STUDY ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF CHOPPED CARBON FIBER REINFORCED SELF COMPACTING CONCRETE

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May June 2016, pp , Article ID: IJCIET_07_03_022 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication STUDY ON THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF CHOPPED CARBON FIBER REINFORCED SELF COMPACTING CONCRETE BISWAJIT JENA M. Tech, Department of Civil Engineering, National Institute of Technology, Rourkela , INDIA ASHA PATEL Asso. Prof., Department of Civil Engineering, National Institute of Technology, Rourkela , INDIA ABSTRACT As compared to conventional concrete the benefits of SCC comprising more strength like non SCC, may be higher due to better compaction, similar tensile strength like non SCC, modulus of elasticity may be slightly lower because of higher paste, slightly higher creep due to paste, shrinkage as normal concrete, better bond strength, fire resistance similar as non SCC, durability better for better surface concrete. Incorporation of fibers further enhances its properties specially related to post crack behavior of SCC. The fibers used in the study are 12 mm long chopped glass fiber and carbon fiber. The volume fraction of fiber taken is 0%, 0.1%, 0.15%, 0.2%. The project comprised of two stages. First stage consisted of development of SCC mix design of M30 grade and in the second stage, different fibers like Glass and carbon Fibers are added to the SCC mixes and their fresh and hardened properties were determined and compared. The study showed remarkable improvements in all properties of self-compacting concrete by adding fibers of different types and volume fractions. Carbon FRSCC exhibited best performance followed by glass FRSCC in hardened state. Key words: Self Compacting Concrete, Carbon Fiber, Mechanical Properties, Volume Fraction, Microstructures Cite this Article: Biswajit Jena and Asha Patel, Study On The Mechanical Properties And Microstructure Of Chopped Carbon Fiber Reinforced Self Compacting Concrete, International Journal of Civil Engineering and Technology, 7(3), 2016, pp

2 Biswajit Jena and Asha Patel 1. INTRODUCTION The growth of Self Compacting Concrete by Prof. H.Okamura in 1986 [1], [2] has caused a significant impact on the construction industry by overcoming some of the difficulties related to freshly prepared concrete. The SCC in fresh form reports numerous difficulties related to the skill of workers, density of reinforcement, type and configuration of a structural section, pump-ability, segregation resistance and, mostly compaction. The Self Consolidating Concrete, which is rich in fines content, is shown to be more lasting. Addition of more fines content and high water reducing admixtures make SCC more sensitive with reduced toughness and it designed and designated by concrete society that is why the use of SCC in a considerable way in making of pre-cast products, bridges, wall panels etc. also in some countries. Carbon fibers have low density, high thermal conductivity, good chemical stability and exceptional abrasion resistance, and can be used to decrease or reduce cracking and shrinkage. These fibers increase some structural properties like tensile and flexural strengths, flexural toughness and impact resistance [3], [4], [5], [6]. Carbon fibers also help to improve freeze-thaw durability and dry shrinkage. The adding of carbon fibers decreases the electrical resistance. The ductility can be measured by toughness behavior of FRSCC and to determine toughness index. The general idea of this type of test is to measure the amount of energy which is absorbed when the specimen is broken into two halves. From the plot we will conclude that more the area occupied by load-displacement curve more is the toughness index. Different types of glass fibers like C-glass, E-glass, S-glass AR-glass etc. are manufactured having different properties and specific applications. Fibers used for structural reinforcement generally fall into E-glass, AR-glass and S-glass owing to alkali resistant. By far the E-glass is most used and least expensive. Principal advantages are low cost, high strength, easy and safe handling, and rapid and uniform dispersion facilitating homogeneous mixes which in term produce durable concrete. Limitations are poor abrasion resistance causing reduced usable strength, Poor adhesion to specific polymer matrix materials, and Poor adhesion in humid environments [7], [8]. The objective of present research is to mix design of SCC of grade M30 and to investigate the effect of inclusion of chopped carbon fiber on fresh properties and hardened properties of SCC. Fresh properties comprise flow ability, passing ability, and viscosity related segregation resistance [9]. Hardened properties to be studied are compressive strength, splitting tensile strength, flexural strength. Study of micro structures by SEM of SCC reinforced with different fibers at different ages [10]. 2. EXPERIMENTAL PROGRAMME 2.1. Materials Portland slag cement of Konark brand available in the local market was used in the present studies the physical properties of PSC obtained from the experimental investigation were confirmed to IS: [11]. The coarse aggregate used were 20 mm and 10 mm down size and collected from Quarry near Rourkela. Natural river sand has been collected from Koel River, Rourkela, Orissa and conforming to the Zone-III as per IS [12], [13]. Elkem Micro Silica 920D is used as Silica fume. Silica fume is among one of the most recent pozzolanic materials currently used in concrete whose addition to concrete mixtures results in lower porosity, permeability and bleeding because its fineness and pozzolanic reaction. The SikaViscoCrete Premier from Sika is super plasticizer and viscosity modifying editor@iaeme.com

3 Study on The Mechanical Properties and Microstructure of Chopped Carbon Fiber Reinforced Self Compacting Concrete admixture, used in the present study [14], [15]. Potable water conforming to IS: part 22 &23 [16] and IS was employed in the investigations [17]. Alkali resistant glass fiber having a modulus of elasticity of 72 GPA and 12mm length was used. Carbon fiber of length 12mm was used in the investigations. Fiber variety Length(mm) Density(g/cm 3 ) Table 1 Mechanical Properties of Carbon Fiber Elastic modulus(gpa) Tensile strength(mpa) Elong. at break(%) CARBON GLASS Figure 1 photograph of chopped carbon & glass fiber 2.2. Mixing and curing The mixing of materials was properly mixing in a power operated concrete mixer. Adding coarse aggregate, fine aggregates, cement and mixing it with silica fume were properly mixing in the concrete mixer in dry state for a few seconds. Then the water added and mixing it for three minutes[18]. During this time the air entraining agent and the water reducer are also added. Dormant period was 5mins. To obtain the glass fiber reinforced SCC, carbon fiber reinforced SCC the required fiber percentage was added to the already prepared design mix, satisfying the fresh SCC requirements. Fifty four numbers cubes( )mm, twenty seven numbers cylinders( )mm, fifty four numbers prisms( )mm were cast and investigations were conducted to study the mechanical behavior, fracture behavior, microstructure of plain SCC, glass fiber reinforced SCC(GFC), carbon fiber reinforced SCC(CFC). After casting was done the cubes were kept in room temp. For 24 hours then the moulds were removed and taken to the curing tank containing fresh potable water to cure the specimen for 7 days and 28days. Table 2 Adopted Mix Proportions of SCC Cement (kg/m 3 ) Silica fume(kg/m 3 ) Water(kg/m 3 ) FA (kg/m 3 ) CA (kg/m 3 ) SP (kg/m 3 ) editor@iaeme.com

4 Biswajit Jena and Asha Patel 2.3. Testing methods To determine the fresh properties of SCC, different methods were developed. Slump flow and V-Funnel tests have been proposed for testing the deformability and viscosity respectively. L-Box test have been propose for determine the segregation resistance. To determine the compressive strength[19], after the required curing period of the specimen. So in total fifty four numbers cubes were casted to measure the compressive strength after 7-days and 28-days. The size of the cube is as per the IS code To determine the split tensile strength, after the required curing period of the specimen. So in total twenty seven numbers cylinders were casted to measure the split tensile strength after 28-days. The flexural strength test was carried out on a prism specimen of dimension 100mm 100mm 500mm as per IS specification. So in total fifty four numbers prisms were cast to measure the flexural strength after 28-days. The test instrument consists of a means of producing and introducing a wave pulse into the concrete and a means of sensing the arrival of the pulse and accurately measuring the time taken by the pulse to travel through the concrete. The ductility can be measured by fracture behavior of FRSCC and to determine fracture energy, prisms specimen of dimension 100mm 100mm 500mm were cast with a notch of 5mm width (n0) and 30mm depth as per the specification for the specimen. The schematic diagram of specimen and loading arrangement of test setup shown in the Fig.2 & Fig. 3.During testing, Crack Mouth Opening Displacement (CMOD) were noted using through two dial gauges as shown in fig. To study the Microstructure of the mixes incorporated with different types of fibers SEM analysis were conducted in SEM lab of MM dept. of NIT ROURKELA. The study was done to determine the bond development and different period between different fibers and cement matrix. The sample was cured for 7 and 28 days. Figure 2 Schematic Diagram of Notched Prism Specimen (aₒ = 0.3D, nₒ 5mm, L 3.5D, D 4dₐ) Source: Japan Concrete Institute Standard (JCI-S ) Figure 3 Loading Arrangement for Fracture Test editor@iaeme.com

5 Study on The Mechanical Properties and Microstructure of Chopped Carbon Fiber Reinforced Self Compacting Concrete 3. RESULT AND DISCUSSION 3.1. Fresh properties of SCC The slump flow decreases with increase in fiber percentage. The decrease in flow value is observed maximum 63.88% for carbon fiber, 26.38% for glass fiber and %. This is because carbon fibers absorbed more water from the mix and beyond 0.2% fiber addition the mix did not satisfied the norms of self-compacting concrete. Glass fibers absorb lowest water. The T50 flow, which was measured in terms of time (seconds) increases as the slump flow value decreases. The decrease in slump value is due to the increase in the percentage of fiber which was explained in previous section. The maximum time taken to flow was observed at 0.1% for carbon fiber. The L-Box value increases as the slump flow value increases. The increase in slump value is due to the increase in the percentage of fiber as well as the L-Box value also increases. The maximum value obtained in the case of control mix but as per SCC specification 0.1% carbon fiber fulfill the requirements. The V-Funnel test & T50 flow, which was measured in terms of time (seconds) & both the value measured are dependent with each other. V-Funnel value and T5 flow increases as the slump flow value decreases. The decrease in slump value is due to the increase in the percentage of fiber. It was observed that at 0.1% of carbon fiber the SCC specification were satisfied. Table 3 Results of the Fresh Properties of Mixes sample Slump flow mm T 50 flow 2-5sec L-Box(H 2 /H 1 ) V-Funnel 6-12sec T5 Flow +3sec Remarks PSC GFC-1 Low viscosity (Result Satisfied) Result Satisfied GFC Result Satisfied GFC Result Satisfied CFC Result Satisfied CFC _ CFC _ Too high viscosity Blockage (RNS) Too high viscosity Blockage (RNS) 3.2. Compressive strength Compared with the plain SCC the compressive strength reinforced with glass fiber of volume fraction 0.15% increase by 1.76%. In this study the 7 days compressive strength of glass fiber shows no obvious improvement. Compared with the plain SCC the compressive strength reinforced with carbon fiber of 0.15% and 0.2% increase by 29.9% and 23.22% respectively. Compared with plain SCC, 0.15% of GFC and CFC increase 10.52% and 47.6% respectively. For 0.2% of GFC and CFC increase 15.21% and 35% respectively at 28 days compressive strength editor@iaeme.com

6 Biswajit Jena and Asha Patel (a) (b) Figure 2 (a) comparison of 7days compressive strength w.r.t fiber percentage (b) comparison of 28days compressive strength w.r.t fiber percentage Split tensile strength The percentage enhancement of split tensile strength for glass fiber over plain SCC is 17.31%, 20.73% when adding 0.15% & 0.2% respectively. The percentage enhancement of split tensile strength for carbon fiber over plain SCC is 27.56% & 10.24% respectively. Figure 3 comparison of 28days split tensile strength w.r.t fiber percentage 3.4. Flexural strength All FRSCC specimens show an increase in flexural strength with increase in fiber content. Compared with the plain SCC the enhanced percentage of the flexural strength of carbon FRSCC were observed in the range of 2.03% to 67.16% while 0.15% gave maximum strength. Increase in flexural strength was observed in ranges from 0.95% to 36.77% for GFC with the fiber percentage of 0.1% to 0.2%. Maximum flexural strength 12.32MPa was observed for carbon FRCCC for 1.5% of fiber percentage editor@iaeme.com

7 Study on The Mechanical Properties and Microstructure of Chopped Carbon Fiber Reinforced Self Compacting Concrete Figure 4 comparison of strength effectiveness of flexural strength w.r.t different fiber percentage Mixes Table 4 Hardened Concrete Properties of SCC and FRSCC 7-Day compressive strength (MPa) 28-days compressive strength (MPa) 28-days split tensile strength (MPa) 28-days flexural strength (MPa) PSC GFC GFC GFC CFC CFC CFC Load-CMOD behavior The load vs. crack mouth opening deflection diagrams obtained clearly proved that addition of fibers to SCC increase ductility whereas control beam PSC exhibited brittle behavior. The maximum increment was observed from carbon fiber than the basalt and the lowest from the glass fiber. In each series the mix which gave maximum compressive strength rendered maximum ductility. The area below the load deflection curve represents toughness. Almost same pattern of behavior were observed from all mixes. The observations made during the tests (LOAD-CMOD) were used to draw the LOAD-CMOD curves. The ultimate load and the fracture parameters were determined editor@iaeme.com

8 Biswajit Jena and Asha Patel (a) Figure 5 load-cmod curve for (a) carbon fiber reinforced SCC &(b) glass fiber reinforced SCC 3.6. Microstructure Behavior SEM test is the actual way to study the microstructure of the hydrated cement based products. To assessment the bond characteristics of GFC & CFC mix at 7 and 28days, the microstructure of FRSCC was studied by means of SEM. (b) (A) (B) Figure 6 SEM photographs for (A) 7-Days & (B) 28 days concrete & glass fiber matrix (A) (B) Figure 7 SEM photographs for (A) 7-Days & (B) 28 days concrete & carbon fiber matrix editor@iaeme.com

9 Study on The Mechanical Properties and Microstructure of Chopped Carbon Fiber Reinforced Self Compacting Concrete Fig. shows the photographs of microstructure of fiber surfaces and hydrated concrete matrix. It is observed from fig that glass and carbon fiber SCC surfaces covered with densely hydrated concrete matrix than GFC. 4. CONCLUSION Carbon fiber addition more than 2% made mix harsh which did not satisfy the aspects like slump value, T50 test etc. required for self-compacting concrete. Addition of fibers to self-compacting concrete improve mechanical properties like compressive strength,split tensile strength, flexural strength etc. of the mix. There was an optimum percentage of each type of fiber, provided maximum improvement in mechanical properties of SCC. Mix having 0.15% carbon fiber, 0.2% of glass fiber were observed to increase the mechanical properties to maximum. 0.15% addition of carbon fiber to SCC was observed to increase the 7-days compressive strength by 29.9%, 28-days compressive strength by 47.6%, split tensile strength by 27.56%, flexural strength by 67.16%. 2% addition of glass fiber to SCC was observed to increase the 7-days compressive strength by 1.76%, 28-days compressive strength by 15.21%, split tensile strength by 20.73%, flexural strength by 36.77%. The load vs. crack mouth opening displacement diagrams for FRSCC exhibited increase in fracture energy properties of the mixes. This is owing to crack arresting mechanism of the fibers in the matrix. In this regard the carbon fiber exhibited best performance, and then glass fiber. The SEM analysis of microstructure of FRSCC exhibited good physical bond between all types of fiber and the hydrated matrix. A dense structure of matrix was observed in each mixes owing to addition of silica fume. No apparent variation was observed between mix of 7days and 28 days. ACKNOWLEDGMENT The experimental work was conducted at Structural Engineering lab of Civil Engineering Department of NIT, Rourkela. The work involved mixing, casting and testing of standard specimens. REFERENCE [1] Ouchi M. And Okamura H. Mix-Design for Self-Compacting Concrete, Concrete Library of JSCE, No.25, June 1995(ND), pp [2] Ouchi M. And Okamura H. Effect of Super plasticizer On Fresh Concrete, Journal of Transportation Board, 1997, pp [3] Mustapha Abdulhadi, A comparative Study of Basalt and Polypropylene Fibers Reinforced Concrete on Compressive and Tensile Behavior, International Journal of Engineering Trends and Technology (IJETT) 9 (6)- March 2012 [4] M.g. Alberti, A. Enfedaque, J.C Galvez, On The Mechanical Properties & Fracture Behavior of Polyefin Fiber-Reinforced Self-Compacting Concrete, Construction & Building Material 55 (2014) [5] Chaohua Jiang, Ke Fan, Fei Wu, Da Chen, Experimental study on the mechanical properties and microstructure of chopped basalt fibre reinforced concrete, Materials and Design 58 (2014) editor@iaeme.com

10 Biswajit Jena and Asha Patel [6] M. Vijayanand, NicolaeAngelescu, K.U. Muthu, C.G. Puttappa& H. SudarsanaRao, Flexural Characteristics of Steel Fibre Reinforced Self Compacting Concrete Beams, The Scientific Bulletin of VALAHIA University MATERIALS and MECHANICS Nr. 5 (year 8) 2010 [7] Giri Prasad. G, SeshagiriRao. M.V and Rama Rao. G.V. Computation of Stress- Strain Behaviour of Self-Compacting Concrete in Higher Grade, International Journal of Scientific Computing, 3(2) July December pp [8] Cunha. V.M.C.F, Barros. J.A.O and Sena-Cruz. J.M, An Integrated Approach for Modelling the Tensile Behaviour of Steel Fibre Reinforced Self-Compacting Concrete, Cement and Concrete Research 41 (2011) pp [9] The European Guidelines for Self Compacting Concrete (Specification, Production and Use) May [10] SeshadriSekhar.T, Sravana. P and SrinivasaRao.P, Some Studies on the Permeability Behavior of Self Compacting Concrete, AKG Journal of Technology, 1(2) 2005 [11] IS: Code of Practice for portland slag cement [12] IS: Specification for Coarse and Fine Aggregate from Natural Sources for Concrete. [13] IS: Methods of tests for Aggregates for Concrete (All Parts) [14] IS: Specification for admixtures for concrete [15] Borsoi. A, Collepardi. M, Collepardi. S, Croce. E.N., Passuelo.A Influence of Viscosity Modifying Admixture on the Composition of SCC, Supplementary volume of Eighth CANMET/ACI International Conference on Superplasticizers and other Chemical Admixtures in Concrete, October 29 November 1, 2006, Sorrento, Italy pp [16] IS: part 22 &23 specification for potable water [17] IS code of practice for plain and reinforced concrete [18] Dharani.N, Ashwini.A, Pavitha.G And Princearulraj.G, Experimental Investigation on Mechanical Properties of Recron 3s Fiber Reinforced Hyposludge Concrete, International Journal of Civil Engineering and Technology, 4(1), 2014, pp [19] Maher A. Adam Mohamed Said and Tamer. M. Elrakib, Shear Performance of Fiber Reinforced Self Compacting Concrete Deep Beams, International Journal of Civil Engineering and Technology, 7(1), 2016, pp [20] N. Krishna Murthy, A.V. Narasimha Rao And I.V.Ramana Reddy, Comparison Of Cost Analysis Between Self Compacting Concrete And Normal Vibrated Concrete, International Journal of Civil Engineering and Technology, 5(7), 2016, pp [21] AnirwanSenguptha and Manu Santhanam Application Based Mix Proportioning for Self Compacting Concrete, 31 st Conference On Our World in Concrete 85 Structures, Singapore, August 16 17, 2006, pp [22] IS: Methods of Test for Strength of Concrete editor@iaeme.com