Utilization of Rice Field Conch Shells as a partial substitution of Cement and Fine Aggregate for Split Tensile Strength of Concrete

. Aceh is one of the provinces in Indonesia which has a very large area of rice field production. However, there are many pests that hinder agriculture in Indonesia. One of them is the rice field conch shells which has the potential to cause very high losses to the rice crop harvest. The aim of this research was to determine the ratio of the split tensile strength of concrete using rice field conch shells as a partial replacement for cement and fine sand against normal concrete by 0%, 5%, 10%, and 15%. In addition, it was also seen the effect of immersing concrete specimens using rice field conch shells substitution in tap water and water collected from paddy's farm. This study used the ACI (American Concrete Institute) 211.1-91 and ASTM (American Society for Testing and Materials) methods. The specimens consisted of cylinders with dimensions of 15 cm x 30 cm, totaling 40 specimens with a design concrete compressive strength of 17.00 MPa. The curing of the specimens was carried out using tap water and water collected from paddy's farm for 28 days in the soaking tub. The results showed that 5% substitution of rice field conch shells in cement and fine sand using the tap water immersion method showed a 3% increase in the tensile strength of concrete in comparison with normal concrete. Meanwhile, immersion using the water collected from paddy’s farm method showed a decrease in the value of the split tensile strength of the concrete.


INTRODUCTION
Concrete is a material that is widely used in infrastructure construction.The materials used in the manufacture of concrete are very much needed and these materials cannot be renewed and it is feared that one day they will run out (1)(2)(3).Various studies have been conducted to find alternative materials to replace materials that are renewable and environmentally friendly (4,5).One solution is by substituting substitute materials, both as coarse aggregate, fine aggregate, cement and additives in the manufacture of concrete.
Aceh Province is one of the provinces which has about 310.01 thousand hectares of paddy rice farming land.This figure has decreased in 2019, namely as many as 19.5 thousand hectares or 5.92% compared to 2018 (6).However, there are many pests that hinder agriculture in Indonesia.One of them is the rice field conch shells, these rice field conch shells has the potential to cause very high losses to the rice crop harvest.This is because rice field conch shells have the property of developing very quickly and easily adapting to the environment (polyphagous herbivore).Today's modern concrete technology allows the use of materials derived from nature to be limited (7).The alternative of this research is to try to use rice field conch shells as a partial replacement for cement and fine sand.This is because the utilization of rice field conch shells in Indonesia is not optimal, usually rice field conch shells are only used for the meat while the shells are just thrown away and become scattered waste which can damage the environment and cause a bad smell (8).By optimizing the utilization of rice field conch shells, it is hoped that it will reduce waste that pollutes the environment and provide its own added value (9).
The characteristics of the rice field conch shell, namely the meat is brownish cream and regularly chewy, the rice field conch shells is dark brown with a black line pattern.The component of the rice field conch  is calcium carbonate, the rice field conch shells is one of the organic wastes that is difficult to decompose which in the end only becomes waste that causes pollution.rice field conch shells (Pomacea canaliculata) contains very high levels of CaCO3 (calcium carbonate), so it can react very well with cement as the main ingredient in making concrete (10).Calcium carbonate is a chemical compound with the formula (CaCO3).This compound is a common ingredient found in shells of marine organisms, rice field conch shells (snails), charcoal balls, and egg shells (11,12).
Several studies have stated that the use of waste containing CaCO3 into cement by 5% can increase the strength of concrete.The results of research on the utilization of oyster shells into cement and fine sand by 5% can significantly increase the compressive strength and split tensile strength of concrete (13,14).Research on the use of rice field conch shells as a substitute for cement in the amount of 1% can increase the compressive strength of concrete (15).The results of previous studies stated that the compressive strength, tensile strength, and flexural strength increased when the cement was replaced with rice husk ash of 5% to 15% (16).
In this research, the compressive strength of the concrete used was 17.00 MPa as required in SNI (Indonesian National Standard) regulations that the minimum structural compressive strength of concrete is at least 17.00 MPa (17).Rice field conch shells come from rice fields in Ajee Rayeuk Village, Want Jaya District, Aceh Besar District, Aceh Province.Rice field conch shells are used as a partial replacement for cement and fine sand with a mixed composition of 0%, 5%, 10%, and 15% by soaking tap water and water collected from paddy's farm for 28 days.Tap water is water that comes from a regional drinking water company that meets health requirements (18).Water collected from paddy's farm is water that comes from rainwater, irrigation, surface water and groundwater.Surface water sources are rivers, lakes, reservoirs, and rainfall, while groundwater sources are water that is in the ground (19).
The aim of this research was to know the ratio of the split tensile strength of concrete using rice field conch shells as a substitution material into cement and fine sand against normal concrete.In addition, it was also seen the effect of immersing concrete specimens using rice field conch shells substitution in tap water and water collected from paddy's farm.
The ratio of tensile strength of concrete against compressive strength of concrete is about 9% -15%.The specimen will be split in half when the splitting tensile strength is reached (20).The formula for this test can be seen as follows:

RESEARCH METHODS
Research methods are the most important thing in conducting research.Regulation of ASTM (American Society for Testing of Materials) and ACI (American Concrete Institute) were used in this research.The research was conducted at the Building Materials and Transportation Laboratory, Faculty of Engineering, Universitas Iskandar Muda, Banda Aceh.In order to obtain research results as expected, it is necessary to carry out the following research stages:

2.1
Preparation of materials and equipment to be used Before making the specimen, the first step is material preparation.Materials for making normal concrete and substitute for rice field conch shells are as follows: 1. Portland Cement (PC), the portland cement used is PPC (Portland Composite Cement) and produced by PT.Lafarge Cement Indonesia.
2. Coarse aggregate, the aggregate used is natural aggregate from rocks that pass a sieve with a diameter of 25.4 mm, obtained from the Krueng Aceh river in Jantho sub district, Aceh Besar district.The coarse aggregate obtained was brought to the laboratory to be cleaned of all impurities and then filtered using a 25.4 mm sieve.obtained from the Krueng Aceh river in Jantho sub district, Aceh Besar district.The fine aggregate obtained was brought to the laboratory to be cleaned of all impurities and then filtered using a 4.75 mm sieve for fine sand and a 9.52 mm sieve for coarse sand.4. Water, the water used for mixing concrete is tap water which comes from the Building Materials and Transportation Laboratory, Department of Civil Engineering, Universitas Iskandar Muda, Banda Aceh.

5.
The rice field conch shells used in this study came from rice fields in Ajee Rayeuk area, Aceh Besar district, Aceh Province.The rice field conch shells were collected and brought to the laboratory to be cleaned of dirt attached to them using tap water.Then, the rice field conch shells are soaked in tap water for 24 hours, with the aim that the dirt is completely clean (21).Then, the rice field conch shells were put into the oven at 115 0 C for 24 hours.After drying, the rice field conch shells are burned in a combustion drum and then filtered using a sieve no.200 (size 0.075 mm) which is used as a substitute material into cement (22).The ash of rice field conch shells is also known as filler in concrete (23).For partial substitution of fine sand, the dried rice field conch shells were crushed using a Los Angeles machine and then filtered using a No. sieve.4 (4.75mmsize).6.The soaking water used is tap water and water collected from paddy's farm.The tap water used comes from the tap Office (Regional Water Supply Company) Tirta Diroy which is located at Jl.Mr. Daud Beureueh, Lampineung district, Banda Aceh City.Meanwhile, rice field water is taken from rice fields in Ajee Rayeuk area, Aceh Besar district, Aceh Province.
The equipment used in the study included 1 (one) set of ASTM standard filters, containers or pans, a compressive loading machine with a capacity of 100 tons, an oven, cylindrical specimens with a size of 150 mm x 300 mm, digital scales with a capacity of 15 kg with an accuracy of 0.1 gram, digital scales with a capacity of 5,000 grams with an accuracy of 0.01 grams, a concrete mixer (molen) with a capacity of 90 liters, an iron rod for compacting aggregate with a diameter of 16 mm and a length of 60 cm, equipment for checking concrete mixes, and other equipment (ruler, measuring cup, thermometer, container, scoop, unbreakable bucket, slump test kit, rubber mallet, wire basket, iron bucket filled with water, etc).

2.2
Testing the physical properties of the aggregate Testing the physical properties of the aggregate (fine aggregate and coarse aggregate) is carried out in the laboratory according to the rules in ASTM 2004, consist of bulk density (ASTM C 29/C 29M -97) (24), absorbtion (ASTM C 127 -01) (25), specific graviety and sieve analysis (ASTM C136 -01) (26).

Concrete mix design
The concrete mix is planned according to the ASTM rules (27) and ACI 211.1-91 (28).The concrete mix design starts from determining the slump of (75-150) mm and the concrete compressive strength, namely 17 MPa.The amount of water mixed was obtained based on the maximum size of the aggregate, which in this study used a maximum size of 25.4 mm.The amount of cement is obtained based on the W/C (Water Cement Ratio) value in the ACI table.W/C is obtained based on the design concrete compressive strength of 17 MPa listed in the ACI table.The composition of normal concrete in this study was cement, fine sand, coarse sand, coarse aggregate, and water.The substitution material used in this study was rice field conch shells waste which was substituted into cement and fine sand with substitution rates of 0%, 5%, 10%, and 15%.The percentage of substitute material into cement and fine sand in the concrete is 1:1 (13).The rice field conch shells is divided into 2 parts, namely: the first part is used as a substitute for cement and the second part is used as a substitute for fine sand.The percentage of rice field conch shells substitution in cement and fine sand is 100%.

2.4
Procedure of making and curing the specimen Making concrete mix begins with preparing fine aggregate and coarse aggregate which have been cleaned and filtered using a sieve according to the rules in ASTM.Then, each material is weighed according to the mixture ratio obtained from the concrete mix design.The mixer used in this study has a capacity of 50 liters/mixture with an electric dynamo drive.Before casting, the mixer is wetted with water as well as the mortar storage container.This work is carried out so that the concrete mortar is not sticky and easy to remove.After all the preparations have been completed, the mixing of the concrete mortar is carried out by adding the concreteforming materials, namely coarse aggregate, fine aggregate, fine grain of rice field conch shells, rice field conch shells ash, cement, and water sequentially with the aim of preventing clumping of the concrete mixture.The mixing time is around fiveteen minutes with the tilt of the molen axis around 45°.After the material is mixed thoroughly, the resulting mortar is poured into a mortar container.After the mixing process is complete, the thickness of the mortar mix is checked by means of a slump test.The concrete cylinder specimen was carried out by filling the mortar into the cylindrical specimen in three layers.First layer was compacted using a steel stick 25 times with size the diameter of 16 mm and a length of 60 cm, where each layer was compacted by dropping a compactor from a height of 30 cm.After the specimen is full, the sides of the specimen are tapped with a rubber mallet so that the mortar becomes denser.The specimen is opened and coded after 24 hours as planned in Table 1: Table 1.The design of specimen Source: Author Where: NC = Normal concrete for specimen number 1 to 5 RCSC5% = Rice field conch shells concrete with substitution 5 % of fine sand and cement RCSC10% = Rice field conch shells concrete with substitution 10 % of fine sand and cement RCSC15% = Rice field conch shells concrete with substitution 15 % of fine sand and cement The immersion of the specimens in this study was carried out using tap water and water collected from paddy's farm.The number of concrete cylinder specimens used for each treatment is 20 (twenty) specimens.Immersion of the specimen using tap water begins with placing the specimen into the soaking tub for 28 days, where the influence of the weather is not directly received by the specimen.Meanwhile, immersion of water collected from paddy's farm begins by inserting concrete cylinder test specimens directly into the water collected from paddy's farm for 28 days.Testing procedure The split tensile strength test of concrete was tested in accordance with ASTM C496/496M-17 (29).The split tensile strength test of concrete was tested after the concrete cylinder specimen reached the age of 28 days.The specimens were removed from the soaking tub after ± 24 hours before the concrete split tensile strength test was carried out, with the aim of cleaning and drying the surface water.The specimen is measured and recorded with dimensions and weight using a balance in the laboratory.Then the specimen is placed horizontally on a 200 tf compressive strength tester machine for testing the split tensile strength of concrete, where the speed of the machine is increased slowly until the specimen reaches the maximum split tensile strength so that the specimen is cracked or broken

RESULT AND DISCUSSION
Based on the results of testing the physical properties of the aggregates carried out in the laboratory, it shows that the aggregate used in this study fulfill the requirements as material for forming the specimen.The results of testing the physical properties of the aggregate were shown in Table 2 below.The results of the concrete mix design based on the ACI method obtained a concrete volume weight of 2380 Kg/m3.W/C used in this research is 0.67, while the compressive strength of concrete is around 17 MPa.The results of the composition of the concrete mix design can be seen in Table 3 below.The slump value is the amount of decrease in the concrete/mortar surface.From the test results in the laboratory, a good slump value was obtained, in accordance with the planned slump value, which ranged from 75-100 mm.The results of the slump test for concrete soaked using tap water and water collected from paddy's farm can be seen in Table 4 and Table 5.From Table 4 and Table 5, a good slump value is obtained, which is as planned (75 -100 mm).To get the slump value as planned, it is necessary to reduce the amount of water by 5%.The reduction in water (workability) in this study is due to the use of multifunctional cement (PPC) in this study so that its bonding and hydration are longer than portland cement type I.
The split tensile strength test of concrete was tested when the specimens were 28 days old.Testing the split tensile strength of concrete in this study was carried out with the aim of seeing the differences in the tensile strength values of the specimens immersed in tap water and paddy field water.The results of tensile strength of concrete by immersion in tap water and water collected from paddy's farm can be seen in Figure 1.
Figure 1 The result of splitting tensile strength of concrete using water collected from paddy's farm and tap water From the test results in Figure 1, it is shown that the split tensile strength of concrete with the tap water immersion method for 28 days with a 5% substitution mixture variation has a higher split tensile strength value of 2,41 MPa than 0%, 10% and 15% substitution, namely of 2,34 MPa, 1,94 MPa and 1,41 MPa.Meanwhile, the split tensile strength value of concrete using water collected from paddy's farm immersion method for 28 days with a variation of 0% conch shell substitution mixture has a higher split tensile strength value of 2,16 MPa compared to 5%, 10%, and 15% substitution, which is equal to 2 ,01 MPa, 1,65 MPa and 1,35 MPa.
Based on Figure 1, it can be seen that the split tensile strength of concrete for 28 days using variations of ash and rice field conch shell powder substitution decreased the tensile strength of concrete.The decrease in concrete strength is caused by chemical reactions that occur during the mixing process of ash and rice field conch shell powder in the concrete mixture and the strength characteristics of the dominant rice field conch shells are smaller compared to fine aggregates.So that it cannot be utilized as a substitute material into fine aggregate and there is direct influence due to weather factors which can damage the characteristics and bonding capacity of concrete by using water collected from paddy's farm immersion.
Measurement of the concrete bulk density was carried out when the specimen was 28 days old.The measurement of concrete bulk density in this study was carried out with the aim of seeing the difference in concrete bulk density values for specimens that were soaked using tap water and water collected from paddy's Figure 2 The result of bulk density of concrete using water collected from paddy's farm and tap water Figure 2 shows that the bulk density value of concrete by using the tap water immersion method with substitution of ash and rice field conch shell powder at mixing of 0%, 5%, 10% and 15% are 2476.45kg/m 3 , 2376.33 kg/m 3 , 2353.33 kg/m 3 and 2272.35kg/m 3 .Whereas for immersion using the rice field water method with substitution of ash and rice field conch shell powder at mixing of 0%, 5%, 10% and 15%, namely 2404.66 kg/m 3 , 2335.45 kg/m 3 , 2330.27 kg/m 3 and 2156.91 kg/m 3 .
From Figure 2, it can be concluded that the concrete bulk density values measured when the specimens were 28 days old decreased significantly, especially for immersion using water collected from paddy's farm.This is because the specific gravity of the rice field conch shell is smaller when compared to the specific gravity of cement or fine sand.In addition, water collected from paddy's farm also contains heavy metals, which when reacted with concrete can cause erosion of the concrete, so that the weight of the concrete decreases.

CONCLUSION
The use of PPC type cement can affect the concrete/mortar mixture which causes a long hydration process when mixing the material in the concrete mixer.So that when testing the specimen, the type of concrete with a 5% variation using tap water immersion only experienced an increase in the split tensile strength of the concrete.While for variations of 0%, 10% and 15%, the split tensile strength of the concrete was decrease.By substituting rice field conch shells into fine sand and cement by 5%, the tensile strength of the concrete increases.This is caused by the lime content in rice field conch shells which is able to form a strong bond with cement.Furthermore, the results of measuring the bulk density of the concrete showed that the increasing percentage of rice field conch shell substitution into fine sand and cement, the lower the bulk density of the concrete.This is due to the specific gravity of the rice field conch shell which is relatively lighter than fine sand.

SUGGESTIONS
The results of this research are expected to be utilize both in the scientific development of building materials, especially concrete technology and in practical application in the field.It is hoped that further research can be carried out by other researchers, especially on the following problems: 1. Reducing the amount of concrete mixing water by 5% or 7%, with the aim of obtaining a slump value as planned.2. For further research, it is suggested that the rice field conch shell be used as an additive and not as a substitute, so that the split tensile strength of the concrete can be increased and as planned.
tensile strength of concrete (N/mm 2 ) P = Load at split time (N) l = Height of specimen (mm) d = Diameter of specimen (mm)

Table 2 .
The results of examining the physical properties of the aggregate

Table 3 .
Mix design of concrete for 1 m 3 with W/C 0,67

Table 4 .
Slump test results of the specimen with the tap water immersion method

Table 5 .
Slump test results of the specimen with the water collected from paddy's farm immersion method