Pero Dabić

A conceptual model of the cement hydration process

Cement hydration development has been analyzed on the basis of measured data obtained by the microcalorimetrical method. Based on the most appropriate model assumed, thermokinetic analysis has been carried out for the polymineral and polysize system tested on industrial cement samples. A computer program has been developed to determine specific kinetic parameters describing individual hydration processes. The program makes it possible to determine the controlling processes during hydration and their share. Certain kinetic parameters make it possible to observe differences in hydration of pure clinker minerals and of Portland cement in a subtler way.

Abnormal yields of hydrogen and the mechanism of its evolution during cathodic polarization of aluminium

Abstract The yield of hydrogen formed during cathodic polarization of aluminium in neutral salt solutions was measured volumetrically as a function of current density and temperature. It was established that at any current density above 0.5 mA cm−2 and at any temperature the yield is larger than 200%; implying that a simultaneous dissolution of aluminium is an inherent part of the cathodic process.

Processes on aluminium on the negative side of the open-circuit potential

Abstract Cathodic current—time transients were recorded on high-purity aluminium immersed into a neutral 2 M NaCl solution, when subjected to a potential pulse from a potential around the open-circuit potential, to different negative values. Hydration of the oxide layer occurs at potentials more negative than −1700 mV vs. SCE, whereupon hydrogen is evolved at the metal—hydrated oxide interface. A linear Tafel function is obtained for the maximum current attained in that potential region with a slope of 110 mV dec−1 indicating that the Volmer reaction is the rate-determining step, and the exchange current density for hydrogen evolution at aluminium is estimated at 5 × 10−11 A cm−2. Anodic current responses to the return of the potential to the rest values were also recorded at three different time scales. The presence of some substances, formed at the more negative potentials, other than gaseous hydrogen, was detected and their dependence on potential and cathodic pulse duration is discussed.

A new approach in mathematical modelling of cement hydration development

Abstract This paper describes development of a kinetic cement hydration model, which observes hydration rate relative to time d α /d t = f ( T , t ). The model established makes it possible to observe hydration rate relative to time and not relative to the reaction degree α , d α /d t = f ( T , α ), which offers a new approach to solving the cement hydration kinetics. The model assumes several simultaneous processes sequentially governing individual hydration segments. The model has been tested by means of experimental α – t data obtained from the DSC plots by quantifying the content of Ca(OH) 2 from the cement–water system. The results indicate that the model established is valid and can be applied well.

Examination of reaction between the NSF superplasticizer and cement

Abstract The mechanism of the reaction taking place between NSF superplasticizer and Portland cement was examined with spectrophotometric and conductometric techniques, and strength measurements carried out in the presence of 0.1% – 2% of the admixture. The results obtained for electrolyte conductivity, κ, mass of admixture adsorbed to cement surface, and increase in strength, provided a basis for conclusions on the phenomena and effects occurring between the additive and the cement in the reaction medium.

Evaluation of leaching behavior and immobilization of zinc in cement-based solidified products

This study has examined leaching behavior of monolithic stabilized/solidified products contaminated with zinc by performing modified dynamic leaching test. The effectiveness of cement-based stabilization/solidification treatment was evaluated by determining the cumulative release of Zn and diffusion coefficients, De. The experimental results indicated that the cumulative release of Zn decreases as the addition of binder increases. The values of the Zn diffusion coefficients for all samples ranged from 1.210-8 to 1.1610-12 cm2 s-1. The samples with higher amounts of binder had lower De values. The test results showed that cement-based stabilization/solidification treatment was effective in immobilization of electroplating sludge and waste zeolite. A model developed by de Groot and van der Sloot was used to clarify the controlling mechanisms. The controlling leaching mechanism was found to be diffusion for samples with small amounts of waste material, and dissolution for higher waste contents.

Effects of Mud from a Zinc-plating Plant and Zeolite Saturated with Zinc on Portland Cement Hydration and Properties of Hardened Cement Pastes

This work investigates the impact of mud from a zinc-plating plant and zeolite saturated with zinc on early hydration processes of ordinary Portland cement. During the first 48 hours of hydration, the addition of mud significantly affects the cement hydration kinetics. The partial replacement of cement with zeolite saturated with zinc ions, reduces the negative impact of mud on the hydration processes. Samples with the additions showed lower compressive strength than the sample without additions. With regard to the standard limits for this type of cement, mud shares are eligible up to 5 wt. % and a mixture of mud and saturated zeolite up to 10 wt. %.