The influence of phosphorous pentoxide on the phase composition and formation of Portland clinker

The influence of phosphorous pentoxide (P2O5) on the phase composition and formation of Portland clinker was studied in laboratory conditions. Phosphorous pentoxide in the form of calcium phosphate was added to common cement-making raw meal in graded quantities up to 5 wt.%. The raw meal properties were studied by thermal analysis. The development of clinker formation by burning for periods ranging from 20 s to 30 min in a special semi-automatic oven with a manipulator was followed using light optical microscopy. The phase composition of clinkers burnt to equilibrium was quantified by the optical point counting method. The entry of P2O5 into clinker minerals was determined by electron microprobe analyses. The laboratory tests show that at 0.7 wt.% of P2O5 in the clinker the alite (Ca3SiO5) content decreases and belite (Ca2SiO4) content increases. At a P2O5 content of 4.5 wt.% alite formation was totally blocked and the resulting clinker contained free lime in equilibrium with belite.