PARTIAL REPLACEMENT OF COARSE AGGREGATE WITH COCONUT SHELL IN THE CONCRETE

The high cost of conventional construction material affects economy of structure. With the increasing concern over excessive exploitation of natural aggregates, synthetic lightweight aggregate produced from environmental waste is a viable new source of structural aggregate material. It is becoming more difficult to find natural resources. Therefore the coconut shell as partial replacement for coarse aggregate in concrete is studied. The density, slump and compressive strength of concrete are tested. The replacement of coarse aggregate by coconut shell by 0%, 10%, 20% and 30%. The tests were carried out and the results obtained suggested that the replacement more than 20% leads to lightweight aggregate concrete. The slump found out to be increases as the percentage replacement increased. Similarly the density is reduced as the percentage replacement increased. The compressive strength found to be decreases as the percentage replacement increases.


Introduction
Infrastructure development across the world created demands for construction material. Concrete is the premier civil engineering materials used in the structure. Concrete manufacturing involves consumption of ingredients like cement, aggregates, water and admixtures. Among all the ingredients, aggregates form the major parts. Production is expected to increase to more than billions tons per year by the year. Use of natural aggregates in such a rate leads to a question about the preservation of natural aggregate sources. Using alternative materials in place of natural aggregates in concrete production makes concrete as sustainable and environmentally friendly construction material. The chemical composition of coconut shell is similar to wood and it contains 33.61% cellulose, 36.51 % lignin and 0.61% ash.
Lightweight aggregate concrete can be used produced using a variety of lightweight aggregate. Lightweight aggregate can be originated from natural materials like pumice, the thermal treatment of natural raw materials like clay slate or shale. The other byproduct may include fly ash. The required properties will have bearing on the best type of lightweight aggregate used. the benefits of using lightweight aggregate concrete includes reduction in dead load, improved thermal properties, improved fire resistance and reduction in formwork.

Literature review:
It was studied that palm kernel shell and coconut shell, both of which belongs to the family of palm shells. These are agricultural waste products and are available in large quantities in the tropical regions of the world. Research showed that coconut shell are more suitable as low strength giving light weight aggregate when used to replace common coarse aggregate in concrete production ( [1], [2]).
The researcher suggested that one of the alternatives for coarse aggregate is coconut shell. It is one of the most common agricultural solid wastes in many tropical countries. Density of coconut shell concrete of the typical mixes ranged from 1930 kg/cum to 1970 kg/cum ([3], [7]).
There was researched on the coconut shell use as aggregate in the study which showed that with global economic recession coupled with the market inflator trends. The average compressive strength for concrete cubes with coconut shell 15.6 N/mm2 for 28 days [4].
It was studied studied the compressive strength, split tensile strength, water absorption and sorption for different coconut shell replaced concrete. By replacement of coconut shells in place of aggregates, 10% &20% replacement will have been decreased marginally the strength properties of concrete compared to the normal concrete [18].
The researcher experimented three different concrete mixes namely M20, M35 and M50 grade with different combination of natural material CS content in the proportion 0%, 10%, 20%, 30% and 40% replaced. It was studied that coconut shells are suitable as low strength giving lightweight aggregate [19].
Also the researcher experimented to determine the compressive strength, split tensile strength and flexural strength cube, cylinder and beam section. It was concluded that when coconut shell aggregates in proportions of 15% was used in the conventional concrete comparable compressive strength results were obtained [20].
There was study on experimentation that coconut shell can be grouped under lightweight aggregate because 28 days air dry densities of coconut shell aggregate concrete are less than 2000 kg/cum. It was concluded that this type of concrete can be used in rural areas and wherever the natural aggregates are costly [21].
The experimentation conducted that density of concrete decreases with increases in CS percentage. Workability decreases with increase in CS percentage. Compressive and split tensile strength of CS concrete were lower than normal concrete [22].
It was observed that coconut shell concrete is very suitable for low cost construction in rural areas. It can replace the natural coarse aggregate up to certain limits. This type of aggregate will serve to counteract the scarcity of natural aggregates [23].

Material Specification
For the production of concrete, the constituent materials are cement, fine aggregate, coarse aggregate and water. To get better workability and strength, the material used should have better quality. To maintain the safety of any structure, provisions are provided as per IS 456:2000.

Cement:
In the experimental work cement used is Ordinary Portland cement. Various properties were evaluated such as fineness of cement, setting time, soundness test and compressive strength as shown in the following table no.1.

Coconut shell:
Coconut shells used in the study are brought from local temple. The coconut shells are sundried for five days before using it as an aggregate. The cleaning of coconut shell is carried with the help of sand paper, the smaller extractions on the outer face of coconut is cleaned with the help of water. The outer shell is then broken in smaller parts up to 20 mm. The broking of coconut shell is done with the help of 30 kg hammer. Then the broken pieces are passed through IS 20 mm sieve and pieces are retained on a IS 16mm sieve are used.

Water:
The water used in the study was clean and clear. It was free from bacteria and other impurities. There was no acid content in it. The water cement ratio for the concrete mix is 0.6.

Methodology:
The concrete mix design was carried out for the present work. The concrete mix design is a process of selecting the suitable ingredient of concrete and determining their most optimum proportions economically.
The approximate value for the coarse aggregate volumes are given in IS 10262-2009 for the water cement ratio. For more workable concrete that can flow around any congested reinforcement bars, it may be desired to reduce the coarse aggregate content. The value for the coarse aggregate for different zone of fine aggregate is shown in following table no.5.  The material requirement, quantity and properties of the material required for the concrete is shown in the following table no. 7.

Results
In the present work coarse aggregate is replaced with the coconut shell, by volume. Specimens were casted by replacing 0%, 10%, 20% and 30% of coarse aggregate with coconut shell. Tests were conducted on the cast specimens after 7, 14, 21 and 28 days as mentioned in the IS code. There is no need to treat the coconut shell before use as an aggregate except for water absorption. Tests for workability and compression were conducted and results were obtained. Coconut shell concrete has better workability because of the smooth surface on one side of the shell and the smaller size of coconut shell. The table no. 8 is mentioned below detailing the properties of concrete.
Graph .1: Percentage replacement of coarse aggregate v/s Density (Kg/cum) From the above graph it is observed that as the percentage replacement of coarse aggregate by coconut shell is increased, the density is decreased. This can lead to light weight concrete up to some extent and therefore the applications are filler materials in framed structure, flooring tiles, thermal insulating concrete, etc. Also the slump Value of different mix of the concrete is shown.

Graph 2: Concrete Mix v/s Slump Value
From the above graph the slump value is increased as the percentage of the replacement of coarse aggregate by coconut shell is increased. Therefore the construction work requiring the more slump value, this type of concrete is suitable. The compressive strength of concrete is detailed in the table 8.

Conclusion
Use of coconut shell in cement concrete can help in waste reduction and reduction in pollution. The need of the hour is to encourage such a use of the wastes as construction material in low cost housing. The construction industries have identified many artificial and natural lightweight aggregate that have replaced conventional aggregates thereby reducing the size of the members in the structure. From the experimental work it is clear that the with CS percentage increase the 7 days strength gain also increased with the corresponding 28 days curing strength.
Workability of concrete is increases as the replacement increases. Specific gravity of the concrete reduces as the replacement of coarse aggregate increases. The density of concrete is decreases as the replacement increases. Density of concrete should not be less than 2000 kg/cum.