Analysis Of Use Sea Sand as A Fine Aggregate Replacement To Strong Press Concrete

Concrete is a composite building material made from a combination of aggregate and cement. The limitation of concrete material, in this case, is a fine aggregate (river sand). The utilization of sea sand as an alternative to fine aggregate in the manufacture of concrete is motivated by the availability of sea sand in nature in very large quantities. This study aims to determine the comparison and how much the compressive strength of concrete produced when using sea sand. The test was carried out when the specimens were 7, 14, and 28 days old with the specimens used in this study were concrete cylinders with a diameter of 15 cm and a height of 30 cm. The results showed that the use of sea sand as a substitute for fine aggregate showed an average compressive strength in 7 days of 18.86 MPa, an average compressive strength of 14 days of 25.52 MPa, an average compressive strength of 28 days of 29.00 MPa. Then for the average compressive strength value of the use of river sand in 7 days is 17.17 MPa, the average compressive strength of 14 days is 23.24 MPa, the average compressive strength of 28 days is 26.41 MPa.


Introduction
Sea sand generally has the characteristics of fine and round granules, which are uniform and contain salts that are not beneficial for concrete, so many are advised not to be used in making concrete. Smooth and round granules and uniform gradation, can reduce adhesion and affect the strength and durability of concrete. However, people who live on the coast still use sea sand as one of the fine aggregates on concrete for reasons easy to obtain [1] [2]. Sea sand is a material used as a substitute for ordinary sand for a mixture of cement, fine or coarse aggregate and water, with the mixture when poured into a mold and then allowed to stand hard. By using sea sand, the most important thing is the compressive strength of the concrete [3]. Factors that influence the compressive strength of concrete consist of the quality of the material, cement water, aggregates, how to process it such as mixing, compaction, and age of the test. Concrete is a result of mixing cement, water, fine aggregate, and coarse aggregate. Aggregate is the most important concrete component, which functions as a filler in a concrete mixture [4] [5]. Looking at several kinds of natural materials that can be used for making concrete, substituting or mixing concrete making such as sea sand are often found in various regions, especially Indonesia. And to utilize sea sand which so far has not been much used so as a researcher wants to test how strong the compressive strength of concrete using sea sand. This research is to provide information about the use of sea sand as a substitute for river sand and also to predict the strength of concrete, as well as new breakthroughs in the world of civil engineering that are still needed [6].

Concrete
Concrete (concrete) is the main construction material most widely used besides steel. Concrete is obtained by mixing cement, fine and coarse aggregates, and water by a certain ratio. If the mixture is mixed and poured into a mold and then left, a hardening process will occur. The hardening process occurs because of the continuous chemical reaction between water and cement [7] [8].

Sea Sand Instead of Fine Aggregate
Sea sand is sand taken from the shores of the beach, the shape of the grains are smooth and round due to friction with each other [9]. This sand is bad because it contains a lot of salt. This salt absorbs water content from the air and causes the sand to always be rather wet and cause volume expansion when used on buildings. However, sea sand can be used in concrete mixtures with special treatment, that is by washing it so that the salt content is reduced or lost. Quality characteristics of fine aggregate used as concrete structural components play an important role in determining the quality characteristics of concrete structures produced because fine aggregates fill most of the concrete volume. Sea sand as one type of fine aggregate material has availability in large quantities [10].

Concrete Compressive Strength
Concrete compressive strength is the magnitude of the broad unity load that causes the concrete test specimen to disintegrate when it is burdened with a certain compressive force, which is produced by a press machine [11]. Based on the compressive strength of concrete can be divided into several types which can be seen in

Methods
The method used in this study is experimental, an experiment that aims to investigate the compressive strength of concrete by using sea sand instead of fine aggregate. The specimens made in this experiment were concrete cylinders with a diameter of 15 cm and a height of 30 cm. Compressive strength testing is performed after the concrete is 7, 21, and 28 days old.

SSD Fine Aggregate Specific Gravity
In testing this fine aggregate specific gravity obtained data as follows:

Compressive Strength Test Results
In compressive strength testing at the age of 3-day test specimens obtained the following data:

Concrete Age Conversion Data Results
The results of compressive strength testing on the age of the test object 3 days later carried out the conversion of the concrete age to get the compressive strength data based on the variation in age to be achieved. Conversion data sought is in the form of 7-day, 14-day, and 28-day test specimens. From the conversion results we get the following data: The test data shows that the strength of concrete made using sea sand has an average compressive strength that is relatively higher than that of concrete made using river sand. Based on the compressive strength of concrete can be divided into several types:

Fig 2. Concrete Quality Check
From the graph above, the quality of concrete is considered to meet the requirements (quality is achieved). The value of the compressive strength test results is based on variations in the age of 7 days, 14 days, and 28 days consisting of 3 specimens each, not less than the compressive strength of concrete required, namely fc '15 Mpa.

Conclusion
Based on the results of research and discussion on the use of sea sand as a substitute for fine aggregate against concrete compressive strength as well as a comparison of concrete compressive strength using sea sand and river sand can be drawn several conclusions as follows: 1. Sea sand can be used as a smooth aggregate substitute because the sea sand has a smooth and rounded texture which is great for concrete constituent materials. For a strong value of its own pace is greater than the use of river sand with a mixture of the same concrete quality. 2. The data value of the test results showed that the strength of concrete made by using sea sand has strong press averages which are relatively higher than in concrete made by using river sand. 3. The ratio of strong press concrete by using river sand at 7 days is 17.17 Mpa, 14 days at 23.24 Mpa, and age 28 for 26.41 MPa.
While the strong value of concrete press by using sea sand at 7 days of 18.86 Mpa, 14 day age of 25.52 Mpa, and 28 day age of 29.00 MPa.