Use of Rice Husk Ash as an Admixture to Substitute of Portland Cement i

The increase in rate of construction increases the rate demand of Portland cement now a day. Due to urbanization it is estimated that the production of cement increase up to 200 million ton in 2015. Being development of nation on one side, the side effect grows in form of global warming. Increased rate of industrialization leads to Production of toxic gases like CO, CO2, and other hazardous gases leads to ozone depletion which is main cause of global warming & a threat to environment. CO2 gas contributes in relation to 63.33% of global warming. The factories which manufacture cement are responsible for a quantity of the CO2 gas production because the production of one ton of Portland cement emits around one ton of CO2 into the ambiance. To eliminate the main cause of global threat (CO2), the new idea came in to existence i.e. use of substitute materials in construction industry. For this purpose, the uses of industrial dissipate products and agricultural by products are very beneficial. These industrial dissipate and agricultural by products such as Silica Fume, Rice Husk Ash, Slag, and Fly Ash etc, are capable of used as cementing materials due to their pozzolanic behavior, these products require large tract of lands for dumping. Great amount of dissipate achieve as by products from several of the industries can be the main sources of such alternate materials. The world rice crop is estimated at 596 million tons per year and India is second major producer of rice in the world with yearly production of 146 million tons per year. The RICE HUSK ASH (RHA) can be utilize as a substitute material as replacement for ordinary Portland cement. This technology may possibly | Volume – 2 | Issue – 5 | Jul-Aug 2018 6470 | www.ijtsrd.com | Volume Journal of Trend in Scientific and Development (IJTSRD) International Open Access Journal n Concrete , Mr. Misba Danish Student, Assistant Professor , Al-Falah School of Engineering and Technology , Faridabad, Haryana, India decrease the CO2 discharge to the environment caused by the cement industries. In the present study, a possibility of Rice Husk Ash as an admixture to substitute of Portland cement in concrete, and an effort has been made to explore the strength parameter of concrete. For control concrete, IS method of mix design has taken on and considering this a replacement technique has been finished. Five dissimilar replacement levels 5%, 7.5%, 10%, 12.5% and 15% are selected for the study concern to replacement method with range of curing stage starting from 7 days and 28 days are conside present study. The water/cement ratio used in this study is 0.40. The all results were compared to concrete without RHA. The compressive, split tensile and flexural strength were compared with those concrete without RHA. The results show that t the good performance on compressive, split tensile and flexural strength at the age of 28 days of curing. The results were evaluated with the concrete without RHA. The saturated water absorption results shows that the percentage of water absorption of concrete with containing 7.512.5% replacement of cement by RHA is decrease as compare to concrete without containing RHA. INTRODUCTION The rice husk is the residual material produced during milling process of paddy. The outer covering grain is surrounded by the byproduct known as husk when burning of this rice husk is done in proper Page: 384 2 | Issue – 5 has completed to use basis, mix design for

The increase in rate of construction increases the rate Portland cement now a day. Due to urbanization it is estimated that the production of cement increase up to 200 million ton in 2015. Being development of nation on one side, the side effect grows in form of global warming. Increased rate of on leads to Production of toxic gases like CO, CO2, and other hazardous gases leads to ozone depletion which is main cause of global warming & a threat to environment. CO2 gas contributes in relation to 63.33% of global warming. ture cement are responsible for a quantity of the CO2 gas production because the production of one ton of Portland cement emits around one ton of CO2 into the ambiance. To eliminate the main cause of global threat (CO2), the .e. use of substitute materials in construction industry. For this purpose, the uses of industrial dissipate products and agricultural by products are very beneficial. These industrial dissipate and agricultural by products such Ash, Slag, and Fly Ash etc, are capable of used as cementing materials due to their pozzolanic behavior, these products require large tract of lands for dumping. Great amount of dissipate achieve as by products from several of the industries n sources of such alternate materials. The world rice crop is estimated at 596 million tons per year and India is second major producer of rice in the world with yearly production of 146 million tons The RICE HUSK ASH (RHA) can be utilize as a substitute material as replacement for ordinary Portland cement. This technology may possibly decrease the CO2 discharge to the environment caused by the cement industries.
In the present study, a possibility of Rice Husk Ash as an admixture to substitute of Portland cement in concrete, and an effort has been made to explore the strength parameter of concrete. For control concrete, IS method of mix design has taken on and considering this a replacement technique has been finished. Five dissimilar replacement levels 5%, 7.5%, 10%, 12.5% and 15% are selected for the study concern to replacement method with range of curing stage starting from 7 days and 28 days are conside present study. The water/cement ratio used in this study is 0.40.

INTRODUCTION
The rice husk is the residual material produced during milling process of paddy. The outer covering grain is surrounded by the byproduct known as husk when burning of this rice husk is done in proper In the present study, a possibility has completed to use of Rice Husk Ash as an admixture to substitute of Portland cement in concrete, and an effort has been made to explore the strength parameter of concrete. For control concrete, IS method of mix design has taken on and considering this a basis, mix design for replacement technique has been finished. Five levels 5%, 7.5%, 10%, 12.5% and 15% are selected for the study concern to replacement method with range of curing stage starting from 7 days and 28 days are considered in the present study. The water/cement ratio used in this The all results were compared to concrete without RHA. The compressive, split tensile and flexural strength were compared with those concrete without RHA. The results show that the rice husk ash gives the good performance on compressive, split tensile and flexural strength at the age of 28 days of curing. The results were evaluated with the concrete without RHA. The saturated water absorption results shows ater absorption of concrete 12.5% replacement of cement by RHA is decrease as compare to concrete without The rice husk is the residual material produced during milling process of paddy. The outer covering of paddy grain is surrounded by the byproduct known as husk when burning of this rice husk is done in proper International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 @ IJTSRD | Available Online @ www.ijtsrd.com | Volume -2 | Issue -5 | Jul-Aug 2018 Page: 385 manner in a furnace, the rice husk ash is obtained. In the burning process of rice husk, this husk has approximate 75% organic volatile substance and remaining 25% weight of husk is transformed into ash and this ash is known as rice husk ash (RHA).The RHA contains about 80-90% amorphous silica. In every 1000 kg of paddy, approximate 25% (250 kg) of husk is produced, and around 75% (750 kg) of rice is produce. In the milling process when this husk is burnt in the boiler approximate 25% (55 kg) of rice husk ash is produced.
Rice husk ash acts as a Pozzolanic material which have reactive high silica or alumina, which have little or no binding property, but when this pozzolanic materials react with lime in the presence of water, it will set and become harden like ordinary Portland cement. Pozzolanic materials are best alternative which substitute cementing material instead of ordinary Portland cement. Pozzolanas can be intermingling with OPC for improving the strength and durability of concrete. The pozzolanic material reduces the cost of construction.
From the industrial and agriculture waste a wide variety of siliceous or aluminous materials may be pozzolanic. The rice husk is commonly available from the agriculture waste and is has the greatest potential, after burning of rice husk in rice mill produce large amount of ash which contain high amount of silica (90%). India is a second major country which producing rice, and the huge quantity of husk is produce during milling process of paddy. In India annually approximate 20 million ton of rice husk ash is produced. From 5 ton of rice paddy about one ton husk is produced. The yearly production of RHA is about 20 ton.
Burning of Rice husk ash should be done in proper manner.
At the temperature 550°C -800°C amorphous silica is produced and after the 800°C (at high temperature), crystalline silica is formed. The properties of amorphous silica are different from crystalline silica so it is important to make the desire temperature to get the correct specification for the particular end use. In this study the ordinary Portland cement is replaced by RHA at different proportion such as 5%, 7.5%, 10%, 12.5% and 15% to study different strength properties, saturated water absorption of concrete and comparison of strength at different age of curing.  In this study the researcher suggest a new cementitious material from a mixture of 50% rice husk ash and 50% calcium carbide residue. This mixture shows cementing property and identify as a pozzolanic reaction between the two materials without OPC in the mixture. In this study the different properties such as compressive strength and flow were investigated when rice husk ash and calcium carbide residue were used as a cementitious material. In this study the setting time of new material is greater than the OPC paste. The highest compressive strength of mortar is obtained by the ratio of RHA and CCR of 50:50 by the weight at curing age of 28 days. The mixture from CCR and RHA has a high potential to be used as a cementing material according to compressive strength of mortar.

JUSTIFICATION OF THE STUDY
2. Deepa G. Nair , K.S. Jagadish , Alex Fraaij (2006) This study shows the RHA was produce by the different types of field oven and the property were discussed in this paper. The performance of oven has discussed to classify most suitable method to produce reactive pozzolanic material as a substitute of cement for the low strength of conduction application. The long term strength of RHA pozzolanas with lime or cement is investigated to recommend a sustainable reasonable opportunity in rural construction applications.

Gemma Rodrı´guez de Sensale (2006)
This study gives the information about the improvement of compressive strength of concrete with RHA at the age of 91 days. In this study two different replacement of cement were used by RHA 10% and 20%. Three different water/cement ratios were used in this study 0. permeability are compared with those concrete without RHA. The results show that the residual rice husk ash gives the good performance on compressive strength but the long term behavior of concrete with rice husk ash produces by proscribed burning was more important. The splitting tensile and air permeability results show that the burning temperature of RHA should be in control manner.

Gemma Rodríguez de Sensale (2010)
This paper discuss about the influence on durability aspects by the partially replacement of OPC by RHA and the investigation has done on high performance cementitious materials. Two RHAs (amorphous and partially crystalline optimized by dry-milling) and different water-cementitious materials ratio and different percentages of RHA replacement levels are investigated in this study. The durability aspects were tested namely air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The result was evaluated with the concrete without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes explain different behaviors for chloride ion penetration and air permeability depending on the water-cementitious materials ratio. In mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction.

Hwang Chao-Lung, Bui Le Anh-Tuan, Chen
Chun-Tsun (2011) This study shows the influence of partially replacement of cement by RHA derived from the South Vietnam produced by burring of rice husk in the boiler. For improvement of pozzolanic reactivity of RHA it is ground for 1 hour. The ground RHA and non-ground RHA were investigate to check the strength. The different types of properties were investigated in this study include compressive strength, concrete electrical resistivity, and ultrasonic pulse velocity. In the testing of concrete some properties were investigated compressive strength, concrete electrical resistivity, and ultrasonic pulse velocity. After the testing of concrete the results explain that the non-ground RHA can be applied as a pozzolanic material. The smallest particle size of ground RHA increases the compressive strength of concrete. After the testing of concrete the result shows that the RHA can be used up to 20% with cement without adversely affecting the strength and durability properties of concrete.

Rahmat Madandoust, Malek Mohammad
Ranjbar, Hamed Ahmadi Moghadam, Seyed Yasin Mousavi (2011) In this paper the influence of RHA on concrete properties and durability aspect were studied. To determine the appropriate percentage of rice husk ash for partial replacement of OPC, mixture with 0-30% rice husk ash and test were established and mechanical properties were determined. The durability test was conduct in aggressive environment 5%Nacl with wet dry cycling, was assess for 11 months.
The degree of damage was considered by determining the percentage of decrease in compressive strength and chloride ions penetration as compare with control specimens. The result shows that the partial replacement of cement by rice husk ash enhanced durability and homogeneity but did not increase the early age compressive strength of concrete. Jamil (2011) This paper discuss about production procedure of RHA from rice husk and the quality of RHA produced using rudimentary oven of the National University of Malaysia. Two grinding methods and three combustion methods were used to determine the physical properties and chemical aspects of RHA produced.
Combustion temperature distribution of the furnace, silica crystallization phase, ash particle size, and chemical content of the produced RHA were considered using X-ray diffraction analysis and scanning electron microscopy. The test results shows that the combustion period, chilling duration, and grinding process and duration are essential in obtaining RHA of standard fineness and quality. Air ducts in the furnace are extremely useful in order to provide air for appropriate burning of rice husk producing high performance concrete. The level of cement replacement by RHA was at 0%, 10%, 15 % and 20 % and the particle size of the RHA used was 13.50 μm, 20.43 μm and 29.92 μm. The results show that the use of 10 % RHA with the average particle size of 20.43 μm gave better compressive strength from 3 days onwards compared to control OPC and silica fume and the use of 20% of RHA with the average particle size of 13.50 μm at 28 days gave better compressive strength compared to control OPC and silica fume.
9. Ha Thanh Le, Sang Thanh Nguyen, and Horst-Michael Ludwig (2014) It is an experimental study of the influence of partially replacement of cement by RHA on strength and durability and workability, of high performance finegrained concrete. The results show that the replacement of cement with RHA to HPFGC improved splitting tensile strength, compressive strength and chloride penetration resistance. In this study the results are shows that the ratio of compressive strength to splitting tensile strength of high performance fine-grained concrete was lower than that of normal concrete, especially for the concrete made with 20 % RHA. Compressive strength and splitting tensile strength of HPFGC containing RHA was similar and a little higher, than for HPFGC containing SF.

METHODOLOGY Experimental
The nature of this study is based on experimental program. This study will focus on standard concrete of M40 concrete grade with characteristic strength of 40 N/mm2 at 28 days with ingredients of Ordinary Portland cement and rice husk ash at different percentages such as 0, 5, 7.5, 10, 12.5, 15 percent as binder, 20 mm coarse aggregate and river sand, Conplast SP430 G8 as a superplasticizer. Different percentage of rice husk ash will use as a partially replacement of cement and superplasticizer will use for improve workability. The percentage of superplasticizer will depend upon the workability of concrete. The superplasticizer doses also depend upon the percentage replacement of cement by rice husk ash without loss of workability. By the use of different percentage of rice husk ash in OPC the optimum value of replacement can be find by the compressive strength, split tensile strength and flexural strength of concrete. The compressive strength, split tensile strength, flexural strength test will be on universal testing machine with mold of cube, cylinder and beam respectively at 7 days and 28 days. The process of this experimental study is given below:

CHEMICAL COMPOSITION TEST
The chemical analysis of sample was carried out at SAIFCO cement industries cement plant and following result was obtained.

SUPER PLASTICIZER
The most important chemical admixture is the super plasticizer, which is the High-Range Water-Reducing Admixture (HRWRA). There are four types of super plasticizers name sulphonated malanie-formaldehyde, sulphonated naphthalene formaldehyde, modified lignosulphonated and other types Super plasticizers are water reducers which are capable of reducing water content by about 30 percent. For this present investigation, a super plasticizer that is CONPLAST SP430 G8 has been used for obtaining workable concrete.
Sulphonated naphthalene formaldehyde polymer is a major component of the super plasticizer used here. It take place in neutralizing the surface charges on the cement particles and enhancing water tied up in the cement agglomerations and thereafter reducing the viscosity of the paste and concrete. It promotes dispersing of cement particles and reduces water requirements without affecting the workability, thus International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 Page: 390 resulting high-strength concrete and lower permeability. Super plasticizers are linear polymers containing sulfonic acid groups or carboxylic groups attached to the polymer backbone at regular intervals.

CONPLAST SP430 G8
This chemical super plasticizing admixture manufactured by "FOSCROC Chemicals" used in this project. The main objective of using this super plasticizer is to produce high workability concrete requiring little or no vibration during placing. Conplast SP430 G8 is based on Sulphonated Naphthalene formaldehyde and obtained as a brown liquid instantly dispersible in water. Conplast SP430 G8 has specially formulated to give high water reductions up to 25% without loss of workability or to produce high quality concrete of reduced permeability.

WATER
Water is an essential constituent of concrete as it actively participate in the chemical reaction with cement. It is help to form the strength giving cement gel. The quality and quantity is very important and it should be taken very carefully. Quality of water affects the strength, it is necessary for experimental work to go into purity and quality of water. Water takes part in the chemical reactions with cement to form the hydration product, calcium-silicate-hydrate (C-S-H) gel. Some specification also accept water for making concrete if the pH value of water lies between 6 and 8 and the water is free from organic matter. Carbonates and bi-carbonates of sodium and potassium effect the setting time of cement. While sodium carbonate may cause quick setting time, the bi-carbonates may either accelerate or retard the setting. The other higher concentration of these salts will materially reduce the concrete strength.

PRODUCTION OF RICE HUSK ASH
The RHA produce from the burning of husk in boiler at controlled temperature that fulfils the physical characteristics and chemical composition of mineral admixtures. The pozzolanic behavior of RHA depends upon the silica crystallization phase, silica content and size and surface area of ash. The amount of carbon content in RHA should be smallest. If the carbon contain is more in RHA the strength of concrete will be less. RHA is produce by burning of rice husk at control temperature that has amorphous silica content and large surface area. Appropriate furnace and the good grinding method is necessary for combustion and grinding RHA to obtain the excellent quality of ash.

BURNING PROCESS OF RICE HUSK
The rice husk is burn into ferrocement furnace or sometimes in boilers to produce RHA at controlled temperature. In furnace air ducts are provide which play two role, one is supply air to husk in combustion process and other is act as passages for fire. Air ducts are controlling commotion temperature. Electric fans are attached to air ducts which control the combustion temperature. Air ducts also reduce the carbon content in RHA, if there are no air ducts the carbon content will be more in ash and the strength of concrete will be low. In the burning process of RHA the temperature of boiler or furnace is around 700-800̊ c for 24 hours. After the 24 hours the temperature is about 52̊ c. After the 48 hours the temperature of ash is about 25̊ c. At 700-800̊ c temperate the silica is remain in amorphous silica, above this temperature the amorphous silica is converted into crystalline silica which is not useful in concrete. The air is providing into air ducts at the rate of velocity 12 meter per second. After burning the physical appearance of rice husk ash is shown in figure 4.1.  Table 4.5, were tried for grinding burnt rice husk ash in this study. About 5.0 kg of ash was placed into the Los Angeles machine for every grinding.

GRINDING PROCESS
The grinding process should be done in proper manner in the loss angeles abrasion machine. The finer pozzolanic ash is superior. Fineness of rice husk ash is necessary because it influence the rate of reaction and the rate of gain in concrete strength.
Other than influence the rate of reaction, fineness also influences water-cement ratio, shrinkage, creep. The finer RHA particles yield larger surface area and increases strength of concrete. Chemically reactive very fine RHA would fill empty columns in concrete in an optimum manner. The particles of RHA retained on 45 m sieve should not be more than 12.0%. Therefore, to get the required fineness, proper grinding of burnt ash is very important. In 90 min of grinding, fineness of 5 kg burnt husk obtained by combustion method met the standard requirements. Variation of fineness with grinding duration for rice husk ash obtained

MATERIAL PRODUCTION
The production of RHA was obtained by burning the rice husk in a ferrocement furnace. Only ash that lies within the middle third of the furnace taken for grinding as it was considered as quality ash.

STANDARD CONSISTENCY TEST FOR CEMENT
Standard consistency of a cement paste is defined as the water content at which the paste will permit a vicat plunger having 10 mm dia and 50 mm length to penetrate to a depth of 33 -35 mm from the top of the mould. The test is useful for finding out initial setting time, final setting time. The test is conducted using vicat"s apparatus. The observations obtained during the test are as shown in Table4.7. Weight of cement taken for each trial is 400g. The standard consistency of the cement is obtained as 30% INITIAL SETTING TIME OF CEMENT Initial setting time of cement is regarded as the time elapsed between the moments that the water is added to the cement, to the time that the paste starts losing its plasticity.
In vicat"s apparatus, it is measured as the period elapsed between the time when water is added to the cement and the time at which the needle penetrates the test block to a depth equal to 33 -35 mm from the top at water content of 0.85 times the standard consistency. The observations obtained at a temperature of 80 c are as: Weight of cement =400 g Weight of water =0.85 x 30/100 x 400 = 102 g. Time at which water is added to the cement 2:05 pm Time at which needle penetrates to a depth of 33-35 mm 5:45 pm. Initial setting time is obtained as 3 hr 40 min.

FINAL SETTING TIME OF CEMENT
The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure. In vicat"s apparatus, cement is considered finally set, when, upon, lowering the attachment gently cover the surface of the test block, the centre needle makes an impression, while the circular cutting edge of the attachment fails to do so, that is the needle does not pierce more than 0.5 mm.
The observations obtained are as: Time at which water is added to the cement 2:05 pm Time at which the circular edge fail to make an impression 7:25 pm Final setting time is obtained as 5 hr 20 min.

TRIAL MIX DESIGN
A trial mix has been designed for an assumed compaction factor of 0.80 as per IS 10262 -1982 for M40 grade. The trial mix is obtained as 1:0.865:2.59 for water cement ratio of 0.40.

COMPACTION FACTOR
Compaction factor is defined as the ratio of density achieved when concrete is allowed to fall through a standard height and the density of the same concrete fully compacted.    All materials shall be brought to room temperature, preferably 27±3º C before start the results. The cement samples, on arrival at the laboratory, shall be carefully mixed dry either by hand or in an appropriate mixer in such a manner as to ensure the maximum possible blending and uniformity in the material, care is being taken. The cement shall then be stored in a dry place, preferably in air-tight metal containers. Samples of aggregates for each batch of concrete shall be of the desired grading and shall be in an air-dried condition. In general, the aggregate shall be separated into fine and coarse portion and recombined for each concrete batch in such a way as to produce the desired grading. IS sieve 480 shall be normally used for separating the fine and coarse fractions, but where special grading are being investigated, both fine and coarse aggregate shall be separated into different sizes.

PROPORTIONING
The proportions of the materials, including water, in concrete mixes used for determining the suitability of the materials available, shall be similar in all respects to those to be employed in the work. Where the proportions of the ingredients of the concrete as used on the site are to be specified by volume, they shall be calculated from the proportions by weight used in the test cubes and the unit weights of the materials.

WEIGHING
Weigh batching is the correct method of measuring the materials. For important concrete, invariably weigh batching should be adopted. Use of weight system in batching, facilitates accuracy, flexibility and simplicity. ensure that the mass become homogeneous, uniform in colour and consistency. There are two methods adopting for mixing concrete one is hand mixing and other is machine mixing. In this study the mixing of materials is done by hand.

COMPACTION OF TEST SPECIMENS: (AS PER IS: 516-1959)
Compaction of concrete is the process adopted for expelling the entrapped air from the concrete. In the process of mixing, transporting and placing of concrete air is likely to get entrapped in the concrete. The lower the workability, higher is the amount of air entrapped. In other words, stiff concrete mix has high percentage of entrapped air and, therefore, would need higher compacting efforts than high workable mixes. Therefore, it is imperative that 100% compacting of concrete is one of the most important aim to be kept in mind in good concrete making practices.

COMPACTION BY VIBRATION
When compacting by vibration, each layer shall be vibrated by means of an electric or vibrator or by means of a suitable vibrating table until the specified condition is attained. This is the special case of formwork vibrator, where  the vibrator is clamped to the table or table is mounted  on springs which are vibrated transferring the  vibration to the table. They are commonly used for vibrating concrete cubes. Any specimen kept on the table gets vibrated. This idea adopted mostly in laboratory and in the making small but precise prefabricated R.C.C members. The vibrating table is shown in figure 4.6. The test specimens shall be stored on the site at a place free from vibration, under damp matting, sacks or other similar material for 24 hours + ½ hour from the time of adding the water to the other ingredients. The temperature of the place of storage shall be within the range of 22 to 32º C. After the period of 24 hours, they shall be marked for later classification, removed from the moulds and, unless required for testing within 24 hours, stored in clean water at a temperature of 24 to 30º C until they are transported to the testing laboratory. They shall be sent to the testing laboratory well packed in damp sand, damp sacks, or other suitable material so as to arrive there in a damp condition not less than 24 hours before the time of test. On arrival at the testing laboratory, the specimens shall be stored in water at a temperature of 27 ± 2º C until the time of test. Curing of test specimens are shown in figure 4.7.

TESTS AND RESULTS
The details of experimental investigations carried out on the test specimens to study the strength-related properties of concrete using Rice husk ash. The strength-related properties such as compressive strength, splitting tensile strength, and flexural strength were studied.

TESTS CUBE COMPRESSIVE STRENGTH
For cube compression testing of concrete, 150mm cubes were used. All the cubes were tested in saturated condition, after wiping out the surface moisture.
The tests were carried out after the specimen has been centered in the testing machine.
Loading was continued till the specimen fails and reading note down from the automatic universal

SPLITTING TENSILE STRENGTH
This is an indirect test to determine the tensile strength of cylindrical specimens. Splitting tensile strength tests were carried out on cylinder specimens of size 150 mm diameter and 300 mm length. To avoid the direct load on the specimen the cylindrical specimens were kept below the iron plates .The load was applied gradually till the specimens split and readings were noted. The test set up for the splitting tensile strength on the cylinder specimen, with the iron plates to avoid the direct load on the specimen is shown in Figure 5.3. Pattern of typical splitting tensile failure mode shapes of cylinder specimen is shown in Figure 5.4. The splitting tensile strength has been calculated using the following formula: ft = 2P/π DL Where ft = splitting tensile strength of the specimen in MPa P = maximum load in N applied to the specimen D = measured diameter of the specimen in mm, and L = measured length of the specimen in mm. The flexural strength or modulus of rupture has been calculated using the following formula: fr = PL/BD2 Where fr = flexural tensile strength of the specimen in MPa P = maximum load in N applied to the specimen L = length in mm of the span on which the specimen was supported B = measured width of the specimen in mm, and D = measured depth of the specimen in mm at the point of failure

CUBE COMPRESSIVE STRENGTH
The cube compressive strength results at the various ages such as 7, 28 days and at the replacement levels such as 0%, 5%, 7.5%, 10%, 12.5% and 15% of rice husk ash are presented in  percentage of those mineral admixtures increases. The 7 days compressive strength of the concrete mixes containing rice husk ash slightly decreases. Cement replacement level of 7.5% by rice husk ash in concrete mixes was found to be the optimum level to obtain maximum compression strength at the age of 28 days at w/c ratio 0.40. At the age of 28 days compressive strength of rice husk ash concrete increase. This indicates that addition of rice husk ash as the partial replacement of cement causes increase strength.

SPLITTING TENSILE STRENGTH
The optimum replacement of cement by rice husk ash for rice husk ash concrete was found to be 7.5 percent respectively for achieving maximum splitting tensile strength at the age of 28 days at w/c ratio 0.40. The tensile strength increases along with increase in compressive strength at the age of 28 days.

FLEXURAL STRENGTH
The optimum replacement of cement by rice husk ash for rice husk ash concrete was found to be 7.5 percent for achieving maximum value of flexural strength at the age of 28 days at w/c ratio 0.40. The flexural strength increases along with increase in compressive strength.

EXPERIMENTAL INVESTIGATIONS ON SETTING TIMES
In the present investigation the setting times of cement pastes, with partial replacement of cement by rice husk ash varying from 0% to 15%, are in the range conforming to IS 12269. The setting times of cement paste slightly increases with 5% to 12.5% replacement of cement by rice husk ash. There will be no adverse effect on the cement paste containing rice husk ash in cement. The rice husk ash can be used as cementitious material in concrete as it barely affects the initial and the final setting times of cement paste, and the results remain in range specified in IS code 12269.

COST
In this thesis the replacing of cement by rice husk (RHA) about 7.5 %, the overall cost of the work is decreased by 7.287%. It is the excellent opportunity to make the concrete at low price and the cost of construction will be low.

ENVIRONMENTAL IMPLICATIONS OF
USING RHA The production and use of RHA in India should be considerably increased given the fact that RHA contributes significantly to a green building. It not only reduces the consumption of cement due to blending but also solves the waste disposal problem.

FUTURE SCOPE
The following are the suggestions for future work 1. This experimental work focused only a particular type of cement replacement materials. Hence, investigations can be made on different types of cement replacement materials (Blast furnace slag, silica fume, fly ash and metakaoline) to study the strength and durability-related properties. 2. Studies could be conducted for other properties such as creep, shrinkage, carbonation resistance, microstructure etc. 3. Investigations may be carried out for pre-stressed concrete. 4. The effect of rice husk ash addition in high strength concrete exposed to high temperature should be investigated.