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302 International Journal of Earth Sciences and EngineeringISSN 0974-5904, Vol. 03, No. 02, April 2010, pp. 302-309

#02030316 Copyright 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.

Rice Husk Ash - Lime Blended Building Bricks

DRS.M.ALI JAWAIDCivil Engineering Department, M M M Engineering College, Gorakhpur-273010, India

Email: [email protected]

Abstract: There is a great demand for environmentally safe reuse of rice husk ash thanks

to high rate of its generation in India. This is also need of time to develop alternate methodsof brick manufacturing in order to reduce the use of fertile soil in brick manufacturing, thus,protecting it for agricultural use. Utilization of rice husk ash with lime in brick manufacturing

is reported in this paper. It is found that building bricks prepared by adding 6% of rice husk

ash and 2% of lime with alluvial silts, exhibits compressive strength of 106 kg/cm 2 andwater absorption of 15%.

Keywords:Ash Utilization, Rice Husk Ash, Bricks, Building Industry, Flyash, Waste Disposal

Introduction:

Rice milling generates a by product know as

husk. This surrounds the paddy grain.During milling of paddy about 78 % of

weight is received as rice, broken rice andbran and 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 theparboiling process. This husk contains about75 % organic volatile matter and the

balance 25 % of the weight of this husk is

converted into ash during the firing process,is known as rice husk ash ( RHA ). This RHA

in turn contains around 85 % - 90 %amorphous silica (Jaturapitakkul and

Roongreung, 2003, Gambhir 1995). So forevery ton of paddy milled, about 220 kgs

(22 %) of husk is produced, and when this

husk is burnt in the boilers, about 40 kgs(20 %) of RHA is generated (Mehta 1986).

India is a major rice producing country, andthe husk generated during milling is mostly

used as a fuel in the boilers for processingpaddy, producing energy through direct

combustion and / or by gasification. About

20 million tones of RHA are producedannually(Srivastava, 2005). It is classified

as pozzolanic material according to ASTMC168 (1997 d). Hydrated (or slaked) lime is

very effective in treating clays and silts.Lime reacts chemically with available silica

and alumina in soils. Natural cement

composed of calcium alumino-silicatecomplexes is formed, which causes acementing action. The strength of lime

stabilized soil is generally improved due to

formation of cementing material. Alluvial soil

deposit in Indo-gangetic plains of India,predominantly, consists of silts of low tomedium compressibility (ML/MI). These

deposits are rich in alumina and silica. The

water holding capacity of this soil is around45%. The objective of this research is toutilize the pozolanic effect of rice husk ash

in presence of lime and water for makinghighly cementious and durable bricks usinglocally available alluvial soils. This will not

only reduce the use of fertile soil of this

region for brick manufacturing but also,reduce the waste disposal volume to make abetter world.

Materials and Methods:

Materials used in this experimental program

consist of rice husk ash (RHA), hydrated

lime (HL) and Low/Medium compressibilitySilt (ML/MI). RHA was collected fromfurnaces located at different industrial units

in Gorakhpur industrial area. The ash

obtained is sieved through 75 micronsIndian Standard Sieve in order to remove

the unburnt portion of ash. The major

chemical and physical properties of RHA aregiven in Table 1. The commercially available

unslaked lime is used in this study. It waspulverized, sieved through 425 micron

Indian standard sieve and stored inpolyethylene bag in desiccators. Localalluvial soils were collected for this

experimental study. The importantengineering and chemical properties of soilis given in Table 2. It is reported that 2% of

lime when added with rice husk ash and


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303DR S. M. ALI JAWAID

International Journal of Earth Sciences and Engineering

ISSN 0974-5904, Vol. 03, No. 02, April 2010, pp. 302-309

alluvial soil gave maximum strength(Srivastava, 2005). Thus, 2% of lime was

added with soil and rice husk ash in this

study. Bricks were prepared by mixing theRHA, lime and local alluvial soil in variousproportions and conventional brick making

technique was adopted (Figures 1 and 2).Improvement in the engineering propertiesof the brick, so produced, was studied. The

percentage of RHA and lime were increased

at regular interval and its effect on thecompressive strength of the brick was alsostudied. The same process continued till the

RHA-lime-soil mix proportion exhibit adecline in strength.

Results and Discussion:

The effect of mix proportion on strength,water adsorption capacity and density etc.

were studied experimentally and results aretabulated in Table 3. Discussion on results isgiven in subsequent section.

Compressive Strength of Brick:

Compressive strength of bricks at differentpercentage of rice husk ash is shown in Fig.3. It is evident from Table 3 that the

compressive strength of brick so formed

increases with increase in rice husk ashcontent but decreases with the increase inrice husk ash content beyond 6%. Lime

reacts with fine pozzolanic component toform calcium-silicate gel with soil particles.The silicate gel proceeds immediately to

coat and bind soil particles. In time this gel

gradually crystallized into well definedcalcium silicate hydrates such astobermorite and hillebrandite. The reaction

ceases on drying and very dry soils will notreact with lime or cement (Srivastava, 2005,Ingles, 1972). The mechanism of reaction

can be represented asNaS4H + CH NH +CAS4HNS +degradation product NH+C2SH WhereS=SiO2, H=H2O, A=Al2O3, C=CaO, N=Na2Oand C2SH are the cementitious mixture and

contribute to the compressive strength ofbrick. At an optimum ash percentage, ahomogeneous gel formation will take place

in the entire soil mass in which all the soilparticles will be involved in pozzolanicreaction, which hardens to form

cementitious products rendering maximum

compressive strength. Any further increasein ash content will result in excess of rice

husk ash which remain unused and prevents

the soil particles from point to point contact.The soil grains will float in the matrix ofunused ash, resulting in reduction of

compressive strength.

Density of Brick:

It is observed that the density of brick

decreases as the percentage of additive(Rice husk ash) increases (Fig. 4). Since thedensity of the additive (ash) is equal to 0.53

t/m3, it will float in water. The mixing wasdone with soil by proportion of weight; agreat volume of additive will replace the soilvolume because of their lower density. This

leads to reduction in the density of thebrick.

Water Absorption of Brick:

The major factor affecting the durability ofbrick is water absorption. The lessinfiltration of water in the brick, the more

durable is the brick. So, the internalstructure of brick must be intensive enoughto prevent the intrusion of water. The water

absorption was determined by using the

procedures described in ASTM C67-00(2000). Fig 5 shows the result of waterabsorption test for various percentage of

rice husk ash-lime soil mixture. It is foundthat water adsorption property of preparedbrick decreases initially with an increase in

ash content (Fig 5) up to optimum ash

content of 6%. However, it increasesafterwards. This is due to fact that additionof additive (ash) to the soil generates the

desired heat of hydration which starts thepozzolanic reaction resulting in gelformation. At an optimum ash percentage, a

homogeneous gel formation takes place in

which all the soil particles will be involve inpozzolanic reaction leading to formation of

less porous hard cementitious product. Anyfurther increase in ash proportion in soil will

result in excess of ash which remainsunused and prevents the soil particles from

point to point contact leading to increase in

porosity.


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304 Rice Husk Ash - Lime Blended Building Bricks



Scanning Electron Micrographs

Observations:

Scanning electron microscopy (SEM)technique has been used to visualize the

nature of structure of the brick before andafter the addition of optimum ash content.

The SEM of brick formed with out additive

(ash) and with additive at magnification1546X is shown in Fig. 6 and Fig. 7

respectively. From the micrograph, it can beseen that in conventional brick there are lot

of aggregated packets of soil particles (Fig.6). The soil particles are assembled in such

a manner to give higher density and less

porosity. Fig. 7 shows the SEM of brickformed after mixing with additive (ash) at

optimum percentage. The homogeneous gelformation due to pozzolanic reaction is

distinctly seen in the entire soil mass. Thesilica gel cemented the soil particles to form

aggregates crumbs which make the entiresoil mass becoming porous.

Economic Analysis:

Economic analysis was carried out to

compare the cost of the construction of brickusing conventional soil as well as soil mixed

with optimum percentage of ash. Thedetailed calculation is given elsewhere

(Raghatate, 2003). The above analysis

reveals the following:

1. There is saving of IRs. 0.80 (US $ 0.016)per brick, if the brick is formed with addingoptimum percentage of rice husk ash.

2. By using rice husk ash-lime mixed brick,there is saving of 0.119 m3 of virgin and

fertile soil per one thousand bricks.

Conclusions:

Based on the results obtained in this study,

the following conclusions are drawn:

1. Rice husk ash may be successfully usedfor making bricks. It is found that 6% of ash

with 2% lime is optimum percentage to bemixed with Inorganic silt (ML).

2. Compressive strength of the bricksformed by adding optimum ash and lime is

106.0 kg/cm2. Thus, the bricks so formed

may be classified as 100 class (I class) brickas per Indian Standards (IS: 1077-1976).

3. Rice husk ash-lime mixed bricks arelighter in weight as compared to

conventional brick. It is due to fact that thedensity of ash is less than the soil.

4. It is found that water adsorption property

of prepared brick decreases initially with anincrease in ash content up to optimum ashcontent of 6% and 2% lime content.

However, it increases afterwards.5. Rice husk ash mixed bricks are showinghigher water absorption than the

conventional bricks.

6. There is saving of Indian Rupees 0.80(US$ 0.016) per brick, if the brick is formedwith adding optimum percentage of rice

husk ash. Also, there is saving of 0.119 m3of virgin and fertile soil per one thousandbricks.

Reference:

[1] ASTM (1997). Standard Specificationfor Coal Fly Ash and Raw or Calcined NaturalPozzolan for use as a Mineral Admixture inPortland Cement Concrete, C618-94a,Annual book of ASTM standards, Vol. 04.02,pp. 294-296.

[2] ASTM (2000). Standard Test Methodfor Sampling and Testing Brick andStructural Clay Tile. C67-00, Annual book of

ASTM standards, Vol. 04.05, pp. 41-51.

[3] Gambhir, M. L. (1995). ConcreteTechnology. 2nd Ed. McGraw Hill, New Delhi ,pp. 286-287.

[4] Indian Standard (1976). Specificationof Burnt Clay Bricks (IS: 1077). Bureau ofIndian Standards, New Delhi.

[5] Jaturapitakkul, C and Roongreung, B.(2003). Cementing Material from CalciumCarbide Residue-Rice Husk Ash. Journal ofMaterials in Civil Engg, ASCE, Vol. 15, No. 5,

pp. 470-475.[6] Mehta, P. K. (1986) ConcreteStructures, Properties and Materials.

Prentice Hall, Englewood cliffs, N. J. , pp.

266, 273.[7] Raghatate, S. (2003). Techno-Economic Feasibility Study of Agro-Waste(Ash) Utilization in Brick Industry. M. Tech.

Dissertation, U.P. Technical University,India, pp. 80.

[8] Srivastava, A. (2005). EnvironmentalManagement of Rice Husk Ash Produced inGIDA Project Area, Gorakhpur. M. Tech.Dissertation, U.P. Technical University,

India, pp. 100.


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Table 1: Engineering and Chemical Properties of Rice Husk Ash

Engineering Properties Chemical Composition

S.No.

PropertyTypicalvalue

S.No.

ConstituentTypical

Value, %

1 Specific gravity, G 2.23 1 SiO2 88.00

2 Percent retained on 75 sieve 17.5 2 K2O 4.503 Percent passing 75 sieve 82.5 3 CaO 0.55

4 Atterbergs limitsNon-

plastic4 MgO 0.35

5 pH value 7.93 5 SO32- 0.24

6 Water Holding Capacity, % 93.9 6 Al2O3 0.15

7 Bulk Density, t/m3 0.53 7 Fe2O3 0.16

Table 2: Engineering and Chemical Properties of Soil

Engineering Properties Chemical Composition

S.

No.Property

Typical

value

S.

No.Constituent

Typical Value,

%

1 Specific gravity, G 2.70 1 Total Soluble Solids 0.842 Sand Content, % 15.00 2 CaCO3 12.14

3 Silt Content, % 85.00 3 Si 18.72

4 Atterbergs limitsNon-

plastic4 Al 37.42

5 pH value 7.70 5 Fe2O3 2.11

6Water Holding Capacity,

%44.62

7 Bulk Density, t/m3 1.80

8 I. S. Classification ML

Table 3: Engineering Properties of Tested Brick Samples

S. No. % of rice huskash mixed

% of limemixed

Compressivestrength,kg/cm2

Density ofbrickt/m3

WaterAbsorption,%

1 2.0 2.0 96.50 1.76 15.65

2 4.0 2.0 102.50 1.62 14.50

3 6.0 2.0 106.00 1.50 14.21

4 8.0 2.0 96.15 1.45 15.10

5 10.0 2.0 86.18 1.39 19.52


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Figure 1: Moulding of Rice Husk Ash Mixed Brick

Figure 2: Finished Rice Husk Ash-Lime-Soil Mixed Brick


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80

85

90

95

100

105

110

0 2 4 6 8 10 12

Rice Husk Ash, %

CompressiveStrength

,kg/cm

2

Figure 3: Effect of Rice Husk Ash Percentage on Compressive Strength of Brick.

1.3

1.4

1.5

1.6

1.7

1.8

0 2 4 6 8 10 12

Rice Husk Ash, %

Density,

t/m3

Figure 4: Effect RHA Percentage on Density of Brick


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12

14

16

18

20

0 2 4 6 8 10 12

Rice Husk Ash, %

WaterAbsorption,%

Water absorption criteria for

1st class brick: Below 15%

Figure 5: Effect of RHA Percentage on Water Absorption Properties of Bricks

Figure 6: SEM of Conventional Brick Formed Without Addition of Ash.


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Figure 7: SEM of Brick Formed after Mixing Soil with Optimum Ash Content.