International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
INTERNATIONAL JOURNAL OF CIVIL ENGINE...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
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20320130406019 2

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December, pp. 193-201 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET ©IAEME A STUDY ON THE EFFECT OF ADDITION OF SILICA FUME ON STRENGTH PROPERTIES OF PARTIALLY USED RECYCLED COARSE AGGREGATE CONCRETE Dr. D. V. Prasada Rao1 and G. V. Sai Sireesha2 1 (Associate Professor, Department of Civil Engineering, Sri Venkateswara University College of Engineering, Tirupati, Andhra Pradesh, India) 2 (PG Student, Department of Civil Engineering, Sri Venkateswara University College of Engineering, Tirupati, Andhra Pradesh, India) ABSTRACT This paper presents an experimental investigation on the effect of silica fume (SF) on various strength properties of partially used recycled coarse aggregate (RCA) concrete. It was observed from the preliminary investigation that the strength properties of partially used recycled coarse aggregate concrete decreases with increase in the recycled coarse aggregate content. An attempt has been made to find the effect of silica fume on various strength properties of partially used recycled coarse aggregate concrete. In the present investigation, recycled coarse aggregate was used as 25% and 50% replacement of natural coarse aggregate in addition to silica fume partially replaces 5%, 8% and 12% of cement by weight. To evaluate the partially used recycled coarse aggregate concrete containing silica fume for structural applications, various strength properties of concrete were obtained. Compressive strength, split tensile strength and modulus of rupture test results of M20 and M30 grades of concrete prepared using recycled coarse aggregate and silica fume are presented and then the results are compared with the natural coarse aggregate concrete. Using the test results, it can be concluded that a combination of 25% recycled coarse aggregate and 8% silica fume can be recommended for the preparation of structural concrete, because of its improved strength characteristics compared to the natural coarse aggregate concrete. It can be concluded that the strength properties of partially used recycled coarse aggregate concrete can be improved by the addition of silica fume. The increase in the strength of partially used RCA concrete containing silica fume can be attributed to the availability of additional binder in the presence of silica fume. The availability of additional binder enhances the paste-aggregate bond results the RCA concrete with silica fume has improved strength properties. By adjusting the proportions of recycled coarse aggregate and silica fume in the concrete mix better strength properties can be achieved. Hence, 193
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME recycled coarse aggregate and silica fume offers an economically viable solution to convert the waste materials to valuable resources. Keywords: Recycled Coarse Aggregate, Silica Fume, Partial Replacement, Structural Concrete, Modulus of Rupture. 1. INTRODUCTION Concrete is the most common construction material prepared using cement, natural aggregates and water. With fast industrialization, infrastructure development and increase in the population leads to huge construction activities. Due to increase in the various construction activities the natural resources are fast depleting which in turn results in escalating the cost of construction materials and then the total cost of construction [1]. During the natural calamities like earthquakes, the collapse of reinforced concrete buildings causes a serious concern with respect to the disposal very large quantities of demolished concrete waste material. For the disposal of concrete waste material the availability of open land is also a problem. To preserve the natural resources for our future generations and also to overcome the problem of disposal, the concrete waste can be used to obtain coarse aggregate known as recycled coarse aggregate. The use of recycled coarse aggregate in the preparation of new concrete has various environmental benefits also. Hence, recycling of the concrete waste can be considered as an excellent source of coarse aggregate for the production of new concrete. Hence, recycled coarse aggregate offers an economically viable solution to convert the concrete waste material to a valuable resource. The study on the application of recycled coarse aggregate for concrete preparation has been going on over the last few decades [2, 3]. The properties like water absorption and specific gravity of recycled coarse aggregate are to be determined for the concrete mix design. It has been observed that the recycled coarse aggregate obtained from concrete waste is rough-textured, angular and has higher water absorption than the natural coarse aggregate affecting the concrete mix proportion. The density of recycled concrete aggregate is less than the natural coarse aggregate because of the porous and less dense residual mortar adhering to the surface leading to the reduction in strength of the partially used recycled coarse aggregate concrete. The preliminary studies indicated that as the quantity of recycled coarse aggregates increased the strength of the recycled coarse aggregate concrete is decreased. The present research paper is focused on to understand the effect of silica fume on the strength properties of partially used recycled coarse aggregate concrete. The recycled coarse aggregate was used as partial replacement of natural coarse aggregate and silica fume as partial replacement of cement. Compressive strength, split tensile strength and modulus of rupture of partially used recycled coarse aggregate concrete with the addition of silica fume were obtained using concrete the specimens and then the results were compared with the natural coarse aggregate concrete. 2. EXPERIMENTAL PROGRAMME 2.1 Materials 2.11 Cement In the present investigation Ordinary Portland cement (OPC) of 43 Grade confirming to IS specifications was used [4]. The specific gravity of the cement is 3.15. 194
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME 2.12 Fine aggregate Locally available river sand (Zone - II) confirming to IS specifications with fineness modulus of 2.7 was used as the fine aggregate in the concrete mix [5]. 2.13 Recycled Coarse Aggregate In general, to prepare a specified grade of recycled coarse aggregate concrete, it is difficult to procure the recycled coarse aggregate from the same grade of demolished concrete waste material. To account this practical difficulty, the recycled coarse aggregate used in the present investigation was obtained by mixing the coarse aggregate obtained by crushing M20, M25 and M30 grade natural coarse aggregate concrete cubes tested in the laboratory. The crushing process affects the characteristics of the resulting recycled coarse aggregates [6]. The nominal sizes of recycled or natural coarse aggregate adopted in the present investigation were 20 mm and 10 mm. The properties of the recycled and natural coarse aggregate obtained by tests conducted as per IS specifications are given in Table 1. Recycled coarse aggregate has 10 to 15% lower density and 3 times more water absorption than the natural coarse aggregate; this is due to the porosity of the hydrated cement paste attached to RCA. In general, recycled coarse aggregate was found to be angular and porous compared to natural coarse aggregate. Further, recycled coarse aggregate is to be cleaned and should be free from detrimental levels of impurities and other harmful constituents. Table1: Properties of NCA, RCA and Sand Property Natural Coarse Aggregate Recycled Coarse Aggregate Fine aggregate (Sand) Specific Gravity 2.67 2.48 2.52 Water Absorption (%) 0.46 1.52 0.44 2.14 Silica Fume Silica fume is non-crystalline Silica, a by-product of ferro-silicon industry. Compared to cement, the particle size of silica fume is very finer. It acts as an excellent pore-filling material. Silica fume is usually considered as a supplementary cementitious material [7]. Generally, it can be used in the proportions of 5 – 12% of the cement content. The properties of silica fume used in the present investigation are shown in the Table. 2 Table 2: Properties of Silica Fume S.No. Characteristics Actual Analysis Result 1 Sio2 90.20% 2 Moisture 0.20% 3 Pozzolana Activity Index 127% 4 Specific Surface Area 21m2/gm 5 Bulk density 604 6 > 45 Microns 0.20% 195
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME 2.15 Water The water used for casting and curing concrete test specimens was free of acids, organic matter, suspended solids and impurities which when present can adversely affect the strength of concrete. 2.2 Concrete Mix Proportions In the present research work the effect of silica fume as partial replacement of cement on M20 and M25 grades of partially used recycled coarse aggregate concrete is studied. Concrete specimens were prepared with 25% and 50% of recycled coarse aggregate in addition to 5%, 8% and 12% of silica fume content. M20 and M25 grades of natural coarse aggregate concrete were designed based on Indian Standard method of mix proportioning [8]. In the concrete mix, 10 mm and 20 mm coarse aggregate were used in the ratio of 1:1.5. No superplasticiser was used in the concrete mixes. The mix proportions of M20 and M25 grades of concrete by weight are shown in Table. 3. After obtaining the concrete mix proportions, the recycled coarse aggregate was used as 25% and 50% by weight replacement of the natural coarse aggregate and silica fume partially replaces 5%, 8% and 12% of cement by weight. The mix proportions were obtained by assuming the aggregate were in a saturated-surface dry condition and appropriate moisture adjustments were made to cater for the different water absorption properties of the aggregates. Table 3: Concrete Mix Proportions Grade of Concrete Cement Fine Aggregate Coarse Aggregate Water-Cement Ratio Cement (kg/m3) M 20 1 1.97 3.79 0.55 320 M 25 1 1.71 3.62 0.50 340 2.3 Preparation of Concrete Test Specimens Two types of concrete specimens were prepared using natural coarse aggregates and recycled coarse aggregate with the addition of silica fume. Four sets of concrete specimens for different curing periods 3, 7, 28 and 56 days were prepared. Concrete specimens consist of 150 mm × 150 mm × 150 mm cubes, 150 mm × 300 mm cylinders and 100 mm × 100 mm × 500 mm prisms. The cubes and cylinders were used to find the compressive strength of concrete. The cylinders were also used to obtain the split tensile strength of concrete and the prisms were used to get the modulus of rupture of concrete. 2.4 Testing The compressive and split tensile strengths of concrete were obtained using a compression testing machine. The rate of loading for the compressive and splitting tensile tests is in accordance with Indian Standard specifications [9]. The compressive strength tests on concrete cube and cylinder specimens were carried out at the age of 3, 7, 28 and 56 days. The split tensile strength and modulus of rupture tests were conducted on concrete specimens at the age of 28 days. 196
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME 3. RESULTS AND DISCUSSION 3.1 Compressive Strength The results of the cube compressive strength of M20 and M25 grades concrete for various combinations of RCA and SF at different curing periods is shown in Fig.1. Each value of the cube compressive strength indicates the average of three test results. It can be observed that as the age of concrete increases the cube compressive strength of partially used recycled coarse aggregate concrete also increases with silica fume. (i) 25% RCA (ii)50% RCA (a) M 20 Grade Concrete 25% RCA 50% RCA (b)M 25 Grade Concrete Fig. 1.Variation of Cube Compressive Strength of Partially Used RCA Concrete with different percentages of Silica Fume. 197
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME The variation of 7 day’s and 28 day’s cube compressive strength of M20 and M25 grades concrete containing 25% and 50% of RCA content with increase in the percentage of silica fume is shown in Fig. 2. The compressive strength of RCA concrete initially increases up to 8% percentage of silica fume and then decreases with increase in the silica fume content. (a) M 20 Grade Concrete (b) M 25 Grade Concrete Fig.2. Variation of Cube Compressive Strength (7 Day’s and 28 Day’s) of Partially Used RCA Concrete with different percentages of Silica Fume. Comparison is also made between the cube compressive strength and cylindrical compressive strength of partially used recycled coarse aggregate concrete containing various percentages of silica fume at the age of 28 days. The test results are shown in Table.4. Similar to the natural coarse aggregate concrete, in the case of recycled coarse aggregate concrete with silica fume the ratio of cylindrical compressive strength to the cube compressive strength is also around 0.8 198
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Table 4: Comparison between Cube and Cylinder Compressive Strength of Partially Used Recycled Coarse Aggregate Concrete with varying percentages of Silica Fume Recycled 28 Days 28 Days Ratio of Grade of Coarse Silica Cube Compressive Cylinder Compressive Cylinder Concrete Aggregate Fume Strength of Concrete Strength of Concrete Strength to (%) (%) (N/mm2 ) (N/mm2) Cube Strength 0 0 33.00 26.28 0.80 M 20 5 30.68 24.50 0.80 25 8 34.60 27.20 0.79 12 28.05 22.13 0.79 5 28.00 22.32 0.79 50 8 33.72 27.00 0.80 12 26.31 21.12 0.80 0 0 30.96 25.42 0.82 5 29.50 24.81 0.84 25 8 33.86 27.76 0.82 12 29.36 24.50 0.83 M25 5 25.58 20.72 0.81 50 8 31.68 26.34 0.83 12 25.43 20.85 0.82 3.2 Split Tensile Strength The variation of split tensile strength of M20 and M25 grades of partially used recycled coarse aggregate concrete of 25% and 50% RCA content with increase in the silica fume content is shown in Fig. 3. The split tensile strength of RCA concrete initially increases up to 8% percentage of silica fume and then decreases with increase in the silica fume content. The split tensile strength of M20 and M25 grades of natural coarse aggregate (control) concrete is 3.66 N/mm2 and 3.24 N/mm2 respectively. It is also found that the split tensile strength of RCA concrete with silica fume is found to be approximately 10% of its 28 day’s cube compressive strength. (a) M20 Grade Concrete (b) M25 Grade Concrete Fig.3. Variation of Split Tensile Strength of Partially Used RCA Concrete with different percentages of Silica Fume 199
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME 3.3 Modulus of Rupture The variation of modulus of rupture of M20 and M25 grades of partially used recycled coarse aggregate concrete containing 25% and 50% RCA with increase in the silica fume content is presented in Fig.4. The modulus of rupture of RCA concrete initially increases up to 8% percentage of silica fume and then decreases with increase in the silica fume content. It is found that the modulus of rupture of partially used RCA concrete with silica fume is varying between 13 and 20% the 28 day’s cube compressive strength of concrete. The modulus of rupture of M20 and M25 grades of natural coarse aggregate (control) concrete is 4.20 N/mm2 and 4.96 N/mm2 respectively. (a) M20 Grade Concrete (b) M25 Grade Concrete Fig.4. Variation of Modulus of Rupture of Partially Used RCA Concrete with different percentages of Silica Fume 4. CONCLUSIONS Using the test results, in it can be concluded that as the percentage of silica fume is increased the various strength properties of partially used recycled coarse concrete are also increased up to 8% of silica fume content and then the strength of concrete is decreased with further increase in the silica fume content. The compressive strength, split tensile strength and modulus of rupture test results of concrete prepared with 25% and 50% of recycled coarse aggregate in addition to 5%, 8% and 12% of silica fume content indicates exactly the same trend. The increase in the strength of partially used RCA concrete containing silica fume can be attributed to the availability of additional binder in the presence of silica fume. Silica fume has high amorphous silicon dioxide content and is a very reactive pozzalanic material. As the Portland cement in concrete begins to react chemically, it releases calcium hydroxide. The silica fume reacts with the calcium hydroxide to form additional binder material. The availability of additional binder enhances the paste-aggregate bond results the RCA concrete with silica fume has improved strength properties. The decrease in the various strength characteristics of partially used RCA concrete with increase in the silica fume content beyond 8% is due to the fact that the strength of the additional binder formed in the presence of silica fume decreases due to excessive silica fume content. Hence, low strength properties of partially used recycled coarse aggregate concrete can be improved by the addition of a specified percentage (8%) of silica fume content. The experimental studies indicated that improved strength characteristics of RCA concrete can be obtained with the combined use of recycled coarse aggregate and silica fume compared to the concrete with recycled coarse aggregate only. The influence of varying percentages of recycled coarse aggregate and silica fume on M 20 grade of concrete is studied and it is observed that at a combination of 25% of recycled coarse aggregate and 8% of silica fume best results are obtained. 200
  9. 9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME REFERENCES [1] Fouad M. Khalaf and Alan S. DeVenny. Recycling of Demolished Masonry Rubble as Coarse aggregate in Concrete, Journal of Materials in Civil Engineering, ASCE, 16(4), 2004, 331-340. [2] Bairagi N K, Vidyadhara H S and Kishore R. Mix design procedure for recycled aggregate concrete, Construction and Building Materials, 4 (4), 1990,188-193. [3] Padmini, A.K; Ramamurthy.K. and Mathews, M.S. Influence of parent concrete on the properties of recycled aggregate concrete. Construction of Building Materials, 23, 2009,829836. [4] IS: 8112:1989. 43 Grade Ordinary Portland Cement – Specifications. Bureau of Indian Standards, New Delhi. [5] IS: 383:1970 (Reaffirmed 1997) Specification for Coarse and Fine Aggregates from Natural Sources for Concrete. Bureau of Indian Standards, New Delhi. [6] Kou S C and Poon C.S. Mechanical Properties of 5-year old concrete prepared with recycled aggregates obtained from three different sources. Magazine of Concrete Research, 60(1), 2008, 57-64. [7] Yajun Ji and Jong Herman Cahyadi. Effects of densified silica fume on microstructure and compressive strength of blended cement pastes. Cement and Concrete Research, 33, 2003,1543-1548. [8] IS: 10262-2009. Concrete Mix Proportioning – Guidelines (First Revision). Bureau of Indian Standards, New Delhi. [9] IS 516:1959. Methods of Tests for Strength of Concrete, Bureau of Indian Standards, New Delhi, India. [10] P.J.Patel, Mukesh A. Patel and Dr. H.S. Patel, “Effect of Coarse Aggregate Characteristics on Strength Properties of High Performance Concrete using Mineral and Chemical Admixtures”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 89 - 95, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [11] Madan Mohan Reddy. K , Sivaramulu Naidu. D, Sanjeeva Rayudu. E, “Studies on Recycled Aggregate Concrete by using Local Quarry Dust and Recycled Aggregates”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp. 322 - 326, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [12] P.V.V. Satyanarayana, K. Lewis Chandra, T. Harsha Nandan and S.S.S.V. Gopala Raju, “A Study on the Utilization of Recycled Aggregate and Crusher Dust Mixes as Sub-Base and Base Materials”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 5, 2013, pp. 122 - 129, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 201

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