AN EXPERIMENTAL INVESTIGATION ON GLASS FIBRE REINFORCED HIGH PERFORMANCE CONCRETE WITH SILICAFUME AS ADMIXTURE

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1 AN EXPERIMENTAL INVESTIGATION ON GLASS FIBRE REINFORCED HIGH PERFORMANCE CONCRETE WITH SILICAFUME AS ADMIXTURE Vaishali G Ghorpade*, J.N.T.U.College of Engineering, India 35 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2010, 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 35 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2010, Singapore AN EXPERIMENTAL INVESTIGATION ON GLASS FIBRE REINFORCED HIGH PERFORMANCE CONCRETE WITH SILICAFUME AS ADMIXTURE Vaishali G Ghorpade*, J.N.T.U.College of Engineering, India Abstract High performance concrete (HPC) has been used in various structures all over the world since last two decades. Recently a few infrastructure projects have also seen specific application of high-performance concrete. The development of high performance concrete (HPC) has brought about the essential need for additives both chemical and mineral to improve the performance of concrete. Most of the developments across the work have been supported by continuous improvement of these admixtures. Hence variety of admixtures such as fly ash, rice husk ash, stone dust have been used so for. Also different varieties of fibres have below tried as additions. Hence, an attempt has been made in the present investigation to study the behavior of Glass fibres in High Performance Concrete. To attain the setout objectives of the present investigation, an aggregate binder ratio of 2.0 has been chosen and cement has been replaced partially with Silicafume in four different percentages viz. 0, 10, 20 and 30%. Glass fibres by 0, 0.5, 1.0, and 1.5 % to produce High Performance Concrete. Hardened Glass fibre Reinforced High Performance Concrete (GFRHPC) is tested for Compression, split tension and flexural strengths. The results are quite encouraging for use of Glass fibres in producing High Performance Concrete. Key Words : HPC, Glass Fibres, Silica Fume

3 1. Introduction Concrete is the most important building material in all countries and its consumption is increasing day to day. The reason is its components are available every where and relatively inexpensive, its production may be relatively simple, its application covers large variety of building and civil infrastructures works. High performance concrete sounds like advertising a new product but, in most respects, high performance concrete is not fundamentally different form the concrete that we have been using all along, because it does not contain any new ingredients and does not involve new practices on site. High performance concrete can be made by using mineral admixtures (e.g micro silica, metakaolin, fly ash, blast furnace slag etc.) Actually, high performance concrete evolved gradually over the last 15 years or so, mainly by the production of concrete with higher and higher strengths: 80, 90, 100, 120MPa, and sometimes even higher. The strength and durability properties of HPC with silica fume and metakaolin replacing cement, is found to be enhanced[1,2] relative to conventional concrete. Fiber reinforced concrete (FRC) is another technology which yield similar properties as that of conventional concrete. Basically the Conventional concrete is brittle and has poor resistance to crack opening and propagation. Naaman [3] showed that use of steel fibers in lower strength concretes increases their compressive strength significantly compared to plain un-reinforced matrices and is directly related to volume fraction of steel fiber used. This increase is more for hooked fibers in comparison with straight steel fibers, glass or polypropylene fibers. Mukherjee and Arwikar [4] studied the Performance of externally bonded GFRP sheets on concrete in tropical environments. The tensile strength and modulus of elasticity were determined to assess the degradation, if any. Mechanical properties of high strength concrete reinforced with metallic and non-metallic fibres with silica fume admixture by Sivakumar and Manu Santhanam [5] studied on High strength concrete reinforced with hybrid fibres (combination of hooked steel and a non-metallic fibre) up to a volume fraction of 0.5%. and found the flexural toughness of steel polypropylene hybrid fibre concretes was better to steel fibre concrete. Jian Tong Ding and Zongjinli [6] studied about the effect of metakaolin and silica fume on properties of concrete. Seven concretes were cast at a water/binder ratio of 0.35 with 0, 5, 10 and 15% cement replaced by metakaolin or silica fume. The incorporation of both Metakaolin and Silicafume in concrete can reduce the free drying shrinkage and restrained shrinkage cracking width. Literature review suggest that a very few r search work was reported on the concrete made with glass fibres and Silicafume combining HPC and FRC. In this connection an experimental investigation was carried out to determine the compressive, split tensile and flexural strengths with the use of glass fibres and Silicafume in concrete. The glass fibres were added by 0.5, 1.0, and 2.0% by volume and cement was replaced by Silicafume in three different percentages of 10, 20 and 30%.by weight of cement. 2. Experimental Programme and Materials Used in the Investigation The experimental scheme comprises tests in compression, split and flexure. For obtaining compression strength at 7 and 28 day, 96 (48+48) cube specimens of 150x150x150mm size were used. 48 cylindrical specimens with 150mm diameter and 300mm height were cast to find split tensile strength and 48 beams of size 150x150x600mm each were cast to find flexural strength. Four mixes viz., concrete with 0, 0.5, 1.0, and 1.5% by volume fraction of glass fibre were adopted for the experimental work. At each mix the cement is partially replaced with 0, 10, 20 and 30% by weight of cement. In all four mixes water/binder and aggregate/binder ratio is kept constant as 0.35 and 2.0 respectively. The proposed ratio for coarse to fine aggregate is 60:40 for all the mixes. In order to improve the workability, the superplasticiser is added by 1 % of the weight of cement through out the investigation. For four mixes, materials required per one cubic meter are presented in Table Cement Ordinary Portland cement commercially in India was adopted throughout in carrying out the present investigations. The properties of the cement are shown in Table.2.

4 2.2 Silica fume The Silica Fume is obtained from the ELKEM INDIA Pvt. Limited company at Mumbay in Maharastra. The specific gravity of Silica Fume is 2.2. The Silica Fume is in conformity with the general requirements of pozzolana. 2.3 Sand Natural river sand available in the nearby source was used in the experimentation. The specific gravity, bulk density and fineness modulus are 2.68, 16.0 kn/m 3 and 3.24 respectively. 2.4 Coarse aggregate Crushed granite aggregate available from local source was used. To obtain a good grading, 50% of the aggregate passing through 20mm and retained on 12.5 mm IS sieves and 50% of the aggregate passing through 12.5mm and retained on 10mm IS sieves was used in the preparation of concrete. 2.5 Fibres Glass fibres available in the market are used in the experimentation. The length of fibre is 12mm and the specific gravity of the fibre is Water Potable tap water available form local source was used for mixing and curing of concrete specimens. 2.7 Super plasticizer To improve the workability of concrete, Super plasticizer confirming to IS was used in the present investigation. 2.8 Casting and Testing The required quantities of materials are weighed and place over the plat form. Initially the cement and fine aggregate are mixed together in the dry state until they are thoroughly blended. Then the coarse aggregate, glass fibres are added to dry mix of cement and fine aggregate and they are mixed thoroughly until the coarse aggregate and fibres uniformly distributed throughout the batch. Super plasticizer is mixed in water and added to uniformly distributed mass until plastic concrete of uniform colour is achieved. This plastic concrete is placed in the cube, cylinder and beam moulds. After this the filled moulds are placed over the vibrator for compaction. Later these moulds are kept for 24 hours. After 24 hours the specimens are demoulded and cured for 28 days. After 28 days the specimens are taken out form the curing pond and kept under shade for surface dry. Then the cube specimens are tested in compression testing machine of capacity 200T. The failure load is noted for each cube specimen and compressive strength is determined. In similar way the cylinder is tested using compression testing machine for obtaining split tensile strength. Flexure test is done on a loading frame. The beam element is simply supported on two rollers of 4.5cm diameter over a span of 600mm. The beams are tested using third-point loading method. The load is applied on the specimen using 50 Tonne pre calibrated proving ring at a regular interval of 1kN. The ultimate load was noticed as and when the beam failed and using this ultimate load the flexural strength is found out using standard formula for flexure. 3. Results and Discussions 3.1 Compressive strength The cube compressive strength of glass fibre reinforced high performance concrete is increasing upto to 10% replacement of cement by silica fume. There after the strength is decreasing at 20% and 30% replacement of cement by silica fume. At 30% replacement it is observed that the strength is less than the same mix with out silica fume. It is also observed that as glass fibre percentage is increasing, the cube compressive strength is also increasing upto 1.0% and there after it is decreasing.the maximum percentage increase in cube compressive strength is observed at 1% fibre and 10% silica fume. This behaviour is observed for both 7 days and 28 days. The cube compressive strength is observed as 89.7 N/mm 2 for 0% fibre with 10 % silica fume and N/mm 2 for the same percentage of silica fume but with 1% of Glass fibre there is an increase in strength by 14%. The cube compressive strength is observed as 91.6 N/mm 2 for 1.0% fibre but without silica fume and

5 102.1 N/mm 2 for the same percentage of fibre and 10% silica fume i.e there is an increase in strength by 11% for the same mix with silica fume admixture. 3.2 Split tensile strength The split tensile strength is also increasing upto to 10% replacement of cement by silica fume. There after the strength is decreasing at 20% and 30% replacement of cement by silica fume. Here also it is also observed that as glass fibre percentage is increasing, the split tensile strength is increasing upto 1.0% and there after it is decreasing.the maximum percentage increase in the split tensile strength is observed at 1% fibre and 10% silica fume. The split tensile strength is observed as 6.21 N/mm 2 for 0% fibre with 10 % silica fume and 7.36 N/mm 2 for the same percentage of silica fume but with 1% of fibre i.e there is an increase in split tensile strength by over 18% by using glass fibers. The split tensile strength is observed as 6.97N/mm 2 for 1.0% fibre and without silica fume and 7.36 N/mm 2 for the same percentage of fibre with 10% silica fume of i.e there is an increase in strength by over 6% for the same mix with silica fume admixture. 3.3 Flexural strength It is observed from the Fig 4 that flexural strength is increasing with the volume percentage of fibres. In the present investigation four different fibre volumes percentages (0.5, 1.0, 1.5 and 2%) are used. The flexural strength is increased upto 1% of fibre volume then the strength is decreased. This result is expected because the addition of fibres enhances energy-absorbing capacity and increases its flexural toughness index. The decrease in strength for glass fibres beyond 1.0% may be due to more fibre volume which prevents the concrete from mixing thoroughly with other materials. In this investigation different percentage replacements of Silica fume, ranging from 0 30% were studied. However 10% replacement of cement by Silica-fume is found to be optimum in strength point of view. The increase in flexural strength can be explained by the fact that the presence of Silica-fume results in a much denser matrix. The increase in the denseness of the matrix possibly provides as much improvement in bond between the matrix and the fibre. The flexural strength was observed at 7.15 MPa for 0% fibre and 9.50 MPa for 1% fibre. The maximum percentage increase in flexural strength is observed as 33% with 1% of fibre over the mix without fibre. When Silicafume is used along with fibre the maximum strength observed for 1% fibre is MPa. The flexural strength without fibre at 10% replacement of Silicafume is observed at 8.25 MPa. The maximum percentage increase in strength is noticed to be 53% for the mix with 1% fibre and with 10% replacement of cement by Silicafume and the percentage increase is only 32% for the same mix without fibre content. It is also noticed that major cracks did not appeared before failure on the beams with fibre content. The flexural strength is decreased beyond 10% replacement of cement by Silicafume. These investigations reveal that the flexural strength is increasing as the glass fibre content increasing upto 1%. The use of Silicafume is also contributing to the increase in flexural strength. 4. Conclusions The major objective of this investigation is to use glass fibres in High Performance Concrete based on the present experimental investigation the following conclusions are drawn 1) 1.0% glass fibre volume can be taken as the optimum dosage, which can be used for giving maximum possible compressive strength at any age for glass fibre reinforced high performance concrete. 2) 10% silica fume can be taken as the optimum dosage, which can be used as a partial replacement to cement for giving maximum possible compressive strength at any age for glass fibre reinforced high performance concrete. 3) The percentage increase in compressive strength at 28days of 1% fibre volume with 10% silica fume concrete over plain high performance concrete with out fibre and silica fume is 14%. 4) The compressive strength of glass fibre reinforced high performance concrete 20 and 30% silica fume are as the lower side when compared with that of plain glass fibre reinforced high performance concrete mixes. 5) The percentage increase in split tensile strength at 28days of 1% fibre volume with 10% silica fume concrete over plain concrete with out fibre and silica fume is 18%.

6 6) The split tensile strength of glass fibre reinforced high performance concrete values of 20 and 30% silica fume are as the lower side when compared with that of plain glass fibre reinforced high performance concrete mixes. 7) From experimental results, the optimum percentage recommended as 1.0% fibre volume with 10% silica fume for achieving maximum benefits in compressive strength, split tensile strength and Flexural strength. References [1] Hooton R.D, Influence of silica fume replacement of cement on physical properties and resistance to sulfate attack, freezing and thawing and alali-silica reactivity, ACI Material Journal, 1993, [2] Wild S, Khatib J M and Jones A, Relative strength pozzolanic activit and cement hydration in superplasticised metakolin concrete, Cement and Concrete Research, 1996, [3] Naaman A. E., Al-khairi F. M., and Hammoud H. Mechanical Behavior of High Performance Concretes, Volume 6: High Early Strength Fiber Reinforced Concrete (HESFRC). Strategic Highway Research Program, National Research Council, Washington, D. C., xix, 1993, 297. (SHRP-C-366). [4] Mukherjee A. and Arwikar S.J. Performance of externally bonded GFRP sheets on concretein tropical environments, Composite Structures 2007, [5] Sivakumar.A and Manu Santhanam, A Quantitative Study on the Plastic Shrinkage Cracking in High Strength Hybrid Fibre Reinforced Concrete Cement & Concrete Composites, [6] Jian Tong Ding and Zongjin Li, Effects of Metakaolin and Silica Fume on properties of concrete, ACI Materials Journal, 2002,

7 Table 1. Quantity per 1 cum of GFRHPC S.No Type Cement 1 Basic Mix + 10% Silica Fume 2 Basic Mix + 20% Silica Fume 3 Basic Mix + 30% Silica Fume Silica Fume Coarse Aggregate Fine Aggregate Water Glass Fibre For each mix the glass fibres were added by 0.5,1,1.5 and 2% Table 2. Physical properties of cement S.No. Property Value 1 Fineness of cement 4.0% 2 Specific gravity Normal consistency 33% 4 5 Setting time Initial setting time Final setting time Compressive strength at 3 days 7 days 28 days Table 3: Properties of Silica Fume 40min 6 hours 27 N/mm 2 37 N/mm 2 56 N/mm 2 S.No. Property Value 1. Specific Gravity Bulk Density Kg/M 3 3. Specific Surface Area M 2 /Kg 4. Chemical Analysis, % Loss on Ignition Silica (SiO 2 ) Corban (C) Moisture (H 2 O) Max. 4.0 Min. 84% Max. 2.5 Max. 1.0

8 7 Days compressive strength(mpa) % S.F. 10% S.F. 20% S.F. 30% S.F % of fibre Fig 1. 7-Days Cube Compressive Strength vs % of fibres 28 Days Compressive strength(mpa) % S.F. 10% S.F. 20% S.F. 30% S.F % OF FIBRE Fig Days Cube Compressive Strength vs % of fibres

9 split tensile strength(mpa) % S.F. 10% S.F. 20% S.F. 30% S.F % of fibre Fig Days Split Tensile Strength vs % of fibres 28-Days Flexural Strength N/mm % of fibres 0% M 10% M 20% M 30% M Fig Days Flexural Strength vs % of Fibres