A Study on Use of Rice Husk Ash in Concrete

In the present investigation, a feasibility study is made to use Rice Husk Ash as an admixture to an already replaced Cement with fly ash (Portland Pozzolana Cement) in Concrete, and an attempt has been made to investigate the strength parameters of concrete (Compressive and Flexural). For control concrete, IS method of mix design is adopted and considering this a basis, mix design for replacement method has been made. Five different replacement levels namely 5%, 7.5%, 10%, 12.5% and 15% are chosen for the study concern to replacement method. Large range of curing periods starting from 3days, 7days, 28days and 56days are considered in the present study.


I. Introduction
Concrete is a widely used construction material for various types of structures due to its structural stability and strength.All the materials required producing such huge quantities of concrete come from the earth's crust.Thus, it depletes its resources every year creating ecological strains.On the other hand, human activities on the Earth produce solid waste in considerable quantities of over 2500/MT per year, including industrial wastes, agricultural wastes and wastes from rural and urban societies.Recent technological development has shown that these materials are valuable as inorganic and organic resources and can produce various useful products.Amongst the solid wastes, the most prominent ones are fly ash, blast furnace slag, rice husk, silica fume and demolished construction materials.From the middle of 20th century, there had been an increase in the consumption of mineral admixtures by the cement and concrete industries.The increasing demand for cement and concrete is met by partial cement replacement.Substantial energy and cost savings can result when industrial by-products are used as a partial replacement for the energy intense Portland cement.The use of by-products is an environmental friendly method of disposal of large quantities of materials that would otherwise pollute land, water and air.Most of the increase in cement demand will be met by the use of supplementary cementing materials.Rice milling generates a by-product known as husk.This surrounds the paddy grain.During the milling of paddy about 78 % of weight is received as rice, broken rice and bran.The rest 22 % of the weight of paddy is received as husk.This husk is used as fuel in the rice mills to generate steam for the parboiling process.This husk contains about 75 % organic volatile matter which burns up and the balance 25 % of the weight of this husk is converted into ash during the firing process, which is known as rice husk ash (RHA).Rice husk was burnt approximately 48 hours under uncontrolled combustion process.The burning temperature was within the range of 600 to 850 degrees.The ash obtained was ground in a ball mill for 30 minutes and its color was seen as grey.This RHA in turn contains around 85%-90% amorphous silica.So for every 1000 kg of paddy milled, about 220 kg (22%) of husk is produced, and when this husk is burnt in the boilers, about 55 kg (25%) of RHA is generated.India is a major rice producing country, and the husk generated during milling is mostly used as a fuel in the boilers for processing paddy, producing energy through direct combustion and / or by gasification.About 20 million tons of RHA is produced annually.This RHA is a great environment threat causing damage to the land and the surrounding area in which it is dumped.Lots of ways are being thought of for disposing it by making commercial use of this RHA.In the present investigation, Portland cement was replaced by rice husk ash at various percentages to study compressive and flexural strength.

Descriptions
Conplast SP430A2 is based on Sulphonated Naphthalene Polymers and is supplied as a brown liquid instantly dispersible in water.Conplast SP430A2 has been specially formulated to give high water reduction up to 25% without loss of workability or to produce high quality concrete of reduced permeability.

(iv). Water
Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement.Since it helps to form the strength giving cement gel, the quantity and quality of water is required to be looked in to very carefully.Mixing water should not contain undesirable organic substances or inorganic constituents in excessive proportions.
In this project clean potable water was obtained from Department of Civil Engineering, GIT -GU for mixing and curing of concrete.

B. Mix Design for M20-Grade Concrete
The mix proportions considered for each replacement by replacement method with RHA are presented in table 2.3 Casting of Test Specimens: (As per IS: 516-1959)

Preparation of Materials
All materials shall be brought to room temperature, preferably 270+ 30 C before commencing the results.The cement samples, on arrival at the laboratory, shall be thoroughly mixed dry either by hand or in a suitable mixer in such a manner as to ensure the greatest possible blending and uniformity in the material, care is being taken to avoid the intrusion of foreign matter.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 fraction and recombined for each concrete batch in such a manner as to produce the desired grading.IS sieve 480 shall be normally used for separating the fine and coarse fractions, but where special gradings are being investigated, both fine and coarse fractions shall be further 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
The quantities of cement, each size of aggregate, and water for each batch shall be determined by weight, to an accuracy of 0.1 percent of the total weight of the batch.

Mixing Concrete
The concrete shall be mixed by hand or preferably in a laboratory batch mixer, in such a manner as to avoid loss of water or other materials.Each batch of concrete shall be of such a size as to leave about 10 percent excess after moulding the desired number of test specimens.

Hand Mixing
The concrete batch shall be mixed on a water-tight, non absorbent platform with a shovel, trowel or similar suitable implement, using the following procedure: The cement and fine aggregate shall be mixed dry until the mixture is thoroughly blended and is uniform in color.
The coarse aggregate shall then be added and mixed with the cement and fine aggregate until the coarse aggregate is uniformly distributed throughout the batch, and The water shall then be added and the entire batch mixed until the concrete appears to be homogenous and has the desired consistency.
If repeated mixing is necessary, because of the addition of water in increments while adjusting the consistency, the batch shall be discarded and a fresh batch made without interrupting the mixing to make trial consistency tests.

III. Tests Conducted
Test for Compressive Strength of Concrete Specimen: (As per IS: 516-1959) A. Apparatus:

Testing Machine
The testing machine may be of any reliable type, of sufficient capacity for the tests and capable of applying the load at the specified rate.The permissible error shall be not greater than + 2 percent of the maximum load.The testing machine shall be equipped with two steel bearing platens with hardened faces.One of the platens shall be fitted with a ball seating in the form of a portion of a sphere, the centre of which coincides platen shall be plain rigid bearing block.The bearing faces of the both platens shall be at least as large as, and preferably larger than the nominal size of the specimen to which the load is applied.The bearing surface of the platens, when new, shall not depart from a plane by more than 0.01 mm at any point, and they shall be maintained with a permissible variation limit of 0.02 mm.The movable portion of the spherically seated compression platen shall be held on the spherical seat, but the design shall be such that the bearing face can rotated freely and tilted through small angles in any direction.

B. Procedure
Specimens stored in water shall be tested immediately on removal from the water and while they are still in the wet condition.Surface water and grit shall be wiped off the specimens and any projecting fins removed.Specimens when received dry shall be kept in water for 24 hours before they are taken for testing.The dimensions of the specimens to the nearest 0.2 mm and their weight shall be noted before testing approximately 140 kg/sq cm/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained.The maximum load applied to the specimen shall be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted.

C. Calculation
The measured compressive strength of the specimen shall be calculated by dividing the maximum load applied to the specimen during the test by the cross-sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest kg per sq cm.Average of three values shall be taken as the representative of the batch provided the individual variation is not more than + 15 percent of the average.Otherwise repeat tests shall be made.

D. Apparatus
The testing machine may be of any reliable type of sufficient capacity for the tests and capable of applying the load at the rate specified.The permissible errors shall be not greater than + 0.5 percent of the applied load where a high degree of accuracy is required and not greater than + 1.5 percent of the applied load for commercial type of use.The bed of the testing machine shall be provided with two steel rollers, 38 mm in diameter, on which the specimen is to be supported, and these rollers shall be so mounted that the distance from centre to centre is 60 cm for 15.0 cm specimens or 40 cm for 10.0 cm specimens.The load shall be applied through two similar rollers mounted at the third points of the supporting span that is spaced at 20 or 13.3 cm centre to centre.The load shall be divided equally between the two loading rollers and all rollers without subjecting the specimen to any torsional stresses or restraints.

E. Procedure
Test specimens stored in water at a temperature of 240 to 300C for 48 hours before testing shall be tested immediately on removal from the water whilst they are still in a wet condition.The dimensions of each specimen shall be noted before testing.No preparation of the surface is required.

F. Calculation
The flexural strength of the specimen shall be expressed as the modulus of rupture fb, which, if 'a' equals the distance between the line of fracture and the nearer support, measured on the centre line of the tensile side of the specimen, in cm, shall be calculated to the nearest 0.5 kg/sq cm as follows: fb = p x l b x d2 when 'a' is greater than 20.0 cm for 15.0 cm specimen, or greater than 13.3 cm for a 10.0 specimen, or fb = 3 p x a b x d2 when 'a' is less than 20.0 cm but greater than 17.0 cm for 15.0 cm specimen or less than 13.3 cm but greater than 11.0 cm for a 10.0 specimen Where b = measured width in cm of the specimen, d = measured depth in cm of the specimen at the point of failure l = length in cm of the span on which the specimen was supported, and p = maximum load in kg applied to the specimen If 'a' is less than 17.0 cm for a 15.0 cm specimen, or less than 11.0 cm for a 10.0 specimen, the results of the test shall be discarded.

A. Effect of Age on Compressive Strength:
The 28 days strength obtained for M20 grade Control concrete is 30.3Mpa.The strength results reported in table 11 are presented in the form of graphical variation , where in the compressive strength is plotted against the curing period.The strength achieved at different ages namely 3, 7, 28 and 56 days for Control concrete are also presented in bar chart in figure 13.From the figure, it is clear that as the age advances, the strength of Control concrete increases.The rate of increase of strength is higher at curing period up to 28 days.However the strength gain continues at a slower rate after 28 days.
Strength achieved by M20 grade control concrete at different ages as a ration of strength at 28 days is reported in table 12. From the table, it can be seen that 3 days strength is found to be 0.47 times that of 28 days strength, for 7 days, the strength is found to be 0.67 times that of 28 days strength, for 56 days, the strength is found to be 1.2 times that of 28 days strength.In each of these variations, it can be clearly seen that, as the age advances, the compressive strength also increases.The highest strength obtained at a particular age for different replacement levels with RHA is reported in table 13 for the ages of 3 days, 7 days, 28 days and 56 days respectively.From the above table it can be clearly seen that, the strength is higher for control concrete (i.e 0% replacement) for initial period up to between 3-7 days up to 10% replacement with Rice husk ash, and for 15% replacement with RHA, the strength is very much higher when compared to that of control concrete.The rate of strength development between 7-28 days is maximum when cement is replaced with 5% RHA.Thus from the above table it is clear that the rate of strength development is maximum up to the age of 28 days at all the replacement levels with RHA, and as the age advances from 28 -56 days, the rate of strength development gradually decreases at all the replacement levels.
Comparison between different replacements is made possible if the water cement ration is common.For better pictorial representation, the variations are also represented in the form of bar charts in the figure.The graph is so developed that a common water cement ratio is considered for different replacement, so that for a particular water cement ratio how the variation is observed with different replacement.

Flexural Strength
It is seen that strength of concrete in compression and tension (both tension and flexural tension) are closely related, but the relationship is not of the type of direct proportionality.The ratio of the two strengths depends on general level of strength of concrete.In other words, for higher compressive strength, concrete shows higher tensile strength, but the rate of increase of tensile strength is of decreasing order.The use of pozzolanic material increases the tensile strength of concrete.Rice Husk Ash (RHA) Concrete: Variation of flexural strength with respect to age and percentage of RHA and effect of RHA percentage on Flexural strength of M20 grade concrete is depicted in the figures.The rate of development of flexural strength is higher at 7 days to 28 days.At the later age between 28 days to 56 days only a marginal increase is observed.At 28 days, there is very less variation in flexural strength of RHA concrete at the replacement levels, where as there is a comparative increase in flexural strengths of RHA concrete at higher curing period Rice Husk Ash (RHA) Concrete: Variation of flexural strength with respect to age and percentage of RHA and effect of RHA percentage on Flexural strength of M20 grade concrete is depicted in the figures.The rate of development of flexural strength is higher at 7 days to 28 days.At the later age between 28 days to 56 days only a marginal increase is observed.At 28 days, there is very less variation in flexural strength of RHA concrete at the replacement levels, where as there is a comparative increase in flexural strengths of RHA concrete at higher curing period

V. Conclusion
Based on the limited study carried out on the strength behavior of Rice Husk ash, the following conclusions are drawn: At all the cement replacement levels of Rice husk ash; there is gradual increase in compressive strength from 3 days to 7 days.However there is significant increase in compressive strength from 7 days to 28 days followed by gradual increase from 28 days to 56 days.At the initial ages, with the increase in the percentage replacement of both Rice husk ash, the flexural strength of Rice husk ash concrete is found to be decrease gradually till 7.5% replacement.However as the age advances, there is a significant decrease in the flexural strength of Rice Husk ash concrete.By using this Rice husk ash in concrete as replacement the emission of green house gases can be decreased to a greater extent.As a result there is greater possibility to gain more number of carbon credits.
The technical and economic advantages of incorporating Rice Husk Ash in concrete should be exploited by the construction and rice industries, more so for the rice growing nations of Asia.
w w w. i j e a r.o r g InternatIonal Journal of educatIon and applIed research 77 ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)

Table 2 .Table 1 :
The physical and chemical properties of the cement obtained on conducting appropriate tests as per IS: 269/4831 and the requirements as per IS 1489-1991 are given in Table 1 & Physical properties of procured PPC

Table 2 :
Chemical Properties of Procured PPC

Table 3 :
Physical properties of procured Rice Husk Ash

Table :
Compressive strength of Control concrete in N/mm 2

Table 2 :
Compressive strength as a ratio of 28 days strength at different ages for control concrete B. Effect of age on Compressive Strength of Concrete: Fig.13to fig.14represents the variation of compressive strength with age for M20 grade RHA concrete, in each figure, variation of compressive strength with age is depicted separately for each replacement level of RHA considered namely 5%, 7.5%, 10%, 12.5% and 15%.Along with the variations shown for each replacement, for comparison similar variations is also shown for control concrete i.e., for 0% replacement.

Table 3 :
Highest Compressive strength obtained at different ages

Table 4 :
Increase of decrease in strength of concrete at 3 days w.r.t % replacement of RHA

Table 5 :
Increase or decrease in strength of concrete at 7 days w.r.t % replacement of RHA

Table 6 :
Increase or decrease in strength of concrete at 28 days w.r.t % replacement of RHA Percentage Replacement Increase or decrease in strength

InternatIonal Journal of educatIon and applIed research 79 ISSN: 2348-0033 (Online) ISSN : 2249-4944 (Print)
In each of the above table, the change in strength for M20 grade RHA concrete is presented separately and the following observations are made, The maximum increase in the compressive strength of RHA concrete i.e., 5.0% has occurred at 28 days with 5% replacement, whereas the compressive strength of RHA concrete is found to be decreased by 63.40% at 3 days with 15% RHA replacement.It can be clearly observed that at the age of 28 days, there is gradual increase in the compressive strength of RHA concrete for all the replacement levels with respect to control concrete.Strength development of concrete for different percentage replacements with RHA is presented in table 18.In each table, by what percentage the compressive strength increases with respect to previous age is reported.

Table 8 :
Percentage increase in compressive strength of M20 grade Rice husk ash concrete w.r.t age

Table 9 :
Flexural strength of Control concrete in N/mm 2 ISSN:

Table 10 :
Flexural strength of Control and Rice Husk ash concrete in N/mm 2

Table 11 :
28 Day Compressive and Flexural Strength of Control Concrete & Rice Husk Ash concrete