ABSTRAK
Struktur beton diharapkan memiliki keawetan dan ketahanan yang baik selama waktu yang direncanakan. Kurangnya ketahanan disebabkan oleh banyak faktor, salah satunya berupa serangan zat kimia seperti asam sulfat. Serangan asam sulfat biasanya terjadi pada bangunan laut yang airnya mengandung klorida dan sulfat seperti pada pelabuhan, bangunan tepi pantai, pengeboran lepas, bangunan pengolahan limbah, dan industri air tanah. Asam sulfat merupakan zat kimia yang memiliki agresifitas yang cukup tinggi yang dapat merubah struktur pada beton. Bahan tambah fly ash dapat mengurangi dampak reaksi pasta semen pada beton dengan asam sulfat, meningkatkan kepadatan, dan workability. Penggunaan self compacting concrete juga akan menghasilkan beton dengan workability yang baik dan mengurangi penggunaan air.
Kadar penggunaan fly ash pada beton hingga lebih dari 50% disebut dengan high volume fly ash – self compacting concrete. Kadar fly ash sebagai pengganti sebagian semen dalam beton yang cukup tinggi mampu memperkecil ruang antar agregat sehingga mengurangi reaksi beton dengan asam sulfat yang akan melarutkannya. Meningkatnya durabilitas beton sehubungan dengan penggunaan fly ash dapat ditunjukkan melalui uji resistensi beton dalam melawan serangan asam sulfat. Penelitian ini menggunakan metode eksperimen yang dilakukan di Laboratorium Bahan dan Struktur Jurusan Teknik Sipil Universitas Sebelas Maret. Untuk observasi pengujian perubahan struktur makro dan uji kuat tekan beton digunakan benda uji silinder diameter 15 cm dan tinggi 30 cm sebanyak 144 buah.
Untuk observasi penelitian struktur mikro yang dilakukan di Laboratorium MIPA Universitas Malang dengan menggunakan Scanning Electron Microscope-Energy Dispersive X Ray (SEM-EDX), digunakan benda uji slab slab persegi dengan ukuran 5 mm x 5 mm x 5 mm sebanyak 3 buah. Variasi penambahan kadar fly ash yang digunakan adalah 0% (sebagai pembanding), 50%, 55%, 60%, 65%, dan 70% total berat binder. Benda uji akan direndam dalam air dan asam sulfat (konsentrasi 5%). Pengambilan data benda uji penelitian struktur makro dan uji kuat tekan beton dilakukan saat beton umur 7 hari, 28 hari, 56 hari, dan 90 hari. Pengujian benda uji penelitian struktur mikro dilakukan saat beton umur 90 hari yang direndam air dan direndam asam sulfat. Hasil penelitian pada beton HVFA-SCC menunjukkan penggunaan fly ash yang semakin tinggi dalam campuran beton akan mengurangi dampak buruk akibat reaksi dengan asam sulfat. Beton HVFA-SCC kadar fly ash 65% memiliki perubahan struktur makro dan mikro yang baik, dan memiliki nilai kuat tekan yang optimum pada umur beton 90 hari dibandingkan variasi kadar fly ash lain setelah terpapar asam sulfat
Kata kunci : fly ash, HVFA-SCC, Scanning Electron Microscope.
ABSTRACT
Concrete structures are expected to have good durability and endurance during the planned time. Lack of robustness caused by a relatively stout, among other factors such as chemical attacks such as sulfuric acid. Sulfuric acid attacks usually occur in buildings sea water contains chloride and sulfate as the harbor, waterfront buildings, offshore drilling, building sewage treatment, industrial water and soil. Sulfuric acid is a chemical substance that has a high enough aggressiveness that can change the structure in concrete. The added material will reduce the impact of fly ash concrete reaction with sulfuric acid, increasing the density, and workability. The use of self-compacting concrete also will produce concrete with good workability and reduce water use. Levels of use of fly ash in concrete by more than 50% of so-called high-volume fly ash - self compacting concrete. The levels of fly ash as a partial replacement of cement in concrete high enough able to reduce the space between aggregates, thereby reducing the concrete reaction with sulfuric acid that would dissolve it. Increased durability of concrete in connection with the use of fly ash can be demonstrated by testing the concrete resistance against sulfuric acid attack.
This study used an experimental method which is carried out in the Laboratory of Materials and Structures Department of Civil Engineering University of March. For observation and testing of changes in the macro-structure of concrete compressive strength test specimen used cylinder diameter of 15 cm and 30 cm height of 144 pieces.
For observation of microstructure research conducted at the Laboratory of Mathematics, University of Malang by using Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX), use a square slab slab specimen with a size of 5 mm x 5 mm x 5 mm 3 pieces. Variations addition of fly ash levels used were 0% (for comparison), 50%, 55%, 60%, 65%, and 70% of the total weight of the binder. Test specimen shall be immersed in water and sulfuric acid (5% concentration). Data retrieval research specimen macro structure and concrete compressive strength test performed when the concrete life of 7 days, 28 days, 56 days, and 90 days. The test specimen microstructure research done while the concrete life of 90 days soaked in water and soaked sulfuric acid. Results of research on concrete HVFA-SCC showed that the use of fly ash in concrete mix the higher will reduce the negative effect caused by the reaction with sulfuric acid. HVFA-SCC concrete fly ash content of 65% had changes in the structure of both macro and micro, and have the optimum value of compressive strength of concrete at the age of 90 days compared to the other variations of fly ash levels after exposure to sulfuric acid.
Keywords: fly ash, HVFA-SCC, Scanning Electron Microscope.