Kajian Sifat Mekanik Beton Cor di Dalam Air Gambut (Underwater Concrete)

Pengecoran di dalam air membutuhkan biaya yang lebih mahal dalam pengerjaannya, karena dibutuhkan proses dewatering ataupun semen khusus. Penelitian ini menggunakan Natrium Tripoliphosphate (Na5P3O10) sebagai alternatif pemecahan masalah. Natrium Tripoliphosphate berfungsi sebagai lapisan kedap air dalam campuran beton sehingga campuran beton tidak tercampur dengan air. Dalam penelitian ini, ada dua jenis benda uji yang digunakan, yaitu benda uji Underwater Concrete dan benda uji non Underwater Concrete. Nilai kuat tekan dan kuat tarik belah beton diperoleh berdasarkan pengujian laboratorium dengan beton silinder diameter 10 cm x 20 cm dengan perawatan di dalam air gambut. Hasil pengujian kuat tekan Underwater Concrete selama 14 hari yaitu 12.94 MPa, 28 hari 13.31 MPa, dan 56 hari 14.53 Mpa, sedangkan benda uji non underwater concrete selama 14 hari 12.94 MPa, 28 hari 13.39 dan 28 hari 15.27 MPa. Hasil pengujian kuat tarik Underwater Concrete 28 hari diperoleh sebesar 1.91 MPa, dan 56 hari 1.99 MPa serta pengujian Non Underwater Concrete 28 hari diperoleh sebesar 1.79 MPa dan 56 hari 2.06 MPa. Berdasarkan dua hasil pengujian, tidak ada perbedaan signifikan dalam nilai yang diperoleh. Hal tersebut menunjukkan penambahan Natrium Tripoliphosphate dapat berkerja dengan baik di dalam air gambut.

Behavior of Alkali-Activated Fly Ash through Underwater Placement

Underwater concrete is a cohesive self-consolidated concrete used for concreting underwater structures such as bridge piers. Conventional concrete used anti-washout admixture (AWA) to form a high-viscosity underwater concrete to minimise the dispersion of concrete material into the surrounding water. The reduction of quality for conventional concrete is mainly due to the washing out of cement and fine particles upon casting in the water. This research focused on the detailed investigations into the setting time, washout effect, compressive strength, and chemical composition analysis of alkali-activated fly ash (AAFA) paste through underwater placement in seawater and freshwater. Class C fly ash as source materials, sodium silicate, and sodium hydroxide solution as alkaline activator were used for this study. Specimens produced through underwater placement in seawater showed impressive performance with strength 71.10 MPa on 28 days. According to the Standard of the Japan Society of Civil Engineers (JSCE), the strength of specimens for underwater placement must not be lower than 80% of the specimen’s strength prepared in dry conditions. As result, the AAFA specimens only showed 12.11% reduction in strength compared to the specimen prepared in dry conditions, thus proving that AAFA paste has high potential to be applied in seawater and freshwater applications.