This work deals with the influence of zinc on cement hydration. The amount of zinc in cement has increased over recent years. This is mainly due to the utilization of solid waste and tires, which are widely used as a fuel in a rotary kiln. Zinc can also be introduced to cement through such secondary raw materials as slag, due to increased recycling of galvanized materials. The aim of this work was to determine the effect of zinc on the hydration of Portland cement, blended with ground blast furnace slag (GBFS). This effect was studied by isothermal and isoperibolic calorimetry. Both calorimetry methods are suitable for measurements during the first days of hydration. Isoperibolic calorimetry monitors the hydration process in real-life conditions, while isothermal calorimetry does so at a defined chosen temperature. Zinc was added to the cement in the form of two soluble salts, namely Zn(NO3)2, ZnCl2, and a poorly soluble compound, ZnO. The concentration of added zinc was chosen to be 0.05, 0.1, 0.5, and 1mass percent. The amount of GBFS replacement was 15% of cement dosage. The newly formed hydration products were identified by X-ray diffraction method (XRD).
The heat of hydration evolution of eight paste mixtures of various water to binder ratio and containing various pozzolanic (silica fume, fly ash) and latent hydraulic (granulated blast furnace slag) admixtures have been studied by means of isothermal calorimetry during the first 7 days of the hydration process and by means of solution calorimetry for up to 120 days. The results of early heat of hydration values obtained by both methods are comparable in case of the samples without mineral admixtures; the values obtained for samples containing fly ash and granulated blast furnace slag differ though. The results from isothermal calorimetry show an acceleration of the hydration process by the presence of the fine particles of silica fume and retarding action of other mineral admixtures and superplasticizer. The influence of the presence of mineral admixtures on higher heat development (expressed as joules per gram of cement in mixture) becomes apparent after 20 h in case of fly ash without superplasticizer and after 48 h for sample containing fly ash and superplasticizer. In case of samples containing slag and superplasticizer the delay observed was 40 h. The results obtained by solution calorimetry provide a good complement to the ones of isothermal calorimetry, as the solution calorimetry enables to study the contribution of the mineral admixtures to the hydration heat development at later ages of the hydration process, which is otherwise hard to obtain by different method
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