Perancangan high early strength foamed concrete untuk beton pracetak

Tjahjono, Ricky (2020) Perancangan high early strength foamed concrete untuk beton pracetak. Bachelor thesis, Universitas Pelita Harapan.

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Abstract

Beton pracetak dalam proyek konstruksi masa kini sering kali digunakan. Dengan kuantitas permintaan yang banyak, maka diperlukan percetakan dalam waktu yang singkat. Dengan demikian, kekuatan tekan awal yang tinggi pada beton diperlukan agar beton pracetak mampu menahan beban sendiri pada saat diangkat dari percetakan ke lokasi penyimpanan. Tak hanya itu, elemen struktural yang digunakan harus lebih ringan guna cukup menggunakan alat angkut sederhana dan jumlah pekerja yang sedikit. Foamed concrete merupakan salah satu alternatif yang dapat digunakan. Penelitian ini bertujuan untuk mendapatkan foamed concrete dengan kuat tekan awal 14 MPa pada usia 3 hari, kuat tekan 20 MPa pada usia 28 hari, dan berat jenis kurang dari 1750 kg/m3. Pengecoran foamed concrete yang paling efektif adalah dengan menggunakan metode pengecoran kedua, yakni pengadukan beton dan foam agent yang selesai pada waktu yang sama untuk menghindari adanya gelembung foam yang pecah akibat penundaan waktu penuangan pada beton segar. Kemudian, metode curing paling efektif dengan menggunakan perendaman penuh pada foamed concrete mampu menghasilkan kuat tekan usia 28 hari 121,6% lebih besar dari pada metode curing perendaman singkat. Selanjutnya dilakukan penambahan accelerator dengan persentase substitusi air 5%; 7,5%; dan 10% pada foamed concrete guna meningkatkan kekuatan tekan awal beton. Hasil yang didapatkan pada campuran beton superplasticizer dengan penggunaan accelerator meningkatkan kuat tekan awal menjadi 17,5 MPa; 17,82 MPa; dan 21,64 MPa. Penggunaan accelerator dengan kadar diatas 5% pada campuran beton superplasticizer sudah cukup efektif untuk mendapatkan kuat tekan diatas 14 Mpa pada usia beton 3 hari. Adapun penggunaan material limbah biji plastik LDPE dengan persentase substitusi pasir 5%; 7,5%; dan 10% yang dilakukan untuk mengurangi penggunaan pasir sebagai material yang sumbernya terbatas. Penggunaan biji plastik LDPE pada campuran beton dengan aditif superplasticizer menghasilkan penurunan berat jenis menjadi 1466 kg/m3; 1416 kg/m3; dan 1397 kg/m3 dari 1582 kg/m3. Selain itu, terdapat pengujian Ultrasonic Pulse Velocity (UPV) yang dilakukan untuk mengetahui korelasi antara berat jenis dan kuat tekan terhadap nilai UPV. Hasil tes UPV mendapatkan adanya korelasi kuat pada foamed concrete dengan bahan aditif superplasticizer, tanpa biji plastik dan accelerator dengan nilai R2 usia 28 hari diatas 0,9. / These days, precast concrete is mostly used in the construction of houses. With the enormous amount of demands, the making of the concrete with a high early compressive strength in a short period of time is necessary in order hold its own weight while being delivered to location as ordered. Moreover, a lighter structural elements must also be used in order to ease the carriage of the structural elements so a simple conveyance and less workers will be sufficient for the construction. Foamed concrete is one of the alternatives that can be used in this construction. This research aims to obtain a foamed concrete with an early compressive strength of 14 MPa in its 3rd day, compressive strength of 20 MPa in its 28th day, and also acquire density less than 1750 kg/m3. The most effective way on casting the foamed concrete was the second method, by mixing the concrete and foam agent at the same time to prevent the rupture of the foam agent due to the delay time of pouring into the fresh concrete mixture. Furthermore, the most effective curing method was full immersion of the foamed concrete, that results in the 121,6% stronger compressive strength on its 28th day than the foamed concrete with short immersion curing method. Hereafter, the accelerator were used to substitute 5%; 7,5%; and 10% of the water volume, to increase foamed concrete's early strength. For the superplasticizer concrete mixtures with the use of accelerator, the early compressive strength were increased to 17,5 MPa; 17,82 MPa; dan 21,64 MPa. The use of 5% or more accelerator in the concrete mixture was effective enough to obtain compressive strength of 14 MPa in its 3rd day. With addition, LDPE plastic seeds were used to substitute 5%; 7,5%; and 10% of the sand volume, to reduce foamed concrete's weight. The use of LDPE plastic seeds in concrete mixture with additive superplasticizer reduces 1466 kg/m3; 1416 kg/m3; dan 1397 kg/m3 of the concrete’s the density from 1582 kg/m3. Moreover, an Ultrasonic Pulse Velocity (UPV) Test is done to discover a correlation between density and compressive strength towards the UPV value. UPV Test results in strong correlation between foamed concrete and additive superplasticizer, without plastic seeds and accelerator with R2 value more than 0,9 on its 28th day.

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