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The activities of chromium oxides in a CaO-SiO 2 -CrO x slag system were determined with the electromotive force (EMF) method by equilibrating with metallic chromium at 1873 K. The effect of slag basicity on the activity coefficients of CrO and CrO 1.5 was analyzed. The results showed that increasing the slag basicity increased the activity coefficient of CrO; however, the effect on that of CrO 1.5 was not significant. The oxidation state of chromium in CaO-SiO 2 -CrO x slags was systematically investigated at both 1873 and 1863 K. It was found that divalent and trivalent chromium coexists in the slags. Divalent chromium oxide is favored, instead of trivalent chromium oxide, because of low slag basicity and low oxygen potential. It was concluded that the oxidation state of chromium in the slag system varied greatly from almost pure "CrO" to a composition corresponding to Cr 3 O 4 . In addition, the thermodynamic data in the slag system were assessed based on the regular solution model to mathematically describe the activities of chromium oxides in the slags. A group of model parameters were obtained. The calculated activities of chromium oxides were comparable to the measured data.

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Coal tar bearing emulsions were used in the Netherlands as binder in anti-skid surfaces for runways because of their perfect adhesion and fuel resistance properties. They are however toxic and will not be allowed anymore after 2010. Therefore alternatives need to be developed. As one of the alternatives, two types of two-component epoxy modified bitumen have been investigated by means of direct tensile tests (DTT), relaxation tests (RT) and dynamic shear rheometer (DSR) tests. The effect of the curing temperature on the strength development of the epoxy modified bitumen was tested. The results show that the tensile strength increases with increasing curing time and temperature. DTT and RT results indicate that this new epoxy modified bitumen has a much higher tensile strength, cures faster than a bitumen emulsion as a binder. Furthermore, it shows a good stress relaxation even at lower temperatures. The curing speed and the ultimate tensile strength after full curing can be easily adjusted. The DSR results show that the complex modulus of this epoxy modified binder is less susceptible to changes in temperature. The results also suggest that this epoxy modified bitumen has better anti-crack properties at lower temperature and less permanent deformation than bituminous binders at higher temperatures. All these results shows that this type of two-component epoxy modified bitumen can be promising as a binder in anti-skid layers.

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