Simultaneous thermogravimetric and differential thermal analysis determination of products formed during hydration of blended Portland cement doped with zinc

With the increasing use of secondary raw materials and alternative fuels in the cement production industry, the amount of present trash elements rapidly increases. Most of these problematic elements affect the quality of produced clinker or blended cement. This study focuses on zinc and his influence on the hydration process and the formation of new hydration products. Zinc in percentage by mass of OPC 1% and 5% was added in the form of Zn(NO3)2, ZnCl2 and ZnO for modelling of the formation or modification of newly formed products. These new phases are present in mostly trace quantities, and quantification of even well-known phases such as Ca(OH)2 via X-ray diffraction method (XRD) is not suitable due to poor crystallinity and stoichiometry of some zinc compounds related phases. On the other hand, even smaller quantities of known phases could be precisely characterized via simultaneous thermogravimetric (TG) and differential thermal analysis (DTA). Special emphasis was given to mentioned Ca(OH)2 as one of the hydration degree indicators. With a very high content of chloride and nitrate anoint, the hydration, process was not only retarded by zinc but significantly altered causing creation of new phases mainly ettringite analogues with these anoints. In samples with a high dosage of Zn(NO3)2, ZnCl2 even Ca(OH)2 as hydration product cannot be identified by TG–dTG nor XRD. On the other hand with ZnO as zinc source, significant influence on hydration was proven. Initially as retarding agent for early stages of hydration, but also as the agent that increased final degree of hydration relatively to reference OPC.