The purpose of this article is to describe the results of research models firebrick requirements planning in PT Semen Padang with MRP method. Firebrick is one of the spare parts and essential in the production of operational PT Semen Padang as protective and insulating of shell kiln. This article describes the firebrick requirements planning at all kiln Indarung II / III, IV and V to meet the needs of 2017 up to 2018. One type of firebrick most widely used in PT Semen Padang is spinal firebrick. Spinal firebrick highly susceptible to hydration and moisture as the main component is MgO compound that is hygroscopic so susceptible to damage in the form of cracks firebrick. Based on the research that has been done, get MRP application design that can be used in planning the needs of firebrick PT Semen Padang to come. Plans need firebrick for compliance in 2017 to 2018 : (a) item 422 purchased through two phases in the 4th month of 12.711 pcs and in the 9th month of 24.909 pcs (b) item 622 purchased through two phases in the 4th month of 21.185 pcs and in the 9th  month of 41.515 pcs (c) item P22 purchased through two phases in the 4th month of 446 pcs and in the 9th month of 874 pcs (d) item P + 22 purchased through two phases in the 4th month of 446 pcs and in the 9th month of 874 pcs (e) item 425 purchased in the 8th month of 14.626 pcs (f) item 825 purchased in the 8th month of 20.600 pcs (g) P25 item purchased in the 8th  month of 412 pcs (h) P + 25 items purchased in the 8th month of 412 pcs.

Preventive maintenance is considered as a method to avoid unexpected failure in production machines. Unfortunately, conducting such maintenance is limited by resources availability thus likely causes tardiness. This research aims to minimize total tardiness of preventive maintenance on production machines by developing a scheduling model. This scheduling model takes the availability of time and labor into account to get an optimal scheduling model that can minimize the tardiness. The model of preventive maintenance schedule is developed by using the Integer Linear Programming method. This method provides output in the form of preventive maintenance schedule through a purpose function which considers the specified constraints on the company. As the result, the developed model could propose a preventive maintenance schedule which reduces the total tardiness.

Cement is a construction material with a specific quality that must be meet standard requirements and customer requirements. Through a good and continuous quality control, it will produce cement with consistent quality as its Quality Planning. Cement quality is calculated after adding water by measuring its setting time, compressive strength developing, heat of hydration, expantion/shrinkage, and its durability to environment effect. In cement application, primary parameter to determine cement quality is its compressive strength. Some factors that affect compressive strength of cement are reactivity and amount of Tricalcium Silicate (C3S) of Clinker, Clinker freelime (free CaO), amount of SO3 in Cement, amount of additional materials (insoluble residue/IR and loss on ignition/LOI), and sieve on 45 µm residue of cement. This research is intended to find how insoluble residue/IR, loss on ignition/LOI, and amount of SO3 will affect compressive strength of cement. Various percentages of IR, LOI, and SO3 in cement will result different compressive strength. Taguchi Method is applied to determine material proportion. With Orthogonal Array calculation for 3 factors and 4 levels, it will result 16 calculation running times (L16 4**3). In laboratory scale, cement for this research has been being manufactured and then its compressive strength for 3 days, 7 days, and 28 days will be measured. Determination of optimal proportion will be calculated by statistic method for higher compressive strength and lower manufacturing cost. Keywords: compressive strenght, cement, taguchi method, proportionAbstrak Semen merupakan bahan konstruksi yang memerlukan kualitas yang sesuai dengan permintaan konsumen dan memenuhi persyaratan standar. Melalui pengendalian kualitas yang baik dan dilakukan secara terus menerus akan diperoleh kualitas semen yang stabil dan sesuai dengan perencanaan kualitas (Quality Planning). Kualitas semen diukur, berdasarkan performansinya saat penambahan air, yaitu bagaimana proses pengikatan semen, perkembangan kuat tekan, panas hidrasi, pemuaian/penyusutan volume dan ketahanan semen terhadap pengaruh lingkungan (durability). Dalam praktek pemakaian semen di lapangan, parameter utama untuk menentukan kualitas semen adalah parameter kuat tekan. Beberapa faktor yang mempengaruhi kuat tekan semen adalah reaktivitas dan jumlah trikalsium silikat (C3S) klinker, freelime klinker (CaO bebas), jumlah SO3 dalam semen, jumlah material tambahan (BTL dan LOI) dan kehalusan semen dalam sieve on 45 µm. Pada paper ini akan meneliti faktor yang mempengaruhi kuat tekan semen yaitu parameter BTL, LOI dan SO3. Variasi prosentase parameter BTL, LOI dan SO3 dalam semen akan mempengaruhi pencapaian kuat tekan. Penentuan proporsi material yang akan diteliti menggunakan metode Taguchi. Dengan perhitungan Orthogonal Array untuk 3 faktor dan 4 tingkatan level diperoleh jumlah penelitian yang dilakukan adalah 16 kali (L16 4**3). Pada saat ini sedang dilakukan pembuatan semen skala Laboratorium dan dilanjutkan dengan pengujian kuat tekan semen pada umur 3 hari, 7 hari dan 28 hari. Penentuan proporsi optimal dihitung secara metoda statistika untuk kuat tekan tinggi dan biaya produksi yang rendah.Kata kunci: kuat tekan, semen, metoda taguchi, proporsi

PT. Semen Padang is one of the cement producers competing to meet the needs of the cement. To that end, PT. Semen Padang must ensure the availability of cement on time, quantity, location and at competitive rates. One way to achieve this by optimizing the distribution system because it will be able to maximize sales and increase corporate profits. In this research, the distribution network planning model of PT. Semen Padang considering the cost of transportation, facility capacity, time, and uncertain demand. This model aims to minimize the total cost of product distribution and cost of opening the buffer warehouse and Packing Plant and maximize responsiveness to customers considering the uncertain parameters by using Fuzzy Multi-Objective Programming method. Based on the results of the research, had obtained the product distribution network planning model by using the fuzzy multi-objective programming method with the output is the opening of Packing Plant and buffer warehouse and the amount of product delivery to the final consumer with minimum cost and time of distribution. Search solution or output model assisted with Software Lingo 17.0. The designed model is able to explain the change of output if there are any changes in parameters covering demand between marketing areas, transportation costs between marketing areas and vehicle speed in transporting products from the last distribution center to the marketing area. The model can be implemented in the distribution network planning of PT. Semen Padang by using data in accordance with the conditions in the field.

Cement making process required four main raw materials, Lime Stone as a source of CaCO3, Silica Stone as a source of SiO2, Clay as a source of Al2O3 and Iron Sand as a source of Fe2O3. Proportion of raw materials approximately 80% CaCO3, 15% SiO2, 3% Al2O3 and the remaining 2% for Fe2O3. Due to operational constraints in the mine area, Indarung IV plant is experiencing a shortage of SiO2 source material that is Silica Stone, to anticipate this condition selected Pozzolan as alternative raw material because the SiO2 content in Pozzolan is above 60%. This research uses Linear Programming to get formulation model of optimization of raw material composition with Pozzolan as a substitute of Silica stone by minimizing cost. Ash composition factors and calories of fuel are not made into consideration. The results of this study obtained the most optimal raw material composition with minimal cost and meet the standard strength three days clinker min. 200 kg/cm2, by inputting the oxide composition of each raw material and the minimum and maximum constraint into the model formulation. The use of Pozzolan as a substitute raw material for Silica increases raw material costs 265.74 rp/ton.