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ABSTRAK
Tulisan ini menyampaikan tujuan dan kegunaan proses perawatan beton atau "concrete curing" terhadap beton yang masih berusia dini, terutama untuk pengecoran di daerah tropis seperti di Indonesia. Perawatan dalam hal ini berarti usaha untuk menjaga keseimbangan kadar air dan temperatur yang sesuai dan yang dibutuhkan dalam proses pengerasan beton, agar didapat beton dengan kinerja yang optimal. Dengan demikian perawatan beton berusia dini merupakan suatu proses penting dalam pertumbuhan kekuatan dan kinerja beton, untuk mencapai tingkat yang maksimal.

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Produk headliner mobil dapat diperoleh dari pengembangan pengolahan busa poliuretan dan limbah kulit udang yang mengandung kitosan. Busa poliuretan yang dilapisi kitosan dengan metode pencelupan memiliki tujuan untuk memodifikasi sifat elastis menjadi kaku. Pengujian tarik menunjukkan peningkatan kekakuan, sedangkan Thermogravimetric Analysis (TGA) menunjukkan peningkatan suhu degradasi menjadi 295°C untuk tahap pertama, 309°C untuk tahap kedua, dan 372°C untuk tahap ketiga. Proses curing dapat meningkatkan jumlah hubung silang fisika berupa ikatan hidrogen, kemudian peningkatan waktu curing dapat meningkatkan jumlah hubung silang kimia berupa ikatan kovalen sehingga menyebabkan struktur menjadi homogen dan halus yang ditunjukkan oleh Field Emission Scanning Electron Microscopy (FE-SEM). Namun, suhu curing yang terlalu tinggi atau waktu curing yang terlalu lama menyebabkan ikatan hidrogen bahkan ikatan pada rantai utama terputus sehingga sifat mekanik dan termalnya menurun. Pembentukkan hubung silang fisika dibuktikan dengan Fourier Transform Infrared Spectroscopy (FTIR) yaitu peningkatan intensitas ikatan O-H, N-H, dan C=O berikatan hidrogen, sedangkan peningkatan intensitas ikatan C-N dan C-O-C mengindikasikan hubung silang kimia. Busa poliuretan yang dilapisi kitosan dengan proses curing pada 100°C selama 120 menit memiliki kekuatan tarik maksimum 5,56 kgf/cm², elongasi 7%, dan densitas 28,9 kg/m³ yang mendekati spesifikasi sifat mekanik dan fisika produk headliner pada umumnya.

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Car headliner can be obtained from the development of processing polyurethane foam and shrimp skin waste containing chitosan. Polyurethane foam coated by chitosan using immersion method has purpose of modifying elastic become stiff. Tensile testing showed the increasing of mechanical properties, while Thermogravimetric Analysis (TGA) showed the increasing of degradation temperature to 295°C for the first stage, 309°C for the second stage, and 372°C for the third stage. Curing process can add the number of physical crosslinking in form of hydrogen bonds, then the increasing of curing time can add the number of chemical crosslinking in form of covalent bonds, causing the structure become homogeneous and smooth as indicated by Field Emission Scanning Electron Microscopy (FE-SEM). However, if curing temperature is too high or curing time is too long, it will cause hydrogen bonds even main chain to be severed so that its mechanical and thermal properties decrease. The formation of physical crosslinking is evidenced by the Fourier Transform Infrared Spectroscopy (FTIR), which is increasing the intensity of O-H, N-H, and hydrogen-bonded C=O bonds, while increasing the intensity of C-N and C-O-C bonds indicates chemical crosslinking. Polyurethane foam coated by chitosan and then cured at 100°C for 120 minutes has an ultimate tensile strength of 5.56 kgf/cm², elongation of 7%, and density of 28.9 kg/m³ which is close to the specification of mechanical and physical properties of headliner in general.

Abstrak :
Busa poliuretan mempunyai berbagai fungsi dalam dunia manufaktur, dan salah satu fungsinya ialah sebagai headliner pada mobil. Pembuatan headliner mobil membutuhkan properti busa yang rigid dan masih memiliki sedikit elongasi. Sedangkan pembuatan busa rigid membutuhkan zat aditif yang banyak dan relative mahal. Pada saat ini, dilakukan sebuah penelitian berupa pembuatan busa flexible yang dicampurkan dengan 4 gr kitosan dan 0,2 gr kalsium karbonat (CaCO₃) dalam 100 ml larutan 5% asam asetat (CH₃COOH dengan teknik dip coating dan menggunakan vacuum oven. Sampel yang digunakan adalah busa berdensitas 16 kg/m³ dan diberikan perlakuan dengan variable suhu dan waktu curing. Bedasarkan hasil yang diperoleh, perlakuan sampel dengan suhu 100^oC selama 120 menit adalah hasil yang terbaik. Sampel tersebut memiliki nilai ketahanan tarik maksimal dan elongasi yang tergolong baik serta kitosan dan CaCO₃ yang membungkus dengan rata semua pori pada permukaan busa serta memiliki hasil penilaian komposisi kimia dan temperatur dekomposisi yang dapat dikatakan paling baik daripada sampel lainnya. Sehingga dapat disimpulkan perlakuan tersebut dapat dilakukan penelitian atau produksi lanjutan.

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Polyurethane foam has a major function in the world of manufacturing, and one of its functions as a headliner in cars. Making car headliners requires rigid foam properties and still has a little elongation. While making rigid foam requires a lot of additives and is relatively expensive. At this time, research was carried out consisting of making flexible foam mixed with 4 gr chitosan and 0.2 gr Calcium Carbonate (CaCO₃) in 100 ml of 5% acetic acid (CH₃COOH) solution with dip coating technique and using a vacuum oven. The sample used is foam density 16 kg/m3 and given with variable temperature and curing time. Based on the results obtained, sample samples with a temperature of 100^oC for 120 minutes are the best results. This sample has ultimate tensile strength (UTS) and elongation which are classified as good with chitosan and CaCO₃ which wrap with all sizes on the foam surface and also the results of the chemical composition and decomposition temperature which is arguably the best of the other samples. It was agreed that discussions could be carried out for further research or production.

Abstrak :
internal curing is promoted as a way tpo mitigate autogenous shrinkage in high-performance concrete having a low water binder ratio (w/b). Different methods of internal curing have been proposed. In this study, the effect of substituting 20% of normalweight sand by an equal mass of lightweight sand on the development of shrinkage was investigated on a 0.35 w/b high performance concrete . Shrinkage was monitored using vibrating wire gauges cast at the center of 100x100x400 mm (4x4x16 in.) concrete samples. Two samples were sealed with self-adhesive aluminum foil to present a closed curing system without any exchanged of humidity between the concrete and its environment, After demolding at the age if 23 to 25 hours. two other samples were cured under water for 6 days . Thereafter these two samples were removed from water and maintained at 23 C (73 F ) and a 50% relative humidity (RH) Environment . Experimental results clearly demonstrate the effeciency of a 20% substitution of normalweight by a lightweight sand to reduce autogenous and drying shrinkage . The Incorporation of 20% lightweight sand did not significantly affect the 28-day compressive strength. The cementitious matrix presented low chloride ion permeability. Internal curing through the use of partial replacement of normalweight sang by lightweight sand definitely represent and efficient method to diminish autogenous and drying shrinkage in low w/b concretes where external water curing does not allow in-depth curing of concrete

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ABSTRAK
Latar Belakang: LCU prototip dengan metode PWM-kombinasi dengan iradiansi sinar 800, 900, dan 1.000 mW/cm2 telah dibuat untuk mencegah kenaikan suhu pulpa akibat polimerisasi. Tujuan: Menganalisis kekerasan komposit resin yang dipolimerisasi dengan LCU berbeda iradiansi sinar. Metode: Spesimen merupakan komposit resin yang dipolimerisasi dengan LCU prototip (PWMkombinasi) beriradiansi sinar 800, 900, atau 1.000 mW/cm2 atau dengan LCU pembanding (900 mW/cm2). Kekerasan komposit resin diukur menggunakan sistem Knoop. Hasil: Kekerasan komposit resin antar kelompok berbeda bermakna (p<0,05) kecuali yang diberi iradiansi sinar 900 mW/cm2 dari LCU prototip dan LCU pembanding. Kesimpulan: Kekerasan komposit resin dipengaruhi oleh iradiansi sinar dari LCU prototip. LCU prototip atau LCU pembanding dengan iradiansi 900 mW/cm2 menghasilkan kekerasan komposit resin yang sama.

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ABSTRACT
Background: Prototype light curing unit (LCU) with PWM-combined light irradiance of 800, 900, and 1.000 mW/cm2 was made to prevent the pulp temperature rise due to the polymerization. Objective: To analyze the hardness of resin composites polymerized by LCU different light irradiation. Methods: The specimen is resin composites polymerized by prototype LCU light irradiance 800, 900, or 1.000 mW/cm2 or with comparison LCU (900 mW/cm2). Hardness of resin composite test performed by Knoop system. Result: There is significant differences (p<0.05) among the groups except those between using the prototype LCU and comparison LCU that have irradiance of 900 mW/cm2. Conclusions: The hardness of resin composite was influenced by the irradiance of prototype LCU. The hardness of resin composite from prototype LCU is equal to those from comparison LCU irradiance of 900 mW/cm2.

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[Penelitian ini bertujuan untuk menganalisa pengaruh waktu penyinaran resin komposit nanofil menggunakan Light Curing Unit (LCU) LED protototipe terhadap temperatur atap pulpa gigi. Spesimen berupa 30 gigi premolar 1 rahang atas yang dibagi menjadi 3 kelompok dengan jumlah spesimen 10 untuk setiap kelompok. Gigi kemudian direstorasi resin komposit nanofil dan disinari menggunakan LCU LED prototipe selama 10 atau 20 detik dan komersial selama 20 detik. Pengukuran temperatur dilakukan sebelum dan setelah penyinaran resin komposit dan temperatur atap pulpa yang dihasilkan oleh LCU LED prototipe selama 10 atau 20 detik lebih rendah secara signifikan dari yang dihasilkan oleh LCU LED komersial., The aim of the present research was to analyze the effect of curing duration of nanofilled composite resin by the prototype curing light on pulp roof temperature. Thirty extracted human maxillary premolars were divided into 3 groups, 10 specimens for each group. Each teeth restored using nanofilled composite resin and were cured by the prototype LED curing light in 10 or 20 seconds or the commercially available in 20 seconds as a comparison. Pulp roof temperature was measured before and after the curing process. As a result, the temperature induced by the prototype curing light in both 10 or 20 seconds were significantly lower compared to the commercially available.]

Abstrak :
Dentists are often taught that 'overcure' is better than 'undercure'. Undercure is said to cause serious problem with resin composite fillings. Actually it does not always happen this way. Overcure also has several bad impacts that have never been thought before by practitioners. Researchers claim that curing time informed by resin composite manufacturers is not always correct. Filling material is not the only factor that determines the correct curing time for each filling. Light cure unit performance also plays a major role.