20320140502005 2-3-4

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20320140502005 2-3-4

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) IJCIET ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2014): 3.7120 (Calculated by GISI) www.jifactor.com ©IAEME SOME STUDIES ON MODE-II FRACTURE OF ARTIFICIAL LIGHT WEIGHT SILICA FUME PELLETIZED AGGREGATE CONCRETE 1 Dr. V. BHASKAR DESAI, 2 A. SATHYAM, 3 S. RAMESHREDDY 1 Professor, Dept. of Civil Engineering, JNTUA College of Engineering, Anantapuram – 515002, A.P. 2 Conservation Assistant Gr-I, Archaeological Survey of India, Anantapuram Sub Circle, Anantapuram & Research Scholar, JNTUA College of Engineering, Anantapuram – 515002, A.P. 3 M.Tech Student, JNTUA College of Engineering, Anantapuram – 515002, A.P. ABSTRACT The recent advancements in the construction industry necessitate the development of new materials which have high performance than the ordinary conventional concrete. In the present scenario light weight aggregate has been the subject of extensive research which affects the shear strength properties of cement concrete. The adaptation of certain class of light weight concrete gives an outlet for industrial waste which would otherwise create problem for disposal. An attempt has been made to prepare artificial light weight aggregate concrete by using pelletized silica fume aggregate. Shear strength is a property of major significance for wide range of civil engineering materials and structures. Shear and punching shear failures particularly in deep beams in corbels and in concrete flat slabs are considered to be more critical and catastrophic than other types of failures. This area has received greater attention in recent years due to various attempts which have been made to develop Mode-II (sliding shear) test specimen geometries for investigating the shear type of failures in cementitous materials. In this area number of test specimen geometries is proposed for Mode-II fracture of cementitous materials. Out of these the best suited is suggested as Double Centered Notched (DCN) specimen geometry proposed by Sri Prakash Desai and Sri Bhaskar Desai. In this present experimental investigation an attempt is planned to study the Mode II fracture properties of light weight aggregate concrete, with Silica Fume pellets is considered. The Silica Fume pellets were prepared by mixing of 47% Silica fume, 47% lime, 6% cement and 12.50% of water by overall weight of the sample, using pelletization machine. By varying the percentages of Silica Fume pellets in concrete replacing the conventional granite aggregate in percentages of 0, 25, 50, 75, 100 by volume of concrete, the property of in plane shear strength is studied by casting and 33
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME testing around 50x3 samples consisting of 120 notched specimens of size 150mm x150mm x 150mm with different notch depth ratios and 30 no of plain cubes of size 150 x 150 x 150mm for testing after 28 days and 90 days curing. Key words: Light Weight Aggregate, Mode II Fracture, Shear Strength, Silica Fume Pellets. INTRODUCTION Due to continuous usage of naturally available aggregates within short length of time these natural resources get depleted and it will be left nothing for future generations. Hence there is a necessity for preparing artificial aggregates making use of waste materials from agricultural produce and industrial wastes. From the earlier studies it appears that much less attention has been made towards the study of using artificial coarse aggregate. An attempt has been made to use silica fume as the basic ingredient in preparing artificial coarse aggregate which is also light in nature. LIGHTWEIGHT AGGREGATE Structural lightweight aggregate concrete are considered as alternative to concrete made with dense natural aggregate, because of the relatively high strength to unit weight ratio that can be achieved. Other reasons for choosing lightweight concrete as a construction material is more attention is being paid to energy conservation and to the usage of waste materials to replace the exhaustible natural sources. One of the disadvantage of conventional concrete is the high self weight of concrete. Density of the normal concrete is in the order of 2200 to 2600Kg/m³. This heavy self weight will make it to some extent an uneconomical structural material. Attempts have been made and lightweight aggregate concrete have been introduced whose density varies from 300 to 1850 Kg/m³. ARTIFICIAL LEIGHT WEIGHT AGGREGATE The production of concrete requires aggregate as inert filler to provide bulk volume as well as stiffness. Crushed aggregate are normally used in concrete which can be depleting the natural resources and necessitates an alternate building material. This led to widespread research on using a viable waste material as aggregate. Silica Fume is one promising material which can be used as both cementitous materials as well as to produce light weight aggregate. The use of cost effective construction materials has accelerated in recent times due to the increase in demand of light weight concrete for mass applications. This necessitates the complete replacement or partial replacement of concrete constituents to bring down the escalating construction costs. In recent times, the addition of artificial aggregate has shown a reasonable cut down in the construction costs and had gained good attention due to quality on par with conventional aggregate. Despite of its lower compressive strength and lower modulus elasticity, Silica Fume concrete can be potentially used in many kinds of structural elements. PELLETIZING PROCESS The desired grain size distribution of an artificial light weight aggregate is by means of agglomeration process. The Pelletization process is used to manufacture light weight Coarse aggregate. Some of the parameters need to be considered for the efficiency of the production of pellets such as speed of revolution of pelletizer disc, moisture content, angle of pelletizer disc and duration of Pelletization (HariKrishnan and RamaMurthy, 2006)1. The different types of pelletizer 34
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME machine were used to make the pellets such as disc or pan type, drum type, cone type and mixer type. With mixer type pelletizer small grains are formed initially and are subsequently increased. In the cold bonded method increase of strength of pellets is by increase the Silica Fume/ lime & cement ratio by weight. Moisture content and angle of drum parameter influence the size growth of pellets (HariKrishnan and RamaMurthy, 2006)2. The dosage of binding agent is more important for making the Silica Fume balls. Initially some percentage of water is added in the binder and remaining water is sprayed during the rotation Period because while rotating without water in the drum the Silica Fume and binders (Lime & Cement) tends to form lumps and does not increase the distribution of particle size. The pellets are formed approximately in duration of 6 to 7 minutes. The cold bonded pellets are hardened by normal water curing method. The setup of machine for manufacture of Silica fume aggregate is as shown in plate 1. PLATE 1. PELLETIZATION MACHINE MODES OF CRACKING A crack in a structural component can be stressed in three different modes, which are as shown in Fig.1. Mode – I: Opening Mode –II: In-plane shear Mode – III: Out of plane shear Fig.1: Different modes of cracking Normal stresses give rise to the “Opening mode” denoted as Mode-I in which the displacements of the crack surfaces are perpendicular to the plane of the crack. 35
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME In-plane shear results in Mode-II or “Sliding mode”, in which the displacement of the crack surfaces is in the plane of the crack and perpendicular to the leading edge of the crack (crack front). The “Tearing mode” or Mode-III is caused by out-of-plane shear: in which the crack surface displacements are in the plane of the crack and parallel to the leading edge of the crack. With the inter disciplinary research and development in material science and engineering have lead to the development of several important composite construction materials such as concrete made with partial replacement of conventional aggregate by light weight aggregate such as pumice. In this present experimental investigation an attempt is planned to be made to study the Mode-II fracture properties of light weight aggregate concrete, such as Silica Fume aggregate concrete since in recent years an attempt has been made only on normal aggregate and on partial replacement of normal concrete with heavy weight aggregate. If a structural element is considered in which crack has developed due to bad workmanship, due to the application of repeated loads or combination of loads and aggressive environmental conditions, this crack will grow with time. The longer the crack, the higher the stress concentration induced by it. This indicates that the rate of crack propagation will increase with time. The total useful life of the structural component depends on the time necessary to initiate a crack and to propagate the crack from subcritical dimensions to the critical size due to cyclic stresses. Due to the presence of the crack, the strength of the structure will decrease, which will be lower than the original design strength. REVIEW OF LITERATURE In this chapter brief review of the available studies related to the present Mode-II fracture of cementitious materials are presented. Aggarwal and Giare (3) investigated that critical strain energy release rate in Mode-II is less than half of that Mode-I or Mode-III indicating that in the case of fibrous composites, the fracture toughness tests in Mode-II may be more important than the tests in mode-I and Mode-III. Symmetrically notched “Four point shear test specimen was used by Bazant and Pfeiffer (4,6) to study the shear strength of concrete and mortar beams and they concluded that the ratio of fracture energy for Mode II to Mode I is about 24 times for concrete and 25 times for mortar. Watekins and Liu (5) conducted the finite element analysis technique simulating in-plane shear mode, fracture mechanics has been used to analyse fracture behaviour in a short shear beam specimen in plain concrete and fracture toughness, KIIc values are determined. Liu et al(7) examined the in-plane shear behavior of polypropylene and steel fiber reinforced concrete and investigated that the fracture toughness results in shear (KIIc) are independent of the fiber content of the mix and this is in contrast to KIc results for steel fiber reinforced concrete which increases with the increasing fiber content. Devies et al (8) conducted tests on mortar cubes subjected to shear loading, and both analytical and experimental approaches are used in evaluating the fracture toughness of mortar. Prakash Desayi, Raghu Prasad B.K, and Bhaskar Desai.V, (9, 10, 11, 12, 13, 14 and 15) arrived at Double Central Notched specimen geometry which fails in predominant Mode-II failure, They have also made finite element analysis to arrive at stress intensity factor. Using this DCN geometry lot of experimental investigation using cement paste, mortar, plain concrete has been done. Details of DCN test set up are presented in fig 2. 36
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME Square steel bar Supports at bottom (a) Loading and support arrangement (b) Bottom view while testing Top loaded area (c) Top view while testing in elevation while testing Fig 2. Details of DCN test specimen geometry EXPERIMENTAL INVESTIGATION Mix design has been conducted for M20 concrete making use of ISI method of mix design using normal constituents of concrete. An experimental study has been conducted on concrete with partial to complete replacement of conventional coarse aggregate i.e., Granite by light weight aggregate i.e., Silica Fume Aggregate to know the shear strength Double Centered Notched (DCN) specimens having different a/w ratios of 0.30, 0.40, 0.50 and 0.60. Analysis of the results has been done to investigate the shear strength variation in Mode-II fracture with addition of different percentages of Silica Fume Aggregate. Variations of various combinations have been studied. The constituent materials are used in the present investigation are presented in table.1. CONSTITUENT MATERIALS: The constituent materials used in the present investigation for making artificial light weight aggregate are; SILICA FUME: Silica fume is by product of the reduction of high purity quartz with coal in electric furnaces in the production of Silicon and ferro silicon alloys. Before mid 1970’s nearly all silica fume was discharged into the atmosphere. After environmental concerns necessitated the collection and land filling of Silica fume, it became economically justified to use silica fume in various applications. Silica Fume consists of very vitreous particles with a surface area ranging from 13,000 to 30,000 m2/Kg when measured by nitrogen absorption technique with particles approximately 100 to 150 times smaller than the cement particle. Silica fume is procured from Ferro silicon unit, Kurnool. Because of its extreme fineness and high silica content, it is an effective pozzolanic material and is used in concrete to improve its properties. It has been found that Silica Fume improves compressive strength, bond strength, abrasion resistance and reduces permeability and therefore helps in protecting reinforcing steel from Corrosion. 37
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME CEMENT: Ordinary Portland cement of Ultra-tech 53 grade with specific gravity of 3.07 is used as binder. Initial setting and final setting times are 60 minutes and 420 minutes respectively. LIME: Locally available lime used is as another binder. WATER: Locally available potable water which is free from concentration of acids and organic substances has been used in this work for mixing and curing. TABLE 1: PROPERTIES OF CONSTITUENT MATERIALS IN M20 GRADE CONCRETE Sl.No Name of the material Properties of material 1 489 min 4% Normal consistency 33.50 % Specific Gravity 2.60 Fineness modulus 4.10 Specific Gravity 2.68 Fineness modulus 4.23 Bulk density compacted 1620 Kg/m3 Specific Gravity 1.14 Fineness modulus 4.20 Bulk density compacted 4 60 min Fineness Fine Aggregate passing 4.75mm sieve 3.07 Final Setting time 3 Specific Gravity Initial setting time 2 OPC – 53 Grade 1035 Kg/m3 Coarse Aggregate passing 20 – 10 mm Silica fume pelletized Aggregate passing 20 – 10 mm The constituent materials are presented from plates 2 to 5. PLATE 2. CEMENT PLATE 3. FINE AGGREGATE 38
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME PLATE 4. COARSE AGGREGATE PLATE 5. PELLETIZED COARSE AGGREGATE TEST PROGRAMME In this present investigation it is aimed to study the Mode-II fracture properties of concrete by modifying the conventional concrete with Silica fume aggregate which is replaced in percentages of 0%, 25%, 50%, 75% & 100%, by volume of natural aggregate in concrete and designated as mixes SF-0, SF-25, SF-50, SF-75 & SF-100 respectively. Hence cement, fine aggregate, coarse aggregate, i.e., Granite and Silica fume aggregate in required percentages were calculated. Then required quantity of water is added to this and mixed thoroughly by hand mixing. MIXING, CASTING AND CURING The mix adopted here is M20 designed mix concrete with the mix proportion of 1:1.55:3.04. It means that 1 part of cement, 1.55 parts of fine aggregate and 3.04 parts of coarse aggregate consisting of granite and Silica fume aggregate with required replacement are mixed with water cement ratio of 0.5. Keeping the volume of concrete constant with saturated and surface dry Silica fume aggregate was added to concrete in 5 different volumetric fractions to prepare five different mixes which are designated as shown in table 2. Name of the Mix SF- 0 SF- 25 SF- 50 SF- 75 SF- 100 TABLE: 2 DETAILS OF MIX DESIGNATION Replacement of Coarse Aggregate by No of specimens cast Volume percentage Natural Pelletized Silica DCN Plain Aggregate fume Aggregate specimens specimens 100 0 24 6 75 25 24 6 50 50 24 6 25 75 24 6 0 100 24 6 Total 120 30 To proceed with the experimental program initially steel moulds of size 150x150x150 mm with different a/w ratios of 0.3, 0.4 ,0.5, and 0.6 along with plain moulds each in 3 numbers were taken and these moulds were cleaned without dust particles and were brushed with machine oil on all inner faces to facilitate easy removal of specimens after 24 hours of casting. 39
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME To start with, all the materials were weighed in the ratio 1:1.55:3.04. First fine aggregate and cement were added and mixed thoroughly and then coarse aggregate of granite and required percentage of surface dry Silica Fume aggregate were mixed with them. All of these were mixed thoroughly. No admixture i.e. super plasticizer was added as the slump of mix is around 2.5 cm to 5 cm and compaction factor is 0.92 to 0.93. Each time 15 cube specimens, out of which 12 specimens with a/w ratios 0.3, 0.4, 0.5, and 0.6, 3 numbers of plain cubes were cast and casted specimens as shown in plate 6 and 7. For all test specimens, moulds were kept on the vibrating table and the concrete was poured into the moulds in three layers each layer being compacted thoroughly with tamping rod to avoid honey combing. Finally all specimens were vibrated on the table vibrator after filling up the moulds up to the brim. The vibration was effected for 7 seconds and it was maintained constant for all specimens and all other castings. The steel plates forming notches were removed after 3 hours of casting carefully and neatly finished. However the specimens were de moulded after 24 hours of casting and were kept immersed in a clean water tank for curing as shown in plate 8. After 28 and 90 days of curing the specimens were taken out of water and were allowed to dry under shade for few hours. PLATE 6. PLAIN CUBES IN GREEN STATE PLATE 7. DCN SPECIMENS IN GREEN STATE PLATE 8. CURING POND 40
  9. 9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME TESTING OF SPECIMENS COMPRESSION TEST ON PLAIN CUBES Compression test is done as per IS: 516-1959. All the concrete specimens were tested in a 3000KN capacity automatic compression testing machine with 0.5KN/sec rate of loading until the specimens are crushed. Concrete cubes of size 150mm x150mm x 150mm are tested for compressive strength. The displacements were automatically recorded through 3000KN digital compression testing machine. The maximum load applied to the specimens has been recorded and dividing the failure load by the area of the specimen, the compressive strength has been calculated. The test set up of 3000KN compression testing machine with specimens as shown in plate 9 and 10. Compressive strength = ࡸ࢕ࢇࢊ ࡭࢘ࢋࢇ in N/mm2 PLATE 9: TEST SETUP FOR CUBE COMPRESSIVE STRENGTH TEST BEFORE TESTING PLATE 10: VIEW SHOWS THE CUBE COMPRESSIVE STRENGTH TEST AFTER TESTING Variations of cube compressive strength with various percentage replacements of silica fume replacement of natural aggregate in concrete for 28 and 90 days curing has been calculated and variations are recorded vide table 3, and graphically super imposed variations are represented for the above periods vide fig 3. 28 days curing period 90 days curing period scale x-axis 1 unit = 25% 2 y-axis 1 unit = 5 N/mm cube compressive strength in N/mm 2 50 45 40 35 30 25 20 15 10 5 0 0 25 50 75 100 percentage of pelletized silicafume aggregate replacing natural aggregate Fig 3. Superimposed variation between cube compressive strength and percentage of pelletized silica fume aggregate replacing natural aggregate 41
  10. 10. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME MODE-II FRACTURE TEST ON DCN SPECIMENS The Mode-II fracture test on the double centered notched cubes was conducted in 3000KN digital high arm compression testing machine. The rate of loading was applied at 0.5KN/sec. The specimens after being removed from water were allowed to dry under shade for 24 hours and white washed for easy identification of minute cracks, while testing. For testing double centered notched (DCN) specimen of size 150x150x150mm, supports in the form of square steel bar throughout the width were introduced at one third portion slightly away from notches as shown in fig 2. Uniformly distributed load was applied over the central one third part between the notches and square cross section steel supports were provided at bottom along the outer edges of the that the central portion could get punched and sheared through along the notches on the application of loading. The test set up is shown vide plate 12 and 13. The notch depths provided were 45, 60, 75 and 90mm running throughout the width of the specimen. Thus the values of a/w ratio were 0.3, 0.4, 0.5, and 0.6 where ‘a’ is the notch depth and ‘w’ is the specimen depth 150mm. The distance between the notches is kept constant at 50mm and width of the notch was 2mm. For Double centered notch specimens the ultimate loads are recorded through 3000KN high arm digital compression testing machine. The test results were recorded vide table no 4 to 7 for ultimate load in Mode-II for DCN samples with a/w ratios of 0.3, 0.40, 0.50 & 0.60. Superimposed Variations for percentage of Silica fume aggregate replacing natural aggregate and ultimate load for 28 and 90 days are represented graphically vide fig 4 to 6. Also Superimposed Variations for percentage of Silica fume aggregate replacing natural aggregate and in-plane shear stress for 28 and 90 days are represented graphically vide fig 7 to 9. a/w a/w a/w a/w scale x-axis 1 unit = 25% y-axis 1 unit = 10 KN 28 days curing period 150 140 130 120 = 0.30 = 0.40 = 0.50 = 0.60 ultimate load in KN 110 100 90 80 70 60 50 40 30 20 10 0 0 25 50 75 100 Percentage of pelletized silica fume aggregate replacing natural aggregate ultimate load in KN Fig 4. Superimposed variation between ultimate load and percentage of pelletized silica fume aggregate replacing natural aggregate a/w a/w a/w a/w scale x-axis 1 unit = 25% y-axis 1 unit = 10 KN 90 days curing period 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 0 25 50 75 = 0.30 = 0.40 = 0.50 = 0.60 100 Percentage of pelletized silica fume aggregate replacing natural aggregate Fig 5. Superimposed variation between ultimate load and percentage of pelletized silica fume aggregate replacing natural aggregate 42
  11. 11. Ultimate load in KN International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME Scale x-axis 1 Unit = 25% y-axis 1 Unit = 10 KN 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 28 Days Curing a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 90 Days Curing a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 0 25 50 75 100 Percentage of pelletized silica fume aggregate replacing natural aggregate Fig 6. Superimposed variation between ultimate load and percentage of pelletized silica fume aggregate replacing natural aggregate Scale X-AXIS 1 UNIT = 25% 2 Y-AXIS 1 UNIT = 0.50 N/mm Curing period = 28 Days In-Plane shera streSS in N/mm 2 4.5 4.0 a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 Percentage of pelletized silica fume aggregate replacing natural aggregate Fig 7. Superimposed variation between in-plane shear stress and percentage of pelletized silica fume aggregate replacing natural aggregate Scale X-AXIS 1 UNIT = 25% 2 Y-AXIS 1 UNIT = 0.50 N/mm Curing period = 90 Days In-Plane shera streSS in N/mm 2 6.0 5.5 a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 Percentage of pelletized silica fume aggregate replacing natural aggregate Fig 8. Superimposed variation between in-plane shear stress and percentage of pelletized silica fume aggregate replacing natural aggregate 43
  12. 12. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME Scale x-axis 1 Unit = 25% 2 y-axis 1 Unit = 0.50 N/mm 6.5 6.0 5.5 28 Days Curing a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 5.0 90 Days Curing a/w = 0.30 a/w = 0.40 a/w = 0.50 a/w = 0.60 4.5 Y Axis Title 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 X Axis Title Fig 9. Superimposed variation between in-plane shear stress and percentage of pelletized silica fume aggregate replacing natural aggregate DISCUSSION OF CRACK PATTERNS The presence of cracks is a characteristic structural feature of most cement based materials. Micro cracking may takes place first as a consequence of the partial segregation of the aggregates and plastic shrinkage while the fresh concrete is setting. Temperature differences and drying shrinkage promote further cracking of concrete. After the concrete hardens, various factors aggravate the already existing micro cracks and cause the initiation of new ones. It is thought that cracks whatever their origin is (mechanical, thermal, chemical etc) can act as major pathways for water or aggressive chemical ions to penetrate into concrete, reducing its strength. In case of cubes under compression initial cracks are developed at top and propagated to bottom with increase in load and the cracks are widened at failure along the edge of the cube more predominantly along the top side of casting. In case of DCN specimens during testing, for most of the specimens with a/w= 0.3 initial hair line cracks started at the top of one or both the notches, and as the load was increased further, the cracks widened and propagated at an inclination and sometimes to the middle of the top loaded zone. Simultaneously the cracks formed at the bottom of one or both the notches and propagated downwards visible inclination. In some cases cracks branched into two either at the two edges of the supporting square bar at bottom or at the edge of the loaded length at top or at both places. In a few cases, initial cracks started at the bottom of the one or both notches. As the load was increased propagation of theses cracks at an inclination was observed along with the formation of cracks at top of the notches. These cracks finally propagated toward the middle of the top loaded zone leading to failure of the specimen. Hence failure of the specimens with a/w = 0.3, could be attributed to the flexure cum shear type of failure. For most of the specimens with a/w = 0.4, 0.5, 0.6, as the load was applied formation of initial hair line cracks at the top of one or both the notches was observed. With the increase of load propagation of these cracks in more or less vertical direction along with the formation of new cracks at the bottom of one or both the notches was observed. Finally the specimens failed by shearing along the notches. In most of the cases the cracks branched into two to join either the two edges of the supporting square bars at bottom or at the edge of the loaded length at top or at both places. In this case also, in a few specimens, initial cracks started at the bottom of one or both the notches. As the load was increased propagation of these cracks in more or less vertical direction along with formation of new cracks at top of the one or both the notches was observed leading to final collapse of the specimens along the notches. Thus except for some of the specimens of lower notch-depth ratio i.e., 0.3, the specimens of other higher a/w ratios of cement concrete failed all along the notches in more or less vertical 44
  13. 13. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME fashion. The breaking sound of aggregate is more for 100% replacement of natural aggregate by Silica fume aggregate. Natural aggregate does not have any sound while crushing. In general the crack widths are more in light weight aggregate than in normal aggregate concrete. Plate 11 and 14 shows the DCN specimens before and after testing respectively. a/w= 0 a/w=0.60 a/w= 0.50 a/w = 0.40 a/w=0.3 PLATE 11. DCN SPECIMENS BEFORE TESTING PLATE 12. TEST SET UP OF DCN CUBES PLATE 13. DCN SPECIMENS AFTER TESTING 45
  14. 14. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME a/w= 0 a/w=0.3 a/w = 0.40 a/w= 0.50 a/w=0.60 PLATE 14. CRACK PATTERN AFTER TESTING DISCUSSION OF TEST RESULTS INFLUENCE OF PELLETIZED COMPRESSIVE STRENGTH SILICA FUME AGGREGATE ON CUBE In the present study Silica fume aggregate has been replaced by natural aggregate in volumetric percentages of 0, 25%, 50%, 75% and 100%. The variation of compressive strength versus percentage replacement of Silica fume aggregate with natural aggregate is presented in table 3 and superimposed graphical variation for the two periods of curing are represented in fig 3. From this figure and table, it is observed that the decrease in compressive strength of concrete with 100 % replacement of Silica fume aggregate with natural aggregate is 65.60 % at 28 days and 43.07% at 90 days of curing. The cube compressive strength is found to increase drastically from 28 days to 90 days of curing. The target mean strength of M20 grade of concrete i.e., 26.6 N/mm² has been found to be achieved when the natural aggregate is replaced even with 100% of Silica fume aggregate after 90 days of curing as tabulated in table 3. However the target mean strength of M20 grade of concrete i.e. 26.60 N/mm2 at 28 days has not been achieved with any percentage of replacement of silica fume aggregate with natural aggregate. INFLUENCE OF PELLETIZED SILICA FUME AGGREGATE ON ULTIMATE LOAD All the DCN specimens with different a/w ratios i.e., 0.3, 0.4, 0.5 and 0.6 and with different percentages of Silica fume aggregates i.e., 0%, 25%, 50%, 75%, 100%, were tested with load in Mode-II (in-plane shear). The variations of ultimate loads versus percentage of Silica fume aggregate replacement of natural aggregate in concrete are presented in the tables 4 to 7. Super imposed variation of percentage decrease in ultimate load verses percentage of Silica fume aggregate replacement of natural aggregate in concrete are represented vide fig 4 to 6 for different a/w ratios (i.e., 0.3, 0.4, 0.5, 0.6). From the above figs, it may be observed that 46
  15. 15. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME with the addition of Silica fume aggregate the ultimate load in in-plane shear of the specimens decreases continuously up to 100% replacement of natural aggregate by Silica fume aggregates and increases with age i.e. from 28 days to 90 days curing. INFLUENCE OF PELLETIZED SILICA FUME AGGREGATE ON IN-PLANE SHEAR STRESS The In-plane shear stress at ultimate load for different percentage replacements of Silica fume aggregate (0- 100%) and for different notch depth ratios for 28 and 90 days are presented in tables 8 to 11. Also the super imposed variations of in-plane shear stress versus percentage replacement of Silica fume aggregate with a/w ratios of 0.3, 0.40, 0.50 and 0.60 are presented vide fig 7 to fig 9 for 28 and 90 days curing. It is observed that In-plane shear stress is decreasing continuously with the increase in percentage replacement of conventional granite aggregate by Silica fume aggregate (i.e., 0%, 25%, 50%, 75%, 100%) and increasing with age from 28 to 90 days of curing for notch depth ratios of 0.30, 0.40, 0.50 and 0.60. TABLE 3: CUBE COMPRESSIVE STRENGTH Sl. No Name of the mix Percentage volume replacement of coarse aggregate (%) Natural aggregate 1 2 3 4 5 SF-0 SF-25 SF-50 SF-75 SF-100 100 75 50 25 0 Compressive strength N/mm2 Pelletized Silica Fume Aggregate 0 25 50 75 100 Percentage of decrease in compressive strength 28 Days 90 days 28 days 90 days 41.08 16.00 14.65 14.39 14.13 47.39 40.83 34.68 30.62 26.98 0.00 -61.05 -64.34 -64.97 -65.60 0.00 -13.84 -26.82 -35.39 -43.07 TABLE 4: ULTIMATE LOAD AND PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w= 0.3 Sl. No 1 2 3 4 5 Name of the mix SF-0 SF-25 SF-50 SF-75 SF100 Percentage volume replacement of coarse aggregate (%) Natural aggregate 100 75 50 25 0 Pelletized Silica Fume Aggregate 0 25 50 75 100 Ultimate load in KN Percentage of increase or decrease in Ultimate load of N.A. 28 days 90 days 28 days 90 days 144.00 100.00 93.00 89.67 86.33 194.67 115.00 105.67 101.33 88.33 0.00 -30.56 -35.42 -37.73 -40.05 0.00 -40.93 -45.72 -47.95 -54.63 47
  16. 16. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME TABLE 5: ULTIMATE LOAD AND PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w=0.4 Sl. No 1 2 3 4 5 Name of the mix SF-0 SF-25 SF-50 SF-75 SF100 Percentage volume replacement of coarse aggregate (%) Natural aggregate 100 75 50 25 0 Pelletized Silica Fume Aggregate 0 25 50 75 100 Ultimate load in KN Percentage of increase or decrease in Ultimate load of N.A. 28 days 90 days 28 days 90 days 105.00 97.33 89.33 88.33 83.00 138.00 112.33 103.00 100.33 87.33 0.00 -7.30 -14.92 -15.88 -20.95 0.00 -18.60 -25.36 -27.30 -36.72 TABLE 6: PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w= 0.5 S.N o 1 2 3 4 5 Name of the mix SF-0 SF-25 SF-50 SF-75 SF-100 Percentage volume replacement of coarse aggregate (%) Natural aggregate 100 75 50 25 0 Pelletized Silica Fume Aggregate 0 25 50 75 100 Ultimate load in KN Percentage of increase or decrease in Ultimate load of N.A. 28 days 90 days 28 days 90 days 95.00 90.67 86.33 85.33 60.67 124.67 98.33 93.67 89.33 73.00 0.00 -4.56 -9.13 -10.18 -36.14 0.00 -21.13 -24.87 -28.35 -41.45 TABLE 7: PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w= 0.6 Sl. No Name of the mix Percentage volume replacement of coarse aggregate (%) 1 2 3 4 SF-0 SF-25 SF-50 SF-75 100 75 50 25 Pelletized Silica Fume Aggregate 0 25 50 75 5 SF100 0 100 Natural aggregate Ultimate load in KN Percentage of increase or decrease in Ultimate load of N.A. 28 days 90 days 28 days 90 days 90.33 86.00 82.67 74.33 95.67 94.33 92.33 86.00 0.00 -4.79 -8.48 -17.71 0.00 -1.40 -3.49 -10.11 57.33 64.33 -36.53 -32.76 48
  17. 17. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME TABLE 8: IN-PLANE SHEAR STRESS (MODE-II) FOR DCN SPECIMENS WITH a/w= 0.30 WITH PERCENTAGE DECREASE Sl. No Name of the mix Percentage volume replacement of coarse aggregate (%) Natural aggregate 1 2 3 4 5 SF-0 SF-25 SF-50 SF-75 SF-100 100 75 50 25 0 Pelletized Silica Fume Aggregate 0 25 50 75 100 In-plane shear stress in N/mm2 Percentage of increase or decrease in Ultimate load with N.A. 28 days 90 days 28 days 90 days 4.57 3.17 2.95 2.85 2.74 6.18 3.65 3.35 3.22 2.80 0.00 -30.63 -35.45 -37.64 -40.04 0.00 -40.94 -45.79 -47.90 -54.69 TABLE 9: IN-PLANE SHEAR STRESS (MODE-II) FOR DCN SPECIMENS WITH a/w= 0.40 WITH PERCENTAGE DECREASE Sl. No Name of the mix Percentage volume replacement of coarse aggregate (%) Natural aggregate 1 2 3 4 5 SF-0 SF-25 SF-50 SF-75 SF-100 100 75 50 25 0 Pelletized Silica Fume Aggregate 0 25 50 75 100 In-plane shear stress in N/Sq.mm Percentage of increase or decrease in Ultimate load with N.A. 28 days 90 days 28 days 90 days 3.89 3.60 3.31 3.27 3.07 5.11 4.16 3.81 3.72 3.23 0.00 -7.46 -14.91 -15.94 -21.08 0.00 -18.59 -25.44 -27.20 -36.79 TABLE 10: IN-PLANE SHEAR STRESS (MODE-II) FOR DCN SPECIMENS WITH a/w= 0.50 WITH PERCENTAGE DECREASE Percentage of increase Percentage volume In-plane shear stress or decrease in replacement of coarse in N/Sq.mm Ultimate load with aggregate (%) Sl. Name of N.A. No the mix Pelletized Natural Silica Fume 28 days 90 days 28 days 90 days aggregate Aggregate 1 SF-0 100 0 3.69 5.54 0.00 0.00 2 SF-25 75 25 3.53 4.37 -4.34 -21.12 3 SF-50 50 50 3.44 4.16 -6.78 -24.91 4 SF-75 25 75 3.29 3.97 -10.84 -28.34 5 SF-100 0 100 2.70 3.24 -26.83 -41.52 49
  18. 18. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME TABLE 11: IN-PLANE SHEAR STRESS (MODE-II) FOR DCN SPECIMENS WITH a/w= 0.60 WITH PERCENTAGE DECREASE Percentage of increase Percentage volume In-plane shear stress or decrease in replacement of coarse in N/Sq.mm Ultimate load with aggregate (%) Sl. Name of N.A. No the mix Pelletized Natural Silica Fume 28 days 90 days 28 days 90 days aggregate Aggregate 1 SF-0 100 0 3.45 5.31 0.00 0.00 2 SF-25 75 25 3.28 5.24 -4.93 -1.32 3 SF-50 50 50 3.19 5.13 -7.54 -3.39 4 SF-75 25 75 3.13 4.78 -9.28 -9.98 5 SF100 0 100 2.19 3.57 -36.52 -32.77 CONCLUSIONS From the limited experimental study the following conclusions are seem to be valid: From the study it may be concluded that the cube compressive strength has decreased continuously with the increase in percentage of Silica fume aggregate. The target mean compressive strength of M20 concrete i.e., 26.6 N/mm² has been achieved when the natural aggregate is replaced even with 100% of Silica Fume aggregate after 90 days of curing. But the cube compressive strength is found increase from 14.13 N/mm2 to 26.93 N/mm2 for 100% replacement of Silica fume aggregate from 28 days to 90 days of curing. From the study it may be observed that the percentage of decrease in compressive strength is increased with the percentage of increase in silica fume aggregate (0- 100%) and with 25% replacement the percentage decrease is 61.05 and with 100% replacement it is 65.60% and it is observed that the effect of percentage replacement of natural aggregate with silica fume aggregate is almost same at 28 days. It is also observed that the compressive strength increases with age and the increase is around 15.36% for natural aggregate (28 to 90 days) and for 100% silica fume aggregate it is 90.94% after 90 days over the 28 days strength. Ultimate loads in Mode-II fracture are found to decrease continuously with the percentage increase in silica fume aggregate content Ultimate loads in Mode-II fracture are found to decrease continuously with the increase in a/w ratio. It may be observed that In-plane shear stress at ultimate load decreases continuously with the percentage increase in silica fume aggregate content and the In plane shear stress increases from 2.80 N/mm2 to 3.57 N/mm2 for 100% replacement of Silica fume aggregate for 90 days of curing period with increase in a/w ratio i.e., from 0.3 to 0.60 and the in-plane shear stress increases with age for all a/w ratios from 28 days to 90 days of curing. Based on the experimental investigations it is concluded that cold bonded artificial aggregate manufactured from industrial waste i.e., Silica fume aggregate is in no way inferior to naturally available light weight aggregate. 50
  19. 19. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME BIBLIOGRAPHY 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Harikrishnan KI, Ramamurthy (2006). Influence of Pelletization Process on the Properties of Fly Ash Aggregates. Waste Manag., 26: 846-852. Harikrishnan KI, Ramamurthy (2006). Influence of Pelletization Process on the Properties of Fly Ash Aggregates. Waste Manag., 26: 846-852. Agarwal, B.D. and Giare, G.S., “Fracture toughness of short-fiber composites in Modes-I and II”, Engineering Fracture Mechanics, Vol. 15, No. 1, 1981, pp.219-230. Bazant , Z.,p, and Pfeiffer, P.A., “Shear fracture tests of concrete”, materials and structures (RKLEM), 1984, vol. 19, pp.111-121. Watkins, J. and Liu, K.L.W., “A Finite Element Study of Short Beam Test Specimens under Mode-II loading”, The International Journal of Cement Composites and Light Weight Concrete, Vol.7, No.1, Feb.1985, pp.39-47. Bazant , Z.,p, and Pfeiffer, P.A., “Tests on shear fracture and strain softening in concrete”, proceedings of second symposium on interaction of Non-nuclear Munition with structures Florida, USA, April 1985, pp. 254-264. LIU ,B., Barr , B.I.G., and Watkins , J., ”Mode-II fracture of fiber reinforced concrete materials”’ International Journal of cement composites and light weight concrete, Vol.7, No.2, May, 1985, pp.93-101. Davies, J., Yim, C.W.A and Morgan, T.G., “Determination of Fracture parameters of punch through shear specimens”, The International Journal of Cement Composites and Light weight Concrete, Vol. 9, No. 1, Feb. 1987, pp. 33-41. Bhaskar Desai . V, “Some studies on Mode - II fracture and stress – strain behavior in shear of cementitious materials”, Ph.D thesis, Indian Institute of Science, Banglore”. Prakash Desayi, Raghu Prasad.B.K, and Bhaskar Desai. V, “Experimental determination of KIIc from compliance and fracture energy”, proceedings national seminar on Aerostructures, organized by IIT, Kanpur, India, 29-30, Dec, 1993, pp. 33-34. Prakash desayi, B.K.Raghu Prasad and V.Bhaskar Desai, “Mode – II fracture of cementitious materials- part – I : Studies on specimens of some new geometries”, Journal of Structural Engineering, Vol.26, No.1, April 1999, pp.11-18. Prakash desayi, B.K.Raghu Prasad and V.Bhaskar Desai, “Mode – II fracture of cementitious materials- part – II: Fracture toughness of cement paste, mortar, concrete and no-fines concrete. Journal of structural engg Vol. 26, No. 1, April 1999, pp. 19-27. Prakash desayi, B.K.Raghu Prasad and V.Bhaskar Desai, “Mode – II fracture of cementtiotus materials- part – III: Studies on shear strength and slip of cement paste, mortar, concrete and no-fines concrete. Journal of structural engg Vol. 26, No.2, July 1999, pp. 91-97. Prakash desayi, B.K.Raghu Prasad and V.Bhaskar Desai, conducted Mode-II fracture of cementitious materials- part-IV: Fracture toughness, shear strength and slip of fibre reinforced cement mortar and concrete. Journal of structural engg. Vol. 26, No. 4, Jan 2000, pp. 267-273. Prakash desayi, B.K.Raghu Prasad and V.Bhaskar Desai, conducted Mode-II fracture of cementitious materials- part-V: Size effect on fracture toughness shear strength and slip of cement mortar and concrete reinforced with and without fibers. Journal of structural engg, Vol, 27, No. 2, July 2000, pp. 99-104. Dr. D. V. Prasada Rao and G. V. Sai Sireesha, “A Study on the Effect of Addition of Silica Fume on Strength Properties of Partially used Recycled Coarse Aggregate Concrete”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 6, 2013, pp. 193 - 201, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 51

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