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Abstract: Nowadays, except for very few imported furnaces, the monitoring of the conversion of the produced plaster at the Pole Plaster of Araripe is not done with aid of online techniques. This research work shows a simulation of operational conditions with an online meter of chemically combined water in plaster, by means of Central Composite Rotatable Designs (CCRD) and nuclear technique of gamma-ray transmission. In the family of central composite rotatable designs, the CCRD is more efficient than the others, regarding uniformity of variances of the points at the same distance from the center of the design. This process is a simulation of operational conditions with an online meter of the chemically combined water in plaster, by means of gamma radiation transmission technique. Such determination can be achieved by the effect caused by the variation of the mass attenuation coefficient of the partially dehydrated material. An Americium-241 gamma source (60 keV) was simulated in the implementation of the Beer–Lambert equation. The nuclear data required for simulation were obtained from XMuDat software, available from the site of the International Atomic Energy Agency. A program in Matlab programming language has demonstrated the possibility of monitoring at all stages of the dehydration process, with measurements of the specific mass of the sample having an estimated error of the order of 1%. To verify the operating conditions suitable for the process, experiments were simulated using a CCRD. The independent variables were the sample thickness and the amount of chemically combined water in plaster. Optimal conditions of the process were determined, which allowed the derivation of a model represented by response surface of the gypsum conversion. [Copyright &y& Elsevier]

Abstract: The estimated amount of plaster wastes in the construction industry is 45%. The reduction of these wastes is of concern, as the cost of lost material and the waste management can affect the competitiveness of the industry. The blend of plaster with a particular resin generates a composite, which gives the pre-molded obtained from this mixture, special properties. In this case, the plasticity of the plaster generates pre-molded products with wealth of details. Additionally, the use of nuclear techniques for initiation of the polymerization reaction to obtain this type of composite can eliminate the need for a heat source, which is the conventional way to obtain polymerization, considerably reducing the costs of the process. As a function of the availability of styrene monomer, in the initial phase of the research test samples were prepared from plaster composites with this type of material. The test samples, composed of plaster and styrene, were irradiated with a Cs-137 (662 keV) gamma source for a period of time of two days in an air pressurized chamber (total dose of 43.2 kGy). Tests of resistance to compression, tensile strength in bending and water absorption, were based on a type of experimental design, CCRD (Central Composite Rotatable Design). The percent average weight of polymer by weight of the test sample was 14%. The presence of a polymerized resin gives the sample qualities such as being highly impervious to water and having high mechanical strength, allowing its use in the manufacture of different types of materials. [Copyright &y& Elsevier]