Pengaruh penambahan boraks dan superplasticizer terhadap waktu pengerasan dari beton geopolimer berbasis abu terbang = Effect of borax and superplasticizer as admixture to the setting time of fly ash based geopolymer concrete

Christian, Andreas (2023) Pengaruh penambahan boraks dan superplasticizer terhadap waktu pengerasan dari beton geopolimer berbasis abu terbang = Effect of borax and superplasticizer as admixture to the setting time of fly ash based geopolymer concrete. Bachelor thesis, Universitas Pelita Harapan.

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Abstract

Beton geopolimer merupakan beton yang menggunakan semen geopolimer dan bukan semen Portland konvensional sebagai binder Waktu pengerasan beton geopolimer merupakan faktor yang sangat penting dalam perencanaan pembangunan menggunakan beton geopolimer. Beton geopolimer diinginkan mengeras setelah pengecoran pada bekisting telah dilaksanakan. Karena mekanisme pengerasan yang berbeda dengan semen Portland konvensional, retarder yang digunakan belum tentu efektif. Terdapat 2 bahan retarder yang diketahui bisa memperlambat waktu pengerasan, boraks dan superplasticizer berbasis polycarboxylate. Boraks dapat memperlambat waktu pengerasan melalui pengurangan aktifitas polimerisasi dengan menggantikan alumunium (Al) dalam reaksi polimerisasi dengan boron (B) sedangkan superplasticizer berbasis polycarboxylate menghambat reaksi polimerisasi melalui efek steric hindrance karena rantai senyawa yang kompleks pada superplasticizer berbasis polycarboxylate. Penelitian ini bertujuan untuk melihat pengaruh penambahan boraks dan superplasticizer berbasis polycarboxylate terhadap waktu pengerasan beton geopolimer berbasis abu terbang pada penambahan 1%, 2%, 3%, dan 4% dari massa abu terbang. Terlihat setelah pengujian bahwa boraks dapat memperlambat waktu pengerasan awal dari 33,57 menit pada kontrol sampai dengan 54,54 menit pada penmabhana 4% sedangkan pada superplasticizer berbasis polycarboxylate sampai 55 menit pada penambahan 4%. Sedangkan pada penambahan boraks terlihat pemerlambatan waktu pengerasan akhir dari 55 menit pada kontrol sampai dengan 100 menit pada penambhana 4% sedangkan pada superplasticizer berbasis polycarboxylate sampai dengan 90 menit pada penambahan 4%. Uji kuat tes tekan juga memperlihatkan bahwa penambahan boraks hanya mengurangi kuat tekan beton sampai 3,69% dari kuat tekan kontrol pada penambahan 3% sedangkan superplasticizer berbasis polycarboxylate dapat mengurangi kuat tekan beton secara signifikan sampai 14,03% pada penambahan 4%. Penurunan pada penambahan superplasticizer berbasis polycarboxylate bisa terjadi karena penyebaran yang terjadi karena efek steric hindrance dan ketidakstabilan superplasticizer berbasis polycarboxylate dalam lingkungan alkalin tinggi./Geopolymer concrete is a concrete that uses geopolymer cement rather than the conventional Portland cement Setting time is an important factor to consider when constructing a building using geopolymer concrete. The concrete has to set after the geopolymer concrete has been poured. Retarders that are effective on conventional concrete might not be effective on geopolymer concrete. There are 2 retarders that is known to be effective, borax and polycarboxylate-based superplasticizer. Borax slows the setting time by replacing alumunium (Al) with boron (B) so the polymerization activity is lowered while polycarboxylate-based superplasticizer hinders polymerization through steric hindrance effect from the complexity of the chemical chain. This research is done to see the effect of using borax and polycarboxylate-based superplasticizer as retarders on the setting time of fly ash based geopolymer concrete with addition of 1%, 2%, 3%, and 4% of fly ash mass. After testing, it is seen that addition of borax can retard the initial setting time from 33,57 minutes up to 54,54 minutes on 4% addition while the addition of polycarboxylate-based superplasticizer retards the initial setting time up to 55 minutes on 4% addition. Meanwhile addition on borax retards the final setting time from 55 minutes up to 100 minutes on 4% addition while the addition of polycarboxylate-based superplasticizer retards the final setting time up to 90 minutes on 4% addition. Compression test also shows that addition of borax only reduce compression strength by 3,69% with the addition of 3% while the addition of polycarboxylate-based superplasticizer can affect the compression strength significantly, decreasing as much as 14,03% with the addition of 4%. Decrease on addition of polycarboxylate-based superplasticizer can happen because of dispersion caused by the steric hindrance effect and polycarboxylate-based superplasticizer might not be stable on high alkaline environment.

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