Kepah Shell Waste as A Coarse Aggregate Substitution Material on Concrete Mixture

This research uses kepah shell waste as a substitute for coarse aggregate. The purpose of this study is to determine the value of slump and compressive strength values in concrete variations. Variations of concrete consist of normal concrete, mixed shells of waste concrete with 5%, 10%, and 15% substitution of coarse aggregate. The concrete maintenance period was carried out for 7 days, 14 days, and 28 days. The results of the slump value research show that the lowest slump value is normal concrete, while the highest slump value is concrete with a mixture of 15% kepah shell waste. For the results of the compressive strength value, the highest compressive strength value is concrete with a mixture of 5% kepah shell waste. For the most economical cost with high quality of concrete compression strength is the concrete mixture with 5% of kepah shell waste. The greater the percentage of kepah shell waste, the cheaper the concrete price, but higher percentage of kepah shell waste will result a decrease in the quality of concrete.


Introduction
Indonesia is a country that has many islands with large water areas.[1] Indonesia has a water area of 5.8 million km and a coastline of 81,000 km, Indonesia has marine wealth that can be processed as useful materials for the community [2].The wealth of the sea that often sought after by the community is the seashells.People often only use seashell meat.[3] The seashell waste is not used by the community.[4] The waste of seashell can cause environmental pollution.[5] In general, the kepah shells are usually referred to as Geloina erosa and another name for the kepah shells is Polymesoda erosa.[6] Polymesoda erosa lives in tidal areas, foraging activities influenced by tidal movements of water.[7] Polymesoda erosa is one of the three common species of the genus Polymesda from the family Corbiculidae, class Bivalvia that can be found inhabiting the mangrove areas in Southeast Asia.[8] Based on the shape of the kepah shell, it has a shell shape like a plate or cup.[9] Where the kepah shell has two poles which is called bilaterally symmetrical.In addition, the edges of the mussel shells are flat and convex in the middle of the kepah shells [10].The shell has three layers consisting of Periostracum, Prismatic and Nacreas.Periostracum which is a layer that is black and usually made of horns known as coochiolin, Prismatic which is a layer composed of crystals of calcium carbonate, where the lime is shaped like a prism.Nacreas layer which is a layer consisting of calcium carbonate [11].The shell has a hinge that functions as a connective tissue between the shells.This tissue is known as the ligament.[12] IOP Publishing doi:10.1088/1755-1315/1324/1/012041 2 Kepah shells contain calcium carbonate (CaCO3) [13].The content of calcium carbonate in kepah shells has higher levels than limestone, glass, ceramics.It can also be seen that kepah shell has a hard shell so it can be said that the harder the shell, the higher the calcium carbonate (CaCO3) content.
The use of kepah shell waste as a substitute for coarse aggregate in this study is due to the accumulation of seashell in coastal areas and cities that are not managed by the community, resulting the environmental pollution.[14] The utilization of shell waste as one of concrete ingredient was conducted as one the pollution solution.[15] In this study, the concrete mixtures were using 5%, 10% and 15% of kepah shell waste as a substitute of concrete coarse aggregate.

Research Methodology
In the process of this research, testing is carried out in the laboratory.The test consists of coarse aggregate, fine aggregate, slump test, and concrete compressive strength testings.Tests on coarse aggregate were carried out to determine the loose bulk density, moisture content, silt content, specific gravity, absorption, and fineness modulus.Tests on fine aggregate were carried out to determine the loose bulk density, compacted bulk density, moisture content, silt content, specific gravity, absorption, and fineness modulus.After testing the aggregates, the mix design was planned according to the SNI 7656:2012 [16].In this study, kepah shell wastes were used as a substitute for coarse aggregate with curing or maintenance ages of 7 days, 14 days, and 28 days.During the mixing process, the concrete tested to find the slump value.After the slump test carried out according to the desired target, the concrete was casted into a concrete mold in the form of a cylindrical mold with a size of 150 mm x 300 mm.The concrete samples used can be seen in Table 1.
Table 1 Mix design was planned to find out how much aggregate, sand, cement, and water needed in the manufacture of concrete.The mix design planned according to the SNI 7656:2012, a procedure for selecting mixtures for normal concrete, heavy concrete and mass concrete.The normal concete was designed to have concrete compressive strength of 20 MPa.The concrete mixture carried out according to the SNI 03-3976-1995, a procedure for mixing and casting concrete [17].

Results and Discussion
To determine the weight and volume of the required materials, a mix design was carried out in accordance with SNI 7656:2012.Table 2 explains the mix design, how much weight and volume of material that needed in the concrete mixing process.The slump test can be carried out after the concrete mixing has been done.[18] Slump value testing on concrete aimed to maintain the workability of the concrete [19].The slump value test followed the reference from SNI 1972:2008 [20].The results of slump tests can be seen in Figure 1.

Figure 1. Slump Test Comparison for Each Variation
From the results of the slump test for each variation of concrete, it can be seen that the normal concrete with a design quality of 20 MPa, reaches a slump value of 90 mm.The target value of slump design was 25 mm to 100 mm.Slump testing on concrete with 5 % of kepah shell waste reached the slump value of 95 mm.Slump testing on concrete with 10 % of kepah shell waste obtained the slump value of 105 mm.Slump testing on concrete with 10% of kepah shell waste obtained the slump value of 110 mm.
The factor that causes higher slump value is because of the addition of large amounts of waste.The slump value becomes higher, due to the shape of the kepah shell that do not have a pivot so the concrete cannot absorb water optimally.This can affect the quality and compressive strength of the concrete.With the test results above, it can be concluded that the addition of excessive kepah shell waste will obtain the higher slump value.
The compressive strength of concrete was tested on specimens aged 7 days, 14 days, and 28 days.The compressive strength of concrete is tested using the Dial Compressive Machine Test.The concrete compressive strength test has 60 samples with 4 different variations.The test object used was a cylindrical test object with a size of 15 cm x 30 cm.Testing the compressive strength of concrete can be done if the test object has been curing according to the age of the concrete.In addition, the test object IOP Publishing doi:10.1088/1755-1315/1324/1/0120414 must be fitted with a cap using sulphur powder so that the surface of the test object becomes flat so the received load can be distributed evenly and facilitate the compressive strength testing process.The results can be seen in Figure 2.

Figure 2. Comparison between Each Variation of Concrete
There are expenses for the cost of concrete materials.Concrete materials in this study contained several materials such as cement, fine aggregate, coarse aggregate and kepah shell waste.The following was a price analysis for each material used in each variation of the concrete can be seen in Figure 3. From the comparison results of the price and quality per 1m 3 of concrete, it can be seen that concrete with a mixture of 5% kepah shell waste has a price difference compared with normal concrete of Rp. 6,495.77or 0.6% cheaper than normal concrete.anda decrease of 4.86% in the concrete compressive strength.Meanwhile the concrete with a mixture of 10% kepah shell waste has a decrease of 1.2 % in price or Rp.12.991.55cheaper than the normal concrete.And the concrete compressive strength was also decreasing13.36%compared to the normal concrete.For concrete with a mixture of 15% kepah shell waste, the price difference with normal concrete was Rp. 19,487.32 or 1.80% lower.But the concrete compressive strength was decreasing 20.98 % compared to the normal concrete.
From the results of the comparison of the price and quality of concrete for each variation of concrete specimens, it can be concluded that the greater the percentage of addition of kepah shell waste, the cheaper the production price, but the addition of an excessive percentage of kepah shell waste will result a decreasing number in the concrete compressive strength.Therefore, further research is needed to obtain higher quality concrete at a lower price and maintain environmentally friendly concrete aspects.

Conclusion and Sugestion
The following are the conclusions of the research results as follows: a.Based on the results of the slump value test for each variation, it can be concluded that the slump value in concrete with a mixture of kepah shell shell waste is 15% higher than normal concrete.This is because of the kepah shell waste has a non-porous shape which makes it unable to absorb water, so the concrete has excess water which results in a high slump value.From the results of the slump value test, it can be concluded that the addition of the percentage of kepah shell waste will increase the slump value, but will make the quality of the concrete decrease; b.Based on the results of testing the compressive strength values for all variations, it can be concluded that the compressive strength value of concrete with a mixture of 5% kepah shell waste is higher than the addition of 10% and 15% kepah shell waste percentages.It can be seen from the test results, the addition of an excessive percentage of kepah shell waste will make the compressive strength value of the concrete decrease; c.The addition of excessive kepah shell waste into the concrete mixture will result the decreasing quality of the concrete.It can not reach the design target of concrete compressive strength.It can be seen in the variation with a mixture of 15% kepah shells waste, the concrete compressive strength was reduced to 18.34 MPa; d.Based on the manufacturing costs for each variation of concrete, concrete with a mixture of 5% kepah shell waste has a more economical price with a concrete quality that is almost the same as normal concrete.
From the research conducted, there are several suggestions that can be explored in further research: a.It is necessary to add additives to the concrete mixture, to determine the effect of adding additives to the quality of concrete; b.Substitution of seashell waste can be carried out on fine aggregate or cement to determine the results of the concrete compressive strength, so it can be used as a comparison with this study; c.Tests for variations can be carried out by methods other than testing the compressive strength of concrete, to find out other parameters that may affect the quality of concrete; d.Need to obtain higher quality concrete at a lower price and maintain environmentally friendly concrete aspects.

Figure 3 .
Figure 3.Comparison of Price and Quality of Concrete for Each Variation 1m 3 of Each Test Object

Table 2 .
Material Weight and Volume Requirement Variation Concrete