Pengaruh Suhu Perawatan Terhadap Penetrasi Ion Klorida Pada Beton Geopolimer

Pada bangunan lepas pantai air laut memiliki kandungan garam yang tinggi yang dapat menggerogoti kekuatan dan keawetan beton. Hal ini disebabkan klorida (Cl) yang terdapat pada air laut yang merupakan garam yang bersifat agresif terhadap bahan lain, termasuk beton. Reaksi antara beton dan dan air laut yang agresif, terpenetrasi ke dalam beton dengan senyawa-senyawa di dalam beton mengakibatkan beton kehilangan sebagian kekuatan dan mempercepat proses pelapukan. Kadar fly ash yang tinggi pada beton mengakibatkan penurunan tingkat penetrasi klorida. Berbagai metode perawatan beton geopolimer yaitu dengan cara direndam dalam air, dimasukan ke dalam uap (suhu 60ºC selama 24 jam), tanpa perawatan, dan dimasukan ke dalam oven (suhu 250 ºC selama 24 jam) kuat tekan paling tinggi dicapai pada beton yang dirawat dalam uap. Bahan dasar beton geopolimer yang digunakan adalah fly ash yang diaktifkan dengan natrium hidroksida (NaOH) 8 M dan sodium silikat (Na2SiO3) . Perbandingan massa NaOH : Na2SiO3 yaitu 1:1,5 ; 1:2 ; 1:2,5. Benda uji berupa silinder dengan diameter 10 cm tinggi 20 cm. Sedangkan untuk pengukuran laju korosi digunakan balok berukuran 10x10x15 cm yang diberi tulangan polos diameter 16 mm. Benda uji dirawat pada suhu ruangan dan disteam pada suhu 40ºC, 60ºC, 80ºC selama 24 jam .Kemudian direndam di air tawar sampai umur 28 hari, selajutnya direndam dilarutan air garam. Pengujian beton geopolimer ini meliputi uji kuat tekan, tes porositas dan penetrasi ion klorida pada umur 28 hari, 60 hari (30 hari perendaman air garam), 90 hari (60 hari perendaman air garam), 120 hari (90 hari perendaman air garam). Laju korosi diukur dengan Half Cell Potential pada benda uji balok. Dari penelitian ini didapatkan, suhu perawatan sangat mempengaruhi beton geopolimer. Semakin tinggi suhu perawatan dari suhu normal ke suhu 80ºC maka akan meningkatkan nilai penetrasi ion klorida, tetapi kuat tekan ikut meningkat . Kuat tekan paling tinggi berada pada variasi 2,5-80º yaitu sebesar 80,47 MPa pada umur 90 hari ================================================================================================================== The offshore building in sea water has a high salt content which can damage the strength and durability of concrete. It is caused by chloride (Cl) contained in sea water. Salt in sea water has an aggressive behavior for materials, especially on concrete. The reaction between the concrete and sea water, which was penetrated into the concrete with some compounds of it will lose some strength and accelerate the weathering process of concrete. High content of fly ash in concrete results the decreased of chloride penetration level. There are some curing methods of geopolymer concrete such as soak geopolymer concrete in water, steam it in temperature 60°C for 24 hours, without treatment,and put it into the oven (temperature of 250 ° C for 24 hr). The highest compressive strength is obtained by steam curing. Fly ash as based material for geopolymer concrete was used in this study. Fly ash was mixed with sodium hydroxide (NaOH) 8 M and sodium silicate (Na2SiO3) as the alkali. Mass ratio of NaOH: Na2SiO3 was kept at 1: 1,5; 1: 2; 1: 2,5. The size of cylindrical specimens were prepared with a diameter of 100 mm and 200 mm high. The measurement of corrosion rate is using beam with each size of specimen was 10x10x15 cm. Steel bar with a diameter of 16 mm was embedded for each beam spesimens. The specimens were cured at room temperature and steamed at 40ºC, 60ºC, 80ºC for 24 hours. After that, allspecimens were soaked in fresh water for 28 days. And then, the immersion was continued in two conditions, which tap water and salt water 3.5%. There are some testing of the sample, such as compressive strength test, porosity test, chloride penetration test at 0, 30, 60, and 90 days of immersion. The corrosion rate was measured on beam specimens by using Half Cell Potential test. From this study, temperature of curing was greatly affected geopolymer concrete. The higher of curing temperature (normal temperature to 80ºC) increased the chloride penetration and the compressive strength. The highest compressive strength was 80.47 MPa at 2,5-80ºC for 90 days