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African cement inffastructure is quite complex. Apart from Northern Africa and South Africa in particular, cement plants are scarce resulting in highly unstable cement pricing. Clinker and cement are imported from overseas, e.g. from Portugal, Turkey, Pakistan, Indonesia, and China. Imports are typically determined by the lowest price, and as a result the countries of origin of products vaiy regularly yielding large scatter of properties. Quality control and a good quality infrastructure are thus of utmost importance for the safety of the popuiace, an issue, which is actually often neglected. With funding of the German Metrology Institute (PTB) and Support of the SPIN project, a proficiency testing scheme for cement testing according to EN 196 was set up for African laboratories. Proficiency testing schemes, also called round robins. are interlaboratory performance comparisons allowing participants to evaluate themselves against pre-established criteria. Thev are a powerful tool to help laboratories improve their performance as well as demonstrate their competences to accreditation bodies or Customers. 26 laboratories from 20 nations, 18 of which from Africa, participated. The BAM Federal Institute for Materials Research and Testing acted as coordinator and provider of the scheme. The aim of the round robin was to interpret the submitted data further beyond the pure statistic analyses. The data provided a positive picture of the performance of the participants in general, but it also exhibited a number of technical fields that need improvement. The paper provides the general results of the scheme and analyses identified strengths and weak points based on the submitted and non submitted data as well as on discrepancies from the EN 196 procedures during measurements. The application of EN Standards for material testing is critically discussed and since quality infrastructure is also always an issue between industrial and political stakeholders, suggestions for the mitigation of the identified shared problems are given.
Polysaccharides modify the rheological properties of cement based systems. Depending upon their chemistry, molecular architecture, and adsorption tendency, they have different modes of action. Some polysaccharides like diutan gum have strong effect on the fluid phase; others like starch strongly interact with particles. This paper presents effects of diutan gum and starches in presence of polycarboxylates. Rheometric investigations with varied particle volume fractions and increasing coarse aggregate diameters were conducted. The results show that starches have stronger influence on the rheology at high particle volume fractions than diutan gum. At lower particle volume fractions this trend is inverted. Experiments with aggregates sizes up to 16 mm (0.63 in.) indicate that stabilizing agent influences on the effects of aggregates on yield stress were small; however up to 1.0 mm (0.04 in.), a significant effect on the plastic viscosity could be observed, which levelled off at larger diameters.