Judul: THE EFFECTIVENESS OF BACILLUS SUBTILIS BACTERIA AND CALCIUM LACTATE FOR CONCRETE CRACKS REPAIR
Abstrak: Beton bertulang merupakan bahan konstruksi yang paling banyak digunakan. Namun karena kuat tariknya yang lemah dan sifatnya yang getas maka beton sering retak. Retak dapat memudahkan masuknya zat agresif ke dalam baja dan menyebabkan korosi pada tulangan. Retak halus atau micro cracks akan mengalami peningkatan ukuran jika dibiarkan sehingga upaya pemeliharaan dan inspeksi infrastruktur menjadi hal yang penting. Pemanfaatan bakteri menjadi hal yang menarik untuk diterapkan sebagai bahan penyembuh untuk perbaikan retak beton. Bacillus subtilis digunakan sebagai agen penyembuhan dalam penelitian ini, selain itu kalsium laktat juga ditambahkan sebagai nutrien bagi bakteri. Tujuan penelitian ini yaitu untuk mengidentifikasi jumlah kalsium karbonat (CaCO3) yang terbentuk, mengevaluasi perbaikan keretakan beton, serta menganalisis pengaruh penambahan bakteri dan kalsium laktat (CaL) terhadap sifat mekanis beton seperti kuat tekan, permeabilitas, dan daya serap. Penelitian dilakukan pada bulan Oktober 2021-Mei 2022. Beberapa alat utama yang digunakan yaitu universal testing machine (UTM), alat uji permeabilitas, inkubator, autoklaf, kamera HP Samsung galaxy note 10+, mikroskop digital, dan mikroskop elektron. Bahan utama yang digunakan yaitu semen portland composite cement (PCC), agregat kasar berupa kerikil lebak wangi, agregat halus berupa pasir cimangkok, kalsium laktat teknis, strain bakteri Bacillus subtilis, nutrient agar, dan nutrient broth. Prosedur penelitian dimulai dengan pengujian propertis agregat, penghitungan mix design, kuktur mikroorganisme, pengujian test-tube, pembuatan sampel beton, curing beton, pengujian image processing, pengujian sifat mekanis seperti kuat tekan, permeabilitas, dan daya serap beton, serta pengujian dengan menggunakan scanning electron microscope (SEM) dan mikroskop digital dengan seri VHX 7000 untuk mengkonfirmasi morfologi atau topografi beton. Larutan dengan konsentrasi CaL 65,4 g/L dan penambahan 2 mL bakteri menghasilkan massa kalsit tertinggi. Komposisi tersebut diaplikasikan pada campuran beton secara langsung. Perbaikan retakan diamati secara visual pada umur 28 hari dengan retakan yang terlihat tertutup. Hasil pengolahan dengan software imageJ pada beton bakteri + CaL menghasilkan rasio perbaikan retak mencapai 95,94%. Penambahan bakteri dan CaL meningkatkan kuat tekan pada beton retak sebesar 13,16%. Efek positif juga terjadi pada sifat permeabilitas maupun penyerapan, permeabilitas berkurang hingga 53,12% dan penyerapan berkurang sebesar 22,20%. Efek positif terhadap sifat mekanis ini disebabkan oleh adanya endapan CaCO3 yang terbentuk akibat metabolisme bakteri sehingga pori pori lebih rapat dan retak permukaan tertutup. Hal tersebut dikonfirmasi dengan pengujian SEM yang menunjukkan hasil bahwa di dalam matriks beton terdapat kristal kalsit. Hasil pengamatan dengan mikroskop digital versi VHX-7000 menunjukkan kristal-kristal yang terdapat pada area retakan beton., Reinforced concrete is the most widely used construction material, but because of its weak tensile strength and brittle nature, the concrete often cracks. the racks can facilitate the entry of aggressive substances into the steel and cause corrosion of the reinforcement thereby reducing the durability of the concrete and shortening the concrete age. Fine cracks or micro cracks will increase in size if left unchecked, so maintenance and inspection of infrastructure is important. The use of bacteria is an interesting thing to be applied as a healing agent for repairing concrete cracks. In this study, Bacillus subtilis was used as a healing agent and calcium lactate was also added as a nutrient for bacteria. The purpose of this study was to identify the amount
Keyword: Bacillus subtilis, CaCO3, kalsium laktat, kalsit, retak beton

Judul: Utilization of Soybeans as Bio-Catalyst in Calcite Precipitation Method for Repairing Cracks in Concrete
Abstrak: Beton merupakan material yang memiliki kuat tekan tinggi tetapi memiliki kuat tarik yang lebih rendah sehingga beton seringkali retak. Metode perbaikan mulai beralih dari cara konvensional kepada konsep self-healing concrete yang melibatkan pengendapan CaCO3. Pengendapan CaCO3 dapat dilakukan dengan metode enzymatically-induce carbonate precipitation (EICP) melalui kombinasi urease, urea, dan CaCl2 menjadi larutan. Penelitian ini menggunakan ekstrak kedelai sebagai bahan pengganti enzim urease murni. Variasi kadar konsentrasi tepung kedelai yang digunakan sebagai larutan injeksi yaitu variasi kadar tepung kedelai 15 g/L karena menghasilkan massa kalsit optimum sebesar 2.62 gram. Terjadi peningkatan kuat tekan pada beton retak yang diinjeksi (BI) terhadap beton retak (BR). Selain itu, terjadi penurunan nilai permeabilitas dan porositas seiring dengan jumlah injeksi yang dilakukan. Peningkatan kuat tekan, penurunan permeabilitas, dan penurunan porositas pada beton ini disebabkan karena adanya deposisi CaCO3 pada beton yang mampu menutupi pori-pori serta celah keretakan pada beton, Concrete is a material that has a high compressive strength but has a lower tensile strength so that the concrete often cracks. The repair method began to shift from the conventional method to the concept of self-healing concrete which involves the deposition of CaCO3. Precipitation of CaCO3 can be done by enzymatically-induced carbonate precipitation (EICP) method through a combination of urease, urea, and CaCl2 into a solution. This research used soybean extract as a substitute for pure urease enzyme. Variations in the concentration of soybean flour used as injection solution were variations in the content of soybean flour 15 g/L because it produced an optimum calcite mass of 2.62 grams. There was an increase in the compressive strength of injected cracked concrete (BI) against cracked concrete (BR). In addition, there was a decrease in the value of permeability and porosity along with the number of injections carried out. The increase in compressive strength, decrease in permeability, and decrease in porosity in concrete is due to CaCO3 deposition in the concrete which is able to cover the pores and cracks in the concrete
Keyword: Beton, CaCO3, kuat tekan, permeabilitas, porositas, Concrete, compressive strength, permeability, porosity

Judul: Thermal Characteristics and Dynamics of Tropical Cyclone over Western North Pacific Ocean: A Case Study of Typhoon Songda (Chedeng) 2011
Abstrak: The frequent occasion of Tropical Cyclone (TC) over Western North Pacific (WNP) Ocean lies from 10˚N to 26˚N and 121˚E to 170˚E. Sources of TC development come from warm ocean temperature where latent heat is released during condensation processes and subsequently concentrated in the boundary layer. Relative humidity at 850-700 hPa is responsible to produce the most intense storm. Meanwhile, weak vertical wind shear between 850-200 hPa is one of the dynamical factors that lead to the development of TC. Pressure level of 850-200 hPa is chosen to minimize the thermodynamic effect in the lower troposphere. Typhoon Songda (Chedeng in the Philippines) or TSC lasted from May 18th to 30th, 2011 and strengthened into powerful Super Typhoon stage between May 24th and 27th. Long curving track and the exhibition of all sequences of TC life cycle, TSC is then considered as an ideal case of TC. The objective of the study with case of TSC is to investigate the role of thermal characteristics and dynamics on TC intensity. The research is carried out by using Advanced Research of Weather Research and Forecasting model (WRF ARW model) version 3.3. Two domains are employed in the model. The first domain situate from 02˚N to 40˚N and 118˚E to 149˚E and cover spatial resolution () of 33.1 km. The second domain situate from 09˚N to 27˚N and 119˚E to 132˚E with of 11 km. Timestep of the model () is 120 seconds. The model is supported by the following physical parameterization, i.e., Yonsei University Scheme (YSU) in the boundary layer, Kain-Fritsch scheme (KF) in the cumulus, and WRF Single-Moment 3-class scheme in the microphysics. Initial meteorological condition prior to the formation of the cyclone is generated using WRF ARW standard-release model. Sensitivity of the model output is obtained from a selected single-parameter change scenarios, namely, 10 % to 20 % decrease and increase of wind shear initial data at 850-200 hPa, and by 10 % to 20 % decrease of relative humidity initial data at 850-700 hPa. The result showed that the negative correlations between wind shear and intensity are found in wind shear scenarios. Wind shears of 10 ms-1 which lead to strengthening of the wind intensity in the early period of Typhoon development are found in wind shear scenarios. The effect of wind shear changes on wind intensity is statistically significant in the 20 % wind shear scenarios. During mature stage, weak wind intensity occurred when wind shear increase as given in the WRF standard-release and the 20 % decreasing scenario. Different situation is found in the 20 % increasing scenario where wind shear tend to weak and lead to strong wind intensity at this stage. Meanwhile, the reduction of moisture supply at 850-700 hPa resulting from 20 % decreasing relative humidity play a major role in the weakening of wind intensity and reduces mechanical energy of the cycle process as much as 300 J kg-1.
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