Comparison of Normal Compacted Concrete and Self Compacted Concrete in Shear & Torsion

Size: px

Start display at page:

Download "Comparison of Normal Compacted Concrete and Self Compacted Concrete in Shear & Torsion"

Julia Chase
6 years ago
Views:

1 Comparison of Normal Compacted Concrete and Self Compacted Concrete in Shear & Torsion Prof. Kishor S. Sable, Prof. Madhuri K. Rathi Abstract-- Self-compacting concrete (SCC) offers several economic and technical benefits; the use of steel fibers extends its possibilities. Since fly ash is not highly reactive, the heat of hydration can be reduced through replacement of part of cement with fly ash. Therefore, a research work was performed to compare the mechanical properties like shear and torsion strength of SCC and NCC with and without fibres with different aspect ratio. A comparison is made between NCC and SCC; in SCC, a marginal improvement in all properties is observed. Results indicate that with optimum volume fraction i.e. 5%, concrete with type steel fibre giving better performance in terms of strength compare to all other type of fibres and both type of concrete. Index Terms Self-compacting concrete, fibre reinforcement, fly ash, workability, strength, aspect ratio I. INTRODUCTION Concrete is life form old over 1 years. It is assorted, located into form and then compacted. It is essential to condense the concrete so that it should completely cover up the reinforcement and fill all the space in the form for meeting strength and durability constraint. The air entrained in concrete during amalgamation has to be totally expelled out for getting uniform dense mass. If compaction is not complete, it will lead to thrashing in strength and also affect performance of the structure. The compaction becomes complex when percentage of reinforcement is high which does not allow insertion of vibrator at some places. Also the vibration increases noise level in and around construction site. Self-compacting concrete was therefore developed to overcome the problems mentioned above. Self compacting concrete is defined as a concrete which is capable of self consolidating without any external efforts like vibration, floating, poking etc. The mix is therefore required to have ability of passing, ability of filling and ability of being stable. Concrete is heterogeneous material and the ingredients having various specific gravity values and hence it is difficult to keep them in cohesive form. This is principally true when the consistency is too high. The material having higher specific gravity would like to settle down which makes the mix no more a concrete and it becomes system of sediment layers of concrete ingredients. To overcome this, one can add more amounts of fines and use super-plasticizers. Superplasticisers reduce water demand and at the same time increase fluidity. However, there is a probability of bleeding and mix may become adhesive. To overcome this problem viscosity-modifying agent (VMA) is required to be added. VMA is a pseudo plastic agent, which thickens the water and keeps the mixture under suspension, providing segregation resistance. The principle of sedimentation velocity is inversely proportional to the viscosity of the floating medium is applied in the system. The VMA offers high shear resistance to the ingredients at rest and less shear resistance at movement and this property keeps the coarser particles under suspension in self-compacting concrete. The intrinsic insufficiency of SCC as any other type of concrete is to defend against tension. In basic concrete the crack appears as soon as principal stresses increases the tensile strength of concrete and after the first crack immediately the collapse occurs. The inherent weakness of concrete to resist tension can be overcome to some extent by mixing the steel fibres in concrete. So fibre reinforced concrete is an alternative to traditional stirrup reinforcement which leading to lowered labour costs. To be able to access mechanical properties of the fibre reinforced concrete, knowledge of final spread and directions of fibres is necessary. Fly ash has high reactivity and low price as compared to silica fume and fly ash as it is a manufactured product. It reduces free drying shrinkage and restrains the shrinkage cracking width. It also helps in enhancing the compressive strength and durability of concrete. The objective of this study is to compare the mechanical properties like shear strength, torsion strength and moment of self compacted concrete (SCC) with normal compacted concrete with and without different types of fibre having different aspect ratio in addition to the 30% fly ash by the weight of cement. 74

2 II. METHODOLOGY The present research work is experimental and requires preliminary investigations in a methodological manner. A. Cement The cement used in this experimental work is Ultratech 53 grade Ordinary Portland Cement. All properties of cement are tested by referring IS Specification for 53 Grade Ordinary Portland cement. The specific gravity of the cement was 15. The initial and final setting times were found as 74minutes and 385 minutes respectively. Standard consistency of cement was 30%. B. Fine aggregate Locally available Pravra river sand passed through 4.75mm IS sieve was used. The specific gravity 75 and fineness modulus of 6 were used as fine aggregate. The loose and compacted bulk density values of sand are 1600 and 1688 kg/m3 respectively, the water absorption of 1.1%. C. Coarse aggregate Crushed granite aggregate available from local sources has been used. The coarse aggregates with a maximum size of 12mm having the specific gravity value of 70 and fineness modulus of were used as coarse aggregate. The loose and compacted bulk density values of coarse aggregates are 1437 and 1526 kg/m3 respectively, the water absorption of 0.4%. D. Fly ash Fly Ash (FLA) is available in dry powder form and is procured from Dirk India Pvt. Ltd., Nasik. It is available in 30Kg bags, colour of which is light gray under the product name "Pozzocrete 60". There are no standard performance tests and procedures specified for assessing the suitability of MAs to FAC. The Fly ash produced by the company satisfies all the requirements of the IS 3812: 1981, BS 3892: Part I: E. Chemical admixtures A polycarboxylic type superplasticizer (SP) was used in all concrete mixtures. In addition to the SP, a viscosity modifying admixture (VMA) was also used. The properties of both admixtures, as provided by their manufacturers, are shown in Table I. Table I: Properties of chemical admixture Chemical admixture Dosage Main component SP 1% Polycarboxylic ether VMA 0.5% Aqueous dispersion of microscopic silica F. s The main variables used in the study are three different types of steel fibres i.e. hook ended steel fibre (), crimped type steel fibre(cr), straight type steel fibre() 75 with two values of aspect ratios ( and ). 5 % constant dosages of fibres are used by weight of cement. G. Mix Design for M-30 Grade Conventional Concrete Cement: Fly Ash: Sand : C. A. : Water 1 : 0.3 : 1.06 : 00 : 0.38 H. Mix Design for M-30 Grade Self Compacting Concrete Cement: Fly Ash: Sand : C.A. : Water 1 : 0.3 : : 1.48 : I. Testing on Fresh Concrete: Test conducted for verifying the flow characteristics of fresh concrete are Slump flow V-Funnel L Box J Ring Table II: Requirements of Workability Tests Method Unit Typical Ranges of Values Min. Max. 1. Slump flow by Abrams cone mm 6 0 T cm Slump flow Sec 2 5 J-ring mm V-funnel sec V-funnel at T5 minutes sec L-box H2/H The Table II show requirements of workability tests are to be fulfilled at the time of placing of concrete. The experimental investigation consist of casting and testing steel fibre reinforced self compacted concrete and normal concrete beams under combined effect of shear and torsional loading. The size of each beam is 100 mm x 1 mm x 1000 mm. The volume fraction of the fibre content is constant of 5 % weight of cement. The proportioning of concrete is maintained constant throughout the investigation. A concrete mix targeting a compressive strength of 30 MPa is used. The cured beams are white washed a day before testing to facilitate the crack identification. One end of the beam is supported on rollers, while the other end is supported on rigid support. This type of test setup Facilitates free rotation of roller end and provides stability to the test specimen during testing. Specially made twist arms or twist angles are placed at both supports of the beam having an arm length of 0.60 m. Load on the twist arm is applied through a hydraulic jack and the loading is monitored through a proving ring attached to the jack. Absolute care has taken such that the plane of loading and twisting arm perpendicular to the longitudinal axis of the beam.

3 This avoids any possibility of bending of the beam instead of twisting and as a result the beam between the two supports is subjected to pure torsion. The complete test setup is schematically presented in Fig 1. It shows the actual test set up in 3D view. Load is applied at an eccentricity of 0.66 m from the centre of the beam. For every applied load, the corresponding dial gauge readings are noted. Which were placed at L/3 distance from both end and considering average of two readings. For 10 divisions of proving ring that is 0.01 readings the multiplying factor is 769 Kg and Weight of jack is Kg. Hence the shear strength, experimental moment and torsional moment of beam are calculated by the following formulas, Shear force in kn = (Proving ring reading ) 100 [1] Experimental moment= liver arm of triangle shear force [2] (T) = GƟJ/L [3] Where, G = Modulus of rigidity in N/mm 2 Ɵ = Angle of twist in radian J = Polar moment of inertia in mm 4 L = Span of beam in mm As per guidelines of EFNARC, for slump flow by Abrams cone typical range of value is 6 to 0 mm, for T cm slump flow, range is 2 to 5 Sec and for v-funnel, range is 8 to 12 Sec. Hence from above observation the dose of superplastisizer is taken as 1% of volume of cement which satisfies the requirement of flow for SCC. B. Fresh Concrete Test Results of Self Compacting Concrete Table IV: Slump Cone Test by Abrams Cone Steel Slump Flow by Abrams Cone T - Horizontal Time Slump (Sec.) / / / / CR / Steel Table V: V-Funnel Test V-Funnel Test Flow Time (Sec.) Flow time at T5minutes (Sec.) / / III. Fig.1: 3D- View of Test Setup RESULT AND DISCUSSIONS To satisfy flow requirement of SCC very first step is to determine the optimum dose of superplastisizer. A. Trials for Optimum Dose of Superplastisizer Table III: Trials for Optimum Dose of Superplastisizer Slump Cone Test V Funnel Test Horizontal T - Flow Slump Time Time (Sec.) (Sec.) Dose of Superplastisizer 1% % % % / / CR / Steel Table VI: L-Box Test L Box Test T20 T40 Time Time (Sec) (Sec) H 2/H / / / / CR. /

4 ISSN Steel Table VII: U Box Test U Box Test H 1 H 2 H 2 -H / / / / 6. CR / Table VIII: J Ring Test J Ring Test Steel H 1 H 2 H 1 -H / / / / CR / From the results of above tests carried out for the flow of fibre concrete, it shows that the /130 (aspect ratio=) not satisfying the requirement of V-funnel test. Also all types of mixes are not satisfying the requirement of V-funnel test at T5 min. C. Test Results for Shear and Torsion Test: Table IX: Shear Strength on Beam of Normal Concrete at the End of 28 Days Type Deflection Shear Shear of at Crack Force Force (kn) (kn) % CF Table X: Shear Strength on Beam of SCC at the End of 28 Days Type Deflection Shear Shear of at Crack Force Force (kn) (kn) % CF Graph 1: Comparative Chart of Shear Strength at the End of 28 Days It can be seen from Graph 1, For NCC as well as SCC; shear strength of is higher than all types of fibre. Shear strength of SCC with and without fibre is more than shear strength of NCC with and without fibre. For SCC and NCC, maximum percentage increase in strength is 51.56% and 502% respectively. It is observable that shear strength of SCC is somewhat more than shear strength of NCC in each case. Table XI: Calculation for Normal Concrete at the End of 28 Days Type of 1. 0% 4. Deflection at Crack

5 Table XII: Calculation for SCC at the End of 28 Days Type Deflection of at Crack % % CF NCC SCC Graph 2: Comparative Chart of at the End of 28 Days From Graph 2, it is observed that the moment of RFC beam is greater for beam for both NCC and SCC. The higher moment is due to reason that the steel fibres resisting the load. From the observations and graphs it is seen that the steel fiber beam having maximum moment compare to beam without fibre. Average increasing in moment for SCC and NCC beam is 51.24% and 520% respectively. In all cases, moment of SCC is greater to some extent than moment of NCC. No Table XIII: Torsion Strength on beam of Normal Concrete at the End of 28 Days Type Deflection Proving of at Crack Ring Reading 1. 0% Table XIX: Torsion Strength on beam of SCC at the End of 28 Days Type Deflection of at Crack %

6 ISSN % CF NCC SCC Graph 3: Comparative Chart of at the End of 28 Days From Graph 3, for both NCC and SCC, the results are obvious that the torsional moment of fibre concrete is higher than the concrete without fibre. In this case also fibre giving higher strength as compare to the strength of concrete mix with other type of fibres. Average increasing in torsional moment for SCC and NCC beam is 41.02% and 37.27% respectively. From above graph, it is clear that in every case average torque of SCC is faintly more than NCC. IV. CONCLUSION The present investigation has shown that it is possible to design a steel fibre reinforced self-compacting concrete incorporating fly ash. The RSCCs have a slump flow in the range of mm, a flow time ranging from 89 to 5 sec, V-funnel flow in the ranging from 7.2 to 159 sec and 9.02 to sec at T5minutes, a L-Box ratio ranging from to and a J-Ring test value ranging from 2 to 7 mm. It was observed that it is possible to achieve self compaction with different types of steel fibre with different aspect ratio. Although results obtained from all of the mixes satisfy the lower and upper limits suggested by EFNARC (The European Federation of Specialist Construction Chemicals and Concrete Systems), all mixes had good flow ability and possessed self-compaction characteristics. The SCC developed shear strengths ranging from 56 to 7.29 kn at the end of 28 days and the NCC developed shear strengths ranging from 11 to 6.62 kn at the end of 28 days. The SCC developed moment strengths ranging from 35 to 4.82 knm at the end of 28 days and the NCC developed moment strengths ranging from 05 to 4.38 knm at the end of 28 days. The SCC developed torsional strengths ranging from 20. to knm at the end of 28 days and the NCC developed torsional strengths ranging from to knm at the end of 28 days. Also it is observed that for same aspect ratio the hook ended fibre showing pronounce improvement in all properties of concrete as compare crimped & straight fibre. There is decrease in the strength with decrease in aspect ratio of same fibre type. The straight fibres having less strength as compared with hook end and crimped fibres because of their shape. Due to the shape, it is obvious that the hook end and crimped fibre having good bond and anchorage in the matrix resulting in more strength. In all above cases, the strength of SCC is higher than NCC because of addition of superplastisizer in SCC to maintain flowability gives proper compaction of concrete which enhance all properties of SCC. Also the addition of fly ash in SCC improves microstructure of concrete that also helpful to enhance all mechanical properties with the durability of concrete. Use of fly ash reduces the consumption of cement due to which CO 2 emulsion in manufacturing process is also reduced. By adding fly ash the disposal problem is neglected which reduces air pollution and land pollution. REFERENCES [1]. EFNARC Specifications and Guidelines for Self Compacting Concrete February200 [2]. Hajime Okamura and Masahiro Ouchi Self-Compacting Concrete" Journal of advanced concrete Technology, Volume 1, November 2002, Pages [3]. IS , Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards. [4]. IS 3812 (Part 1) : 2003, Pulverized Fuel Ash Specification, For Use As Pozzolana On Cement, Cement Mortar And Concrete [5]. Joaquim A.O.B., Lucio A.P., Varma R.K. and Delfina M.F., Cost Competitive Steel Reinforced SCC for Structural Applications, The Indian Concrete Journal published by ACC limited, Vol.83, 8, August 2009, pp [6]. Mattur C. Narasimhan, Gopinatha Nayak, Shridhar K.C., Strength and Durability of High-Volume Fly-ash Self-compacting Concrete, ICI Journal, January-March 2009, pp [7]. Mansur, M.A., and Lim, T.Y. "Torsional behavior of reinforced concrete beams", The international journal of Cement Composites and Lightweight Concrete. vol.7, 4. November pp [8]. Narayanan, R., and Kareem Palanjian, A.S. Steel fibre reinforced concrete beams in pure torsion. The international Journal of Cement Composites and Lightweight Concrete. vol.5, 4. November 198 pp [9]. Sable K.S, Mehetre A. J and Kandekar S. B," Performance of concrete beams under shear and torsion with fly ash and steel fibres",' Elixir Cement & Con. Com', Vol.41,2011, pp [10]. Sable K.S, Suryawanshi Y. R. and Mehetre A. J," Behavior of Concrete in Shear and Torsion with Different Types of Steel Using Constant Volume Fractions and Different ", 'Civil Engineering Portal', 201 [11]. Subramania B. V., Ramasamy J.V., Ragupathy R. and Seenivasan, Workability and Strength Study of High Volume Fly Ash Self Compacting Concrete The Indian Concrete Journal published by ACC limited, March 2009, pp AUTHOR S PROFILE: Prof. Kishor S. Sable, Civil Engg. Dept, Amrutvahini college of Engg ( -shivasonu@rediffmail.com) Dist-Ahmednagar, Maharastra, India. Mobile No Prof. Madhuri K. Rathi, Civil Engg Dept, Amrutvahini college of Engg ( -madhurirathi25@gmail.com) Dist-Ahmednagar, Maharastra, India.Mobile No

STUDY ON PROPERTIES OF SELF- CONSOLIDATING CONCRETE WITH FLY ASH AND SILICA FUME

STUDY ON PROPERTIES OF SELF- CONSOLIDATING CONCRETE WITH FLY ASH AND SILICA FUME A.Deepika 1, Dr S.Krishnamoorthi 2, G.S.Rampradheep 3 P.G. Student, Department of Civil Engineering, Kongu Engineering College,