Parametric investigation of coconut shells as partial replacement of coarse aggregates in sustainable concrete

. Sustainable construction materials for resource efficiency and environmental effect have grown in popularity .Coconut shells, a waste product of the coconut industry, are plentiful in tropical climates. They are lightweight and permeable, making them an attractive alternative to coarse aggregates. Coconut shells can reduce trash disposal and gravel and sand use by adding them to concrete mixtures. Coconut shell aggregates improve concrete's mechanical strength and durability, although at a lesser rate than conventional aggregates. Coconut shell replacement depends on particle size, surface properties, and curing conditions. Coconut shells with concrete improve thermal insulation, density, and acoustics. In this investigation compressive and flexural strengths of Grade M20 has been studied by replacing natural coarse aggregates with coconut shells at 0%, 10%, 20% and 30% by weight at curing intervals of 7,14 and 28 days. Cubes and beams were casted and then tested and the tests revealed that coconut shells can be used upto 10% in replacement of natural aggregates imparting a strength almost equivalent to conventional concrete.


INTRODUCTION
* Corresponding author: ghanghaskaushal@gmail.comToday, more than ever, concrete is the composite material of choice.Coarse aggregate, fine aggregate, binding substance and water are the four components that make up concrete.The rapid growth in development has resulted in a severe shortage of traditional building supplies [5].More concrete manufacturing causes aggregate depletion and ecological imbalance [7].Many researchers want to replace coarse aggregate to make concrete cheaper and more sustainable [6].Infrastructural development is concerned about this environmental factor [8]. Sugarcane bagasse, wood chips, plastic waste, fabric waste, polyethylene, rice husk ash, rubber tires, vegetable fibers, paper and pulp industry waste, peanut shell, waste glass, and broken bricks can replace concrete aggregates [2][3][4].Thus, an appropriate natural stone replacement material must be found.Coconut shells are tough.Coconuts are naturally accessible and their shells are non-biodegradable, thus they can be utilized in concrete to mimic the original shape of concrete [1][2][3].Coconut is farmed worldwide and India grows coconuts on two million hectares [2].4300 nuts per acre yields 8000 million nuts per year [3].India produces 25% of the world's coconut oil and is expected to grow as demand rises [9].However, as a solid waste producer of 3.18 million tonnes of shells, it is also the nation's biggest polluter.The considerable agricultural waste from local coconut industry poses major disposal issues for the local ecology.Coconut shell, a hard, non-degradable substance, can replace coarse aggregates [10][11][12][13][14][15].Coconut shell trash, which is abundant in underdeveloped nations, can be used in building.This reduces construction material costs and disposes of wastes.Conventional aggregates are rapidly disappearing.One alternative is waste coconut shell.Coconut shells can be used as coarse aggregate for concrete due to their high strength and modulus, high lignin content that makes composites more weather resistant, low cellulose content that absorbs less moisture than other agricultural waste, and non-biodegradability. Concrete is sustainable and eco-friendly when made with alternative ingredients instead of natural aggregates [16][17][18][19][20]. Coconut shell has 33.61% cellulose, 36.51% lignin, and 0.61% ash.Literature are available about coconut as replacement agent in concrete, but experimental investigation as replacement of coarse aggregate are very limited in case of green concrete.So, In this article an attempt has been made for utilization od coconut shell as the partial replacement of coarse aggregate of basic concrete constituents.

EXPERIMENTAL INVESTIGATION
As part of the experimental program, concrete cubes and beams were casted with and without coconut shells.The ingredients for concrete include Portland cement, sand, coarse aggregates, coconut shells, and water.Compressive strength was evaluated using the cubes, while flexural strength was evaluated using the beams.

Materials
Cement, fine aggregates (sand), coarse aggregates (gravel), coconut shells, and water were employed in this experiment.The materials were tested in accordance with ASTM specifications.Cement, as a binder, may hold many substances together.It has been determined what physical properties Ordinary Portland Cement impart and compared to the codes.Portland cement that confirmed to the specifications of ASTM 150 was utilised.Sand is a granular material that occurs naturally and is made up of very small particles of other materials.The fine material that was employed was the kind that made it through sieve 4.75 mm but was primarily retained on sieve 75 m.The fineness modulus of the sand is equal to 2.6, and its specific gravity is measured at 2.67.The bulk density of the sand is measured at 1647 kg/m 3 .For the purpose of this research, natural crushed stone aggregate with a maximum size of 20 mm and bulk density of 1545 kg/m3 was used.The material known as coconut shell is a waste-product.Specific gravity, bulk density, and the shell thickness of coconut shells are 1.25, 650kg/cm 3 , 2-6 mm respectively.The amounts of this waste material will continue to accumulate, and as a result, it will have an impact on our ecosystem.As a result, the utilisation of this substance to enhance the qualities of concrete is absolutely necessary.For both the mixing procedure and the curing, clean water was used.Using sieve test equipment, the particle size distribution of the samples has been determined.The samples are dried in an oven for 24 hours to get rid of the moisture before testing.The average particle size of coconut shells was found to be 4.75 mm, with 20.38 percent of the particles being smaller than 1.18mm.The largest particles measured 10 millimeters in size.Figure 1 displays the results of a comprehensive sieve analysis.

Methods
Using coconut shells in place of coarse aggregates in concrete could increase its strength, as was previously explained.The experimental method was determined by testing the flexural tensile strength and compressive strength of concrete.First of all a batch of control concrete with only cement, sand, aggregate, and water was produced.The coarse aggregates are then replaced with different amounts of coconut shells.Compressive strength and flexural tensile strength were each evaluated on a scale from 0% to 30%.We used 150mm cubes to measure compressive strength and 100mm x 100mm x 500mm beam specimens to measure flexural strength.The mix proportions are vital to a strong and lasting concrete.The mix design should accomplish the desired workability of concrete to prevent segregation and allow for ease of placing.In this regard, using the conventional mix design according to IS code, the mixture was developed for giving compressive strength of concrete of 20 MPa after 28 days of curing.The mix proportion was prepared as (1:1.5:3).Table 1 indicates the percentage of mixture components.The percentages of coconut shells (0, 10, 20, and 30 %) were utilised instead of coarse aggregates.Mx-0 represents concrete having 0% coconut shells whereas Mx-1, Mx-2and Mx-3 represents concrete containing 10%, 20% and 30% coconut shells respectively.

RESULT AND DISCUSSION
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Morphology of Coconut Shells
The particle size of the coconut shells was respectively 2.36mm.The shells had uneven forms and rough surface.The coconut shells have never been subjected to any kind of physical or chemical processing.Scanning Electron Microscope (SEM) provides further characterization.The SEM analysis outcomes are displayed in Figure 2.

Compressive Strength Test
An evaluation of the strength development of concrete with varying coconut shells percentages was performed using a compressive strength test at 7, 14, and 28 days of age.Table 2 demonstrates the change in compressive strength when percentage of coconut shells is increased.The results show that the strength almost equivalent to conventional concrete may be achieved by raising the coconut shells to a level of 10%, and that after this point, further increases in coconut shells result in a fall in the strength of the concrete.The compressive strength at early stages that is after 7 days and 14 days was much lesser as compared to normal concrete however it was much better after 28 days and achieved a satisfactory strength when coconut shells replaced 10% coarse aggregates.The same can be depicted through graph shown in figure 3.   3 displays the data showing that as the amount of coconut shells increases to 10%, the flexural tensile strength also increases.The flexural strength got increased even after 7days and 14 days of curing period when coconut shells replaced 10% of aggregates.When coconut shells replaced 20% coarse aggregates the strength at 7 days and 14 days curing period increased to some extent as compared to normal concrete but after 28 days it declined.As can be seen in the Figure 4 also, the flexural strength decreases when the percentage of coconut shells increases above 10%.Hence, we may conclude that, within certain parameters, coconut shells can effectively substitute coarse aggregates in concrete, thereby increasing its strength.It follows that recycling has positive effects on the environment and the durability of concrete.

CONCLUSION
• In conclusion, adding more coconut shells reduces the concrete's workability modestly but noticeably with time.When curing time for concrete is stretched out, the resulting strength is enhanced.
• Small gains in flexural tensile strength were seen as the coarse aggregates were replaced by 10% coconut shells however compressive srength did not increase but gave satisfactory results and was almost equal to the conventional concrete.
• So, 10% replacement of coarse aggregates with coconut shells is suggested.Therefore, the alternative is technically and commercially viable.Using recycled coconut shells as aggregate can help create a greener world by lowering the demand for natural resources used to produce conventional material.

Fig. 3 .
Fig.3.Compressive Strength for different percentage of Coconut Shells at varying stages3.4Flexural Strength TestFlexural samples were tested to determine the strength of concrete mixed with different amounts of Coconut shells.Table3displays the data showing that as the amount of coconut shells increases to 10%, the flexural tensile strength also increases.The flexural strength got increased even after 7days and 14 days of curing period when coconut shells replaced 10% of aggregates.When coconut shells replaced 20% coarse aggregates the strength at 7 days and 14 days curing period increased to some extent as compared to normal concrete but after 28 days it declined.As can be seen in the Figure4also, the flexural strength decreases when the percentage of coconut shells increases above 10%.Hence, we may conclude that, within certain parameters, coconut shells can effectively substitute coarse aggregates in concrete, thereby increasing its strength.It follows that recycling has positive effects on the environment and the durability of concrete.

Table 1 .
Concrete mix design summary Coconut Shells

Table 2 .
Compressive Strength of Concrete Containing Coconut Shells Mix designation

Table 3 .
Flexural Strength of Concrete Containing Coconut Shells