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Mechanism of Calcium Carbonate Admixture from Common Cockle Shell (Cerastoderma edule) and Marsh Clam (Polymesoda expansa) in the Early-Age Compressive Strength of Concrete
Researcher:
Mariah A. Cruz
Nabunturan National Comprehensive High School, Nabunturan, Compostela Valley, Philippines
ABSTRACT
This experimental research design explored the potential of mixed ground seashells as an alternative admixture for concrete. The aim of this project was to create a concrete with calcium carbonate admixture from mixed common cockle shell (Cerastoderma edule) and marsh clam (Polymesoda expansa). The cockle shells and marsh clams were washed, boiled, oven-dried and homogenized with the use of mortar and pestle. Calcium carbonate was then produced and was added to the cement mixture. The mortar cubes with different treatments of the calcium carbonate admixture (0%, 1%, and 2%) were tested for its compressive strength using the universal multi-testing machine. Based on the test results, the mortar cube with 1% calcium carbonate admixture has the highest compressive strength of 1988.26 psi compared to the conventional mortar cube with a strength of 887.89 psi. Thus, calcium carbonate may be an alternative source of mineral admixture. The researcher encouraged others to conduct further tests about the environmental impact of the mineral admixture when used in the industry.

Keywords: Calcium carbonate, admixture, conventional mortar cube

INTRODUCTION
Formaldehyde is used as a chemical admixture in concrete this may improve the properties of concrete but it can create a leaching problem (Patel & Deo, 2016; Maganti and Raju, 2013). The said chemical is dangerous to humans for it can cause defects like bronchitis and at high levels, it may build up fluid in the lungs and can lead to death (Toxic Use Reduction Institute, 2014). A chemical which has related effects as of the formaldehyde is radon gas. A person exposed to radon gas is already exposed to constant radiation and that element settles in the lungs (Kohut, 2017).

The United States Environmental Protection Agency stated that about 13,000 non-smoking people die each year due to lung cancer that is related to radon exposure. According to the Philippine Cancer Society, radon exposure in the Philippines is the second leading cause of lung cancer. According to the International Atomic Energy Agency, our country got the largest per capita annual rate of radon inhalation at 48% last 2013. Thus, an alternative solution is needed as soon as possible to save the individuals and to save our planet.

Calcium carbonate is a mineral which is common in seashells and the main component of most admixtures. Mohamed, Yusup, and Maitra (2012) stated that seashells contain 95-99% of calcium carbonate prior to its weight. Further research with regards to the material, seashell wastes are highly available and are dumped with the absence of re-use value (Mo, Jumaat, Alengaram, Yuen, Goh & Lee, 2018). Thus, seashells like marsh clam (Polymesoda expansa) and common cockle shell (Cerastoderma edule) may be an alternative admixture in concrete for it has the same component as of the mineral admixture that is used in the present.

This project aimed to explore the compressive strength of the concretes with two different treatments of calcium carbonate admixture compare to the compressive strength of the conventional concrete.

MATERIALS AND METHODS
This study has three phases: Phase I – Preparation of Raw Materials, Phase II – Preparation of the Concretes, Phase III – Compressive and Flexural Strength Testing. All of the experimentations were done in Nabunturan National Comprehensive High School (NNCHS). And the testing was done in a laboratory in Panacan, Davao City.

Phase I – Preparation of Raw Materials
Seashells
The Common Cockle Shell (Cerastoderma edule) and Marsh Clam (Polymesoda expansa) were collected from the public market in Nabunturan. The cockle shells and marsh clams were washed separately in water to remove the dirt. After washing, the seashells were boiled separately to let the shells open. Then, the meat of it was removed leaving the shells.

Molds
The plywood and nails were collected in a hardware store in Nabunturan. The plywood was cut in 46cm x 15cm x 15cm for the body of the mold and the rectangular prism mold was divided into 3 sections by 2 plywood with a size of 15cm x 15cm x 15cm. Following the recommendation of Ammari, Ghoraishi, Abidou, and Al-Rousan (2017), the researcher made 3 molds with a standard interior size of 150mmx 150mm x 150mm.

Admixture
Adopting the procedure of Mohamed et al. (2012), the cockle shells and marsh clams were placed in the trays separately and underwent the process of oven-drying at 110 degrees Celsius for 2 hours. After 2 hours, both seashells were crushed using a mortar and pestle. After the crushing of seashells, the researcher used a strainer to separate the powder one from the particles that have not been fully crushed. Then, the powdered cockle shells and marsh clams were stored in the crucibles.

Phase II – Preparation of the Concretes
Concretes
Twenty kilograms of cement, 40kg of coarse aggregate and 80kg of fine aggregate were collected in the sand and gravel store in Nabunturan. Then, the researcher made 3 batches of cement and was mixed together with the coarse aggregate and fine aggregate with a ratio of 1:2:4 (Adewole, Ajagbe & Arasi, 2015). After mixing, the researcher added the calcium carbonate admixture from the common cockle shells and marsh clams that have been pulverized in a ratio of 1:1. The admixture were added in different treatments (0%, 1%, 2%) prior to its weight. Then, the researcher added 4 liters of water to the mixture and it was mixed until the workability is achieved. Then, the wet cement mixture with different treatments was placed in the molds and it will be left for 24 hours to dry the cement.
Water Curing
The concretes that have been dried underwent the water curing process in a container filled with tap water for 28 days. After 28 days, the concretes with three different treatments were removed from the water and were left to dry.

Phase III – Compressive Strength Testing
The concrete samples were delivered to the Universal Multi-Testing Solutions Inc. in Davao City to test its compressive strength. The results were released afterward.

Phase IV – Data Collection and Analysis
After the testing of the concrete samples with different treatments, the data were gathered. The researcher computed for its mean of each treatment and made a table to compare the difference of the 3 treatments.

Risk and Safety
Since we are dealing with cement, proper dress code when conducting the experiment is truly important. Wearing the proper dress code and the use of laboratory equipment while working inside the laboratory is a must. In case of difficulties, a help from a professional or an adult is highly recommended.

RESULTS
Table 1: The mean compressive strength (psi) of the mortar cubes in 1% and 2% calcium carbonate admixture
Treatment Compressive strength (psi) of the mortar cubes in three trials with the same curing age MEAN
28 days 28 days 28 days Control (0%) 920.59 791.51 951.59 887.89
CaCO3 (1%) 2303.24 1812.24 1849.30 1988.26
CaCO3 (2%) 566.14 711.08 1960.72 1079.32
Table 1 shows that the mortar cube with 1% treatment has the highest compressive strength at 1988.26 psi. While the mortar cube without treatment has the lowest compressive strength at 887.89 psi.
Table 2: The Percentage Difference of the Three Treatments
Treatments A (control) B (experimental) Difference (in %)
Control (0%) 887.89 887.89 0%
CaCO3 (1%) 887.89 1988.26 >100%
CaCO3 (2%) 887.89 1079.32 22%
Table 2 shows that the mortar cube with 1% treatment has the highest percentage difference at more than 100% compared to the mortar cube with 2% treatment at 22%. While the conventional mortar cube remained as it is.

Discussion
According to the study of Chuan (2014), there is a decrease in the concrete’s workability and compressive strength as the number of admixture increases. Furthermore, the concrete with 1% admixture is serviceable to have the advantage in boosting the strength. Still, if the percentage replacement of ground seashells exceed the maximum quantity will affect the density of the cement mixture resulting to a weak compressive strength in the cement. In the study of Muhit (2013), the admixture showed that 1% dosage obtained the highest compressive strength because overdosage of admixture may lead to bleeding and segregation of cement particles. Results were the same as the other research journals about admixtures. An article from the Industrial Minerals Association stated that “calcium carbonate is an inorganic compound that is commonly found in limestone, chalk, marble and it is produced by sedimenting shells of small fossilized snail, shellfish, and coral over millions of years.” The potential of limestone as a mineral admixture was studied by Li, Huo, and Du (2018) and came out effective which made to be the common admixture used in the industry. But quarrying limestone may result to the production of big holes in the local environment. Seashell waste is an economic and environmental hazard (Ramirez, Barker, Love, Milazzo ; McGuillcuddy, 2015). Seashells contain a high dosage of calcium carbonate at 95-99% compared to the limestone at a dosage of 40% (Mohamed et al., 2012; International Plant Nutrition Institute n.d.). Some commercial admixtures contain resin acids which have a toxic character that when its waste is exposed to the environment may be resulting to the presence of unwanted toxic effects (Togero, 2005; Mascarelli, 2012). With the use of mineral admixture can reduce the adverse effect of cement in the environment (Magudeaswaran, Selvam, ; Gold V., 2015). The calcium carbonate from common cockle shell (Cerastoderma edule) and marsh clam (Polymesoda expansa) showed accurate results which are capable of having a source of cement admixture based in its compressive strength and its availability.

Conclusion
The study evaluated the potential of the ground cockle shell and marsh clam in the durability of a concrete. Based on the gathered data and results, the mortar cube with the treatment of 1% calcium carbonate admixture obtained the highest compressive strength compared to the mortar cube with 2% treatment and the negative control. Therefore I conclude that the mixture of calcium carbonate from the cockle shell and marsh clam has the capability to be an alternative admixture.

Recommendation
The researcher would like to recommend to conduct tests with regards to the environmental impact of the mineral admixture when used in the industry.

Acknowledgement
I would like to express my deepest appreciation to the following people:
First, to God for the blessings and for the hope that you’ve given to me to strive and finish this project successfully. To Mrs. Leah R. Guirigay for giving me the chance to work on this project. For the patience, support and for your pieces of advice that motivated me. To Mrs. Candelaria Bolonos for providing the different apparatuses that I needed for my lab session. To my schoolmates, Brad Lee Tulio and Earl Roed Cabalan for lending me your manuscript as a basis and for helping me throughout this journey. To my parents, Mr. and Mrs. Martin F. Cruz Jr. for helping me on purchasing the different materials that I needed for my study and for believing me that I can do it. To my classmate, Yuanne Emmanuel Eling for helping me on mixing and making the mortar cubes. To my fellow individual, Renee Arianne Madrid for being there always to motivate me through tough times. And to the rest of my classmates and friends, for the never-ending love and support. To God be the glory!
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