STRENGTH CHARACTERISTICS OF HYBRID FIBER REINFORCED SELF COMPACTING CONCRETE SUBJECTED TO SUSTAINED ELEVATED TEMPERATURE

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1 STRENGTH CHARACTERISTICS OF HYBRID FIBER REINFORCED SELF COMPACTING CONCRETE SUBJECTED TO SUSTAINED ELEVATED TEMPERATURE K Ravi*, K.L. Society s Gogte Institute of Technology, Belgaum, India K B Prakash, K.L.E. Society s College of Engineering & Technology, Belgaum, India 33rd Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2008, Singapore Article Online Id: The online version of this article can be found at: This article is brought to you with the support of Singapore Concrete Institute All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information

2 33 rd Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2008, Singapore STRENGTH CHARACTERISTICS OF HYBRID FIBER REINFORCED SELF COMPACTING CONCRETE SUBJECTED TO SUSTAINED ELEVATED TEMPERATURE K Ravi*, K.L. Society s Gogte Institute of Technology, Belgaum, India K B Prakash, K.L.E. Society s College of Engineering & Technology, Belgaum, India Abstract Concrete structures are occasionally high s in reaction vessels, fire, coal gasification vessels etc. In most of the cases such s result in considerable damage to concrete structures. Fibers have been extensively used to improve, ductility and durability properties of concrete. Recently it is found that of fibers can also improve the residual properties of concrete after exposed to sustained. Hybrid fibers used in plain concrete are found to be beneficial in improving the microstructure which results in better durability. In hybrid fiber technology, two or more different types of fibers are rationally combined to produce a composite that derives benefits from each of individual fibers and exhibits a synergistic response and proves to be effective in resisting thermal shocks. Self compacting concrete over comes several problems associated with fiber reinforced concrete or hybrid fiber reinforced concrete. In the present investigation mechanical properties of hybrid fiber reinforced self compacting concrete and mono fiber reinforced self compacting concrete which are sustained are studied. Different fibers considered are steel fibers (SF), polypropylene fibers (PPF), galvanized iron fibers (GIF), and waste plastic fibers (WPF). Hybrid fiber combinations used in the experimentation are (SF +PPF), (SF+GIF) and (SF+WPF). It is found that the resistance of hybrid fiber reinforced self compacting concrete to is better than that of mono fiber reinforced self compacting concrete. Key words: Mono fibers, hybrid fibers, self compacting concrete, s,.

3 1 Introduction. The fire resistance capacity of concrete is very complicated because not only is concrete a composite material with components having different thermal characteristics, it also has properties that depend on moisture and porosity [1].The application of high concrete is increasing since it offers various benefits derived from its higher and stiffness.. At the same time the risk of high concrete exposing to s is also ever increasing [2]. The high concrete has such disadvantages as poor fire resistance, being more prone to explosive spalling due to their low permeability and high brittleness [3][ 4]. The spalling of concrete is highly related to build up of pore pressure in consequence of vaporization of physically and chemically bound water. [5].Thermal cracking induced by thermal mismatch has been one of the problems in a cement based composite material under s.[6].to prevent such problems, different fibers were induced to enhance resistance of high concrete. Earlier investigations on cement mortar revealed that fiber type affects both heat and mass transfer as well as the extent of spalling of mortar at s [7][8]. The current practice involves the use of mono fibers. Clearly, a given type of fiber can be effective only in a limited range of crack openings and deflections [9]. There has been much enthusiasm recently in the field of fiber reinforced concrete for the development of hybrid fiber system where two or more types of fibers are combined. This is done with the intent of confirming the best performance characteristic of each of the constituents fiber types to the composite material [10]. A common problem associated with the use of fibres in concrete is the resulting reduction in workability, especially at high fibre contents. In case of self compacting concrete (SCC), the coarse aggregate content is usually reduced compared with that in ordinary concrete. Reducing it further and increasing mortar content to enhance workability can be costly. Therefore carefully designed hybrid fibre combinations in SCC can allow striking a balance between workability and mechanical performance of fiber reinforced self compacting concretes (FRSCC) [11] In the present investigation, mechanical properties of hybrid fiber reinforced self compacting concrete and mono fiber reinforced self compacting concrete, which are sustained of C for 4 hours are studied. Different fibers considered are steel fibers (SF), polypropylene fibers (PPF), galvanized iron fibers (GIF), and waste plastic fibers (WPF). The hybrid fiber combinations used in the experimentation are (SF +PPF), (SF+GIF) and (SF+WPF).Different tests conducted are compressive, split tensile, flexural and impact. These tests are conducted on the specimens before and after. 2 Research Significance. Many times the concrete structures are fire and thermal shocks. In such cases of the concrete will be greatly affected and it is associated with the spalling of concrete cover, which causes further exposure. At present utility of hybrid fiber reinforced self-compacting concrete to enhance residual and to increase the thermal resistance is not explored to a greater extent. Therefore there is a need for research to study the synergistic response of hybrid fibers in selfcompacting concrete to resist the fire and thermal shocks 3 Materials and Methods. In this experimentation work, 43 grade OPC was used along with locally available sand and coarse aggregate. Sand used was of zone II and its specific gravity was Coarse aggregates used in experimentation were 12mm and down size and their specific gravity was found to be 2.7. Fibers used in the study and their physical properties are presented in Table No 1. Mono fibers were added at the rate of 1.0% (by volume fraction) and hybrid fibers were added at the rate of (0.5% + 0.5%) in the study. Different hybrid fibers used in the study are (SF+PPF), (SF+GIF) and (SF+WPF). Chemical composition of the fly ash which is used as filler in the self compacting concrete is indicated in Table No 2

4 . Table1. Properties of fibers used Fiber type Length in mm Thickness Aspect ratio Density N/m 3 Steel fiber (SF) 25 1mm Polypropylene fiber (PPF) Galvanized iron fiber(gif) Waste plastic fiber(wpf) µm mm mm Table 2. Chemical composition of fly ash. Oxides Mass percentage SiO Al 2 O Fe 2 O CaO 3.0 MgO 1.0 SO Others 8.0. Mix proportions of the SCC for M20 is shown in Table No. 3.The flow characteristic tests for SCC like slump flow test, Orimet test, V-funnel test, L-Box test, U-Box test were conducted. Concrete cubes of size 150 mm were cast and tested for compression at the age of 28 days as per IS 516: 1959[12].For split tensile, cylinders of 150mm diameter and 300 mm length were cast and tested as per I.S 5816:1999 [13]. For the flexural, the beam specimens of size 100 X 100 X 500mm were cast and tested at the age of 28 days. Two points loading was adopted on an effective span of 400mm while testing the beam specimens as per IS 516: 1959[12]. For impact, the cylindrical specimens of size 150mm diameter and 60mm height were cast. Drop weight test as suggested by Schruder was adopted for testing the specimen[14].after 28 days of curing specimens were kept in high oven where in they were sustained of C for 4 hours. The specimens were tested for their after they attained room.. Table 3. Mix proportion for self compacting concrete Material Cement Fly ash Water Coarse aggregate Fine aggregate SP VMA w/b Quantity Kg/m 4 Results and Discussion. Table No.4 give the results of flow characteristics of reference mix, fiber reinforced self compacting concretes (FRSCC) and hybrid fiber reinforced self compacting concretes (HFRSCC). Table No.5,6,7 and 8 give the compressive, tensile, flexural and impact of FRSCC and HFRSCC before and after sustained of C for 4 hours. The flow characteristics measured by standard methods specified for SCC are presented in table 4.The results obtained in present study are closer to values suggested by EFNARC specifications [15]. Moncef Nehdi[11] et al have also observed lower values of flow with synthetic fibers like

5 polymeric fibers. This was mainly attributed to the high aspect ratio and higher surface area of these fibers, which are detrimental to flow. In this present investigation also synthetic fibers like polypropylene (PPF) and waste plastic fibers (WPF) yielded lower flow values. Higher flow was observed with metallic steel fiber with lower aspect ratio of 25 in comparison to G.I fibers with higher aspect ratio of 40. Interestingly all the hybrid fibers in SCC indicated higher values of flow. However it is possible to improve the flow values with alterations in VMA and superplasticizer dosages From the various test results obtained for hardened self compacting concretes with different fibers, it is observed that inclusion of fibers is feasible in self compacting concrete and indicated the good retention these concretes are exposed to sustained. It is observed that mono fiber SCC with stiff and higher modulus metallic fibers like steel and G.I, yields higher values in comparison to SCC with flexible fibers like PPF and WPF. This is due to the fact that PPF and WPF fibers get melted at s and there will be no significant contribution. However creation of additional voids due to melting of these fibers makes the heat dissipation and prevents spalling of concrete and further deterioration. In the present study, observations indicated no spalling of concrete. The synergistic response of fibers is clearly seen in all hybrid fiber reinforced self compacting concretes with enhancement. The hybrid blend of metallic and non metallic fibers yielded higher values in comparison to respective mono fiber concretes and also reduction in percentage loss of due to exposure to s was observed. The hybrid blend of fibers in SCC is found to be beneficial for better placement, retention after exposure to and also to prevent spalling of concrete. In all the parameters the hybrid blend of both metallic fibers like steel and G.I, have yielded higher s. Both the fibers have similar and higher modulii of elasticity and this may be the reason for yielding higher s. Influence of fibers or hybrid fibers was found to be marginally beneficial in case of compressive s. Remarkable enhancement was observed in case of tensile, flexural and impact which are desired. 5 Conclusions. Incorporation of fibers is feasible in self compacting concretes and flow characteristics can be further increased with alteration in VMA or SP dosages. Synergistic response of fibers is observed in hybrid fiber reinforced self compacting concretes. Metallic fibers like steel and G.I yielded higher values in comparison to non metallic fibers like polypropylene and waste plastic fibers. No spalling of concrete was observed which is due to melting of polypropylene and waste plastic fibers at s. loss due to exposure to s is found to be lower in case of hybrid fiber reinforced self compacting concretes in comparison to mono fiber reinforced self compacting concretes, and Hybrid fiber reinforced self compacting concretes proves to be more beneficial for proper placement in difficult situations, higher retention and to prevent spalling, for concrete structures sustained s.

6 Table 4. Flow characteristics of FRSCC and HFRSCC Description of SCC Slump flow (mm) Orimet time (sec) Filling height (H1-H2) (mm) V-box flow time (sec) Blocking ratio (H2/H1) L-box test T20 (sec) T40 (sec) SCC without fibers (ref. mix.) SCC with SF SCC with PPF SCC with GIF SCC with WPF SCC with(sf+ppf) SCC with (SF+GIF) SCC with (SF+WPF) Table 5. Compressive of FRSCC and HFRSCC before and after sustained Description of SCC Compressive before Compressive after increase in compressive w.r.t ref. mix loss in compressive SCC without fibers (ref. mix.) SCC with SF SCC with PPF SCC with GIF SCC with WPF SCC with (SF + PPF) SCC with (SF +GIF) SCC with (SF + WPF)

7 Table 6. Tensile of FRSCC and HFRSCC before and after sustained Description of SCC Tensile before Tensile after increase in tensile w.r.t ref. mix loss in tensile SCC without fibers (ref.mix.) SCC with SF SCC with PPF SCC with GIF SCC with WPF SCC with (SF + PPF) SCC with (SF +GIF) SCC with (SF + WPF) Table 7. Flexural of FRSCC and HFRSCC before and after sustained. Description of SCC Flexural before Flexural after increase in flexural w.r.t ref. mix temp loss in flexural SCC without fibers (ref.mix.) SCC with SF SCC with PPF SCC with GIF SCC with WPF SCC with (SF + PPF) SCC with (SF +GIF) SCC with (SF + WPF)

8 Table 8. Impact energy of FRSCC and HFRSCC before and after sustained. Description of SCC Impact energy before subjecting to (N-m) Impact energy after (N-m) increase in impact energy w.r.t ref. mix subjected to temp loss in impact energy subjected to temp first crack final failure first crack final failure first crack final failure first crack final failure SCC without fibers (ref.mix.) SCC with SF SCC with PPF SCC with GIF SCC with WPF SCC with (SF + PPF) SCC with (SF +GIF) SCC with (SF + WPF)

9 Acknowledgements The authors would like to express their sincere thanks to Shri. S.M Kulkarni Chairman, Karnatak Law Society Belgaum, Shri. S.G Punekar, Chairman, Governing council G.I.T, Dr.D.H.Rao, Principal, G.I.T, Belgaum,India and Dr.S.C. Pilli, Principal, K.L.E.S. College of Engineering and Technology, Belgaum and all the management authorities of both the colleges who constantly boosted the morale by giving all the help required. Our sincere thanks to Dr. H.P. Kincha, Hon. Vice-Chancellor and Dr. K.V.A. Balaji, Registrar of Visvesvaraya Technological University, Belgaum, India for the moral support. Thanks are also due to authorities of FOSROC Chemicals (India) Pvt Ltd. and Grasim Industries Cement Division Bangalore for the material support and Shri. M.N Acharya, Abhishek Alloys Belgaum for providing experimental facilities. References. [1] Min li, Chung Xiang Qian, Wei Sun Mechanical properties of high concrete after fire. Cement and Concrete Research, Vol.34, 2004, pp [2] Noumowe.A. Mechanical properties and micro structure of high concrete containing polypropylene fibers exposed to s up to C. Cement and Concrete Research, Vol.35, 2005, pp [3] Sanjayan.G., Stocks..L.J, Spalling of high silica fume concrete in fire. ACI Material Journal Vol. 90(2), 1993, pp [4] Ali. F.A, O Connor.D. Abu-Tair Explosive spalling of high concrete columns in fire. Magazine of Concrete Research. Vol. 53(3), 2000, pp [5] Mathhias Zeiml, David Leithner,Roman Lackner, Herbert.A. Mand. How do polypropylene fibers improves spalling behavior of in-situ concrete?.. Cement and Concrete Research, Vol.36, 2006, pp [6] Fu.Y.F, Wong.Y.L, Tang C.A., Poon C.S Thermal induced stresses and associated cracking in cement based composites at s-part1.thermal cracking around single inclusion. Cement and Concrete Research, Vol.26, 2004, pp [7] Sarvaranta L., Elomaa.M, Jarvela..E A study of spalling behavior of PAN fiber reinforced concrete by thermal analysis. Fire and Materials 17(5),1993, pp [8] Sarvaranta L.,Mikkola.. E Fiber mortar composites in fire conditions. Fire and Materials, 18(1),1994, pp [9] Bantia.N and Nandakumar N, Crack growth resistance of hybrid fiber reinforced cement composite, Cement and Concrete Composites, Vol. 25, 2003, pp 3-9. [10] Lawler J.S,Zampini D, Shah S.P. Permeability of cracked hybrid fiber reinforced mortor under load ACI Material Journal, Vol.99 (4), 2002, pp [11] Moncef Nehdi, Jennifer Duquette Ladanchuck, Fiber in reinforced self compacting concrete, ACI Material Journal, Nov/Dec 2004, pp [12] IS , Method of test for of concrete [13] IS 5816:1999 Splitting tensile of concrete method of test. [14] Ernest.K.Schruder Impact resistance and test procedure for concrete,aci Material Journal March-April, [15] EFNARC Specifications on self compacting concrete,2002.