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  • 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. 17-30 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET ©IAEME STUDIES ON RICE HUSK ASH CEMENT CONCRETE 1 Er. S. THIROUGNANAME, 2 Dr. T.SUNDARARAJAN 1 M.Tech., MIE., MISTE., FIAH., MIWWA., AMISE., MITArb., Assistant Engineer, Public works Department, Puducherry, India 2 Professor, Department of Civil Engineering, Pondicherry Engineering College, Puducherry, India ABSTRACT Rice husk which is an agricultural by–product is abundantly available all over the world. Most of the rice husk, which is obtained by milling paddy, is going as a waste materials even though some quantity is used as bedding material, fuel in boilers, brick kilns etc., The husk and its ash, which not only occupy large areas causing space problems, but also cause environmental pollution. In this experimental investigation, the strength of RHA- Cement concrete is evaluated for two grades of concrete (M15, M20) at various replacement levels of RHA (ranging from 5% - 20%). The results obtained are compared with conventional concrete. It is concluded that 20% of OPC can be replaced with RHA to attain comparable compressive strength of M15 grade and that only 10% of OPC can be replaced with RHA to attain the comparable compressive strength of M20 grade. Keywords: Rice Husk, Mortar, Rice Husk Ash (RHA), Ordinary Cement (OPC). INTRODUCTION Cement is the most important binding material in structural constructions as it is used at different stages of construction in the form of mortar or concrete. Conventional building materials are becoming increasingly uneconomical. On the other hands, rapid industrialization has let to widespread pollution of air, water and soil and accumulation of large industrial wastes (solid, liquid) posing disposal and environmental problems. It would be worthwhile to make use of suitable waste products to replace some of the conventional materials. The use of such materials would minimize the use of scarce materials and hence, there will be economy in the cost of construction. Most important and highly expensive building material is Ordinary Portland Cement (OPC). The use of OPC attracted every one in the construction industry and its application in steadily increasing when compared to other material used in those days. 17
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME With the present level of OPC production, it is not possible to meet the dowelling needs of the country and also for pavement of roads, bridges, canal works etc. M15 grade concrete is used in general construction works, as this characteristic strength is sufficient for most of the building elements. From above, it is clearly seen that a high strength binder like OPC is not needed for most of the general works and hence it can be substituted partially or fully by producing a binder from waste materials at lesser cost but with a desirable degree of strength and durability. The answer to the above question has been realized in the form of Rice Husk Ash (RHA), which has been proved to be a successful replacement up to 50% of OPC [1]. Rice Husk which is an agricultural by-product is abundantly available all over the world, more so, in the countries like India, where it is a staple food. Due to this abrasive character, poor nutritive value, very low bulk density and high ash content, a small portion only is used as bedding material, fuel in boilers, brick kilns etc. To overcome the above problems, studies initiated by several investigators on the use of RHA led to its use as a pozzolanic material, in view of its high silica content (say about 90%). LITERATURE REVIEW In this chapter, the work carried out by various investigators (in India and abroad) on the use of RHA for the production of cementitious material; use of RHA as partial replacement of OPC for producing concrete and mortar are reviewed and presented. HYDRAULIC CEMENT FROM RHA As early as in 1974, P.K. Mehta [2] developed a process for making cement from Rice Husk in which the rice husk is burnt under controlled conditions and the ash mixed with hydrated lime. Since the silica in the amorphous RHA is already in a very reactive form, a hydraulic cement can be produced simply by blending or by intergrinding the RHA with lime. As long as lime and silica are present in active state in an anhydrous material, the cementing property can be obtained in aqueous environments through formation of the calcium silicate hydrates. In some experiments, blends of Portland Cement with RHA yielded good quality hydraulic cements. One unique characteristic of RHA cement is a permanent black colour which is useful in making black concrete for glare-free pavements or for architectural applications. The second unique characteristic of RHA cements. is the excellent resistance of the materials to acidic environments. Upon hydration of these cements, none of the lime would be present in the form of free Ca(OH)2. The products of hydration consists of calcium silicate hydrates and silica gel and therefore more resistant to acid attack. CEMENTITIOUS BINDER FROM WASTE LIME SLUDGE AND RICE HUSK CBRI, India has evolved a cementitious binder from waste lime sludge and rice husk. The powder form of waste lime sludge and rice husk are dry mixed together roughly in equal amounts by weight and the required quantity of water added to dry mix, for making cakes. After drying them, they are fired in open with a grating base or in a trench. The fired material are then ground in a ball mill to achieve sufficient fineness. The binder thus obtained had inherent characteristics of lime based compositions. Some of the important properties of the above types of binders are given in Table 1. 18
  • 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 1: Properties of the Binder produced from Waste Lime and Rice Husk Property Value S. No. 1. Bulk density (Kg/m3) 360(on firing) 700(on grinding) 2. Setting times Initial (min) Final (min) 3. 60 - 90 480 – 600 Water retention 1:1.5 (Binder:sand) 1:20 (BInder:sand) 4. Soundless (Le-Chatlier) (mm) 71%(flow) 60%(flow) 1.50 Note: Water retention is tested as per IS :2250, ‘Code of practice for preparation and use of masonry mortars’. The crushing strength values of the above binder (tested as per IS: 712-1973, Specification for building lime) using one part of binder and three parts of standard sand and using three types of sludge, namely, sugar sludge, carbide sludge and paper sludge satisfied the requirement of class-A lime i.e. eminently hydraulic (14 and 28 days stipulating strength being 17.5 kg/cm2 and 28.0 kg/cm 2). The above binder was recommended for plastering and can be used as plain cement concrete (PCC) works in foundations, floors, using conventional aggregates for use in precast hollow or solid blocks for light loading purpose, for stabilizing soil; bricks with sand under pressure using semi-dry mix. In spite of the above indicated uses, it did not gain popularity due to quick-setting nature of the cementitious material and the process was found to be cumbersome and not suitable for large-scale commercial production. CEMENT FROM RICE HUSK ASH At I.I.T., Kanpur, two alternate routes were developed for making cement from RHA namely i)ASHMENT process and ii) ASHMOH process. In the ASHMENT process, RHA is ground alone in a ball mill and mixed with Portland cement in a specified weight ratio, in the range of 3/2 to ½ and the resulting blend called as ASHMENT cement. However, in the planted ASHMOH process, RHA, lime and an additive are ground together in a ball mill to form ‘ASHMOH cement’. The same plant can employ ‘ASHMOH’ and or ‘ASHMENT’ technologies without any modifications. RAW MATE RIAL S, CEMENT PROPERTIE S AND APPLICATIONS OF ASHMOH Raw Materials RHA obtained from the combustion process of rice husk as fuel or rice husk heaps burnt in open fields, hydrated lime containing atleast 85% CaO content; OPC as an additive (8 – 10%) to hasten the setting time, are the raw materials required (i.e. 64%; 27%; 9% - RHA; hydrated lime; additive- OPC) ASHMOH cement obtained by the process had the properties as given in Table 2. 19
  • 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 2: Properties of ASHMOH Cement Property Sl.No. 1 Setting times Initial (min) Final (hrs) 2 3 4 Value 60 - 90 6 -7 Compressive Strength (ASHMOH : sand = 1:3 and W/B = 0.475 – 0.5) at 3 days ( Kg/cm2) 7 days ( Kg/cm2) 28 days ( Kg/cm2) 110 – 150 140 – 180 220 – 280 Compressive Strength of 1:2:4 ASHMOH concrete W/c = 0.55-0.65) ( Kg/cm2) 140 – 190 Bulk density ( Kg/cm2) 700 - 750 Note: The loose bulk density of ASHMOH is about 50% of that OPC and hence when preparing mixes by volume, 1.8 to 2.0 times the required volume of ASHMOH cement is taken, to maintain the weight ratios constant. Applications ASHMOH cement is not recommended for reinforced or prestressed concrete load bearing structures, such as roofs, lintels etc. It is eminently suitable for non-critical routine applications such as masonry work, sand-cement bricks and blocks, soil stabilization, village roads; water tanks, canal lining, water conduits; foundation concrete etc., but not for RCC works. ASHMOH is compatible with OPC in all proportions. A mixture of the two, containing more than 30% OPC, is for all intents and purposes indistinguishable from conventional cement (OPC) Inspite of the certain properties claimed by the investigators at IIT Kanpur, tests conducted at Annamalai University (2) indicated that the initial setting time is about 30 minutes and the strength at 28 days of normal curing 120 kg/cm2 only, which was normally expected of a binder, such as indicated above. CEMENT FROM RICE HUSK, CLAY AND HYDRATED LIME A process has been developed to make high quality pozzolanic materials from rice husk and clay. The pozzalonic which mixes with lime gives a very good cementitous material and when blended with Portland Cement gives a Portland Pozzolana cement. To make lime-pozzolana cement, the finely ground Pozzolana as obtained is intimately mixed in the dry hydrated line in the ratio of 2:1 (by volume). This may be mixed insitu at the construction site or during grinding of the pozzolana. Following are the various properties of the rice husk clay pozzolana, obtained by the above process. Loss of ignition Specific gravity Lime reactivity (IS 1727 – 1967) Lime pozzolana mortar - 1.5% 2.34 64 to 106 ( Kg/cm2) 44 to 72 (Kg/cm2) 20
  • 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 strength properties of Rice Husk Clay pozzolana are given in the Table 3. Table 3: Strength Properties of Rice Husk Clay Pozzolana Compressive Strength Composition ( Kg/cm2) Water Retention 7 days 28 days 1:6 (cement : sand) 1:2:6(lime:Pozzolana:sand) 1:2:9(lime:Pozzolana:sand) 12-20 24.4 13 20-30 45.2 22.5 30 72 67 The lime pozzolana has superior properties and chaper in cost and can replace OPC in normal construction works as a mortar for masonry and for plastering. However, it should not be used for any RCC work. RESEARCH CARRIED OUT AT ANNAMALAI UNIVERSITY ON CEMENITIOUS MATERIALS FROM RICE HUSK During 1979-82, research work on the production of paddy husk cement from paddy husk and lime was carried out in different stages at Annamalai University (2,3) Systematic experimental studies were conducted on the type of furnace required to obtain good burnt clinkers of rice husk and lime by open burning, the effect of various ratios of the blend of RHA and lime on the compressive strength and on the effect of type of curing (normal and stem curing) on the strength attainment and various strength characteristics. Gypsum was used as an additive (5% , 10% and 15%) to control the setting times of the cementitious material and to study its effect on the strength of cement. From the extensive test results obtained it has been concluded that the i) Compressive strength of rice husk is the same both for normal and steam curing at 28 days and it is the order of 90 ( Kg/cm2) ii) The adhesive strength of the above mortar (1:4, by wt) is about 50% of that of conventional cement. iii) It is found that the rice husk cement has good setting properties when compared to that of OPC. iv) The bulk density of rice husk cement is only 790 ( Kg/m3) which is about 50% of the bulk density of OPC. Thus, the rice husk cement mortar ratio of 1:1:5 (volume) is the same as 1:3 by weight. The above mortar can be recommended for wall plastering and floor etc., v) The compressive strength of brick masonry blocks plastered with rice husk cement on all the sides was found to be equal to that of the strength of OPC blocks and, vi) Stem curing produces a further rate of increase in hardening of cement and that the optimum period of stem curing is 7 hours. They have also suggested further studies on the effect of stem curing pressure (I,e, at low, medium and high) on the various properties. STUDIES ON RHA – CEMENT CONCRETE AND MORTAR Studies in Taiwan Taiwan produces abundant quantity of rice husk containing primarily silica, rice husk possesses reactive characteristics after burning and hence, large potential for use in concrete than for 21
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME soil stabilization. The reactive of RHA is dependent on both its origin and its treatment. The effect of RHA on the microstructure, shrinkage, porosity and strength development characteristics of the cement paste were studied by Hwang and Wu (4). They investigated the effect of temperature of burning rice husk on the reactivity of the resulting RHA, which was quantitatively and qualitatively investigated by means of X-ray diffraction and EDAX. In addition, the effect of RHA on cement properties, was investigated covering the aspects such as workability, bleeding, setting times, shrinkage, absorption, compressive strength and heat of evolution in the paste during hydration. Moreover, ignition loss, optical microscopy, SEM and MIP investigations were employed to analyze both hydration mechanisms and micro-structure. From the above studies they have concluded that i) Factors such as, heating rate, burning period, ambient furnace conditions will affect the quality of ash, ii) At a higher burning temperature of 700 C, rice husk forms ash primarily composed of SiO2 Higher temperature do no yield greater quantities of SiO2 iii) The heat of hydration varies inversely with the water-cement ratio (w/c) regardless of whether or not the system contains RHA. iv) The amount of bleeding is inversely proportional to the RHA content in the paste and v) The water retaining effect of RHA and the increased quantity of C-S-H get generated by the ash that fills the space previously occupied by free water both influence the strength and physical properties. Cement paste containing RHA at a higher w/c (0.52 to 0.54), develops higher ultimate strength than that without ash after 60 days, although their early strengths are similar. Studies in Japan Sugita and others (5) studied i) the temperature effect on the incineration of rice husk to obtain large amounts of non-crystaline ash, ii) pozzolanic reactivity of RHA using the Ca(OH)2 solution in electric conductivity in relation to the X-ray diffraction method; iii) pulverizing property of RHA iv) the relationship between the compressive strength of mortar with RHA and conductivity data v) the porosity changes and drying shrinkage of mortar with RHA and vi) resistance to acid attack and carbonation of mortar containing RHA. From the above studies they concluded that i) Lower combustion temperature over the flash point and shorter combustion periods, the higher the amount of non-crystalline RHA. ii) Higher the non-crystalline form of RHA, lower the energy required to pulverize it. iii) Variation in electric conductivity indicates the amount of non-crystalline RHA present in the sample. iv) RHA obtained in electric hearth below 600°C and pulverized for 80 minutes, had a higher pozzolanic activity than other pozzolanic materials, such as fly ash, v) Drying shrinkage of mortar increased with the addition of RHA, which may be due to the increase in fine pores in the mortar. vi) There is improvement in the resistance to acid attack by using highly non-crystallized RHA. vii) Depth of neutralisation of mortar with RHA was estimated to be similar to that of controlled mortar (without RHA) and, viii) Freeze-thaw resistance of mortar with RHA was similarly to that of controlled mortar, which depends on the W/B and the amount of RHA. 22
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Studies in Turkey Mazlum and Vyan(6) studied the temperature effect of incinerating rice husk in furnaces at 400° C and 500° C for 1, 5 hours to obtain silica of amorphous state by sudden cooling. They studied the effect of environmental sulphate attack (Na2SO410H2O) on the flexural and compressive strength of mortars after 4,8, 12 weeks of exposure in the above medium, for RHA contents in cement ranging between 10% - 30% (by weight) at a constant W/B = 0.57 and using a super plasticiser (naphthalene formaldehyde). The specimens were exposed to the medium only after 28 days of normal curing and the results were compared with that of controlled mortar. From the above studies, they concluded that i) the flexural and compressive strengths of ash mortars (cured in water) are greater than those of controlled mortars ii) the flexural strength of ash mortars exposed to Na2SO4 medium have greater values than that of controlled mortars and ash mortars kept under normal curing and iii) that RHA is an active pozzolana and it can be used in sulphate environments, successfully. Studies on RHA Cement Concrete in India Seshagiri Rao and others (7) carried out detailed investigations on RHA cement concretes to evaluate its use as a structural material (i.e. for RCC applications and as a pavement material). The investigations were carried out to find the influence of a) fineness of ash; b) water/cement ratio; c) Cement-RHA content and; d) strength and durability of RHA concretes. Compressive strength, flexural strength (on PCC beams), flexural strength of RCC beams and slabs were studied. In order to study the durability, tests on permeability, abrasion resistance and resistance to dilute acids (5% HCI, H2SO4 and Acetic acid; 30 – 90 days of immersion, change in weight) were determined for RHA levels of 0-40%. From the above studied they have concluded that i) ii) iii) iv) v) vi) RHA fineness of 16,000 cm2/gm is optimum Upto 30% cement can be replaced by RHA for M15 and M20 grades. Flexural strengths are comparable with reference concretes. There is reduction in permeability. There is improved abrasion resistance and to acid attack and, RHA reinforced concretes are in no way inferior to conventional reinforced concretes. However, the above studies were not directed in evaluating RHA cement concrete as a pavement material, excepting the abrasion resistance test, i.e. whether it conforms to pavement quality concrete (PQC) has not be evaluated. EXPERIMENTAL INVESTIGATIONS The experimental investigations to study the compressive (cube and cylinder), tensile and flexural strengths of RHA cement concrete. PROPERTIES OF MATERIALS USED Cement, graded coarse aggregate (CA) of maximum size of 20 mm; fine aggregate (FA) (sand conforming to Zone-II gradation based on IS: 383-1970); Rice Husk Ash are the various materials used in this study. The basic properties of the above materials are given below. 23
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Cement 43 grade OPC (ACC brand) is used as the primary binder. The required quantity was procured a single batch, stored and used throughout the whole programme. The physical properties of cement obtained and used are given in Table 3.1. Sl.No 1 2 3 4 5 6 7 Table 3.1: Physical Properties of OPC Property Normal Consistency Initial setting time Final setting time Fineness (Blaines air permeability) Fineness (by dry sieving) Specific gravity Soundness value (Le-Chatlier Compressive strength (*) 3days 7 days 28 days Results 29% 110 min 160 min 285 m2/kg 9% 3.15 2.5mm 20.87 N/mm2 25.88 N/mm2 36.02 N/mm2 Note (*) Standard sand is used Coarse Aggregate (CA) Graded coarse aggregate (crushed granite stones) of maximum size of 20 mm is used. Table 3.2 shows the properties of the above CA. Sl. No. 1 Table 3.2: Properties of Coarse Aggregate Property Results Specific gravity 2.60 2 Water absorption 3 0.45% Particle shape Angular Fine Aggregate (FA) Sand conforming to grading Zone-II of IS: 383 -1970 is used as fine aggregate (FA). Its properties are given in Table 3.3 Sl. No. 1 2 3 Table 3.3: Properties of Fine Aggregate Property Results Specific gravity 2.60 Water absorption 0.55% Fineness modulus 2506 Rice Husk Ash (RHA) Paddy husk obtained from PAPSCO, Puducherry is used to prepare ash. Only a mixed variety of paddy husk could be obtained from the above source. Heaps of 25-30. Kg was burnt in open yard for over 24 hours at a time and the ash obtained was collected in clean bags. Initial dry sieving indicated the presence of large quantities of particles higher than cement size and hence, it was 24
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME decided to pulverize the ash so that cement sized particles could be obtained i.e. 90% of particles passing through 90 micron sieve. The above process was done in M/s. Kumar Minerals Mettupalayam Industrial Estate, Puducherry. Only such ash is used in the present study after again dry sieving them to ascertain its fineness. Ash obtained by the above process was used for the partial placement of OPC, the replacement levels ranging 5 – 20% (by weight). The various chemicals properties of RHA are determined in the chemical testing and analytical laboratory Guindy, Chennai32 and the physical properties by standard laboratory methods. The above results are given Table 3.4 and 3.5 respectively. Sl.No 1 2 Table 3.4 Chemical Properties of RHA Property 3 Moisture PH of 5% solution Electrical conductivity (EC) of 5% solution in milli mohz 4 5 6 7 Total Carbon (C) Total Potassium as K2O Silicon as Si Total Phosphorus as P2O5 Value 0.67% 8.70 0.55 29.68% 0.89% 35.65% 0.49% Water Ordinary potable tap water available in laboratory was used for making mortar and concrete and for curing purposes. Sl.No 1 2 3 4 5 Table 3.5: Physical Properties of RHA Property Value Normal Consistency 30% Fineness (before pulverizing) Dry sieving 77% (wt. retained on 75 µ) Fineness (before pulverizing) Dry sieving 12.5% (wt retained on 75µ) Wet Sieving 18.2%(Wt. retained on 75 µ) 17.9% (wt. retained on 45 µ) Specific gravity 2.14 Compressive strength (MPa) on mortar Cubes 1:3 using standard sand ) at 3days 10.5/8.5/7.1/5.1 7 days 13.1/10.9/7.9/6.3 28 days 18.7/17.7/16.9/16.7 Note: The four values of compressive strength correspond to 5% 10%, 15% and 20% replacement levels of RHA in OPC, in that order of occurrence, in the above table. TESTS ON WET RHA –CEMENT CONCRETE Normal consistency of RHA-Cement mortar, setting times (initial and final) and workability studies (slump, compaction factor) were carried out on wet concrete. 25
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Normal Consistency and Setting Times Sl.No. 1 2 3 Table 3.6: Consistency and Setting Times of RHA- Cement Description Replacement of RHA levels 5% 10% 15% 20% Normal Consistency (%) 35 39 43 45 Initial setting time (min) 169 150 105 90 Final Setting time (min) 203 195 190 185 The quantity of water required to produce a cement paste of standard consistency at various replacement levels of OPC by 5, 10, 15 and 20% by RHA and their corresponding setting times were determined by standard testing procedures. The above results are given in Table 3.6. Workability Studies Workability tests on two grade of concrete (1:2:4 and 1:1.5:3) with partial replacement of cement by RHA ( 5 – 20% by weight) and for W/B ratios varying 0.40 to 0.65 adopting standard testing procedures were carried out and the above test results are given in Table 3.7. Table 3.7: Results on Workability Studies on RHA-Cement Concrete RHA Replacement Level W/B Sl 5% 10% 15% 20% Mix Ratio No. Slump CF Slump CF Slump CF Slump CF 1 0.40 0 0.81 0 0.80 0 0.82 0 0.81 2 0.45 0 0.82 0 0.82 0 0.83 0 0.82 M15 3 0.50 0 0.85 0 0.83 0 0.83 0 0.82 4 0.55 0 0.86 0 0.84 0 0.84 0 0.82 5 0.60 5 0.86 7 0.85 3 0.84 0 0.82 6 0.65 10 0.88 8 0.86 10 0.85 5 0.83 7 0.40 0 0.82 0 0.83 0 0.79 0 0.79 8 0.45 0 0.82 0 0.83 0 0.80 0 0.80 M20 9 0.50 0 0.84 0 0.84 0 0.81 0 0.81 10 0.55 0 0.84 0 0.86 0 0.83 0 0.81 11 0.60 10 0.85 12 0.86 8 0.84 0 0.81 12 0.65 12 0.88 15 0.87 10 0.85 5 0.82 Note: CF – Compaction Factor Mix Proportioning First reference mixes (M15, M20 grades) were proportioned using conventional materials adopting IS method of mix design. The details of mix proportioning are given in Appendices A and B. The mix proportions obtained are 1:1.838:3.489 for M15 grade with W/B = 0.575 and 1:1.493:3.031 for M20 grade with W/B = 0.50. OPC was replaced by RHA (5%, 10%, 15% and 20% by weight) in the above mixes and the mix proportions adjusted for the specific gravity of RHA, to arrive at the mix proportion for each combination of RHA and OPC. The details of mix proportioning for various levels of RHA replacement are given in Appendices. The mix proportions thus obtained are given in Table 3.8. 26
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Sl.No. Table 3.8: Mix Proportions of RHA – Cement Concrete Binder Content Mix Proportion W/B Ratio OPC : RHA 100 : 00 1 : 1.838 : 3.489 0.575 95 : 05 1 : 1.831 : 3.477 0.575 90 : 10 1: 1.824 : 3.464 0.575 4 85 : 15 1: 1.818 : 3.451 0.575 5 80 : 20 1: 1.811 : 3.438 0.575 6 100 : 00 1: 1.493 : 3.031 0.500 7 95 : 05 1 : 1.487 : 3.018 0.500 90 : 10 1 : 1.480 : 3.005 0.500 9 85 : 15 1: 1.474 : 2.992 0.500 10 80 : 20 1: 1.467 : 2.979 0.500 1 2 3 8 M15 M20 Test Conducted Following tests were conducted on hardened concrete after 28 days of normal immersed curing i) compressive strength – cube and cylinder, ii) Split tensile strength (on cylinders) and iii) flexural strength (on prisms) 150 x 150 x 150 mm cubes, and 150 mm x 300 mm height cylinders for determining compressive strength; 100 x 200 mm height cylinders for split tensile strength and 100 x 100 x 500 mm beam specimens for determining the flexural strength were cast for each combination of the mix proportion given in Table 3.8. RESULTS, DISCUSSION AND CONCLUSIONS The results of the various tests conducted on the two grades of concrete M15 and M20 considering partial replacement of cement by RHA in the range of 5 -20% Workability Results of the above tests are given in Table 3.7. From the above results, it can be inferred that slump test is not giving reliable results for all RHA levels. On the other hand, CF test yields reliable results for all RHA content and for the two grades considered. As the RHA content increases in the binder there is a decrease in workability for all water-binder ratios and there is a increase for increase in water binder ratios. 27
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Compressive Strength Cube Compressive strength of reference and RHA cement concrete (for 4 different % replacements) for M15 and M20 are given in Table 4.1. From the above results, it can be seen that the compressive strength (at 28 days) of RHA cement concrete yields comparable strength of reference concrete, for RHA replacement levels upto 20% for M15 grade concrete and upto RHA replacement levels upto 10% for M20 grade concrete. However, the cylinder compressive strength of RHA cement concretes (given in Table 4.1) has comparable strength as that of the cube compressive strength for all grades of concrete considered in this study (i.e. M15, M20). Table 4.1: Compressive Strength of Different Grades of RHA-Cement Concrete Ratio of Description Average Compressive Strength (N /mm2) Cyl. To Sl.No. Cubic Cube Cylinder Comp. OPC RHA 7 Days 14 Days 28 Days 56 Days 28 Days Strength M15 100 95 90 85 80 M20 100 95 90 85 80 1 2 3 4 5 1 2 3 4 5 0 5 10 15 20 15.53 20.81 19.93 17.04 16.82 21.07 25.41 24.82 22.15 20.66 23.00 29.55 28.81 28.37 24.22 26.33 31.12 31.78 29.00 26.00 12.91 19.43 18.12 18.82 16.94 0.56 0.66 0.63 0.66 0.70 0 5 10 15 20 23.57 22.15 22.52 19.56 21.55 27.93 26.96 26.44 22.96 25.41 31.28 32.96 30.74 27.41 29.56 34.47 35.78 36.11 30.45 31.56 18.71 22.36 21.67 20.28 21.88 0.60 0.68 0.70 0.74 0.74 Split Tensile and Flexural Strengths The results of the above tests for various types of concretes are given in table 4.2. All the values, irrespective of RHA replacement levels and grades of concrete are always less than that of conventional concrete. Table 4.2 Split Tensile and Flexural Strength of RHA-Cement Concrete Sl.No RHA Avg. Split Tensile strength Avg. flexural strength at 28 Replacement at 28 days (N / mm2) days (N / mm2) (%) M 15 M20 M 15 M20 1 2 3 4 5 0 5 10 15 20 2.575 1.872 1.863 1.612 1.848 3.184 1.924 1.839 1.858 1.919 28 2.620 2.634 2.573 2.574 2.284 3.667 3.225 2.905 2.631 1.716
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME CONCLUSIONS Based on the extensive experimental investigation carried out on RHA –Cement Concrete and the following conclusions are drawn. i) Normal consistency and setting times of RHA-Cement are comparable to that of OPC. However, there is an increase in the consistency (value) of RHA-Cement due to increase in RHA content in the above type of cement. This may be due to the presence of unburnt particles, which absorb more water. ii) As the RHA content increases, workability decrease, which may be due to absorption of water by the unburnt (unhydrous) particles present in RHA. This phenomenon is the same for M15 & M20 grades. iii) Compressive strength of M15 RHA – Cement concrete attains comparable strength with that of conventional concrete, upto 20% replacement level of RHA. However, for M20 grade concrete RHA – Cement concrete attains comparable strength with that of conventional concrete, only upto 10% replacement of level of RHA. This Phenomenon may be due to the presence of unburnt rice husk, as the ash was obtained only by firing in open fields. REFERENCES 1) Seshagiri Rao M.V. Saibaba Reddy E. Ramamohan Rao K. (1996) ‘Rice Husk Ask Cement Concrete’ Proceeding of National Seminar on Alternate Construction Materials in Civil Engineering held at REC Hamipur December 10-11, 1996, PP 321 – 330. 2) Lakshman S. (1980) Investigations on the Properties of Paddy Husk Cement, M.E. Thesis submitted to the Annamalai University, Department of Applied Mechanics and Structural Engineering PP.62 3) Subramanian C. (1982) ‘Further study on Cement from Paddy Husk’ M.E. Thesis submitted to the Annamalai University, Department of Applied Mechanics and Structural Engineering PP.55 4) Hwang C.L. Wu D.S. (1989) ‘Properties of Cement paste containing Rice Husk Ash’ Proceedings of the Third International Conference on Natural Pozzolans in Concrete Trondheim, Norway, SP-114, published by ACI, Malhotra V.M. (Ed). Volume – I PP. 733 762. 5) Sugita S, Shoya M. and Tokuda H. (1992) ‘Evaluation of Pozzolanic Activity of Rice Husk Ask’ Proceedings of the Fourth International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Istanbul, Turkey, SP – 132, published by ACI, Malhotra V.M. (Ed), Volume I, PP.495 – 512. 6) Mazlum F., and Uyan M. (1992) ‘Strength of Mortar made with Cement Containing Rice Husk Ash and Cured in Sodium Sulphate Solution, Proceedings of (as in 5 above), PP. 513 – 532. 7) Seshagiri Rao M.v. Prasada Rao A. (1997) ‘Rice Husk Ash Cement Concrete for Rigid Pavements’ Indian High ways, Volume 25, No.9, PP 13 – 22. 8) Mohammad Qamruddin and Prof.L.G.Kalurkar, “Effect of Unprocessed Rice Husk Ash as a Cementitious Material in Concrete(A Comparison with Silica Fume)”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 240 - 246, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 9) Raju Sathish Kumar, Janardhana Maganti and Darga Kumar Nandyala, “Rice Husk Ash Stabilized Compressed Earth Block-A Sustainable Construction Building Material – A Review”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 1, 2012, pp. 1 - 14, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 29
  • International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME BIBLIOGRAPHY 1. 2. 3. SP:23 IS:269 IS:383 - 1982 - 1976 - 1970 4. 5. 6. 7. 8. 9. 10. 11. IS:456 IS:516 IS:1199 IS:1727 IS:2250 IS:3812 IS:4031 IS:5816 - 1978 1959 1959 1967 1981 1981 1988 1970 Hand Book on Concrete Mix Specification for Ordinary and Low Heat Portland Cement Specification for Coarse and Fine Aggregate from Natural Sources for Concrete. Code of Practice for Plain and Reinforced Concrete. Methods of Test for Strength of Concrete. Methods of Sampling and Analysis of Concrete. Methods of Test for Pozzolanic Materials Code of Practice for preparing and Use for Masonry Mortars’ Specification for Fly Ash for use as Pozzolana and Admixture. Methods of Physical test for Hydraulic Cement (Part VII) Methods of Test for Splitting Tensile Strength of Concrete Cylinders. AUTHOR’S DETAIL Er. S.THIROUGNANAME, M.Tech., MIE., MISTE., FIAH., MIWWA., AMISE., MITArb., Assistant Engineer, Public works Department, Puducherry. 30