MPa and equilibrium density of 1120-1920 kg/m3, consisting entirely or partially of lightweight aggregates, while the high strength lightweight concrete is the structural lightweight concrete having compressive strength of more 40 MPa.

Addition of high strength steel fibers to concrete [3] results in better ductility and higher load carrying capacity compared to concrete with normal steel fibers, in the absence of main reinforcement bars. Use of optimal steel fiber weight ratio in high strength concrete produces high performance bending elements having elastic-plastic behavior similar to that of normal strength concrete members [4].

According to a research study conducted on fiber reinforced SCC [5], it was observed that SCC behaves in a similar way as that of NVC and shows increase in flexural strength with increase in fiber content. In another research [6] it was observer that the addition of steel fibers to concrete increases ductility, first crack strength and flexural strength while the compressive strength of concrete is less affected. Additionally it was concluded that addition of short steel fibers produces softening behavior while with longer fibers, concrete shows hardening behavior. A study [7] indicated that there is increase in flexural strength of concrete with increase in steel fiber content giving the maximum value of flexural strength at steel fiber content of 3.5%. Further increase in fiber content decreases the flexural strength.

A research [8] conducted to study the properties of very high strength concrete reinforced with alkali resistant propylene fibers and polyvinyl alcohol micro fibers indicate a clear reduction in compressive strength and modulus of elasticity of concrete.

In another study [9], it was noticed that the bond of fibers in SCC is better as compared to NVC. So we may say that we can obtain the maximum benefits of fiber addition in SCC.

This research is conducted to study the properties of HSLSCC incorporating different amount of micro steel fibers. Fresh state properties studied in this research are workability, density and air content, while hardened properties include compressive strength, splitting tensile strength, modulus of elasticity and flexural strength of concrete.

The objectives of this study are as under:

• Development of HSLSCC with slump flow of more than 600mm and 28 days cylinder compressive strength of more than 50 MPa.

• Study the effect of change in micro steel fiber content on fresh state properties i.e. workability, air content and fresh state density.

• Study the effect of change in steel fiber content on hardened properties i.e. compressive strength, splitting tensile strength, modulus of elasticity and flexural strength of HSLSCC.

In this study, the powder type SCC is used which has already been developed in the early phase of this research study. The fiber content used was 0.5%, 0.75%. 1% and 1.25% volume fraction denoted as FRC0.5, FRC0.75, FRC1 and FRC1.25.

2. Methodology

The fresh state properties studied in this research are the workability [10], air content and the fresh state density [11]. The hardened properties included compressive strength, splitting tensile strength, modulus of elasticity and the flexural strength of the concrete. The ASTM procedures are followed for testing of all the properties under consideration. Slump flow test was conducted to know about the workability of concrete. 3 cylinders each with a diameter of 100 mm and 200 mm height were casted to test the compressive strength [12], splitting tensile strength [13] and modulus of elasticity [14]. 3 small scale beams with dimensions 80 x 80 x 400 mm3 with a clear span of 300mm, each were tested for flexural strength [15] of each concrete type using third point loading test.

3. Concrete mix design

A powder type HSLSCC was developed using expanded clay lightweight round course aggregate having size of 4-8 mm and crushed fine aggregate 0-4 mm in size. Portland cement CEM-I 42.5R was used and fly ash was the only filler used. Polycarboxylatether based superplasticizer (Glenium ACE 391 (FM)) was used as high range water reducing agent. The micro steel fibers were used with length of 13 mm and diameter of 0.2 mm. The material composition of all the four types of concrete mixtures is given in Table 1.

Table 1. Concrete mix composition

Concrete Quantities (kg/m3)

type Cement Fly ash Super pl. VMA Steel fibers Coarse Agg. Fine Agg. Water

FRC0.5 465 125 14 0 40 305 525 272

FRC0.75 465 125 14 0 60 305 525 272

FRC1 465 125 14 0 80 305 525 272

FRC1.25 485 130 15 3 100 305 525 296

4. Results and discussion

4.1. Fresh mix properties

Table 2 represents the fresh state properties of the concrete mixes studied. As the fiber content increases, the slump flow decreases especially above 0.75% steel fiber content. For the concrete mix with fiber content of 1.25%, the slump flow dropped below 600 mm which was the minimum requirement. So to increase the workability, powder content and water-cement ratio were increased slightly. Additionally it can be observed from table that despite the addition of steel fibers which are quite heavier, the fresh concrete density remained almost constant due to increase in air content.

Table 2. Fresh state properties

Concrete type Slump flow (mm) T500 (sec) Density (kg/m3) Air content (%)

FRC0.5 725 7 1744 3.63

FRC0.75 715 8 1749 4.17

FRC1 620 9 1744 5.25

FRC1.25 630 9 1746 5.32

The change in workability and air content of all the 4 mixes are graphically represented in Fig. 1. It is clear from

Shahid Iqbal et al. / Procedia Engineering 122 (2015) 88 - 94 this figure that, with increase in steel fiber content, the workability reduces while the air content increases.

800 10 —•— Slump flow (mm)

9 —•— Air content (%)

700 m s 8 —• %) (%

$ 600 tne

I 500 lu Sl ---- ___ 6 --• 5 4 3 tn o c Sh

300 2

0,5 0,75 1 Fiber content (% VF) 1,25

Fig. 1. Slump flow and air content variation

4.2. Hardened concrete properties

The results for hardened concrete properties at 28 days are summarized in Table 3.

Table 3. Hardened properties at concrete age of 28 days

Concrete Compressive Splitting tensile Modulus of Flexural

type strength (MPa) strength (MPa) elasticity (MPa) strength (MPa)

FRC0.5 64.03 4.76 15,782 4.42

FRC0.75 61.01 5.02 15,595 6.13

FRC1 60.94 5.42 15,672 6.36

FRC1.25 59.74 5.64 15,349 7.62

4.2.1. Compressive Strength

As it can be seen from Table 3 that with the increase of steel fibers content, there is slight decrease in the compressive strength of the concrete. This relation is evident in the compressive strength at the concrete age of both 7 days and 28 days. The relationship is graphically represented in Fig.2. The compressive strength of concrete with 0.5% steel fiber content is 64.03 MPa while that with 1.25% steel fiber content is 59.74 MPa. So there is almost 7% reduction in compressive strength with steel fiber content increased by 0.75%.

70 —•—7 day CS

£ 65 ___ -•-28 days CS

£ 60 tg n re --•

e ■§ •..... res 50

rp pm 3 45

0,5 0,75 1 Fiber content (% VF) 1,25

Fig. 2. Variation in compressive strength of concrete

4.2.2 Splitting Tensile strength

The results for splitting tensile strength of the concrete mixes are summarized in Table.3. The results are graphically represented in Fig.3. It is evident that with the increase of steel fiber content, there is clear increase in splitting tensile strength of the concrete mixes. Results show that there is around 18% increase in splitting tensile strength of the tested specimens with increase in steel fiber content from 0.5% to 1.25%.

® 5'5

r- c 5

M ~~ c •

0,5 0,75 1 1,25

Fiber content (% VF)

Fig. 3. Variation in splitting tensile strength of concrete

4.2.3 Modulus of Elasticity

The results for modulus of elasticity of all the four types of concrete mixes are summarized in Table 3. As it can be observed from the table that there is very slight reduction in the modulus of elasticity of concrete with increase in steel fiber content but the change is not significant and the values remain almost at the same level.

4.2.4 Flexural strength

The flexural strength tests results data is summarized in Table 3. It can be clearly seen from the results that the

flexural strength increases with the increase in steel fiber content. The results are graphically represented in Fig. 4. The concrete mix with 0.5% steel fibers exhibits strain softening behavior with first crack load and peak load being equal to each other. But once the fiber content is further increased, the concrete shows strain hardening behavior, as there is further increase in peak load after the first crack. The peak load also increases with the increase in fiber content, the maximum being for the concrete mix with 1.25% steel fiber content.

Fig. 4. Variation in flexural strength of concrete

5. Conclusions

This research has been carried out to study the change in properties of HSLSCC with different micro steel fiber content. The main conclusions that can be extracted from this study are as under:

1. HSLSCC can be developed with slump flow of more than 600 mm, concrete density of around 1700 kg/m3 and having high compressive strength in the range of 60 MPa.

2. Once there is an increase in steel fiber content, compressive strength tends to slightly decrease. In this study there was 7% decrease in compressive strength with increase of steel fiber content from 0.5% to 1.25%.

3. Splitting tensile strength tests suggests that there is an increase in splitting tensile strength which is around 18% with increase of steel fiber content by 0.75%.

4. There is slight decrease in modulus of elasticity of concrete with increase of steel fiber content although the change is not significant.

5. Concrete exhibits strain hardening behavior once steel fiber content of 0.75% or more is used. The flexural strength increases considerably i.e. around 70% increase in flexural strength but slight increase around 11% in first crack load with increase of steel fiber content from 0.5% to 1.25%.

References

[1] ACI committee report 237R-07 self-consolidating concrete, 2007, American concrete institute.

[2] ACI committee report 213R-03 self-consolidating concrete, 2003, American concrete institute.

[3] K. Holschemacher, T. Müller, H. Kieslich, Flexural behavior of high-strength concrete with combined steel fiber and bar reinforcement, Proceedings of the International Seminar on "Advanced Concrete Technology and its Applications", 2014, 45-51.

[4] I. Iskhakov, Y. Ribakov, K. Holschemacher, T. Müller, Experimental investigation of full scale two-layer reinforced concrete beams, Mechanics of Advanced Materials and Structures, 2014, 21, 273-283.

[5] M. Pajak, T. Ponikiewski, Flexural behavior of self-compacting concrete reinforced with different types of steel fibers. Construction building material, 2013, 47, 397-408.

[6] R.S. Olivito, F.A. Zuccarello, An experimental study on the tensile strength of steel fiber reinforced concrete, Composites, 2012, Part B, 41, 246-255.

[7] B.J. Vinayak, M.N. Mangulkar, Flexural behavior of self-compacting high strength fiber reinforced concrete (SCHSFRC), International journal of engineering research and applications (IJERA), 2013, 3(4): 2503-2505.

[8] T.M. Abu-Lebdeh, E. Fini, M. Lumpkin, Flexural and tensile characteristics of micro fiber-reinforced very high strength concrete thin panels. Americal journal of engineering and applied sciences, 2012, 5(2): 185-197.

[9] K. Holschemacher, Y. Klug, Pull-out behavior of steel fibers in self-compacting concrete. Fourth international RILEM symposium on self-compacting concrete, 2005, 461-466.

[10] EFNARC, 2002, Specification and guidelines for self-compacting concrete, European project group, UK.

[11] ASTM C138/C138 M, Standard test method for density (Unit weight), yield and air content (Gravimetric) of concrete, ASTM international.

[12] ASTM C39/C39 M, Standard test method for compressive strength of cylindrical concrete specimens, ASTM international.

[13] ASTM C496/C496 M, Standard test method for splitting tensile strength of cylindrical concrete specimens, ASTM international.

[14] ASTM C469/C469 M, Standard test method for static modulus of elasticity and poison's ration of concrete in compression, ASTM international.

[15] ASTM C78/C78 M, Standard test method for flexural strength of concrete (Using simple beam with third-point loading), ASTM international.