Incorporation of trace elements in Portland cement clinker: Thresholds limits for Cu, Ni, Sn or Zn

This paper aims at defining precisely, the threshold limits for several trace elements (Cu, Ni, Sn or Zn) which correspond to the maximum amount that could be incorporated into a standard clinker whilst reaching the limit of solid solution of its four major phases (C 3S, C 2S, C 3A and C 4AF). These threshold limits were investigated through laboratory synthesised clinkers that were mainly studied by X-ray Diffraction and Scanning Electron Microscopy. The reference clinker was close to a typical Portland clinker (65% C 3S, 18% C 2S, 8% C 3A and 8% C 4AF). The threshold limits for Cu, Ni, Zn and Sn are quite high with respect to the current contents in clinker and were respectively equal to 0.35, 0.5, 0.7 and 1 wt.%. It appeared that beyond the defined threshold limits, trace elements had different behaviours. Ni was associated with Mg as a magnesium nickel oxide (MgNiO 2) and Sn reacted with lime to form a calcium stannate (Ca 2SnO 4). Cu changed the crystallisation process and affected therefore the formation of C 3S. Indeed a high content of Cu in clinker led to the decomposition of C 3S into C 2S and of free lime. Zn, in turn, affected the formation of C 3A. Ca 6Zn 3Al 4O 15 was formed whilst a tremendous reduction of C 3A content was identified. The reactivity of cements made with the clinkers at the threshold limits was followed by calorimetry and compressive strength measurements on cement paste. The results revealed that the doped cements were at least as reactive as the reference cement.