IJMTER | Impact Factor 4.364 - Axial behavior of ferrocement … · 2017. 4. 7. · International Journal of Modern Trends in Engineering and Research e-ISSN No.:2349 -9745, Date:

International Journal of Modern Trends in Engineering and Research

www.ijmter.com e-ISSN No.:2349-9745, Date: 28-30 April, 2016

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Axial behavior of ferrocement confined cylindrical concrete specimens with different sizes

Kale Shekhar P1 ,Aher Dhiraj D.2 Shirsath H.A.3

Department of Civil Engineering S.N.J.B.’S K.B.J.College Of Engineering, Chandwad,[email protected].

Department of Civil Engineering S.N.J.B.’S K.B.J.College Of Engineering, Chandwad,[email protected]

Department of Civil Engineering S.N.J.B.’S K.B.J.College Of Engineering, Chandwad,[email protected]

_____________________________________________________________________________________ Abstract-This paper presents an experimental study on the axial behavior of ferrocement confined cylindrical concrete specimens. The present study also intends to investigate the effect of specimen size on the confinement action of ferrocement jacket. Three types of 27 concrete cylinders with diameters of 150, 100, and75 mm are cast and tested under axial compression. Each type of specimens is confined with single layer and double layer welded wire mesh ferrocement jacket having a constant thickness of the jacket. The experimental results demonstrate the effectiveness of ferrocement confinement in enhancing the strength, ductility and energy absorption capacity of concrete specimens. The confinement action is found more effective in case of smaller specimens. A post-peak descending branch in the axial stress–strain curve is observed in all the confined specimens. The stress–strain behavior and the failure pattern indicate that single layer mesh ferrocement jacket cannot provide significant confinement; at-least two layer mesh is required for substantial confinement. A new analytical model for the strength of ferrocement confined circular concrete specimen is proposed based on the test results of this work and verified with the recent experimental data obtained from the literature. Key words-Concrete cylinders, Size effect, Wire mesh, Ferrocement, Strength model ______________________________________________________________________________

I. INTRODUCTION Concrete is a widely used construction material all over the world. However, it often suffers deterioration due to various environmental (like earthquake, flood) and structural (like overloading)factors. A variety of materials and methods have been tried by the engineers to increase the strength and ductility of unsafe or deteriorated concrete structures. The materials and techniques applied for such strengthening activities should be structurally effective ;and also cost effective as cost effectiveness is another major concern for developing countries. Fiber reinforced polymer (FRP) is widely used nowadays as a confining /strengthening material for upgrading the strength of concrete members. However, FRP is very expensive, and its installation also requires highly skilled labor. Installation of FRP in hot and humid weather is

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very difficult and need special measures during its installation. On the other hand, ferrocement is very cost effective technology in developing countries as its raw materials are easily available in these countries. Ferrocement is a form of RC using closely spaced single or multiple layers of mesh and/or small-diameter skeletal rods completely infiltrated with , or encapsulated, in mortar. Although, ferrocement is an old technology, it is extensively used as a construction material with advanced technology in both developed and developing countries due to its ease of fabrication. It could be one of the promising materials for confining the concrete 1.1Experimental program

The experimental study was carried out on 27 concrete cylinders of three different sizes. The height and diameter of the cylinders were 300 mm, 200 mm, 150 mm; and 150 mm, 100 mm, 75 mm, respectively. Nine cylinders were prepared for each size; three of them were kept non-jacketed (denoted as NJ); three were jacketed with ferrocement having a single layer wire mesh; and the rest three were jacketed with ferrocement having a double layer wire mesh. The thickness of the external ferrocement jacket was kept constant (12.5 mm) for the jacketed specimens of all sizes. The external jacket was consisted of single or double layer welded wire mesh infiltrated with mortar. In general, 150 mm diameter specimens are designated as LS, 100 mm diameter specimens are designated as MS, and 75 mm diameter specimens are designated as SS. Fig. 1 demonstrates the details of the test Specimens. The specifications of the specimens are shown in Table 1.

1.2. Aggregates

The coarse aggregate used was 12 mm downgrade crushed stone. Its specific gravity and water absorption capacity was 2.62% and 1.05%, respectively. The fine aggregate used was locally available coarse river sand. The specific gravity and water absorption capacity of sand were 2.58% and 0.95%, respectively. The same sand was used in preparing mortar for ferrocement after conforming ACI 549.1R-93 [20]. Both the fine and coarse aggregate used in mixing concrete were saturated and surface dried. 1.3 Wire mesh

The wire mesh used as reinforcement for ferrocement jacket was welded wire mesh. The opening of the mesh (grid size) was 12.5 mm square opening. The diameter of wires in the mesh was 0.85 mm. The yield strength of individual wires of the mesh was 415 Mpa. 1.5 Concrete mix

The concrete mix was designed to obtain a concrete strength of 20 MPa at28 days. The design amounts of materials in the mix were 400 kg/m3 cement,1026 kg/m3 coarse aggregate, 624 kg/m3 fine aggregate, and 180 kg/m3 free water.



Figure-1.1. Details of test specimens

Specimens Designation Height Diameter Thickness

of jacket

Small ss-nj 150 75 12.5

ss-nj 150 75 12.5

ss-nj 150 75 12.5

Medium ms-sj 200 100 12.5

ms-sj 200 100 12.5

ss-sj 200 100 12.5

Large Ls-dj 300 150 12.5

Ls-dj 300 150 12.5

Ls-dj 300 150 12.5

Table-1.1. Details of non-jacketed and ferrocement jacketed specimens.

1.6 Preparation of concrete cylinders Cylindrical steel molds of required sizes were used for casting of concrete specimens. Before concreting, all the molds were oiled first and then placed on the vibration table. After that, concrete mix was prepared according to the mix design described in Section 2.2.1 and placed into the molds. The casting of concrete was done in three layers for 150 mm and 100 mm diameter



specimens. For 75 diameter specimens, the casting was done in two layers. In order to achieve proper compaction of concrete, low speed table vibration for 30 s was used after pouring each layer of concrete. All 27 specimens were cast from the same batch of concrete mix to maintain the same strength of concrete. However, three different size specimens are not compacted at the same time, only similar size specimens were placed on the vibration table at a time. All the specimens were covered with plastic sheets after casting of concrete. The specimens were de-molded after 24 h and placed under water for proper curing. Non-jacketed specimens were cured for 28 days. Ferrocement jacketing The concrete specimens were jacketed with Ferrocement after 14 days of concrete casting. After 14 days of curing, the specimens were taken out of the water tank and kept for 2 h in order to achieve a dry surface. After achieving the dry surface, six horizontal strain gauges were placed at two opposite sides of the specimens. The strain gauges were placed at three different levels, e.g., at mid height, 25 mm from the top and bottom faces of the specimen. After that, the wire mesh was wrapped around the specimens. A circular aluminum sheet was placed around the specimen for placing the mortar. The diameter of the circular aluminum sheet was 25 mm more than the diameter of each cylinder. This circular aluminum sheet was used in order to get a constant thickness of ferrocement throughout the height of the specimens and to expedite the jacketing process. Then, the mortar was placed into the round aluminum sheet. All specimens were jacketed with ferrocement from the same batch of mortar mix. A 10 mm gap was kept in between the concrete cross-sectional surface and the ferrocement jacket surface at both top and bottom. This gap was kept to avoid the direct compressive load on the ferrocement jacket. The aluminum sheet was removed after 24 h and the newly jacketed specimens were placed under water to finish 28 days of curing from the date of concrete casting.



Fig. 2 demonstrates the ferrocement jacketing process of the concrete specimens. Conclusion In this study a total of 27 concrete cylinders with different size were tested under monotonic compression. Based on the obtained test results, the following conclusion can be drawn: 1. The external ferrocement jacket can enhance the load carrying capacity, ductility and energy absorption capacity of concrete specimens. This enhancement is more prominent in smaller specimens. 2. The failure pattern and stress–strain behavior indicates that single layer mesh ferrocement jacket cannot provide significant external confinement. However, double layer mesh ferrocement jacket can provide sufficient confinement to enhance the behavior of confined concrete. 3. An analytical model is proposed to predict the strength of ferrocement confined concrete. The predicted results agree very closely with the test data available in the literature.

REFERENCES

[1] Singh KK, Kaushik SK. Ferrocement composite columns. Proceedings of the third International Conference on Ferrocement, Roorkee, India; 1988, p. 216–225 [2] Balaguru P. Use of ferrocement for confinement of concrete. Proceedings of the third International Conference on Ferrocement, Roorkee, India; 1988, p. 296–305.

[3]Mourad SEM. Performance of Plain Concrete Specimens Externally Confined with Welded Wire Fabric. Research Report, College of Engineering Research Center, King Saud University, Saudi Arabia; 2006.

[4]Kaish ABMA, Wahed MA, Alam MR. Behavior of Ferrocement encased square reinforced concrete column under eccentric loading. International Conference on Structural Engineering, Construction and Management, CD ROM, Kandy, Sri Lanka, 15–17 December 2011. [5] ACI 549.1R-93. Guide for design, construction & repair of ferrocement. ACI, MI, USA; 1993.

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IJMTER | Impact Factor 4.364 - Axial behavior of ferrocement … · 2017. 4. 7. · International Journal of Modern Trends in Engineering and Research e-ISSN No.:2349 -9745, Date: