Quality control of products according to different standards

This paper will explain how Ruukki Mineral Products implements quality control in the case of the blast furnace slag from the Raahe Works in order to take account of all its applications.

Quality control is a challenge for the manufacturers of industrial products and raw materials, especially when the same product can be used in a number of applications. This means the products have to meet several standards simultaneously and be subjected to quality control from different standpoints.

The blast furnace slag (BFS) produced at the Raahe Steel Works is a CE-certified product that conforms to the standard EN13242 and is used as a structural layer material and stabilising agent in earthworks and road construction, for liming purposes in agriculture, and as a raw material in the cement industry. It has also gained RALA acceptance and its use in agriculture is regulated by the Law and Statute on Fertilisers.

As far as the cement industry is concerned, its quality control is subject to the National Building Code of Finland (RakMK B4) and the new standard prEN 15167 for ground granulated BFS (GGBFS). Its various uses mean that the same product can even have a slightly different grain size according to the standard applied.

Materials produced by granulation and air-cooling of BFS are used for a number of purposes, so that they are subject to varying quality requirements. Since liability for the quality of the material lies with the producer, quality control in this case has to cover testing with respect to all these requirements.

The requirements with regard to blast furnace products in Finland have been quite clear for a long time as far as the use of these products for lime-related purposes in agriculture and as an input in the building materials industry is concerned. Moreover, the relevant authorities are engaged in supervising the quality of these products and the uses to which they are put. A new aspect has been introduced, however, with the granting of a CE certificate for their use in earthworks and road construction, giving rise to certain new test requirements and clearly defined determination methods that must be used in quality control. Environmental acceptability is also a key criterion in the case of earthworks and road construction, and it is necessary to know the behaviour of the product on site as well as its general solubility properties. The major challenge for the producer therefore lies in maintaining a straightforward, rational quality control system in the face of a plethora of varying requirements and determination methods.

The products, their main requirements and official practices in Finland

Marketable products for various uses can be obtained from molten BFS either by granulation or by air-cooling and crushing. Granulated BFS is a viable product for use in the building materials industry and for earthworks and road construction purposes, while air-cooled slag is crushed and sieved to typical grain sizes of 0-32mm, 0-20mm or 0-14mm for earthworks and road construction. Granulated or air-cooled slags intended for lime-based applications are sieved to a grain size of 0-3mm.

The Finnish authorities supervise the quality of slag products intended for the building industry or for lime-based projects by taking annual control samples from the producer's stocks. The principal requirements placed on these products according to their intended use are set out in Table 1.

Table 1: Main requirements placed on blast furnace slag products, sorted by intended use.

The National Building Code and the Law on the Manufacture of Fertilisers contain clear numerical criteria with which the products must comply. The main problem with the Building Code RakMk B4 and the old Fertiliser Law was that they did not define the methods to be used in quality control or the testing of samples taken by the authorities, which often led to discrepancies between the producer's own quality control and the analysis results obtained by the authorities. It was nevertheless possible to reach a separate agreement with the test laboratory used by the authorities supervising the building industry under which the test methods were precisely defined. The determination methods laid down in the new standard EN15167 apply to ground slag but not to granulated slag intended for use as a raw material, even though the standard does also state quality requirements for granulated slag.

The Finnish legislation on materials to be used for lime-based purposes was under revision during 2006-2007, and the new statute specifies the test methods. These are standard methods, wherever the adoption of such has been possible, but there are some components for which the supervising authority's own test methods or work instructions has been accepted as official.

In the case of earthworks and road construction, it is the technical properties of the products as building materials that are decisive. Once these have been clearly defined there has been no need to test the products on a monthly or even a yearly basis. The principal standard to be met by the producers of mineral aggregates in Finland is acceptance by the Construction Quality Association RALA, which is a requirement for the supplying of aggregates to National Road Administration projects. RALA carries out annual inspections of producers' quality control systems, but does not itself test the products. If the producer's quality control system meets the ISO 9001 specifications, this will correspond to acceptance by RALA.

The CE certification demanded of products for use in earthworks and road construction in many countries requires the regular inspection of production methods and quality control by an independent authority approved by the EU. But again, this authority does not test the products as such. If the manufacturer has an ISO 9001-certified quality control system this will greatly facilitate CE certification. The practice of approving only CE-certified products for National Road Administration projects is about to be introduced in Finland.

Quality control of granulated BFS

Quality control in the case of granulated BFS may be divided into three categories according to the use for which the product is intended, as shown in Table 2. The test requirements make reference to 11 standard methods.

Table 2: Quality control requirements for granulated blast furnace slag.

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 that 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 two branches of production gain some support from each other with respect to quality control, but in practice liming materials must be tested entirely separately from other products. The quality control measures that apply in the case of granulated BFS produced at the Raahe Works for earthworks and road construction purposes are presented in Figure 1.

The laboratory staff at the Raahe Works are 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 behaviour. 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 vitrification 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 analysed twice a month. This enables better management of quality control and provides a fairly precise indication of the quality received by the customer, an essential aspect of the ISO 9001 requirements.

CE certification

CE-certified products are generally regarded as safe and of high quality, and in practice certification can be taken as a mark of the manufacturer's quality control and supervised production. The CE certificate is always awarded for compliance with a certain standard, which in the case of mineral aggregates is the EN 13242 standard. In practise, an EU-licensed authority examines the manufacturer's quality control and production systems, approves these and awards the manufacture the right to attach a CE certificate to its products.

The main requirement for CE certification is internal quality control. The principles for evaluating a quality control system are laid down in Appendix C to the EN 13242 standard and are the same as for the ISO 9001 standard. If a manufacturer has a quality control system that complies with this standard, practically all the measures required for CE certification will be covered by it, i.e. definition of rights and responsibilities, management inspections, supervision of documentation, supervision of subcontractors, production management and the handling, warehousing and storage of the products. It is possible to revise these criteria with respect to inspection and testing of the products, the testing methods and frequencies being laid down in the EN 13242 standard.

The essential details regarding mineral aggregate products that have to be mentioned on a CE certificate include:

• Shape, size and solid density of the grains;
• Purity, specifically fines content and nature of the fines;
• Proportion of grains with a cracked surface;
• Impact resistance/crushability;
• Volume stability;
• Chemical composition, i.e. acid-soluble sulphates and total sulphur content;
• Resistance to wear;
• Presence of harmful substances, i.e. solubility of heavy metals;
• Resistance to erosion;
• Resistance to freezing and thawing.

The standard also lays down whether a certain property should be expressed in terms of a set of grades, a limit value, simple accept/reject criteria or a value indicated by the manufacturer for the product in question. If a certain component is not subject to any official requirement in the country concerned with respect to use of the product, the manufacturer need not determine or indicate any value for that property. In this instance, 'NPD', 'No Performance Determined', can be recorded on the certificate. If a limit value is laid down for the property concerned the NPD alternative is inapplicable.

In addition to the properties required, the CE certificate must carry the code number of the inspection authority, the name or identification code of the manufacturer and the company's registered address, the last two digits of the year in which the certificate was granted, the number of the factory's internal quality control certificate, a reference to the EN 13242 standard and a description of the product. The CE certificate should be visible on the product's label, packaging or commercial document, e.g. delivery note.

The principle has been adopted in Finland for the time being that the certificate can appear on the manufacturer's web pages, provided that customers know where to look for it. This information could be given on the weighing note, for instance. The CE certificate for granulated BFS produced by Ruukki at the Raahe Works is shown in Figure 2.

The CE certificate in Figure 2 indicates that the grain size of the product is in the range 0–6.3mm and that it is a fine-grained aggregate (GF85) with a maximum of 7% material passing though a -0.063 sieve (f7). No requirement exists with respect to acid-soluble sulphate (ASNR), and total sulphur is at most 2% (S2). The producer's value of 2.36mg/m³ is given for solid density.

Once a producer has the right to append a CE certificate to his products, certificates may be attached to each load separately. This would not be practicable, however, and instead a producer will give sufficiently broad ranges of values that the product will always fall within them. Then one CE certificate can be used throughout.

It is not necessary, however, to indicate functional characteristics of the product such as heat conductivity or capillarity on a CE certificate, even though data of this kind would be of considerable use for construction work under Finnish conditions, for instance. On the other hand, even grain size data can be misleading, as a value of 0–6.3mm will no longer hold good a month later, on account of hardening. Thus a CE certificate is not in practise of any use to planners in Finland, at least.

The reason why Ruukki Mineral Products has acquired the right to use a CE certificate lies in its market value: in future only products bearing such a certificate will be accepted for road construction projects and a company that does not have this certificate will not be able to supply aggregate to these large-scale construction sites. In addition, the certificate is a clear indication that the production process has been subject to the appropriate quality control.

The CE certificate is frequently linked to national standards as well as those in European. At present, criteria are being developed in Finland for the application of the EN 13242 standard, providing a clarification of what properties constitute relevant data and should be indicated on a CE certificate. This is of relevance chiefly to the points at which the NPD alternative might be used.

The draft national standard set the permitted sulphur content of air-cooled BFS at 2%, for instance. One of the reasons given for this is that the classification used in the European standard EN 13242 will come to an end. Another reason was due to environmental considerations, and the controversy aroused in Sweden by the use of BFS and its assumed detrimental effects on nearby cultivated fields.

The sulphur content of crushed BFS from the Koverhar Works in Finland is approximately 2.7%, and if the upper limit for sulphur in the national standard were to remain at 2% this would render the Koverhar product ineligible for use in road construction even though it still qualifies for a CE certificate. Since there is no scientific evidence that a sulphur content of over 2% will be harmful for local soils or groundwater, the boundary value could equally well be 3%.

The challenge of quality control for producers

The numerous standard methods employed in quality control are in themselves a challenge for producers. Although slags have been studied intensively on a world scale and are relatively even in quality, the pressures for quality control are increasing and it is impossible to compromise in this respect. The testing of new methods and the provision of instructions for their use in practical laboratory work can be a severe drain on time and resources. Furthermore, some of the more unusual and less frequently measured parameters often have to be analysed in external laboratories, or else direct determinations must be performed by the authorities themselves.

The weakest link in quality control at the moment concerns what is known as environmental quality control. Although solubility tests are performed on slags on a regular basis, this is not enough. It is important to know how they behave in use, and what their solubility is in soil. Similarly, it is not enough for the environmental authorities to know that slags are used for liming fields and are defined as acceptable products under laws and statutes drawn up by other ministries, or that they have been approved for use in organic cultivation.

There is no problem with granulated BFS, as in practise this is insoluble in soil, but when crushed, air-cooled BFS is used in a groundwater extraction area, questions of sulphate solubility and the effects on the environment come to the fore.

Groundwater quality has been monitored over a period of some years at certain previous road construction sites, so that reference cases now exist, and the results suggest that the soluble sulphate in crushed BFS has not led to any increase in sulphate concentrations in the groundwater, which are well below the limits set for domestic water supplies. This was also helpful when discussing the sulphur concentration limit for air-cooled BFS with the national standards working group in connection with CE certification. More reference sites are needed for all types of slag as far as environmental observations are concerned; otherwise producers and project administrators will be at a disadvantage in their dealings with the authorities.

Summary and future prospects

Product liability and testing requirements can be major challenges for producers of goods, who always need to be one step ahead of competitors, i.e. they must be able to answer new questions concerning their products even before these questions have been asked. This means that they must have sufficient information. In addition to research projects, regular quality control is extremely important, but the maintaining of quality control calls for resources and active monitoring of the legislation and the progress of working groups on standards.

It is not only statutory and technical requirements that present challenges, however, but also customers, the authorities and prospects for the future. Slags fall within the scope of REACH (Registration, Evaluation, Authorisation and Restriction of Chemical substances, a new EU law that entered into force on 1 June 2007). REACH and harmonised determination methods are due to be introduced into the testing of construction materials for harmful substances (in connection with CE certification). It is still unclear how slags will be implicated in this at a national level and what overlapping or differences there may be with REACH. It is also unclear whether future testing methods will be approved for evaluating products under the national environmental legislation, or whether the latter will have its own requirements in this respect. The problem of overlapping comes to a head in the case of products that have a number of uses, such as granulated BFS. It is quite certain that we shall be expected in the future to demonstrate that our products will remain environmentally acceptable at the site of their use for decades to come, and it is possible that quality control will also be expanded in that direction.

References

1. EN 13242 'Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction'.

2. National Building Code of Finland

3. EN 15167-1 'Ground granulated BFS for use in concrete, mortar and grout'.

4. Finnish Law and Statute on Fertilisers (539/2006 andmmM 12/2007).

5. ISO 9001 'Quality management system'