Fibrous Triple Blended Concrete Composites Study of Strength Properties

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1 Fibrous Triple Blended Concrete Composites Study of Strength Properties Arfath Khan Md 1, Abdul Wahab 2, B. Dean Kumar 3 1 Asst Prof, CED, NITS, 2 Asst Prof, CED, NSAKCET, 3 Assoc Prof, CED, JNTUHCEH. Abstract- Requirements for high strength and better performance of concrete are leading the researchers for developing better structural concrete. concrete is made by using supplementary cementitious materials like fly ash, silica fume, metakaolin, nanosilica and other materials using various reinforcing materials like different type of fibers for achieving better performance of concrete than the normal concrete. In the present experimental investigation, high strength concretes of M60 & M80 are tried using triple blended technique with ternary blend of condensed silica fume (CSF) and metakaolin(mk) as partial replacement by weight of cement at various blended percentages ranging between 5% to 15%.Steel fibers having aspect ratio of 50 are also used. The various proportions of steel fibers are added at 0.5%, 0.75%, 1.0%, 1.25% and 1.5% as total fiber percentages of the volume of concrete. The optimum replacement of cement by metakaolin and condensed silica fume from which maximum benefit in strengths and workability can be obtained has been studied. The results of fiber reinforced specimens with various percentages of ternary blending are compared with control specimens to study the behavior of FRC properties. It is concluded that specimens with total fiber content of 1.5% showed better strength in all proportions and blend proportion of 10% condensed silica fume and 5% metakaolin showed maximum strength in compression, tension and flexure. Keywords - Nana Silica, Met kaolin, Fly ash, Silica Fume, Compressive Strength. I. INTRODUCTION Concrete is one of the versatile heterogeneous materials, civil engineering has ever known. High strength concrete is used extensively throughout the world. Oil, gas, nuclear and power industries are among the major uses. Mineral admixtures such as silica fume, metakaolin and ground granulated blast furnace slag are used in concrete to increase the strength and durability. The addition of admixtures to the concrete mixture increases the strength by pozzolanic action and by filling in the small voids that are created between cement particles. Metakaolin is the pozzolanic material which is mainly derived from a clay mineral kaolinite and it is calcined at higher temperatures and so it s named as metakaolin. A further advantage of pozzolonas is their lower environmental impact, when compared to OPC, due to lower energy consumption during production and CO 2 absorption by carbonation. The addition of metakaolin and CSF to mortars and concretes also has a positive effect in terms of durability. Calcium hydroxide accounts for up to 25% of the hydrated Portland cement, and calcium hydroxide does not contribute to the concrete s strength or durability. Pozzolonic admixtures combine with calcium hydroxide to produce additional cementing compounds, the material responsible for holding concrete together. Less calcium hydroxide and more cementing compounds means stronger concrete. Metakaolin and CSF because they are very fine and highly reactive by nature, give fresh concrete a creamy, non-sticky texture that makes finishing easier. Condensed silica fume is very fine pozzolanic material composed of amorphous silica produced by electric arc furnaces as a byproduct of the production of elemental silica or ferro-silicon alloys. High-purity quartz is heated to 2000 o c with coal, coke or wood chips as fuel and an electric arc introduced to separate out the material. As the quartz is reduced it releases silicon oxide vapour. This mixes with oxygen in the upper parts of the furnace where it oxidizes and condenses into micro spheres of amorphous silicon dioxide. II. LITERATURE REVIEW Balendran R.V et al (2) concluded that addition of pulverized fuel ash and Mk has been found to improve the fire performance of HPC both in terms of residual strength and durability. Malvin Sandvik et al (11) concluded that at a partial replacement of cement by 20% CSF, the compressive strength at 28 and 90 days was increased by 43 and 55%, respectively with respect to the strength at 7 days. Sabir B.B et al (13) reviewed the work done on the use of Mk as a partial pozzolanic replacement for Portland cement (PC) in mortar and concrete. Wild et al (14) also showed that increasing the specific surface of Mk reduced the age at which maximum strength occurs but did not influence the long term (90 day) strength. Curio et al (5) tested mortars at 15% replacement of PC with Mk and SF. 541

2 They found that superplasticized mortars gave compressive strengths similar to, and in some cases, greater than SF mixtures. Kostuch et al (10) found that Mk is effective at reducing the rate of diffusion of Cl- and Na+ ions in mortar and in reducing the rate of water absorption. Caldarone et al (4)produced concretes with 5% and 10% Mk that exhibited slightly greater strengths than concretes containing the same levels of SF. Sabir et al (12) concluded that the optimum Mk replacement was10% at 20 o C with water-binder ratio of Brooks et al (3) showed that increasing pozzolan levels increased setting time for for Mk this was observed up to a 10% replacement level. A. Materials III. EXPERIMENTAL INVESTIGATION Cement: Locally available Ordinary Portland Cement of 53 grade confirming to IS standards has been procured. Metakaolin: The Metakaolin is obtained from the 20 Microns limited Company at Vadodara in Gujarat by the brand name Metacem 85 C. The specific gravity of Metakaolin is 2.5. The Metakaolin is in conformity with the general requirements of pozzolana (1, 7, 8,9). Condensed silica fume: Condensed Silica fume powder is normally grey in color but this can vary according to the source. It is obtained from M/s. V.B.C. Ferro Alloys Ltd., Hyderabad. Fine aggregate: The locally available natural river sand conforming to grading zone-ii has been used as fine aggregate. Tests have been carried out as per the standard procedures. Coarse aggregate: Machine crushed granite confirming to I.S. code (6) consisting of 20 mm maximum size of aggregates has been obtained from the local quarry. Water: Potable water has been used in this experimental program for mixing and curing. Super plasticizer: The super plasticizer of standard brand was used in this research work. B. Triple Blending mixes: In the present investigation, triple blending cement concrete mixes have been tried for various strength properties. Mineral admixtures like CSF & Mk have been employed along with cement and triple blended cement concrete mixes are prepared. The respective percentages of CSF & Mk have been varied from 0% to 15% as replacement of cement. Steel fibers of 1mm diameter and 50mm length with an aspect ratio of 50 have been tried along with above mixes. The fiber % has been varied from 0 to a maximum of 1.5% In the present investigation M60 and M80 grades have been considered. The mixes were designed by the DOE method. The specimens are tested for Compressive strength test, Split tensile strength test and Flexural strength test. C. Mixing, Casting, Curing and Testing All the triple blended composites were mixed in the pan mixer. Required number of specimens for various combinations were cast. Continuous curing was maintained upto the age of 28 days. Mixing, casting, curing and testing were carried out as per the standard specifications. IV. RESULTS AND DISCUSSIONS In the present experimental investigation of triple blended cement concrete mixes, cement is replaced by condensed silica fume and metakaolin with different percentages from 0 to 15%. Steel fibers from 0 to 1.5% are also varied along with above. Cubes, cylinders and prisms were cast with M60 and M80 grade concrete design mixes. The results can be discussed under the following heads. Figs. 1 and 2 are plotted for compressive strength of M80 concrete for 0% and 1.5% of fibres. Similarly figs. 3 and 4 for tensile strength and 5 and 6 for flexural strength are plotted for the two fibre percentages. i. Workability: With water cement ratio of 0.33 and with an addition of maximum 2% superplasticizer the M60 concrete mixes with blended admixtures of condensed silica fume and metakaolin were found to have a compaction factor of 0.89 to 0.76.The tests showed decreased values of slump and compaction factor with increase in total percentage of blended admixtures of CSF and Mk. With total steel fibre percent of 0.5, 1.0 and 1.5 and 1.5 super plasticizer in the M60 concrete mix with blended admixtures of 10% CSF and 5% Mk and for the same water cement ratio the workability is found to be nearly 0.86 to Hence in the triple blended cement concrete mixes with steel fibers somewhat high dosages of super plasticizers are necessary to maintain workability at medium level. ii. Compressive Strength: It has been observed (figs. 1 and 2) that with the addition of Silica fume and Metakaolin, the strength of concrete at the age of 28 days has increased with various proportions of the mix. The increase in strength is in the range of 2.01% % for M60 and 2% % for M

3 On analysing the tested specimens it is observed that the bonding between the concrete materials is of very high quality. The combination of blended admixtures of 10% CSF and 5% Mk by partial replacement by weight of cement has showed high increase in strength by 20.94% & 10.36% when compared to base reference mix. The Blended mix proportions beyond this combination of 10% CSF and 5% Mk showed decreasing trend in compressive strength showing minimum strength of 87.0 N/mm 2, at a combination of 10% CSF and 15% Mk in the M80 concrete mix but still exhibited higher strength and an increase of 3.67% than the base reference mix without any admixtures Fig 1: Compressive strength of triple blended concrete mix (M80) at 0% steel fibers The same trend is observed with steel fibres in the M80 Concrete mix with various combinations of blended percentages of CSF and Mk. It is found that the M80 mix concrete with total steel fibre percentage of 1.5 and admixture percentages of 10% CSF and 5% Mk showed maximum increase in strength of 27.41% when compared to base reference mix without admixture and fibre and other specimens with total fibre percentages of 0.5, 0.75, 1.0 and 1.25 also exhibited higher strengths when compared to base reference mix. Fig. 2: Compressive strength of triple blended concrete mix (M80) at 1.5% steel fibers In the case of blended CSF and Mk at higher percentage of replacement by weight of cement, the strength has decreased when compared to mixes with lower replacement. 15% is focused to be optimum with both the admixtures. Out of all the blended cements tried in the investigation mixture of 10%CSF and 5%Mk with cement is found to give the highest compressive strength. In the case of M80 mix the increase is 10.37% and is same in both the high strength mixes considered. Among the fibres percentages, 1.5% is found to give the highest compressive strength among all the fibrous mixes. Compared to the same mix without fibres the strength increase is nearly 17% and compare to base mix it is 27.38%.It is clear from the above discussions that the blended mixes are giving higher compressive strength compared to the base mix even without fibres. iii. Split Tensile Strength: It has been observed (figs. 3 & 4) that with the addition of Silica fume and Metakaolin, the strength of concrete at the age of 28 days has increased with various proportions of the mix. The increase in strength is in the range of 1.88% % for M60 and 16.75% % for M80. On analysing the tested specimens it is observed that the bonding between the concrete materials is of very high quality. The combination of blended admixtures of 10% CSF and 5% Mk by partial replacement by weight of cement has showed high increase in strength by 18.16% & % respectively when compared to the base reference mix. 543

4 The blended mix proportions beyond this combination of 10% CSF and 5% Mk showed decreasing trend in compressive strength showing minimum strength of 7.96 N/mm 2, at a combination of 10% CSF and 15% Mk in the M80 concrete mix, but still exhibited higher strength and an increase of 38.92% than the base reference mix without any admixtures Fig. 3: Split Tensile strength of triple blended concrete mix (M80) at 0% steel fibers The same trend is observed with steel fibers in the M80 Concrete mix with various combinations of blended percentages of CSF and Mk. It is found that the M80 mix concrete with total steel fibre percentage of 1.5 and admixture percentages of 10% CSF and 5% Mk showed maximum increase in strength of % when compared to base reference mix without admixture and fibre. Other specimens with total fiber percentages of 0.5, 0.75, 1.0 and 1.25 also exhibited higher strengths when compared to the base reference mix. In the case of blended CSF and Mk at higher percentage of replacement by weight of cement, the strength has decreased when compared to mixes with lower replacement. 15% is found to be optimum with both the admixtures. 20 Out of all the blended cements tried in the investigation mixture of 10%CSF and 5%Mk tried as replacement to cement is found to give the highest split tensile strength. In the case of M80 mix the increase is % and is same in both the high strength mixes considered. Among the fibres percentages, 1.5% is found to give the highest split tensile strength among all the fibrous mixes. Compared to the same mix without fibres the strength increase is nearly 96% and compared to base mix it is %. It is clear from the above discussions that the blended mixes are giving higher split tensile strength compared to the base mix even without fibres. iv. Flexural Strength: It has been observed (figs.5 and 6) that with the addition of Silica fume and Metakaolin, the strength of concrete at the age of 28 days has increased with various proportions of the mix. The increase in strength is in the range of 2.09% % for M60 and 18.21% % for M80. On analysing the tested specimens it is observed that the bonding between the concrete materials is of very high quality. The combination of blended admixtures of 10% CSF and 5% Mk by partial replacement by weight of cement has showed high increase in strength by 18.81% & 66.16% respectively when compared to the base reference mix Fig. 4: Split Tensile strength of triple blended concrete mix (M80) at 1.5% steel fibers Fig.5: Flexural strength of triple blended concrete mix (M80) at 28 days curing period for different %CSF with different % MK and 0% steel fibers. The Blended mix proportions beyond this combination of 10% CSF and 5% Mk showed decreasing trend in flexural strength showing minimum strength of 9.83 N/mm 2, at a combination of 10% CSF and 15% Mk in the M80 concrete mix but still exhibited higher strength and an increase of 34.65% than the base reference mix without any admixtures. 544

5 The same trend is observed with steel fibers in the M80 Concrete mix with various combinations of blended percentages of CSF and Mk. It is found that the M80 mix concrete with total steel fiber percentage of 1.5 and admixture percentages of 10% CSF and 5% Mk showed maximum increase in strength of % when compared to base reference mix without admixture and fiber and other specimens with total fiber percentages of 0.5, 0.75, 1.0 and 1.25 also exhibited higher strengths when compared to the base reference mix. In the case of blended CSF and Mk at higher percentages of replacement by weight of cement, the strength has decreased when compared to mixes with lower replacement. 15% is found to be optimum with both the admixtures. Out of all the blended cements tried in the investigation, mixture of 10%CSF and 5%Mk with cement is found to give the highest flexural strength. In the case of M80 mix the increase is 66.16% and is same in both the high strength mixes considered. Among the fibres percentages, 1.5% is found to give the highest flexural strength among all the fibrous mixes. Compare to the same mix without fibres the strength increase is nearly 98% and compared to base mix it is %. It is clear from the above discussions that the blended mixes are giving higher flexural strength compared to the base mix even without fibres %Condensed silica fume 5%Condensed silica fume 10%Condense d silica fume 15%Condense d silica fume Fig.6: Compressive strength of triple blended concrete mix (M80) at 28 days curing period for different %MK with different %CSF and 1.5% steel fibers. V. CONCLUSIONS Based on the experimental study undertaken the following conclusions are drawn. 1. An effective and efficient triple blended concrete mix can be prepared with the addition of condensed silica fume and Metakaolin to OPC. This triple blended mix is not only cost effective also it renders the concrete to achieve several beneficial properties. 2. When the mineral admixtures like silica fume or Metakaolin are added at higher percentages to cement, the workability of concrete is getting reduced. There is a need to add superplasticizer to maintain constant medium workability. 3. In the case of triple blended concrete 10% CSF & 5% Mk gives highest strength without fibre reinforcement 4. As the total percent of fibre is increased the compressive strength is also increasing. 5. The highest compressive strength for fibre mixes is obtained with 10% CSF & 5% Mk and 1.5% steel fibre. 6. Split tensile strength is more in the case of triple blended concrete. Highest tensile strength is obtained with 10% CSF and 5% Mk and 1.5% steel fibre. 7. Flexural strengths are also higher for triple blended concretes with various combinations, these values are further increased with addition of fibres. 8. Without fibres for a combination of 10% CSF and 5% Mk the flexural strength is higher than the reference. For other combinations the increase is in between. 9. The highest flexural strength with 10% CSF 5% Mk and 1.5% fibre is high by nearly % than that of reference mix. 10. On the basis of the present experimental study it is finally concluded that optimum concrete mixes can be obtained by carrying out triple blending with Condensed silica fume and Metakaolin. These mixes posses not only higher strength but also many other beneficial properties like better durability, better crack resistance, low permeability, cost effectiveness etc. Triple blended concrete mixes are quite suitable for high performance concrete(hpc). Use of fibres along with triple blending enhances to a larger extant the split tensile and the flexural strengths also. REFERENCES [1 ] ACI 234R-06 Guide for the use of Silica Fume in Concrete. American Concrete Institute. [2 ] Balendran R.V, Rana T.M., Maqsood T, Tang W.C., "Strength and durability performance of HPC incorporating pozzolans at elevated temperatures", Structural Survey, Vol. 20,2002, pp [3 ] Brooks J.J. et al Effect of admixtures on the setting times of highstrength concrete Cement Concrete Compos, vol 22, 2000, pp

6 [4 ] Caldarone M.A. et al High reactivity metakaolin: a new generation mineral admixture. Concrete Int, vol.34, November 1994, pp: [5 ] Curcio F. et al Metakaolin as a pozzolanic microfiller for highperformance mortars. [6 ] I.S , Specification for coarse and fine aggregate from natural sources for concrete. BIS. [7 ] I.S India standard specification for pozzolanas BIS. [8 ] I.S , Specification for admixtures for concrete. BIS. [9 ] I.S. 7869(part 2)-1981: Indian standard specification for admixtures for concrete, BIS. [10 ] Kostuch J.A. et al High performance concrete incorporating metakaolin - a review, Concrete University of Dundee, September 1993, pp: [11 ] Malvin Sandvik and Odd Gjorv E, Effect of Condensed Silica Fume on the Strength Development of Concrete, special publications, vol.93, feb1986. [12 ] Sabir BB. The effects of curing temperature and water/binder ratio on the strength of metakaolin concrete. In: Sixth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Supplementary volume. Bangkok, Thailand; pp [13 ] Sabir B.B, Wild S, Bai J, Metakaolin and calcined clays as pozzolans for concrete: a review Cement and Concrete Composites, Volume 23, Issue 6, December 2001, Pages