Beton Non Pasir Geopolimer dengan Fly Ash dan Ground Granulated Blast Furnace Slag
Angeline Yuhasnita, Ir. Suprapto Siswosukarto, Ph.D., IPM.; Prof. Ir. Iman Satyarno, M.E., Ph.D.
2024 | Tesis | S2 Teknik Sipil
Beton non pasir adalah beton
porous yang memiliki sifat khusus yaitu bersifat isolasi panas dan mudah untuk
meloloskan air yang mempunyai pori-pori dalam beton tersebut mencapai volume
rongga sekitar 20-25%. Pada
pembuatan beton non pasir, bahan pengikat yang umumnya digunakan adalah semen Portland.
Namun, penggunaan semen Portland memiliki dampak lingkungan yang
signifikan karena tingginya emisi karbon dioksida selama proses pembuatannya.
Perlunya penelitian lebih lanjut mengenai bahan pengikat alternatif yang lebih
ramah lingkungan, seperti geopolimer. Bahan pengikat geopolimer sering kali
menunjukkan waktu pengerasan yang cepat, sehingga memerlukan penggunaan
retarder seperti boraks. Tujuan penelitian ini untuk mengetahui campuran
pasta optimal untuk beton non pasir geopolimer dengan menguji pengaruh variasi
rasio alkali aktivator terhadap binder (A) 0,25; 0,30; dan 0,35, dengan
penambahan boraks (C) 3?n 5% terhadap flow dan waktu
pengerasan. Selain itu, penelitian ini juga bertujuan untuk mengetahui mengetahui
kemampuan sifat mekanis beton non pasir geopolimer seperti, berat jenis, volume
rongga, modulus elastisitas, kuat tekan, dan kuat lentur.
Hasil
penelitian menunjukkan bahwa pengurangan rasio (A) dari 0,35
menjadi 0,25 dapat mengurangi flow pasta. Meningkatkan kandungan boraks
(C) dari 3% menjadi 5?pat memperpanjang waktu pengerasan dan
menurunkan flow (Dari 20,25 menjadi 19,25 cm pada rasio (A) 0,30).
Diketahui hasil campuran pasta yang paling optimal untuk pembuatan beton non
pasir geopolimer adalah sampel B5050M10R2A030C5. Hasil uji sifat mekanis diketahui
semakin rendah rasio semen terhadap agregat hasil berat jenis, kuat tekan,
modulus elastisitas, dan kuat lentur semakin tinggi. Semakin banyak pasta
membuat beton semakin padat, rongga beton lebih banyak diisi oleh pasta. Pada
sampel B5050M10R2A030C5P14, Berat jenis yang diperoleh mencapai 2031,90 kg/m3 dengan volume rongga udara 25,13%.
Hasil kuat tekan tertinggi mencapai 28,55 MPa dan modulus elastisitas
sebesar 6060,67 MPa. Hasil pengujian kuat
lentur tertinggi pada rasio volume (P) 1:4 sebesar 3,70 MPa termasuk
klasifikasi jalan lokal menurut Syarat Spesifikasi Khusus Interim 2023.
No-fines
concrete is porous concrete with special properties that are
heat-insulating and easy to pass water with pores in the concrete, reaching a
cavity volume of about 20-25%. In the manufacture of no-fines concrete, the
commonly used binder is Portland cement. However, the use of Portland cement
has a significant environmental impact due to high carbon dioxide emissions
during manufacturing. Further research is needed on
alternative binders that are more environmentally friendly, such as
geopolymers. Geopolymer binders often exhibit rapid hardening times,
requiring the use of retarders such as borax. The purpose of this
study was to determine the optimum paste mix for geopolymer no-fines concrete
by examining the effect of varying the ratio of alkali activator to binder (A)
0.25, 0.30, and 0.35, with the addition of borax (C) 3% and 5% on flow and
hardening time. In addition, this study also aims to determine the mechanical
properties of geopolymer no-fines concrete, such as unit weight, void volume,
modulus of elasticity, compressive strength, and flexural strength.
This
research uses two types of geopolymer materials, namely fly ash and ground
granulated blast furnace slag (GGBFS) as a substitute for cement with a ratio (B) of
50:50. In the formulation of geopolymer no-fines concrete, the absolute volume
of geopolymer paste is equivalent to the volume of cement paste and water with
a water-cement ratio (w/c) of 0.40, with a ratio of cement volume to aggregate
volume of 1:4, 1:6, and 1:8. After finding the most optimal geopolymer paste
mixture, the alkali activator/binder ratio (A) was set at 0.30, with the
addition of borax (C) at 5%. Concrete was made using gravel aggregate from
Merapi, Yogyakarta, through ambient curing. The cylindrical specimens used were
10 x 20 cm, and the flexural strength test used 10 x 10 x 50 cm beams. No-fines
concrete mix is made conventionally using a mixer machine.
The
results showed that reducing the ratio (A) from 0.35 to 0.25 can reduce paste
flow. Increasing the borax content (C) from 3% to 5?n prolong the hardening
time and reduce the flow (from 20.25 to 19.25 cm at ratio (A) 0.30). It is
known that the most optimal paste mixture for the manufacture of geopolymer no-fines
concrete is sample B5050M10R2A030C5. The results of the mechanical properties
test showed that the lower the ratio of cement to aggregate, the higher the unit
weight, compressive strength, modulus of elasticity, and flexural
strength. The more paste makes the concrete denser, the more concrete
voids are filled by the paste. In sample B5050M10R2A030C5P14, the specific
gravity obtained reached 2031.90 kg/m3 with an air void volume of 25.13%.
The highest compressive strength results reached 28.55 MPa
and elastic modulus of 6060.67 MPa. The highest flexural strength
test results at volume ratio (P) of 1:4 of 3.70 MPa included the classification
of local roads according to the Interim Special Specification Requirements 2023.
Kata Kunci : Beton non pasir; Geopolimer; Fly Ash; GGBFS; Boraks