News Date:2015-09-14
There is considerable degree of overlap between the various standards. There are two standards for the determination of fines content, for instance, the CE standard EN 933-1 and that for lime-based materials EN 12948. There are also three standard methods for acid-soluble sulphate (calculated as SO3). The GGBFS standard EN 15167 requires SO3 to be determined by the EN 196-2 method, which is also that used by the laboratory, and approved by the Finnish authorities for the testing of granulated BFS under the National Building Code. On the other hand, CE certification of mineral aggregates, (EN 13242), requires SO3 determination in accordance with EN 1744-1. In practice the method is the same for both standards, the only difference being that the sample should be 1g larger under the EN 1744-1 standard than for EN 196-2. The third method is DIN 4226 Teil 3, which gives results that are an order of magnitude smaller than those obtained with EN 196-2.
There can also be several variations on methods for determining the same component even within one standard. The EN 1097-6 standard, for instance, includes five methods for determining the solid density of BFS, as became apparent when changing over to the pycnometric method necessary for CE certification.
One essential aspect of earthworks and road construction is environmental acceptability and although slags are also used for lime-based purposes the same quality control procedures cannot be applied to both. The issue with liming materials is largely a question of the concentrations of certain components – whereas the criteria for the road construction materials are expressed in terms of solubilities – is largely on account of the fact that the legislation originates from different ministries.
The laboratory staff at the Raahe Works is responsible for testing the granulated BFS samples, as well as those required for the determinations of grain size and moisture content demanded in the case of earthworks and road construction. Samples are collected every week and at the bottom of the conveyor belt, i.e. immediately after granulation. These 154 weekly samples are stored and combined to form 315 cumulative samples representing the past three months for solubility testing. Elemental analysis is also performed on the same samples in order to obtain reliable long-term data on element concentrations and solubility behavior. As granulated BFS is also used in house construction, a sample is sent annually to the Radiation and Nuclear Safety Authority in order to measure gamma radiation and radon yield.
The Raahe Works has two blast furnaces, and there can sometimes be differences between their granulation processes. This can affect the verification of the granulated slag, which in turn can lead to variations in the hydraulic properties of the ground material. Consequently, the better-quality granulated slag (as determined by eye) is separated out and placed in a covered store for eventual transportation to customers in the cement industry. Another reason for the product proceeding via an intermediate store is its moisture content, which is 13–14% a few hours after granulation but is reduced to 10–12% during storage. This in turn reduces energy costs in one customer's own grinding plant. Weekly samples are taken from the covered store, combined into two-week samples and analyzed twice a month. This enables better management of quality control and provides a fairly precise indication of the quality received by the c
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