Influence of Silica Fume & Recycled Concrete Aggregates on Mechanical Properties of Concrete

Transcription

1 Influence of Silica Fume & Recycled Concrete Aggregates on Mechanical Properties of Concrete Ranjodh Singh 1, Sudhir Arora 2 1 Assistant Professor, DAV University, Jalandhar, 2 Assistant Professor at DAV University, Jalandhar Abstract Ordinary Portland cement is the most important ingredient of concrete and plays an important role in strength and durability parameters. Large scale production of cement is causing environmental problems and also depletion of natural resources. This threat to ecology is overcome by using supplementary cementations materials like silica fume, recycled concrete in making concrete. The main advantage of these supplementary materials like silica fumes and recycled concrete to replace certain amount of cement and natural coarse and reduces cost of cement. Silica fume is a mineral admixture and is byproduct of producing silicon metal or ferrosilicon alloys. Recycled concrete are made from demolished building or structures which can be used in making concrete as a partial replacement material of natural coarse in concrete. As a result of this the disposal of waste materials is reduced and also negative impacts on environment. The main parameter investigated in this study is to determine the compressive strength and flexural strength of concrete on partial replacement of coarse and cement by Recycled and silica fume respectively. Cubes and beam specimens were casted and variation in compressive strength and flexural strength was studied at age of 7, 14 and 28 days of curing. The maximum size of recycled concrete which are used is 20mm. Keywords:Silica fume recycled concrete, compressive strength, and flexural strength. 1. INTRODUCTION Concrete is widely used construction material all over the world for various types of structures due to its strength and stability. The ingredients of concrete like cement, fine and coarse plays an important role in the strength and durability of structures. The ordinary Portland cement is one of the main ingredients used for production of cement causes various environmental problems involves emission of large amount of CO 2 gas into the atmosphere, a major contribution for greenhouse effect and global warming. So to reduce these problems we use the supplementary cementations materials like fly ash, silica fume, ground granulated blast furnace slag, rice husk ash, metakaolin as a partial replacement material of cement. A number of studies are going on in India and other countries to study the effect of these materials as replacement materials. Silica fume is a mineral admixture and a very reactive pozzolan and it causes high strength and durability. Silica fume a byproduct of producing silicon metal or ferrosilicon alloys. Coarse are the major ingredient of concrete and play an also important role in strength of concrete. But due to increase in population in India, the requirements of natural are not only required to fulfill the demand for the upcoming projects, but also are the needs of the extensive repairs or replacements required for existing infrastructure. So to reduce burden on natural resources, we can easily use recycled concrete which are easily available from demolished buildings or structures. In many countries throughout the world have now introduced various measures aimed at reducing the use of natural coarse and increasing the use of recycled concrete. When pozzolanic materials are used in concrete, then silica present in these materials reacts with calcium hydroxide released during the hydration of cement and forms additional calcium silicate hydrate. Silica fume is also known as micro silica, condensed silica fume or silica dust. It is usually grey colored powder similar to ordinary Portland cement. Silica fume is a pozzolanic admixture that is effective in enhancing the mechanical properties to a great extent. This experimentation has been carried out to determine the mechanical properties of conventional concrete and 215 Ranjodh Singh, Sudhir Arora

2 concrete by using silica fume and recycled concrete. Silica fume and recycled concrete are used in various replacement ratios and then strength is compared with conventional concrete. 2. LITERATURE REVIEW Previous studies about Recycled concrete (RCA) and Silica fume Literature review aims at collecting the important or useful data regarding the study from the previously published papers or journals. Jeena Mathew (2012)studied the effect of silica fume on strength and durability properties of M35 grade concrete with partial replacement of cement. The different percentages of silica fume are 0, 5, 10, 15 and 20%. The optimum 7 and 28 days compressive strength and flexural strength has also been obtained in range of 10-15% silica fume replacement level. PatilShreekedar (2013)studied the effect of mineral admixture in mix proportioning of high performance concrete. The results show that the maximum replacement level of micro silica is 15% for M60 grade high performance concrete. Debabrata Pradhan (2013) studied the properties of silica fume concrete such as compressive strength, compacting factor and workability. He replaced cement by silica fume at different levels to know what percentage of silica fume gives the optimum value of compressive strength and for all replacements water to cement ratio is kept constant. JianzhuangXiaoa (2004)studied themechanical properties of recycled aggregate concrete under uniaxial loading. He concluded that the compressive strength of concrete containing recycled concrete decrease with increasing recycled concrete content. For 100% replacement of natural coarse with recycled concrete, the elastic modulus is reduced by 45%. Hiren A Rathod (2013)studied the recycled concrete as a substitute to natural aggregate for sustainable development in India. He concluded that when recycled concrete are added in concrete then results in increased water demand, reduction in workability, slump value as compared to concrete made with Natural coarse. He concluded that decrease in strength of concrete with increase in percentage of replacement ratio of recycled concrete. 3. MATERILALS USED AND THEIR PROPERTIES 3.1Cement Ordinary Portland cement of 43 grade is used in study. The main components of ordinary Portland cement are lime, silica, alumina, calcium sulphate, iron oxide, magnesia, sulphur and alkalies. The harmful components of ordinary Portland cement are alkali oxides and magnesium oxide. The main properties of ordinary Portland cement of 43 grade is shown in following table. 3.2 Fine Natural sand as per IS: is used that is locally available river sand. The to be used for cement concrete work should be durable and clean. The should be completely free from lumps of clay, organic and vegetable matter, fine dust etc.the material which is passed through BIS test sieve no. 480 is termed as fine 3.3 Coarse Crushed confirming to IS: is used. Maximum size of coarse used is 20mm.The to be used for cement concrete work should be durable and clean. The should be completely free from lumps of clay, organic and vegetable matter, fine dust etc. The material which is retained on BIS test sieve no. 480 is termed as a coarse. 3.4 Silica fume Grey color silica fume is used. The silica fume is used as a partial replacement of cement. Silica fume consists of fine particles with specific area on order of 20000m 2 /kg. Silica fume contains more than 90% silicon 216 Ranjodh Singh, Sudhir Arora

3 dioxide which is amorphous. Other constituents are carbon, sulfur, oxides of aluminum, iron,calcium, magnesium, sodium and potassium.most of the particles of silica fume are size smaller than 1 micron. 3.5 Recycled concrete Locally available recycled concrete are used in concrete production of M30 grade having specific gravity Recycled concrete have high water absorption and low specific gravity than natural coarse and thus produce concrete with higher drying shrinkage and creep. The water absorption of recycled concrete is more than natural coarse due to the adhered mortar on its surface. Table- 1:Properties of materials used S.N o Property Cement Fine 1. Normal consistency 28.75% 2. Initial setting time 33 min Coarse Silica fume Recycled concrete 3. Specific gravity Fineness 9% 5. Specific surface 281m 2 /kg 6. Fineness modulus Grading zone Bulk density 576 kg/m 3 9. Size 0.1 micron 10. Surface area m 2 /kg 4. MIX PROPORTIONING For this M30 grade of concrete is designed with water/ cement ratio is Mix design is based on IS According to IS mix design trial mixes are designed to investigate the strength of various mixes and compare the strength of mixes with conventional concrete mix.cubes and beam specimens are casted and compressive strength and flexural strength is studied at age of 7, 14 and 28 days of curing. 0%, 5%, 10%, 15%, 20% of cement and 0%, 25%, 50%, 75%, 100% of natural coarse are replaced with silica fume and recycled concrete. The maximum size of recycled concrete which are used is 20mm. This is the quantity of materials for various mixes required for one cube specimen of standard size of 150mm x 150mm x 150mm with constant water/cement ratio is Table- 2:Quantities of materials for various mixes Mix Cement in Kg Fine in Kg Coarse in Kg Silica fume in Kg Recycled concrete in Kg Water/ce ment ratio Water in liters M M M M M Ranjodh Singh, Sudhir Arora

4 Strength in MPa International Journal of Engineering Technology, Management and Applied Sciences 5. EXPERIMENTAL PROCEDURE The specimenof standard cube of size 150mm x 150mm x 150mm and specimen of standard beams of size 50mm x 10mm x 10mm are casted to determine compressive and flexural strength of concrete. Silica fume and recycled concrete are used as a partial replacement material of cement and natural coarse in concrete production. Five mixes are designed to determine compressive and flexural strength of concrete such as M1 (0% silica fume and 0% RCA), M2 (5% silica fume and 25% RCA), M3 (10% silica fume and 50% RCA), M4 (15% silica fume and 75% RCA), M5 (20% silica fume and 100% RCA) with constant water/cement ratio is specimens of cubes and 5 specimens of beams are casted in each mix of concrete. These specimens of cubes and beams are tested for 7, 14 and 28 days of curing to determine the compressive and flexural strength of concrete. The concrete is filled in layers and each layer is well compacted. The specimen was removed from mould after 24 hours and cured in clean water for 7, 14 and 28 days and then strength is determined and compared with strength of conventional concrete. The temperature of cured water is 27±2º C. 6. RESULTS The results of the compressive strength and flexural strength at age of 7, 14 and 28 days of curing is shown in figure that is variation of compressive strength and flexural strengthat age of 7, 14 and 28 days of curing. The following figures 1 and 2 shows that the variation of compressive strength at 7, 14 and 28 days and variation of flexural strength of 7, 14 and 28 days of curing. The compressive strength and flexural strength at age 7, 14 and 28 days of curing is in decreasing trend. Variation of compressive strength at 7, 14 and 28 days days strength 14 days strength 28 days strength M1 M2 M3 M4 M5 Mix Fig-:Variation of compressive strength at 7, 14 and 28 days 218 Ranjodh Singh, Sudhir Arora

5 Strength in MPa International Journal of Engineering Technology, Management and Applied Sciences 7 Variation of flexural strength at 7, 14 and 28 days days strength 14 days strength 28 days strength 1 0 M1 M2 M3 M4 M5 Mix Fig-2:Variation of flexural strength at 7, 14 and 28 days Table- 3:Ratio of different strengths at 7, 14 and 28 days of curing Mix Ratio of compressive strength to flexural strength at age of 7 days of curing Ratio of compressive strength to flexural strength at age of 14 days of curing Ratio of compressive strength to flexural strength at age of 28 days of curing M M M M M The compressive strength and flexural strength of various mixes in which silica fume and recycled concrete are used as a partial replacement materials in place of cement and natural coarse is less than the strength of conventional concrete mix M1. The compressive strength and flexural strength of various mix is in decreasing trend that is decreased gradually. This is due to the amount of adhered mortar in recycled concrete and high water absorption of recycled concrete as compared to natural coarse. As the percentage of silica fume and recycled concrete is increased, then compressive strength and flexural strength is decreased at all ages like 7, 14 and 28 days of curing. Table 3 gives the ratio of compressive strength to flexural strength at age of 7 days, 14 days and 28 days of curing. It gives the mean value of ratio of compressive strength to flexural strength at age 7, 14 and 28 days of curing. 219 Ranjodh Singh, Sudhir Arora

6 7. CONCLUSIONS From the experimental work carried here, the following conclusions can be concluded-: The consistency of concrete mixes by using silica fume and recycled concrete is decreased gradually. There is gradually decreasing trend of slump of various concrete mixes. The decrease in slump value of concrete is due to high water absorption of recycled concrete than natural coarse.the compressive strength and flexural strength of various concrete mixes is in decreasing trend. The compressive and flexural strength of various concrete mixes by using silica fume and recycled concrete is decreased gradually at age of 7, 14 and 28 days of curing. The compressive strength of concrete mix M2 (5% silica fume & 25% RCA) is 0.48% less than standard concrete mix M1. The compressive strength of mix M3 is 8.36% less than M2 and compressive strength of mix M4 is 6.02% less than M3 concrete mix and mix M5 is 5.85% less than M4 concrete mix at age of 7 days of curing. The compressive strength of various concrete mixes is decreased gradually also at age of 14 and 28 days of curing. The compressive strength of concrete mix M2 (5% silica fume & 25% RCA) is 1.57% less than standard concrete mix M1. The compressive strength of mix M3 is 5.48% less than M2 and compressive strength of mix M4 is 3.72% less than M3 concrete mix and mix M5 is 13.55% less than M4 concrete mix at age of 14 days of curing. The compressive strength of concrete mix M2 (5% silica fume & 25% RCA) is 6.88% less than standard concrete mix M1. The compressive strength of mix M3 is 7.25% less than M2 and compressive strength of mix M4 is 1.68% less than M3 concrete mix and mix M5 is 1.18% less than M4 concrete mix at age of 28 days of curing. The compressive strength of concrete mixes M4 and M5 is almost same (close to each other) at age of 28 days of curing which is shown in graph of 28 days compressive strength of different mixes. The flexural strength of concrete mix M2 (5% silica fume & 25% RCA) is 6.37% less than standard concrete mix M1. The flexural strength of mix M3 is 8.24% less than M2 and flexural strength of mix M4 is 11.46% less than M3 concrete mix and mix M5 is 2.28% less than M4 concrete mix at age of 7 days of curing. The flexural strength of various concrete mixes is decreased gradually also at age of 14 and 28 days of curing. The flexural strength of concrete mix M2 (5% silica fume & 25% RCA) is 4.39% less than standard concrete mix M1. The flexural strength of mix M3 is 6.53% less than M2 and flexural strength of mix M4 is 15.87% less than M3 concrete mix and mix M5 is 3.82% less than M4 concrete mix at age of 14 days of curing. The flexural strength of concrete mix M2 (5% silica fume & 25% RCA) is 6.23%% less than standard concrete mix M1. The flexural strength of mix M3 is 9.36% less than M2 and flexural strength of mix M4 is 12.21% less than M3 concrete mix and mix M5 is 6.42% less than M4 concrete mix at age of 28 days of curing. Recycled concrete produced harsh mix with lower workability than natural coarse because recycled concrete have high water absorption capacity. REFERENCES [1] Shreekedar P et al. (2013) Study on effect of mineral admixtures in mix proportioning of high performance concrete, IJRAT, 1(5). [2] Pradhan D et al. (2013) Effects of silica fume in conventional concrete IJIRSET, 3(4). [3] Xiaoa J et al. (2004) Mechanical properties of recycled aggregate concrete under uniaxial loading. [4] Rathod. A.H et al. (2013) A study on recycled concrete as a substitute to natural aggregate for sustainable development in India. [5] Wagih M.A et al. (2013) Recycled construction and demolition concrete waste as aggregate for structural concrete, HBRC journal 9, pp [6] Exteberruia M et al. (2006) Influence of amount of recycled concrete aggregate and production process on properties of recycled aggregate concrete, Cement and concrete research, pp [7] Jalaja M et al. (2014) Effect of types on flexural strength of concrete, IJSET, 3(7), pp [8] Amudhavalli N.K et al. (2012) Effect of silica fume on strength and durability parameters of concrete, IJESET, 3(1), pp [9] Ashteyat M.A et al. (2011) Effect of fly ash and silica fume on compressive strength of self compacting concrete under different curing conditions, Ain Shams engineering journal, pp [10] Zing B et al. (1993) Properties of silica fume concrete and mortar, ACI materials Journal, 90(4), pp Ranjodh Singh, Sudhir Arora