1. Introduction

In conventional concrete, density of concrete where is in the order of 2200 to 2600 kg/m³ makes it an uneconomical structural material compared to low density fly ash aggregate concrete. In order to produce concrete of desired density to suit the required application, the self-weight of structural and non-structural members are to be reduced. Hence economy is achieved in the design of supporting structural elements which lead to the development of light weight concrete. Lightweight concrete is defined as a concrete that has been made lighter than the conventional concrete by changing material composition or production method and made by replacing the usual coarse aggregate by lightweight aggregates. Though lightweight concrete cannot always substitute normal concrete for its strength potential, it has its own advantages like reduced dead load, and thus economic structures with enhanced seismic resistance, high sound absorption and good fire resistance can be erected. Because of the above reasons the study on fly ash pellets concrete is taken in this research work.

2. Formation of Fly Ash Pellets

The constituents like cement, fly ash and water are used to produce the fly ash aggregates. Water facilitates the binding material to react and paves the way for the function of the aggregate with good bond property.

Figure 1. Fly Ash Pellets

3. Preparation of Fly Ash Pellets

The fly ash coarse aggregate is prepared by mixing the cement and fly ash in 70:30 and 60:40 ratios. The manufacturing process goes as follows,

♣ First the required quantity of fly ash is taken in the mixer machine and then the exact ratio of the cement quantity is put in the mixer for 60:40ratio.

♣ Now for mixing take the water cement ratio as 0.3.

♣ The water must be added slowly care must be taken to avoid excess addition of water.

♣ As the mixer rotates the cement and fly ash combine and form a spherical shaped aggregate by process of pelletisation.

♣ After some time the mixer is lowered and formed fly ash aggregate is collected.

♣ The same procedure is followed for the other ratios also.

4. Preparation of Fly Ash Pellets Concrete

4.1. Mix Design

The preparation of fly ash concrete is made as the conventional concrete. But the changes in the mix design must be done to corresponding to the changes in the densities of the aggregates. Here are the list of materials used along with their quantity and the final mix design.

(i) Cement = 50 kg

(ii) Sand = 71.25 Kg

(iii) C. A = 86.4 Kg

(iv) Water =25 Kg

(v) Extra quantity of water added for the absorption of Coarse aggregate for 1% = 1.295 Litres

0.5: 1 : 1.425:1.728 is the required mix proportion for M20 mix

5. Characteristic Compressive Strength PF Fly Ash Pellets Concrete

5.1. FOR CUBES

Table 1. Compressive strength of cube specimen Grade of concrete Concrete with 60:40 Fly Ash pellets Concrete with 70:30 Fly Ash pellets 7 days curing M20 29.704 MPa 24.852 MPa 28 dayscuring M20 36.62 MPa 34.12 MPa

5.2. For Cylinder

Table 2. Split strength of cylinder specimen Grade of concrete Concrete with 60:40 Fly Ash pellets Concrete with 70:30 Fly Ash pellets 7 days curing M20 15.36 MPa 15.18 MPa 28 dayscuring M20 24.14MPa 23.03 MPa

6. Comparisons of Strength and Cost

6.1. Comparison of Physical Properties of Conventional Aggregate with Fly ash Aggregate

♣ The above table shows that even though the impact value of both the ratio of fly ash aggregate is high they can be used in the building concrete but they can’t be use be used as a road materials.

♣ The above table also shows that the abrasion value of the fly ash aggregate is less when compared to conventional aggregate so they are good in abrasion.

♣ The 60:40 ratio aggregates attrition value is high, but 70:30 aggregate is good in attrition.

Figure 2. Impact Value Graph

Figure 3. Crushing Value Graph

Figure 4. Deval Abrasion Graph

Table 3. Properties Of Fly ASH Pellets And Conventional aggregate S.NO PROPERTIES CONVENTIONAL COARSE AGGREGATE FLY ASH COARSE PELLETS 60:40 70:30 1. Shape Angular Spherical Spherical 2. Specific gravity 2.75 1.456 1.45 3. Impact value 22.14% 29.96% 36.46% 4. Crushing value 19.5% 30.85% 30.34% 5. Size (mm) 4.75 to 20 4.75 to 20 4.75 to 20 6. Abrasion Value 6.03 4.85 2.7 7. Attrition value 1 5.7 4.6

Figure 5. Deval Attrition Graph

6.2. Comparison of Compressive Strength of Conventional Concrete and Fly Ash Pellets

Table 4. Comparison of Compressive strength S.NO SPECIMEN DAYS CONVENTIONAL CONCRET FLY ASH PELLETS CONCRET 60:40 70:30 1. Cube 7 34.27 MPa 27.904 MPa 24.352 MPa 2. Cylinder 7 11.66 MPa 15.36 MPa 15.18 MPa 3. Cube 28 46.65 MPa 36.62 MPa 34.12 MPa 4. Cylinder 28 21 MPa 24.14 MPa 23.03 MPa

Figure 6. Cube Compressive Strength

Figure 7. Cylinder Comprezssive Strength

6.3. Comparison of Cost of both Conventional Concrete and Fly Ash Pellets Concrete for One Cube (.15m x .15m x.15m)

Relating cost of both conventional concrete and fly ash aggregate concrete for one cube (.15m x .15m x.15m).

Table 5. Cost Analysis CONVENTIONAL CONCRETE FLY ASH PELLETS CONCRETE 70:30 60:40 S.NO MATERIAL QUANTITY RATE QUANTITY RATE QUANTITY RATE 1. Cement 2.5 Kg Rs 17/- 2.5 Kg Rs 17/- 2.5 Kg Rs 17/- 2. Fine aggregate 5 Kg Rs 10/- 3.56 Kg Rs 7/- 3.56 Kg Rs 7/- 3. Coarse aggregate 7 Kg Rs 24/- 4.32 Kg Rs 13 4.32 Kg Rs 17/- 4. Total Rs 51/- Total Rs 37/- Total Rs 41/-

Figure 8. Cost Analysis Graph

Figure 9. Total Cost Graph

Figure 10. Coarse aggregate Cost Graph

♣ The above table compares the cost of conventional concrete and fly ash pellets concrete for a cube.

♣ From comparison it is found the concrete from 70:30 ratio pellets shows more cost efficient i.e. nearly 27% of cost saving when compared conventional .

♣ The cost efficiency is directly proportion to efficiency in manufacturing of pellets. That is if the production is 100% efficient the cost efficiency will increase to a greater extend.

7. Conclusions

The following conclusions can be drawn from the above test and analysis of the result.

♣ The physical properties of the fly ash pellets which were made artificially has attained the required strength as mentioned in the code IS 456-2000.

♣ The compressive of the Class F fly ash pellets concrete has surpassed the minimum strength that a M20 concrete must have.

♣ The cost analysis also proved that Class F fly ash pellets is coat effective than conventional aggregate.

♣ From above comparison and result it can be said that the conventional aggregate can be successfully replaced by the Class F fly ash pellets concrete.

♣ When comparing both ratios 60:40 & 70:30 can be used successfully to replace conventional aggregate.

♣ We prefer 70:30 ratio pellets Since it is more economical when compared to 60:40 ratio pellets.

♣ The aggregates are vital elements in concrete. The usage of enormous quantities of aggregates results in destruction of hills causing geological and environmental imbalance. The environmental impacts of extracting river sand and crushed stone aggregates become a source of increasing concern in most parts of the Country. Pollution hazards, noise, dust, blasting vibrations, loss of forests and spoiling of natural environment are the bad impacts caused due to extraction of aggregates. Landslides of weak and steep hill slopes are induced due to unplanned exploitation of rocks

♣ Fly ash is also one of the hazardous environment pollutants which cannot be disposed that it is suggested that use of aggregate made from fly ash in the future.